I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2110
CHz
/ \
(--CHI-CH
I
CH-CHr-CH-)z
I
b
N
(-CH~-CI~-CHzI
L
O
(7)
A\ /'
H CH-)z CHz
Formula 8 represents a possible cyclic structure but probably 0
0
does not predominate in the insolubilized polymer since this should be soluble in alcoholic solvents and treated polymer is not soluble in any solvent. The other and simpler way of representing the formation of a crom link is indicated in Formula 9 in which the acetal link is formed by reaction of two adjacent hydroxyls from one chain with the aldehyde group of a neighboring chain.
(-CHn-CH-CHn-CH-CH2CH-)z
Vol. 42, No. 10
a water-insoluble form. Of course there are some uses for mluble resins where this property would be undesirable, but there are many other places where it would be a desirable result. For example, these polymers may be used as a permanent finish on fabrics or aa a permanent size on paper which materially increases the wet strength. They may be used to anchor various modifying agents to the surface of fabrics or paper. A recently issued British Patent (1) covers the use of the polymers to anchor pigments to the surface of fabrics. Because they are in solution, the polymers penetrate well into the interstices of a fabric or paper and bond the fibers together as well as anchor the modifying material to the surface. Launderability of such materials is still satisfactory because, although the resin is not soluble in wateaafter proper application, it is highly swollen by water and fabrics are limp in water and, as a matter of fact, cannot be distinguished from untreated fabrics when wet. However, on drying and ironing they immediately assume a starched appearance and this operation can be repeated many times without loss of effect. Of course there are other resins that can be used to produce such effects. Most of them, however, are applied from emulsions containing organic solvents and their ease of application is seriously affected by the necessity for either a good ventilating aystem or a solvent recovery system, neither of which is necessary with resins which have water as their only solvent. LITERATURE CITED
Dahlen, M. A., and Shaws, O., Brit. Patent 620,791 (1949). Hubner and Genther, Ann., 114,47 (1860). (3) Izard, E.F., U.S.Patent 2,485,239 (1949). (4) Minsk, L. M.,and Unruh, C. C., U. S. Patent 2,471,404 (1948). (1) (2)
A polymer such as this should have unique uses. I t is a watersoluble polymer which can be applied from water solution and by simple aftertreatment with either heat or acid be converted into
(6) Wohl and Maag, Ber., 43, 3293 (1910). RECEIVED February 11, 1950. Presented a8 a part of High Polymer Forum before the Division of Paint, Varnish, and Plastics Chemistry at the 118th Meeting, AMERICANCHEMICAL Q o c m w ,Atlantic City, N. J.
Properties of Heat-Reactive Oil-Soluble Phenolic Resins EFFECT OF COMPOSITION AND pH R. H. RUNK Westinghouse Research Laboratories, East Pittsburgh, Pa. T h e influence of composition and pH during reaction has been investigated for a series of p-tert-butylphenolformaldehyde resins modified with various tri- and tetrafunctional phenols. The resins were combined with tung oil, maleic treated linseed oil, and heat polymerized linseed oil to form heat-reactive varnishes. The properties investigated are of primary interest in electrical insulating varnishes: solubility of the resins in drying oils; heat hardening of the varnishes; and resistance of the heat polymerizedvarnishes to transformerand lubricating oils. On the basis of the data presented, optimum conditions appear to be adjustment to pH of 5.5 to 5.7 after initial alkaline condensation. The most favorable combination of properties is found in modification of p-tert-butylphenol with 2,2-bis(4-hydroxyphenyl) propane. In general, oil solubility of the resins, especially with polymerized oils, and oil resistance of the varnishes are favored by lower pH over the range of 4 to 9. Heat reactivity is diminished as pH is lowered.
D
URING the past decade thermosetting insulating varnishes
based on heat-reactive phenolic resins and the more reactive conjugated drying oils have assumed an important role in the protection and insulation of electrical equipment. This is especially true in rotating electrodynamic machinery. Here the high temperature of operation causes liquefaction of the thermoplastic ungelled subsurface found in deep sections of oleo resinous or alkyd varnishes. During high speed rotation, this liquid varnish may be expelled by centrifugal force, Alkyd and oleoresinow varnishes lend themselves readily to oxygen induced surface drying, but in the course of normal commercial baking schedules the deeper masses of varnish, filling crevices and interstices, are relatively uncured. Other advantages of phenolic-type varnishes are: high tolerance for inexpensive aliphatic solvents; relative freedom from skinning as compared to principally oxygenconvertible resin-oil systems; adequate flexibility and heat resistance; excellent maintenance of high dielectricstrength and insulation resistance under high humidity; and good oil resistance, especially when modified with alkyd resins.
