Abstract:
An improvement in a process for producing 2-methylthiazole or 2,4-dimethylthiazole by reacting diethylamine, ethylidene-ethylamine or diisopropylamine with sulfur, the improvement comprising conducting said reaction in a reactor wherein a carbon layer has been formed on the inner surface of the walls of said reactor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field Of The Invention 
     The present invention relates to a process for producing 2-methylthiazole or 2,4-dimethylthiazole. 
     2. Description Of The Prior Art 
     The above-mentioned thiazoles are useful as intermediates for preparation of agricultural chemicals and pharmaceutical compounds. 2-methylthiazole is especially useful as an intermediate for preparation of many active ingredients of agricultural insecticides. Processes for producing 2-methylthiazole and 2,4-dimethylthiazole are known and have been disclosed in Japanese Pat. No. 26861/1968. The chemical reactions involved in these processes are as follows: ##STR1## In these known processes, a dialkylamine or dialkylimine is fed with nitrogen into a reactor where it mixes with a separate flow of sulfur fed with nitrogen. Upon mixing at 250° - 750° C., reaction ensues. In accordance with this conventional process, the yield of the object product is quite low, about 40% or less. In order to utilize these reactions on an industrial scale, it has been desired to improve the yield. Using conventional considerations, the present inventors have tried various catalysts or additives in the above-mentioned reactions. However, advantageous effects have not been found. Consequently, there remains a need for an improvement in the conventional process which is capable of increasing the resultant product yield. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of this invention to provide a process for producing 2-methylthiazole or 2,4-dimethylthiazole in higher yields. 
     Briefly, this and other objects of this invention, as will hereinafter become clear from the ensuing discussion, have been attained by providing a process for producing 2-methylthiazole or 2,4-dimethylthiazole comprising reacting diethylamine, ethylidene-ethylamine or diisopropylamine with sulfur in a reactor whose inner surface is coated with a carbon layer. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As can be seen below, when diethylamine, for example, is used as the starting material, the yield of 2-methylthiazole can be increased to a level higher than 60% so as to make the reaction very suitable for industrial operation. This is a typical result of the improvement of the present invention. 
     In accordance with the process of this invention, a carbon layer is formed on the inner surface of the reactor before the starting materials are fed therein. For example, the carbon layer may be formed on the inner surface of the reactor by feeding a hydrocarbon and oxygen or sulfur therein and reacting them. Thereafter, diethylamine, ethylidene-ethylamine or diisopropylamine and sulfur can be fed into the reactor which is covered with the carbon layer and reacted to produce 2-methylthiazole or 2,4-dimethylthiazole. 
     In the process of this invention, the reactor can be made of glass or metal and preferably is made of Pyrex glass or stainless steel. Suitable methods of forming the carbon layer on the inner surface of the reactor include the following. A hydrocarbon, e.g., n-hexane, toluene, and the like and sulfur or oxygen can be mixed in the reactor at 400°-500° C., whereby they will react and form a carbon layer by dehydrogenation. Alternatively, a trialkylboron can be decomposed by heating it in the reactor, thereby forming a carbon layer on the inner surface of the reactor. In industrial operation, it is advantageous to react the hydrocarbon with sulfur to form the carbon layer on the inner surface of the reactor and thereafter change the feed of the hydrocarbon to the appropriate amine feed, whereby the amine will react with sulfur to produce the object products. 
     The method used to form the carbon surface in the reactor is not critical and other conventional techniques may be used. 
     In order to separate the object product from the reaction mixture, well-known conventional methods such as distillation may be used. 
     The yields of 2-methylthiazole in the process of this invention were determined by varying the reaction temperature, the reaction time (retention time), the equivalent ratio of sulfur to the amine and the type of carrier gas used in the reaction of the amine with sulfur. The results are shown in Tables 1-4. The tests were conducted in accordance with the process and apparatus of Example 4 for the experiments of Tables 1, 2 and 3, and in accordance with the process and the apparatus of Example 1 for the experiments of Table 4. 
     
                       Table 1______________________________________Effect of reaction temperature on the yield of 2-methylthiazoleReaction temperature (° C)           Yield of 2-methylthiazole (%)______________________________________400             63.9430             66.2450             67.0500             58.7550             56.9______________________________________ Notes: Reaction time (retention time) : 4 seconds; Equivalent ratio of sulfur to diethylamine : 1.2 : 1. 
    
     
                       Table 2______________________________________Effect of reaction time on the yield of 2-methylthiazoleReaction time(retention time) (seconds)           Yield of 2-methylthiazole (%)______________________________________2               60.63               65.04               67.06               48.68               44.7______________________________________ Notes: Reaction temperature: 450° C; Equivalent ratio of sulfur to diethylamine: 1.2 : 1. 
    
     
                       Table 3______________________________________ Effect of the equivalent ratio of sulfur to diethylamineon the yield of 2-methylthiazoleEquivalent ratio of sulfur to             Yield of 2-methylthiazolediethylamine      (%)______________________________________0.8 : 1           51.31  : 1            58.51.1 : 1           63.11.2 : 1           67.01.4 : 1           59.8______________________________________ Notes: Reaction temperature: 450° C; Reaction time: 4 seconds. 
    
