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
2424
sulfur poisoning, and to attain a reasonable catalyst life the sulfur content must be less than 1 grain per 1000 cubic feet. The sulfur sensitivity of catalysts for the alcohol syntheses appears to vary considerably with catalyst composition. However, these catalysts areinmost cases lesssensitive to sulfur poisoning than FischerTropsch catalysts. Some alcohol catalysts, for example, those for the is0 synthesis, are unaffected by high concentration of sulfur (16). ACKNOWLEDGMENT
The authors are pleased to acknowledge the assistance of Charles Zahn and of R. A. Friedel in the analysis of the products obtained from the nitrided iron catalyst.
(11) Ingersoll, A.
(12) (13) (14) (15) (16) (17) (18) (19) (20)
LITERATURE CITED
(1) Anderson, R. E., Friedel, R. A., and Storch, H. H., J . Chem. Phys., 19, 313 (1951). (2) Anderson, R. E., Shulta, J. F., Seligman, B., Hall, W.K., and Storch, H. H., J . Am. Chem. SOC.,72, 3502 (1950). (3) Brown, R. L., and Galloway, A. E., IND.ENG.CHEW,21, 310
(1929).
W.M. D., and Smith, D. &I., J . Am. Chem. SOC.,57,57 (1935). (5) Eliot, T. Q., Goodwin, S. C., Jr., and Pace, P. S., Chem. Eng. Progress, 45, 532 (1949). (6) Elving, P. J., and Warshowsky, B., Anal. Chem., 19, 1006 (1947). (7) Frolich, P. K., and Cryder, D. S., IND. ENG.CHEY.,22, 1051 (1930). (8) Gall, D., Gibson, E. J., and Hall, C. C., paper presented at the XIIth International Congress of Pure and Applied Chemistry, Section 7 , New York, Sept. 12, 1951. (9) Graves, G. D., IND. ENG.CHEhf., 23, 1381 (1931). (10) Hirst, L. L., in “Chemistry of Coal Utilization,” Vol. 11, Chap. 20, New York, John Wiley & Sons, 1945. (4) Bryant,
Vol. 44, No. 10
(21) (22)
W.,“Org. Reactions,” Vol. 2, p. 393, New York, John Wiley & Sons, 1944. Kummer, J. T., Podgurski, H. H., Spencer, W. B., and Emmett, P. H., J . Am. Chem. Soc., 73, 564 (1951). Mitchell, J., Jr., and Smith, D. M., Anal. Ckem., 22, 748 (1950). Morgan, G. T., Douglas, D. V. N., and Proctor, R. A., J. SOC. Chem. I d . ( L o n d o n ) , 41, 1T (1932). Pichler, H., and Ziesecke, K. H., U. S. Bur. Mines, Bull. 488 (1950). Pichler, H., and Ziesecke, K. H., Oel u. Kohle, 45, 13, 60, 81 (1949). Pichler, H., Ziesecke, K. H., and Titzenhaler, E., Ibad., 45, 333 (1949). Pichler, H., Ziesecke, K. H., and Traeger, B., Ibid., 46, 361 (1950). Reisinger, Tech. Oil Missions Reel 13, Bag 3043, Item 3. Scheuerman, A. in report of Zorn, H., PB 97, 368; FIAT Final Rept. 1267 (1949). Shultz, J. F., Seligman, E., Shaw, L., and Anderson, R. E., IND. E i i G . CHEM., 44, 397 (1952). Storch, H. H., Golumbic, N., and Anderson, R. B., “The Fischer-Tropsch and Related Syntheses,” Chap. 1, New York, John Wiley & Sons, 1951.
(23) Ibid., p. 571. (24) Weitkamp, A. W., t o be published. (25) Wender, I., Friedel, R. A., and Orchin, M., Science, 113, 206 (1961). (26) Wender, I., Levine, R., and Orchin, M., J . Am. Chem. SOC.,71, 4160 (1949). (27) Wender. I.. Metlin. S.. and Orchin. M..Ibid.. in mess. (28) Wender, I., Orchin, M., and Starch,". H., Armed-Forces Chem. J . , IV, 4 (1950). RECEIVED for review October 19, 1951. ACCEPTEDMay 9, 1952, Presented before the X I I t h International Congress of Pure and Applied Chemistry, Fuel, Gas, and Petroleum Chemistry Section, New York, September 1951.
FILM STUDIES P. S. HESS AND G . A. O’HARE Congoleurn-Nairn,Inc., Kearny, N. J.
