Separation of Individual CRESOLS and XYLENOLS from Their Mixtures DONALD R. STEVENS Mellon Institute of Industrial Research, Pittsburgh, Penna.
Mixtures of meta- and para-cresols, and mixtures of xylenols and ethylphenols can be resolved by a process involving alkylation with isobutylene, separation of the tertiary butylated phenols by fractional distillation, and debutylation of the isolated derivatives t o yield isobutylene and the individual parent phenols.
0
RTHO-CRESOL can be isolated from cresol mixtures by fractional distillation, but owing to the closeness of their boiling points the meta and para isomers require more troublesome procedures for their separation. The xylenols are also difficult to separate and hence in industry only the easily recrystallized 3,bdimethylphenol is isolated and marketed. A number of methods have been proposed for separating meta- and para-cresols from their mixtures. The most practical of these depend on the preferential 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 to yield pure p-cresol (7, 17, 24, 25). The sulfonation of the cresol mixture yields the mono acids; when steam distillation is applied, the meta acid hydrolyzes to the cresol a t 116-120" C., but the para acid does not decompose until 133-135' C. is reached ( I ,23). Another method makes use of the fact that p-cresol sulfonic acid is the less soluble of the two (22). By an alternative procedure, mcresol is selectively sulfonated; the unreacted p-cresol is recovered by solvents or by vacuum distillation, and the meta acid is hydrolyzed separately (IO,II, 16,30, 56). A variant of the above procedure involves forming an ammonium or sodium salt of the meta acid which is separated from the p-cresol by crystallization (3, 22). 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 ( l o ) . 2. Formation of the calcium salts of the two cresols, followed by differential steam hydrolysis of the meta salt (84,36) or by a separation based on the relatively greater solubility of the para compound (5). 3. Formation of insoluble addition compounds of m-cresol with either nitrous acid ( I I ) , phenol ( d ) , quinone chlorimide ( I 4 ) , sodium acetate (8, 6), or urea (96-%?9). 4. Combination treatments using sodium acetate and oxalic acid (8) or urea and oxalic acid (9).
characteristic of these compounds is that, when heated in the presence of an acid catalyst, they lose their attached tertiary butyl groups (as isobutylene gas) and revert to the original phenols; in like manner tertiary amylphenols are dealkylated. The process to be described (52)separates phenols from their mixtures by a combination of steps, embracing the alkylation of the phenolic mixture with isobutylene, the separation of the alkylation products by fractional distillation, and the dealkylation of the tertiary butyl derivatives to yield the parent phenols. Cresol separation is now practiced on a commercial scale by this method. A description of some of the engineering features involved in the alkylation and fractionation steps so used was recently published (37'). SEPARATION OF CRESOLS
On distillation, coal-tar and petroleum cresylic acids first yield phenol (boiling point 181.2' C.) and then o-cresol (boiling point 190.5'); next a mixture of m-cresol (boiling point 202.2') and p-cresol (b. p., 202.1") is collected. The cresol mixture generally contains the meta and para isomers in the proportion of 60 to 40, respectively. On alkylation with isobutylene in the presence of an acid catalyst, the main products of the reaction are 3-methyl-4,6-di-tert-butylphenol (boiling point 167.0' C. at 20 mm. pressure) and 4-methyl2,6-di-tert-butylphenol (147.0' C. a t 20 mm.), together with smaller amounts of monobutylated cresols and some isobutylene polymer; all of these compounds are insoluble in dilute aqueous alkali. The narrower the boiling range of the original cresol mixture, the sharper are the plateaus of the fractionation curves of the butylated product. The boiling points of the various tert-butyl derivatives of m- and p-cresol, a t several pressures, are given in Table I ; the derivatives of phenol and o-cresol are also included. It is evident that the boiling points of the di-tert-butyl derivatives of m- and p-cresols are sufficiently spaced for the efficient separation of these compouhds by fractional distillation. When heated separately in the presence of an acidic catalyst, each derivative will decompose to yield isobutylene and the pure individual cresol.