     
                       Table 4______________________________________Effect of type of carrier gas on the yield of 2-methylthiazoleDiethylamine mixed       Sulfur mixed gasgas fluid   fluidType of  Flow rate           Type of  Flow rate of                              Yieldcarrier  of carrier           carrier  carrier gas                              of 2-methyl-gas    gas      gas      (l/hr)    thiazole (%)______________________________________nitrogen  40 1/hr. nitrogen 40        60.6&#34;      &#34;        H.sub.2 S                    40        62.0benzene  330 g/hr.           nitrogen 40        61.0toluene  330 g/hr.           &#34;        40        61.5none   --       &#34;        40        54.7______________________________________ Notes: Reaction temperature: 500° C; Reaction time: 4 seconds; Equivalent ratio of sulfur to diethylamine: 1.1 : 1. 
    
     These results indicate the preferred reaction conditions as follows. From the data of Table 1, the reaction temperature is preferred to be in the range of 400°-550° C., especially 400°-450° C., in order to attain the highest yield. When it is lower than 400° C., the amount of the unreacted material is relatively high and when it is higher than 550° C., the amounts of byproducts of thiazoles, acetonitrile, and carbon disulfide are high. From the data of Table 2, the reaction time (retention time in the reactor) is preferred to be in the range of 2- 8 seconds, especially 2- 4 seconds. From the data of Table 3, the equivalent ratio of sulfur to diethylamine is preferred to be in the range of 0.8:1- 1.4:1, especially 1.1:1- 1.2:1. From the data of Table 4, it is preferable to conduct the reaction in an atmosphere of an inert gas, and nitrogen, benzene, toluene and hydrogen sulfide are suitable carrier gases. The reactions of diethylamine with sulfur have been illustrated in detail in the above data. However, the same results and conclusions can be applied to the reactions of ethylidene-ethylamine or diisopropylamine with sulfur. 
    
    
     Having generally described the invention, a more complete understanding can be obtained by reference to certain specific examples, which are provided for purposes of illustration only and are not intended to be limiting unless otherwise specified. 
     EXAMPLE 1 
     In a vaporizer maintained at 400° C., n-hexane was fed at a rate of 700 g/hr., and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. In another vaporizer maintained at 580° C., sulfur was fed at a rate of 520 g/hr. (a molar ratio of 20 relative to n-hexane), and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. Both of the mixed gases were fed into a reactor made of Pyrex glass (having an inner diameter of 75 mm and a length of 1000 mm) to mix them. The mixture was passed through the reactor at 450°-500° C. using 10 seconds retention time for a total of about 30 minutes, whereby a carbon layer was formed on the inner surface of the reactor. Then, 2-methylthiazole was produced by the reaction of diethylamine with sulfur. In the vaporizer maintained at 400° C., diethylamine was fed at a rate of 750  g/hr., and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. 
     In another vaporizer maintained at 580° C., sulfur was fed at a rate of 1,600 g/hr. (an equivalent ratio of 1.2 relative to diethylamine) and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. Both of the mixed gases were fed into the reactor (having a carbon layer already formed on its inner surface) to react them at 450° - 500° C. using a retention time of 4 seconds for a total of 1 hour. A part of the reaction mixture was sampled and was analyzed by gas chromatography. The results are shown in Table 5. The conditions used in the gas chromatographic analysis are as follows: 
     
         ______________________________________Type of gas chromatograph:            GC-3AH            (manufactured by Shimazu            Seisakusho,K.K.)Length of column 1 mTemperature of column:            180° C.Filler of column:            Porapak-Q (manufactured by            Nishio Kogyo K.K.)Carrier gas:     heliumPressure of carrier gas:            1 kg/cm.sup.2 G______________________________________ 
    
     
                       Table 5______________________________________Products     Yield per 1 hour (g)                       Yield (%)______________________________________2-methylthiazole        670            65.9thiazole     39.3            4.5acetonitrile 29.5            7.0carbon disulfite        30.0           --______________________________________Note: The yield was measured by gas chromatography and -the molar yieldis based on the amount of diethylamine used. - ##STR2## 
    
