March, 1926
IND CSTRIAL A N D ENGINEERING CHEMISTRY
225
Phenol Resins and Resinoids’,z By L. H. Baekeland and H. L. Bender 247 P . 4 R K A V E N U E
A N D CO1,IJMBIA
UNIVERSITY. NEWY O R K . N. Y.
One of the most promising methods in the present state of HE resinous bodies resulting from the condensation of phenols and aldehydes or substances exercising knowledge seems to be the further study of the first steps equivalent functions, as through an active methylene of the reaction, where relatively simple substances are formed group, are of two distinct types. Some of them show dis- and isolated, which can be handled by present available tinctly the resin characteristics; these are rather analogous to chemical methods. The present research was therefore the natural resins and have been designated by Baekeland’,* as confined to some of the first phases of the reaction. It is well known that an immense number of compounds will Novolaks. The others, although resulting from the same raw materials, are in their final stage infusible, and are known take part in these phenol resinoid reactions. I n the place of phenol may be used any under various trade names of the substituted phenols as Bakelite, Resinit, RedA historical discussion of previous investigations on -for instance, even such a manol, Sipilite, Condensphenol resins and resinoids is given to show the difficulties sluggish phenol as the ite, Bmberite, Faturan, in the way of purification and identification of the end phenyl ether of s a l i c y l i c Formit, Phenoform, Suloid, products in the phenol resinoid reaction, and that the only acid. I n place of formaldeAmberdeen, etc., etc. Both apparent way out is by a study of the possible intermediate hyde may be used the algroups are commonly desproducts. The present investigation is an attempt to dehydes, the ketones, the ignated &s “phenol resins.” gather some data on these possible intermediates and to dihalides, from both the alSevertheless, the infusible indicate the lines along which future research should be dehydes and ketones, and group, although they may directed. all those compounds which externally resemble natural Further evidence is advanced to indicate the order of are equivalent in action to resins, are decidedly differreaction in the first stages of the infusible condensation aldehydes such as hexaent from the resins in their products of phenol and aldehydes designated as resinoids, methylenetetramine, a c e t physical and chemical beand the composition of Novolak resins and phenol resinals, and many others. The havior. N a t u r a l r e s i n s oids made from various aldehydes. Novolak resins p h e n o l r e s i n s , of t h e melt when heated, can be made from new starting materials, and resinoids from Novolak type, are changed dissolved in suitable solthese Novolak resins, are described. The importance of to the phenol resinoid or invents, and are rather britthe phenoxyphenol rearrangement in the phenol resinoid fusible type by reaction with tle, the strongest of them series is shown and a theory as to the constitution of the compounds equivalent to being amber. On the other final product of the resinoid reaction is announced. free methylene groups, such hand, the resinous products as formaldehvde and substiwhich form thesubject of the present research work are, after they have reached their final tuted formaldehyde, hexamethylenetetramiie, methylene stage of stability, decidedly infusible. Furthermore, they are ethers, methylenechloride and others. Homologs of either insoluble in ordinary solvents and are incomparably stronger phenol or formaldehyde were thus chosen which would permit and more resistant to chemical and physical agents than the obtaining intermediate compounds that could be separated natural resins or the artificial resins of the Novolak type; in and studied by known chemical means. From the study of order to differentiate them from all these, we feel warranted these intermediate bodies one may be permitted to hazard a in designating them more accurately under the name of “phe- more or less approximate or intelligent guess as to what may happenin the final stages of the reaction. Some attempts nol resinoids.” These phenol resinoids by their unusual properties have along these lines have already been undertaken, as shown by acquired a vast field of new applications in numerous branches the publications of Baekeland,’ Redman, Weith, and Brock,85 of technology. They are used, for instance, in the electrical and Raschig.66 and automotive industries, as well as in various other arts, Early Products Discarded where they are performing services which are out of reach of the natural resins or the older plastics, although the latter The preparation and utilization of the phenolic condensaare obtainable a t lower prices. On this account, research in tion products has been repeatedly described both in patent the field of phenol resinoids is generally more concerned literature and special publication^.^-^ The literature on the with higher qualities, better technical effects, than mere cost manufacture and the applications of these products is increasof production. Whatever be the ultimate goal of research ing rapidly, but the theoretical side, while not neglected, in this field, it is highly desirable to get a better understanding has not been able to keep pace with the practical information. of the reactions which engender these products. Unfor- It can be easily understood why even men like Adolf and von tunately, the study of the chemical reactions involved in these Baeyer in 18726were not much attracted by the difficult probprocesses is certainly not an easy one. Bodies of a resinous lems involved in the further study of vaguely described and or colloidal nature, which neither crystallize, nor melt, nor rather indefinite resins obtained from the action of aldehyde on distil, nor dissolve, are not easy to purify nor ran they be phenol. I n the same way Kleeberg in 1891’ abandoned his studied with much hope of accuracy.1 We are thus compelled mixture of resinous products because they were untreatable. to build up a series of approximations by obserx ing various It should be mentioned here that the interaction of phenol and phases of the reactions involved. aldehyde does not necessarily form resinous bodies, and if 1 Received February 2 , 1929 resinous bodies are produced they may vary from the fusi2 Submitted in partial fulfilment of the requirements for the degree of ble resins to the infusible and very useful resinoids. Doctor of Philosophy, Department of Chemical Engineering Columbia Under certain conditions phenol and formaldehyde (or their University equivalents as noted above) react to gire definite and known * For numbers in text see bibliography a t end of article
T
226
INDUSTRIAL A N D ENGINEERISG CHEMISTRY
chemical substances. Formaldehyde may act here as methylene glycol to give the crystalline o-oxybenzyl alcohol (saligenin) and p-oxybenzyl a1cohol.l Saligenin in its turn is easily changed by dehydration into a resinous mass. This dehydration may occur on heating and is much hastened by the presence of strong acids or other chemical means. Baekeland* has established the presence of noticeable quantities of oxybenzyl alcohol, even when strong acids are used as condensing agents in the reaction of formaldehyde upon phenol, These resinous dehydration products of phenol alcohols have been described as saliretin p r o d u c t ~ . g - ~ ~ Saliretin Resins
Various structural formulas have been proposed for these insoluble phenol resin^;^^^^^ but the important fact remains that, since they are amorphous and not subject t o purification by ordinary chemical methods, fancy here has had free play and no two investigators have agreed as to their composition. Baekeland13 states that it is very probable that they are not only very complicated as to molecular structure, and are not well-defined chemical individuals but varying mixtures of several colloidal bodies which exist in solid solution. All that we can state with any degree of certainty is that, the crystalline and well-defined oxybenzyl alcohols lose water to become illdefined resinous products which are classed under the generic name of “saliretins.” De Laire14 showed that for the industrial transformation of these phenol alcohols into fusible resins or saliretin products it is not necessary to produce the pure phenol alcohol first, but that the two succeeding reactions of condensation and dehydration can be carried out at the same time; or as fast as phenol alcohol is formed it can be dehydrated and resinified. A few years earlier, Blumer16 described similar resins which were more soluble, more fusible, generally.less reactive, and mechanically weaker than saliretin obtained from pure oxybenzyl alcohols. Baekeland16 proved this to be d w t o a slight excess of phenol, which, when removed, gives a residue similar to the saliretin resin made without free phenol. Indications and Complications From the simple fusible resins Baekelandl succeeded in isolating 1 to 2 per cent of Crystalline p-dihydroxydiphenylmethane, CH2(CJ&OH)2. Possibly these diphenylmethane compounds are formed as direct intermediate compounds or indirectly by the succeeding action of a phenol alcohol on another phenol molecule. The formation of the diphenylmethane group is probably one of the earlier steps of the resinification process. Raschig17 has called attention to the large number of isomers that might possibly exist in case diphenylmethane derivatives are formed, and expresses the opinion that it becomes impossible to separate and identify these different bodies. He suggests further that the soluble resin is perhaps a mixture of three isomeric dihydroxydiphenylmethanes with excess of free phenol and corresponding phenol alcohols. If this were the true picture then hot water should extract abundant amounts of diphenylmethane compounds; yet the limit of diphenylmethane compounds obtained hitherto has been about 2 per cent. All these fusible and soluble phenol aldehyde resins of the Novolak type have rather much the same general chemical and physical properties, differing only in some details resulting from variation in their methods of preparation and the amounts of free phenol contained in them. The importance of the free phenol has been pointed out by Baekeland. 8. 16t18 On the other hand, Baekelandlgproduced a fusible resin or h’ovolak by heating for 3 hours a t 180” C. in a sealed tube, 100 grams of p-dihydroxydiphenylmethane with 10 grams of paraform. By increasing the proportion of paraform he
Vol. 17, No. 3
produced a hard and infusible true phenol resinoid. Beatty20 describes a similar reaction starting with an analogous diphenol, dimethyl-p-dihydroxydiphenylmethane,obtained by the method of Dianin.21 It should be borne in mind that in these reactions the diphenol may be considered as acting in one or another of two distinct ways-either as an intermediate compound or as a phenol starting material of phenolic functions. Speculations The constitution of the infusible phenol resinoid becomes immeasurably harder to unravel than that of the fusible Novolak resins; so it seems hardly necessary here to dwell too much upon the speculations that have been advanced in this field, except to say that any opinion on this phase of the reactions is necessarily a mere guess based on observations of the first steps in the reaction.’* All the theories follow the facts outlined above except that of Woh1,22who, after a study of acrolein derivatives of phenols, mentions the resins as probable polymerization products of methylene deriva/CH=CH\
tiyes of the tautomeric phenol
CHFC
\CH=CH/
C=O.
