A PROCESS FOR PRODUCING 0,0-DILOWER-ALKYLCHLOROTHIOPHOSPHATE

Abstract: A continuous process for producing O,O-di-lower-­ alkylchlorothiophosphates, which are very important as intermediates for organo-phosphate series agricultural chemicals, comprises continuously reacting phosphorus sulfochloride with a lower alcohol in the presence of caustic soda according to a multi-stage reaction comprising from 3 to 8 stages in which the following conditions are satisfied: (1) The amount of caustic soda used shall be from 2 to 2.2 moles, and that of the lower alcohol shall be at least lO moles, based on l moles of phosphorus sulfochloride. (2) Caustic soda, water and the lower alcohol shall be used as a caustic soda/water/lower alcohol solution, in which the caustic soda concentration shall be from 3O.O to 99.5 wt. %. (3) To the 1st reaction stage shall be continuously supplied the whole amount of phosphorus sulfochloride required and from 45 to 85 wt.% each of the amounts of caustic soda and the lower alcohol required; and to the 2nd and subsequent reaction stages shall be continuously supplied the residual caustic soda and lower alcohol in divided portions so that the substantial amounts supplied become successively smaller toward the final reaction stage. (4) The temperature of the reaction system shall be -5°C or lower. (5) The residence time in the reaction system shall be within 4 hours.

Description: The present invention relates to an improved continuous process for producing O,O-di-lower-alkylchlorothiophosphates. O,O-di-lower-alkylchlorothiophosphates are very important compounds which are widely used as intermediates for organo-phosphate series chemicals for use in agriculture such as O,O-dimethyl-O-(4-nitrophenyl)thiophosphate, O,O-dimethyl-O-(3-methyl-4-nitrophenyl)thiophosphate, O,O-dimethyl-O-(4-cyanophenyl)thiophosphate, O,O-dimethyl-O-(2,6-dichloro-4-methylphenyl)thiophosphate and O,O-diethyl-O-(4-nitrophenyl)thiophosphate. For their production, a process of continuously reacting phosphorus sulfochloride with sodium lower-alcoholate is well known (US-A-3723580). However, as a result of an alteration in the electrolytic process which has been required to avoid environmental pollution owing to the use of mercury, easy access to large quantities of sodium lower-alcoholate, which is a starting material for this reaction, has become difficult, and therefore this well-known process is no longer considered to be an advantageous one. Because of this, there has been a great demand for the development of a process for producing O,O-di-lower-alkylchlorothiophosphate continuously and easily without using sodium lower-alcoholate and yet in a yield of at least the same degree as in the conventional process. In view of this present situation, with the object of developing a continuous process for producing O,O-di-lower-alkylchlorothiophosphate without using sodium lower-alchololate, we studied an industrially advantageous continuous process for producing O,O-di-lower-alkylchlorothiophosphate using cheaply and easily available caustic soda and lower alcohol as materials. Methods are known for producing an O,O-di-lower alkylchlorothiophosphate using phosphorus sulfochloride, a lower alchohol and caustic soda and which can be carried out either on a batchwise or a continuous basis. Each of these known methods involves a two stage process in which two separate respective reaction steps are carried out. In the first reaction step, dichloro-O-monoalkylthiophosphate is obtained and in the second step this is converted to the monochloro-O,O-dialkylthiophosphate. Thus, US-A-3336422 describes such a method in which the reactants and conditions in the second are slightly more severe than those in the first reaction step. Each reaction is carried out in an organic solvent and the lower alcohol is added very slowly to the phosphorus sulfochloride (step 1) and dichloro-O-monoalkyl thiophosphate (step 2) in the presence of an alkali so as to mop up the hydrogen chloride which would otherwise be obtained, and form an alkali metal chloride which absorbs the water of reaction. On the other hand, in DD-A-109639 and CS-A-166992 (Chem. Abs. 87:38866w), the first reaction step in which the dichloro-O-monoalkylthiophosphate is produced does simultaneously produce hydrogen chloride. As explained in DD-A-109639, it is necessary to remove this by a separate water washing stage prior to the second reaction step. It will be readily appreciatd from the above that known methods involving the above-mentioned two-step reaction would be economically disadvantages when carried out on an industrial scale. Furthermore, it should be borne in mind that phosphorus sulfochloride which is a starting material, O,O-di-lower-alkylchlorothiophosphate