ESSENTIAL STEPS IN THE CATALYTIC CONDENSATION OF

[CONTRIBUTION No. 27

FROM THE

DEPARTMENT OF ORGANIC CHEMISTRY, FORDHAM UNIVERSITY]

ESSENTIAL STEPS IN THE CATALYTIC COXDEXSATIOS OF ALDEHYDES; NEW SYNTHESIS OF GLYCOL ESTERS1s2 MARTIN S. KULPINSKI

AND

F. F. FJORD3

Received February 10, 1949

Claisen (1) observed that benzaldehyde when treated with sodium alkoxides yields benzyl benzoate. Tischtschenko et al. in 1906 (2) discovered that aluminum alkoxides are able to condense smoothly aliphatic and aromatic aldehydes t o form simple esters. Hence, with the aid of these catalysts, Claisen's original observation received an important extension and generalization. Kord and his co-workers (3) showed for the first time that two dissimilar aldehydes in the presence of aluminum alkoxides react through an oxidationreduction interchange and form mixed esters. The reaction of this type proved to be of a rather general nature, as was shown by the study of numerous pairs of aldehydes. Many other investigators continued the research following similar lines (4). In view of the diverse examples, it was deemed suitable to condense an aliphatic saturated aldehyde, such as, butyraldehyde with an aliphatic unsaturated aldehyde, such as crotonaldehyde. Condensation of crotonaldehyde alone (2) and acrylic aldehyde alone ( 5 ) , with the aid of aluminum ethoxide resulted in failure, due to the extensive polymerization of these substances. Since polymerization seemed to be the main reaction to overcome, it was thought that with an appropriate control of conditions, as for example, temperature, solvents, time of reaction, exclusion of oxygen, use of polymerization inhibitors, and variation of alkoxides, the mixed condensation could be realized. In spite of all these variants, the mixed unsaturated esters, Le., butyl crotonate and crotonyl butyrate, in accordance with the usual course of the reaction, could not be isolated. Rearing in mind the sensitiveness of crotonaldehyde to alkali, a milder form of the catalyst could possibly bring about the desired result. A catalyst hitherto unapplied to this type of reaction was resorted to, Le., magnesium-aluminum ethoxide. In contradistinction to the simple aluminum alkoxide, it is a coordination compound (6) of the formula: Mg [Al(OCzH5)4]2. The complex catalyst did not lead to the mixed esters when crotonaldehyde was condensed with butyraldehyde. On the other hand, examination of the higher-boiling product 1 Abridged from the dissertation of M.S.K., submitted in partial fulfillment of the requirements of Doctor of Philosophy to the Graduate School of Fordham University, June, 1943. Presented before the Fall meeting of the American Chemical Society, Buffalo, N. Y., September, 1942. 3 For a preliminary communication see Kulpinski and Nord, Nature, 161, 363 (1943). 256

257

NEW SYNTHESIS OF GLYCOL ESTERS

obtained, revealed that the main reaction took a different course. The higher condensate proved to have the following structure : H H H H

I

H

I

I I I CJ&C=C-C-C-C-O-CC~HY I 1 I

0

1I

OHCzH6 H

The formulation of the above was deduced from the following determinations: C and H analysis, molecular weight obtained from the saponification equivalent, absorption of one molecule of hydrogen, formation of a monoacetylated derivative, catalytic hydrogenation to the corresponding saturated glycol ester, saponification, which yielded butyric acid and an unsaturated glycol which was converted to the corresponding saturated glycol. Hence, a condensation occurred, whereby two molecules of butyraldehyde and one of crotonaldehyde reacted to form an unsaturated glycol ester. From a consideration of its structure, it is indicated that the compound is formed in two stages. First, the formation of a mixed unsaturated aldol between one molecule of crotlonaldehyde and one of butyraldehyde, and then an esterification between the aldol and a second molecule of butyraldehyde: H H O

I

I

I/

CH3C==C--CH

H O

H H OHH

11

I

0

I I I I I I -+ CHaC=C-C-C-CH I I

+ HC-CH

catalyst

I

CzHs

H CzHs H H H OHH

catalyst

0

1I CaHrCH

>

I I T I I CHIC=C-C-C-C-O-CC~H~ I

H

I

0

II

I

CzHs H

Additional evidence for such a formulation was derived from the isolation of the cis and trans isomeric forms of the conjugated aldehydes, which can result from the dehydration of the mixed aldol during the course of the condensation : H H

i

H H

I 1

I

C&C=C-CH

l

C&C=C-CH

li ;7

O II HC-C CzHrj CzHs C-CH (cis) (trans) 2-Ethyl-2, 4-hexadiene-1-a1

The latter were shown to have the same empirical formula, but different physical constants, Le., density and refractive index. They both took up hydrogen equivalent to two double bonds. The 2,4-dinitrophenylhydrazones and the

258

MARTIN S. KULPINSKI AND F. F. NORD

semicarbazones have different melting points. On hydrogenation they yielded the same saturated aldehyde derivative of 2 4-dinitrophenylhydrazine, namely that of alpha-ethylhexaldehyde. The position isomer, 2-ethy1-2,Ei-hexadiene1-allwhich could arise from the rearrangement of the double bond in the original crotonaldehyde from the 2 position to the 3, and which on hydrogenation could yield the same derivative as mentioned above, can be discounted. Young (7) who studied the composition of crotonaldehyde, states that such a rearrangement is very unlikely, since there is no substitution in position 3. Morametz (8) attempted to effect a trimolecular condensation between a-methyl-S-ethylacrolein (a homolog of crotonaldehyde) and isobutyraldehyde in the presence of alcoholic potassium hydroxide, but obtained only the following mixed unsaturated aldol : H CHS OHCHB 0 )