In this connection a more recent publication of Glenz23is of interest. He expresses the view that phenol itself exists as a polymer in concentrated solution, BaekelandZ4has shown that phenol resinoid of highest resistivity is obtained only when the proportion of methylene groups to phenol groups is a t least slightly greater than 1to 1. p-Hydroxybenzyl alcohol, to which 5 per cent of its weight of paraform had been added, heated in a sealed tube for 6 hours a t 160” C., gave phenol resinoid of highest resistivity. Since o-hydroxybenzyl alcohol will change to some of the para compound under the influence of heat and the para compound will partly change to the ortho compound,26 then both compounds may give the same phenol resinoid. The homologs of formaldehyde seem to give the para-substituted product^,?^-^^ so the weight of evidence would lead t o the belief that the para compounds are the important ones in the corresponding phenol resinoid series. In the further discussion stress will be laid on the para compounds with the understanding that there may also be formed varying amounts of the ortho and meta compounds. I n this connection the theories of Sat0 and Sekine33are mentioned merely for the sake of completeness. They consider the very soluble and fusible resins as para-substituted, the moderately soluble resins as ortho-substituted, and the infusible resins as meta-substituted. So far no evidence has been advanced in support of their view. There are some characteristics and reactions of these fusible resins which have led to considerable confusion in the literature of this subject. Thus, Claw and Trair1er3~made a noncrystallizable resin which was soluble in alkali and the combustion analysis of which indicated p-dihydroxydiphenylethane as its probable structure. On the other hand, Fabinyi35 by the same reaction obtained a crystalline product which gave the same properties and combustion analysis. There must, then, be either great difficulty in the crystallization of this compound or there exists another form or rearrangement of the same compound which is not crystalline. It is interesting to note that the same difficulties in making the same compound by a different method have come to light in recent 1 i t e r a t ~ i - e . ~ ~ The Starting Point We therefore learn from the somewhat conflicting data of various investigators that: 1-The
reaction may be controlled under certain conditions
to give definite yields of such intermediate products as the hydroxybenzyl alcohol or other phenol alcohols.
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1925
2-From the industrial fusible Novolak resins varying small amounts of other possible intermediate products may be isolated, as p-dihydroxydiphenylmethane. 3-Fusible Novolak and infusible phenol resinoids can be made from both these classes of possible intermediate compounds. 4-The weight of evidence seems to indicate prevalence of para compounds. 5-The same reaction may, under slightly varied conditions, give two products alike in composition and in some reactions, but differing in appearance and in physical and chemical properties.
It is well known that aldehydes act on alcohols to give addition products somewhat similar to the aldols (I) and the acetals (11), and that in case the reaction is sluggish the acetal can be produced by using, instead of the aldehyde, its corresponding dichloride. R\
C=O
H/
+ C2HsOH
R\/OH C H/\OCd& (1)
+
C2HsOH R\/OC*H5 +
c
H/\OCzHs (11)
+ Hz0
This led the first investigators of the phenol aldehyde condensation to expect the formation of the phenyl acetals or diphenoxy compounds. The solubility of the compounds in alkali and the formation of crystalline p-dihydroxydiphenyl compounds soon gave the conviction that the hydroxy group increased the activity of the para hydrogen, causing it to act directly on the aldehyde; also that the resulting compounds were difficult to crystallize when certain other products were present. The view13 that the initial resins are not a single compound or two compounds, but very complex mixtures in colloidal solid solution, is somewhat strengthened by the solvent and associating powers of phenol for the phenol resins and resinoids. A small percentage of phenol with any of these possible intermediate products seems to influence their properties greatly. Many of these products show very erratic molecular weights in phenol as a solvent.
I n 1901 M a ~ k e n z i ein~ ~attempting to make acetals from benzophenone chloride (111),obtained instead p-dihydroxyshowed why tetraphenylmethane (IV). G ~ m b e r gin~ 1915 ~ Mackenzie failed to get the expected acetals. The failure was due to the use of phenol as a solvent. Gomberg proved the reaction to proceed by steps as follows: /c1
c
C6H5/ \a (111)
+
C6H5\ 2CsH5OH
+
/OC& C C6&/ \OCsHs
+
CsHsOH
H/
2HC1
cbHs\c/ocas -+
\Cl
H/ \Cl
-Rearrange
Ca5\
/CeH,OH C f CBHsOH --c H/ \C1 Ci“\ /C6-I4OH csHs\ /CsH4OH -+ C C H / \OCsH5 Rearrange H/ \C6H40H Resin (V) Crystals C&\ /C&OH H20 and acid CsH5\ /C&OH Also C -C CsHsOH H / \OCsH, Hydrolysis H / \OH Resin Crystals
+
G ~ r n b e r ghas ~ ~shown that in making the analogous compound p-dihydroxytetraphenylmethane,(CJ&W (CJ&oH)z, the first phenoxy group rearranges very quickly and that the second group rearranges slowly. Since this research was along lines rather removed from the resin field, the intermediate resin stage and its significance seem to have been overlooked. It is interesting to note that benzophenone dichloride and phenol a t room temperature will give a resin soluble in caustic soda solution and which requires rather high temperature and prolonged treatment to convert into the corresponding dihydroxy compound (IV) :
CsH5\&’CaH4OH
CsHsOH
CeH5/ \ c l /CsHaOH c&\ /CsH40H C + C CsH5/ \OCeH6 Rearranges CsH5/ \C&OH (VI) Resin slo~ly (I\-)Crystals C&\
Gombergd2 also investigated the reaction between benzyl chloride and sodium phenoxide, and obtained a t will either the benzyl ethers (VII) or the benzyl phenols (VIII). H\ /C6H5 C H/ \Cl
Important Discoveries in Related Fields
c6&\
CsHs\dC1 +
227
/C&s + CsHjOH-+H\ C H/ \OC&
- c
H\
/Cas
Rearranges H/ \CsHdOH easily (VIII)
(VII)
Gomberg and Snow6’ within the past year have given a very clear description of some of these related rearrangements. They isolated three of the compounds formed by the rearrangement of diphenoxydichloromethane. R e y ~ h l e made r ~ ~ methoxyphenoxymethane (IX), and found that by the action of mineral acids a t room temperature it gave resins similar to those from formaldehyde and phenol called saliretin resins. This would be easily explained by a rearrangement :
This acetal by rearfangement gave the diphenol. This same rearrangement was noted by Claisen in 1887.40 (
Mackenzie41 also attempted to make the phenyl acetal from benzal chloride and phenol, and obtained, after long heating, p-dihydroxytriphenylmethane in 87 per cent yield. I n repeating this work of Mackenzie the writers noticed that heating for short periods gave resins which, when apparently freed from crystals of the p-dihydroxytriphenylmethane, would give additional crystals after a heat treatment. The possible steps in this reaction might - be represented as follows:
H \ /OCsH5 C ---+ H / \OH Rearrange
1x1
H\ /CeHaOH C H/ \OH
-
Saliretin Presence of resins mineral acid
Importance of Para Rearrangement The para rearrangement from monophenoxy compounds to monophenols is well shown by Ludwig, Claisen, and E i ~ l e r . They ~ ~ changed all types of aromatic allyl ethers quantitatively by heat to the corresponding phenols. This
IiYDUSTRIAL iiiYD ENGINEERING CHEiMISTRY
228
para rearrangement in phenols and in amines has been well shown by many investigators, as Hoffman, Claisen, and many others; yet the bearing of this rearrangement on the problems of the phenol resinoids seems to have been entirely overlooked. It is of interest to note that in 1922 Fabre46condensed resorcinol and benzaldehyde and obtained an amorphous yellow substance which, when heated 6 hours on a water bath, gave a well-defined crystalline product but on long heating again resinified. Research published in 192446on the condensation of betanaphthol with acetylene (equivalent to acetaldehyde) shows that the main product is the acetal with a little of the diphenol, whereas the alpha-naphthol gives only the diphenol. As has been shown, CIaisen in 188740explained this as a rearrangement. I n the well-known Kolbe synthesis of salicylic acid there is first formed sodium phenylcarbonate, which rearranges to either the ortho or para compound.
-
/ OCeHs
o=c
\ONa (X)
\ONa
-
/OC& Rearranged o=C \C&OH (XII)
H/
c=o
+ CsHsOH+
R\ /OCKH~
C €I/ \OCsHs
For example:
R\ /C~HIOH C
---f
R‘/ \OH (XVII I) R\
/C&LOH
o=c
\Ce&OH (XIII)
R\c/oH H/ \OCeHs (XXV)
-
CeH60H
____, Rearranges
(XIV) R\ /CeH4OH R\ /C&OH -~ C c H/ \OCe,H6 Rearranges H/ \C&OH (XV) (XW Also R\ /OH R \ p H C C/ \OC& Rearranges H/ \C6H&H (XXV) (XVII)
-
Where ketones are used instead of the aldehydes, we obtain compounds of the general type RR’C (C&OH),. Then as intermediate compounds up to the dihydroxydiphenylmethane (XVI) stage there would be the phenoxy alcohol (XXV), the diphenoxymethane (XIV), the p-hydroxyphenylphenoxymethane (XV), and the p-hydroxyphenylcarbino1 (XVII). Of these compounds and their homologs, in addition to those already cited, are known the diphenoxy methane,4Qand diphenoxyethane.60 I n case the phenol does not act as an alcohol in this series of reactions, the intermediates would be the hydroxybenzyl alcohols (XVII) and the diphenols (XVI). I n addition to these known crystalline bodies, the series of reactions give other bodies (resins) which can find no place in this scheme and which apparently act as true intermediate compounds.
/CH=CH\
/OH CeHsOH ---+ C \CH=CH/ \OH (XIX)
c=c
R’/ R\ R’/
/CH=CH\
c=c
\CH=CH/ (XX)
/OCeHs C \OH R\ R’/
-Rearranges
/CH=CH\
c=c
/CH=CH\
c=c
R’/
There is, then, some justification from the literature to expect that phenol might act as an alcohol in this condensation, going through a series of definite intermediate steps. R\
The situation, even in these first steps, may be much further complicated by the quinone rearrangement.
R\
(XI)
Michael4’attempted to make phenyl salicylate and obtained 2,4’-dihydroxybenzophenonein good yields. Staede148proved this to be due to a rearrangement. He rearranged salol (XII) to 2,4‘-dihydroxybenzophenone,and phenyl-p-hydroxybenzoate to 4, 4‘ dihydroxybenzophenone (XIII).
