Process for preparing m-alkylhydroxybenzene

An improved process for preparing m-alkylhydroxybenzene which comprises heating alkylbenzene or an isomeric mixture of alkylbenzenesulfonic acid in the presence of sulfuric acid and an inorganic salt at a temperature of from 150.degree. to 210.degree. C. to form an isomeric mixture of alkylbenzenesulfonic acid which is rich in the m-isomer, selectively hydrolyzing the isomers of alkylbenzenesulfonic acid other than the m-isomer, and caustically fusing the unhydrolyzed alkylbenzenesulfonic acid.

The present invention relates to a process for preparing 
m-alkylhydroxybenzene and, in particular, to an improved, economical and 
industrially applicable process for preparing m-alkylhydroxybenzene. 
It is well known that substantially pure m-alkylhydroxybenzene can be 
prepared from alkylbenzene via alkylbenzenesulfonic acid as disclosed in 
Japanese Patent Publn. (examined) Nos. 33192/74 and 33193/74, Japanese 
Patent Publn. (unexamined) No. 110638/74, etc. The known process comprises 
the following steps: (a) heating alkylbenzene, or an isomeric mixture of 
alkylbenzenesulfonic acid obtained by sulfonation of alkylbenzene with 
sulfuric acid at a low temperature, in the presence of sulfuric acid at a 
temperature of 150.degree. to 210.degree. C. to form an isomeric mixture 
of alkylbenzenesulfonic acid being rich in the m-isomer; (b) selectively 
desulfonating the isomers other than the m-isomer in the m-rich mixture by 
contacting such mixture with water, preferably steam, to hydrolyze the 
other isomers into alkylbenzene and sulfuric acid, and removing the 
alkylbenzene as an azeotropic mixture with water; (c) converting the 
unhydrolyzed m-isomer into an alkali salt; and (d) caustically fusing the 
alkali salt to form m-alkylhydroxybenzene. 
However, the known process has various disadvantages. The first 
disadvantage is due to the fact that while the yield of the m-isomer in 
the sulfonation and isomerization, i.e. at the step (a), increases with 
the elevation of the reaction temperature, a high temperature above 
190.degree. C. causes not only rapid oxidation and decomposition but also 
dealkylation and tar-formation, whereby the sulfonation product becomes 
black and tarry. Also, the desulfonation in the step (b) requires a high 
reaction temperature and a long period of time, which cause the 
simultaneous or successive desulfonation of the m-isomer or any other side 
reaction and result in depression of the purity or quality of the product 
and of the yield of the product. 
The second disadvantage is the presence of a large quantity of the 
inorganic salt in the conversion into the alkali salt, i.e. at the step 
(c), and in the caustic fusion, i.e. at the step (d). When the reaction 
mixture of alkylbenzene and sulfuric acid is alkalized with sodium 
hydroxide to convert sulfonic acid into the alkali salt, simultaneously 
the excessive sulfuric acid is neutralized, and the total amount of the 
obtained mixture is subjected to caustic fusion, stirring can not be 
efficiently done due to the high viscosity owing to the presence of a 
large quantity of sodium sulfate, and sodium sulfite as by-product loses 
its utility value due to contamination with sodium sulfate. If, in the 
above process, precipitated sodium sulfate is removed by filtration before 
the fusion, troublesome operations such as washing with water, 
concentration and refiltration are required in order to minimize the loss 
of the sulfonic acid which is adhered on the sodium sulfate. In order to 
obviate this disadvantage, it was attempted to remove the excessive 
sulfuric acid in the sulfonation mixture by an appropriate method. The 
usual removing method is the so-called "liming-sodation method" in which 
sulfuric acid is removed as calcium sulfate. However, this method is not 
advantageous from the industrial viewpoint because of costly steps such as 
treatment of waste calcium sulfate, concentration of sulfonate solution 
and consumption of high energy. Recently, there was proposed a method in 
which alkylbenzenesulfonic acid is extracted with a mixture of a primary, 
secondary, tertiary or quaternary amine and a water-immiscible organic 
solvent (Japanese Patent Publn. (unexamined) No. 154935/80). Again, this 
method is not advantageous because large quantities of the amine and 
solvents and costly equipments are required for the extraction of 
alkylbenzenesulfonic acid, though the method is useful in recovery of a 
dilute organic acid. 