I

t

I I

CPHSC=C-C-C-CH

I I

I

H CH, Although no mixed aldol was isolated in our work, its formation was indirectly confirmed by the isolation of its dehydration products. However, Morawetz’s condensate, being entirely analogous to the aldol, which is assumed to be the intermediary stage of the Condensation described herein, supports the correctness of the structural formulation given for it. Since the condensation with the aid of the complex catalyst is trimolecular, butyraldehyde alone would be expected to condense in the same way and yield the corresponding saturated glycol ester. This view proved to be correct. Accordingly, the condensation of butyraldehyde with crotonaldehyde in the presence of the coordination alkoxide represents another type of the “crossed” Cannizzaro reaction, in which the condensation of the dissimilar aldehydes proceeds via a mixed aldol and another molecule of the saturated aldehyde, through the bifunctional agency of the catalyst. In view of this behavior of the catalyst, it was deemed justifiable to test its general applicability in the aliphatic series of saturated aldehydes, both for preparative purposes, as well as from the possibility of a closer study of its manner of action. Magnesium-aluminum isopropoxide and aluminum-magnesium butoxide were also employed in order to investigate any qualitative or quantitative differences in this type of catalyst. Comparison was also made of the action of these coordination alkoxides with the simple aluminum alkoxides under the same conditions. The results of the experiments have shown that coordination catalysts of the magnesium-aluminum alkoxide type are generally applicable to the a-CH2 saturated aldehydes, enabling a trimeric condensation to take place to form glycol esters. In Table I are presented the percentage yields of the glycol esters obtained with such aldehydes under the influence of the various catalysts. The low yield of the glycol ester from the self-condensation of acetaldehyde is attributed to sidepolymerization reactions, ie., formation of metaldehyde and paraldehyde.

259

R'EW SYNTHESIS OF GLYCOL ESTERS

Search of the literature showed that workers of the Lieben school (9) had obtained glycol esters in the presence of alkali, only from the condensation of a-alkyl aldehydes, namely, isobutyraldehyde and methylethylacetaldehyde. Rosinger's claim to have obtained a glycol ester from isovaleraldehyde, prepared from fermentation amyl alcohol, was disproved by Cihlar, who, using the synthetic product, obtained under the original conditions only the aldol and the unsaturated aldehyde. TABLE I CATALYST

I

GLYCOL ESTER,

%

Acetaldehyde

MgAlEt MgAlIsopr MgAlBut

24.4 23.5 monoacetate of 1,3-butanediol 24.0

Propionaldehyde

MgAlEt MgAlIsopr

65 61

n-Butyraldehyde

MgAlEt MgAlIsopr MgAlBut AlIsopr AlEt

54.5 44.5 42 monobutyrate of 2-ethyl-l , 3-hexanediol

Isovaleraldehyde

MgAlEt

52 .O monoisovalerate of 2-isopropyl-6-methyl1,3-hexanediol

n-Valeraldehyde

-n-Hexaldehyde

n-Heptaldehyde

-

62'5 monovalerate of 2-propyl-I,3-heptanediol 57.1

RlgAlIsopr MgAlEt MgAIEt MgAlIsopr AlIsopr MgAlEt MgAlBut AlIsopr

monopropionate of 2-methyl-I ,3-pentanediol

61

1

63 61

monohexanoate of 2-butyl-1,3-octanediol

-

51 51

-

monoheptanoate of 2-amyl-l , 3-nonanediol

The Iieben school also proved the structure of the glycol esters, which was later confirmed by v. Braun and Manz (10). However, a-CH, aldehydes exhibited a much different behavior, leading solely to aldolization and crotonization. Grignard and Fluchaire (ll),doing esterification studies with catalysts of the general formula, ROMgI, isolated the glycol ester of butyraldehyde as a byproduct of the condensation of the aldehyde with C2H5OMgI. It is evident that the action of the complex alkoxides is essentially different from that of the simple alkoxides. Under the conditions employed, the latter give only simple esters and no higher distillable products arise. On the other hand, with the coordination compounds, the formation of the simple esters

260


occurred as a side reaction, which proceeded to a very small extent. Noreover, the trimolecular condensation yielded in small amounts a ,P-unsaturated aldehydes, the dehydration products of the aldols. Their isolation gave an indication of the probable course of the reaction. In contradistinction to the a-CH2aldehydes, the a-alkyl substituted aldehydes exhibited a surprisingly different behavior. With simple alkoxides, both types of aldehydes can be condensed in an identical manner and with similar ease to give simple esters. a-CHz

a-ALKYL

Butyraldehyde 80% yield n-Hexaldehyde 60% yield

Isobutyraldehyde 75% yield a-Ethylbutyraldehyde 60% yield

Aluminum isopropoxide was used as a catalyst in the above cases. TABLE I1 a-ALKYL ALDEHYDES

Isobutyraldehyde

a-Ethylbutyraldehyde

a-Ethylhexaldehyde

a

b

CATALYST

Mg.4lEt MgAlIsopr Mg AlBut AlIsopr

10 * 9" 12.8~ 20.60

MgA41Et MgAlIsopr MgAlBut -4lIsopr

6.0b 4.0b 4.0b

MgAlEt MgAlIsopr MgAlBut AlIsopr

SIMPLE ESTER,

!LYCOL ESTEP,Y

-

-

%

56.5

56'3 Isobutylisobutyrate 50.1 75.0 57.4 59 2-ethyl-butyl-2-ethyl58 butyrate 60 75 69 75 75

2-ethylhexyl-2-ethylhexanoate

Monoisobutyrate of 2,2,4-trirnethyl-l,3-~entanediol. Monoethylbutyrate of 2,2,4-triethyl-l,3-hexanediol.

This lack of distinction no longer exists when the complex alkoxides are employed. As was mentioned previously, with a-CHz aldehydes, the main products of the reaction are the glycol esters. On the other hand, the a-alkyl aldehydes condense to give mainly the simple esters, the trimeric condensation occupying a secondary place. In the last case mentioned, the complex catalysts, therefore, behave like the simple alkoxides. Moreover, with the increase in the length of the chain in the a-alkyl aldehydes, the yield of the glycol ester is considerably lowered in the following order: isobutyraldehyde, a-ethylbutyraldehyde, a-ethylhexaldehyde (Table 11). The last one gives no glycol ester at all. Such a sharply contrasting behavior can readily be explained on the basis of the primary stage of aldolization. The important role that the aldol plays in the intermediary stage is brought out as follows: In practically all of the cases where the a-CH2 aldehydes had been condensed, unsaturated aldehydes, i.e., dehydration products of the aldols, were obtained under the influence of the complex catalysts. Ordinarily, with alkali, aldolization, which is a reversible

26 1


process, is carried to completion through dehydration to the a ,P-unsaturated aldehydes. Such a dehydration can be prevented if the aldol is “trapped,” as it, were. by another molecule of the reactant. Accordingly, the formation of the glycol esters can be embraced in such a concept: Two molecules of the aldehyde react to form the aldol, and then, instead of the expected dehydration, under the strong esterifying influence of the coordination catalyst, the aldol is trapped by another molecule of the original aldehyde, thus producing the glycol ester:

