Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfonic acids or salts thereof
Reexamination Certificate
2001-05-15
2003-03-11
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfonic acids or salts thereof
Reexamination Certificate
active
06531629
ABSTRACT:
The invention relates to a process for the preparation of alkanesulfonic acids.
Alkanesulfonic acids are used in a number of industrial applications. Long-chain alkanesulfonic acids have, for example, surfactant properties, while short-chain alkanesulfonic acids, such as methanesulfonic acid, can, for example, be used as auxilary chemicals for the electrodeposition of noble metals such as tin or lead in the tin plating of printed circuit boards for electronics or in the preparation of tinplate.
The literature describes a number of processes for the preparation of alkanesulfonic acids. For this purpose, alkylmercaptans or dialkyl disulfides, in particular, are used as starting materials, which are usually prepared by the reaction of hydrogen sulfide with alcohols. The oxidation reaction of the alkylmercaptans or of the dialyl disulfides to give the corresponding alkanesulfonic acid can be achieved using a variety of oxidizing agents. For example, the oxidizing agent can be hydrogen peroxide, chlorine, dimethyl sulfoxide or mixtures of dimethyl sulfoxide and hydroiodic acid, and electrochemical oxidation.
WO 98/34914 describes an oxidation of mercaptans and/or dialkyl disulfides using Br
2
to give alkanesulfonic acids. The Br
2
is preferably obtained from HBr to make handling easier. The oxidation of HBr to Br
2
can be carried out with oxygen in the presence of catalytic amounts of nitric acid or with nitric acid itself as oxidizing agent. The nitrogen oxides which form in the oxidation of HBr with nitric acid are reoxidized with oxygen to give nitric acid. In order to avoid over-oxidation of the sulfur compounds present in the process to give sulfuric acid, the oxidation of HBr to Br
2
and the oxidation of the mercaptans and/or dialkyl disulfides with Br
2
can be carried out in separate reactors.
Another method of preparing alkanesulfonic acids is the oxidation of alkylmercaptans or dialkyl disulfides with oxygen in the presence of nitrogen oxides or nitric acid. The oxidation with oxygen in the presence of nitric acid is described, for example, in U.S. Pat. Nos. 2,697,722 and 2,727,920.
These publications relate to the oxidation of alkylmercaptans or polysulfides (such as dialkyl disulfides) with oxygen absorbed in nitric acid. The alkylmercaptan or the polysulfide is oxidized in stages to give the desired alkanesulfonic acid. During the oxidation, mixtures of nitrogen monoxide, nitrogen dioxide and nitrous oxide form. The nitrogen monoxide and the nitrogen dioxide are converted by the oxygen absorbed in the nitric acid into pure nitrogen dioxide or into nitric acid, which in turn are available for the formation of alkanesulfonic acids. The nitrous oxide is excluded from the system. A disadvantage of this process is the high content of nitrous oxide formed which, as a “greenhouse gas” similar to halogenated methanes and ethanes, leads to ecological problems and must therefore be separated off from the offgas stream in an industrial plant, which is a complex procedure. Furthermore, the offgases also comprise relatively large amounts of nitrogen and sulfur compounds, which likewise must be removed in a complex procedure.
The reaction temperatures for these reactions are usually in the range between 25 and 70° C. However, at these temperatures complete conversion to the alkanesulfonic acid is not achieved. Thus, for example, in the reaction to give methanesulfonic acid, under these reaction conditions the reaction partially remains at the stage of the intermediate product S-methyl methanethiosulfonate. This intermediate is an unstable compound which releases sulfur dioxide from 90° C. and decomposes spontaneously and extremely exothermally at 170° C.
It is therefore an object of the present invention to provide an economically attractive process which permits the preparation of alkanesulfonic acids in high purity and in good yields, and suppresses virtually completely the formation of nitrous oxide.
This object is achieved by a process for the preparation of alkanesulfonic acids, comprising the following steps:
(a) oxidation of alkylmercaptans and/or dialkyl disulfides and/or dialkyl polysulfides having from three to nine sulfur atoms with nitric acid to form alkanesulfonic acids, water, nitrogen oxides and other byproducts,
(b) regeneration of the nitrogen oxides obtained from step (a) with oxygen to give nitric acid and recycling of the nitric acid to step (a).
The process according to the invention comprises carrying out the steps (a) and (b) in reaction chambers separate from one another.
Accordingly, the net reaction carried out is an oxidation of the alkylmercaptan or of the dialkyl disulfide with (atmospheric) oxygen.
The nitrogen oxides which form in step (a) are low oxidation state nitrogen compounds (NO/NO
2
mixtures), which are reoxidized in step (b) to give pure nitric acid or nitric acid containing nitrogen dioxide. The nitric acid used in the process according to the invention can, accordingly, be pure nitric acid or nitric acid containing nitrogen dioxide.
The spatial separation of the oxidation of mercaptans and/or dialkyl disulfides and/or dialkyl polysulfides having from three to nine sulfur atoms to give alkanesulfonic acid (step (a)) and the regeneration of the nitrogen oxides (step (b)) is advantageous because both reaction steps, step (a) and step (b), can be carried out separately from another another under optimal reaction conditions. As a result, the formation of nitrous oxide can be suppressed virtually completely, and it is possible to achieve very good yields of alkanesulfonic acids.
The process according to the invention is preferably carried out continuously.
Step (a)
The oxidation is usually carried out at elevated temperature in order to obtain a high conversion and in order to avoid a buildup of hazardous trace components such as methyl nitrate or S-methyl methanethiosulfate as can form during the preparation of methanesulfonic acid. In general, step (a) is carried out at reaction temperatures of from 50° C. to 150° C., preferably from 100° C. to 140° C. The operating pressure in step (a) is generally between 100 mbar and 8 bar, preferably atmospheric pressure.
The mercaptans and/or dialkyl disulfides and/or dialkyl polysulfides used in the process according to the invention contain hydrocarbons which can be aliphatic or cycloaliphatic. Particularly preferably, the hydrocarbon radicals are linear or branched aliphatic hydrocarbon radicals. These preferably contain from 1 to 20, particularly preferably from 1 to 14, carbon atoms. Very particularly preferably, the radicals are methyl radicals and thus the alkylmercaptans or dialkyl disulfides are methylmercaptan or dimethyl disulfide.
Preference is given to using dialkyl disulfides in the process according to the invention. The dialkyl disulfides are generally prepared from hydrogen sulfide and methanol, although other access methods are also known in the literature. Particularly preferably the dialkyl disulfides are prepared by oxidation of alkylmercaptans with sulfur dissolved in an organic dialkyl disulfide using an amine as catalyst. In this process the alkylmercaptans can be used as “crude mercaptan stream”, i.e. as mercaptan stream not purified by extraction or distillation, from the reaction of alcohols with hydrogen sulfide on a suitable catalyst.
An advantage of this preparation process for dialkyl disulfides is that the process can be carried out at atmospheric pressure. This means that dialkyl disulfide which is stored temporarily is not kept in a pressurized container. In addition, dialkyl disulfide is a storage-stable feed material and can therefore be handled safely. This process is described in patent application Ser. No. 198 54 427.8 (official file reference) which has been filed at the same time and has the title “Process for the preparation of dialkyl disulfides”.
The dialkyl disulfide which is preferably used is reacted to give alkanesulfonic acid and must therefore be replenished. Replenishment of dialkyl disulfides can take place into the vapor phase of the reaction mixtu
Ebel Klaus
Eiermann Matthias
Tragut Christian
BASF - Aktiengesellschaft
Killos Paul J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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