As a result of the extensive study, it was found that the aforementioned 
side reactions in the isomerization and desulfonation can be prevented by 
addition of sodium sulfate in a ratio of 1 to 5 mol % of the charged 
sulfuric acid before the sulfonation. 
It was also found that the addition of 5 to 15 mol % of an inorganic salt 
such as sodium sulfate is effective to prevent the side reactions and that 
the excessive sulfuric acid can be easily removed after layer-formation 
which is effected by allowing the selectively desulfonated mixture to 
stand above 80.degree. C. 
According to the present invention, there is provided a process for 
preparing m-alkylhydroxybenzene which comprises heating alkylbenzene or an 
isomeric mixture of alkylbenzenesulfonic acid in the presence of sulfuric 
acid and an inorganic salt in an amount of 1 to 15 mol % of the sulfuric 
acid at a temperature from 150.degree. to 210.degree. C. to form an 
isomeric mixture of alkylbenzenesulfonic acid which is rich in the 
m-isomer, selectively hydrolyzing the isomers of alkylbenzenesulfonic acid 
other than the m-isomer, and then caustically fusing the unhydrolyzed 
alkylbenzenesulfonic acid. After the selective hydrolysis, the reaction 
mixture may be allowed to stand to form layers, from which the 
alkylbenzenesulfonic acid is separated and then subjected to caustic 
fusion. 
As the alkylbenzene, there may be used the one which can provide an 
isomeric mixture of alkylbenzenesulfonic acid being rich in the m-isomer. 
Specific examples are toluene, ethylbenzene, isopropylbenzene, xylene, 
etc. Suitable inorganic salts are sodium sulfate (Glauber's salt), sodium 
hydrogen sulfate, etc. 
The reaction of alkylbenzene with sulfuric acid may be conducted under a 
conventional condition for sulfonation in the presence of an inorganic 
salt. For instance, when alkylbenzene is heated with sulfuric acid in the 
presence of anhydrous sodium sulfate at 50.degree. to 150.degree. C., 
there is produced an isomeric mixture of alkylbenzenesulfonic acid which 
is, however, rich in the p-isomer. Such mixture is then converted into a 
mixture in which the m-isomer content is equal to or higher than the 
p-isomer content by heating with sulfuric acid, preferably in a sulfonic 
acid:sulfuric acid ratio being 2:1, at a temperature of 150.degree. to 
210.degree. C., preferably of 180.degree. to 210.degree. C. Alternatively, 
a mixture in which the m-isomer content is equal to or higher than the 
p-isomer content may be produced by heating alkylbenzene with excessive 
sulfuric acid in the presence of an inorganic salt at a temperature of 
150.degree. to 210.degree. C. 
The sulfonated or isomerized mixture is hydrolyzed by heating with water or 
by steam-distillating at 120.degree. to 180.degree. C., preferably at 
150.degree. to 170.degree. C., to convert selectively 
p-alkylbenzenesulfonic acid into alkylbenzene and sulfuric acid. 
Alkylbenzene is removed as an azeotropic mixture with water and used for 
an additional feed material or a starting material. 
The hydrolyzed mixture is allowed to stand for about 0.5 to 1 hour, 
preferably at 80.degree. to 150.degree. C., to form layers of sulfonic 
acid and sulfuric acid, which are separated from each other. The 
efficiency of layer-formation and separation depend on the amount of the 
inorganic salt, the content of the m-isomer, the temperature, etc. In 
order to attain the stabilization of sulfonic acid, it is essential to add 
the inorganic salt in an amount of 1 to 15 mol % of charged sulfuric acid. 
