PROCESS FOR PREPARING AN ALKANESULPHONIC ACID

Abstract

The present invention relates to a process for preparing alkanesulphonic acid by oxidizing an alkyl mercaptan, a dialkyl disulphide and/or a dialkyl polysulphide having three to nine sulphur atoms with an oxidizing agent, wherein additional oxidizing agentis fed into the oxidation if as yet unoxidized alkyl mercaptan and/or unoxidized dialkyl disulphide and/or at least one intermediate from the oxidation of the dialkyl disulphide and/or of the dialkyl polysulphide is present in the reaction output, and a corresponding apparatus for performance of oxidation reactions.

Claims

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, 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 is determined to be an S-alkyl alkanesulphonate.

3. The process according to claim 1, wherein the at least one oxidation intermediate is determined with UV-vis spectroscopy.

4. The process according to claim 1, wherein the at least one sulphur-containing starting compound is determined by pulsed amperometric detection.

5. The process according to claim 1, wherein, the at least one sulphur-containing starting compound is determined to be a dialkyl disulphide and/or a dialkyl polysulphide.

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

7. The process according to claim 1, further comprising: prior to the determining, performing a chromatographic separation of a sample from the reaction output.

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

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

10. The process according to claim 9, wherein the oxidizing is conducted in at least two reactors arranged in series.

11. The process according to claim 9, 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.

12. The process according to claim 10, 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.

13. 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.

14. 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 non-oxidized 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, and iii) a unit, in contact with the measuring unit, for supplying additional oxidizing agent to the reactor.

15. The apparatus according to claim 14, wherein the measuring unit is a UV-vis spectrometer and/or an amperometric detector.

Description

FIGURES

[0136] FIG. 1: Chromatogram of Comparative Example 1

[0137] FIG. 2: Chromatogram of Comparative Example 2

[0138] FIG. 3: Chromatogram of Comparative Example 3

[0139] FIG. 4: Chromatogram of Comparative Example 4

[0140] FIG. 5: Chromatogram of Example 1

[0141] FIG. 6: Chromatogram of Example 2

[0142] FIG. 7: Chromatogram of Example 3

[0143] FIG. 8: Chromatogram of Example 4

[0144] FIG. 9: .sup.1H NMR spectrum of Comparative Experiment 5

EXAMPLES

I. Technical Equipment

1. Equipment Used:

[0145] Professional Sample Processor 858 (No. 2.858.0010 from Metrohm) sample handling device equipped with an 800 Dosino 800 (No. 2.800.0010 from Metrohm) metering system. 882 Compact IC plus (No. 2.850.9110 from Metrohm) ion chromatograph equipped with a Vario 944 (No. 2.944.0010 from Metrohm) UV/VIS detector, an IC Amperometric Detector (No. 2.850.9110 from Metrohm) and a pressure gauge.

[0146] 883 Basic IC plus (2.883.0020 from Metrohm) ion chromatograph equipped with a conductivity detector in the form of the module iDetector (standard equipment of the 883 Basic IC plus ion chromatograph) and a pressure gauge.

[0147] In the experiments, the first device is the sample handling system, followed by the ion chromatograph which is equipped with a relevant detector.

2. Chromatography Columns:

[0148] In the 882 Compact IC plus ion chromatograph, a column of the type Phenomenex Gemini 5U C6-Phenyl 110A 250/4.6 is used. Alternatively, a column of the type ProntoSil 120-5-C18 AQ 150/4.0 (6.1008.100 from Metrohm) may also be used.

[0149] In the 883 Basic IC Plus ion chromatograph, a Metrosep A Supp 1 Guard/4.6 was used as pre-column or guard column and an anion separating column Metrosep A Supp 5 250/4.0 as main column. A Metrohm Suppressor-Module MSM was also used as cation exchanger.

3. Eluents:

[0150] Chemicals used: [0151] ultrapure water having a conductivity resistance of 18.2 MOhm and a TOC of 5 ppb, where TOC stands for total organic carbon and states the sum of the whole organic carbon in a water sample (from a Milli-Q Advantage A10 ultrapure water system with Q-POC dispenser or a Millipore system), [0152] LiChrosolv HPLC Grade (high performance liquid chromatography) methanol (1.06007 from Merck), [0153] potassium dihydrogenphosphate 99% (1.04873 from Merck), [0154] phosphoric acid 85% (1.00573 from Merck), and [0155] methanesulphonic acid (471356 from Sigma Aldrich).