-
Theory of Color Changes
/Ce&OH
o=c
Vol. 17, No. 3
\CH=CH/
\CH=CH/ (=I)
c=c
/C&OH C \OH
/CH=CH\ \CH=CH/
----
Rearranges
/OH C
\OH
(XXII)
G ~ m b e r ghas ~ ~shown the change from (XVIII) to (XIX) for p-hydroxytriphenylcarbinol, the structure (XXIII) being colorless and (XXIV) yellow. The series represented by (XX) and (XXI) are as yet unknown, but if they exist it seems possible that they could be yellowish resins. The structure (XXII) should be more highly colored, and since there is an intense red compound which can be easily formed in these series this rearrangement may be the longsought explanation of these color changes. For instance, a sample of colorless crystalline p-dihydroxydiphenylmethane changed to a deep red on standing several weeks a t a slightly elevated temperature. This phenomenon has been variously explained as an oxidation or as the effect of impurities. It is possible that a better explanation will be found in the compensating oxidation and reduction of the quinoid rearrangement. The fact that colored compounds of unknown structure are found in this series is well known and many attempts have been made both to prevent and to use these properties. The fusible resins turn a deep red on exposure to air, to slight acid fumes, or to alkalies in water solution. Varnishes made from these resins gradually acquire a beautiful mahogany shade without the addition of any coloring matter. That this color reaction is due to an intermediate compound is indicated by the trend of patent literature and by the fact that as the resins approach the infusible stage this power of color change is largely lost. The statement has been often made that this color change in the fusible Novolak resins is due to free phenol. Yet a fusible resin, from which seemingly all free phenol has been removed by heating a t 250” C. for 3 hours under a pressure of 20 mm. of mercury, still showed the same degree of color change as before heating when the two pieces were exposed under the same conditions. There would, then, be two possible isomers of p-dihydroxydiphenylmethane, the one (XXII) more highly colored than the other (XXI). Wohl and Mylo22 mention the quinoid possibility in this field, and Gomberg3$ in a somewhat related series isolated two isomeric p-hydroxytriphenylcarbinols, one colorless and the other yellow.
Jlarch, 1925
I S D C S T R I A L A S D Eh'GINEERI,VG CHEMISTRY
At the start of the infusible phenol resinoid reaction we are confronted with two possibilities: First, the reaction may go between the aldehyde and the ring hydrogen of the phenol, giving the hydroxyphenylcarbinols and then the diphenols. Second, the phenol may act as an alcohol, which enters into the acetal reaction giving acetals and these rearrange to the diphenols. The second series seems very probable, even though Baeyer,53 Ter RIeer,62F a b i n ~ iand , ~ ~C l a u ~who , ~ ~first investigated in this field, decided in favor of the reactivity of the ring hydrogens of the phenol.
229
series are known and the hydroxyphenyl alcohols have been studied in connection with the phenol resinoid reaction. This formidable array would carry one to the first apparent way station in the phenol resinoid reaction-that is, a t the fusible product called Novolak resin. On a foundation of such study one could perhaps venture a guess as to the next molecular change in that puzzling mass called phenol resinoid. Preliminary Findings
The Novolak reaction resulting from the use of acids as catalysts seems easier to follow than the reaction when alkaline catalysts are used. Hydrochloric acid was therefore chosen I n whatever theoretical speculation we engage on this as a catalyst. The aldehydes of higher molecular weight are subject, we must not lose sight of the fact that the nature of appreciably more sluggish than those of smaller molecular this condensing agent may have an enormous influence on the weight, so normal butaldehyde and phenol were chosen in way the reaction takes place, even if a t the end the products order to obtain some indications of the course of the reaction. look very much alike and are more or less similar.51 For A mixture of phenol and normal butaldehyde, when held a t instance, when an acid condensing agent is used the process room temperature and without a catalyst, showed no noticeproceeds very differently from what happens when alkalies able signs of reaction after 4 months. But when to the theoare used. Then again when ammonia is used the reactions retical proportion of 1 gram molecular weight of aldehyde and which succeed each other seem to be quite different from what 2 gram molecular weights of phenol there were added a few happens when fixed alkalies are employed.24 These apparent cubic centimeters of dry hydrogen chloride gas, or a drop of differences may be due to catalytic changes of speed of the concentrated hydrochloric acid, reaction began a t once. The different succeeding and simultaneous reactions in the same reaction mass first gave out heat without any other visible series. That related reactions are very sensitive to environ- signs of change either of viscosity or color. After a time the ment changes is well shown by C l a i ~ e nwho , ~ ~found that these mixture cooled without any very apparent change. Then rearrangements would occur in some solvents but not in others. cloudiness appeared and the viscosity increased with but little He obtained the ethers in alcohol solution and the phenols in heat evolution, The mass became more and more viscous benzene solution a t room temperatures. Pauly and Schanz66 and brownish in color, until a t the end of 2 hours it had the found the presence of traces of water to be an important influ- appearance of heavy molasses. At the end of a week it was ence in related reactions. jelly-like, with about one-third of the mass as a suspension of Practical experience bears out the contention that the differ- crystals of p-dihydroxydiphenylbutane. If the reaction was ences found in the intermediate bodies from different catalysts stopped by dilution a t various points in this change, resins may be due to specific action of the catalysts on different and gummy masses were always formed. I n one experiment reactions in the same series and that the final product may in after 2 days the reaction mass showed only a small amount of all cases be much the same. excess phenol. By extraction with boiling water and recrysIn approaching this problem the writers incline to the view tallization from water of the resulting crystals 35 to 38 per that the hydroxyl hydrogen is more active than the para cent yields of p-dihydroxydiphenylbutane, with a melting hydrogen, and will therefore first react with the aldehyde to point of 136" C., were obtained. give the phenoxy compounds. These then rearrange to the More than 60 per cent of the initial reaction product of the corresponding phenols. But whatever their theories in the action of normal butaldehyde on phenol was left as a resinous matter, the complexities of the reactions involved and the mass similar to the fusible, soluble, Novolak type resins. difficulties of purification and identification of the end products Boiling sodium carbonate solutions gave no p-dihydroxyof either the fusible Novolak resins or of the infusible phenol diphenylbutane from this resin. By the use of toluene as a resinoids, make the establishment of more facts necessary in or- solvent no crystals could be obtained from this re&. Also, der to render a decision. So many complexities make it im- whenever a few of the crystals were added to the resin they perative that before a valid decision can be reached these could very easily be recovered by crystallization from toluene. possible intermediate compounds should be carefully studied It does not, then, seem possible that this resinous lpass could and tried as a starting point for the phenol resinoid reaction. contain any important amounts of crystalline p-dihydroxydiphenylbutane prevented by impurities from crystallizing. Aim of This Investigation I I n order to determine if this resinous mass from butaldeThe difficulties of purification of the end products in the hyde and phenol was a dihydroxy phenol of the same type as phenol resinoid reaction render of slight use many of those p-dihydroxydiphenylbutane-as, for instance, the 0-, p-dichemical methods which have resulted in such clear elucida- hydroxy compound-the amount of sodium hydroxide needed tion of other series of reactions. No investigator has yet been for solution was determined. Excess normal sodium hydroxide certain of having an infusible resinoid that was pure. Only solution was used to dissolve the sample and the excess tione general method of advance therefore seems to be available. trated with normal acid. A permanent slight cloudiness due The logical means of advancing the knowledge in this field to precipitation was used as the end point. The method seems to be to build up a series of the theoretical intermediate should give somewhat low results. compounds and to try such possible intermediate compounds Crystalline p-dihydroxydiphenylbutane by this method in the resinoid reaction, required almost the theoretical amount of sodium hydroxide It becomes desirable to study as many as possible of the fol- expected for a dihydroxy compound. This resinous mass lowing series of compounds: phenoxy alcohols (XXV), p-hy- required only 48.4 per cent of the amount needed for a didroxyphenyl alcohols (XVII) and their tautomeric forms hydroxy compound; or, calculated for a monohydroxy com(XIX), diphenoxymethane (XIV), .phenoxy-p-hydroxyphe- pound, 96.8 per cent as much sodium hydroxide was used as nylmethane (XV), and the tautomeric forms of pdihydroxy- was expected for a monophenol. diphenylmethane (XXI) and (XXII). Of these, some memWe are dealing here with a resin that is, no doubt, impure, bers of the p-hydroxyphenyl alcohols and diphenoxymethane the sample used containing, perhaps, some occluded toluene Different Classes of Catalysts
Vol. 17, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY,
230
or toluene residues. Furthermore, since the analytical method used is certain to give results more or less low due to the solubilities of the precipitates in the solution, the results are as near as can be expected and seem to point to the resin as a monohydroxy compound. Both the resin and the crystals were analyzed for replaceable hydrogen by the action of metallic sodium in a xylene solution. In this case both the compounds gave but one replaceable hydrogen, and this method is of no value in differentiating between these two compounds. This condition arises seemingly because the monosodium salt is in each case insoluble in xylene, a result expected and differing from the action of the sodium salts in water solutions. This resinous mass from butaldehyde and phenol, when heated with 10 per cent paraform in a sealed tube a t 182" C. for 6 hours, gave an infusible, insoluble resin of the phenol resinoid type. The crystalline p-dihydroxydiphenylbutane under the same conditions gave a similar insoluble resinoid. It is evident that either, or both, of these products might be intermediates in making a phenol resinoid from butaldehyde and phenol.