which is the desired product, and O-lower-alkyldichlorothiophosphate which is an intermediate therefor, are all known to be unstable to water. When, as mentioned above, a lower-alcoholate is used as described in US-A-3723580, such a problem does not arise because no water is formed by the reaction. When, however, caustic soda is used as in the present invention, water is formed by the reaction and besides a caustic soda/water/lower alcohol solution is used, so that a large quantity of water is present in the system as a matter of course. We have conducted extensive investigations in an attempt to develop a process for producing the desired O,O-di-lower-alkylchlorothiophosphate industrially advantageously under such severe conditions, and as a result, found that an efficient manufactuirng method on a commercial scale cannot be established until all the conditions specified by the present invention are satisfied. The present invention provides a continuous process for producing O,O-di-lower-alkylchlorothiophosphate by continuously reacting phosphorus sulfochloride with a lower alcohol in the presence of caustic soda according to a multi-stage reaction form comprising from 3 to 8 stages characterised in that the following conditions are satisfied: (1) The amounts of caustic soda and a lower alcohol used shall be from 2 to 2.2 moles and 10 moles or more, respectively, based on 1 mole of phosphorus sulfochloride. (2) Caustic soda, water and the lower alcohol shall be used as a caustic soda/water/lower alcohol solution, and besides the caustic soda concentration of the aqueous caustic soda in the caustic soda/water solution shall be from 30.0 to 99.5 wt.%. (3) To the 1st reaction stage shall be continuously supplied the whole amount of phosphorus sulfochloride required and from 45 to 85 wt.% each of the amounts of caustic soda and the lower alcohol required; and to the 2nd and subsequent reaction stages shall be continuously supplied the residual caustic soda and lower alcohol in divided portions so that the substantial amounts supplied become successively small toward the final reaction stage. (4) The temperature of the reaction system shall be -5°C or lower. (5) The residence time in the reaction system shall be within 4 hours. Hereafter, "lower alcohol" referred to herein means an aliphatic alcohol having from 1 to 3 carbon atoms. Embodiments of the present invention will be explained below with reference to the accompanying drawing. Fig. 1 is a schematic view illustrating a continuous reaction apparatus comprising n reaction vessels (3≦n≦8). Every reaction vessel of from R₁ to R n is equipped with a stirrer, a caustic soda/water/lower alcohol solution supply pipe (A₁ to A n ), an overflow pipe for the reaction solution (C₁ to C n ) and a cooling apparatus for keeping the reaction solution at a low temperature, and the 1st reaction vessel is equipped with a phosphorus sulfochloride supply pipe B. Phosphorus sulfochloride, a material for reaction, is continuously supplied to the 1st reaction vessel through the supply pipe B. The caustic soda/water/lower alcohol solution is continuously supplied in divided portions to the reaction vessels R₁ to R n through the supply pipes A₁ to A n so that the amounts of caustic soda and the lower alcohol are in respective proportions required by the process of the present invention. By this method, the main reaction is carried out in the 1st reaction vessel, and the reaction solution from the reaction vessels R₁ to R n-1 are supplied to the respective successive vessels R₂ to R n in which the reaction is continued. Finally, the reaction solution after completion of the reaction is withdrawn from the last reaction vessel R n . In this reaction, to employ the multi-stage reaction form is very important to increase the yield of the desired product, and particularly the multi-stage reaction form comprising from 3 to 8 stages is practically very important in terms of yield and economy. For example, in batch processes or continuous ones with only one or two stages, the yield of O,O-di-lower-alkylchlorothiophosphate is as low as at best about 75% with the formation of large quantities of impurities such as O,O-lower-alkyldichlorothiophosphate, O,O,O-tri-lower-alkylthiophosphate, etc. By increasing the number of stages, however, for example in the continuous processes with 5 or 6 stages, the yield of O,O-di-lower-alkylchlorothiophosphate can markedly be improved. However, if the number of stages is increased to more than 8, a further improvement in yield cannot be expected, so that the provision of such additional stages results only in that the apparatus becomes complicated and therefore rather disadvantageous industrially. Consequently, the number of stages is generally within eight. Another important factor in the reaction of the present invention is the proportion of each of the caustic soda and the lower alcohol supplied to each reaction stage. That is, to the 1st reaction stage, from 45 to 85 wt.