Odober 1950
The purpose of this paper is to present data concerning the effect of both composition and conditions of reaction, specifically pH, on the properties of the heat-reactive oil-soluble resins. Composition was varied by including small amounts of tri- and tetrafunctional phenols as modifiers of the basic bifunctional reactant, gtertbutylphenol. p H was varied by neutralization or acidification of the initial alkaline condensation products prior to distillation and resin formation.
360 6 %
2.
m
-- 320d
THEORETICAL
As early as 1938 Turkington, Shuey, and Shechter (10) observed that the changes in viscosity, density, and refractive index in nonheat-reactive phenolic resin-drying oil system were greater than could be ascribed to the additiveeffect of the individual components. At that time these workers offered no explanstion for the observed phenomena other than the suggestion of a reaction between the resin and oil. In a subsequent paper Turkington and Allen (9) reported that these oil-reactive types of resins accelerated the thermal polymerization of the oil as well as air-drying of the film. They found that the differences in the resins are magnified as the drying speed of the oil is reduced -for example, going from tung to linseed to soybean oil. Lilley ( 4 ) added further evidence to the theory of oil reactivity by observing differences in evolution of formaldehyde and water in bodying resins and oils together and separately. It remained for Hultzsch (3)to propose a mechanism by which highly methylolated alkaline-catalyzed phenolic resins can react with the systems of double bonds found in the fatty acid nuclei of drying oils. Hultzsch postulated the following reaction mechanism based on studies of the reaction of methylolphenols with simple olefinic compoundssuch aa maleic esters and styrene:
MET HY LOLPHENOL
CHROMANE RING
Farmer (2) investigated the reaction of substances more closely resembling the drying oils such aa dihydromyrcene (2,bdimethyl 2,hctadiene) and rubber hydrocarbon. Evidence of the chromane ring structure is supported by disappearance of double bonds determined chemically and by ultraviolet absorption speetra. Singer (8) has suggested that the ring formation may be achieved through the formation of an intermediate, the quinone methide, derived by dehydration from the methylolphenol. The presence of quinone methide in the complicated scheme of polymerization of phenolic resins had been reported by Hultzsch (3). Based on diminution of the diene value in tung oil and of the iodine value in linseed oil, Singer proposed the followring mechanism of reaction between resin and drying oil:
2
\
160
1 W
z
F
120
pH AFTER NEUTRALIZATION
Figure 1. Effect of pH after Neutralization on Reactivity of Unmodified and Modified Phenolic Resins w i t h Tung Oil
an inert diluent, and in the presence of both conjugated and unconjugated oils. In an unconjugated oil such as unbodied linseed oil, little evidence of chemical reaction is found below 180' C. These authors, however, are cautious as to the extent that the reaction of simple phenol dialcohols with oils can be taken as a criterion of the behavior of fully condensed resins. However, they state that the parallel is not unreasonable, since Hultzsch (8) has shown that the dibenzyl ether derived from 3,5dimethyl-&hydroxybenzyl alcohol yields the same chromane ring derivative aa the simple methylolphenol. Thus
OIBENZYL
ETHER
8)
METHYLOLPHENOL METHYLENE OUINONE
QRYING OIL CHROMANE RING DOUBLE BOND SYSTEM
Charlton and Perrins (1) further substantiated the reaction of phenol dialcohols with conjugated drying oils (tung and heat polymerized linseed oil) at temperatures below 180" C. Their work is based on careful measurements of water and formaldehyde liberated by heating the pure dialcohols done, in the presence of
I
OR
cnpon
METHYLOLPHENOL
2111
INDUSTRIAL A N D ENGINEERING CHEMISTRY
i"
nc
c -0 -c2n,
II
0
DIETHYLMALEATE
The most recent work in this field is the publication by Lilley and Osmond (6) of a method for determination of the methylol content of both phenol alcohols and fully condensed resins. A later article (6) seeks to relate oil reactivity a t the active methylol groups (determined by the analysis) to the Flory-Stockmayer theory of functionality and gelation. The foregoing illustrates the theory that haa been evolved in the course of a decade concerning the reaction of intermediates
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2112