If the inorganic salt is less than 1 mol %, the side reactions such as 
oxidation and decomposition can not be efficiently prevented. If the 
inorganic salt is more than 15 mol %, the desulfonation is prevented and 
the content of the p-isomer can not be decreased. The amount of inorganic 
salt is further limited in order to effect layer-formation. If the 
inorganic salt such as sodium sulfate is less than 4 mol %, sulfuric acid 
can not be separated because the layer-formation of the mixture does not 
occur at or above 80.degree. C. The layer-formation below 80.degree. C. is 
not distinct. In addition, cooling requires much time. Accordingly, when 
the inorganic salt is less than 4 mol %, it is advisable to fuse 
caustically the mixture without separating sulfuric acid, and such process 
is also advantageous as compared with the conventional process. When the 
inorganic salt is not less than 5 mol %, the hydrolyzed mixture forms 
easily layers of sulfuric acid and sulfonic acid by allowing to stand at 
80.degree. to 150.degree. C. 
The sulfonic acid dissolved in the sulfuric acid layer does not exceed 1% 
by weight. The inorganic salt dissolved in the sulfuric acid layer, which 
crystallizes out at the ordinarily temperature, can be easily removed by 
filtration and reused. The filtrate may be used for other purposes as 
sulfuric acid with high concentration. The inorganic salt may be added 
either before the sulfonation or after the sulfonation and before the 
isomerization. When the stabilization of the sulfonic acid only during the 
desulfonation is desired, the inorganic salt may be added just before the 
desulfonation. The layer-formation and separation of sulfuric acid can be 
effected only after and not before the desulfonation, even after the 
sulfonation or isomerization. This fact suggests that the effect of the 
inorganic salt on layer-formation is owing to the proportion of isomers; 
i.e. the effect can be obtained only in the case that the content of the 
m-isomer is more than a certain value. 
The alkylbenzenesulfonic acid obtained by desulfonation of the isomers 
other than the m-isomer or separated as a layer after standing the 
desulfonated mixture at 80.degree. to 150.degree. C. is caustically fused 
to give the desired m-alkylhydroxybenzene. The caustic fusion may be 
carried out under the conventional conditions, for example, forming the 
alkaline metal salt with an alkali (e.g. sodium hydroxide) and fusing with 
sodium hydroxide. 
The process illustrated above has various advantages, of which the typical 
one is that the amount of the alkali for neutralization is reduced and 
accordingly the cost is lowered, because free sulfuric acid is decreased 
by the layer-separation. Another advantage is that the inorganic salt 
formed by the neutralization does not need to separate or can be easily 
separated without concentration, because its amount is very small. 
In the extensive study, it was observed that, when the above described 
process is carried out in the industrial scale, the content of the 
m-isomer in the desulfonated mixture somewhat decreases after the caustic 
fusion. It was proved that the decrease of the content of the m-isomer is 
due to partial desulfonation of the m-isomer and to sulfonation of the 
alkylbenzene by sulfuric acid. The decrease of the content of the m-isomer 
can be avoided by adding water immediately after the desulfonation in 
order to reduce the temperature and the concentration of sulfuric acid. 
Therefore, according to the present invention, there is also provided a 
process for preparing m-alkylhydroxybenzene which comprises heating 
alkylbenzene or an isomeric mixture of alkylbenzenesulfonic acid in the 
presence of sulfuric acid and an inorganic salt at a temperature of 
150.degree. to 210.degree. C. to form an isomeric mixture of 
alkylbenzenesulfonic acid which is rich in the m-isomer, selectively 
desulfonating the isomers of alkylbenzenesulfonic acids other than the 
m-isomer, adding water thereto to lower the temperature to or below 
150.degree. C. immediately after the selective desulfonation and 
caustically fusing the undesulfonated alkylbenzenesulfonic acid. 