T
HE subject of drying and deterioration of paint films has occupied for many years a n important place in academic and industrial research. Most of the experimental work has been related t o film studies of natural oils and recently to synthetically prepared fatty acid triglycerides containing a single fatty acid component, such as trilinolenin or trilinolein. The purpose of this paper is to report experimental data accumulated over more than one year on the oxygen absorption and weight change of synthetic fatty acid triglycerides and natural drying oils. Many investigators have studied these subjects, but in most instances oxygen absorption and weight gain and loss have not been correlated on the same film and in the majority of cases the experiments were not conducted over a sufficient length of time. A further objective of this study is to gain information on film yellowing and to compare films cast with different oils under various conditions for their changes in physical appearance. EXPERIMENTAL PROCEDURE
The glycerol esters of linolenic, linoleic, and oleic acid (trilinolenin, trilinolein, and triolein) were obtained from the Hormel Institute of the University of Minnesota. I n addition, commer-
cially available alkali-refined linseed oil and soybean oil were included in this study. Table I gives the physical and chemical properties of these triglycerides and their approximate purity.
FILMAPPLICATION AND DRYING OF OILS. To form a continuous smooth oil film it was essential that the glass slides be scrupulously clean. For oils containing no drier it vias necessary to use frosted-glass plates to prevent creeping. The microscope slides of uniform thickness (0.10 =k 0.002 em.) were etched with a water-carborundum slurry prior t o final cleaning. The films were applied with a Bird applicator resulting in approximate film thicknesses of 3 mils, weighing 0.05 i 0.005 gram. For each individual oil, films were cast on a t least 20 slides, five of which were used t o obtain checks on the weight measurements; oxygen determinations were made by scraping the oil film at different times from the remaining plates. The percentage of oxygen was determined by using a combustion apparatus for the semimicro determinations of carbon and hydrogen. Excellent reproducibility on weight change and oxygen percentage was obtained by adhering strictly to the given procedure. The drier consisted of a mixture of lead and cobalt naphthenate. 0.5% of lead and 0.05% cobalt metal based on the weight of oii were added to the samples. Drying occurred in a room conditioned at all times to 7 3 ” i 2 ” F. and 60 i 4% relative humidity.
October 1952
0
INDUSTRIAL AND ENGINEERING CHEMISTRY
2425
appears that setting up occurs close t o the point where the weight absorption curve bends SP. Color nL6 Peroxide Acid Iodine Oxygen, Gravity Di-Conju- Appro5 sharply and thereafter com(Gardner) Valuea Value Valueb % at 25'C. gationo, % Purity paratively little additional Trilinolenin Water white 1,4859 23.4 0.16 255.5 10.93 0,934 1.45 98.5 Trilinolein Waterwhite 1.4759 3.19 0.16 171.7 10.85 0.920 0.64 99.4 weight is gained. This applies Triolein Water white 1.4657 2.06 0.24 85.0 10.97 0.909 0 99.8 especially for trilinolenin, triLinseed 6 1.4789 28.0 2.02 177.0 11.82 0.929 0 .. Sosbean 6 1.4730 4.62 1.20 131.0 11.50 0,925 0 .. linolein, and linseed oil. The From (3). set-to-touch point occurs someConventional 1-hour Wijs method. C Estimated by ultraviolet absorption at 232 mp and peroxide values. what later for soybean oil, probably because of the relatively high oleic content. The weight per cents gained after 20 hours of drying for trilinolenin, linseed, DRYINGOF OILS CONTAINING DRIER. After addition of the trilinolein, and soybean oil are 11.7, 10.5, 9.4, and 7.1, respecdrier, the oils were allowed t o stand 48 hours before the casting tively. The weight gain curves up to 20 hours follow a definite of films. The set-to-touch, dust-free, and tack-free times were pattern, evidenced by the fact that the individual curves subdetermined by the finger touch method. The results presented sequent to the set-to-touch point are essentially parallel to in Table I1 are the composite averages of three examiners. each other. The oleic constituent appears to be rather unreactive as compared to the more unsaturated radicals in the initial stages of film formation, as is indicated by the negligible amount TABLE 11. DRYING OF OILSCONTAINING DRIER of weight gained after 20 hours. Set-to-Touch, Dust-Free, Tack-Free, Min. Min. Min. The per cent weight gain and loss is plotted against days in Trilinolenin 110 170 300 Figure 2. Trilinolenin reaches maximum weight after approxiTrilinolein 150 210 300 mately 10 days of drying. This is only about 1 to 11/~% more Triolein5 ... ... ..... Linseed 150 200 320 than gained after the first 20 hours. Thereafter a slight loss in Soybean 310 370 720 C weight occurs and constancy is reached after 30 days. The a Did not dry. weight attained after this 30-day period has not changed over a time that has now been extended to over 400 days. The weights decreased after the initial 24 hours, both for linseed oil and trilinoThe same relative results in the drying relationship of these lein, the latter a t a faster rate; thereafter the loss in weight is oils were obtained by performing the experiment in total darkvery slow. The weights of