based on simple monofunctional disubstituted phenols, as then the chromanes can be isolated. The theory has been extended to cover the more complicated products of reaction encountered in t,he use of polyfunctional phenols. The resins covered in this paper are complicated by the presence of minor, but important, quantities of tri- or tetrafunctional phenols to produce resins of enhanced heat reactivity. It is resins of this type which have found application in the rapid-curing varnishes mentioned previously. It is a well known fact that hard resins prepared from tri- or tetrafunctional phenols such as m-cresol, phenol, or 2,2-bis(4hydroxypheny1)propane (diphenyl01 propane) are extremely heat reactive. Unfortunately these resins are insoluble in drying oils, whereas palkyl bifunctional phenols produce resins of maximum oil solubility and minimum heat reactivity, especially when acid catalyzed. Admittedly the latter phenols produce resins of a low order of heat reactivity when catalyzed with alkali, but neither the oil resistance nor the heat reactivity of varnishes made from them is satisfactory. For such purposes there has been evolved a class of resins based on palkyl phenols modified with various polyfunctional phenols. EXPERIMENTAL PROCEDURE
REACTANTS. Using as a base p-tert-butylphenol (bifunctional) the following polyfunctional phenols were investigated as modifiers (* indicates points of reaction or functionality):
*6*
FUNCTIONALITY
I PHENOL
9
pH-meter using the special electrodes described by Lykken et al. (7). But it was later found that Hydrion papers could be used with greater ease without sacrifice of accuracy. The accuracy of the Hydrion papers was confirmed by the pH-meter and organic dye indicators. Following adjustment of pH the resins were stirred vigorously for 15 minutes a t 80" C. If there was any drift of pH it was readjusted to the desired value. The aqueous layer was then drawn off and the hydrophobic layer was subjected to vacuum distillation at 27 inches gage. After removal of water the clear sirups were polymerized to hard resins by heating a t 120" to 130" C. under atmospheric pressure until the softening point of the resin reached 80" to 95" C. (ball and ring test-A.S.T.M. E 28-42T). At this stage the resins were poured out on polished stainless steel plates, chilled, and crushed to form noncaking powders. SOLUBILITY TEST. The solubility in tung oil, maleinized linseed oil, and Y-bodied linseed oil was evaluated by heating and stirring 5 grams each of oil and resin to 150" C., holding 5 minutes and observing the clarity of the cooled mass a t 25" C. HEATREACTIVITY TEST. Five grams each of oil and powdered resin were placed in a test tube, which was then immersed in a thermostatically controlled hot wax bath, and stirred together until gelation occurred. The time interval between initial immersion and gelation was recorded as the gel time. The bath temperature was 150' * 1' C., producing a temperature of 143" C. in the resin-oil mass. PREPARATION OF VARNISH. A thermosetting varnish was prepared from either tung oil or nialeinized linseed oil as follows:
3
100 grams powdered resin
120 grams drying oil
it
2,CRESYLIC ACID
*G*
* 6 c n A V . FUNCTIONALITY-2.5
CH 3
P -CRESOL
*
Heat the drying oil to 250' C. and let cool to 200' C. in 15 minutes. At this point resin is added whlch rapidly cools the mass to about 110' C. Maintain the temperature a t 110' to 130' C. until all the resin has been dissolved. Raise temperature
M -CRESOL
3 . 2 , 2 - BIS (4-HYDROXYPHENYL) PROPANE
FUNCTIONALITY = 4
tu,
5
320
lW n
5
Approximate composition of the cresylic acid : m-Cresol. 33% p-Cresol 17% o-Cresol,' 3% Higher boiling tar acids, 5%
2,3-, 3,4-, 3.5-Xylenols, 30% 2,6-, 2,4-, 2,5-Xylenols, 10% Phenol, 2%
FORMULATION AND PREPARATION OF RESINS. The method of preparation was similar, in part, to the method used by the Albert Chemische Werke in the production of Albertols. Whereas the Albertols are produced under conditions favoring high methylol phenol content-that is, high concentrations of alkaline catalyst and low temperature condensation at 25" to 60" C.-the method used in this work employed small amounts of alkali and a short refluxing period a t 96" to 98 a C. The combined phenols were refluxed with 37% aqueous formaldehyde in the ratio of 1.6 moles of formaldehyde per mole of combined phenols for 1.5 hours a t 96" to 98' C. The catalyst used was 0.6% sodium hydroxide by weight based on the combined weight of phenols, This concentration produced a pH of 8 to 9 a t the beginning of reflux. After cooling the condensation product to 80' C., 10% aqueous sulfuric acid was added to effect the desired pH value. The pH of the mixture was varied over a range of 8 to approximately 4 for the various samples reported here and was found to have a pronounced effect on properties. The pH measurements were first mgde by means of a Beckman
Vol. 42, No. 10
280 W
N
5
W
240
x!
