Method for preparing 3-methylthiopropionaldehyde

Abstract

The present invention relates to a method for preparing 3-methylthiopropionaldehyde by reacting methyl mercaptan with acrolein, in which deviations in the stoichiometry of methyl mercaptan to acrolein in the reaction to give 3-methylthiopropionaldehyde are compensated for by supplying or by forming 1,3-bis(methylthio)-1-propanol, and also to the use of 1,3-bis(methylthio)-1-propanol as a storage form of methyl mercaptan and/or 3-methylthiopropionaldehyde.

Claims

1. A method for continuously preparing 3-methylthiopropionaldehyde, the method comprising: reacting methyl mercaptan with acrolein to obtain the 3-methylthiopropionaldehyde, wherein deviations in a stoichiometry of the methyl mercaptan to the acrolein during the reacting to obtain the 3-methylthiopropionaldehyde are compensated for by supplying or forming 1,3-bis(methylthio)-1-propanol, and wherein: if the methyl mercaptan is present in excess with respect to the acrolein, an excess methyl mercaptan is converted to the 1,3-bis(methylthio)-1-propanol with the 3-methylthiopropionaldehyde, wherein the 1,3-bis(methylthio)-1-propanol formed is intermediately stored, or if the acrolein is present in excess with respect to the methyl mercaptan, the 1,3-bis(methylthio)-1-propanol is supplied to the reacting of the methyl mercaptan with the acrolein, wherein a molar amount of intermediately stored 1,3-bis(methylthio)-1-propanol to be supplied is at least as large as an amount of an excess acrolein.

2. The method according to claim 1, wherein a molar ratio of the methyl mercaptan to the 3-methylthiopropionaldehyde during the reacting to obtain the 1,3-bis(methylthio)-1-propanol is from 0.1:1 (mol/mol) to 1:1 (mol/mol).

3. The method according to claim 1, wherein an excess acrolein is present and the excess acrolein is reacted with the 1,3-bis(methylthio)-1-propanol to obtain the 3-methylthiopropionaldehyde.

4. The method according to claim 1, wherein a portion of a stream comprising the methyl mercaptan is branched off before the reacting to obtain the 3-methylthiopropionaldehyde and is supplied to the forming of the 1,3-bis(methylthio)-1-propanol by reacting the 3-methylthiopropionaldehyde with the methyl mercaptan.

5. The method according to claim 1, wherein a minimum stream of the methyl mercaptan is branched off before the reacting to obtain the 3-methylthiopropionaldehyde and in parallel, a minimum stream of the 1,3-bis(methylthio)-1-propanol is supplied to the reacting of the methyl mercaptan with the acrolein.

6. The method according to claim 1, wherein, if the acrolein is present in excess with respect to the methyl mercaptan, intermediately stored 1,3-bis(methylthio)-1-propanol is supplied to the reacting of the methyl mercaptan with the acrolein and is reacted with an excess acrolein to obtain the 3-methylthiopropionaldehyde.

7. The method according to claim 1, wherein a molar amount of 1,3-bis(methylthio)-1-propanol supplied is at least as large as an amount of an excess acrolein.

8. The method according to claim 6, wherein unreacted 1,3-bis(methylthio)-1-propanol is recovered.

9. The method according to claim 8, wherein the 1,3-bis(methylthio)-1-propanol recovered is intermediately stored.

10. The method according to claim 8, wherein, if the acrolein is present in excess with respect to the methyl mercaptan, a stream with an excess acrolein is branched off before the reacting to obtain the 3-methylthiopropionaldehyde and is reacted with the unreacted 1,3-bis(methylthio)-1-propanol separated from a product mixture to obtain the 3-methylthiopropionaldehyde.

11. The method according to claim 8, wherein equal amounts of the unreacted 1,3-bis(methylthio)-1-propanol separated from a product mixture and the acrolein are reacted to obtain the 3-methylthiopropionaldhyde.