the films after 400 days were not ness, I n general trilinolenin sets t o touch faster and becomes appreciably different from those after 30 days. dust free earlier than any of the other oils. The dried trilinoThe total per cent oxygen is plotted against drying time in lenin film is also harder and more scratch resistant than the Figures 3 and 4 for trilinolenin, trilinolein, and linseed oil. trilinolein or linseed oil films. Linseed oil has somewhat better Figure 3 indicates that initially trilinolenin absorbs oxygen a t a film characteristics than trilinolein. Differences in hardness of faster rate than trilinolein or linseed oil. A calculation of the these oil films are still apparent after more than 1 year's exposure stoichiometric amount of oxygen addition which is needed to to air under the stated conditions. Soybean oil was considerably cause saturation of the double bonds of trilinolein gives a figure slower in drying than linseed oil or the pure triglycerides. These of 15.9%. This may be assumed to be the maximum amount of observations indicate that a t room temperature and in the presoxygen which could be added to trilinolein without any decomence of driers a difference exists in the air-drying behavior of position of the molecule. Any additional oxygen over this perfilms of trilinolenin and trilinolein, both in drying rate and nature centage, then, is indicative of oxidative degradation. The of films. The experiments bear out the thought that the presoxygen percentage for these oils after 30 days' exposure remains ence of more linolenic components in an oil results in tougher relatively constant a t 30%. This amount is greater than the films, indicating perhaps more cross linking during drying. The possible total of 26.9%, which includes both the stoichiometric difference in behavior between trilinolenin, trilinolein, and the addition during drying and that initially present in the molecule other oils is further substantiated in Figures 1 and 2 where the in the form of an ester. per cent gain in weight has been plotted against drying time. From this it is concluded that decomposition products remainI n Figure 1, weight gain is plotted against hours of drying. It AND CHEMICAL PROPERTIES OF THE TRIGLYCERIDPS TABLE I. PHYSICAL
::[
- ' - I BO
(
-
8
TRlOLelN
0 I 10 '
HOURS
,
(E
,
'
I
li
O
'
16
,
I
'
n
le-=
Figure 1. Weight Gain of Oil Films Containing 0.5% Lead and 0.05% Cobalt
Figure 2. Weight Gain of Oil Films Containing 0.5% Lead and 0.05qo Cobalt
INDUSTRIAL AND ENGINEERING CHEMISTRY
2426
11
"c-
20
1
2
4
6
1
8
1 0
12
~
14
I6
I8
~
20
HOURS
Figure 3.
Oxygen Content of Oil Films Containing 0.5% Lead and 0.05% Cobalt
ing in the formed film are responsible for this higher value. This becomes even more apparent by comparing the oxygen data with the percentage of weight gained, eince the amount of oxygen in the film a t any given moment is greater than can be accounted for by gain in weight. It must be concluded, therefore, that decompasition and the formation of lower molecular weight oxygenated materials become factors in film drying the moment oxygen adds to the reactive centers in the molecule. The fact that both the weight and the per cent oxygen of the films reach constancy a t an early stage of the drying process appears to emphasize the relative stability or a possible dynamic equilibrium which exists in an oil film if exposed to air under constant conditions. The film-dqing experiments with oils containing drier indicate that trilinolenin reacts differently from trilinolein, especially as far as decomposition is concerned. Increasing the amount of linolenic components appears to decrease the amount ol volatile decomposition and add to the stability of the film. Fewer decomposition products apparently are evolved during oxidative drying of trilinolenin than of trilinolein or linseed oil. According to the present data the behavior of linseed oil on air drying is detween that of the pure triglycerides. DRYINGOF OILS CONTAININQ N o DRIER. The respective set-to-touch times of trilinolenin, trilinolein, and linseed oil with and without drier are as follows:
Trilinolenin Trilinolein Linseed oil
With Drier, Rlin. 110 150 180
Without Drier, Days 1.5
3.5 4.5
This demonstrates that driers play an active part in speeding up the drying process. The drying speed of the pure triglycerides as well as that of linseed oil was greatly accelerated by drier addition. A comparison of Figures 1 and 5 i1lustrate.ethis action. It is further indicated in this comparison that driers are effective in overcoming the inhibiting eff ectc of naturally occurring minor components. With driers, the drying behavior as indicated by set-to-touch time and weight gain does not diffcr markedly between trilinolein and linseed oil (which has natural inhibitors) in the early stages. Without driers, however, there is a very definite induction period for linseed oil. Keight is gained a t a slower rate than in the case of trilinolein. After 31/2 days the per cent weight gain is the same for each oil but the set-to-touch time for linseed oil occurs at a higher weight percentage and consequently after a longer drying period. The per cent gain in weight for oils having no drier is shown in Figures 5 and 6. A comparison of Figures 2 and 6 points out that drier has an effect on weight gain, as can readily be seen
Vol. 44, No. 10
I
~
Figure 4.