% preferably from 65 to 85 wt.% of the respective total amounts of each of caustic soda and the lower alcohol required are supplied, and to the 2nd and subsequent reaction stages, the residual caustic soda and lower alcohol are supplied in divided portions so that the substantial amount added to each reaction stage becomes successively small toward the final reaction stage. When the proportions of caustic soda and the lower alcohol supplied to the 1st reaction stage are beyond the above ranges, the percent decomposition of phosphorus sulfochloride increases, and the amount of O,O,O-tri-lower-alkylthiophosphate increases to lower the yield of the desired porduct. Also, the amounts supplied to the 2nd and subsequent reaction stages should be successively decreased toward the final reaction stage. When the amounts supplied to the latter reaction stages are larger than those supplied to the preceding ones, the amount of O,O,O-tri-lower-alkylthiophosphate increases to lower the yield of the desired product. Hereupon, "to supply so that the substantial amounts become successively small toward the final reaction stage" need not be interpreted with extreme strictness, but should be considered to mean the tendency of supply viewed from the whole. For example, it is also allowable to supply the same amount to a plural number of serial reaction stages, and to make the amount supplied to the latter reaction stages larger than that supplied to the preceding ones if a difference in amount is small. Even in the latter case, however, it is preferred to decrease the amount successively and clearly for at least the first half of the whole series of reaction stages. Another important factor in the reaction of the present invention is the amount of each of the caustic soda and the lower alcohol based on phosphorous sulfochloride. In particular, the amount of caustic soda used is very important, being generally from 2 to 2.2 moles, preferably from 2.05 to 2.15 moles, per mole of phosphorus sulfochloride. When the amount of caustic soda is less than 2 moles per mole, or larger than 2.2 moles per mole, based on 1 mole of phosphorus sulfochloride, O-lower-alkyldichlorothiophosphate and O,O,O-tri-lower-alkylthiophosphate are produced respectively in large amounts to lower the yield of O,O-di-lower-alkylchlorothiophosphate. The amount of the lower alcohol used is 10 moles or more, preferably 12 moles or more, per mole of phosphorus sulfochloride, and the upper limit is not particularly limited from the standpoint of reaction. Generally, however, the amount is 16 moles per mole, preferably 14 moles per mole chiefly from the economical standpoints such as a reduction in the reaction efficiency owing to increased reaction volume and recovery of the unreacted lower alcohol. When the amount of the lower alcohol is less than 10 moles per mole based on phosphorus sulfochloride, the yield of O,O-di-lower-alkylchlorothiophosphate lowers. In the process of the present invention, caustic soda and the lower alcohol supplied to every reaction vessel need to be supplied in the form of a caustic soda/water/lower alcohol solution, and besides, the caustic soda concentration of the aqueous caustic soda in the caustic soda/water solution needs to be adjusted so as to correspond to from 30.0 to 99.5 wt.%, preferably from 40.0 to 99.5 wt.%. When the caustic soda concentration of the aqueous caustic soda is lower than 30.0 wt.%, the reaction rate becomes slow and phosphorus sulfochloride decomposes to lower the yield of the desired O,O-di-lower-alkylchlorothiophosphate. If the lower alcohol contains water, it may be used if the caustic soda concentration calculated including that water satisfies the above range. In preparing the caustic soda/water/lower alcohol solution, optional methods may be employed such as mixing of the lower alcohol with an aqueous caustic soda solution previously adjusted to the prescribed concentration, mixing of solid caustic soda with water and the lower alcohol or an aqueous lower alcohol solution, etc. Generally, the caustic soda/water/lower alcohol solutions supplied to every reaction vessel have the same composition, but so far as the conditions described above are satisfied, the solutions need not have the same composition. The most important point to the method of the present invention is to maintain the temperature of the reaction system at -5°C or lower. In the method of the present invention, maintaining the temperature of the entire reaction system at -5°C or lower has effects of inhibiting