RU2368598C1 - Combined method of obtaining 4-amino-2,6-dinitro- and 2,4,6-triaminotoluenes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to organic chemistry and particularly to a combined method of obtaining 4-amino-2,6-dinitro- and 2,4,6-triaminotoluenes, which involves reacting a solution of 2,4,6-triaminotoluene in aliphatic alcohol with titanium trichloride in aqueous solution of hydrochloric acid in molar ratio of 2,4,6-triaminotoluene to titanium trichloride equal to 1:(8-9), with subsequent removal of aliphatic alcohol in a vacuum and extraction of the obtained 4-amino-2,6-dinitrotoluene in form of its hydrochloride through filtration. The filtrate undergoes electrochemical reduction in a diaphragm cell, which has a cathode and an anode. The catholyte is subsequently evaporated in a vacuum at temperature 50-60°C and the formed 2,4,6-triaminotoluene is extracted in form of its trihydrochloride through filtration with subsequent return of the obtained filtrate to the reaction.

EFFECT: proposed method is not explosive and virtually produces no wastes.

2 cl, 4 ex

Description

The present invention relates to the field of organic chemistry and relates, in particular, to a combined method for producing 4-amino-2,6-dinitro- and 2,4,6-triaminotoluenes. These compounds are potentially of undoubted interest in terms of their use as monomers, starting compounds in the synthesis of dyes and various biologically active compounds. Currently, there is great interest in aromatic condensation polymers belonging to the class of heat-resistant compounds, including the use of affordable and cheap raw materials, such as 2,4,6-trinitrotoluene. In this regard, the possibilities of both complete (all three nitro groups) and mono-reduction of 2,4,6-trinitrotoluene to p- and o-isomers of aminodinitrotoluene with the aim of producing polyamides and polyimides with aliphatic and aromatic groups with improved characteristics compared with appropriate unsubstituted polymers (A.L. Rusanov, L.G. Komarova, D.Yu. Likhachev, S.A. Shevelev, V.A. Tartakovsky "Condensation monomers and polymers based on 2,4,6-trinitrotoluene." Success Chemistry, 2003, 72 (10), 1011-1024).

The literature describes methods for producing both 4-amino-2,6-dinitrotoluene (p-isomer) and 2,4,6-triaminotoluene (TAT) by reduction of 2,4,6-trinitrotoluene (TNT), using, as a rule, three types of reduction: chemical, catalytic and electrochemical. A known method for producing the p-isomer by mono-reduction of 2,4,6-trinitrotoluene, based on the action of H ₂ S as a reducing agent on a substrate dissolved in dioxane in the presence of NH ₄ OH. The yield of the p-isomer is 44% (ATNielsen, LSKristian, APChafin, WSWilson. Synthetic Routes to Aminodinitrotoluenes, J. Org. Chem., 1994, v. 59, p.1714). The disadvantages of the method are the low yield of the target product and a significant amount of waste.

There is also a method for producing the p-isomer by preparative electroreduction of 2,4,6-trinitrotoluene in a potentiostatic mode in an electrolyzer with a cathode and anode spaces separated by a cation exchange membrane (V.N. Leibzon, A.P. Churilina, M.Yu. Leonova, L . V.Mikhalchenko, A.Kh.Shakhnes “Regioselectivity of partial chemical and electrochemical reduction of 2,4,6-trinitrotoluene.” Electrochemistry, 2000, 36, No. 2, 190-193). Catholyte - 95% MeOH containing 2.5% hydrochloric acid, anolyte - 7% sulfuric acid. Mercury was used as the cathode material, and platinum or platinum titanium was used as the anode material. It was shown that during the electroreduction of 2,4,6-trinitrotoluene under the given conditions, hydroxylamine derivatives are formed, after which the aqueous reduction with a hydrochloric acid solution of TiCl ₃ results in a mixture of the p-isomer and o-isomer with a yield of 75.5% and 24.5%, respectively, separation which is a rather time-consuming process, accompanied by the formation of a large amount of waste.