The author observed that the constituents of a phenolic mixture, when alkylated with olefins, form substitution products of much wider boiling range than the starting material, and that efficient separation of the derivatives by fractional distillation is possible. If isobutylene is used as the alkylating agent, tertiary butylphenols are formed. A
A middle cut of 250 grams, covering a 1' C. PROCEDURE. boiling range, was removed from 450 ml. of ordinary 3" m-pcresol mixture by distillation through a ten-plate column. To 655
656
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
Vol. 35, No 6
m-cresol, weighed 75.2 grams. When 74.8 grams of the latter, to which had been added 0.52 gram of sodium acid carbonate t o neutralize the sulfuric acid catalyst, were distilled through a ten-plate column, the fractions shown in Table I11 and curve of Figure 2 were obtained. In similar experiments m-cresol of 11.5' C. freezing point and 100 per cent purity by the Raschig nitration test was obtained when a fifteen-plate column was used for the final fractionation. DEBUTYLATION OF ~-METHYL-~,~-~~-~~?'~-BuTY By LPHENoL. the same procedure 115.1 grams of di-tert-butyl-p-cresol and 0.228 gram of 95 per cent sulfuric acid 'Ivere heated to cause debutylation. The isobutylene evolved amounted to 56.4 grams; the theoretical amount of isobutylene available was 58.1 grams. The residue from the debutylation, containing the p-cresol and the catalyst, weighed 57.4 grams. This material was distilled in the presence of 0.196gram sodium acid carbonate through a ten-plate column. The data and fractionation rurve are also shown in Table I11 and Figure 2. In the case of the p-cresol obtained in this way, it is somewhat more difficult to fractionate out all the impurities present, because the boiling points of the butylatcd phenolic contaminants (mainly o-ethyl henol and the low-boi!ing xylenols) lie rloscr tc that of di-tert-iutyl-p-cresol than t o that of di-tert-butyl-mcresol. Using a forty-five-plate column, however., a product freezing at 33.5" C. was obtained. When a highly purified sample of 4-methyl-2,6-di-tert-butylphenolwas debutvlated, p-cresol of 34" C. freezing point was secured on distilling the dealkylate through a five-plate column. ALKYLATION OF CRESOLS
Fractionating Equipment for Separating Alkylated Phenols, and Cottrell Boiling Point Apparatus for Determining Vapor Pressure-Temperature Relations of Individual Phenolic Compounds
The cresols, as well as most of the other phenols, call be alkylated with olefins in the presence of an acid condensing agent. Koenig (18), working at room temperature, used a large molar excess of sulfuric acid mixed with an equal volume of glacial acetic acid. Niederl and Natelson (81) employed molar amounts of sulfuric acid alone as the condensing agent but kept the alkylation temperature belon7 0" C. Evans and Edlund ( I S ) , however, demonstrated that alkylation could be carried on satisfactorily with the aid of small amounts of sulfuric acid as a catalyst a t ordinary temperatures. Phenol sulfonic acids and alkyl sulfuric acid esters are also effective alkylation catalysts. With the use of these acid catalysts, not only does substitution take place with ease and with the formation of only small amounts of side products, but alkylation proceeds more nearly to completion-i. e., to give polyalkylated phenols where possible. This is especially true if isobutylene or trimethylethylene is used as the alkylating agent. The position taken by the substituent groups depends upon the structure of the phenol alkylated. Studies on both cresols and xylenols indicate that, under the conditions employed, tert-butyl groups are not inserted between two methyl groups, or between a methyl and a hydroxyl group,
this cut were added 12.5 grams of concentrated sulfuric acid and isobutylene gas was passed with rapid agitation into the reaction mixture as fast as it could be absorbed. The temperature was kept below 70" C . by P water bath. Within 30 minutes 197.5 gpms of isobutylene were taken up, and in 50 minutes butylation was complete; the addition of two moles of isobutylene roughly doubled the weight of the oriuinal cresol. Natural gas was aassed through thc reaction product to-remov; dissolved isobutylene. After neutralization by two washes POINTS O F PHENOL, CRESOLS, te?t-BUTYLATED PHENOL with aqueous sodium carbonate, the final volume TABLEI. BOILIKG was 525 ml. and the weqht was 484 grams. AND CRESOLS, AND ISOBUTYLENE POLYMERS Of this product, 521 ml. (480.2grams) were disBoiling Point, C -----tilled through a fifteen-plate column; operating ;O mm. 20 m u . 50 r.m. lOOmm 760mm. a t a reflux ratio of 20 to 1, the fractions shown Phenol 72.0 85.0 104.0 119.5 181.2'1 in Table I1 were collected. 