H O

I

II

Rs-C-.-C-H I H

+

H O

H OHH 0

R

H H R H OHH H

1 11 catalyst I i I I I HC-CH + RC-C-C-CH I l l I catalyst

H

O

1

1

1

1

RC-C-C-C-0-C-CR

H O

I II

H

This being the case, we should expect the over-all yield of the higher ester to be dependent on conditions favorable toward intermediary aldolization. Such conditions are evidently not present for the trimolecular condensation of a-alkyl aldehydes. One factor would be, for example, the ease of aldolization. Apparently, the aldol takes a longer time to form in the case of these aldehydes, and the equilibrium would be greatly on the side of the unreacted aldehyde. The variance in the yields of the glycol esters with the lengthening of the chain can be understood on the basis that such an increase impedes aldolization. Support for this view can be found in the work of Usherwood (12), who made studies of the equilibration of a-alkyl aldehydes and their aldols. In the isobutyraldehyde-aldol system the equilibrium conditions greatly favor the aldehyde. .A still more pronounced effect is observed in the next higher homolog, a-methylbutyraldehyde. Furthermore, under the conditions of the experiment, only very small amounts of the a-methylbutyraldol were isolated and only by cold treatment for several weeks, could moderate amounts be obtained. For the observation of temperature effects, an experiment was performed with isobutyraldehyde wherein the spontaneous evolution of heat was allowed to continue without external cooling as was usual in the general procedure. Comparison (of the yield with and without external cooling shows that the yield of the glycol ester is reduced by approximately half, and at the same time the quantity of the simple ester is noticeably increased: ISOBUTYRALDEHYDE AND MAQNESIUM-ALUMINUM-ISOPROPOXIDE GLYCOL ESTEB

Without cooling With cooling

6.5%

12.8%

S W L E ESTEP

65% 56.3%

262


Because of the apparent greater difficulty of aldol formation with a-alkyl aldehydes, the esterification role of the catalyst is brought to the fore, and consequently the main part of the aldehyde is converted to the simple ester. From the above considerations x e may conclude that one of the conditions for the formation of glycol esters with coordination catalysts in satisfactory yields is that the aldehyde must have a CH2 group in the ct position. Alkyl substitution brings in structural limitations which appear to diminish the rate of aldolization, which is requisite as one of the intermediary stages in the synthesis of glycol esters. There are no qualitative differences among the complex alkoxides. Quantitatively magnesium-aluminum ethoxide is a somewhat better condensing agent but its difficulty of preparation and its low yield must be borne in mind. Trimolecular condensations of the type described of acetaldehyde, propionaldehyde, n-valeraldehyde, isovaleraldehyde, n-hexaldehyde, and a-ethylbutyraldehyde are not reported in the literature. EXPERIMENTAL4

'

Materials. Acetaldehyde obtained from Eastman Kodak Co. (E.K.), b.p. 20-22'. Propionaldehyde, from E.K., dried with sodium sulfate and fractionated, b.p. 49-50". Isobutyraldehyde (E.K.), redistilled, b.p. 63.5'. n-Butyraldehyde (E.K.), redistilled, b.p. 74-75". n-Valeraldehyde (E.K.), redistilled, b.p. 102-103". Isovaleraldehyde, from the potassium dichromate oxidation of refined isoamyl alcohol, obtained from US. Industrial Chemicals, Inc. The alcohol was carefully fractionated in an electrically jacketed glass-helice-packed column and the portion boiling a t 130-130.5" (n" 1.3882) was used for the oxidation; boiling point of the aldehyde, 92.5". n-Heptaldehyde (E.K.), redistilled, b.p. 40-42" (10 mm.). a-Ethylbutyraldehyde, obtained from the Carbide and Carbon Chemicals Corp. (C. and C.). Dried with sodium sulfate and fractionated, b.p. 115-116'. %-Hexaldehyde (C. and C.), dried and fractionated, b.p. 66.5-67.5" (93 mm.). a-Ethylhexaldehyde (C. and C.), dried and fractionated, b.p. 71-71.5" (28 mm.). Crotonaldehyde (C. and C.), dried and fractionated, b.p. 102-103'. Preparation of catalysts. For the preparation of the simple alkoxides, i.e. aluminum ethoxide and aluminum isopropoxide, the customary procedure was essentially followed. Coordination catalysts. Magnesium-aluminum butoxide [AZ(OC,Hp)41&?g. Magnesium (9.6 9 . ) and 21.6 g. of aluminum were added to a large excess of dry n-butyl alcohol, in a one liter r.b. flask attached to a reflux condenser provided a t the top with a drying tube. A few crystals of iodine and 2 g. of mercuric chloride were then introduced. A moderate evolution of hydrogen ensued which became more vigorous as the contents became warmer from the heat of reaction. After the self-reaction subsided, the contents were refluxed for several hours. The blackish, viscous mass was then transferred to a large Claisen flask with a low, wide side-arm, and the excess alcohol distilled off by suction. A t lower pressure the complex alkoxide came over at 290-295' (2 mm.) as a viscous liquid which solidified in the receiver as a milky-white, glass-like solid. It could be readily broken up with a porcelain spatula. The amount totalled 231 g.; yield 88%. Magnesium-aluminum isopropoxide: [AZ(OCsHr)J,Mg. Four and eight-tenths grams of magnesium and 10.8 g. of aluminum were added to an excess of anhydrous isopropyl alcohol. The microanalyses here reported were performed by Mr. Joseph Alicino of this laboratory. 5 The authors' indebtedness for certain starting materials used in this investigation is expressed t o Carbide and Carbon Chemicals Corporation, New York, N. Y . , and to the U.S. Industrial Chemicals, Inc., Baltimore, Md.