As for 2,4,6-triaminotoluene, the literature describes a method for its preparation by reduction of 2,4,6-trinitrotoluene with iron in concentrated hydrochloric acid in the presence of certain amounts of SnCI ₂ to accelerate the recovery and improve the quality of the resulting triamine derivative (V.Chimatal, ZJAllan, F.Musik "Aromatische diazo- und Azjverbindungen XXXIX. Darstellung des Tritriazobenzols und seiner derivate". Coll. Czech. Chem. Commun., 1959, 24, 2, 484-493). However, from a technological point of view, it is difficult to find it satisfactory due to the formation of a significant amount of waste. (It is necessary to spend 0.5 kg of SnCI ₂ and about 4 kg of powdered iron to recover 1 kg of trinitrotoluene; the costs of conc. HCl are high.) The toxicity of tin salts must also be taken into account.

A completely technologically advanced method for producing 2,4,6-triaminotoluene in the form of a free amine readily oxidizable in air with a yield of 95% by catalytic hydrogenation of 2,4,6-trinitrotoluene in ethyl acetate (M. Lubber, S.Sholles, Proc.23-rd Intern. Annual Congr.of ICT, Germany, Kariruhe, 1992, 81). However, the method is fire and explosive, which seems to be a significant drawback when working with explosive compounds.

A known method for the electrosynthesis of 2,4,6-triaminotoluene using a carrier mediator - titanium salts (VNLeibzon, LVMikhalchenko, M.Vu.Leonova, and VPGultyai "Electrochemical reduction of aromatic polynitrocompounds". Abstracts of 197-th Meeting of Toronto, May 14 -18, 2000, Vol.2000-1, Abstract No. 1069, Electrochemical Reduction of aromatic Polynitrocompounds). The yield of the target product is 95-97%. The following recovery parameters are proposed: an electrolyzer with a cation exchange membrane separating the cathode and anode spaces (cathode — lead, anode — platinum or platinum titanium), current density 400–500 Am ^{– 2} , anolyte — 5–7% sulfuric acid, catholyte — aqueous solution hydrochloric acid containing 6-12% (of theoretically necessary) TiCl ₃ . At 100% conversion of 2,4,6-trinitrotoluene, the yield of 2,4,6-triaminotoluene in the form of its trichlorohydrate in the substance is 95%.

However, to date, a combined method for the preparation of both 4-amino-2,6-dinitrotoluene and 2,4,6-triaminotoluene has not been described.

The objective of the present invention is to provide a waste-free combined method for producing 4-amino-2,6-dinitro- and 2,4,6-triaminotoluenes while maintaining a high yield of target products and using a simplified scheme for their preparation.

The problem is achieved by the proposed combined method, namely, that a solution of 2,4,6-trinitrotoluene in aliphatic alcohol is reacted with titanium trichloride in an aqueous solution of hydrochloric acid at a molar ratio of 2,4,6-trinitrotoluene and titanium trichloride equal to 1- (8-9), followed by removal of the aliphatic alcohol in vacuo and isolation of the resulting 4-amino-2,6-dinitrotoluene as its hydrochloride by filtration, and the filtrate thus obtained is subjected to electrochemical reduction injection in a diaphragm electrolyzer equipped with a cathode and anode, followed by evaporation of the catholyte in vacuum at a temperature of 50-60 ° C and isolating the 2,4,6-triaminotoluene formed in the form of its trichlorohydrate by filtration, followed by returning the obtained filtrate back to the reaction.

As the aliphatic alcohol, for example, methyl or ethyl alcohols are used. Electroreduction is carried out in galvanostatic mode using an electrolyzer with a volume of 0.15 liters. Anolyte - 15-20 ml of a 5-7% solution of N ₂ SO ₄ is placed in a glass from a cation exchange membrane located in the center of the cell and fixed in the electrolyzer using a lid of fluoroplastic with holes. Lead (especially pure, S-OOOO grade or technical grade S-1) is used as the cathode, and the anode is a platinum mesh or platinum titanium.