+
5
UNMODIFIED PTB P n 200
W u)
a 0
3-
-I W c)
160
w
ootobor 19%
INDUSTRIAL AND ENGINEERING CHEMISTRY
2113
TABLE I. UNMODIFIED pi4rtBUTYLPHENOL RESINS
Resin No, 1 2 3 4
pH after Treatment with HzSO4 8.6 7.6 4.2 3.6
Tung oil Turbid Turbid C C
(Moles CHtO per mole of phenol, 1.6; basic catalyat, 0.6% NaOH) Testa on Varnish (Tung Oil Base) -. Cake Hardness Shore A Durometer Time t o Compatibility 2-inah string Gel time Viscosity Baked Baked 6 hr. a t 136' C. Maleiniaed Y-bodied a t 150. C., a t 136' C., 60 0 solids, 6 hr. at plus 48 hr. in transformer linneed oil linseed oil nun. hr. &her 136'C. oil at l l O o C. Turbid Incompatible 12'h 3 F 30 Disintegrates Inoom atible 4'/r 2'/I I 39 10 badly swelled Turbid C D 16 0' 46 41tr 69 &/a 5 15 C C
e
TABLE11.
PHENOL
MODIFIEDpteT&BUTYLPHENOL RESINS
(Moles CHIO per mole of phenol, 1.6; basic catalyst, 0.6% NaOH)
Testa on Varnish (Tung Oil Base) Cake Hardness Bodying Shore . - A- Duramater -.. time Clnmnati hilitva Compatibility' C;el Viscasity 607 Baked 13s" Baked C. plus 6 hr.48 a$ hr. 2-inch Moles pH after Maleinieed Y-bodied time string 6 hr. a t In transformer linseed linseed a t 16qo c . , a t 136' C.. H&Or Tung Moles Resin p-tsrthr. GardnAr 136" C. oil a t 110* C. oil oil oil nun. Phenol Treatment Butylphenol No, H 20 Disintegrates 7.8 C C C 18 1/18 6 6 20 G 7 bad1 swelled C 6.9 C 39 l/a 27 G C C 20 lb, ba& swelled 8.2 7 8/4 i/4 0 7 7, less swelling C C 30 7.5 8 '/4 v 4 H 20 40 12, less swelling 6.9 C C C 9 '/4 1/4 G 10 0, least swelling C C C. 65 6 . 0 10 i/4 H-I VI* 8.2 C C c-I 13 Diaintegrates 11 ., ... 4.0 C I I 12 '/a 13 I/% 4.0 I I I C compatible; I = incompatible; C-I resin orieinslly compatible with oil, but beaame incompatible after heating a t 135' C. for 3 to 6 hours.
- ___
solid
2
a
8-'
-
-
..
...
... ...
... * ..
..... ...
~~
TABLE 111. CRESYLIC ACIDMODIFIED pteT&BUTYLPHENOLRESINS (Moles CH:O per mole phenol, 1.6; bbsic catalyst, 0.6% NaOH) Taata nn Varnish b
Moles p-tsttButylphenol
Moles Cresylic Acid
Compatibilitym Maleiniied Y-bodied linseed linseed oil oil C c-I
14
'/4
v 4
pH after H;SOr Treatment 6.2
16
'/4
1/r
6.5
C
C
c-I
16
'/4
v 4
4.0
C
C
C
5
I I
I
I I
Resin No.
Tung oil C
Bodying time 2-inch stiing a t 160 C., min. 24K 16L 35K 24L 66K 34L
Gel time
Viscosity
11/4 1% 1%
E
i%k
at 135' C., hr. Gardne; 1% F E
a
Cake Hardness Shore A Durometer Baked 6 hr. at Baked l3q" C. plus 48 6 hr. at hr. In transformer 136' C. oil a t 110" C. 46 16, badly swelled 20 Disintegrated 23 15, swelled 5 swelled 25 5 l b , swelled 20 6 , least swelling
1a/4 D &/a 17 '/a I 3.6 18 I/* I/@ a C = compatible. I = incompatible. C-I = resin ori 'nally compatible with linseed oil but became incompatible after heating a t 135O C. for 3 to 6 hr b IC = maleiniaed h e e d oil base; L Y-bodied iinseefoil baee.
