Process for preparing an alkanesulphonic acid

1. A process for preparing an alkanesulphonic acid, the process comprising:

a) oxidizing at least one sulphur-containing starting compound with an oxidizing agent, thereby producing a corresponding alkanesulphonic acid, wherein the at least one sulphur-containing starting compound is selected from the group consisting of alkyl mercaptan, dialkyl disulphide and dialkyl polysulphide having three to nine sulphur atoms,

b) determining the at least one sulphur-containing starting compound and/or at least one oxidation intermediate from the oxidizing the at least one sulphur-containing starting compound to the corresponding alkanesulphonic acid in a reaction output from the oxidizing, wherein the at least one oxidation intermediate is determined to be an S-alkyl alkanesulfonate and is determined with UV-vis spectroscopy, and the at least one sulphur-containing starting compound is determined to be a dialkyl disulphide and/or a dialkyl polysulphide and is determined by pulsed amperometric detection, and

c) supplying an additional oxidizing agent in the oxidizing to complete a oxidation reaction after the determining.

2. The process according to claim 1 , wherein the at least one oxidation intermediate and the at least one sulphur-containing starting compound are independently determined in separate samples from the reaction output.

3. The process according to claim 1 , further comprising:

prior to the determining, performing a chromatographic separation of a sample from the reaction output.

4. The process according to claim 1 , wherein the oxidizing agent is an oxidizing agent with free oxygen and/or with oxygen in bound form.

5. The process according to claim 1 , wherein the oxidizing is conducted in at least one reactor.

6. The process according to claim 5 , wherein the oxidizing is conducted in at least two reactors arranged in series.

7. The process according to claim 5 , wherein the determining and optionally the supplying is conducted downstream of a first reactor and

if more than two reactors arranged in series are present, the determining and optionally the supplying is conducted downstream of a second reactor and each reactor thereafter.

8. The process according to claim 6 ,

wherein the oxidizing in a first reactor is conducted with free oxygen and

if more than two reactors arranged in series are present, oxygen in bound form is optionally fed into a second reactor and each reactor thereafter.

9. A method for preparing at least one alkanesulphonic acid, the method comprising:

preparing the at least one alkanesulphonic acid with UV-vis spectroscopy and/or pulsed amperometric detection.

10. An apparatus for conducting at least one oxidation reaction, the apparatus comprising:

i) a reactor for oxidizing at least one starting compound,

ii) a measuring unit, downstream of the reactor, for determining at least one nonoxidized starting compound and/or at least one oxidation intermediate from the oxidation reaction of the at least one starting compound to a desired target compound in a reaction output from the oxidization reaction, wherein the measuring unit is a UV-Vis spectrometer and/or an amperometric detector, and

iii) a unit, in contact with the measuring unit, for supplying additional oxidizing agent to the reactor.

11. The process according to claim 1 , wherein the at least one sulphur-containing starting compound is selected from the group consisting of alkyl mercaptan of formula R—SH, dialkyl disulphide of formula R—S—S—R, and dialkyl polysulphide of formula R—S n —R with n=3 to 9, wherein R is alkyl group.

12. The process according to claim 1 , wherein the alkyl mercaptan, dialkyl disulphide and/or dialkyl polysulphide have linear or branched alkyl groups, each having 1 to 12 carbon atoms.

13. The process according to claim 1 , wherein the alkyl groups are selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl and tert-butyl.

14. The process according to claim 1 , wherein the sulphur-containing starting compound is methyl mercaptan, dimethyl disulphide and/or dimethyl polysulphide having three to nine sulphur atoms, and the alkanesulphonic acid to be prepared is methanesulphonic acid.

15. The process according to claim 1 , wherein, if the sulphur-containing starting compound is dimethyl disulphide and/or dimethyl polysulphide, the process comprises preceding the oxidizing by preparing dimethyl disulphide and/or dimethyl polysulphide.

16. The process according to claim 15 , wherein the dimethyl disulphide and/or dimethyl polysulphide is prepared by reacting methyl mercaptan with elemental sulphur.

17. The process according to claim 16 , wherein hydrogen sulphide is formed and fed into the process for preparation of methyl mercaptan.