[0156] The eluent for the 882 Compact IC plus ion chromatograph was composed of: [0157] 70% ultrapure water, [0158] 30% methanol, [0159] 10% potassium dihydrogenphosphate, and [0160] 1.2 g of phosphoric acid.

[0161] The eluent for the 883 Basic IC plus ion chromatograph was composed of: [0162] 100% ultrapure water, [0163] 3.2 mmol of sodium carbonate, and [0164] 1.0 mmol of dihydrogencarbonate.

II. Amperometric Detection at Constant Voltage

[0165] For comparison with pulsed amperometric detection, dimethyl disulphide (DMDS) in a sample from the preparation of methanesulphonic acid (MA) by oxidation of dimethyl disulphide was determined by means of amperometric detection at constant voltage: An analyte was used, which was provided by dissolving 2 drops of the sample from the methanesulphonic acid preparation in 50 ml of a mixture of acetonitrile and water (ratio by volume 30:70) (referred to as analyte V below). The measurements were conducted over a period of about one hour using a 882 Compact IC Plus 1 ion chromatograph (2.850.9110 from Metrohm), which was equipped with a ProntoSil 120-5-C18 AQ150/4.0 separating column (6.1008.100 from Metrohm), a Metrosep RP2 Guard/3.5 (6.1011.030 from Metrohm) and an amperometric detector (2.850.9110 from Metrohm). This detector has a measurement cell of the wall jet cell type (6.5337.020 from Metrohm), equipped with a glassy carbon working electrode (6.1257.220 from Metrohm) of diameter 3 mm, a silver/silver chloride reference electrode (6.1257.720 from Metrohm) and an auxiliary electrode (6.1247.000 from Metrohm). The injection volume was 20 l and the temperature of the separating column was about 25 C.

[0166] Thereafter, the determinations of dimethyl disulphide were compared with one another in order to be able to make conclusions as to the reproducibility and reliability of the amperometric determination at constant voltage. For this purpose, the values for the area under the peak for dimethyl disulphide in the relevant chromatograms were compared with one another.

Comparative Example 1

[0167] At time t=0 min, the analyte V was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0168] Eluent: MeOH: H.sub.2O (3:7)+2 g/l KH.sub.2PO.sub.4+2 g/l H.sub.3PO.sub.4 [0169] Flow rate: 1.2 ml/min [0170] Pressure: 173.1 bar [0171] Recording duration: 20.7 min

[0172] The components determined in the eluate of this ion chromatography are listed in table 1 and the chromatogram of this determination is shown in FIG. 1. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 1.

TABLE-US-00001 TABLE 1 Results of the determination in Comparative Example 1 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 2.997 0.0253 0.176 Bromide 2 3.457 0.0163 0.148 Nitrate 3 4.415 0.4227 3.483 Phosphate 4 15.835 352.7363 958.275 DMDS

Comparative Example 2

[0173] At time t=22 min, the analyte V was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0174] Eluent: MeOH: H.sub.2O (3:7)+2 g/l KH.sub.2PO.sub.4+2 g/l H.sub.3PO.sub.4 [0175] Flow rate: 1.2 ml/min [0176] Pressure: 170.8 bar [0177] Recording duration: 18.5 min

[0178] The components determined in the eluate of this ion chromatography are listed in table 2 and the chromatogram of this determination is shown in FIG. 2. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 2.

TABLE-US-00002 TABLE 2 Results of the determination in Comparative Example 2 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 2.988 0.0230 0.163 Bromide 2 3.455 0.0140 0.149 Nitrate 3 4.405 0.3272 2.717 Phosphate 4 15.752 321.3513 891.404 DMDS

[0179] When an identical analyte was used, by amperometric determination at constant voltage, only 22 minutes after the first measurement (Comparative Example 1), an area value 8.9% lower is obtained for the determination of dimethyl disulphide in methanesulphonic acid.

Comparative Example 3

[0180] At time t=42 min, the analyte V was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0181] Eluent: MeOH: H.sub.2O (3:7)+2 g/l KH.sub.2PO.sub.4+2 g/l H.sub.3PO.sub.4 [0182] Flow rate: 1.2 ml/min [0183] Pressure: 173.1 bar [0184] Recording duration: 20.7 min

[0185] The components determined in the eluate of this ion chromatography are listed in table 3 and the chromatogram of this determination is shown in FIG. 3. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 3.