The process proceeds as follows:

At the stage of chemical reduction, always more than 8 molar equivalents of titanium trichloride are always added so that the starting compound does not remain in the reaction mixture. This condition is important to observe both in terms of the purity of the target compound, and to ensure explosion safety when processing the reaction mixture (which is especially important in the case of 2,4,6-trinitrotoluene).

In the interaction of 2,4,6-trinitrotoluene with titanium trichloride in a molar ratio of 1 to 8-9, two monomers of monoamines and a certain amount of diamine derivatives are formed. In this case, titanium passes into the tetravalent state. When the aliphatic alcohol is removed, the p-isomer precipitates without impurity of the corresponding o-isomer. In this case, it is possible to isolate up to 60% of the pure p-isomer from the reaction medium.

After separation of the p-amine salt, the filtrate contains the following (scheme): titanium tetrachloride, o-isomer, isomeric diamine derivatives and p-amine remaining in the solution. This difficult-to-separate mixture of organic substances has never before been used as a starting material for the preparation of 2,4,6-triaminotoluene. In the proposed method, the solution is sent to the electrolyzer and electroreduction is carried out to hydrogen evolution. The catholyte is evaporated under vacuum until a precipitate of 2,4,6-triaminotoluene trichlorohydrate appears, then the solution is cooled to -5 ° C, the precipitate is filtered off, washed with a cooled solution of 7% hydrochloric acid in methyl alcohol and, after drying, analytically pure trichlorohydrate 2,4 is obtained. 6-triaminotoluene.

If necessary, for example, to increase the yield of the secreted 2,4,6-triaminotoluene salt in the filtrate obtained after isolation of 4-amino-2,6-dinitrotoluene hydrochloride and which is then sent to the cathode space of the electrolyzer, the initial 2,4,6-trinitrotoluene is added (trinitrotoluene, TNT). In this case, it is possible to isolate up to 90% of 2,4,6-triaminotoluene trichlorohydrate.

The filtrate obtained after separation of the 2,4,6-triaminotoluene salt, which is a solution of the titanium (III) salt, saturated with 2,4,6-triaminotoluene, is used for mono-reduction.

It is important to emphasize that both chemical reduction and EV use the same electrochemically regenerated reducing agent - TiCl ₃ , which can be used repeatedly, which allows you to create a virtually waste-free production.

Thus, a new practically non-waste method for producing both 4-amino-2,6-dinitrotoluene and 2,4,6-triaminotoluene according to one technological scheme has been proposed, which allows to obtain pure 4-amino-2,6-dinitrotoluene in high yield . In addition, the process is explosion-proof, since during the processing of the reaction mixture it does not contain explosive TNT (TNT). With this method of obtaining the target products, the laborious stage of utilization of solutions after mono reduction containing isomeric intermediate products of reduction of nitro groups is excluded, since the process for obtaining TAT involves introducing into the electrolysis a mixture of isomeric intermediate products of reduction of nitro groups, which has never been used before to obtain 2,4,6 -triaminotoluene.

It is important to emphasize that in the proposed method for producing 4-amino-2,6-dinitro- and 2,4,6-triaminotoluene, the cycle was closed by sequential chemical mono reduction and subsequent electroreduction of all intermediate chemical reduction products with separate isolation of 4-amino hydrochloride salts 2,6-dinitrotoluene and 2,4,6-triaminotoluene in the form of precipitates.