12. A method for storing methyl mercaptan and/or 3-methylthiopropionaldehyde, the method comprising: storing the methyl mercaptan and/or 3-methylthiopropionaldehyde in form of 1,3-bis(methylthio)-1-propanol, wherein the 1,3-bis(methylthio)-1-propanol originates from and/or is supplied to a process for continuously preparing the 3-methylthiopropionaldehyde, wherein the process comprises: reacting methyl mercaptan with acrolein to obtain the 3-methylthiopropionaldehyde, wherein deviations in the stoichiometry of the methyl mercaptan to the acrolein in the reacting to obtain the 3-methylthiopropionaldehyde are compensated for by supplying or forming the 1,3-bis(methylthio)-1-propanol, and wherein: if the methyl mercaptan is present in excess with respect to the acrolein, an excess methyl mercaptan is converted to the 1,3-bis(methylthio)-1-propanol with the 3-methylthiopropionaldehyde, wherein the 1,3-bis(methylthio)-1-propanol formed is intermediately stored, or if the acrolein is present in excess with respect to the methyl mercaptan, the 1,3-bis(methylthio)-1-propanol is supplied during the reacting of the methyl mercaptan with the acrolein, wherein a molar amount of intermediately stored 1,3-bis(methylthio)-1-propanol to be supplied is at least as large as an amount of excess acrolein.

Description

EXAMPLES

(1) A. Methods Used

(2) 1. Determination of Methyl Mercaptan by Argentometric Titration

(3) Chemicals used: 2-propanol (technical grade) sodium acetate in ethanol (0.1 mol/l), Bernd Kraft, Cat. No. 16590.3700 silver nitrate standard solution (0.1 mol/l), Sigma-Aldrich, Cat. No. 35375 nitrogen

(4) Alternatively, reagents from other manufacturers with comparable quality may also be used.

(5) Equipment used: Titrando 907, Metrohm, Cat. No. 2.907.0020 Dosino 800, Metrohm, Cat. No. 2.800.0020 Tiamo™ (titration software), Metrohm, Cat. No. 6.6056.221 Ag Titrode with sulphide coating, Metrohm, Cat. No. 6.0430.100S, with 854 iConnect, Metrohm, Cat. No. 1.854.0010 titration vessel (150 ml), Metrohm, Cat. No. 6.1415.250, with lid having 5 openings, Metrohm, Cat. No. 6.1414.010 retaining ring for titration vessel, Metrohm, Cat. No. 6.2036.000 magnetic stirrer 801 with stand, Metrohm, Cat. No. 2.801.0040 magnetic stirrer bars (length 25 mm), Metrohm, Cat. No. 6.1903.030 magnetic stirrer bar remover glass beaker wash bottle disposable syringes (1 ml), Luer disposable cannulae (70 ml), Luer analytical balance

(6) Alternatively, other equipment configurations from other suppliers with comparable performance characteristics may also be used.

(7) The titration vessel was initially charged with 80 ml of a sodium acetate solution in ethanol (0.1 mol/l). Nitrogen was slowly introduced into the precharged sodium acetate solution for approx. one minute. During the sparging of the sodium acetate solution, 0.2 ml of the methyl mercaptan sample to be determined were withdrawn from the sample flask using a disposable syringe and a disposable cannula. The weight of the syringe filled with the sample was determined with an analytical balance. After terminating the nitrogen supply, the sample was added in the titration vessel and the exact amount of sample was determined by re-weighing. The titration was conducted using silver nitrate standard solution (0.1 mol/l) and the endpoint was determined by means of the Ag Titrode with sulphide coating.