the formation of by-products such as O,O,O-trimethylthiophosphate, etc. to increase the selectivity of O,O-di-lower-alkylchlorothiophosphate, and inhibiting the hydrolysis of phosphorus sulfochloride, O-lower-alkyldichlorothiophosphate and O,O-di-lower-alkylchlorothiophosphate which are unstable to water. Particularly, it is surprising that the foregoing effects are remarkably developed when the temperature is lowered below -5°C specified by the present invention. Further, in the present invention, it is important to control the total of the average residence times at every reaction stage to within 4 hours. We believe that we were the first to find that, from the standpoint of inhibition of hydrolysis, it is preferred to control the total of periods of time during which the above phosphorus sulfochloride and thiophosphates are brought into contact with water, i.e. average residence times at every reaction stage within 4 hours, preferably within 2 hours. Since the reaction of the present invention is an exothermic one, heat removal becomes a problem when the average residence time is shortened. This problem, however, can be solved by mounting an external heat-exchanger on every reaction vessel. Also, the reaction of the present invention produces sodium chloride as a by-product, but if stirring is of high efficiency, the sodium chloride is dispersed in fine particles in the reaction solution, giving no adverse effect to this reaction. By carrying out reaction operations as described above, the reaction solution from the final reaction vessel consists of two layers, one layer being an aqueous lower alcohol solution layer containing O,O-di-lower-alkylchlorothiophosphate, a main product, and small amounts of O-lower-alkyldichlorothiophosphate, O,O,O-tri-lower-alkylthiophosphate, etc. which are by-products, and the other layer being one comprising partially separated O,O-di-lower-alkylchlorothiophosphate, etc. These two layers, however, turn into one layer when the water content of the caustic soda/water/lower alcohol solution is lowered. These layers are in a stage wherein fine particles have been almost uniformly dispersed, but the desired O,O-di-lower-alkylchlorothiophosphate may be separated by suitable treatment of the reaction solution. For example, the desired product can be separated by pouring the reaction solution into cold water to dissolve and remove the lower alcohol and sodium chloride, followed by dehydration and rectification of the resulting oily layers. In some cases, the separated oily layer itself may be sent to the next reaction step. Thus, according to the method of the present invention, the desired O,O-di-lower-alkylchlorothiophosphate can be produced not only in high yields, but also economically very advantageously on industrially large scales using easily available cheap materials. Embodiments of the present invention will now be illustrated in more detail with reference to the following Examples, but it is not limited to these Examples. Parts in the Examples are by weight. Example 1 A continuous reaction apparatus comprising 6 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 6th reaction vessels is 6:3:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.3 parts/hour of phosphorus sulfochloride and 954.9 parts/hour of a caustic soda/water/methanol solution (caustic soda concentration, 13.6%; methanol concentration, 68.3%; water content, 18.1%) were sent usually at constant rates. To the 2nd to 6th reaction vessels, 95.7 parts/hour, 60.7 parts/hour, 48.3 parts/hour, 18.0 parts/hour and 18.0 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.04 and 12.8, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -15°C, -20°C, -20°C, -17°C, -16°C and -15°C, respectively. The total of the average residence times was 82 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes, and to this solution was added 350 parts of cold water. The separated oily layer and an organic layer obtained by extracting the separated aqueous layer with toluene were dried over calcium chloride and analyzed by gas chromatography to find: O,O-dimethylchlorothiophosphate, 73.1 parts (yield, 91.5%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-tri-methylthiophosphate, 3.7 parts (yield 5.0%). The phosphorus analysis of the aqueous layer showed that 1.2 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.5%. Example 2 The same reaction apparatus and caustic soda/water/methanol solution as used in Example 1 were used. To the 1st reaction vessel, 338.3 parts/hour of phosphorus sulfochloride and 661.8 parts/hour of the caustic soda/water/methanol solution were sent usually at constant rates. To the 2nd to 6th reaction vessels, 302.5 parts/hour, 140.6 parts/hour, 70.3 parts/hour, 15.4 parts/hour and 