The intermediates shown by Gomberg were followed in an attempt to find if this series showed any similarities to the phenol resinoid reactions. Good yields of diphenoxydiphenylmethane (XXVII) and p-hydroxytriphenylcarbinol (XXIII) are possible. A resin (XXIX) was obtained as one intermediate, which split on acid hydrolysis to give p-hydroxytriphenylcarbinol and phenol. This resin has the general properties of the Novolak resins; that is, it is permanently fusible under certain conditions and hardens with the same proportions of hexamethylenetetramine to give a true phenol resinoid. From this formation and decomposition it is perhaps largely p-hydroxytriphenylphenoxymethane (XXIX) . By para rearrangement it goes to p-dihydroxytetraphenylmethane (XXVII). 2CsHs
+ ccl4 -k AlCla
Cs&\
-+
(CsHs)tCC12AICIs + (CsHfi)iCC12 Ice
+ C6HsOHd CsHfi\ C/OCsHs ----
/c1
C CsHa/ \el
\cl CsHsOH (XXVIII) Not isolated
(111)
Action of Heat o n Butaldehyde Resin The resinous mass and the crystalline p-dihydroxydiphenylbutane gave the same molecular weights in benzene solution. Combustion analyses also indicate the resin and crystals to be the same in composition. After heating this resinous mass for an hour a t 260" C. and crystallizing from toluene, about 80 per cent of its weight could be obtained as pure crystals of p-dihydroxydiphenylbutane. The product after heat treatment is thus very different from that which has not been heated. This resinous mass must, then, be an intermediate product which is converted by heat to the crystalline compound. This resinous mass, on one distillation, under high vacuum, gave almost pure p-dihydroxydiphenylbutane, which crystallized in beautiful crystals in the receiver. As has been stated previously, the resinous mass from butaldehyde and phenol gave a true monosodium salt with sodium hydroxide and was not affected by sodium carbonate. On the other hand, the crystals of p-dihydroxydiphenylbutane gave a disodium salt with sodium hydroxide and under certain conditions were affected by sodium carbonate. Since we have here a phenol which by some rearrangement goes to the p-diphenol, it would seem possible that the resin is 1-phenoxy-1-p-hydroxyphenyl-n-butaneand that the change which takes place is para rearrangement. CHaCHzCH*\ /OC6Hs C H/ \CbHdOH
CHsCHXHs\ /Ce"OH C Rearranges H/ \ceH4OH
---A
Phenoxy-@-hydroxyphenylbutane p-Dihydroxydiphenylbutane Resin (XXXVII) Crystals (XXVI)
Important Advances from Another Field Large-scale production of benzophenone dichloride or of benzophenone seems possible by the action of carbon tetrachloride on benzene in the presence of anhydrous aluminium chloride or ferric chloride. By careful hydrolysis of the intermediate aluminium compound almost pure benzophenone chloride (111) was obtained by distilling off the unattacked benzene. By following Gomberg'P method for benzophenone chloride and Mackenzie's3* method for p-dihydroxytetraphenylmethane, molecular runs were made, with 50 per cent final yields. No particular attempt was made to obtain maximum yields, and small runs indicated a final yield of 80 per cent, with little loss from by-products. Al.coho1was used as a solvent for crystallization.
CaHs/ \OCsHs (XXVII) Crystals Also CsHs\ /OCe& CeHs\ /Ce&OH c ~ HC ~\e1 / Rearranges C&/ C\Cl )r
(XXX) Not isolated
(XXVIII) CsHs\
Rearranges
____*
/CH=CH\
/OH C CsHs/ \CH=CH/ \cl (XXXI) Not isolated
c=c
Mainly
-
GHs\ /CeH4OH __ C C6HS/ \cl CeHsOH Furthermore CBHS\ /OCsHs C Ce&/ \OC6Hs Rearranges (XXVII) Crystals Then C6&\
/C&OH C CsHs/ \OCsHs (XXIX) Resin
CeH6\ /CeH4OH C CeHa/ \CeH4OH (IV) Crystals
And under certain conditions C a s \ /CE"OH C a s \ /CsH4OH b C C CeH6/ \OC&& Acid hydrolysis C6HS/ \.OH (XXIX) (XXIII)
+ CeHsOH
The normal course of the reaction is (111) + (XXVIII) + (XXX) -+ (XXIX) which may go to (IV). The reactions are relatively rapid, except the change from (XXIX) to (IV). The compounds (XXX), (XXVIII), and (XXXI) were not isolated, but were suspected as being a probable cause of the intense red intermediate color which is always developed immediately on the addition of phenol to benzophenone dichloride and disappears with the last of the chlorine content. Infusible, insoluble phenol resinoids were obtained from both the resin (XXIX) and the crystals (IV) by heating to 280" C . for 6 hours with 10 per cent paraform in sealed tubes. The color changes of the two tautomeric p-hydroxytriphenylcarbinols were very evident.39 CsHs\ /C&LOH C CeHs/ \OH Colorless crystals
e
CeHs\ CeHs/
c=C
/CH=CH\
/OH C
\CH=CH/ \OH Yellow crystals
I S D CS T R fA L A S D ENGINEERING CHEMLS TR Y
March, 1925
Unessential Compqunds
The fact that many compounds unite directly with the aldehydes, as for instance hydrogen cyanide, led to the hope that phenol would to some extent show the same action. No action could be detected between phenol and n-but aldehyde in contact without a catalyst for 4 months a t room temperature. Reaction can be brought about without a catalyqt a t elevated temperatures, however, as is shown by the .4ylsworth process.56 To avoid use of the dangerous hydrogen cyanide the hydroxy acids are often made from the aldehyde bisulfite compound and an alkali cyanide. I n the same way it was thought that the phenoxy alcohols (XXXII) might be obtained. R\
+
HCN
+ \O-SO
NaCN
C=O
H/ R\c/OH H/
‘Nad
R\/”OH H/ \O-SO
+
hTaOC&
R \/OH -+
-
H/ \CN R\ /OH C H/ \CN
4- NazSOs
R\, /OH
NaO
(XXXII)
I n attempting to make phenoxymethyl alcohol in this way there was obtained instead its methyl ether. This methoxyphenoxymethane seems of no interest in the normal phenolresinoid reactions as determined by the hardening test with hexamethylenetetramine; yet it has interest in that it forms typical saliretin resins on acid hydrolysis-a fact which is explained best by a rearrangement, as has already been pointed out. Phenoxybutyl alcohol was made by this method and proved to have no tendency to harden under treatment with hexamethylenetetramine. The diphenoxy compounds were then made by starting with the dichloride. I n this case it was necessary to work in the ‘absence of free phenol, as the latter compound seems greatly to influence the rearrangement of the phenyl ether group. Methylene chloride and sodium phenoxide reacted t o give the diphenoxymethane and a resin which seemed identical with the fusible resin from phenol and formaldehyde. The diphenoxymethane showed no tendency to harden under treatment with hexamethylenetetramine, and therefore as such does not seem to enter directly into the phenol reqinoid reaction. These facts should clear away some of the mists of uncertainty and allow us to construct the first steps in the series of reactions which take place in the manufacture of phenol resinoids. Course of the Reaction The phenol first unites directly with the aldehyde to form a mixed ether-alcohol compound ( X S S I I I ) , and the resulting ether group very rapidly rearranges to the phenol. R\
c=o
R’/
R\ /OH
f HOCoHs+ c R r / \OC&
Rearranges R\, /OH rapidly
(XXXIII)
*
c
R’,’ \CsH,OH (XXXI\’)
C ~ H ~ O R\ H / O C ~ H ~ Sometimes rearranges R\, /C~H,OH
c
--*
R’/ \CoH,OH (=VI. :L
-
slowly
c
R’/ \CbHdOH (XXXVI)
Either the resin (XXIEV) or the crystals (XYXT’I) will enter. into theifinal s%sges of the phenol resinoid reaction and give the s&rnekqphr& product., which foreems t o the con-
231.