~
-
" 0
TRILINOLENIN
TRlLlNOLEiN
~
Oxygen Content of Oil Films Containing OS",, Lead and 0.0570 Cobalt
when the niaiimuni weight gains with and without drier are compared : With drier
Trilinolenin Trilinolein Linseed oil
Wt. 5 e i n , % W i t h o u t drier 17.4 10.4 12.0
The efTect of driers on gain in weight is most pronounced for trilinolenin. The weight gained for trilinolein and linseed oil without drier is not much greater than that for the oils to which drier had been added. A loss of weight After maximum absorption had occurred is evidenced for each of the oils (Figure 6). This loss is most pronounced for trilinolein. hfter approximately 70 drying days an equilibrium is approached which is still maintained after 400 dags; this equilibrium corresponds closely for both the oil films containing drier and those having no drier. The presence of driers speeds up the oxygen uptake as well as the gain in aeight. This is denionstra.ted in Figures 3 and 7. Oils with no drier reach a higher oxygen percentage prior t o the point where little oxygen absorption occurs. After 10 days the oxygen values are approximat'cly equivalent to thoae of oils with drier and which were exposed to air for only 1 day. Similar to the results obtained for oils with drier, an equilibriuin oxygen percentage is reached and maintained for over 400 da.ys for oils containing no drier. The last values determined were 30.22, 31.06, and 28.38%, respectively, for trilinolenin, trilinolein, and linseed oil. The more important findings of the film drying studies may be summarized as follows: Trilinolenin dries to a harder film t.0 the touch in somewhat faster time than does either linseed oil or trilinolein; this is tiue in the presence of driers or without driers. Soybean oil dries to a softer film than linseed or trilinolein. Triolein appears to be unaffected by atmospheric oxygen under the same conditions. The presence of driers speeds up the oxygen absorption of films. The maximum amount of oxygen absorbed, however, is no greater than that of the oile without drier. After prolonged drying the properties of the films of any one oil with and without drier appear to be similar, as is indicated by oxygen determination, weight, and physical examination of the films. Although in the initial drying the weight increase of the oil films is only slightly less than the quantity of oxygen gained, the higher oxygen values after the sekting up of the films cannot be accounted for by weight gains. Oxidative degradation becomes a factor influencing the drying process from the moment oxygen reacts with the active centers of the molecule. Trilinolein appears to be more subject t'o decompoPition into volatile by-products than does trilinolenin. From these observations it may be speculated that the linolenic acid component is desirable in prolonging the life of the
~
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
October 1952 r
I
I
I
2427
I
I
-
24222 0 7
IP
/I
5 16
5
i
/
I
1
I
I
1
I
Figure 6. Weight Gain and Loss of Oil Films Containing No Drier film in actual use. This may be attributed to a more complex molecular structure, which upon air drying gives rise to a minimum amount of volatile decomposition products and, along with this, results in film surfaces which are homogeneous and consequently impervious t o atmospheric conditions. The hardness and, as will be pointed out later, the alkali resistance of the trilinolenin film support this view. COLOR MEA SUR EM ENT S
Three-mil f i l m of oils containing drier were applied over white enameled paper. Color measurements were made with the Hunter multipurpose reflectometer described in (1 ), using the blue, amber, and green tristimulus filters. Essentially the same method was followed as has been described in the Federal Standard Stock Catalog (TT-P-141-a-43); the yellowing factor was calculated according to the formula
Y (yellowness)
=
A (amber) - B (blue) G (green)
Figure 7 .