15.7 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.05 and 12.9, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -20°C, -20°C, -20°C, -20°C, -18°C and -15°C, respectively. The total of the average residence times was 72 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 72.2 parts (yield, 90.1%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 4.2 parts (yield, 5.6%). The phosphorus analysis of the aqueous layer showed that 1.6 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 3.4%. Example 3 A continuous reaction apparatus comprising 5 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 5th reaction vessels is 6:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.7 parts/hour of phosphorus sulfochloride and 983.6 parts/hour of a caustic soda/water/methanol solution (caustic soda concentration, 13.7%; methanol concentration, 72.1%; water content, 14.2%) were sent usually at constant rates. To the 2nd to 5th reaction vessels, 143.4 parts/hour, 71.9 parts/hour, 15.3 parts/hour and 15.2 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.11 and 13.9, respectively. The temperatures of the 1st to 5th reaction vessels were kept at -20°C, -21°C, -21°C, -22°C and -14°C, respectively. The total of the average residence times was 60 minutes. Thereafter, after-treatment and analysis were carried out in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 72.1 parts (yield, 90.1%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 4.8 parts (yield, 6.4%). The phosphorus analysis of the aqueous layer showed that 1.2 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.5%. Example 4 A continuous reaction apparatus comprising 6 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 6th reaction vessels is 6:3:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.3 parts/hour of phosphorus sulfochloride and 789.0 parts/hour of a caustic soda/water/methanol solution (caustic soda concentration, 16.51%; methanol concentration, 83.16%, water content, 0.33%) were sent usually at constant rates. To the 2nd to 6th reaction vessels, 79.0 parts/hour, 49.4 parts/hour, 40.5 parts/hour, 14.8 parts/hour and 14.8 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.05 and 12.9, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -21°C, -21°C, -21°C, -24°C, -14°C and -14°C, respectively. The total of the average residence times was 77 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 74.6 parts (yield, 93.3%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 3.0 parts (yield, 4.0%). The phosphorus analysis of the aqueous layer showed that 0.80 part of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 1.7%. Example 5 A continuous reaction apparatus comprising 5 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 5th reaction vessels is 6:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.7 parts/hour of phosphorus sulfochloride and 789.0 parts/hour of a caustic soda/water/methanol solution (caustic soda concentration, 16.51%; methanol concentration, 83.10%; water content, 0.33%) were sent usually at constant rates. To the 2nd to 5th reaction vessels, 114.5 parts/hour, 58.3 parts/hour, 12.8 parts/hour and 12.8 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.04 and 12.9, respectively. The temperatures of the 1st to 5th reaction vessels were kept at -21°C, -21°C, -21°C, -24°C and -14°C, respectively. The total of the average residence times was 65 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 5th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 74.0 parts (yield, 92.5%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 3.8 parts (yield, 5.1%). The phosphorus analysis of the aqueous layer showed that 0.66 part of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 1.4%. Example 6 The same reaction apparatus and caustic soda/water/methanol solution as used in Example 1 were used. To the 1st reaction vessel, 338.3 parts/hour of phosphorus sulfochloride and 649.0 parts/hour of the caustic soda/water/methanol solution were sent usually at constant rates. To the 2nd to 6th reaction vessels, 148.5 parts/hour, 116.6 parts/hour, 57.8 parts/hour, 13.0 parts/hour and 13.0 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.06 and 13.0, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -20°C, -20°C, -20°C, -20°C, -18°C and -15°C, respectively. The total of the average residence times was 72 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 74.0 parts (yield, 92.3%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 3.7 parts (yield, 5.0%). The phosphorus analysis of the aqueous layer showed that 1.3 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.7%. Examples 7 to 9 The procedure was carried out in the same manner as in Example 5 except that the temperatures of the 