clusion that this final rearrangement is immaterial to the success or failure of the production of phenol resinoids. we can start with either (XXXV) or (XXXVI) ty;pe compounds to make phenol resinoids, it becomes important to know if there is any essential difference in the action of the two classes of compounds. A study of the amount of methylene groups needed properly to harden various homologs of types (XXXV) and (XXXVI) was undertaken. There resulted the conviction that one molecular weight d methylene group would harden one molecular weight of the homologs of either type. A summing up of the data available in the literature and of the writers’ own experience leads to some general conclusions which have a direct bearing on the next step in the series of reactions. First, any aldehyde or ketone (or their equivalent) may be used to make the fusible resin; but only bodies giving up methylene groups will enter rapidly enough into the second step, or hardening action, to give commercial infusible phenol resinoids. Second, in comparing the time in which these different fusible resins harden, it seems that changes in the phenolic bodies used make comparatively lesser differences in the hardening time, whereas changes in the aldehydes and ketones make greater differences. Third, a mol of fusible resin may be reacted with a mol of methylene compound and still give a fusible or reactive A type resin which, under the influence of heat, may go to a B and then to a C type phenol resinoid. Therefore from the fusible Novolak resin stage there still seems to be two steps-first a further condensation, and then a hardening or polymerization ~ t a g e . ~ ’ ~ ~ ~ The resinous nature of the commercial intermediate Novolak resin involves some difficulties in the technical production of the final products. The possible improvement in control by starting with crystalline p-dihydroxydiphenylmethane makes this compound of commercial interest. Experiments with Fusible Novolak Resins
Attempts were therefore made to determine something of the composition of fusible Novolak resins, and if possible to change them into crystalline products. These resins showed molecular weights, in benzene, of the same order as the molecular weights of the crystals obtained from them by water extraction. Thus, the formaldehyde-phenol fusible Novolak resin gave molecular weights of 200 f 5 , which checked with the molecular weights obtained for pure p-dihydroxydiphenylmethane(200 * 2). In the same way the weights for acetaldehyde phenol resin corresponded to the molecular weight of p-dihydroxydiphenylethane. Since distillation of the resin from the butaldehyde phenol condensation resulted in crystals of p-dihydroxydiphenylbutane, it became important to know if this method could be applied in other cases. A resin was made from acetaldehyde and phenol in the same way as was used with butaldehyde. The product was a resinous, fusible mass of the Novolak type, from which only a few crystals could be extracted. The extracted resin was distilled under a pressure of 10 to 15 mm. of mercury and approximately half its weight obtained as good crystals of p dihydroxydiphenylethane. .4n attempt was then made to distil the formaldehydephenol fusible Novolak resin. Under 15 mm. pressure it averaged 4 per cent, with a boiling point near that of phenol, 6 per cent crystals of p-dihydroxydiphenylmethane and 89 per cent of a residue which would not distil but when heated to about 270’ C. polymerized suddenly to a saliretin type resin. This polymerized residue was a foamy mass of solid a t 300’ C. and ‘w-auldwhar a t higher temperatures without melting. Xt was insoluble but would swell to jelly-like masses under longI
232
INDUSTRIAL A N D ENGINEERING CHEMISTRY
continued action of some solvents, such as acetone. Like the saliretin made from hydroxybenzyl alcohols through elimination of water, it lacked the hardness and strength of true phenol resinoids. Composition of Novolak
The main portion of this Novolak resin made from format dehyde and phenol is' a compound or compounds having the same molecular weight, in benzene, as pdihydroxydiphenylmethane. If the heating is stopped in time we have a residue resin which, under suitable conditions, is permanently fusible and which seems to consist of fairly pure phydroxyphenylphenoxymethane (XV). The permanently fusible Novolak resin thus seems to consist of varying mixtures of p-hydroxyphenylphenoxymethane, phenol, and p-dihydroxydiphenylmethane. The phenol acts as a solvent and determines the melting point of the mixture. The amount of free phenol present in the ordinary Novolak varies from about 8 to 12 per cent determined by the action of metallic sodium in xylene, and the amount of crystalline pdihydroxydiphenylmethane varies from 1 to 2 per cent as determined by the extraction method. Formation of Resinoids
When phenols and aldehydes react in the presence of various mineral acids, the product tends towards the fusible class of resins unless a large excess of aldehyde is present and is made to react. Alkalies as catalysts favor the direct formation of resinoids unless a very large excess of phenol is present. The fusible Sovolak resin is changed to the infusible resinoids by the action of more methylene groups in the presence of this second class of catalysts. It is obvious that in the presence of alkalies we may expect difficulty in stopping a t the p-hydroxyphenylphenoxymethane stage, since it might react as soon as formed to give that product which is the next step in the phenol resinoid reaction. If we take any proportion of phenol and formaldehyde which comes between the limits of 0.5 mol of formaldehyde to 1 mol of phenol and 1 mol of formaldehyde to 1 mol of phenol, and compare the results obtained by the use of catalysts in the two classes, we find a very apparent difference. Using dilute hydrochloric acid we have a reaction which very quickly unites to give the fusible resin. Using, for instance, the proportions of 0.87 mol formaldehyde to 1 mol of phenol, the reaction quickly reaahes an apparent equilibrium when part of the phenol and only part of the formaldehyde have been changed to a resin; that is, this rapid change is complet,ed within 15 minutes from the time the reaction mass reaches a boiling temperature. Further change will no doubt occur, but hours rather than minutes are needed to effect appreciable change. If we heat this product to free it from water, we lose not only the water but the unused formaldehyde and some of the unused phenol, and the resulting resin will contain almost no free formaldehyde but about 10 per cent of free phenol. Using the same proportions of 0.87 mol of formaldehyde to 1 mol of phenol with sodium hydroxide, in place of hydrochloric acid, as a catalyst, we obtain an apparently different product. In the first place, the formaldehyde is progressively used until it completely disappears. At this point about a tenth of the phenol is still in the free state and can be reIt should be noted that in moved by steam distillation.*~*6*6B all these reactions it is not so much the amount of aldehyde and phenol brought in contact which determines the result as the amount of the raw materials which are made to react; and this amount depends on many factors, such as temperature, pressure, dilution, time, acidity, etc., in addition to the variations due to the use of commercial products.
VoI. 17, No. 3
If the reaction mass, taken when the formaldehyde has disappeared, is heated to remove the water, some free phenol is also lost. The resulting liquid resin is a variety of the wellknown first or A stage of phenol resinoid. It is a solid, brittle resin when cold and will stand melting and cooling a limited number of times. If it is kept melted for a time i t suffers no very apparent change, until it suddenly, and without warning goes over to a jelly-like mass. This corresponds to the phenol resinoid B stage. If this is held a t the same high temperature it progressively hardens to the C or true end stage of phenol resinoids. If any free phenol has been left after removing water from the initial resin, i t will still be found in this hardened or C type resinoid and will somewhat modify its resistivity to chemical and physical agents. Condensation Followed by Polymerization
There seem, therefore, to be three outstanding features in the condensation of phenol and formaldehyde: First, the condensation of 2 molecules of phenol and 1 molecule of formaldehyde; second, the condensation of this product with another CH2 molecule; and third, the change or polymerization of the resulting product to give the final hardened product, or .resinoid C. Attempt will be made in this paper to explain completely only the first steps in this series of reactions. Endeavor will later be made to clear up the complete series, but direct evidence for solving the problem is so dficult to gather that i t is permissible a t present to speculate as to what happens in these second and third stages of the reaction series. Two Classes of Hardened Products
In order to avoid confusion one must keep well in mind the fact that there are two different hardening processes which give very different products. The fusible or Novolak type resins can be made to harden in some fashion under certain conditions-for instance, elimination of free phenol, without the addition of any more methylene groups-but the result is a saliretin type resin of nondescript properties and of no commercial value. When more methylene groups are added to a fusible or Novolak type resin, the mass will, under the influence of heat, go to the end or C type resinoid. First Condensation
When condensation of phenol and formaldehyde takes place, under the influence of alkalies, only the phenol resinoid type of hardening can be detected unless a large excess of phenol is present. It would seem, then, that mineral acids catalyze certain reactions in the series and have very little or no catalytic effect on the remaining reactions in the series. The catalytic effect of mineral acids enables one rather quickly to reach an apparent equilibrium between phenol, formaldehyde, and phenoxy-phydroxyphenylmethane. Under certain conditions the latter compound may rearrange to the dihydroxy compound, but in the product made from formaldehyde a rather low percentage of rearranged product has been found. So far as has been tested, this tendency to rearrange increases with increasing molecular weight of the aldehyde or ketone used. The character of the phenol used has a decided influence, as has been shown by the differences in the rearrangement of the condensation products made from alphanaphthol and from b e t a - n a p h t h ~ I . ~ ~ * ~ ~ A sample of the fusible Novolak resin which had been heated a t 200" C. for 30 minutes under a pressure of 20 mm. of mercury was dissolved in excess normal sodium hydroxide solution and the excess titrated with acid until a cloudy solution was obtained. Here the caustic sod@ needed for solution was 88 per cent of that expected for the phenoxy-p-
ISDCSTRIAL A S D E2VGI;VEERING CHE-IIISTRY
March, 1925
233
There are also present small amounts of unused phenol, unused hardening agent, generally hexamethylenetetramine, and traces of the various intermediate compounds which are essential in the production of resinoids. With this possibility of formation of unsaturated compounds in mind one can imagine some of the complications that might result under the stimulation of different catalysts. In the case of alkaline catalysts, we seem to be catalyzing the first and second group reactions a t about the same rate, so that a molecule of formaldehyde reacts with two of phenol Second Condensation to give the phenoxy-p-hydroxyphenylmethane, which reacts with another formaldehyde to form the unsaturated This second step in the condensation, where one CH:, compound. This unsaturated body may be conceived to act group unites with one molecule of phenoxy-p-hydroxyphenylas is common among certain classes of unsaturated commethane, may take place in many ways. But various pounds; that is, it polymerizes slowly up to a certain point indications, such as absence of the formation of water and the and then suddenly gelatinizes as is characteristic, for instance, phenolic properties of the product after condensation, eliminate the probability of action on the para-hydroxy group. of China wood oil. These theories, advanced to explain the last two general There remains the possibility of a t least five different points steps in the condensation of phenol and formaldehyde, are, of of attack on benzene rings and one possibility on methane carbon group. Yet reaction at any of the available points on course, only surmises based on general observations under the benzene rings leaves unexplained the phenomenon seem- various conditions; yet they tend best to explain all the phenomena observed. Hope is not abandoned that a t some fuingly best described as polymerization. ture time means will be found to clear up the seemingly unsurmountable difficulties in the last two groups of this comPolymerization plicated series of reactions. Having once granted the possiIf we are to hazard a guess as to this second condensation, bility of the reaction of aldehydes to give a double-bonded the only possibility which seems to explain all observed compound, one would expect a stage of polymerization. phenomena is that the action takes place on the methane References to the polymerization of substituted ethylene, carbon group, giving an unsaturated compound, the so-called and homologs, are very numerous in the literature. Fries phenol resinoid A , which polymerizes progressively through and FickewirthG0call attention to the formation of a resin by the B and C stages. LebedevS8 has the heating of o-hydroxyphenylethylene. only recently explained the results of polymerization of so First stage: comparatively simple a substance as asymmetrical dipheH\ H\ /C~HIOH nylethylene, and one would expect difficulties in elucidating, c=o f 2CsHsOH + C H/ \OCeHs not only the polymerization, but also the existence of the a H/ Fusible resin asymmetrical hydroxyphenylphenoxyethylene and its homologs, since here the substances are not only more complicated Second stage: but also are of a resinous nature. H\/C&LOH H\ H'\ /CeHdOH C c=o+ c=c Experimental Data H/\OCsHj H/ H/ '\OCsHa Phenol resinoid A stage All conclusions concerning the end products in the phenol Third stage: resinoid series seem necessarily to be based on less definite chemical proof than is the case with most chemical compounds. For this reason data in this field should be reported in fairly complete detail; in order that a complete survey of the field Phenol resinoid C stage at some future time may enable one to draw undisputable The phenol resinoid B type is probably a mixture of the conclusions. Therefore some data are given here which are -4and C types. Where ketones or higher aldehydes are used, not entirely novel but which seem to be of vital interest in the the result would be a homolog of the above. For instance, resinoid series. from acetone we might obtain a reaction as follows: p -Dihydroxydiphenylbutane
hydroxyphenylmethane. This is a fair enough agreement, as the resin was slightly soluble under the conditions used and this error would tend to give low results. These fusible resins will react with more methylene groupshexamethylenetetramine, for instance-to give a true phenol resinoid C. When one gram molecular weight of this phenoxy-p-hydroxyphenylmethane is heated with one gram molecular weight of methylene group, the result is a phenol resinoid C of full resistivity.
