SU1114677A1 - Process for preparing benzo-2,1,3-thiadiazole - Google Patents

Abstract

METHOD FOR OBTAINING BENZO-2,1,3-TIADIAZOLE by reacting ortho-phenyl nediamine with sulfur dioxide in a solvent medium, followed by separation of the target product, characterized in that, to increase the yield of the target product, pyridine is used as a solvent and the process is carried out to increase the mass of the reaction mixture 2.25-2.45 times. (L

Description

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05 1 -h | 11 The invention relates to organic chemistry, specifically to a method for producing benzo-2,1,3, -diadiazole, which is used as a starting reagent for the synthesis of derivatives of this row and which can be used as a flotation reagent to obtain an enriched 90% lead concentrate from lead-containing polymetallic ores, for example, galena. A known method for the preparation of benzo-2, 1,3-thiadiazole (basic object), according to which benzo-2,1,3-thiadisol is obtained by the interaction of ort o -phenylenediamine with a mixture consisting of benzene as a solvent, a condensing agent thionyl chloride and triethylamine - to bind the liberated hydrogen chloride. The process is carried out at a molar ratio of ortho-phenylenediamine, chlorine, thionyl, triethylamine and benzene 1: 2.54: 4: 67.6. To complete the process, it is necessary to heat the reaction mixture at 80–100 ° C for hours. The extraction of the target product includes the following operations: separation from the final product of triethyl amine hydrochloride and washing it with benzene, distilling benzene from the reaction mass; technical dilution in the mass and retention of this mass at low temperature for 12 h; separation of the target product from water, purification of the product by distillation, which is performed twice. The yield of the target product after the operations performed is 70% of the theoretical value, calculated as ortho-phenylenediamine. The disadvantages of this method are the duration of the process, which is associated with the duration of the operations for the synthesis and release of benzo-2, 1,3-thiadiazole, high consumption of reagents, the use of a large amount of flammable benzene, as well as the high energy intensity of the process associated with heating. reaction mixture, distilling off the solvent and purifying the target product. These deficiencies lead to a high cost of benz -2,1,3-thiadiazole. There is also known a method of producing benzo-2,1,3-thiadiazole by reacting equimolecular amounts of ortho-phenylenediamine, a condensing agent of GO - :: lithium thionyl and a water-removing agent - anhydrous aluminum chloride - in a solvent - pyridine, which simultaneously serves as release of hydrogen chloride. The addition of thionyl chloride to the reaction mass is accompanied by a large release of heat and hydrogen chloride, therefore thionyl chloride is added at such a rate that the process temperature is maintained between 35-45 ° C. The isolation of the desired product is not difficult. The reaction mixture is acidified with hydrochloric acid, the separated product is filtered, washed with water, dried and recrystallized from alcohol. The yield of the target product is 8082% of theoretical, based on Ortho-phenylenediamine 2. The disadvantages of the method include the need to maintain the temperature of the reaction mass with the addition of thionyl chloride within 35-45 ° C, which requires good mixing of the reaction mass and constant attention of the apparatchik, and with large loads of orgo-phenylenediamine and thionyl chloride causes a longer process time. , it is necessary to use anhydrous aluminum chloride, which must be weighed in an airtight container, as it smokes in air, attracts moisture, and which, when dissolved in a feast dine increases until reaction mass temperature that requires cooling the solution to. Using a 15-fold excess of pyridine increases the cost of the target product, and the need to recrystallize benzo-2,1,3-thiadiazole from alcohol takes time and increases the cost of the product. I A known method for producing benzo-2, 1,3-thiadiazole by reacting Ortho-phenylenediamine with a mixture consisting of a condensing agent of sulfur dioxide - and the solvent - dry dimethylformamide. To complete the process, it is necessary to heat the reaction mass at 70-75 ° C for 8 hours while at the same time filling it with sulfur dioxide. The consumption of sulfur dioxide in this method is not specified. The ratio of ortho-phenylenediamine and dimethylformamide is 1:22 mol.

The isolation of the target product includes the following stages: dilution of the reaction mass with water and double extraction with benzene, washing the benzene extracts with water from traces of e; 1 methyl formamide and removal of the solvent, recrystallization of the target product from alcohol. After the operation, 49% of the theoretical value of the desired product, calculated on Opto-phenylenediamine z |.

The disadvantages of this method are the duration of the process, which is associated with the duration of the operations for the synthesis and isolation of benzo-2, 1,3-thiadiazole, the large capacity of the process associated with the heating of the reaction mass and the distillation of the solvent, as well as the need for dimethylformamide. pre-drying. The yield of the target product is relatively low (49%),

The purpose of the invention is to increase the yield of the target product.