1st to 5th reaction vessels were changed as shown in Table 1. Example 10 A continuous reaction apparatus comprising 5 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 5th reaction vessels is 6:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.7 parts/hour of phosphorus sulfochloride and 933.7 parts/hour of a caustic soda/water/methanol solution (caustic soda concentration, 14.0%; methanol concentration, 74.5%; water content, 11.5%) were sent usually at constant rates. To the 2nd to 5th reaction vessels, 137.3 parts/hour, 68.1 parts/hour, 15.3 parts/hour and 15.3 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.05 and 13.6, respectively. The temperatures of the 1st to 5th reaction vessels were kept at -20°C, -21°C, -21°C, -22°C and -14°C, respectively. The total of the average residence times was 60 minutes. Thereafter, after-treatment and analysis were carried out in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 73.0 parts (yield, 91.2%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 4.2 parts (yield, 5.6%). The phosphorus analysis of the aqueous layer showed that 1.0 part of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.2%. Example 11 The same reaction apparatus and caustic soda/water/methanol solution as used in Example 4 were used. To the 1st reaction vessel, 338.3 parts/hour of phosphorus sulfochloride and 449.3 parts/hour of the caustic soda/water/methanol solution were sent usually at constant rates. To the 2nd to 6th reaction vessels, 291.3 parts/hour, 164.9 parts/hour, 57.3 parts/hour, 12.8 parts/hour and 12.8 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.06 and 12.9, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -20°C, -20°C, -20°C, -20°C, -18°C and -15°C, respectively. The total of the average residence times was 72 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-dimethylchlorothiophosphate, 71.3 parts (yield, 89.0%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 4.27 parts (yield, 5.7%). The phosphorus analysis of the aqueous layer showed that 2.0 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 4.3%. Example 12 A continuous reaction apparatus comprising 6 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 6th reaction vessels is 6:3:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel 337.3 parts/hour of phosphorus sulfochloride and 954.9 parts/hour of a caustic soda/water/methanol solution (caustic soda concentration, 13.6%; methanol concentration, 68.3%; water content, 18.1%) were sent usually at constant rates. To the 2nd to 6th reaction vessels, 95.7 parts/hour, 60.7 parts/hour, 48.3 parts/hour, 18.0 parts/hour and 18.0 parts/hour, respectively, of the caustic soda/water/methanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole methanol to phosphorus sulfochloride were 2.04 and 12.8, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -10°C, -9°C, -10°C, -11°C, -9°C and -9°C, respectively. The total of the average residence times was 82 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes, treated in the same manner as in Example 1 and analyzed by gas chromatography to find: O,O-dimethylchlorothiophosphate, 71.9 parts (yield, 90.0%); O-methyldichlorothiophosphate, 0.82 part (yield, 1.0%); and O,O,O-trimethylthiophosphate, 4.5 parts (yield, 6.0%). The phosphorus analysis of the aqueous layer showed that 1.4 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 3.0%. Example 13 A continuous reaction apparatus comprising 5 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 5th reaction vessels is 6:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.7 parts/hour of phosphorus sulfochloride and 1077.8 parts/hour of a caustic/water/ethanol solution (caustic soda concentration, 12.06%; ethanol concentration, 87.69%; water content, 0.25%) were sent usually at constant rates. To the 2nd to 5th reaction vessels, 156.5 parts/hour, 79.6 parts/hour, 17.5 parts/hour and 17.5 parts/hour, respectively, of the caustic soda/water/ethanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole ethanol to phosphorus sulfochloride were 2.04 and 12.9, respectively. The temperatures of the 1st to 5th reaction vessels were kept at -16°C, -19°C, -17°C, -15°C and -14°C, respectively. The total of the average residence times was 77.9 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 5th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-diethylchlorothiophosphate, 86.0 parts (yield, 91.5%); O-ethyldichlorothiophosphate, 0.89 part (yield, 1.0%); and O,O,O-triethylthiophosphate, 5.3 parts (yield, 5.5%). The phosphorus analysis of the aqueous layer showed that 0.95 part of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.0%. Example 14 A continuous reaction apparatus comprising 6 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 