Color measurements were made on: Films which were allowed to dry in artificial light at 73" f 2" F. and 60 =k 4% relative humidity for 48 hours. Measurements were made after 6 weeks of storage under the same conditions. Films which were allowed t o dry in total darkness a t 73" f 2" F. and 60 f 4% relative humidity for 48 hours. Measurements were made again after 6 weeks of storage under the same conditions. Films which were baked at 100" C. for 30 minutes and subsequently bleached for 1 week in direct daylight and aged for 6 weeks in darkness.
All measurements were compared with a standard white enameled paper treated similarly to the applied oil films. The yellowing factor was calculated according to the previously given formula. The results tabulated in Table I11 represent the observed yellowing factor of the applied film on the standard paper.
-
TABLE 111. YELLOWINGFACTOR OF FILMSDRIED UNDER VARIOUSCONDITIONS
Trilinolenin Trilinolein Linseed goybean Yaper control
At 100e C. Bleached
Artificial Light In Darkness After Aged 24 hr. 6 wk. 24 hr. 6 wk.
After baking
(daylight)
(dark)
0.218 0.143 0.151 0.148
0.302 0.188 0.201 0.159
0.462 0.289 0.382 0.270
0.398 0.272 0.304 0.274
0.475 0.308 0.368
0.104 0.134 0.110 0.111
0.121
0.130
0.134
0.327 0.305 0.214 0.213
0.220 0.155 0.172 0.182
1 wk.
Aged
6 wk.
0.297
Oxygen Content
of Oil Films Containing No
Drier
These results demonstrate that trilinolenin yellows to a greater extent than the other oils after 24 hours of drying. Linseed oil, which contains an appreciable amount of trilinolein, displays after 24 hours more yellowness than trilinolein. Films of trilinolein and soybean oils prior to aging have approximately the same yellowing factor. I n every instance the air-dried films yellowed after 6 weeks' aging. Although the factor, after 24 hours, of trilinolein dried in light is low, a considerable amount of yellowing develops after 6 weeks, and a t that time the factors for the pure triglycerides are of the same order; linseed oil and soybean oil, correspondingly, are considerably less affected. The dried films have approximately the same factor whether the drying was conducted in light or darkness. Upon aging, however, less yellowness developed when the filnis were kept in the dark. This was much more pronounced with trilinolein and soybean oil. Baking a t elevated temperatures causes films to yellow more than under the previously stated conditions. Upon bleaching, the yellowing factor decreases appreciably for trilinolenin and linseed oil but very little for trilinolein or soybean oil. The color data on films dried a t 73" =k 2" F. lead to the preliminary conclusion that the yellowing of trilinolenin is lesa photosensitive under the illuminating conditions of the experiment than trilinolein. This is based on the observation that the yellowing factor of trilinolenin is approximately the same whether the films were stored in light or darkness. According to the pre-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2428
viously discussed data on film drying, this may be attributed to the fact that relatively little decomposition occurs and that the chromophoric configuration is inherent and is the same regardless of light condition. This does not appear to be the case for trilinolein; more decomposition occurs for this oil on drying, and the results indicate that the pronounced yellowing upon aging in light might be attributed to chromophoric groupings created by reactions involving decomposition products. Theresultsobtained with linseed and soybean oils fall in line with this reasoning. The yellowing factors obtained on baking of the films cannot be compared with the foregoing since different chemical processes are involved at the elevated temperatures; however, after-yellowing is much less of a factor than for air-driedfilms, sincemany colorforming reactions may have already taken place during the baking. Since these results apply to the specific conditions of the experiment, it is possible that the order of magnitude of yellowing may be somewhat different under other conditions. Alkali resistance was checked on oils ALKALIRESISTANCE. containing drier. Films were cast on test tubes by dipping. After 48 hours of drying the tubes were immersed a t 73" i 2' F. in a 0.5yosodium hydroxide solution. The alkali reeistance of trilinolenin proved to be far superior to all the other oils. These results are similar to those reported by Scofield and
Vol. 44, No. 10
Williams a t the Chicago meeting of the Federation of Paint and Varnish Production Clubs (8, 4). The studies of Scofield on weight gain and Williams on oxygen content were carried out independently of each other. In the present studies both sets of data were obtained on the same films. I n many instances similar conclusions were drawn. Williams ( 4 ) in his work on the chemical composition and adsorptive properties of clear films has shown that the weight per cent of insoluble matter in carbon tetrachloride of oil films of trilinolenin and trilinolein approaches an equilibrium. This further substantiates the fact that clear films under ordinary conditions are stable products, as has been concluded from weight change and per cent oxygen data. LITERATURE CITED
(1) National Bureau of Standards, Research Paper 1345 (1950). (2) Scofield, F., Oficial Digest Federation P a i n t & V a r n i s h Production Clubs, 311, 1012-19 (1960). (3) Wheeler, D. H., Oil & S o a p , 9,89-97 (1932). (4) Williams, C. C., Oficial Digest Federation P a i n t & V a r n i s h Production Clubs 311, 1020-32 (1960). RECEIVED for review July 2 , 1951. ACCEPTED May 19, 1952. Presented before t h e Division of Paint, Varnish, and Plastics Chemistry a t the 119th Meeting of t h e AMERICAN CHEMICAL SOCIETY,Boston, Mass., April 1951.