263

Upon addition of small quantities of iodine and mercuric chloride, immediate evolution of hydrogen set in. When the initial reaction subsided, the contents were refluxed for several hours. The excess alcohol was then driven off by suction from the blackish-gray mass. The complex alkoxide came over as a clear white, viscous liquid a t 225-2213' (6 mm.). I t began to crystallize in clumpy white needles. However, only a small part solidified, the main portion retaining a sirupy consistency; yield 92 g. (S5%). Magnesium-aluminum ethoxide: [Al(OC2Hs)41zNg. This was the most difficult to prepare and the yields were rather low. Because it solidified very rapidly when distilled, difficulties were encountered when i t choked up the side-arm of the distilling flask. The procedwe was followed out as above. From 2.5 g. of magnesium and 4.8 g. of aluminum in excess ethyl alcohol, 25 g. of the coordination compound was obtained; yield 56%. On distillation i t came over a t 235-237" (1 mm.). I t rapidly solidified into a transparent crystalline mass. General procedure for the condensation. A definite quantity of the aldehyde was weighed into an Erlenmeyer flask and a weighed amount (5%) of the catalyst was then added and the flask quickly stoppered. Warming took place and the temperature began t o rise rapidly. Consequently, the contents were cooled under the tap from time to time. The rise in temperature usually stopped within an hour, and the flask was allowed to stand overnight. During the condensation the conteiits attained a color varying from yellon-ish to greenish amber to amber red, depending on the nature of the reactant. Moreover, in most cases a fluorescence appeared. The simple allroxides dissolved very slowly as the reaction proceeded, whereas the complex catalysts readily went into solution. I n the instance where the triniolecular condensation took place, the completion of the reaction was indicated upon shaking of the reactants by formation of a foam on the surface of the liquid, which lasted for a few minutes. Without further treatment, the condensate was transferred to a flask provided with an electrically jacketed fractionating column of the Vigreux type. The lower-boiling components were distilled off by suction and the pressure gradually lowered. The higher condensates, i.e., the glycol esters were separated a t the vacuum of an oil-pump. The glycol ester fractions were treated with a dilute solution of potassium carbonate and taken up with ether. The ethereal layer was dried with sodium sulfate, evaporated off, and the remainder slowly rectified. The products treated in this manner were used for further analytical determinations. Refractometer readings were frequently employed, either to establish the identity of fractions in the various runs, or as an indication of the completmess of separation of the various components. General analytical procedures. Acetylation. About 3 to 4 cc. of the glycol ester was mixed with twice the amount of acetic anhydride and gently refluxed for several hours. When the reaction mixture no longer gave a positive test for the hydroxyl group with the ceric nitrate reagent, it was poured into 100 cc. of cold water. The excess anhydride was then treated with sodium carbonate. The oily layer was taken up with ether, well shaken, and separated. After drying with sodium sulfate, the ethereal extract was evaporated and the residue distilled in a vacuum. Saponi$cation. A definite amount of the ester was added to a large excess of alcoholic alkali. The contents were gently refluxed for several hours. Most of the solvent was then removed by ordinary distillation. Water was subsequently added for the separation of the glycol layer. The latter was extracted twice with ether and separated from the aqueous layer. The ethereal solution was thoroughly dried with anhydrous sodium sulfate, evaporated, and the remainder distilled in a small Claisen flask. The water layer was acidified with sulfuric acid to Congo red, extracted with ether, and upon sep.tration was treated in the same way as the glycol extract. Hydrogenation. The apparatus and procedure as described by Rampino and Nord (13), and palladium-polyvinyl alcohol catalyst were employed. One- to two-gram samples of the unsaturated compound were taken for the hydrogenation. For isolation of the hydrogenated derivative, the contents were transferred to an Erlenmeyer flask and saturated

264


with sodium sulfate to 5occulate the colloidal catalyst. After filtration, the saturated substance was extracted twice with ether and separated. The ether solution was evaporated after having been dried with sodium sulfate. The residue was then distilled in a vacuum. Miscellaneous derivatives. For the preparation of these the customary directions were essentially utilized (14). The p-bromophenacyl esters of the acids and the 3,5-dinitrobenzoates of the alcohols were mixed with authentic specimens for further identification. Condensation of butyraldehyde with crotonaldehyde. Seventy grams (1 mole) of freshly distilled crotonaldehyde and 72 g. (1 mole) of butyraldehyde were treated with 7 g. of magnesium-aluminum ethoxide. The condensate was a somewhat viscous amber 5uid. Four such runs were made and submitted to separate fractionations in a D. M. Smith glasshelice, electrically jacketed column. It will be unnecessary to record the data of all the components obtained in all the four runs, since we are merely concerned with the higherboiling portions. However, complete data of the first run (A) nyill be given.

FRACTIONATION OF CONDENSATE PUN

A

FMCTION

B.P.'C

PPESS. MM.

YIELD

1 40-45 (120) 17 g. crotonaldehyde '( 2 45-46 (62) 10 g. I' 3 30-35 (62) 6 g. 4 28-35 (6) 3 g. butyl butyrate 5 45-50 (6) 19 g. 6 50-58 (6) 16 g. 7 58-75 (6) 10 g. B 5 46-60 (3) 25.5 g. 6 65-70 (3) 21 g. C 5 40-60 (1) 20 g. 6 60-75 (1) 14 g. D 5 35-45 (5) 14 g. 6 45-58 (5) 15 g. 60-80 (4) 10 gr. 7 All the fractions numbered 5 were combined and shaken twice with 5% potassium carbonate, extracted with ether, dried and again fractionated. The same procedure was carried out for the combined remaining fractions, Le., -46 and 7,B 6, C 6, D 6 and 7. Rectification of the combined fractions numbered 5: 1. 32-34" (2 mm.) 12 g. nZ4 1.4848 1.5O32 2. 35-40' (2 mm.) 12 g. 1.4682 3. 42-50' (2 mm.) 14 g. At this point the combined higher-boiling portion was added and fractionation resumed: 4. 35-42' (2 mm.) 9 g. n23 1.4817 5. 42-50' (2 mm.) 7 g. 1.4668 6. 53-58' (2 mm.) 22 g. 1.4580 7. 62-70' (2 mm.) 16 g. 1.4540 1.4552 8. 68-71" (2 mm.) 15 g. As indicated by the refractive indices, all the fractions with the exception of 1, 2,and 4, are mainly composed of the same substance, as was subsequently found out by distillation in a Claieen 5ask. Moreover, the boiling points observed were much higher than those above. The difference in the value of the boiling points and their wide range is due to the unavoidable cooling and 5ooding which occurred a t the top of the fractionating column in the vacuum employed. Rectification in a Claisen 5ask: 3rd fraction 103-105" (2 mm.) 10 g. nZ4 1.4510 5th fraction 103-105' 1.4512 (2 mm.) 6 g. 6th fraction 104.5-105.5" (2 mm.) 22 g. 1.4530 1.4512 7th fraction 103-105" (2 mm.) 15 g. 1.4538 8th fraction 105-106" (2 mm.) 14.5 g.