to 150" C., stir, and record time to reach 2-inch strin from thermometer (hot). Add solvent mixture (73 grams of%olsol light solvent plus 147 gmms of high solvency mineral spirits). Stir to dissolve and filter. VARNISH TESTS A. Viscosity at 50y0 solids 25" C. wm tasted by Gardner bubble viscometer. B. Gel time at 135' C. was determined on a 20-gram sample in an open-top aluminum dish. C. Cake hardness at 25' C. was measured by Shore type A Durometer after 6 hours' baking at 135" C. on sample described in B. D. Oil resistance was determined by measuring the hardness of the cake described in B and C after 48 hours' immersion in transformer oil at 110" C. Degree of swelling was also noted. E. Claritz of the cake was also observed after baking for 6 hours at 135 C. F. Proof tests on the most promising varnishes were made according to A.S.T.M. D-115 test specification for electrical insulating varnishes as follows: drying time a t 150' C.; heat endurance at 150' C. (flexible life); and wet and dry dielectric strength. RESULTS
The results are presented in Tables I to V, describing the composition of the resins, the pH after addition of sulfuric acid, and the properties of the resins. Figures 1 and 2 illustrate the effect of pH after initial alkalime condensation on the gel time of some of the resins dissolved in both tung and maleinized linseed oil.
The data presented show that there is a general trend in going from the alkaline to the acid eide after initial alkaline condenaation. As the pH falls compatibility with drying oils increases, especially in the bodied linseed oil, as well as the resistance of the baked varnish to transformer oil. On the other hand heat reactivity is decreased as Figures 1 and 2 illustrate. This is true regardless of which polyfunctional modifier is used for the base p tertbutylphenol. Only fairly acid resins are permanently compatible with the heat polymerized linseed oil. Since heat reactivity is just as important as oil resistance, the choice must be l e t e d to that polyfunctional modifier which produces fast gelling varnishes as well as maximum oil resistance. Examples 21 and 24, containing 2,2bis(4hydroxylphenyl)propane, appear to be most advantageous with a pH of approximately 5.5. Cresylic acid appears to be effective in bodied linseed oil at a pH range of 4.0 to 4.5. Phenol follows as a poor third choice. Unmodified ptertbutylphenol resins lack sufficient thermosetting qualities to be of interest. From the data on compatibility it is clear that initial compatibility can be misleading. Resins 14, 15, and 16 were initially compatible with Y-bodied linseed oil in preparation of the varnishes. However, retention of compatibility, after baking a t 135' C., and oil resistance appear to be directly influenced by pH aa follows: Resin 14 pH = 6.2,clear to turbid in 1.5hours at 135"C. Resin 15 pH 5.5,clear to turbid in 3 houm at 135" C. Resin 16 pH = 4.0,permanently clear after 6 hours at 135' C .
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2114
Vol. 42, No. 10
TABLE Iv.
2,2-BIS(4-HYDROXYPHENYL)PROPANEMODIFIEDp-tert-BUTYLPHENOL RESINS (Moles CHaO per mole phenol, 1.6; basic catalyst, 0.6% NaOH) Tests on Varnishb Cake Hardness Bodying Shore A Durometer Moles time, 2,2-bis(4Compatibility4 %inch Gel Baked 5 hr. a t Moles Hydroxy- pH after Maleiniaed Y-bodied string time Viscosity Baked 135' C. plus 48 p-tertphenyl)Ha804 Tung linseed linqeed a t 150' C., a t 135'C., 50% 6 hr. a t hr. a t l l O o C. in Resin No. Butylphenol propane Treatment oil oil 011 min. hr. solids 135O C. transformer 011 19 7/s 8.0 I vt I I ... . ... 6.4 C C I 12T a/ 1 J 42 30, swelied ' 1/1 20 '/t C 5.5 '/8 C I 27K 1l/r E 37 33, little swelling '/* 21 C 5.0 C C 25T 22 11/4 I 30 15 VI VI 4.6 C 23 C C 25T 1' / t '/4 M 45 30, least swelling 24 "/16 1/18 5.5 C C I 11/4 E K 46 35, least swelling Commercial heat reactive oil-soluble phenolic C C C 27K 16 4 , swelled, soft 13/4 resin BR-10282 (Bakelite Corp.) C = compstible; I = incompatible. T 'ang oil base; K = maleiniaedlinseed oil base.