TABLE-US-00003 TABLE 3 Results of the determination in Comparative Example 3 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 1.908 0.0337 0.175 MSA 2 2.992 0.0234 0.175 Bromide 3 3.458 0.0148 0.154 Nitrate 4 4.403 0.2953 2.442 Phosphate 5 6.002 0.0066 0.030 MMTS 6 15.705 303.7108 853.682 DMDS

[0186] Only 42 minutes after the first measurement (Comparative Example 1), by means of amperometric determination at constant voltage, an area value 13.9% lower was obtained for dimethyl disulphide.

Comparative Example 4

[0187] At time t=62 min, the analyte V was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0188] Eluent: MeOH: H.sub.2O (3:7)+2 g/l KH.sub.2PO.sub.4+2 g/l H.sub.3PO.sub.4 [0189] Flow rate: 1.2 ml/min [0190] Pressure: 168.0 bar [0191] Recording duration: 25.0 min

[0192] The components determined in the eluate of this ion chromatography are listed in table 4 and the chromatogram of this determination is shown in FIG. 4. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 4.

TABLE-US-00004 TABLE 4 Results of the determination in Comparative Example 4 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 2.720 0.0037 0.059 Nitrite 2 3.000 0.0232 0.150 Bromide 3 3.468 0.0191 0.154 Nitrate 4 4.402 0.2589 2.106 Phosphate 5 15.682 275.3675 771.120 DMDS

[0193] 62 minutes after the first measurement (Comparative Example 1), the area value for the determination of dimethyl disulphide was actually 21.9% below the starting value.

[0194] Comparative Experiments 1 to 4 show that amperometric detection at constant voltage is basically unsuitable for reproducible and reliable determination of dialkyl disulphides in alkanesulphonic acids and particularly of dimethyl disulphides in methanesulphonic acid.

III. Pulsed Amperometric Detection

[0195] By means of pulsed amperometric detection, dimethyl disulphide in a sample from the preparation of methanesulphonic acid by oxidation of dimethyl disulphide was determined over a period of more than one hour.

[0196] An analyte was used for this purpose (referred to as analyte B below), which was provided by dissolving 3 drops of the sample from the methanesulphonic acid preparation in 100 mL of a mixture of acetonitrile and water (ratio by volume 30:70).

[0197] The same instrumental arrangement was used as for the amperometric detection at constant voltage. The injection volume was 20 l and the temperature of the separating column was about 25 C.

[0198] The electrooxidation potential had a value of 1.15 V and a duration of 300 ms, with a measurement duration of 100 ms. The cleaning potential had a value of 1.5 V and a duration of 50 ms, and the conditioning potential had a value of 0.1 V and a duration of 200 ms. The total duration of a measurement cycle was therefore 550 ms.

Example 1

[0199] At time t=0 min, the analyte B was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0200] Eluent: MeOH: H.sub.2O (3:7)+4.2 g/l KH.sub.2PO.sub.4+0.2 g/l H.sub.3PO.sub.4 [0201] Flow rate: 1.2 ml/min [0202] Pressure: 160.1 bar [0203] Recording duration: 25.0 min

[0204] The components determined in the eluate of this ion chromatography are listed in table 5 and the chromatogram of this determination is shown in FIG. 5. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 5.

TABLE-US-00005 TABLE 5 Results of the determination in Example 1 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 1.631 3.7303 17.486 Fluoride 2 4.390 5.6792 48.794 Phosphate 3 6.644 0.2156 1.330 MMTS 4 15.716 333.7089 771.120 DMDS

Example 2

[0205] At time t=42 min, the analyte B was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0206] Eluent: MeOH: H.sub.2O (3:7)+4.2 g/l KH.sub.2PO.sub.4+0.2 g/l H.sub.3PO.sub.4 [0207] Flow rate: 1.2 ml/min [0208] Pressure: 161.2 bar [0209] Recording duration: 21.7 min

[0210] The components determined in the eluate of this ion chromatography are listed in table 6 and the chromatogram of this determination is shown in FIG. 6. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 6.

