US2889361A - Manufacture of aromatic sulfonic acids - Google Patents

Description

MANUFACTURE F AROMATIC SULFONIC ACIDS Richard F. Brooks, Webster Groves, Mo., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application December 6, 1956 Serial No. 626,594

4 Claims. (Cl. 260-505) No Drawing.

This invention relates to the sulfonation of aromatic hydrocarbons and more particularly pertains to the manufacture of monosulfonic acids of aromatic hydrocarbons.

Aromatic sulfonic acids are manufactured in large quantitles as intermediates in the synthesis of phenolic compounds and as intermediates in the synthesis of other organic chemical compounds. In the past, aromatic hydrocarbons such as benzene, and naphthalene, toluene, xylene and other lower alkyl substituted benzenes as well as the alkyl substituted benzenes having long alkyl chains such as keryl benzene, dodecyl benzene and the like have been sulfonated to the corresponding monosulfonic acids by reacting the hydrocarbon in the liquid phase with a sulfonating agent such as sulfuric acid, oleum or sulfur trioxide. However, sulfonation of benzene and such other aromatic hydrocarbons as the lower alkyl substituted benzenes having 1 to 4 carbon atoms in the alkyl groups with sulfur trioxide as with the use of oleums is accompanied by the objectionable formation of large quantities of aromatic sulfones.

The formation of aromatic sulfones is objectionable since the sulfones represent the consumption of a sizeable portion of the aromatic hydrocarbon reactant. Furthermore, in the synthesis of phenols, the formation of phenyl sulfone, tolyl sulfone, xylyl sulfone and naphthyl sulfones not only consumes two moles of the aromatic hydrocarbon per mole of sulfone formed but the sulfone does not react with caustic to form a phenate. The sulfones also add an undesirable property to the sulfonic acid product which would carry over in the synthesis of derivatives of the sulfonic acid.

In a liquid phase sulfonation of aromatic hydrocarbons with sulfur trioxide the quantity of sulfones formed can be as high as 30%, that is, the amount of sulfone formed represents the consumption of 30% of the aromatic hydrocarbon raw material. This is especially true in the sulfonation of benzene and toluene with sulfur trioxide for the sulfone formation can go as high as 30% and about 25% respectively. In the sulfonation of xylene the sulfone formation is not quite as high, attaining a maximum of about 8 to 10%.

Various methods have been proposed for the reduction of objectionable formation of sulfones in the reaction of an aromatic hydr carbon with sulfur trioxide. it has been proposed, for example, to carry out the sulfonation reaction in the presence of a solvent such as chloroform or liquid sulfur dioxide. It has also been proposed to use a sulfur trioxide complex such as a complex with trioxane as a sulfonating agent. It has been proposed that various sulfone inhibitors be employed. As sulfone inhibitors there have been suggested alkali metal and alkaline earth metal sulfates, sodium sulfate apparently being the preferred inhibitor of this class. It has also been proposed that alkali metal and mkaline earth metal sulfonates be employed as the sulfone inhibitor. As sulfone inhibitors it has also been proposed to use lower saturated alkyl acids, especially those containing 2 to 3 carbon atoms. The amount of sulfone inhibitor suggested as satisfactory Patented June 2, .1959

according to these prior processes has been about 10% or less by weight based on the weight of the aromatic compound to be sulfonated. However, as has been pointed out the use of a greater amount of the sulfone inhibitor is not deleterious to the sulfonation reaction except in some instances where the sulfone inhibitor itself becomes sulfonated and in these cases the use of larger quantities of inhibitor will consume large portions of $0 in sulfonating the inhibiting material. The use of large quantities of other inhibiting material such as the alkali metal or alkaline earth metal sulfonates while not having a deleterious effect on the sulfonation step does, of course, present a problem of removal of said amount from the reaction medium. If not removed, the excess quantities of the sulfonates would be objectionable, as for example, in the fusion step in the synthesis of phenol.

It has now been discovered that pyridine added to the sulfonation reaction in an amount equal to about 2% to about 30% of the aromatic hydrocarbon charged will suppress the formation of sulfones in the sulfur trioxide sulfonation of said aromatic hydrocarbon.

More specifically, the process of this invention consists in reacting sulfur trioxide with a liquid aromatic hydrocarbon in the presence of 2% to 30% of pyridine at a reaction temperature as heretofore used, under about 120 C., but preferably the reaction temperature being in the range of about 70 C. to about 90 C. There can be employed as the source of sulfur trioxide, oleum having an 80;, content of 20% and above up to and including 100% 80;; with no sulfuric acid being present. In the process of this invention there should be used at least about 2% by weight of pyridine based on the weight of the aromatic compound to be sulfonated. However, the use of greater than 30% by weight offers no advantage in the suppression of the formation of sulfones. Hence, as a practical limitation it has been found that the upper limit on the amount of pyridine is about 30% by weight.

The following specific examples further illustrate the process of this invention.

Example I To a suitable sulfonating apparatus there is added 282 parts by weight'or" a mixture containing 76.5% benzene sulfonic acid, 17.9% sulfuric acid, 4.5% water and 1.1% sulfone, this mixture having been prepared by a previous monosulfonation of benzene with oleum of about 30% 80;. The mixture containing benzene sulfonic acid is stirred and heated to about 80 C. and there are added about 47 parts by weigl t of sulfur trioxide. Thereafter 89 parts by weight of benzene and 89 parts by weight of sulfur trioxide are added simultaneously at equal weight rates while the reaction temperature is maintained between and 79 C. After all of the reactants are added the resulting mixture is stirred and maintained at 80 to C. for about one hour. From an analysis of the resulting reaction mixture and from the composition of the starting material it is determined that about 18% of the benzene charged is converted to sulfones.