(8) If the sample contains no hydrogen sulphide in addition to the methyl mercaptan to be determined, the titration curve has only one inflection point in a range of potential between −100 and +100 mV. The methyl mercaptan content in the sample solution (in % by weight) is given by the formula:

(9) $\mathrm{MC}\mathrm{content}=\frac{\begin{array}{c}V\left(\mathrm{standard}\mathrm{solution}\right)*c\left(\mathrm{standard}\mathrm{solution}\right)*\\ \mathrm{molar}\mathrm{weight}\left(\mathrm{MC}\right)*100\end{array}}{\mathrm{sample}\mathrm{weight}}$

(10) During the titration a yellow precipitate of silver methyl mercaptide precipitated out. In samples which also contained hydrogen sulphide in addition to methyl mercaptan, the presence of hydrogen sulphide was indicated by a black precipitate of silver sulphide on addition of silver nitrate. In this case, the titration curve showed an inflection point in a range of potential between +250 and +4550 mV. The methyl mercaptan and hydrogen sulphide content in the sample (in % by weight) is given by the following formula:

(11) $\mathrm{MC}\mathrm{content}=\frac{\begin{array}{c}V\left(\mathrm{std}.\mathrm{sol}.,2.\mathrm{WP}\right)-V\left(\mathrm{std}.\mathrm{sol}.,1.\mathrm{WP}\right)*\\ c\left(\mathrm{std}.\mathrm{sol}.\right)*\mathrm{molar}\mathrm{wt}.\left(\mathrm{MC}\right)*100\end{array}}{\mathrm{sample}\mathrm{weight}}$$H2S\mathrm{content}=\frac{V\left(\mathrm{std}.\mathrm{sol}.,1.\mathrm{WP}\right)*\left(\mathrm{std}.\mathrm{sol}.\right)*\mathrm{molar}\mathrm{weight}\left(H2S\right)*100}{\mathrm{sample}\mathrm{weight}*2}$

(12) Std. sol., 2. WP. and std. sol., 1. WP signify the volume (in ml) of the silver nitrate standard solution (concentration given in mol/l) consumed which was required to reach the second or first inflection point in the titration curve. The sample weight was in g and the molar weight was inserted in g/mol.

(13) 2. Determination of Acrolein in 3-Methylthiopropionaldehyde by Photometry

(14) Chemicals used: demineralized water

(15) Equipment used: UV-Vis photometer of the type UV-1202 from Shimadzu UV-Vis cuvettes with a path length of 10 mm transfer pipettes

(16) Alternatively, other equipment configurations from other suppliers with comparable performance characteristics may also be used.

(17) Before the actual determination of acrolein in 3-methylthiopropionaldehyde, a calibration against water was firstly carried out. For this purpose, the UV-Vis cuvette was filled with demineralized water and the blank sample thus obtained was measured photometrically. Subsequently, another UV-Vis cuvette was first conditioned by at least one-time rinsing with 3-methylthiopropionaldehyde. About 1 ml of the sample to be investigated was then placed in the UV-Vis cuvette, using the transfer pipette, which was sealed and measured photometrically (at a wavelength of 366 nm). To determine the acrolein content in the sample, the absorption measured by the UV-Vis photometer was multiplied by a factor of 0.5220. The acrolein content from the UV-Vis photometer was then stated in % with a precision of three decimal places. Using this method, concentrations of up to about 0.6% acrolein in a matrix comprising 3-methylthiopropionaldehyde can be determined with sufficient precision.

(18) 3. Determination of N,N-Dimethylbenzylamine (DMBA) in 3-Methylthiopropionaldehyde by Titration

(19) Chemicals used: electrolyte solution for Ag/AgCl reference system c(KCl)=3 mol/l (250 ml), Metrohm, Cat. No. 6.2308.020 storage solution for combined pH glass electrodes with reference electrolyte c(KCL)=3 ml, Metrohm, Cat. No. 6.2323.000 buffer solution pH 4.00 (25° C.) in disposable portion sachet, Metrohm, Cat. No. 6.2307.200 buffer solution pH 7.00 (25° C.) in disposable portion sachet, Metrohm, Cat. No. 6.2307.210 buffer solution pH 9.00 (25° C.) in disposable portion sachet, Metrohm, Cat. No. 6.2307.220 perchloric acid in glacial acetic acid (0.01 mol/l), Bernd Kraft, Cat. No. 05101.3700 glacial acetic acid (ReagentPlus®), Sigma-Aldrich, Cat. No. A6283 2-propanol (Chromasolv®), Sigma-Aldrich, Cat. No. 34863 LiCl solution, saturated in ethanol

(20) Alternatively, chemicals from other manufacturers with comparable quality may also be used.