In this process, alkylbenzene as the starting material, conditions for 
sulfonation, isomerization and desulfonation and the amount of the 
inorganic salt are substantially the same as the previously described 
process. The only difference is that, in the latter process, water is 
poured into the desulfonation mixture in order to reduce temperature of 
the mixture below 150.degree. C. as quick as possible. For this purpose, 
it is preferable to use water as cold as possible, such as ice or 
ice-water. If necessary, the outer surface of the reaction vessel may be 
cooled. This will be useful for decreasing the amount of water. It is 
preferable to reduce the temperature below 150.degree. C. within a short 
period, for instance, within 1 hour and preferably half an hour. The 
layer-formation, neutralization and caustic fusion are substantially the 
same as the previously described process. 
According to the processes in the present invention, the oxidative 
decomposition of alkylbenzenesulfonic acid is remarkably prevented and 
therefore the sulfonation, isomerization and desulfonation at a high 
temperature and for a long period can be operated without significant side 
reactions. The content of the m-isomer can be kept unchanged after the 
desulfonation and through the caustic fusion. As the result, the isomeric 
mixture containing more than 98% of the m-isomer can be obtained 
economically.

The invention will now be further illustrated by means of the following 
examples, which are not, however, intended to limit the scope of the 
invention. 
EXAMPLES 1 TO 5 AND COMATIVE EXAMPLES 1 AND 2 
In these examples and comparative examples, ethylbenzene was sulfonated 
with sulfuric acid in the presence of anhydrous sodium sulfate, 
isomerized, hydrolyzed (desulfonated), separated from excess sulfuric 
acid, neutralized and fused with an alkali to give m-ethylphenol. The 
composition of the reaction mixture in each step was examined, and the 
relationship with the quantity of sodium sulfate was investigated. 
A four-necked flask (1 liter-volume) was charged with 98% sulfuric acid 
(600 g). Anhydrous sodium sulfate was added thereto with stirring in 
respective amounts expressed as mol % of sulfuric acid given in Table 1. 
To this mixture, ethylbenzene (424 g) was added over 30 minutes. The 
temperature of the mixture was gradually elevated to 200.degree. C. over 2 
hours, during which the evaporated water was withdrawn. The heating was 
continued at the same temperature with stirring for 4 hours in order to 
isomerize. The composition of the mixture is shown by weight % in Table 1 
wherein BSA, TSA and ESA are the abbreviations of benzenesulfonic acid, 
toluenesulfonic acid and ethylbenzenesulfonic acid, respectively. 
TABLE 1 
______________________________________ 
Composition of sulfonic acids after isomerization 
Composi- 
Example Comparative 
tion 1 2 3 4 5 1 2 
______________________________________ 
Na.sub.2 SO.sub.4 
2 5 7 10 15 0 20 
(mol %) 
BSA 2.1 1.1 0.3 0.3 0.3 4.8 0.3 
TSA trace trace trace trace 
trace 0.9 trace 
o-ESA 2.6 2.6 2.5 1.5 1.7 2.5 2.7 
m-ESA 52.8 53.4 55.5 58.5 57.3 44.7 51.8 
p-ESA 41.5 41.0 41.1 39.2 40.4 44.9 44.9 
Remainder 
1.0 0.8 0.6 0.5 0.3 2.2 0.3 
______________________________________ 
The isomerized mixture was cooled to 170.degree. C. Water (1100 ml) was 
dropped at a uniform rate into the stirred mixture at the same temperature 
over 10 hours in order to hydrolyze. The obtained reaction mass was left 
to stand at 150.degree. C. for 30 minutes to form layers. The layer of 
sulfonic acids was separated. The composition in weight % of the sulfonic 
acids layer and the cutting percentage of sulfuric acid are shown in Table 
2 wherein BSA, TSA and ESA have the same meaning as those in Table 1. In 
the cases that the amount of sodium sulfate was 0 and 2 mol %, there were 
not formed layers even at 80.degree. C., and accordingly the cutting 
percentage of sulfuric acid was 0. 