+
Constitution of Infusible Resinoids
Those commercial phenol resinoids which are made from phenol and formaldehyde would then consist mainly of the compound
which will be found in all stages from the initial or unpolymerized molecule to the completely polymerized form, together with a small amount of
Eighteen and eight-tenths grams of phenol were melted and poured into 7.2 grams of normal butaldehyde. A few cubic centimeters of hydrogen chloride gas were bubbled through the mass and the whole was allowed to stand in a closed vessel for 7 days. The reaction mass was then steamdistilled until the distillate showed only a slight trace of phenol, then was allowed to cool. The water was poured off and the resin and the crystals dissolved, by heating, in 50 cc. of toluene. After separating the hot toluene solution from water, cooling and filtering, 8.5 grams of crystals were obtained. The filtrate from these crystals was distilled in v a c w (22 mm. pressure) and the distillate adjusted, by adding toluene, to a total of 35 cc. The distillate was heated to effect solution of the crystals, and recrystallized by cooling. Seven grams of crystals were obtained. The distillate was redistilled in vacuo and adjusted, by adding toluene, to 25 cc. of distillate. This solution, on crystallization, gave 5 grams of
Iiz'DUSTRIAL AND ENGINEERING CHEMISTRY
234
crystals. These three lots of crystals were put together and recrystallized from toluene, giving 19 grams of p-dihydroxydiphenylbutane melting a t 136-7 " C. (All temperatures mentioned in this paper are uncorrected unless otherwise stated.) The combined residue from the mother liquors and distillations gave 4 grams of a dark, hard, fusible resin. This resin was again distilled under low pressure until about one-half had distilled over. After dissolving in hot toluene and cooling, 1 gram of crystals was obtained. There was left in the distilling flask 2 grams of a dark, hard, brittle, fusible resin. The molecular weight of this residue was determined in acetic acid as 376. The crystalline p-dihydroxydiphenylbutane distilled between 270" and 273' C. under 22 mm. pressure. Under atmospheric pressure it partly decomposed. Decomposition apparently began a t about 285" C. The calculated molecular weight for the three compounds with the formula C16H&--that is, p-dihydroxydiphenylbutane, p-hydroxyphenylphenoxybutane, and diphenoxybutane-is 242.1. The p-dihydroxydiphenylbutane crystals gave molecular weights of 242 * 3 in acetic acid, as checked by two different operators.* Combustion analyses of the crystals confirm the formula CI6HleO2. Calculated for C16H1802, C = 79.30 per cent, H = 7.48 per cent. Sample Gram 0 2017 0 1892
CO?
Gram 0 5834 0.5467
HzO Gram 0 1353 0 1221
C
Per cent
79.01 78 80
H
Per cent 7 52 7.18
Average of all determinations made gives 79.68 per cent C and 7.43 per cent H. By analogy with the action of p-dihydroxydiphenylmethane, the crystalline p-dihydroxydiphenylbutane should give a phenol resinoid when heated with hexamethylenetetramine under pressure. The crystals were heated at 180" C. for 3 hours in a sealed tube with 10 per cent by weight of hexamethylene tetramine. The product was an infusible, insoluble resin of the phenol resinoid type. p-Dihydroxydiphenylbutane crystals were dissolved in excess normal sodium hydroxide solution and the excess was titrated with normal acid solution to the point of permanent cloudiness. Very close checks could be obtained. From an average of five determinations 99.9 per cent as much sodium hydroxide was required for solution as was calculated for the dihydroxy phenol. Phenoxy - p -hydroxyphenylbutane
Eighteen and eight-tenths grams of phenol were mixed with 7.2 grams of normal butaldehyde, subjected to the action of a few cubic centimeters of hydrogen chloride gas, and the mass allowed to stand for 7 days. The product was then steamdistilled to remove phenol and was Crystallized from toluene. On evaporation of the filtrate a residue of 15 grams of a hard, brittle resin was obtained. The color of the resin was somewhat improved by subjecting it to a high vacuum a t 200" C. for 5 minutes. It was also improved by refluxing in toluene solution in the presence of animal charcoal. The final product was of a light straw color. The resin was distilled under 22 mm. pressure and the temperature of the vapors ranged from 260" to 310" C., giving a distillate which crystallized to a solid mass on cooling, The distillate was recrystallized from toluene, giving a weight of p-dihydroxydiphenylbutane crystals equal to 79 per cent of the, weight of the resin distilled. Two samples of the resin gave molecular weights in benzene of 253 and 239, which is about as near the theoretical 242 as can be expected from a I * Thanks are expressed here for the cooperation of Prof. E. L. Krause, of Marietta College, in checking many of the molecular weight determinations and combustion analyses in this article.
Vol. 17, No. 3
resinous product. The resin was insoluble in sodium carbonate solution. KO crystals could be obtained from the resin on crystallization from toluene. Ten per cent by weight of crystals of p-dihydroxydiphenylbutane were melted with the resin and 98 per cent of these crystals were easily recovered on one crystallization from toluene. So this resin cannot be considered crystalline p-dihydroxydiphenylbutane prevented by impurities from crystallizing. Combustion analyses of the resin gave an average value of 78.4 per cent carbon and 7.46 per cent hydrogen, as against a calculated value of 79.3 per cent for carbon and 7.48 per cent for hydrogen. This resin is therefore a compound which rearranges to p-dihydroxydiphenylbutaneon heating. From its reactions one can eliminate consideration of the diphenoxy type compound. There are left only the mixed ether-phenol type and the different arrangements of the diphenol type. The amount of sodium hydroxide needed to hold the resin in dilute solution was determined as only 48.4 per cent of that needed for a dihydroxy compound. Since this is equivalent to 96.8 per cent of the amount that would be used if it were a monohydroxy compound, one is forced to the interpretation that it is a monophenolic compound. The resin is known to have an appreciable solubility in a solution of its o m sodium salt, so the method used is certain to give a slightly low result. Yet solubility will not explain the fact that less than half as much caustic soda is needed to dissolve the resin as to dissolve the same weight of the crystalline diphenol. Accordingly, the resin can be considered a monohydroxy compound, phenoxy-p-hydroxyphenylbutane,which will rearrange, under the influence of heat, to p-dihydroxydiphenylbutane. It should be noted here that nearly fifty years ago Baeyer161and somewhat later Michael,62obtained the same combustion analytical results from both a fusible resin and a crystalline product made from an aldehyda phenol condensation, indicating that their resinous and crystalline products had the same composition. p-Dihydroxytetraphenylmethane
By using the method of G ~ m b e r 85 g ~to ~ 90 per cent yields of crude benzophenone chloride were easily obtained. Two hundred and fourteen grams of the crude benzophenone chloride were mixed with 175 grams of phenol. Hydrogen chloride was given off. The reaction mass was allowed to stand a t 40" C. for 10 hours and then heated gradually to 125" C. and held a t this temperature for 24 hours. The product was then cooled and the mass crystallized from alcohol, 191 grams of crystals melting a t 285-6" C. being obtained. p-Dihydroxytetraphenylmethane crystals heated in a sealed tube with 10 per cent by weight of hexamethylenetetramine, a t 290" C. for 6 hours, gave an infusible, insoluble resinoid. Phenoxy- p - hydroxytriphenylmethane By heating the phenol-benzophenone chloride mixture suddenly to expel the hydrogen chloride quickly, the product was a resin which resembled the Novolak resins, but was darker in color. This resin, on acid hydrolysis, gave some crystals of p-hydroxytriphenylcarbinol. No attempt was made to determine the constitution of this resin beyond establishing the fact that on hydrolysis it would give the carbinol and that on heat treatment it gave almost quantitative yields of the diphenol. It is a true fusible resin under certain conditions and gave a true phenol resinoid on heating with hexamethylenetetramine. p-Hydroxytriphenylmethyl Alcohol As stated above, this compound can be obtained by boiling the resin in water containing some acid. However, it is best made by the iiiethod of Gomberg,39 which does not isolate the
March, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
intermediate resin. I n this method it would seem that sufficient hydrochloric acid is generated from unused benzophenone chloride to cause the hydrolysis on steam distillation. The advantage of the method arises from the fact that the low temperature used prevents the rearrangement of the second ether group to a phenol group, and therefore less p-dihydroxytetraphenylmethane is formed. Diphenoxydiphenylmethane
This is easily made in 65 per cent yield by the method of G ~ i i i b e r g . ~The ~ diphenoxydiphenylmethane was unaffected by treatment with hexamethylenetetramine a t 180" C. so it seems to have no special interest in the phenol resinoid series of reactions. Phenoxybutyl Alcohol
