Method for producing alkanesulfonic acids

Details Method for producing alkanesulfonic acids Method for producing alkanesulfonic acids

2001-08-03

2002-12-17

Richter, Johann (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Sulfonic acids or salts thereof

C562S117000, C562S115000, C562S118000

Reexamination Certificate

active

06495714

ABSTRACT:

The invention relates to a process for preparing alkanesulfonic acids.
Alkanesulfonic acids are used in a number of industrial applications. Long-chain alkanesulfonic acids have, for example, surfactant properties, while short-chain acids such as methanesulfonic acid can be used, for example, as auxiliaries in the electrolytic deposition of base metals such as tin or lead in the tin plating of circuit boards for electronics or in the production of tin plate.
The literature describes a number of processes for preparing alkanesulfonic acids. In these, particularly in the case of lower alkanesulfonic acids, starting materials employed are alkyl mercaptans or dialkyl disulfides which are usually prepared by reacting hydrogen sulfide with alcohols. The oxidation of the alkyl mercaptans or dialkyl disulfides to the corresponding alkanesulfonic acids can be achieved by means of various oxidizing agents. Thus, it is possible to use hydrogen peroxide, chlorine, dimethyl sulfoxide and hydroiodic acid as oxidizing agent or to employ electrochemical oxidation.
A further way of preparing alkanesulfonic acids is the oxidation of alkyl mercaptans or dialkyl disulfides by oxygen in the presence of oxides of nitrogen or of nitric acid. The oxidation using oxygen in the presence of nitric acid is described, for example, in U.S. Pat. Nos. 2,697,722 and 2,727,920.
These processes have the disadvantage that they start out from the extremely toxic or unpleasant-smelling substances hydrogen sulfide, alkyl mercaptan and/or dialkyl disulfide. Even in very small concentrations far below the MAC (maximum workplace concentration), these have an extremely strong odor and their handling therefore requires a considerable outlay in terms of safety measures.
It is an object of the present invention to provide a process for preparing alkanesulfonic acids which avoids the use of these toxic and unpleasant-smelling substances and can thus be carried out with less outlay in terms of safety. We have found that this object is achieved by a process for preparing alkanesulfonic acids from dialkyl sulfites, which comprises the following steps:
rearrangement of dialkyl sulfite in the presence of a suitable catalyst to form the corresponding alkyl alkanesulfonate and
hydrolysis of the resulting alkyl alkanesulfonate to give the corresponding alkanesulfonic acid.
Rearrangement of Dialkyl Sulfite to Form the Corresponding Alkyl Alkanesulfonate
The rearrangement of the dialkyl sulfite to form the alkyl alkanesulfonate is carried out in the presence of a suitable catalyst. Useful catalysts are, for example, bases such as amines, preferably tertiary amines, e.g. dimethylaniline or tri-n-butylamine, or heterocyclic amines such as piperidine or pyridine. Alkyl iodide and quaternary ammonium salts, quaternary phosphonium salts or tertiary sulfonium salts and also alkylating agents are also suitable. Preference is given to using tri-n-butylamine as catalyst.
The catalyst is generally used in an amount of from 0.01 to 20 mol %, preferably from 0.1 to 10 mol %, particularly preferably from 1 to 5 mol %.
The rearrangement is usually carried out at from 20 to 250° C., preferably from 50 to 200° C., particularly preferably from 120 to 180° C.
Such rearrangements are described in W. Voss et al., Justus Liebigs Ann. Chem. 485 (1931) 258-283; W. E. Bissinger et al., J. Am. Chem. Soc. 70 (1948) 3940; A. Simon et al., Chem. Ber. 89 (1956) 883; A. J. W. Brook et al., J. Chem. Soc. B (1971) 1061.
The reaction mixture obtained at the end of the reaction, which comprises the alkyl alkanesulfonate, is worked up if necessary, preferably by distillation, particularly preferably by vacuum distillation in order to avoid excessively high temperatures at the bottom and thus partial decomposition of the reaction product, which frequently takes place.