TABLE 2 
______________________________________ 
Composition of sulfonic acids after desulfonation 
and cutting percentage of sulfuric acid 
Composi- 
Example Comparative 
tion 1 2 3 4 5 1 2 
______________________________________ 
Na.sub.2 SO.sub.4 
2 5 7 10 15 0 20 
(mol %) 
BSA 2.3 1.8 1.0 1.1 1.1 7.0 1.1 
TSA trace trace trace trace 
trace 1.0 trace 
o-ESA 1.8 1.7 trace 0.8 0.2 1.5 1.8 
m-ESA 92.3 93.1 97.4 95.7 94.8 83.6 90.1 
p-ESA 1.8 1.7 1.5 2.3 3.8 3.4 3.5 
Remainder 
1.7 1.6 0.1 0.1 0.1 3.5 3.5 
Cutting 0 57 64 67 72 0 38 
percentage 
of H.sub.2 SO.sub.4 
______________________________________ 
The separated sulfonic acid layer was neutralized to pH 8 with 50% 
potassium hydroxide to form a slurry, which was added dropwise to a 
mixture of sodium hydroxide (282 g) and potassium hydroxide (42 g) 
mutually melting at 330.degree. C. The mixture was heated to 340.degree. 
C. and maintained with stirring at this temperature for 1 hour. Then, the 
mixture was dissolved in water (1000 ml) and neutralized to pH 7.2 with 
35% hydrochloric acid. 
The produced phenols were extracted with ether, distilled, and further 
fractionally distilled. The composition in weight % of phenols and the 
yield of ethylphenol based on consumed ethylbenzene are shown in Table 3 
wherein PH, CR and EP are the abbreviations of phenol, cresol and 
ethylphenol, respectively. 
TABLE 3 
______________________________________ 
Composition of phenols after caustic 
fusion and yield of ethylphenol based 
on consumed ethylbenzene 
Composi- 
Example Comparative 
tion 1 2 3 4 5 1 2 
______________________________________ 
Na.sub.2 SO.sub.4 
2 5 7 10 15 0 20 
(mol %) 
PH 2.8 2.6 2.6 1.1 1.3 4.2 1.3 
CR 0.3 0.3 0.5 0.3 0.3 1.7 0.3 
o-EP 1.2 0.7 0.4 0.9 1.5 1.6 1.8 
m-EP 93.0 93.9 93.8 94.3 92.8 83.4 91.2 
p-EP 1.9 1.7 2.1 2.6 4.1 4.6 4.6 
High b.p. 
0.8 0.8 0.6 0.8 trace 4.5 0.8 
substance 
Yield (%) 
71.0 72.0 71.0 72.0 71.0 48.0 71.0 
______________________________________ 
It can be clearly seen from above Examples and Comparative Examples that, 
when ethylbenzene is sulfonated in the presence of sodium sulfate, the 
production of toluenesulfonic acid and other impurities is decreased and 
ethylphenol is obtainable in high yield and high purity, as compared with 
the case in the absence of sodium sulfate. Accordingly, it can be said 
that the presence of sodium sulfate in the amount of 1 to 15 mol % of 
charged sulfuric acid contributes in stabilization of ethylbenzenesulfonic 
acid and prevention of side reactions. When, however, the amount of sodium 
sulfate is less than 2 mol %, the formation of layers can not be attained, 
and sulfuric acid can not be separated, though the prevention of side 
reactions is recognized. The formation of layers is observed from about 4 
mol % of sodium sulfate. When the amount of sodium sulfate exceeds 15 mol 
%, the hydrolysis (i.e. desulfonation) is inhibited, the concentration of 
the p-isomer increases, and the boundary surface between the sulfonic acid 
layer and sulfuric acid layer becomes unclear. 