:A
4
b
...
...
..
K
-
TABLEV. A.S.T.M. D-115 TESTSON ELECTRICAL INSULATING V.4RNISHES Composition Example 21 (rnaleinieed linseed ,oil) Example 16 (Y-bodied linseed oil) plus medium oil length linseed alkyd
Drying Time a t l l O o C., Hr. 1
1.5
In conclusion it must be stated that the most interesting question is still unanswered-namely, what intermediate stages of the phenolic condensation and polymerisation process are produced aa a function of pH to influence this wide variation in properties. As yet quantitative analytical tools are either lacking or unproved. Thus far the author has been unable to corroborate methylol determinations by the method of Lilley and Osmond. It is hoped that either conventional analytical methods, such m those of Lilley and Osmond, or infrared spectra will ultimately provide the answer.
Heat Endurance a t 150° C., Hr. 18-20
Oil Proofneas Passes
84-96
Passes
Dielectric Strength Dry, Wet (24 hr.) volts/rnil 2430 1740
I
volts/mil 1281
950
LITERATURE CITED
(3) Hultssch, K.,J . prakt. Chem., 158,No.2,275(1941). (4) Lilley, H. S., Varnish Making, Oil & Colour Chem. Assn., 11321, Chem. Publishing Co.,Ino., New York (1940). ( 5 ) Lilley, s., and Osmo,,d, D. 'w. J,, J . sot, Chem. I d , (London), 66,425-7 (1947). (6) Lilley, H. S., and Osmond, D. 15'. J., Paint Technol., 13, 21724 (1948). (7) Lykken, Porter, Ruliffson, and Tuemmler, IND.ENG.CHEW, ANAL.ED., 16,219-34 (1944). (8)Singer, R. J. R., Kemisk, 23,49-61 (1942): (9) Turkington, V. H.,and Allen, I., presented before the Division of Paint, Varnish, and Plastics Chemistry at the lOlst Meeting, AMERICANCHEMICAL SOCIETY, St. Louis, Mo. (10) Turkington, V. H., Shuey, R. C., and Shechter, L., IND. ENQ. CHEM.,30,984 (1938).
w.,and Perrins, L., J . Oil &? CO~OUT Chemists' A8SOC., 30, No.324, 185 (1947). (2) Farmer, E.H., J . Chem. Soc., 1943,472.
RECEIVED October 8, 1949. Presented before the Division of Paint, Varnish, and Plastics Chemistry a t the 116th Meeting, AMXXWXN CHEMICAL SOCIETY, Atlsntic City, N. J.
(1) Charlton,
Catalytic Synthesis of Benzofurans J
J
CHROMIUM CATALYSTS FOR CY CLODEHYDROGENATION OF 0-ALKYLPHENOLS CORWIN HANSCH, CARLETON SCOTT1, AND HOWARD KELLER2 Pomona College, Cluremont, CaZg. This paper discusses the vapor phase catalytic dehydrocyclization of o-ethylphenol, o-isopropylphenol, 0allylphenol, and thymol to benzofuran, 3-methylbenzo-
furan, 2-methylbenzofuran, and 3,6-dimethylbenzofuran, respectively. The investigation of several chromium-oncharcoal catalysts for this reaction is reported.
I
conditions for a given reaction such as the conversion of heptane to toluene. With the exception of the interesting work being done by Orchin et al. ( 6 )little has been done with the more complicated molecules. The work reported here was directed primarily toward increasing the scope of the reaction, particularly with respect to heterocyclic molecules. The need for more suitable procedures for the industrial preparation of this increasingly more important class of compounds was one of the motivating factors in this research. This work was of a scouting nature; the expensive development of optimum conditions will be left to larger better equipped laboratories.
N LINE with increasing interest in the catalytic synthesis of aromatic molecules by dehydrocyclisation, a program has been undertaken in this laboratory to investigate the vapor-phase catalytic synthesis of some of the larger aromatic molecules, especially the heterocycles. Previous interest in the dehydrocyclization reaction has centered mostly on the conversion of relatively simple aliphatic hydrocarbons to simple aromatics. This work has been devoted to gaining an insight into the mechanism of the reaction ( 4 ) or toward improvement of processing 1 Present addrers, XIascnchusetts Institute of Technology, Cambridge. Masr. 2 Preqent address. Leffinqwell Company, Whittier. Calif.