Seven and two-tenths grams of normal butaldehyde were rapidly mixed with a cooled, saturated water solution containing 10.4 grams of sodium bisulfite. After the reaction was completed, sufficient water was added to make R saturated solution a t 70" C. To this was added, at 70" C., a saturated water solution of sodium phenate containing 11.6 grams, The solutions were well mixed and allowed to stand 24 hours. The reaction mass was then steam-distilled and the light oil separated from the water. Thirteen grams of oil were obtained. This was washed with 10 per cent sodium hydroxide solution to free from phenol, washed with water, and distilled. Eleven grams distilled between 172" and 177" C. The product was a clear, colorless oil with a distinctive pine-like odor, which floated on water and steam-distilled about 1 part to 20 parts water. It discolored bromine water but did not give a precipitate. It was slightly soluble in concentrated sodium hydroxide solution, but precipitated on dilution. Molecular weight determinations were made by three M e r ent operators. Most of the determinations were made by the freezing point method using benzene as a solvent. Twelve determinations were made with results of 166 * 4. The average of all determinations was 167, in place of the calculated molecular weight of 166. From the method in which it is made, the fact that it is insoluble in caustic, and that it gives a molecular weight of about 166, it would seem to be phenoxybutyl alcohol. Heated with 20 per cent hexamethylenetetramine a t 180 " C. for 3 hours in a sealed tube, it gave a very small amount of a light yellow fusible resin. The phenoxybutyl alcohol obtained was a somewhat unstable substance. It quickly turned yellow in the light. It was insoluble when extracted with dilute caustic solution and yet after standing a week an appreciable amount was dissolved by the same caustic solution. On treatment with acids, even with sulfur dioxide, it would darken and partly resinify. A 4 per cent yield of this phenoxybutyl alcohol was obtained from a phenol-aldehyde condensation. I n this case 1 mol of phenol and 2 mols of butaldehyde were reacted a t room temperature for 30 days with only a trace of hydrogen chloride gas as a catalyst. When the same procedure was used as that given for making p-dihydroxydiphenylbutane,except reacting for shorter periods, traces of this phenoxybutyl alcohol could be obtained. I n one reaction, where it had stood only 2 hours, a yield of 0.5 per cent of this oil was obtained. From part of the same reaction mass, which had stood 10 days, no trace of the oil could be found. This phenoxybutyl alcohol, as such, did not harden with hexamethylenetetramine. All the reactions by which resins could be obtained from it were reactions in which rearrangement was expected. It was thought, therefore, that if this compound acts as an intermediate in the phenol resinoid se-
235
ries of reactions it must, under the conditions of the condensation reaction, immediately rearrange to the corresponding hydroxy compound. Phenoxy-p-hydroxyphenylmethane
Eleven cubic centimeters of 40 per cent formalin solution were added to a concentrated water solution containing 10.4 grams of NaHSOa and allowed to stand 1 hour. To this was then added a concentrated water solution containing 11.6 grams of sodium phenoxide. The mass was allowed to stand for 48 hours and then acidified slo~vly,a t room temperature, with 5 per cent hydrochloric acid. 4 clear, soft resin settled to the bottom. This was separated from the water, dissolved in ether, dried with sodium sulfate, and the ether distilled off, The product was a firm, clear, light-colored resin, soluble in caustic, with a weight of 11 grams. I n acetic acid it gave a slightly cloudy solution and a molecular weight of 264 On combustion analysis it gave the formula C1~HInO2.Calculated molecular weight is 200.1, C = 78.00 per cent, H = 6.04 per cent. Sample Gram 0,2619 0,2319
cog
Gram 0.7483 0.6541
HzO Gram 0.1445 0,1299
c
Per cent
H
ZS.30
Per cent 6.13
(8.03
6.04
Of the possible compounds with the formula C13H1202,two compounds-diphenoxymethane, which is a liquid with a boiling point of 293-5 O C., and p-dihydroxydiphenylmethane, which is crystalline-can be eliminated by a comparison of properties. By analogy with the phenoxy-p-hydroxyphenylbutane resin it seems possible that this resin is phenoxy-p-hydroxyphenylmethane. This resin was in every way comparable with the ordinary fusible Novolak resin from phenol and formaldehyde, and tests were accordingly made on the Novolak resin. Composition of Fusible Novolak Resin from Phenol and Formaldehyde
This resin, on attempted distillation in an inert gas, gave from 18 to 30 per cent phenolic bodies as a distillate and 40 to 50 per cent of a dark, infusible resin as a r e s i d ~ e . ~ 3Distillation a t 20 mm. pressure gave 4 per cent phenolic oil, 6 per cent crystals of p-dihydroxydiphenylmethane,and 89 per cent of a residue which polymerized suddenly a t 280" C. to an infusible, insoluble saliretin type resin. From the same fusible resin only 1.8 per cent of p-dihydroxydiphenylmethane could be extracted by boiling water. The 4 per cent difference may be due to rearrangement by heating. An attempt was made to convert more of the resib into p-dihydroxydiphenylmethane. Twenty grams were heated with an equal weight of phenol to 180" C. for 2 hours. A stream of dry hydrogen chloride was passed continuously through the mass. The hydrogen chloride was then discontinued and t8hemass kept at 125" C. for 48 hours. The mass was then fractionated under 18 mm. pressure and 5 grams of the diphenol were obtained, or 25 per cent instead of the 6 per cent in the former distillation. The fact that phenolic bodies were obtained in large percentage on heating a t atmospheric pressure, and only minor quantities on vacuum distillation, and that higher amounts of p-dihydroxydiphenylmethane were obtained by distillation and by heating in the presence of phenol and hydrogen chloride, point rather strongly to a phenyl ether group in the intermediate Novolak resin. A sample of the fusible Novolak resin was heated under 20 mm. pressure until the phenolic oil and p-dihydroxydiphenylmethane were removed. The mass was kept just below the temperature of polymerization for about 10 minutes and then cooled. It was still a fusible resin and supposedly nearly free from phenol and diphenol,
I S D r S T R I A L A,VD E.YGIL:ISEERISGCHEMISTRY
236
The amount of sodium hydroxide needed for solution of the p-dihydroxydiphenylmethanecrystals and also of the resin was determined. The amount of caustic soda needed to hold p-dihydroxydiphenylmethane in solution was 94 per cent of that calculated for the dihydroxy compound. The sodium hydroxide required for solution of the resin was 87.9 per cent of the amount calculated for a monohydroxy compound. As expected, these results are somewhat low owing to solubility of these substances in solution of their sodium salts. The Novolak resin, from which the phenol and diphenol had been removed by distillation, gave molecular weight determinations varying from 194 to 204. The average of four determinations was 202 instead of the calculated 200. Since from this resin only a small amount of p-dihydroxydiphenylmethane can be extracted, and its properties do not correspond with diphenoxymethane, the fusible Novolak resins seem to be largely the phenoxy-p-hydroxyphenylmethane or a compound immediately related to it. Phenoxymethoxymethane (Methylenephenylmethyl Ether)
To 10 cc. of formaldehyde solution, 40 per cent by volume, 10.4 grams of NaHSOa were added and stirred until no more heat was evolved. One hundred cubic centimeters of alcohol, and then 100 cc. of an alcohol solution containing 11.6 grams of sodium phenoxide, were added and the mixture was refluxed for 4 hours. The solid was removed by filtration, the filtrate evaporated to 40 cc. and again filtered. The remaining alcohol was distilled off under vacuum. The residue of about 5 grams of oily liquid was dissolved in ether, dried with anhydrous sodium sulfate, the ether allowed to evaporate, and the residue warmed with 10 cc. of petroleum ether to extract the phenol. The lower layer was separated and subjected to vacuum to remove any petroleum ether. Three grams of liquid were obtained. This liquid dissolved in water, but on addition of a drop of hydrochloric acid precipitated as a clear resin. When more acid was used it gave an infusible product resembling the saliretin resins. The liquid was so reactive that all attempts a t further purification resulted in the production of resins. Combustion of the liquid gave the following results: Sample cor Hz0 C H Gram
Gram
Gram
Per cent
Per cent
0.2104 0,2168
0.5330 0.5807
0.1384 0.1386
69 09 69.37
7.31 7.10
Calculated for H\/OC& C H/\OH Calculated for H\/OCsHs C H/\OCHs
C = 67.70per cent H = 6.49 per cent C = 69.52 per cent H = 7.23 per cent
The properties of this methoxyphenoxymethane check well with those given by Rey~hler,'~ who made the compound from chlorodimethyl ether. He also found it to be a liquid very easily resinified. As has been pointed out, this resinification is easily explained by a rearrangement which is followed by hydrolysis. Diphenoxymethane or Methylenediphenyl Ether Seventeen grams of methylene chloride, 23 grams of sodium phenoxide and 50 cc. of 95 per cent alcohol were put into a pressure flask and heated 3 hours a t 150' C. The alcohol was distilled off, the residue taken up with water, and extracted with ether. The ether solution was washed with 5 per cent sodium hydroxide solution to free it from phenol and dried with calcium chloride. The ether was removed by distillation and the residual oil distilled. Twelve grams came over a t 290-6" C. This fraction gave molecular weight determinations from 198 to 206, the average value being 202.