EXAMPLE 6 
A four-necked flask (2 liters-volume) was charged with 98% sulfuric acid 
(1200 g). Anhydrous sodium sulfate (102 g, 6 mol %) and then ethylbenzene 
(424 g) were added thereto in 30 minutes while stirring. Temperature was 
gradually elevated to 200.degree. C. over 2 hours while evaporated water 
was withdrawn. The heating was continued with stirring for 4 hours at the 
same temperature in order to isomerize. Then, the mixture was cooled to 
170.degree. C. Water (2000 g) was dropped at a uniform rate into the 
stirred mixture at the same temperature over 10 hours in order to 
hydrolyze. The obtained reaction mass was left to stand at 150.degree. C. 
for 30 minutes to form layers. The layer of sulfuric acid (854 g) was 
removed. The layer of sulfonic acid (1074 g) was neutralized to pH 7.8 
with 50% potassium hydroxide and added dropwise to a mixture of sodium 
hydroxide (563 g) and potassium hydroxide (83 g) mutually melting at 
330.degree. C. in a 2 liter reaction vessel. The mixture was heated to 
340.degree. C. and maintained with stirring at this temperature for 1 
hour. Then, the mixture was dissolved in water (2000 ml) and neutralized 
to pH 7.2 with 35% hydrochloric acid. The produced phenols were extracted 
with ether and distilled to give crude m-ethylphenol (348 g, 71% yield 
based on consumed ethylbenzene), which showed a purity of 98.2% after 
fractional distillation. 
EXAMPLE 7 
A 1-liter flask was charged with 98% sulfuric acid (1090 g), and anhydrous 
sodium sulfate (103 g, 6.7 mol %) was added thereto. Then, toluene (503 g) 
was added thereto in 30 minutes while stirring. Temperature was gradually 
elevated to 195.degree. C. over 2 hours. The heating was continued with 
stirring for 4 hours at the same temperature in order to isomerize. Then, 
the mixture was cooled to 165.degree. C. Water (1000 g) was dropped at a 
uniform rate into the stirred mixture at the same temperature over 10 
hours, during which toluene (216 g) was distilled out with vaporous water. 
After hydrolysis, the obtained mass was left to stand at 150.degree. C. 
for 30 minutes to form layers. The layer of sulfuric acid (695 g) was 
removed from the layer of sulfonic acid (1040 g). The latter was, as in 
Example 6, neutralized with 50% potassium hydroxide, caustically fused, 
post-treated and fractionally distilled to give m-cresol (242 g) of 98% 
purity. 
EXAMPLE 8 
A 3-liter flask was charged with 98% sulfuric acid (1700 g). Anhydrous 
sodium sulfate (120 g, 5 mol %) and then m-xylene (1100 g) were added 
thereto while stirring. Temperature was elevated to 180.degree. C. over 
2.5 hours. The heating was continued at 175.degree.-180.degree. C. for 3 
hours in order to isomerize. Then, the mixture was cooled to 150.degree. 
C. Water (700 g) was dropped continuously into the mixture at the same 
temperature over 3 hours. The obtained mass was left to stand for 1 hour 
to form layers of sulfonic acid (2334 g) and sulfuric acid (760 g, 60% in 
concentration) which were separated with each other. During the operation, 
m-xylene (270 g) was recovered. The layer of sulfonic acid was, as in 
Example 6, neutralized, caustically fused and post-treated to give 
3,5-xylenol (707 g) of 97% purity. 
EXAMPLE 9 
A 6000-liter reaction vessel was charged with 98% sulfuric acid (3600 kg), 
and anhydrous sodium sulfate (60 kg) was added. Then, ethylbenzene (2544 
kg) was added dropwise to the mixture with stirring over 1 hour. 