4-tert-Butylphenol 117.0 130.5 152.0 170.0 .. . 2 4-Di-tert-butylphenol 130.0 146.0 170.0 190.0 The distillation data are illustrated in more 214,6-Tri-tert-butylphenol 142.0 158.0 182.0 203.0 .. .. .. detail in Figure 1. To recover the individual o-Cresol 90.0 190.5'3 cresols, the di-tert-butyl-m-cresol and di-tert2-Methyl-s-tert-butylphenol 1oi:o 118.0 14o:o 1i9:o butyl-p-cresol are debutylated separately. 2-R.Ietbyl-y-tcrt-butylpbenol 117.0 132.0 155.0 174.0 183.0 149.0 174.0 194.0 2-JIethyl-4,6-di-tert-butylphenol DEBUTYLATION O F 3-M E T H Y L - 4 , 6 - D I - 6 e T t 85.0 101.0 122.0 139.0 202.2y BUTYLPHENOL. Complete detachment of the ferfm-Cresols 110.0 129.5 152.0 171.0 .. . 3-Methyl-x-tert-butylphenol butyl groups is brought about by heating the 3-hlethyl-4,8-di-fel.i-butylphenol 160.0 167.0 191.0 211.0 . .. compound in the presence of an acid catalyst to the refluxing tem erature of the cresol. 4 nitrop-Cresol 88.5 101.0 121.0 138.0 202.1" 4-if ethyl-2-tert-butylphenol 112.0 126.0 149.0 167.0 .. benzene va or gath was used as the heating 4-hIethyl-2,6-di-terl-butylphenol 131.0 147.0 171.0 190.0 , .. medium. &hen 152.1 grams of di-tert-butyl... ... 102.0 Diisobutylene m-cresol and 0.304 gram of 95 per cent sulfuric Triisobutylene 66.5 70.0 92.0 iio:o 179.0 acid (0.2 per cent) were heated, 75.8 grams of Tetraisobutylene 108.6 124.5 148.0 167.5 , .. isobutylene were collected in a gasometer' the Values from International Critical Tables, Vol. 111, pp. 221, 223 (1928). theoretical amount of isobutylene avahable was 77.5 grams. The residue, containing crude .
.
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1943
the reaction and give sec-butyl derivatives which are undesirable contaminants. W h e n 1o we r t e m p e r a t u r e s (around 15-25' C.) are maintained, alkylation proceeds satisfactorily enough, but the solubility of isobutylene in the reaction mixture then becomes sufficiently high to allow considerable polymer formation. The course of the alkylation is illustrated by Figure 3 which records the distribution of p-cresol and alkylated p-cresol as isobutylene (2 moles) is slowly added to the system held at 81.0' C. At the time of 0.5 mole isobutylene absorption, the di-tert-butyl derivative makes its first appearance, and some unreacted p-cresol persists until about 1.6 moles of isobutylene have been added.
ISC
PER CENT BY VOLUME
Figure 1. Fractionation Curve for the Product from Alkylating a Mixture of rn- and p-Cresols with Isobutylene
placed meta to each other. For example, 3,5-dimethylphenol does not add isobutylene. I n the laboratory operation about 3 to 5 per cent by weight of concentrated sulfuric acid is added directly to the cresol mixture with stirring to avoid localized overheating. Pure isobutylene gas, or a refinery butane cut containing it, is passed into the reaction vessel a t the bottom; the gas bubbles are broken up by vigorous agitation. The isobutylene is taken up a t an extremely rapid rate, the absorption slowing down somewhat near the end of the reaction. Each of the cresols takes up nearly 2 moles of the olefin to form the di-tert-butylated cresols as the main products; butylation is never quite complete because
657
I W I-
I20
I IO
.
100
Ik
a,
,b
~
of the reaction equilibrium. The reac9 4 ?o i o PER CENT BY VOLUME Jo 70 Eio 90 tion is exothermic, and i t is necessary t o provide some cooling to keep the Figure 2. Fractionation Curves for the Products from Debutylating temperature below 70' C. a t the start. 3-Methyl-4,6-di-tert-butylphenol(above) and 4-Methyl-2,6-di-tertUnder these conditions the reaction is butylphenol (below) highly specific toward isobutylene; for this reason a refinery butane-butene cut can be employed, although the isoThe reaction sequence is illustrated by the following equabutylene content should be above 20 per cent if alkylation tions; high temperatures force the equilibrium toward the is to take place at atmospheric pressure. If, on using the refinery gas, the temperature is raised to much above left: Cresol isobutylene e mono-tert-butylcresol (1) 100' C. and if the alkylation is conducted under sufficient pressure, there is a tendency for 1- and 2-butenes to enter Mono-tert-butylcresol isobutylene di-tert-butylcresol (2)
+
TABLE11. FRACTIONATION OF BUTYLATED CRESOL MUCTTJRE Fraction
A B C D
E
Residue Loss
Temperature Pressure, Volume, Weight Range, ' C. Mm. M1. Grams' 86-200 0 99-147 147 149 0-149 0-167 0 0 167 0-167 5
732 20 20 20 20
45 123 122 30 192
0 0 0 0
32 115 114 27 180
29 3 9 0
8 2 1 7
Identity
+
Polymer 1 ml. H20 Mainly mono-tert-butylcresols 4-Methyl-2 6-dl-tert-butylphenol Transitionhaterial 3-Methy1-4,B-di-terl-butylphenol
. . ....,. . .. . .