Separation of and p4resols from T eir Mixtures r n w
SIDNEY A. SAVITTI AND DONALD F. OTHICIER Polytechnic I n s t i t u t e of Brooklyn, Brooklyn, N . Y .
INAp
revious paper (,94), vapor-liquid equilibrium studies of binary systems with m- or p-cresol boiling points 202.4' C. and 202.0 C., respectively, as one of the components showed that separation of mixtures of m- and p-cresol could not be effected by the utilization of any of 14 different entrainers in either azeotropic or extractive distillation. I n an attempt to use precipitation or crystallization as a separating mechanism, freezing point data were determined for the meta-para cresol binary and for the binary systems of mcresol and pyridine, 2-aminopyridine, acetamide, p-t oluidine benzidine, and p-phenylenediamine. Similar data were obtained for each of these compounds and p-cresol in order to evaluate the possibilities of utilizing the second component to form addition compounds with the cresols, a separation being feasible if the physical characteristics of these two addition compounds differed sufficiently. It mas found that differences do exist between the freezing point curves of the two mixtures with benzidine, and a method described by Bentley ( 1 ) was then modified to utilize these differences and to resolve mixtures of m- and p-cresols into the almost pure individual components by a process involving precipitative crystallization with benzidine. O
SUMMARY OF SEPARATION PROCESSES
A number of methods have been proposed for separating mand p-cresols from their mixtures (55). Physical methods, such as distillation or even azeotropic or extractive distillation, have been unsuccessful owing to closeness of properties of these isomers (24). The most practical of these depend on the preferential 1 Present address, Consolidated Products Co., Inc., 15 Park Row, New York 38. N. Y.
formation of an oxalic acid complex or on the differing properties of the cresol sulfonic acids. Oxalic acid reacts selectively with p-cresol to form an insoluble compound which can be separated and decomposed t o yield pure p-cresol (11, 21, 27, 28). The sulfonation of the cresol mixtures yields the mono acids; when steam distillation is applied, the meta acid hydrolyzes to the creeol a t 116" t o 120" C., but the para acid does not decompose until a temperature of 133" to 135" C. is reached ( 2 , 25). Another method makes use of the fact that p-cresol sulfonic acid is the less soluble of the two ( 2 6 ) . By an alternate procedure, mcresol is selectively sulfonated, the unreacted p-cresol is recovered by solvents or by vacuum distillation, and the m-cresol is hydrolyzed separately (14, 16, 20, 34, 38). A variant of the above procedure involved forming an ammonium or sodium salt of the meta acid which is separated from the p-cresol by crystallization ( 4 , 8 6 ) . Other proposals described in the literature are:
1. The formation of the phosphates of the cresols, followed by petroleum ether extraction of the meta compound (Z2j 2. Formation of the calcium salts of the two cresols, followed by differential steam hydrolysis of the meta salt (37, 59)or by a separation based on the relatively greater solubility of the para compound ( 6 ) 3. Formation of insoluble addition compounds of m-cresol with either nitrous acid ( 16 ) ,phenol ( 6 ) ,quinone chlorimide ( 1Q), sodium acetate (5,10) or urea (30-33) 4. Combination treatments using sodium acetate and oxalic acid ( 1i?)or urea and oxalic acid ( 13) A recently developed method involves the alkylation of the isomeric cresols with isobutylene (36), separation of the tertiary butylated phenols by fractional distillation, and debutylation of the isolated derivatives to yield isobutylene and the individual