TABLE-US-00006 TABLE 6 Results of the determination in Example 2 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 3.620 0.7375 6.608 Nitrate 2 4.985 0.2138 1.922 Phosphate 3 15.689 327.0947 825.014 DMDS

Example 3

[0211] At time t=2.5 h, the analyte B was injected into the ion chromatograph. The parameters for the ion chromatography conducted were: [0212] Eluent: MeOH: H.sub.2O (3:7)+4.2 g/l KH.sub.2PO.sub.4+0.2 g/l H.sub.3PO.sub.4 [0213] Flow rate: 1.2 ml/min [0214] Pressure: 161.2 bar [0215] Recording duration: 21.7 min

[0216] The components determined in the eluate of this ion chromatography are listed in table 7 and the chromatogram of this determination is shown in FIG. 7. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 7.

TABLE-US-00007 TABLE 7 Results of the determination in Example 3 Peak Retention time Area Height No. [min] (nA) * min [nA] Component 1 1.576 0.4106 8.942 Fluoride 2 3.629 0.4906 4.236 Nitrate 3 4.994 0.2911 1.955 Phosphate 4 15.652 332.5320 811.847 DMDS

DISCUSSION OF THE MEASUREMENT RESULTS

[0217] The accuracy of pulsed amperometric detection was assessed using the values for the area under the peaks for dimethyl disulphide determined in Examples 1 to 3. This is because this value is an indication of the concentration of the dimethyl disulphide to be determined.

[0218] The area values determined in Examples 1 and 2 only differed from each other by 1.98%. The difference in the area values for Examples 1 and 3, which are the furthest apart from one another in time, was actually only 0.35%. Since the values determined in Examples 1 and 3 were virtually identical, pulsed amperometric detection therefore permits reliable determination of dimethyl disulphide. The difference that occurred in Example 2 is not therefore attributable to any lack of reproducibility of the measurement results, but to a measurement error.

[0219] The dimethyl disulphide concentration determined in this example was identical to that from Example 1. Moreover, the difference from the area value determined in Example 1 was only 0.35%, which is still significantly below the already small measurement error of Example 2. Compared to Comparative Examples 2 to 4, the differences in respect of the area value in Examples 2 and 3 are considerably lower, and, moreover, over a period more than twice as long as the total measurement duration in the comparative examples. Consequently, pulsed amperometric detection represents a reliable and reproducible determination of dimethyl disulphide in methanesulphonic acid.

IV. Comparison of Ion Chromatography and Pulsed Amperometry with NMR

[0220] Since it has been shown that pulsed amperometric detection is a suitable method for reproducible and reliable determination of dialkyl disulphides in alkanesulphonic acids, particularly of dimethyl disulphide in methanesulphonic acid, the accuracy of this method was compared with nuclear spin resonance.

Example 4

[0221] The same instrument arrangement as above was used as for the amperometric detection at constant voltage. A mixture of 3 drops of a sample from the preparation of methanesulphonic acid by oxidation of dimethyl disulphide in 100 ml of a mixture of acetonitrile and water (30:70 v/v) was used as analyte. The volume injected into the ion chromatograph was 20 l, and the temperature of the separating column was about 25 C. [0222] Eluent: MeOH: H.sub.2O (3:7)+4.2 g/l KH.sub.2PO.sub.4+0.2 g/l H.sub.3PO.sub.4 [0223] Flow rate: 1.2 ml/min [0224] Pressure: 162.3 bar [0225] Recording duration: 25.0 min

[0226] The components determined in the eluate of this ion chromatography are listed in table 8 and the chromatogram of this determination is shown in FIG. 8. The numbers of the peaks in this table correspond to the correspondingly numbered peaks in the chromatogram of FIG. 8.

TABLE-US-00008 TABLE 8 Results of the determination in Example 5 Retention Peak time Area Height Concentration No. [min] (nA) * min [nA] [% by wt.] Component 1 1.686 2.3189 8.449 MA 2 3.510 2.5620 12.960 Nitrate 3 15.926 190.6092 430.759 2.567 DMDS

Comparative Example 5

[0227] Dimethyl disulphide in methanesulphonic acid was also determined by means of nuclear spin resonance. The analyte used for this determination was composed of 26.95 mg of a sample from the preparation of methanesulphonic acid by oxidation of dimethyl disulphide and 39.16 mg of naphthalene, and the latter compound served as solvent due to its inert character with respect to dimethyl disulphide and methanesulphonic acid. The nuclear spin resonance measurement was conducted with a 600 MHz Bruker Avance (Ill) spectrometer from Bruker Niospin, equipped with a Bruker Ascend 600 MHz magnet system from Bruker Biospin and a Prodigy CryoProbe probe head, and using MeOD as deuterated solvent. The measurement time was 20 minutes. The proton spectrum of this measurement is shown in FIG. 9, and the results obtained from this spectrum are summarized in Table 9.