+
I n addition, a secondary reaction between unreacted cresol and a di-tert-butylcresol may take place-for example :
+
4-Methyl-2,6-di-tert-butylphenoI p-cresol 2(4-methyl-2-fert-butylphenol) (3)
This homogenization reaction proceeds a t an appreciable rate, even a t 70" to 80' C. When mixed cresols are alkylated, four possible reactions of this type can occur; they are important only while free cresol is present in the system.
INDUSTRIAL AND ENGINEERING CHEMISTRY
658
-
Care must be taken, in neutralizing the reaction mixture, to remove all traces of acidic compounds so that dealkylation will not occur in the subsequent fractional distillation. When pure isobutylene is used as the alkylating agent, thorough washing with hot aqueous sodium acid carbonate or sodium carbonate will generally remove all the free sulfuric acid, cresol sulfonic acids, or any tert-butyl acid ester that may be present, without affecting the mono- and dialkylated cresols. When a refinery butane-butene cut is utilized as the source of isobutylene, there may be some formation of di-sec-butyl sulfate, an excellent dealkylation catalyst, which is resistant to removal by the aqueous carbonate washing. In the laboratory this ester is decomposed by refluxing the washed reaction mixture with alcoholic potassium hydroxide for several hours. The alcoholic alkali-treated material is washed several times with water, and the washings are neutralized. Any separated upper layer is returned to the bulk of the aqueous alkali-insoluble material to be fractionated.
TABLE111. RECOVERY OF INDIVIDUAL CRESOLS Weight, Boiling Ragge at Freezing Vol., MI. Grams 20 Mm., C. Point, C. Fractionation of the m-Cresol Obtained by Debutylation of 3-Methyl-4,6-di-tert-butylphenol 10.0 10.2 99.6-100.0 8.7 51.0 52.3 100.0-100.5 10.6 C 5.0 5.3 100.5-101.5 .. 2.5 2.4 101.5-125.0 D Residue 3.7 Loss 0.9 .. Fractionation of the p-Cresol Obtained by Debutylation of 4-Methyl-2,6-di-tert-butylphenol A 10.0 10.5 99.2-100.3 25.9 B 25.0 25.7 100.3-100.6 30.9 C 12.5 12.9 100.6-101.0 29.5 D 4.0 4.0 101.0-125 Residue 2.9 .. Loss 0.8 ..
Fraction
$
.. ..
......... .........
.. ..
.........
..
I
Vol. 35, No. 6
.
..
.........
When m- and p-cresol mixture is alkylated, there is some evidence to indicate that the m-cresol reacts more readily. For instance, in partial alkylation studies, if isobutylene is reacted with the cresol mixture in an amount equivalent to 58 per cent of that required to add two tertbutyl groups, it is found (assuming the meta and para isomers to be present in the proportion of 60 to 40) that 0.216 mole of 4-methyl2,6-di-tert-butylphenol is formed for each mole of p-cresol in the starting mixture; 0.45 mole of 3-methyl-4,6-tert butylphenol is formed from each mole of m-cresol present. These yields are in the ratio of 1.95 to 1. When the alkylation is carried 79 per cent to completion, the ratio decreases t o 1.64 and is 1.2 at 88 per cent alkylation. These findings are in accord with those of Hone1 (16') who selectively butylated m-cresol, in a m-p-cresol mixture, by treatment with tertbutyl chloride in the presence of aluminum chloride. Meyer and Bernhauer (20) reported the selective butylation of mcresol with isobutyl alcohol, using 80 per cent sulfuric acid as the condensing agent. They reasoned that the hydroxyl group directs substitution to the para position; but because this position is already occupied in p-cresol, there is a preference toward m-cresol alkylation. At 70" C. relatively little isobutylene is converted to polymer. Alkylation takes place so much more readily than polymerization that the latter becomes evident only toward the end of the reaction. Some cresol may react with diisobutylene to give octyl derivatives, but this occurrence is not serious and can be minimized if the alkylation is not carried to completion-i. e., if the supply of isobutylene is limited t o a little less than the theoretical amount, say 1.8 or 1.9 moles per mole of cresol.