In contrast to the foregoing process in which no sulfone inhibitor is employed, the following examples employing the process of this invention illustrate the results obtained by the use of varying amounts of pyridine.

Example II To suitable sulfonation apparatus there is charged 234 parts by weight of the benzene sulfonic acid mixture described in Example 1 containing 76.5% benzene sulfonic acid, 17.9% sulfuric acid, 4.5% water and 1.1% suifone, this mixture having been prepared by a previous monosulfonation of benzene in the presence of a sulfone inhibitor which had been removed. There is added to this mixture 9 parts by weight of pyridine, the resulting mixture heated to about 80 (3., about 47 parts by weight of sulfur trioxide added and thereafter about 89 parts by weight of each of benzene and sulfur trioxide added at equal weight rates over a period of about minutes. Thereafter the reaction mixture is maintained at a temperature of from 80 to 85 C. for about an hour. An analysis of the resulting mixture shows that it contains 73.8% benzene sulfonic acid, 21.1% sulfuric acid, 0.6% water, 1.7% sulfones, 1.9% pyridine and 0.9% benzene. From the composition of the starting mixture and the mixture resulting from this reaction it is determined that 4.4% of the benzene employed is converted to sulfones.

Example Ill The process of Example II is repeated except that 282 parts of the starting mixture and 24.9 parts by weight of pyridine are employed. Also about 50 parts by weight of sulfur trioxide are added before the remaining 110 parts by weight thereof and 110 parts by weight of henzene are added substantially simultaneously in equal weight rates. The reaction temperature during the addition of the reactants is maintained at about to 81 C. and held at to 85 C. for about one hour after all the reactants have been combined. An analysis of the resulting reaction mixture shows that there is present 72.4% benzene sulfonic acid, 21.3% sulfuric acid, 0.3% water, 0.9% sulfone, 4.1% pyridine and about 1% benzene. From the composition of the starting mixture and the composition of the reaction mixture produced by this process it is determined that 0.9% of the benzene charged has been converted to the sulfones.

A comparison of the results of the process of this invention, as illustrated in Examples II and III with the results produced by the process of Example I where no sulfone inhibitor was employed, demonstrates how the use of a small amount of pyridine reduces the excessive formation of sulfones in the monosulfonation of benzene. In a similar manner there can be suppressed the sulfone formation which would otherwise occur during the nuclear monosulfonation of an aromatic hydrocarbon such as toluene, naphthalene and other alkyl substituted benzenes as well as naphthalene and the like.

It is realized that the complex formed by pyridine with sulfur trioxide has been suggested as a sulfonating agent. However, it has been found that the pyridine complex with sulfur trioxide is not a satisfactory nuclear sulfonating agent for aromatic hydrocarbons and especially benzene and alkylated benzenes. Although the pyridine complex with sulfur trioxide may form in the process ofthis invention it is not employed as a sulfonating agent, but rather the presence of pyridine either alone or as the complex with sulfur trioxide appears to only function as a sulfone inhibitor. This is clearly illustrated by the process of Example III in which the amount of pyridine employed was about 22% by weight of the benzene charged. Amounts of pyridine greater than the 22% employed in Example III can be employed. However, the amount of reduction in the sulfone formation will be decreased very slightly with the use of such greater amounts of pyridine. Thus, for the practical application of the process of this invention, the amount of pyridine employed should not be above about 30% by weight of the total amount of benzene employed.

What is claimed is:

1. A method of preparing monosulfonic acids of aromatic hydrocarbons by the nuclear sulfonation of a benzene ring which comprises reacting sulfur trioxide with an aromatic hydrocarbon in the liquid phase and in the presence of from about 2% to about 30% by weight of pyridine based on the weight of said aromatic hydrocarbon.

2. A method of preparing lower alkyl benzene monosulfonic acids by the nuclear sulfonation of the benzene ring which comprises reacting an alkyl benzene in a liquid phase with sulfur trioxide in the presence of from about 2% to about 30% by weight of pyridine based on the weight of said alkyl benzene.

3. A method of preparing benzene monosulfonic acid which comprises reacting liquid benzene and sulfur trioxide in the presence of from about 2% to about 30% by weight of pyridine based on the weight of said benzene.

4. A method of preparing benzene monosulfonic acid which comprises reacting at a temperature below about C. benzene and sulfur trioxide in the presence of from about 2% to about 30% by weight of pyridine based on the weight of said benzene.

OTHER REFERENCES Gilbert in The Chemistry of Petroleum Hydrocarbons, edited by Brooks, pages 611-641, vol. 3 (particularly pages 612-617, 620-633, 20 pages), 1955.

Claims (1)

1. A METHOD OF PREPARING MONOSULFONIC ACIDS OF AROMATIC HYDROCARBON BY THE NUCLEAR SULFONATION OF A BENZENE RING WHICH COMPRISES REACTING SULFUR TROIXIDE WITH AN AROMATIC HYDROCARBON IN THE LIQUID PHASE AND IN THE PRESENCE OF FROM ABOUT 2% TO ABOUT 30% BY WEIGHT OF PYRIDINE BASED ON THE WEIGHT OF SAID AROMATIC HYDROCARBON.