     The process for forming the carbon layer on the inner surface of the reactor of Example 1 was repeated using the same reactor except for feeding air at a rate of 300 liter/hr. instead of sulfur. The reaction of diethylamine with sulfur and the gas chromatographic analysis were conducted under the same conditions as used in Example 1. The yield of 2-methylthiazole was 60.5%. 
     EXAMPLE 3 
     The process for forming the carbon layer on the inner surface of the reactor of Example 1 was repeated using the same reactor except for feeding a tetrahydrofuran solution of tri-n-decaneboron (30 wt.%) at a rate of 700 g/hr. into a vaporizer maintained at 350° C., and for feeding the gas into the reactor at 400° C. for 2 hours to form a carbon layer. The reaction and the analysis of Example 1 were repeated in the reactor using the same conditions. The yield of 2-methylthiazole was 63.2%. 
     EXAMPLE 4 
     The process for forming a carbon layer on the inner surface of the reactor of Example 1 was repeated except for using a reactor made of stainless steel (SUS 27) (having an inner diameter of 75 mm and a length of 1000 mm) instead of the reactor made of Pyrex glass. The reaction and the analysis of Example 1 were repeated in the reactor using the same conditions. The yield of 2-methylthiazole was 63.2%. 
     EXAMPLE 5 
     The process for forming the carbon layer on the inner surface of the reactor of Example 1 was repeated except for using a reactor made of stainless steel (SUS 27) and using toluene instead of n-hexane (an equivalent ratio of 2 relative to sulfur). The reaction and the analysis of Example 1 were repeated in the reactor using the same conditions. The yield of 2-methylthiazole was 61.1%. 
     EXAMPLE 6 
     A carbon layer was formed on the inner surface of the reactor in accordance with the process of Example 4. Into a vaporizer maintained at 400° C., a benzene solution of 28 wt. % ethylidene-ethylamine was fed at a rate of 1080 g/hr. and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. Into another vaporizer maintained at 580° C., sulfur was fed at a rate of 490 g/hr. and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. Both of the mixed gases were fed into the reactor at 450° - 500° C. under a retention time of 8 seconds and reacted for a total of 1 hour. In accordance with the method of Example 1, the reaction mixture was analyzed showing that 2-methylthiazole was obtained at a rate of 257.9 g/hr. The yield was 61.2%. 
     REFERENCE EXAMPLE 1 
     The process of Example 1 was repeated using the same conditions and the same analysis except for using a reactor made of Pyrex glass without formation of a carbon layer on its inner surface. The yield of 2-methylthiazole was 45.8%. 
     REFERENCE EXAMPLE 2 
     The process of Example 4 was repeated using the same conditions and the same analysis except for using a reactor made of stainless steel without formation of a carbon layer on its inner surface. The yield of 2-methylthiazole was 44.4%. 
     EXAMPLE 7 
     In a vaporizer maintained at 400° C., n-hexane was fed at a rate of 700 g/hr. and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. On the other hand, in another vaporizer maintained at 580° C., sulfur was fed at a rate of 520 g/hr. (a molar ratio of 20 relative to n-hexane) and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. 
     Both of the mixed gases were fed into a reactor made of stainless steel (SUS 27) (having an inner diameter of 75 mm and a length of 1000 mm) at 450° - 500° C. using a retention time of 10 seconds for a total of about 30 minutes to form a carbon layer on the inner surface of the reactor. The feed of n-hexane was stopped and replaced by a feed of diisopropylamine to react the latter. 
     In a vaporizer maintained at 400° C., diisopropylamine was fed at a rate of 955 g/hr. and nitrogen gas was fed at a rate of 40 liter/hr. to form a mixed gas. Also, in a vaporizer maintained at 580° C., sulfur was fed at a rate of 1574 g/hr. (1.3 equivalents relative to diisopropylamine) and nitrogen was fed at a rate of 40 liter/hr. to form a mixed gas. Both of the mixed gases were fed into the reactor at 450° C. using a retention time of 4 seconds for reaction for a total of about 1 hour. A part of the reaction mixture was sampled and analyzed by gas chromatography. The amount of 2,4-dimethylthiazole formed was 438 g giving a yield of 59.0% (based on diisopropylamine). The conditions used in the gas chromatographic analysis are as follows: 
     
         ______________________________________Type of gas chromatograph:           GC-4AH           (manufactured by Shimazu           Seisakusho K.K.)Length of column:           3 mTemperature of column:           140° CFiller of column:           polyethyleneglycol 20 wt.% on a           carrier of zeolite 545.Carrier gas:    heliumPressure of carrier gas:           1 kg/cm.sup.2 G.______________________________________ 
    
     EXAMPLES 8, 9 and 10 
     The process of Example 7 was repeated using the same apparatus except for varying the reaction temperature, the reaction time and the equivalent ratio of sulfur to isopropylamine. In accordance with the method of Example 7, an analysis for 2,4-dimethylthiazole was conducted. The results are shown in Table 6, together with the results of Example 7. 
     
                       Table 6______________________________________                      Equivalent  Reaction   Reaction ratio  Temperature             time     of sulfur to                                 YieldEx.    (° C.)             (sec)    diisopropylamine                                 (%)______________________________________7      450        4        1 : 1.3    59.08      450        6        1 : 1.2    53.69      500        4        1 : 1.2    56.8 10    550        4        1 : 1.2    53.0______________________________________ 
    
     REFERENCE EXAMPLE 3 
     The process of Example 7 was repeated using the same conditions and the same analysis except for using a reactor made of stainless steel without formation of a carbon layer on its inner surface. The yield of 2,4-dimethylthiazole was 41.0%. 
     Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.