FRACTIONATION OF t e r t - B U T Y L A T E D CRESOLS
Vapor-liquid equilibrium studies of pertinent tert-butylated cresol mixtures, using an Othmer still, showed that no azeotropic solutions are formed and that Raoult's law can be employed satisfactorily in the design of columns capable of separating the constituents. The small amount of polymer generally present, made up of di- and tri-isobutylene, is removed by fractionation a t atmospheric pressure. After the system cools to some extent, the fractionation is continued under vacuum; a pressure of 20 mm. of mercury is
BO c w z
u 60 K w a
40 0
20
0
0.2
0.4 0.6 0.8 10 . 1.2 1.4 1.6 MOLES I S O B U T Y L E N E P E R M O L E PARA-CRESOL
Induction Period, Sec.
Catalyst
2.0
Figure 3. Change in Composition of Reaction Mixtures as p-Cresol Is Alkylated with Isobutylene (Drawn f r o m data obtained b y C. W.Montgomery, G u l f Research and Development Company)
c.
O F 4-METHYL-2,6-DI-tert-BUTYLPHENOL IN TABLEIv. RATEO F DEBUTYLATION
Extrsgo!ated
1.8
PRESENCE O F VARIOUS CATALYSTS AT 202' Sec. Required to Collect Following Amount of Available % Isobutylene Collected Isobutylene: in: 10% 30% 50 % 70% 90% 1800 8ec. 3000 8ec. 1800 90 91.8s 118 281 20 52 850 95.2 96.30 182 330 69 112 298 500 920 98.5 100.0 130 200 91.4 100.0 645 1090 1725 256 428
Ha804 (95%)
2.0 1.0 0.5 0.2
11 58 115 220
(CsHdzSOd
1.49 0.75 2.04 1.0 0.5 0.2
875 1220
795 1110
1155 1610
1425 1960
1735 2230
1955 2645
79.0 41.0
100.0 100.0
0
15 62 110 320
42 131 222 627
91 221 361 965
185 387 635 1685
440 660 1050 2810
100.0 100.0 100.0 72.6
100.0 100.0 100.0 92.5
0.77 0.84
13 30
34 51 17 460
92 104 124
187
388 320 771
912 640 1570
98.1 100.0 92.9 13.0
100.0 100.0 100.0
Beniene sulfonic acid Phenol sulfonic acid AlCli 5
50 136 260
1.0
0
0.5
0
Some isobutylene lost as polymer and to reactions with sulfuric acid.
..
180 354
..
..
..
*.*
June, 1943
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
convenient for use. The mono-tert-butyl mand p-cresols boil too close for separation unless a high-efficiency column is used. For this reason they are generally collected together and returned to the alkylation unit for further butylation. The boiling points of the di-tert-butylated cresols are 20" C. apart, sufficiently spaced for separation of the two compounds through a column of practical efficiency. The 3-methyl-4,6-di-tertbutylphenol and 4-methyl-2,6-di-fert-butylphenol are collected separately. As these two alkylated cresols melt a t 62" and 70" C., respectively, provision must be made to prevent their crystallization in the delivery and collection parts of the distillation apparatus. The transition material, collected between the two di-hrt-butyl cresol plateaus, can be further separated by refractionation.
659
TABLE V. BOILINU POINTS OF XYLENOLS, ETHYLPHENOLS, AND THEIR tert-BnTYL DERIVATIVES r
10 mm. Low-boiling xylenols 2,4-Dimethylphenol 2 4-Dimethyl-6-tertbutylphenol 2,5-bimethylphenol 2,5-Dimethyl-4-tert-butylphenol 2,6-Dimethylphenol (not in coal tar or petroleum oresylio aoids) 2,6-Dimethyl-4-tert-butylphenol (alkaJ sol.) Medium-holhng xylenols 3,5-Dimethylphenol (does not butylate) 2,3-Dimethylphenol
2,3-Dimethyl-4-tert-butylphenol 2,3-Dimethyl-4,6-di-tart-butylphenol High-boiling xylenols 3,4-Dimethylpheno
3,4-Dimethyl-6-tert-butylphenol
Ethylphenols
o-Ethylphenol 2-Ethyl-uteri-butylphenol
2-Ethyly-tert-butylphenol 2-Ethyl-4,6-di-t~t-butylphenol
m-Ethylphenol
DEBUTYLATION OF tert-BUTYLATED CRESOLS
3-Ethyl-z-tertbutylphenol 3-Ethyl-4,6-di-tert-butylphenol
Boiling Point, C. 20 mm. 50 mm. 100 mm. 760 mm.a
92.0 115.0
105.0 131.0
126.0 154.0
92.0
135.0
105.0 151.0
126.0
175.0
...