This goal is achieved by the fact that, according to the method for obtaining benzo-2,1,3-thiadiazole by reacting ortho-phenylenediamine with sulfur dioxide in a solvent, followed by extraction of the target product, pyridine is used as a solvent and the process can be increased up to 2.25 -2.45. Studies have shown that sulfur dioxide and pyridine, in addition to performing their known functions, namely, as a condensing agent (SO) and solvent (pyridine), manifest a new feature - water removal ayuschego agent.

In the reaction in question, along with the formation of the target product, pyridine sulfo-dioxide is formed from pyridine and sulfur dioxide, which exhibits water-removing properties in this reaction and therefore shifts the equilibrium process that takes place in the system (sulfur dioxide dimethylformamide) towards quantitative formation of the target product and gives the ability to carry out the process without introducing a special water-removing agent (for example, anhydrous aluminum chloride), which provides simplification and cheapening

process and increase chig.toty target product.

The method is carried out as follows.

Sulfur dioxide is bubbled into the solution of ortho-phenylenediamine in pyridine at room temperature and the ratio of ortho-phenylenediamine and pyridine 1: 8 to 2.25-2.45 times the mass of the reaction mixture, after which the desired product is made by diluting the reaction mixture water at a volume ratio of the reaction mixture and water 1: 2.5-3, followed by filtering the precipitate.

Example 1. 2g (0.0185 mol) of ortho-phenylenediamine is dissolved in 11.4 ml (11.7 g, 0.148 mol) of pyridine at room temperature. The solution (13.7 g) is saturated with sulfur dioxide for 3 hours before the weight of the reaction mixture increases by 17.25 g, i.e. 2.25 times. The reaction mixture is introduced into 35 ml of water and the precipitated precipitate is filtered off, washed with 10 ml of water and dried. 1.88 g (74.90%) of benzo-2,1,3-thiadiazole are obtained, m.p. 43-44 C. The substance does not depress the melting point with substances obtained by the known method. R 0.72 (Silufol UV-254, acetone: water system 1: 1, occurring in iodine vapor).

Example 2. 2g (0.0185 mol) of OrT-phenylenediamine is dissolved in 11.4 ml (11.7 g, 0.148 mol) of pyridine at room temperature. The solution (13.7 g) is saturated with sulfur dioxide for 3.5 hours before the weight of the reaction mixture is increased by 18.65 g, i.e. 2.36 times. Pour the mixture into 40 ml of water and filter the precipitate filtered off, washed with 10 ml of water and dried. Get 2 g (80%) of benzo-2,1, 3-thiadiazole, so pl. 43-44 ° Ci, 72 (Silufoi UV-254, acetone: water system 1: 1, occurring in iodine vapor). The Rf substances of examples 1 and 2, as well as benzo-2,1,3-thiadiazole, obtained by the known procedure, coincide.

Example 3. 2g (0.0185 mol) of ortho-phenylenediamine is dissolved in 11.4 ml (11.7 g; 0.148 mol) pyridine at room temperature. The solution (13.7 g) is saturated with sulfur dioxide for 4 hours before increasing the mass of the reaction

mixtures of 20 g, i.e. in times. The mixture is poured onto 45 ml of water, the precipitate formed is filtered off, washed with 10 ml of water and dried. Get 2,11 g (84,06%) benzo-2,1,3-thiadiazole, so pl. 43-44 ° C; , 72 (Silufol UV-254, system acetone: water 1: 1, occurring in iodine feasts). R substances in examples 1-3, as well as substances obtained by known methods, the same.

It should be noted that the yield of benzo-2, 1,3-thiadiazole in all examples can be increased by 8-12%, if you carry out 3-fold extraction of filtrates with chloroform (20 ml).

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Thus, the application of the proposed method in comparison with the prototype simplifies the process, since it is not necessary to maintain a certain reaction temperature; It is not necessary to mix the reaction mass, and, in comparison with the basic object, along with the above advantages, it allows to increase the process safety technique by replacing the flammable benzene with pyridine.

Claims (1)

METHOD FOR PRODUCING BENZO-2,1,3-THIADIAZOLE by reacting ortho-phenyl ndiamine with sulfur dioxide in a solvent medium followed by isolation of the target product, characterized in that, in order to increase the yield of the target product, pyridine is used as a solvent and the process is carried out to increase the mass of the reaction mixture is 2.25-2.45 times. SU, 1114677> 1 1I14677