Distillation of the reaction mixture comprising the alkyl alkanesulfonate is advantageous since this may enable distillation of the alkanesulfonic acid prepared in the following step to be avoided. An acid distillation, such as that of the alkanesulfonic acid, generally has to be carried out in corrosion-resistant apparatuses at high temperatures, while the distillation of the corresponding ester can generally be carried out at lower temperatures and in a simpler distillation column made of material which is not corrosion resistant.
The reaction product of this step, namely the alkyl alkanesulfonate, can be obtained in yields of generally >60% (based on the dialkyl sulfite used).
Hydrolysis of the Alkyl Alkanesulfonate to Give the Alkanesulfonic Acid
The hydrolysis of the alkyl alkanesulfonate to give the corresponding alkanesulfonic acid can be carried out directly using water (W. Voss et al., Justus Liebigs Ann. Chem. 485 (1931) 265; P. M. Laughton et al., Can. J. Chem. 34 (1956) 1714-1718).
In general, the hydrolysis is carried out at elevated temperature without catalyst. For this purpose, water is added in an amount of generally from 50 to 500 mol %, preferably from 100 to 200 mol %, particularly preferably 120 mol %. The hydrolysis is generally carried out at from 80 to 180° C., preferably from 100 to 150° C., particularly preferably 120° C. The hydrolysis is preferably carried out in a continuously operated reactor having a superposed column via which the alcohol liberated is removed.
The hydrolysis forms the desired alkanesulfonic acid, usually in aqueous solution, and the alcohol corresponding to the alkyl alkanesulfonate used. The alcohol is distilled off. If a nonaqueous alkanesulfonic acid is required, the aqueous solution has to be worked up, e.g. by distillation.
Synthesis of Dialkyl Sulfite
The dialkyl sulfite used for the synthesis of the alkyl alkanesulfonate can be prepared in any desired way. Thus, for example, dimethyl sulfite can be prepared
1
from thionyl chloride and methanol (W. Voss, DE-A 487253; A. J. Vogel et al., J. Chem. Soc. 16 (1943) 16; W. E. Bissinger et al., J. Am. Chem. Soc. 69 (1947) 2159). However, these reactions starting from thionyl chloride have the disadvantage that they form hydrogen chloride which, in terms of corrosion, places particular demands on the materials to be used.
In a preferred embodiment, the dialkyl sulfite is therefore obtained by reaction of alkylene sulfite with an alcohol. In this reaction, the diol corresponding to the alkylene sulfite is formed as by-product. As alcohol, it is usual to use a monohydric alcohol, i.e. an alcohol having one OH group. The alkyl radical of the alcohol used corresponds to that of the alkanesulfonic acid desired as end product.
As alkylene sulfite, it is possible to use alkylene sulfites of the formula I:
In the formula I, n is generally from 1 to 6, preferably from 1 to 4, particularly preferably 1 or 2, very particularly preferably 1. R
1
, R
2
, R′
n
and R″
n
are independently hydrogen, alkyl or aryl radicals. Particularly preferably, R
1
, R
2
, R′
n
and R″
n
are independently hydrogen or methyl radicals. Very particular preference is given to using ethylene sulfite and propylene sulfite.
The diol formed as by-product in this reaction, very particularly preferably ethylene glycol, has a variety of uses in industry, for example as a component for cooling fluids, as medium for heat transfer, as hydraulic fluid, as solvent or as starting material for further syntheses.
This reaction of the alkylene sulfite with an alcohol to give the desired dialkyl sulfite and the diol corresponding to the alkylene sulfite is an equilibrium reaction. In order to shift the equilibrium in the direction of dialkyl sulfite, continual removal of the diol formed is necessary.
A simple, continual distillation of the diol from the reaction mixture is generally not possible, since, particularly in the preparation of dimethyl sulfite, the alcohol used is usually the lowest-boiling component and would therefore distil off first. This would result in a shift in the equilibrium to the left, i.e. in the direction of the starting materials.
However, a generally quantitative reaction of the alkylene sulfite with

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