Temperature of the mixture was gradually elevated to 200.degree. C. over 2 
hours while evaporated water was withdrawn. The heating was continued at 
the same temperature for 4 hours in order to isomerize. Then, the mixture 
was cooled to 170.degree. C. Steam (corresponding to 7800 liters of water) 
was blown continuously into the stirred mixture at the same temperature 
over 12 hours in order to hydrolyze, whereby ethylbenzene (1260 kg) was 
recovered. The ratio of m-isomer to p-isomer (hereinafter referred to as 
"m/p ratio") of ethylbenzenesulfonic acid in the desulfonated reaction 
mass was 97.0/3.0. The concentration of sulfuric acid in the 
water-sulfuric acid system (excluding ethylbenzenesulfonic acid) in the 
same mass was 63%. 
The mass, after taking up the samples for analysis and subsequent 
experiment, was cooled from the outside. Simultaneously, water (500 
liters) was poured into the mass over 30 minutes in order to cool and 
dilute the mass. The obtained mass, temperature of which was 130.degree. 
C., had an m/p sulfonic acid ratio of 95.9/4.1 and a sulfuric acid 
concentration of 56%. The mass was neutralized to pH 8 with 47% sodium 
hydroxide. Sodium sulfate was removed by filtration at 80.degree. C. The 
filtrate was added dropwise to a mixture of sodium hydroxide (1709 kg) and 
potassium hydroxide (250 kg) mutually melting at 330.degree. C. in a 6000 
liter fusing vessel. The mixture was heated to 340.degree. C. and 
maintained with stirring at this temperature for 1 hour. Then, the mixture 
was dissolved in water (6000 liters) and neutralized to pH 7.2 with 35% 
hydrocloric acid. The produced phenols were separated and distilled to 
give crude m-ethylphenol of 94.1% purity, which gave on fractional 
distillation m-ethylphenol of 97.9% purity. The yield of m-ethylbenzene 
was 70% on the basis of consumed ethylbenzene. 
COMATIVE EXAMPLE 3 
A sample taken out in 1/1000 scale from the hydrolyzed mass in Example 9 
was cooled to 130.degree. C. over 4 hours only from the outside and 
without adding water. The obtained sulfonic acid had an m/p ratio of 
91.5/8.5. After treating in a manner similar to that in Example 9, there 
was obtained crude m-ethylphenol of 90.5% purity, which gave on fractional 
distillation m-ethylphenol of 94.1% purity. 
EXAMPLES 10 TO 12 
To samples taken out in 1/1000 scale from the hydrolyzed mass in Example 9 
was added water in order to attain the concentrations of sulfuric acid (in 
the water-sulfuric acid system) as shown in Table 4, and the mixtures were 
maintained at the temperatures as shown in Table 4. After the reaction, 
the m/p ratio of the obtained sulfonic acids was determined to give the 
values as shown in Table 4. Also, the purity of m-ethylphenol obtained by 
fusing and post-treating according to Example 9 is shown in Table 4. 
COMATIVE EXAMPLES 4 TO 6 
Samples taken out in 1/1000 scale from the hydrolyzed mass in Example 9 
were maintained without adding water thereto at the temperature as shown 
in Table 4, and the m/p ratio of the sulfonic acid and the purity of 
m-ethylphenol were determined to give the values as shown in Table 4. 
TABLE 4 
______________________________________ 
Composition of sulfonic acid and 
purity of m-ethylphenol 
Purity 
of m- 
Temper- m/p ratio ethyl- 
ature H.sub.2 SO.sub.4 
End of After phenol 
Example (.degree.C.) 