265

The above were combined and redistilled. Final boiling point 104.5-105.5" (2 mm.) n22 1.4530. This component was identified as the condensation product between two molecules of butyraldehyde and one of crotonaldehyde, i.e., monobutyrate of 2-ethyl-4-hexene1,%diol ; dz* 0.9541 ; nZ21.4530. A n a l . Calc'd for C12H2208: C, 67.24; H, 10.36; Sapon. equiv. (mol. wt.), 214.3. Found: C, 66.72; H, 10.33; Sapon. equiv. (mol. tvt.), 227.5,224.1. It took up hydrogen equivalent to one double bond. Monoacetyl derivative: b.p. 89-90' (1 mm.) ; dz3 0.9462; n23 1.4412. A n a l . Calc'd for C14Hz404: C, 65.58; H, 9.44. Found: C, 65.06; H, 9.63. Conversion to the saturated glycol ester. Catalytic hydrogenation of the double bond yielded a somewhat viscous, water-white liquid, b.p. 100-102" (0.5 mm.). This proved to be ideniical with the glycol ester obtained from the condensation of butyraldehyde (see later) alone, i.e., the monobutyrate of 2-ethyl-1,3-hexanediol; $1 0.9492; nzl 1.4462. : H, 11.19. A n a l . Calc'd for C I ~ H Z ~ OC,P 66.62; Found: C, 66.67; H , 10.79. Saponification. The hydroxy compound was a viscous, almost colorless liquid, boiling a t 92-98" (3 mm.). Upon redistillation i t passed over a t 88-90' (1 mm.); n231.4600. Hydrogenation converted i t to the corresponding saturated dihydroxy compound, i.e., 2-ethyl1,a-hexanediol (see later); nz51.4515. A n a l . Calc'd for CgHl8O2:C, 65.73; H, 12.38. Found: C, 65.27; H, 12.36. The acid portion yielded butyric acid. The p-bromophenacyl ester melted at 62". 2-Ethyl-2,4-hexadiene-l-a1(cis and trans). The fractions 1, 2, and 4 previously mentioned were combined and rectified. They yielded two close-boiling components which proved to be cis and trans isomeric conjugated aldehydes: I, b.p. 42-43' (2 mm.); 11, b.p. 44-45" (2 mm.). Both were yellow, readily flowing liquids with a pungent odor. I, d21.5 0.8857; n21.6 1.4780; 11, d21 5 0.9112; nzl5 1.5040. A n a l . Calc'd for C8HI2O:C, 77.36; H, 9.74. Found: (I), C, 77.15; H, 9.68; (11),C, 77.10; H, 9.76. Semicarbazones. Twice recrystallized from 50% alcohol, white, flaky, flat, shiny plates, (I) m.p. 185-186"; (11)m.p. 201-202". -4nal. Cdc'd for CgH15NsO: S , 23.18. Found: (I),N, 23.15; (11),N, 23.19. Z,Q-3i'nitrophenyEhydrazones. Twice recrystallized from alcohol, (I) small, red crystals, m.p. 13&-137". (11) Crimson red, fine fluffy needles, m.p. 187.5-188.5". A n a l . Calc'd for ClrH&404: N, 18.42. Found: (I), h-, 18.46. (II), N , 18.34. Hydrogenation. Hydrogen calculated for two double bonds was taken up. The aldehydic product derived therefrom yielded the same 2,4-dinitrophenylhydrazonesin both cases; (I;l,m.p. 114"; (11),m.p. 114". A n a l . Calc'd for C14HmN404: N , 18.18. Found: (I),N, 18.10; (11),N, 17.91. When the two were mixed, the melting point was not depressed. When each was separately mixed with the 2,4-dinitrophenylhydrazine derivative of 2-ethylhexaldehyde, no depression of the melting point was observed. Condensatton of butyraldehyde: (monobutyrate of 2-ethyl-l,3-hexanediol). Forty-eight grams of the freshly distilled aldehyde was treated with 2.4 g. of the alkoxides. Magnesium-aluminum butoxide: The glycol ester portion boiled at 114-120° (2 mm.); 18 g., yield (baued on the reacted aldehyde) 42%. All subsequent yields will be calculated on this basis. Magnesium-aluminum isopropoxide: The main fraction boiled a t 105-109" (1 mm.); yield 20 g. (44.5%). Magnesium-aluminum ethoxide: Glycol ester portion boiled a t 105-107" (0.5 mm.); yield 23.2 g . (54.5%). Aluminum isopropoxide: Only the simple ester, butyl butyrate was obtained, b.p. 59-61" (14mm.); yield 38 g. (80%). Aluminum ethoxide: Only the simple ester was obtained, b.p. 52-54' (13 mm.); yield 40 g. (83%).