6th reaction vessels is 6:3:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.3 parts/hour of phosphorus sulfochloride and 1248.1 parts/hour of a caustic soda/water/ethanol solution (caustic soda concentration, 10.45%; ethanol concentration, 75.63%; water content, 13.91%) were sent usually at constant rates. To the 2nd to 6th reaction vessels, 125.0 parts/hour, 78.1 parts/hour, 64.0 parts/hour, 23.4 parts/hour and 23.4 parts/hour, respectively, of the caustic soda/water/ethanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole ethanol to phosphorus sulfochloride were 2.05 and 12.9, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -15°C, -20°C, -20°C, -17°C, -16°C and -15°C, respectively. The total of the average residence times was 98.2 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes, treated in the same manner as in Example 1 and analyzed by gas chromatography to find: O,O-diethylchlorothiophosphate, 84.9 parts (yield, 90.5%); O-ethyldichlorothiophosphate, 0.89 part (yield, 1.0%); and O,O,O-triethylthiophosphate, 5.5 parts (yield, 5.8%). The phosphorus analysis of the aqueous layer showed that 1.3 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.7%. Example 15 A continuous reaction apparatus comprising 5 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 5th reaction vessels is 6:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.7 parts/hour of phosphorus sulfochloride and 1365.4 parts/hour of a caustic soda/water/isopropanol solution (caustic soda concentration, 9.52%; isopropanol concentration, 90.28%; water content, 0.20%) were sent usually at constant rates. To the 2nd to 5th reaction vessels, 198.2 parts/hour, 100.8 parts/hour, 22.2 parts/hour and 22.2 parts/hour, respectively, of the caustic soda/water/isopropanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole isopropanol to phosphorus sulfochloride were 2.04 and 12.9, respectively. The temperatures of the 1st to 5th reaction vessels were kept at -15°C, -18°C, -16°C, -15°C and -14°C, respectively. The total of the average residence times was 77.9 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 5th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-diisopropylchlorothiophosphate, 99.1 parts (yield, 91.8%); O-isopropyldichlorothiophosphate, 0.96 part (yield, 1.0%); and O,O,O-triisopropylthiophosphate, 5.9 parts (yield, 5.1%). The phosphorus analysis of the aqueous layer showed that 0.99 part of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.1%. Example 16 A continuous reaction apparatus comprising 6 vessels of a form shown in Fig. 1 was used (volume ratio of the 1st to 6th reaction vessels is 6:3:2:2:3:3, but the net volumes somewhat change depending upon the stirring rate). To the 1st reaction vessel, 337.3 parts/hour of phosphorus sulfochloride and 1524.4 parts/hour of a caustic soda/water/isopropanol solution (caustic soda concentration, 8.52%, isopropanol concentration, 80.15%; water content, 11.34%) were sent usually at constant rates. To the 2nd to 6th reaction vessels, 152.6 parts/hour, 95.4 parts/hour, 78.2 parts/hour, 28.6 parts/hour and 28.6 parts/hour, respectively, of the caustic soda/water/isopropanol solution were sent usually at constant rates. The molar ratios of the whole caustic soda and the whole isopropanol to phosphorus sulfochloride were 2.04 and 12.8, respectively. The temperatures of the 1st to 6th reaction vessels were kept at -15°C, -20°C, -20°C, -17°C, -16°C and -15°C, respectively. The total of the average residence times was 98.2 minutes. After a stationary state was reached, the reaction solution from the overflow pipe mounted on the 6th reaction vessel was sampled for 15 minutes and treated and analyzed in the same manner as in Example 1 to find: O,O-diisopropylchlorothiophosphate, 97.8 parts (yield, 90.8%); O-isopropyldichlorothiophosphate, 0.96 part (yield, 1.0%); and O,O,O-triisopropylthiophosphate, 6.5 parts (yield, 5.6%). The phosphorus analysis of the aqueous layer showed that 1.2 parts of phosphorus, as converted to PO₄, was contained in the aqueous layer, the percent decomposition being 2.6%. The results of Examples 1 to 16 will be collectively shown in Tables 2, 3 and 4. Comparative Examples 1 to 10 Reaction was carried out under the conditions shown in Table 5 using the continuous reaction apparatus of a form shown in Fig. 1. 4. Brief Explanation of the Drawings: Fig. 1 shows a continuous reaction apparatus for practicing a process embodying the present invention in the form of flow sheet. In the figure, R₁ to R n represent reaction vessels, B represents a phosphorus sulfochloride supply pipes, A₁ to A n represent caustic soda/water/lower alcohol solution supply pipe, C₁ to C n represent overflow pipes and n represents an integer of from 3 to 8.