(21) Equipment used: Titrando 907 potentiometric titrator, Metrohm, Cat. No. 2.907.0020 Dosino 800 metering system, Metrohm, Cat. No. 2.800.0020 Tiamo™ (titration software), Metrohm, Cat. No. 6.6056.221 Dosing Unit 10 ml metering unit, Metrohm, Cat. No. 6.3032.210 Dosing Unit 50 ml metering unit, Metrohm, Cat. No. 6.3032.250 Solvotrode electrodes for titration in non-aqueous media, Metrohm, Cat. No. 6.0229.100 titration vessel (150 ml), Metrohm, Cat. No. 6.1415.250, with lid having 5 openings, Metrohm, Cat. No. 6.1414.010 retaining ring for titration vessel, Metrohm, Cat. No. 6.2036.000 magnetic stirrer 801 with stand, Metrohm, Cat. No. 2.801.0040 magnetic stirrer bars (length 25 mm), Metrohm, Cat. No. 6.1903.030 magnetic stirrer bar remover glass beaker wash bottle disposable syringes (1 ml), Luer disposable cannulae (70 ml), Luer analytical balance

(22) Alternatively, another equipment configuration with comparable performance characteristics may also be used.

(23) Prior to the first measurement, the pH electrode was calibrated with buffer solutions at a pH of 4, 7 or 9 in each case. Subsequently, DMBA in MMP was determined by potentiometric titration. A plastic beaker was filled with ca. 50 ml of glacial acetic acid, ca. 50 g of sample were then added, wherein the exact amount of sample was determined by weighing. The titration was carried out using perchloric acid in glacial acetic acid (0.01 mol/l), the end point being detected by means of an electrode for titration in non-aqueous media, e.g. Solvotrode, Metrohm.

(24) $\mathrm{DMBA}\mathrm{content}\mathrm{in}\mathrm{MC}\left[\mathrm{wt}.\text{-}\%\right]=\frac{V\left(\mathrm{std}.\mathrm{sol}.,\mathrm{ml}\right)*c\left(\mathrm{std}.\mathrm{sol}.,\frac{\mathrm{mol}}{l}\right)*M\left(\mathrm{DMBA},\frac{g}{\mathrm{mol}}\right)}{m\left(\mathrm{sample},g\right)}$

(25) V. (std. sol., ml) corresponds to the volume of perchloric acid standard solution consumed in ml.

(26) c (std. sol., mol/l) corresponds to the concentration of perchloric acid standard solution in mol/l.

(27) M (DMBA, g/mol) corresponds to the molar mass of the DMBA (N,N-dimethylbenzylamine) to be determined in g/mol.

(28) m (sample, g) corresponds to the weight of the sample in g.

(29) 4. Residue Determination Using a Vacuum Distillation Unit

(30) The determination of the residue is carried out in a vacuum distillation unit (e.g. Kugelrohr (“ball tube”) evaporator, Büchi, GKR-50)

(31) To determine the container empty weight, the vessel for the substance to be distilled was weighed. Subsequently, 15 g of the liquid to be distilled were weighed into the container and the distillation unit was assembled. The pressure regulator of the vacuum pump was set to a pressure of 30 mbar. The heating of the distillation container was set to a temperature of 200° C. After a period of 20 minutes, the distillation was terminated. After cooling the distillation unit, the apparatus was vented, the vacuum pump was switched off and the glass parts were disassembled. The distillation container was weighed and the residue determined with the aid of the formula below:

(32) $\mathrm{Residue}\left[\mathrm{wt}.\text{-}\%\right]=\frac{m\left(\mathrm{contained},\mathrm{after}\mathrm{dist}.\right)-m\left(\mathrm{container},\mathrm{empty}\right)}{m\left(\mathrm{container},\mathrm{before}\mathrm{dist}.\right)}$
5. Gas Chromatography

(33) The gas chromatographic investigations were carried out using a gas chromatograph of the HP 6890 type from Agilent, which was equipped with a 19091J-213 HP-5 5% phenylmethylsiloxane capillary column from Agilent and a flame ionization detector. The analysis was conducted using a temperature gradient from 40 to 325° C. at a temperature rate of 15° C. per minute.

(34) In the context of the present invention, gas chromatography—in addition to other methods—was used for the determination of 3-methylthiopropionaldehyde, methyl mercaptan and acrolein. The 1,3-bis(methylthio)-1-propanol formed from 3-methylthiopropionaldehyde and methyl mercaptan was unstable at the temperatures applied in the gas chromatography and therefore already decomposed into the starting compounds 3-methylthiopropionaldehyde and methyl mercaptan prior to detection.

(35) B. Experiments 1 to 4:

(36) 25.16 g of stripped 3-methylthiopropionaldehyde (methylmercaptopropionaldehyde MMP) (93.19% by weight) from industrial production were initially charged in a flask and heated using a water bath. The amount of methyl mercaptan (MC) (12.41 ml, 11.09 g) required for the formation of 1,3-bis(methylthio)-1-propanol (MMP-MC) was charged in a cooled dropping funnel. 0.027 g or 0.095 g of a catalyst mixture composed of N,N-dimethylbenzylamine (5.2% by weight based on the catalyst), acetic acid, tartaric acid and water were added to the MMP of experiments 2 and 4. The methyl mercaptan was added dropwise via the dropping funnel to the 3-methylthiopropionaldehyde over a period of ca. 7 to 10.5 minutes such that a temperature of ca. 25° C. (experiments 1 and 2) or ca. 40° C. (experiments 3 and 4) was not substantially exceeded. Subsequently, the resulting product mixture was stirred for 15 minutes at 25° C. (experiments 1 and 2) or at 40° C. (experiments 3 and 4).

(37) Next, the resulting product mixtures overlayed with nitrogen were stored in a flask for 1 day or 7 days at 15° C. In the NMR spectra of the product mixtures, the signals corresponding to MMP-MC, MMP and MC are primarily observed. By-products are at most observed in traces.

(38) C. Experiments 5 to 12:

(39) A sufficient amount of MMP (industrially produced, 93.19% by weight) was initially charged in a flask. 10.43 g (94.91% by weight) of the MMP-MC prepared in experiments 1 to 4 and stored one day or 7 days and 3.76 g (96.97% by weight) of acrolein were added dropwise from dropping funnels to the MMP over a period of ca. 7.5 minutes such that a temperature of ca. 60° C. in the liquid phase in the flask was not exceeded. The addition of catalyst was carried out according to the figures in the table below. The product mixtures were then stirred at 60° C. for 60 minutes.

(40) The MMP-MC used in experiment 5 was prepared at 25° C. and stored for one day at 15° C. The addition of catalyst was carried out in the second step (preparation of MMP from MMP-MC and AC).

(41) The MMP-MC used in experiment 6 was prepared at 25° C. and stored for seven days at 15° C. The addition of catalyst was carried out in the second step (preparation of MMP from MMP-MC and AC).

(42) The MMP-MC used in experiment 7 was prepared at 25° C. and stored for one day at 15° C. The addition of catalyst was carried out in the first step (preparation of MMP-MC from MMP and MC).

(43) The MMP-MC used in experiment 8 was prepared at 25° C. and stored for seven days at 15° C. The addition of catalyst was carried out in the first step (preparation of MMP-MC from MMP and MC).