266


Identification of the glycol ester. The higher condensate was shaken with dilute potassium carbonate and redistilled, b.p. 103-104" (0.5mm.); d210.9433;nZ11.4438. Anal. Calc'd for C&!403: C, 66.62;H , 11.19;Sapon. equiv. (mol. wt), 216.3. Found: C, 66.37;H, 11.13;Sapon. equiv. (mol. wt.), 209.1,208.9. Monoacetyl derivative, b.p. 86-88' (0.5mm.) ; da50.9570;nZ51.4368. Anal. Calc'd for C14Hz604: C, 65.10;H, 10.14. Found: C, 65.20;H, 10.06. Saponification. The dihydroxy compound, which was a viscous, colorless liquid, boiled a t 94-96' (0.5mm.) (2-ethyl-1,3-hexanediol); dZ20.9325;nZ21.4530. A n d . Calc'd for CsH1802: C, 65.72;H, 12.40. Found: C, 65.79;H, 12.12. The acidified part was identified as butyric acid, m.p. of the p-bromophenacyl ester 63". Diacetyl derivative of the glycol, b.p. 87-88' (1mm.); d2a0.9759;n231.4328. Anal. Calc'd for Cl2H2204: C, 62.60;H, 9.60. Found: C, 62.88;H , 9.88. Just before the glycol ester fraction, small amounts of a-ethyl-b-isopropylacroleindistilled over. Redistillation gave the b.p. 173-175.' The 2,4-dinitrophenylhydrazonemelted a t 123-124". The melting point was not lowered when the derivative was mixed with a known sample. The butyl butyrate was identified by conversion into butyric acid (p-bromophenacyl ester m.p. 63") and butyl alcohol (3,4-dinitrobenaoate, m.p. 63-63.5"). Condensation of acetaldehyde: (monoacetate of 1,s-butanediol). Magnesium-aluminum butoxide: 4 g. of the aldehyde was treated with 2.2g. of the catalyst; high-boiling portion, 80-90" (13 mm.), 10.5 g., yield 24%. Magnesium-aluminum ethoxide: 55 g. of the aldehyde and 2.5 g. of the alkoxide; higher condensate, b.p. 80-90" (13 mm.) 13.4 g., yield 24.4%. Magnesium-aluminum isopropoxide: 52 g. of the aldehyde and 2.5 g. of the catalyst; higher fraction: b.p. 80-92" (13 mm.), 13.4 g., yield 23.5%. Other products which formed in the course of the condensation were ethyl acetate, crotonaldehyde (identified through the 2,4-dinitrophenylhydrazone,m.p. 189-190"), paraldehyde and metaldehyde (decomposed with dilute sulfuric acid to acetaldehyde). Identification of the glycol ester. After treatment with dilute potassium carbonate i t was rectified, b.p. 87-89' (13 mm.), as a colorless, somewhat mobile liquid; d25 1.005;nZ5 1.4182. -4nal. Calc'd for CEH,ZO~: C, 54.55;H, 9.09;Sapon. equiv. (mol. wt.), 132.2. Found: C, 54.50;H, 8.89;Sapon. equiv. (mol. wt.), 128.5. Acetylation. The final distillate boiled a t 92-94' (13 mm.), i.e., the diacetate of 1,3butanediol; d25 1.028;n25 1.4145. Anal. Calc'd for CsH1404: C, 55.15;H , 8.09;Sapon. equiv. (87.1 X 2 mol. wt.); 174.2. Found: C, 55.14;H, 8.16;Sapon. equiv. (87.48X 2 mol. wt.), 175. Saponification of the diacetate. Numerous extractions of the reaction mixture after saponification with ether-ethyl acetate mixture gave a very small quantity of a viscous liquid boiling at 203-205" from the unacidified portion of the saponified ester. It was extremely hygroscopic, and as a result did not give a satisfactory analysis: 1,3-butsnediol. Anal. Calc'd for C4H1(102: C, 53.27;H , 11.11. Found: C, 51.27;H, 11.18. The acidified portion readily yielded acetic acid, p-bromophenacyl ester, m.p. 85'. Condensation of propionaldehyde: monopropionate of 2-methyl-1,%pentanediol. Magnesium-aluminum isopropoxide: 64 g. of the aldehyde was treated with 2.5 g. of the alkoxide; main fraction 86-90' (2mm.), 37.6 g., yield 61%. Magnesium-aluminum ethoxide: 48.8 g. of the aldehyde and 2.5g. of the catalyst; main component 89-92' (3mm.), 29.4g.; yield 65%. I n the course of the condensation a small amount of a-methyl-j%ethylacrolein was formed. The 2,4-dinitrophenylhydrszonemelted a t 159.5". Mixing with a known sample produced no depression of the melting point. Identification of the glycol ester. The higher-boiling condensate was redistilled after

NEW- SYNTHESIS OF GLYCOL ESTERS

267

shaking with dilute potassium carbonate, final boiling point 92-94" (2 mm.); d m 0.9788; n m 1.4369. Anal. Calc'd for C*Hl8O3:C, 62.06; H, 10.44. Found: C, 61.76; H, 10.50. Monoacetyl derivative, b.p. 71-72' (0.5 mm.) ; d18.5 0.9985; nl'3.5 1.4302. Anal. Calc'd for CllH&: C, 61.07; H, 9.33. Found: C, 60.77; H, 9.20 Saponification. Glycol: 2-methyl-1,3-pentanedioI,b.p. 85-86" (I mm.) ; d22 0.9737; n Z 21.4486. Anal. Calc'd for CSHl402: C, 60.96; H, 11.94. Found: C, 60.86; H, 11.88. Acid: Propionic acid, p-bromophenacyl ester, m.p. 63". Condensation of isovaleraldehyde: monoisovalerate of 2-isopropyl-6-methyl-1,3-hesanediol. Magnesium-aluminum ethoxide: 42 g. of the aldehyde was treated with 2 g. of the catalyst; high-boiling fraction, b.p. 142-149" (2 mm.), 22 g.; yield 52%. After the usual treatment i t boiled at 137-139" (1 mm.); d320.9242; n32 1.4421. Anal. Calc'd for C16H~03:C, 69.74; H, 11.70. Found: C, 69.60; H, 11.44. Mono,scetylated product: b.p. 126-128" (1 mm.); d28 0.9386; nZ81.4381. Anal. Calc'd for C1&@4: C, 67.96; H, 10.75. Found: C, 67.87; H, 10.64. Saponification. Glycol: 2-isopropyl-6-methyl-1,a-hexanediol, b.p. 105-106" (1 mm.). In spite of repeated fractionation the glycol could not be obtained analytically pure; d23 0.9161; n23 1.4528. Acid: Isovaleric acid, p-bromophenacyl ester, m.p. 67.5". Conde:nsation of n-valeraldehyde: the monovalerate of 2-propyl-1, S-heptanediol. Magnesium-aluminum ethoxide: 40 g. of the aldehyde and 2 g. of the catalyst yielded a highboiling liquid, b.p. 145-160" (2 mm.); yield 26.2 g. (62.5%). Magnesium-aluminum isopropoxide: 35 g. of the aldehyde and 2 g. of the alkoxide; main fraction b.p. 144-155" (2 mm.); yield 20.2 g. (57.1%). 1denti:licstion of the glycol ester: After the usual treatment and redistillation, b.p. 138-139" i(1E m . ) ; dB 0.9203; nB 1.4442. Anal. Calc'd for C1&7&: C, 69.74; H, 11.70. Found: C, 70.03; H , 11.82. hlonoacet,ylated product, b.p. 135-137" (1 mm.); dz3 0.9344; nZ81.4368. Anal. Calc'd for Ct7H8204: C, 67.96; H, 10.75. Found: C, 68.00; H, 10.60. Saponification: Glycol, 2-propyl-1,3-heptanediol, b.p. 107-108" (1 mm.); d" 0.9155; nB 1.4513.