...
...
...
212 0
119.0
135.0
158.0
176.0
...
... ,..
... . ..
219.5
...
...
...
...... ... 1ii:O
... ... ... .... .. 1bi:O
117.0 112.0 139.0 174.0
122.0 143.0
101.5
129.0 141.0 156.0 114.6 142.0 174.0
...
l66:O
143.0 172.0 143.0 195.0
...
1ii:O
.. .. ,. .,. .. ....
... ...
198:O
2is:O
... ...
...
211.5 zii:5
.. ,
218.0
...
...
225.06
.. ,
2-06.5 207.5C
... ...
2ii:od
...
2ii.5-
The tertiary groups are lost by the alkyp-Ethylphenol 116.0 219.5 4-Ethyl-2-tert~butylphenol iii:o 137.0 iliO:o iii:o ... lated cresols on heating in the presence of a 4-Ethyl-2,6-di-tert-bntylphenol 137.0 154.0 178.0 198.0 ... small amouht of acid catalyst, Sulfuric acid Values from Lange's Handbook of Chemistry, 4th ed., 1941. At 756 mm. d A t 752 mm. b At 757 mm. is a good agent for this purpose, although aromatic sulfonic acids ($3) or sulfuric acid esters (39) allow faster dealkylation rates and considerably reduce the time required for the controlled. At the refluxing temperature of the cresols, catalyst to effect contact with the butylated cresol. The debutylation is somewhat complex in that two monomolecular however, debutylation proceeds vigorously to completion. reactions and one bimolecular reaction take place simultaneThe data given in Table IV were obtained upon decomposously. In the case of the di-tert-butylated p-cresol, for example: in the presence of various ing 4-methyl-2,6-di-tert-butylphenol dealkylating agents. Heating was effected by the vapor of a PMethyl-2,6-di-tert-butylphenol+ boiling nitrobenzene bath. The isobutylene evolved was 4-methyl-2-tert-butylph~nol isobutylene collected in a gasometer, corrections being made for tempera4-Methyl-2-tert-butylphenol-+p-cresol isobutylene 4-Methyl-2,6-di-tert-butylphenoI p-cresol + ture, pressure, and the vapor pressure of water. Figure 4 2 [4methyl-2-tert-butylphenol] shows the progress of dealkylation as 4-methyl-2,6-di-tertbutylphenol is heated a t the refluxing temperature of p-cresol The last reaction becomes less important as the temperature in the presence of various amounts of sulfuric acid catalyst. is raised, and dealkylation can proceed to completion. Isobutylene evolution becomes noticeable at about 100' C., SEPARATION OF XYLENOLS but the rate is slow. For example, when an amount of 4 The six isomeric xylenols may be divided into three methyl-2,6-di-tert-butylphenol, sufficient to yield a liter of isogroups-low, medium, and high boiling. Except for 3 , s butylene upon complete debutylation, was treated with dimethylphenol, each is readily alkylated with isobutylene 2.5 per cent of sulfuric acid a t 99" C. for one hour, only 36 cc. and the products formed have widely spaced boiling points; of the gas were released. Another sample, heated to 137" C. the tert-butyl derivative of 2,B-dimethylphenol is the only one for an hour, gave off 147 cc. of isobutylene. T h w , by reguthat is soluble in dilute aqueous alkali. By first dividing lating the temperature, the extent of dealkylation can be the xylenol mixture by efficient fractional distillation into its low-, medium-, and high-boiling groupings, and butylating each group separately, it is possible to fractionate out or to ,100 remove by aqueous alkali extraction each of the tert-butyl z W 0 derivatives of the various xylenols. The derivatives, in turn, E 80 are debutylated separately to give isobutylene and the P individual xylenols. 'a W The procedure becomes somewhat more complicated for Io 60 commercial xylenol mixtures, however, because of the presW -I ence of the three ethylphenols in cresylic acids from coal tar -I and petroleum. Difficulties arising from the overlapping of 40 Id the boiling points of several of the butylated derivatives ? require the insertion of additional steps at two places in the / course of the separation and the use of more efficient fractionation columns throughout. The boiling points of the xylenols, ethylphenols, and their tert-butyl derivatives are listed in Table V. 400 800 I200 1600 2000 2400 2800 TIME, SEC. The lowest boiling phenol in Table V, o-ethylphenol (boiling point 207.5' C. a t atmospheric pressure), is suffiFigure 4. Rates of Debutylation of 4-Methyl-2,6-diciently spaced in boiling point from m- and p-cresol (202.2tert-butylphenol in Presence of Varying Amounts of Sul202.1' C. a t atmospheric pressure) and from the low-boiling furic Acid at 202 C. 0