(44) The MMP-MC used in experiment 9 was prepared at 40° C. and stored for one day at 15° C. The addition of catalyst was carried out in the second step (preparation of MMP from MMP-MC and AC).

(45) The MMP-MC used in experiment 10 was prepared at 40° C. and stored for seven days at 15° C. The addition of catalyst was carried out in the first step (preparation of MMP-MC from MMP and MC).

(46) The MMP-MC used in experiment 11 was prepared at 40° C. and stored for one day at 15° C. The addition of catalyst was carried out in the first step (preparation of MMP-MC from MMP and MC).

(47) The MMP-MC used in experiment 12 was prepared at 40° C. and stored for seven days at 15° C. The addition of catalyst was carried out in the first step (preparation of MMP-MC from MMP and MC).

(48) The catalyst mixture contained 5.2% by weight N,N-dimethylbenzylamine.

(49) TABLE-US-00001 TABLE 1 Overview of experiments 1 to 12. Reactants DMBA MMP- Storage in sol. Cat. Residue Experiment MMP/MC MC/AC [d] [ppm] [g] [% by wt.] 1 1/1   — — 89 — 0 2 1/1.08 — — 129 0.027 0 3 1/1.04 — — 92 — 0.01 4 1/1.06 — — 232 0.095 0.01 5 — 1/0.91 1 143 0.026 0.1 6 — 1/1.05 7 147 0.026 0.08 7 — 1/1.03 1 113 — 0.13 8 — 1/1.03 7 113 — 0.05 9 — 1/1.02 1 150 0.028 0.01 10 — 1/1.03 7 151 0.028 0.01 11 — 1/1.03 1 151 — 0.01 12 — 1/1   7 149 — 0.03

(50) With a test sample of ca. 100 mg (experiments 5 to 12), gas chromatograms of the respective product mixtures were generated—using n-dodecane as internal intensity standard. The results of the analysis are compiled in the following table:

(51) TABLE-US-00002 TABLE 2 Overview of the analyses of experiments 5 to 12. GC [wt %] Experiment MMP MC AC 5 92.42 0.50 — 6 94.66 0.03 — 7 93.88 0.15 — 8 93.90 0.12 — 9 94.11 0.16 — 10 95.67 0.14 — 11 94.55 0.02 — 12 94.60 0.04 —

(52) In addition, 15 g of each product mixture were distilled using the Kugelrohr distilling bulb. Here, a brown film of 0.01 to 0.03% by weight remained on the flask wall which was determined as the dimer of MMP.

(53) The experiments show that independently of whether the MMP-MC was prepared at 25 or 40° C., whether it was stored for one day or seven days, and independently of whether the catalyst was added to the MMP-MC or to the MMP preparation, there was no influence on the formation of high-boiling residues.

(54) D. Experiment 13:

(55) 90 units by weight of MMP were initially charged in a reactor and then 100 units by weight of acrolein (95.7%) were introduced per hour over a period of 24 hours. Simultaneously, 83.5 units by weight of methyl mercaptan (96.1%) were introduced per hour over a period of 24 hours. In addition, 0.02 units by weight of N,N-dimethylbenzylamine, dissolved in an excess of acetic acid, were added per hour. To compensate for the excess of methyl mercaptan, 28.5 units by weight of a solution of MMP/MMP-MC comprising 7 percent by weight methyl mercaptan were introduced. The temperature was maintained at 60° C. The amount of MMP which caused an increase in the fill level in the reactor was discharged. This amount was pumped into a residence time reactor with a residence time of 0.5 hours and again discharged accordingly. The reaction solution was freed of low-boiling by-products of the acrolein and methyl mercaptan preparation in a stripping column.

(56) Analysis of the reaction solution thus obtained revealed that 206.1 units by weight of MMP were obtained per hour. A sample of the reaction mixture was concentrated to constant weight at 220° C. and 30 mbar. A non-evaporable residue of 0.3% by weight remained. Determination of the MMP concentration revealed a content of 97.1%. This corresponds to a yield of more than 98%.