(%) reaction 
4 hrs (%) 
______________________________________ 
10 150 57 97.0/3.0 
96.6/3.4 
97.5 
11 150 52 97.0/3.0 
96.7/3.3 
98.1 
12 130 52 97.0/3.0 
97.0/3.0 
98.4 
Compar- 
ative 
4 170 63 97.0/3.0 
91.5/8.5 
92.5 
5 150 63 97.0/3.0 
93.1/6.9 
93.2 
6 130 63 97.0/3.0 
96.3/3.7 
96.5 
______________________________________ 
It can be clearly seen from the results in Examples 10 to 12 and 
Comparative Examples 4 to 6 that, when the hydrolyzed (i.e. desulfonated) 
products are allowed to stand at a temperature which is the same as or 
slightly lower than the hydrolyzing temperature, the hydrolysis of 
m-isomer proceeds further with the increase of the p-isomer. Also, it can 
be seen that the side reaction can be prevented to a certain extent by 
rapid cooling without adding water (Comparative Example 6); however, slow 
cooling (Comparative Example 3) is quite ineffective even though the 
temperature is lowered finally to 130.degree. C. Rapid cooling with adding 
water is significantly effective despite the temperature is 150.degree. C. 
which is higher than 130.degree. C. 
EXAMPLE 13 
A 3000-liter reaction vessel was charged with toluene (1509 kg). Anhydrous 
sodium sulfate (140 kg) was added to the toluene. Then, 98% sulfuric acid 
(3270 kg) was added dropwise to the mixture with stirring over 1 hour. 
Temperature of the mixture was elevated to 190.degree. C. over 2 hours. 
The heating was continued at 185.degree. to 190.degree. C. for 4 hours in 
order to isomerize. Then, the mixture was cooled to 160.degree. C. Steam 
(corresponding to 3000 liters of water) was blown continuously at a 
uniform rate into the mixture over 10 hours maintained at 
160.degree.-165.degree. C. to hydrolyze p-toluenesulfonic acid into 
sulfuric acid and toluene. The toluene (741 kg) was recovered 
azeotropically with water. 
The hydrolyzed mass, which has an m/p sulfonic acid ratio of 96.8/3.2, was 
immediately cooled from the outside and simultaneously diluted with water 
(250 liters) over 30 minutes, whereby the temperature was lowered to 
120.degree. C. The m/p ratio (96.4/3.6) was practically unchanged. The 
cooled mass was neutralized with 47% sodium hydroxide, fused and 
post-treated according to Example 9 to give m-cresol (584 kg) of 98.2% 
purity. 
COMATIVE EXAMPLE 7 
Example 13 was substantially repeated except that cooling was effected only 
from the outside; i.e. dilution with water was not done. The time for 
cooling took 3 hours. As the result, m-cresol (574 kg) of 94% purity was 
obtained. 
EXAMPLE 14 
A 6000-liter reaction vessel was charged with 98% sulfuric acid (3600 kg), 
and sodium sulfate (306 kg, 6 mol %) was added with stirring. Then, 
ethylbenzene (2544 kg) was added to the mixture over 1 hour. Temperature 
of the mixture was gradually elevated to 200.degree. C. in 2 hours while 
evaporated water was withdrawn. The heating was continued with stirring at 
the same temperature for 4 hours in order to isomerize. Then, the mixture 
was cooled to 170.degree. C. Steam (corresponding to 6000 liters of water) 
was blown at a uniform rate into the mixture over 10 hours. The mixture 
was cooled from the outside and simultaneously diluted with water (500 
liters) over 30 minutes, whereby the temperature was lowered to 
130.degree. C. The mixture, in which m/p ratio was 96.0/4.0, was left to 
stand at 130.degree. C. for 30 minutes to form layers of sulfonic acid and 
sulfuric acid. The sulfonic acid layer was separated and neutralized to pH 
7.8 with 50% potassium hydroxide, and the neutralized solution was added 
dropwise to a mixture of sodium hydroxide (1700 kg) and potassium 
hydroxide (250 kg) mutually melting at 330.degree. C. in a 6000-liter 
fusing vessel. The mixture was heated to 340.degree. C. and maintained at 
the same temperature for 1 hour. Then, the mixture was dissolved in water 
(6000 liters) and neutralized to pH 7.2 with 35% hydrochloric acid. The 
separated oil was distilled to give crude m-ethylphenol (1044 kg, yield, 
71% on the basis of consumed ethylbenzene), which gave on fractional 
distillation m-ethylphenol of 98.0% purity.