Yol. 17. S o . 3
From the stability of this compound and from the fact that no trace of it could be detected in the various condensations between phenol and formaldehyde, it is thought that this compound is not normally present in the resinoid series of reactions. I t was noticed that this diphenoxy compound gave a resin on standing for several weeks, a t room temperature, in contact with concentrated hydrochloric acid. This may be due to hydrolysis back to the aldehyde and then recombination. Resin from Benzal Chloride and Phenol
Rixteen grams of benzal chloride were gently warmed with 19 grams of phenol until the hydrogen chloride was mostly removed, and then heated to about 180" C. for a few minutes. The product on cooling was a red resinous mass, from which a few crystals of p-dihydroxytriphenylmethanewere extracted. The residual resin weighed 27 grams. The resin dissolved in chloroform, but would not crystallize from it on cooling. Molecular weight determinations of the resin in acetic acid as a solvent gave values of 275 * 11. The average value of all results was 274 as comDared to the theoretical CeHs\ /CeH,OH value of 275 for C H/ \ O W L This resin on heating a t 180" C. with 10 per cent hexamethylene in a sealed tube gave a n infusible resinoid. p-Dihydroxytriphenylmethane
Six grams of phenol and 2 grams of benzal chloride were heated gently to 120" C. for 10 hours. The mass wae subjected to a vacuum (24 mm. pressure) and the phenol removed. The temperature was allowed to rise to 200' C. The residue was dissolved in chloroform, treated with a little animal charcoal to remove $he color, and crystallized by cooling. Two grams of crystals were obtained which melted a t 160-1" C. These crystals would dissolve slightly in water, and crystallize from water in fine colorless needles. Heated with 10 per cent hexamethylenetetramine, the p-dihydroxytriphenylmethane gave an infusible resinoid. Additional Evidence of Rearrangement
A sample of the phenoxy-p-hydroxyphenylbutane resin required 96.8 per cent of the calculated amount of sodium hydroxide required for one hydroxyl group in order to remain in solution. A gram of this resin was weighed in a small flask and then heated for 1 hour a t 200" C., under a pressure of 18 mm. A small amount sublimed into the receiver but was disregarded. The residue was treated with excess standard sodium hydroxide solution and titrated back with acid. The residue from heating 1 gram required 113.8 per cent of sodium hydroxide needed for the solution of the monohydroxy compound as contrasted with 96.8 per cent required by the unheated resin. Thus the rearrangement of this resin in 1hour a t 200" C. approximates 15 per cent. Determining Free Phenol i n Fusible Resins
No good method for the determination of free phenol in fusible resins has so far been published. The method given below is based on the unpublished method of Meighan.'j' It allows the determination of one phenol in the presence of another where the one is soluble and the other insoluble in the solvent used. It therefore depends on the distribution of the phenol between two immiscible liquids. The determination is based on the measurement of hydrogen liberated from the soluble phenol by the action of metallic sodium. The solvent used must be one not affected by metallic sodium. The resin must be in the liquid state a t the temperature of the determination. It should be noted that in some cases one phenol can be determined in the presence of another even when
ISDCSTRI,4 L A S D ENGINEERISG CHEMISTRY
March, 1925
both are soluble in the solvent used. Several samples of commercial fusible resins were analyzed, and showed a variation in phenolic content from 8.74 to 13.35 per cent. .4sample of fusible resin was tested for free phenol, and several closely agreeing results gave the average figure of 9.33 per cent. Then 0.0735 gram of phenol was put in a tube with 1.0212 grams of this resin, the tube sealed, and solution effected by heat and agitation. This gave a resin with a phenolic content calculated as 15.59 per cent. This mixture was analyzed and the value 15.69 per cent obtained. In the same manner, to a resin with a phenolic content of 2.42 per cent was added phenol to a total of 10.95 per cent. The phenolic content was then determined as 10.48 per cent. Resinoids from Various C o m p o u n d s
The compounds given in the following table were heated with hexamethylenetetramine in the proportion of 1 mol of resin or crystals to one equivalent of CH2 group-that is, 23.3 grams of hexa. In all cases products of true phenol-resinoid characteristic were obtained. The following table shows the source and physical structure of various compounds which hardened to infusible, insoluble resinoids when heated with methylene-furnishing compounds in the proportions of 1 mol of the compound to 1 mol of available CH, group: FORM
COMPOUND
SOURCE
9-Dihydroxydiphenyldimethylmethane Phenoxy-p-hydroxyphenyldimethylmethane 9-Dihydroxydiphenylbutane Phenoxy-9-hydroxyphenylbutane P-Dihydroxytetraphenylmethane
Crystals
Acetone and phenol
Resin Crystals Resin Crystals
Phenoxy-p-hydroxytriphenylmethane
Acetone and phenol N-butaldehyde and phenol .N-butaldehyde and phenol Benzophenonedichloride and phenol
Resin
9-Dihydroxytriphenylmethane
Crystals
Benzophenone d i c h l o r i d e and phenol Benzal chloride and phenol, also benzaldehyde and phenol
Phenoxy-p-hydroxydiphenyl. methane
Resin
0-Dihydroxydiphenylmethane Crystals Phenoxy-p-hydroxyphenylmethane Resin P - Dihydroxydiphenylethane Crystals Phenoxy-9-hydroxyphenylethane Resin
Benzal chloride and phenol, also benzaldehyde and phenol Formaldehyde and phenol Formaldehyde and phenol Acetaldehyde and phenol Acetaldehyde and phenol, also acetylene and phenol
Summary
1-Further evidence has been advanced to indicate the order of reaction in the first stages of the infusible condensation products of phenol and aldehydes designated as phenol resinoids and also known as Bakelite, Resinit, Sipilite, Redmanol, Amberite, Formit, Condensite, Phenoform, Nuloid, Amberdeen, etc., etc. (a) Condensation takes place between the hydroxyl hydrogen of the phenol and the oxygen of the aldehyde or ketone. ( b ) The resulting phenoxy group rearranges to a para-hydroxy compound. ( c ) Condensation takes place between the resulting alcohol and the hydroxyl hydrogen of another phenol molecule. ( d ) This mixed phenoxyphenol compound sometimes rearranges to a diphenol. (e) The rearrangement in ( d ) is immaterial to the success or failure of the resinoid reaction.
2-Further details as to the composition of Novolak resins and phenol resinoids made from various aldehydes have been given. 3-Novolak resins have been made from new starting materials, as from carbon tetrachloride, benzene, and phenol, and from benzal chloride and phenol. 4-Resinoids have been made from these new Xovolak resins by causing them to react with substances containing methylene groups. &Evidence has been advanced to show the importance of the phenoxyphenol rearrangement in the phenol resinoid series.
237
6-A theory as to the constitution of the final product of the resinoid reaction has been announced. Bibliography 1-Baekeland, J . Ind. Eng. Chcm., 6, 506 (1913). 2-Manasse, U. S. Patent 526,786 (1894). 3-De Laire, French Patent 350,180 (1905). 4-Aylsworth, U. S. Patent 1,020,593 (1912). 5-Baekeland, U. S. Patent 939,966 (1909). 6-Baeyer, Ber., 6, 25, 280, 1094, 1095 (1872). 7--Kleeberg, A n n . , 263, 283 (1891). 8-Baekeland, J. I n d . Eng. Chem., 4, 737 (1912). 9-Moitessier, Jahresber., 676 (1886). l&Schotten, B e y . , 11, 784 (1878). 11-Piria, A n n . , 48, 7 5 (1843); 66, 37 (1845); 81, 245 (1852); 96, 357 (1855). 12-Ellis, “Synthetic Resins.” p. 99. 13-Baekeland, J. I n d . Eng. Chcm., 6, 507 (1913). 14-De Laire, D . R. P., 189, 262 (1905). 15--Blumer, British Patent 12,880 (1902). l+Baekeland, J. I n d . Eng. Chcm., 1, 545 (1909). 17-Raschig, Z . angcw. Chcm., 26,1945 (1912). 18-Baekeland, J . I n d . Eng, Chem., 1, 149 (1909). Ig-Ibid., 6, 508 (1913). gO-Beatty, French Patent 447,648 (1912). al-Dianin, J . Russ. Phys.-Chem. Ges., 1,488,523,601 (1891). 22-Wohl and Mylo, Ber., 46, 2046 (1912). 23-Glenz, Heleefica C h i n . Acta, 6 , 826 (1923). 24--Baekeland, J . I n d . Eng. Chem., 6 , 511 (1913). 25-Ibid., 6 , 510 (1913). 26-Auwers, A n n . , 366,124 (1907). 39, 1094 (1908). 27-Shorigin, J . Russ.Chcm. SOC., 28--Lunjac, J . Russ. Phys.-Chcm. Gcs., 36, 301 (1905) ; 39,1094 (1908). 29--Buttenberg, J . Chem. SOC.(London), 66, 502A (1894). Ibid., 66, 1188A (1889). 3@-RUSSdnOff, 31-Fabinyi, Ber., 9, 283 (1878). 32-Wagner, J . firakt. Chcm., 66, 313 (1902). 33-Sat0 and Sekine, J. Chcm. I n d . ( J a g a n ) , 24, 321, 332, 580 (1921) 34-Claus and Trainer, Bcr., 19, 3004 (1886). Ber., 9, 286 (1878). 35-Fabinyi, 36-Wenzke and Nieuwland, J . A m . Chcm. SOC.,46, 177 (1924). 37--Lunjac, J . Russ. Phys,-Chem. Gcs., 40, 466 (1909). 38-Mackenzie, J. Chem. SOL.(London), 79, 1209 (1901); 121, 1695 (1922). 39-Gomberg and Jickling, A m . Chem. J., 37,2575 (1915). IC--Claisen, Ann., 237, 270 (1887). 41-Mackenzie, J. Chcm. SOC.(London), 79, 1216T (1901). 42-Gomberg and Buchler, J. A m . Chem. Soc., 42, 2059 (1920). 43-Reychler, Bull. SOC. chim.. 1, 1195 (1907). 44--Ludwig, Claisen, and Eider, Ann., 401, 21 (1913). Ij-Fabre, Ann. chim., 18, 49 (1922) 46-Wenzke and Nieuwland, J . A m . Chem. SOC.,46, 178 (1924). 47-Michael, J . Chcm. SOC.(London), 67, 2338 (1895). 48-Staedel, Ann., 283, 164 (1894). 49-Bentley, Haworth, and Perkin, J . Chcm. SOC.(London). 69, 166T (1896). 5O--Mackenzie, Ibid., 79, 1205T(1901); also Fossi, Comfit. rend., 130, 725, 1194 (1900). 51-Baekeland and Harvey, J . I n d . Eng, Chcm., 13, 153 (1921). 52-Ter Meer, Be?., 7, 1197, 1201 (1874). 53-Baeyer, Ibid.. 6, 280, 1094 (1872). 54-Claisen, Z . angcw. Chem., 36, 478 (1923). 55-Pauly and Schanz, Bcr., 66B,979 (1923). 56-Aylswortl1, U. S. Patent 1,102,630 (1914). 57-Jablonower, J . A m . Chcm. SOC.,36, 811 (1913). 58-Lebedev. Ber., 66B,2349 (1923). 59-Baekeland, J. I n d . Eng. Chcm., 6,950 (1913). 60-Fries and Fickewirth, Ber., 41, 367 (1907). 61-Baeyer, Bn.,6, 25 (1872). 62-Michael, Zbid., 19, 1388 (1886). 63-Herzog, Z . angcw. Chem., 34, 97 (1921); abstracted C. A , , 16, 1969 (1921). 64-Meighan, method soon to be published from the Chemical Engineering Department of Columbia University. G b R e d m a n , Weith, and Brock, J . I n d . Eng. Chcm., 6 , 3 (1914). 6 6 R a s c h i g , Z . anorg. Chcm., 26, 1946 (1912). 67-Gomberg and Snow, J . A m . Chcm. SOC.,47, 199 (1925).
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