Claims: A continuous process for producing O,O-di-lower-alkylchlorothiophosphate by continuously reacting phosphorus sulfochloride with a lower alcohol in the presence of caustic soda according to a multi-stage reaction form comprising from 3 to 8 stages in which the following conditions are satisfied: (1) the amounts of caustic soda and lower alcohol used are from 2 to 2.2 moles and 10 moles or more, respectively, based on 1 mole of phosphorus sulfochloride, (2) the caustic soda, water and the lower alcohol are used as a caustic soda/water/lower alcohol solution, and the caustic soda concentration based on the weight of caustic soda and water in said solution, is from 30.0 to 99.5 wt.%, (3) to the first reaction stage is continuously supplied the whole amount of the phosphorus sulfochloride required and from 45 to 85 wt.% of each of the amounts of caustic soda and the lower alcohol respectively required; and to the second and subsequent reaction stages is continuously supplied the residual caustic soda and lower alcohol in divided portions so that the amounts supplied become substantially successively smaller toward the final reaction stage, (4) the temperature of the reaction system is -5°C or lower, and (5) the residence time in the reaction system is within 4 hours. A process for producing an O,O-di- C₁₋₃ alkylchlorothiophosphate in which phosphorus sulfochloride is reacted with a C₁₋₃ alcohol in the presence of caustic soda characterised in that (A) the process is a continuous process comprising at least three reaction stages, at least a portion of the reaction mixture from each stage other than the final stage passing to a subsequent said stage, (B) to a first said stage is supplied (i) the whole of the phosphorus sulfochloride, (ii) from 45 to 85 wt. % inclusive of the total amount of caustic soda, and (iii) from 45 to 85 wt. % inclusive of the total amount of C₁₋₃ alcohol, to be used in the reaction, (C) to each subsequent stage is supplied a part of the residual amounts of each of the caustic soda and C₁₋₃ alcohol for admixture with the reaction mixture passing from the preceding stage, (D) the amounts of the caustic soda and C₁₋₃ alcohol supplied to the final stage are each less than the respective amounts supplied to the first stage, (E) the total amount of caustic soda used in the reaction is from 2 to 2.2 moles per mole of phosphorus sulfochloride, (F) the total amount of C₁₋₃ alcohol used in the reaction is at least 10 moles per mole of phosphorus sulfochloride, (G) to each said stage, the caustic soda and C₁₋₃ alcohol are supplied as a caustic soda/C₁₋₃ alcohol/water solution, (H) at each said stage, the weight ratio of the caustic soda to the water in the caustic soda/C₁₋₃ alcohol/water solution is from 30:70 to 99.5:0.5 inclusive, (I) at each said stage, the temperature of reaction is not higher than - 5°C, and (J) the total residence time of each of the phosphorus sulfochloride and C 1-3 alkylchlorothiophosphate in the reaction system is not greater than 4 hours. A process according to Claim l or Claim 2, wherein the amount of the caustic soda and C 1-3 alcohol supplied to a given said stage is not substantially greater than the amount supplied to the preceding said stage. A process according to any preceding claim, wherein portions of the said said caustic soda/C 1-3 alcohol/water solution are supplied to respective said stages. A process according to any preceding claim, wherein from 65 to 85 wt. % inclusive of the respective total amounts of each of the caustic soda and C 1-3 alcohol are supplied to the first stage. A process according to any preceding claim, wherein the total amount of caustic soda used in the reaction is from 2.O5 to 2.l5 moles per mole of phosphorus sulfochloride. A process according to any preceding claim, wherein the total amount of C l-3 alcohol used in the reaction is from l2 to l4 moles per mole of phosphorus sulfochloride. A process according to any preceding claim, wherein at each stage, the concentration of the caustic soda in the said caustic soda/C 1-3 alcohol/water solution is from 4O to 99.5 wt. % inclusive. A process according to any preceding claim, wherein the said total residence time is not greater than 2 hours. A process according to any preceding claim, which is a 5-or 6-reaction stage process.

Inventors: HIOKI,TAKESHI, KAMEMOTO, KOICHI, OHSU, MOTOMASA, TOKUMARU, TOORU, UEDA, HIROSHI, YAHATA, MANABU
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1987
Main classification: C07F9
IPC codes: C07F9