0
+
+
O
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
660
xylenols (211.5-212.0' C. a t atmospheric pressure) for gross concentration by distillation. On alkylation, the main product is 2-ethyl-4,6-di-tert-butylphenol(boiling point 156.0' C. a t 20 mm.), which is separable by fractional distillation from any di-tert-butyl derivatives of m- and p-cresols (boiling points 167.0" and 147.0" C. a t 20 mm., respectively) which might be present as contaminants. The contaminants appear to be mainlymembers of groups higher boiling than the one under tsudy. In general, the low-boiling xylenol cut does not contain appreciable amounts of phenol or cresols, and the middleboiling xylenol fraction is relatively free of the low-boiling group. LOW-BOILING XYLENOLS.The three lower-boilingxylenols are segregated by close fractionation. Each takes on one mole of isobutylene to give a monoalkylated xylenol : Boiling Point, ' C. Atm. 20 mm.
pressure
pressure
211.5
105.0
...
2,5-Dimethylphenol 2,5-Dimethyl-4-terl-butylphenol
2.6-Dimethylphenol
2,6-Dimethgl-4-tert-butylphenoi
211.5
... 212.0 ...
131.0 105.0
151 .o
1iir:o
On using an efficient fractionation column, no trouble is experienced in separating the tert-butyl derivatives of the three low-boiling xylenols. The problem is further simplified by the fact that 2,6-dimethylphenol is apparently not found in coal tar or petroleum cresylic acids. I n mixtures where it is present, the solubility of the derivative in dilute aqueous alkali is an additional aid in separation; the derivatives of the other two xylenols are not thus soluble. Contaminants found are small amounts of the tert-butyl derivatives of 0- and m-ethylphenol and the middle-boiling xylenols. When o-ethylphenol is present, its di-tert-butyl derivative (boiling point 166.0" C. a t 20 mm.) is collected along with 2,5-dimethyl-4-tert-butylphenol(151.0' C. a t 20 mm.). To separate these compounds, a roundabout method must be employed. The mixture is partially dealkylated by digesting with an acid catalyst a t a slightly elevated temperature, 125' to 150' C. The di-lert-butyl-oethylphenol loses its isobutylene more readily, giving a monotert-butyl derivative which is fractionally distilled from the monobutylated 2,5-dimethylphenol. Any 2,5-dimethylphenol, formed by the simultaneous dealkylation of its derivative, is recovered from the alkali washings. The separated mono-lert-butyl derivatives are dealkylated separately t o yield o-ethylphenol and 2,5-dimethylphenol. The presence of m-ethylphenol in the low-boiling xylenol fraction is not troublesome, as its di-tert-butyl derivative boils at 174.0' C. (20 mm.) which is sufficiently high for complete separation from either the butylated low-boiling xylenols or dibutylated o-ethylphenol. MIDDLE-BOILING XYLENOLS. The middle-boiling xylenol group contains 2,3- and 3,5-dimethylphenol. Of these compounds, the latter does not butylate under the conditions employed, and is recovered by either distilling or alkali washing the butylated product. No evidence was found of the presence of 2,3-dimethylphenol in the several lots of coal tar acid studied, but it was isolated from petroleum cresylic acids. The di-terhbutyl derivative of 2,3-dimethylphenol boils a t 174.0" C. (20 mrn.) and is thus readily separable from the butyl derivatives of any other xylenol, either low or high boiling, that might be present. Probable contaminants of this group are lllr and p-ethylphenols. The latter forms a di-tert-butyl derivative boiling at 154.0' C. (20 mm.) which is widely separated from the 174.0" C. (20 mm.) boiling point of the 2,3-dimethylphenol