Anal. Calc'd for C10H2202: C, 68.90; H, 12.74. Found: C, 68.81; H, 12.45. Acid: n-valeric acid, p-bromophenacylester, m.p. 74.5". Condensation of n-hexaldehyde: monohexanoate of 2-butyl-1 ,S-octanediol. (About 50% of it remained unreacted with t,he complex catalysts.). Magnesium-aluminum ethoxide: 50 g . of thle aldehyde was treated with 2.5 g. of the alkoxide. First run: Main fraction, b.p. 145-160" (.Imm.), 15 g. yield (61%). Second run: b.p. 135-150" (0.5mm.), 16 g., yield (63%). Magnesium-aluminum isopropoxide: Amounts same as above; main fraction b.p. 150-165" (1 xnm.), :l7.2 g. yield (61%). Identification of the ester: After the usual treatment and rectification, the high condensate boiled a t 150-152" (1 mm.); dg4 0.9240; n241.4500. Anal. Calc'd for C2sHa8Ol: C, 71.95; H , 12.08. Found: C, 71.85; H, 11.92. Monoaeetyl derivative: b.p. 132-134" (0.5 mm.) ; d*10.9388; nZ11.4462. Anal. Calc'd for CmH3804: C, 70.13; H, 12.95. Found: C, 70.36; H , 12.84. Saponification: Glycol, 2-butyl-1,3-octanediol, b.p. 128-129" (1 mm.); d25 0.9184; nZ5 1.4570.

268


Calc'd for ClzHnaOz: C, 71.23; H , 12.95. Found: C, 71.17; H, 12.84. Acid: n-hexanoic acid, p-bromophenacyl ester, m.p. 72". With aluminum isopropoxide (2.5 9.) and 50 g. of the aldehyde, the main component was the simple ester, hexyl hexanoate, b.p. 105-108" (10 mm.); yield 30 g. (60%). There were no higher-boiling fractions. Saponification of the simple ester: Alcohol: n-hexanol, 3,5-dinitrobenxoate, m.p. 58-59". Acid: n-hexanoic, p-bromophenacyl ester, m.p. 72". Condensation of n-heptaldehyde: monoheptanoate of 2-amyl-1,3-nonanediol. Fifty grams of the aldehyde and 2.5 g. of the catalyst were used. Magnesium-aluminum butoxide: main fraction: b.p. 165-180" (0.5 mm.) ; yield 22 g. (51%). Magnesium-aluminum ethoxide: main fraction: b.p. 165-183" (0.5 mm.); yield 23 g. (51%). Aluminum isopropoxide: 34 g. of the simple ester, heptyl heptanoate, b.p. 135-137' (8 mm.); yield 74%. The latter was identified by its saponification products, n-heptyl alcohol, 3,5-dinitrobenzoate, m.p. 46-47'; n-heptanoic acid, p-bromophenacyl ester, m.p. 72". Identification of the glycol ester. After the usual procedure, and a very slow and careful distillation the high condensate boiled a t 167-170" (0.5 mm.); dZ10.9065; nZ11.4510. Anal. Calc'd for C21H4203: C, 73.64; H, 12.35. Found: C, 73.69; H, 12.29. Monoacetyl derivative, b.p. 160-164" (1mm.); d1*4 0.9184; n1*.51.4484. Anal. Calc'd for C28H4404: C, 71.83; H, 11.52. Found: C, 71.97; H, 11.41. Saponification: Glycol, 2-amyl-l,3-nonanediol, b.p. 125-127" (0.5 mrn.); d 2 3 0.8984; nZ31.4545. Anal. Calc'd for C&&: C, 72.98; H, 13.12. Found: C, 73.15; H, 13.34. Acid, n-heptanoic acid, p-bromophenacyl ester, m.p. 71-72". Condensation of isobutyraldehyde: nzonoisobutyrate of 2,8,4-trirnethyl-l, 3-pentanediol. Forty-eight grams of the aldehyde and 2.5 g. of the alkoxides were used. The complex alkoxides gave as the main product the simple ester, isobutyl isobutyrate, and in smaller amounts, the glycol ester. Magnesium-aluminum ethoxide: simple ester, b.p. 53-55" (18 mm.), 26 g. (56.5%), and the glycol ester, b.p. 105-110° (2 mm.), 5.0 g. (10.9%). Magnesium-aluminum isopropoxide: simple ester, b.p. 35-38" (13 mm.), 25.5 g. (56.3%), and glycol ester, b.p. 105-110" (2 mm.), 5.8 g. (12.8%). Magnesium-aluminum butoxide: simple ester, b.p. 56-58' (26 mm.), 23.4 g. (50.1%), and glycol ester, b.p. 96-100" (0.5 mm.), 9.5 g. (20.6%). Aluminum isopropoxide: only the simple ester mas obtained, b.p. 55-56" (24 mm.), 36 g. (7501,). The isobutyl isobutyrate was identified by conversion into isobutanol, 3,5-dinitrobenzoate, m.p. 86", and isobutyric acid, p-bromophenacyl ester, m.p. 77". Identification of the glycol ester. All the higher-boiling fractions mere combined and submitted to the usual procedure. Redistillation, b.p. 85-86" (0.5 mm.); d23 0.9507; nZ3 1.4390. Anal. Calc'd for Cl2HZ4O0:C, 66.62; H , 11.19. Found: C, 66.63; H , 11.02. hlonoacetylated derivative, b.p. 91-93' (2 mm.) ; dZ30.9660; n Z 31.4352. Anal. Calc'd for C14Hz604: C, 65.10; H, 10.14. Found: C, 65.33; H, 10.29. b.p. 81-82' (1 mm.). I t could Saponification: Glycol, 2,2,4-trimethyl-1,3-pentanediol, not be obtained in an analytically pure state; d280.9619; nZ31.4518. Condensation without cooling. Forty grams of the aldehyde was treated with 2.0 g. of magnesium-aluminum isopropoxide. The temperature rose to 85", and after 20 minutes i t gradually fell off. The cessation of ebullition indicated the completion of the reaction. A 26 g. yield of the simple ester was obtained (65%). The yield of the glycol ester amounted to only 2.6 g. (5.8%). Condensation of 8-ethylbutyraldehyde: monoethylbutyrate of 2,8,4-triethyl-l, 3-hezanediol. Fifty grams of the aldehyde was condensed with 2.5 g. of the alkoxides. The main fraction Anal.


