JPS6249259B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying crude dinitrotoluene, and more particularly to the purification of crude dinitrotoluene obtained by nitrating toluene with nitric acid. Dinitrotoluene is known as a raw material for producing tolylene diisocyanate, which is a raw material for polyurethane, and is usually produced by nitrating toluene in a mixed acid consisting of nitric acid and sulfuric acid. In this nitration of toluene, usually 2,4-dinitrotoluene (hereinafter referred to as 2,4-form) and 2,6-dinitrotoluene (hereinafter referred to as 2,6-form) due to the orientation of the nitro group. is mainly obtained, but other dinitrotoluenes other than 2,4- and 2,6-isomers such as 2,3- and 3,4-dinitrotoluene (hereinafter referred to as isomers) are also obtained in about 5 Contains about %. However, isomers other than 2,4- and 2,6-isomers cause harzization during the production process of tolylene diisocyanate, which not only hinders the reaction but also 2,4-isomers.
This method has the disadvantage that the yield of tolylene diisocyanate decreases because the halzation occurs by involving the 2,6-isomer and the 2,6-isomer. Therefore, several methods have been proposed to improve the purity of 2,4- and 2,6-isomers by purifying crude dinitrotoluene obtained by nitration of toluene, but none of them can be said to be sufficient. There's no way. In view of the above circumstances, the present inventors investigated various methods for selectively removing isomers other than 2,4-isomer and 2,6-isomer from crude dinitrotoluene, and found that crude dinitrotoluene was The present invention was completed based on the knowledge that isomers can be separated well by treating the substance with a compound and extracting the treated substance with water. That is, the gist of the present invention is to contact the crude dinitrotoluene obtained by nitrating toluene with nitric acid in a liquid state with at least one compound selected from hydrazines, semicarbazides, hydroxylamines, and ureas to be treated. The present invention relates to a method for purifying crude dinitrotoluene, which is characterized by extracting the dinitrotoluene with water. The present invention will be explained in detail below. Crude dinitrotoluene, which is the object of the present invention, is usually obtained by nitrating toluene in a mixed acid consisting of nitric acid and sulfuric acid. It contains about 2 to 8% of In the present invention, it is essential to contact crude dinitrotoluene with at least one compound selected from hydrazines, semicarbazides, hydroxylamines, and ureas.
Specific examples of these compounds include hydrazine, phenylhydrazine, methylhydrazine,
semicarbazide, 4-phenyl semicarbazide,
4-Methyl semicarbazide, hydroxylamine, N-phenylhydroxylamine, urea, N
- methylurea, etc., and these compounds may be used in the form of salts such as, for example, hydrochlorides or sulfates. The amount of the above compound used is usually 2 to 100 times, preferably 5 to 50 times, the amount of the isomer contained in the crude dinitrotoluene. If the amount used is too small, the isomers cannot be separated well, and if the amount is too large, the effect remains the same and it is not economical. The contact treatment of the crude dinitrotoluene with the above-mentioned compound is carried out with the crude dinitrotoluene in liquid form, ie in a molten state or as a solution in an organic solvent, usually under stirring.
When conducting in the molten state, the melting point of crude dinitrotoluene (56 to
57℃) or higher. Further, when the reaction is carried out in a solution state, it is carried out in an organic solvent that is not miscible with water, such as benzene, toluene, or chlorobenzene. The temperature of the contact treatment is usually in the range of 30 to 200°C, preferably 70 to 100°C, and may be carried out under pressure. Further, the processing time is usually about 1 to 15 hours. When water or an organic solvent is used, the amount of the solvent used is usually 1 to 10 times the weight of crude dinitrotoluene. The pH of the mixture during contact treatment is usually maintained at 8 to 14, preferably 9 to 13. If the pH is too low, the reaction rate of isomers will be slow, and if the pH is too high, the reaction rate of isomers will be low. and 2,6-isomers are also undesirable because they may cause reactions. For example, this PH adjustment is
This can be done by adding an alkaline substance such as caustic soda or soda carbonate. The mixture after the contact treatment is then extracted with water to transfer the isomers converted into water-soluble compounds to the aqueous phase,
It is separated from an organic phase containing 2,4- and 2,6-isomers. Furthermore, when water is used during the above-mentioned contact treatment, it is not necessarily necessary to newly add water after the treatment, and the mixture after the treatment may be separated into liquids as it is. Isomers can be efficiently separated by washing the organic phase recovered by liquid separation with, for example, acidic water and/or hot water. Furthermore, when an organic solvent is used during the contact treatment, the organic phase can be heated, for example, and the organic solvent can be distilled off to obtain purified 2,4- and 2,6-isomers. A preferred embodiment of the present invention is, for example, a method in which a mixture of crude dinitrotoluene and water is brought into contact with the above-mentioned compound under stirring at a temperature above the melting point of dinitrotoluene, and then this treated material is directly separated into liquids. . This method is preferable in terms of operation and isomer removal efficiency. As described above, according to the present invention, by bringing crude dinitrotoluene into contact with a specific compound, the isomer can be changed into a water-soluble compound and removed, and the 2,4-isomer and 2,6-isomer can be removed. There will be no loss. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example In a 500 ml flask equipped with a stirrer and a heating device, crude dinitrotoluene (75.76% of 2,4-isomer, 2,6-isomer) obtained by nitration of toluene was placed.
18.29%, isomer 5.95%) and 205 g of water were added, and a predetermined amount of the compound shown in Table 1 was added thereto.
Furthermore, the PH of the mixture was adjusted to the PH shown in Table 1 with a caustic soda or sodium carbonate aqueous solution, and then the mixture was stirred at the temperature and time shown in Table 1. The treated mixture was separated into an aqueous phase and an oil phase, and the oil phase was washed three times with 100 ml of hot water at 80°C. Regarding the purified dinitrotoluene thus obtained, the content of isomers, 2.4-isomer, 2.6-isomer, 2.6-isomer, etc.
- When the recovery rate of the body was determined, the results shown in Table 1 were obtained. 【table】

Claims (1)

[Scope of Claims] 1 Crude dinitrotoluene obtained by nitrating toluene with nitric acid is brought into contact with at least one compound selected from hydrazines, semicarbazides, hydroxylamines, and ureas in a liquid state, and the processed material is A method for purifying crude dinitrotoluene, characterized by extracting it with water. 2. A mixture of crude dinitrotoluene and water is heated above the melting temperature of dinitrotoluene to dissolve hydrazines,
A method for purifying crude dinitrotoluene, which comprises contacting with at least one compound selected from semicarbazides, hydroxylamines, and ureas, and then separating an aqueous phase.