Vol. 35, No. 6
derivative. But the di-tert-butyl derivative of m-ethylphenol, which boils a t 174.0' C. (20 mm.), is collected along with the di-tert-butyl derivative of 2,3-dimethylphenol. The procedure used for their separation involves complete debutylation of the fraction, neutralization of the dealkylation catalyst, and distillation. A mixture of m-ethylphenol and 2,3-dimethylphenol is obtained. The large spread in melting points between m-ethylphenol (-4.0' C.) and 2,3-dimethylphenol (75.0' C.) is favorable to separation and purification by crystallization. Petroleum ether is a satisfactory solvent. HIGH-BOILING XYLEXOLS.Only one compound need be considered in this group, 3,4-dimethylphenol. The boiling point of its tertbutyl derivative (143.0' C. a t 20 mm.) is well spaced from the boiling points of the derivatives of its likely contaminants, p-ethylphenol and the medium-boiling xylenols; this fact permits isolation by fractional distillation, The pure xylenol is recovered by dealkylation in the customary manner. The tert-butyl derivatives of each of the xylenols (except 2,6-dimethylphenol) and of the m- and p-ethylphenols have been isolated from coal tar or petroleum cresylic acids by the methods described here. The practicability of the xylenol separation process depends largely upon the accuracy with which the original mixture is divided into its three characteristic groups. For clean-cut group division, high-efficiency fractionating columns must be used. The process is necessarily less simple than that of isolating m- and p-cresols. ACKNOWLEDGMENT
The author wishes t o thank W. A. Gruse for the advice received throughout this investigation, and J. E. Nickels and J. B. McKinley for assisting in some of the experimental work. LITERATURE CITED
Bruckner, 2. and. Chem., 75,289 (1928). Byk, German Patent 100,415 (1898). Campbell, IND.ENC.CHEM.,14, 732 (1922). Carswell, U. S. Patent 2,042,331(1936). Chemische Fabrik Ladenburg, German Patent 152,652 (1904); Chem. Zentr., 75, 11, 168 (1904). Compte, U. S. Patent 1,980,384(1934). Ihid., 1,980,385(1934). Darzens, Compt. rend., 192, 1657 (1931). Deaseigne, M 6 m . poudres, 26, 134 (1934-35). Downs and Potter, U. 8. Patent 1,364,547(1912). Ehrlich, Ibid., 1,502,849(1924). Elger, Ibid., 1,025,615(1912). Evans and Edlund, Ihid., 2,051,473(1936). Gibbs, J . Am. Chem. SOC.,49,839 (1927). Hoffmann-La Roche, German Patent 245,892 (1911). Honel, U. 9. Patent 2,058,797(1936). Kahl, Ibicl., 711,572 (1902). Koenig, Ber., 24, 179, 3889 (1891). Kotake, Japanese Patent 130,482 (1939). Meyer and Bernhauer, Monatsh., 53 and 54, 721 (1929). Niederl and Natelson, J . Am. Chem. Soc., 53,272 (1931). Raschig, German Patent 112,545(1900); Chem. Zentr., 71,11, 463 (1900). Raschig, German Patent 114,975(1900); Chem. Zentr., 71,11, 1141 (1900). Rud-Rutgers, German Patent 137,584 (1902): Chem. Zentr. 74, I, 111 (1903). Rud-Rdtgers, German Patent 141,421 (1903); Chem. Zentr., 74,I, 1197 (1903). (26) Sohering-Kahlbaum A.-G., Brit. Patent 297,083(1927). (27) Schering-Kahlbaum A.-G., French Patent 660,091(1928). 297.086 11927). 128) -, Soholl. - - ~ ~Brit. - - ~Patent . (29) Schotte and Priewe, U.'S. Pstent'1,830,559 (1931). (30) Schulke and Mayr, German Patent 268,780 (1912). (31) Stevens and Livingstone, U. 9. Patent 2,297,588(1942). (32) Stevens and McKinley, Ibid., 2,290,602(1942). (33) Ihid., 2,290,603(1942). (34) Terrisse, Chem.-Ztg., 37, I, 394 (1913). (35) Terrisse, French Patent 463,221 (1913). (36) Terrisse and Dessoulavy, German Patent 267,210 (1912). (37) Weinrich, IND.ENG.CHEM., 35, 264 (1943).
.
~
~