[0228] Nuclear spin resonance allows the determination of dimethyl disulphide with a precision of one decimal place or 0.1% by weight, while pulsed amperometric detection enables determination of dimethyl disulphide up to 3 decimal places or 0.001% by weight, which represents greater precision by a factor of 100.

[0229] The dimethyl disulphide concentration determined in Examples 1 to 5 and in Comparative Example 5 always refers to the concentration of this component in the respective analyte. Since this analyte, however, constituted a dilution of the sample from the methanesulphonic acid preparation, the actual concentration of the dimethyl disulphide in this sample was higher by the dilution factor. Consequently, the differences between NMR analysis and pulsed amperometric detection were more notable in more concentrated samples. Because its accuracy is better by about a factor of 100 compared to NMR analysis, pulsed amperometric detection is therefore the method of choice for determination of a dialkyl disulphide in an alkanesulphonic acid.

TABLE-US-00009 TABLE 9 Results of the determination in Comparative Example 5 Peak Corrected Ratio Amount Molar mass Mass Content No. Component Integral Factor integral [mol %] [mmol] [g/mol] [mg] [% by wt.] Naphthalene 464.047 4 116.012 53.0 0.305 128.16 39.07 1 MA 300.000 3 100.000 45.7 0.263 96.11 25.26 93.7 2 DMDS 16.952 6 2.825 1.3 0.007 94.20 0.70 2.6
V. Comparison of the Pulsed Amperometric Detector with a UV Detector

[0230] The higher sensitivity of the (pulsed) amperometric detector for a dialkyl disulphide in an alkanesulphonic acid was shown by a measurement series with a dilution series of dimethyl disulphide in methanesulphonic acid.

1. Sample Preparation:

[0231] The samples were composed of the weights according to Table 10, which were weighed out on a four-figure analytical balance. For calibration in the ppm range, one drop of the sample was weighed into 100 g of ultrapure water. A liquid sample was placed in a 4 ml volume sample vial (Rotilabor) and then closed with a screw cap with seal. The sample was then placed into the sample rack of the 858 Professional Sample Processor. The further dilution of the sample was carried out with the sample handler. This was effected in a mixing vessel with magnetic stirrer, with dilution of the sample in a ratio of 1:100. The sample was then pumped into one or more sample loops of different lengths. In an 882 Compact IC plus ion chromatograph, equipped with a column of the Gemini 5U C6-Phenyl 110A 250/4.6 type, the sample loop had a length of 20 l. This was followed by cleaning steps for the mixing vessel for the next analysis.

2. Deviations/Errors:

[0232] A deviation of about 2% is within the scope of accuracy of ion chromatography. For the determination of dimethyl disulphide calibrations in the order of magnitude of 50 ppm were possible, and for the determination of S-methyl methanesulphonate, also known as methyl methanethiosulphonate (MMTS), calibrations in the order of magnitude of 100 ppm are possible. At even lower concentrations, the errors were significantly greater than the acceptable deviation of 2%.

3. Results

[0233] An 882 Compact IC plus (No. 2.850.9110 from Metrohm) ion chromatograph was used, equipped with a Vario 944 (No. 2.944.0010 from Metrohm) UV/VIS detector, an IC Amperometric Detector (No. 2.850.9110 from Metrohm) and a pressure gauge, the purpose of which was to enable monitoring of a constant pressure during the spectral recording.

[0234] 4 experiments were conducted with the entries stated in Table 10 for the respective analytes.

[0235] The measurement results summarized in table 10 show that a (pulsed) amperometric detector is superior to a UV/VIS spectrometer with respect to the precision in the determination of dimethyl disulphide. This greater precision of (pulsed) amperometry in the determination of dimethyl disulphide actually increases still further with increasing dilution of the dimethyl disulphide in the methanesulphonic acid.