Examples of co-production of 4-amino-2,6-dinitrotoluene (p-isomer) and 2,4,6-triaminotoluene (TAT)

Example 1

To a solution of 1 g of 2,4,6-trinitrotoluene (TNT) in 100 ml of MeOH and 10 ml of conc. HCl with vigorous stirring is rapidly poured 40 ml of a 0.9 M aqueous solution of titanium (III) chloride in 6% Hcl. The molar ratio of TNT to TiCl ₃ is 1: 8.2. After the violet color characteristic of Ti ³⁺ salts disappeared, MeOH was distilled off on a rotary evaporator (the solution was evaporated by 65%). The precipitated 4-amino-2,6-dinitrotoluene hydrochloride (p-isomer) is filtered off and dried in air. The yield of 4-amino-2,6-di nitrotoluene salt is 60% (0.63 g). A filtrate with a volume of 52 ml is sent to the cathode space of the electrolyzer to completely recover the substances remaining after separation of the p-isomer and Ti ⁴⁺ salt. Electroreduction is carried out in galvanostatic mode using an electrolyzer with a volume of 0.15 liters. Anolyte - 15-20 ml of a 7% solution of H ₂ SO ₄ is placed in a glass from a cation exchange membrane located in the center of the cell and fixed in the electrolyzer using a cap made of fluoroplastic with holes. Lead (especially pure, С-OOOO grade) is used as the cathode, and the platinum mesh is the anode. The optimal concentration of the solution is C _{Ti (III)} = 0.9 M and C _HCl = 6.0%. After exhaustive reduction, the catholyte is evaporated under vacuum (15-20 mm) to a volume of 20-25 ml. The temperature of the bath during evaporation is maintained in the range of 50-60 ° C. After crystallization at 5 ° C, the hydrochloric acid salt of the TAT is filtered off and washed. 0.32 g of 2,4,6-triaminotoluene trichlorohydrate, which is 75%, are isolated. One stripped off the catholyte remaining after the deposition of the TAT salt is diluted with water to C _{Ti (III)} = 1.0 M and C _HCl = 0%, and the resulting solution is used in the next TNT monoreduction.

Example 2

The process is carried out analogously to example 1 with the difference that 1.6 g of TNT are added to the cathode space. The electrolysis of the resulting suspension is carried out until hydrogen is released. After isolation and drying of the precipitate, 1.68 g of 2,4,6-triaminotoluene salt are isolated. The yield of the substance is 89%.

Example 3

The process is carried out analogously to example 2 with the difference that EtOH is used instead of MeOH. The salt yield of the p-isomer is 60% (0.63 g). After exhaustive electroreduction, 1.62 g of TAT salt is isolated, which is 86%.

Comparative example. four.

The process is carried out analogously to example 2 with the difference that when evaporating the solution after chemical reduction, not only all the alcohol is distilled off, but also part of the water (only 112 ml) (the solution is evaporated by 75%). The precipitate formed is a mixture of the hydrochlorides of the p-isomer and 2-amino-4,6-dinitrotoluene (o-isomer). The total yield of monoamine salts is 79% (0.74 g), of which the o-isomer is 12%.

As can be seen from this example, the removal of not only alcohol but also water from the reaction mixture leads to the isolation of a difficultly separated mixture of monoaminodinitrotoluene isomers.

Claims (2)

1. The combined method of producing 4-amino-2,6-dinitro- and 2,4,6-triaminotoluene, which consists in the fact that a solution of 2,4,6-trinitrotoluene in aliphatic alcohol is subjected to interaction with titanium trichloride in an aqueous solution of hydrochloric acid at a molar ratio of 2,4,6-trinitrotoluene and titanium trichloride equal to 1- (8-9), followed by removal of the aliphatic alcohol in vacuo and isolation of the resulting 4-amino-2,6-dinitrotoluene in the form of its hydrochloride by filtration and the filtrate thus obtained is subjected to electrochemical reduction refluxing in a diaphragm cell equipped with a cathode and anode, followed by evaporation of the catholyte in vacuum at a temperature of 50-60 ° C and isolating the 2,4,6-triaminotoluene formed in the form of its trichlorohydrate by filtration, followed by returning the obtained filtrate back to the reaction. 2. The method according to claim 1, characterized in that trinitrotoluene is additionally added to the filtrate obtained after isolation of 4-amino-2,6-dinitrotoluene hydrochloride.