269

consisted of the simple ester, 2-ethybutyl 2-ethybutyrate and only very small amounts of the higher condensation product. Magnesium-aluminum butoxide: simple ester, b.p. 95-105" (15 mm.), 28.7 g. (57.453, 3 g. up to 175' (15 mm.) (6%). Magnesium-aluminum isopropoxide: simple ester, b.p. 98-105" (15 mm.), 29.5 g. (59%), 2 g. up to 170' (15 mm.) (4%). Aluminum isopropoxide: only the simple ester was obtained, b.p. 95-100" (12mm.), 30 g. (GO%). ldentqficatzon of I-ethylbutyl 2-ethybutyrate. The ester was shaken with potassium carbonate solution and redistilled, b.p. 100-102" (14 mm); d*5 0.8628; n25 1.4200. A n a l Calc'd for CIzHzrOz:C, 71.94; H, 12.08. Found: C, 72.12; H, 12.18. The t'ster was finally identified by conversion with excess alcoholic alkali to 2-ethylbutanol, b.p. 147-148.5", 3,5-dinitrobenzoate, m.p. 50°, and to 2-ethylbutyric acid b.p. 89-90' (14 mm.), amide, m.p. 125". ldentbjkation of the glycol ester. All the fractions from the various runs were combined, txeated in the usual way and redistilled, b.p. 127-130' (1 mm.); d*a 0.9327; nB 1.4425. The product could not be purified. Acetylation gave definite indication that one acetyl group ivas introduced, but the original impurity remained. Saponification. Because of the small amount available for saponification only a few drops of a viscous liquid were obtained from the alcoholic portion; na 1.4565. Its analysis agreed mith the formula of 2,2,4-triethyl-1,3-hexanediol. A n a l . Calc'd for C12H2802: C, 71.23; H, 12.95. Found: C, 71.10, 71.10; H, 12.71, 12.64. The acid was identified as 2-ethylbutyric acid, through its amide, m.p. 124". Condensatton of 2-ethylhexaldehyde. Only the simple ester, 2-ethylhexyl 2-ethylhexamoate was obtained in all cases. There were no higher distillable products. Fifty grams of the aldehyde and 2.5 g. of the alkoxides were employed. Magnesium-aluminum butoxide: simple ester, b.p. 110-116" (1 mm.), 37.4 g. (75%). Magnesium-aluminum ethoxide: simple ester, b.p. 100-108" (0.5 mm.), 37.4 g. (75%). Magnesium-aluminum isopropoxide: simple ester, b.p. 110-116" (1 mm.), 34.5 g. (69%). Aluminum isopropoxide: b.p. 110-116" (1 mm.), 36.7 g. (73%). Identzjicatzon. The simple ester was shaken with dilute potassium carbonate and redistilled, b.p. 1!2-116" (1 mm.); d2*0.8591; nZ 1.4315. Anal Calc'd for C18H320e:C, 74.93; H, 12.60. Found: C, 74.89; H, 12.55. The ester waR converted by excess alcoholic alkali to 2-ethylhexsnol, a-naphthylurethan, m.p. 59-60", and 2-ethyl-hexanoic acid, amide, m.p. 102" (15). SUlrIhZARY

1. The catalytic condensation of the dissimilar aldehydes, butyraldehyde and crotonaldehyde to yield an unsaturated glycol ester represents a second form of the "crossed" Csnnizzaro reaction. 2. The cis and trans conjugated aldehydes obtained from the condensation of butyraldehyde and crotonaldehyde represent an interesting example of such isomers. 3. The coordination catalysts, i e . , the magnesium-aluminum alkoxides, enable a trimeric self-condensation of saturated aldehydes to occur. This condensation is generally applicable to the (r-CH2aldehydes, and it provides a convenient method for the synthesis of glycol esters of this series. 4. The simple alkoxides, i.e., aluminum alkoxides lead only to dimeric products, that is, the simple esters, whereas the complex catalysts can bring about trimerization, i e . , form glycol esters. 5. The failure to obtain glycol esters as the main products in the case of

270

MARTIN 5. KULPINSKI AND F. F. NORD

a-alkyl aldehydes with the coordination catalysts has been explained as due to the limiting factors imposed on the primary stage of the condensation, that is, aldolization. The similarity of behavior in this instance between the simple and the complex alkoxides originates from the bifunctional nature of the latter. 6 . The complex alkoxides do not differ qualitatively in their action. Magnesium-aluminum ethoxide appears to be a better condensing agent, although it is most difficult to prepare and with low yield. SEW YORK,N. Y. REFERENCES (1) CLAISEN,Ber., 20, 646 (1887). (2) TISCHTSCHENKO et al., Chem. Zentr., 1906, 11, 1309, 1554, 1556. (3) XORD,Biochem. Z., 106, 275 (1920); Beitr. Physiol., 2, 301 (1924); Chem. Rev., 3, 65 (1926); SAKAI, Biochem. Z., 162, 258 (1924); ENDOH,Rec. Trav. chim.,44, 866 (1925). (4) ORLOFF,Bull. SOC. chim.,(4) 36, 360 (1924). NENITZESCU AND GAVAT, Bull. SOC. chim. R o d n i a , 16 (A),42 (1934). DAVIDSONAND BOGERT, J. Am. Chem. SOC.,67, 905 (1935). BAILAR,BARNEY, AND MILLER,J. Am. Chem. SOC.,68, 2110 (1936). (5) ZAPPI A N D LABRIOLA, Chem. Abstr., 29, 5414 (1935). (6) BERSIN,Dissertation, U. of Konigsberg, 1928. (7) YOUNG, J. Am. Chem. Soc., 64, 2499 (1932). Monatsh., 26, 127 (1904). (8) MORAWETZ, A N D KOHN,Monatsh., 19, 16 (1898). (9) FOSSEK,Monatsh., 2, 614 (1881). BRAUCHBAR FRANKE AND KOHN,Monatsh., 19, 354 (1898). KIRCHBAUM, Monatsh., 26, 249 Monatsh., 22, 545 (1901). CIHLAR,Monatsh., 26, 249 (1904). (1904). ROSINGER, iMonatsh., 27, 879 (1906). NEUSTADTER, (10) v . BRAUNAND MANZ,Ber., 67, 1696 (1934). (11) GRIGNARD AND FLUCHAIRE, Ann. chim.,[lo], 9, 5 (1928). (12) USHERWOOD, J. Chem. SOC.,123, 1717 (1923); 126, 435 (1924). (13) RAMPINO A N D NORD,J . Am. Chem. SOC., 63, 2746 (1941). (14) SHRINERAND FUSON, “The Systematic Identification of Organic Compounds,” John Wiley and Sons, iYew York, 1940. (15) RAPER,J . Chem. SOC.,91, 1837 (1907).

ESSENTIAL STEPS IN THE CATALYTIC CONDENSATION OF

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