CS255228B1 - Process for preparing 2,5-dimethyl-4-nitroaniline - Google Patents

Abstract

A method for producing technically pure 2.5-dimethyl-4-nitroaniline as an intermediate for yellow bisazo condensation pigments by nitration of p-xylidine with the HNO3 -HjSO^ system, in which dissolved p-xylidine in concentrated H2SO4 is treated with a nitration mixture in a molar ratio of HNO^:p-xylidine = 1.0-1.1:1 and a mass ratio of H2SO4:p-xylidine = 7-12:1 at a reaction temperature of 0 to 30 °C and the resulting 2.5-dimethyl-4-nitroaniline is precipitated after nitration by dilution in water to form 20 to 50 wt. % sulfuric acid.

Description

It is an object of the invention to produce 2,5-dimethyl-4-nitroaniline from 2,5-dimethylaniline by nitration in the HNO 3 -SO 2 SO 4 system and to easily separate the resulting p-nitroisomer from the o-nitroisomer in dilute sulfuric acid. This gives technically pure 2,5-dimethyl-4-nitroaniline which can be converted to 2,5-dimethyl-1,4-phenylenediamine. It is used as a central component in the synthesis of yellow bisazocondensation pigments. The pigments are highly stable to heat and light and are applied after dyeing polyvinyl chloride and polyethylene, printing textiles, car body paints and the like.

A description of the industrial process for the production of 2,5-dimethyl-4-nitroaniline has not been found in the literature. Only laboratory scale procedures are given. Most syntheses choose an acetylation pathway from 2,5-dimethylacetanilide. Pisher and Walling (J. Am. Chem. Soc. 57, 1700 (1935)) described the nitration of 2,5-dimethylacetanilide in the HNO4 -H2SO4 system while hydrolyzing the system by diluting the water with nitration. The accompanying o-nitroxylidine was separated by steam distillation. Kostanecki (Ber. 19, 2 318 (1886)) prepared the desired compound by partial reduction with a solution (NH 4 S from the corresponding dinitro compound. Chang and Adams (J. Am. Chem. Soc. 56, 2, 089 (1934)) similarly synthesized 2,5-dimethyl-4-nitroaniline from p-xylidine in the HNO ₃ -H ₂ SO _{4 system} sequentially by acetylation, acetylation of the acetylderivative and acid hydrolysis with nitro compounds. xylidine was also published by Adams and Nagarkatti (J. Am.

Chem. Soc. 72, 4,601 (1950)). Successive acetylation, nitration in the HNO 3 -H 2 SO 4 system and alkaline hydrolysis yielded p-nitroxylidine in a yield of 60% based on p-xylidine.

The representation of nitroisomers after nitration of 2,5-dimethyl acetanilide in the HNO 3 -H 2 SO 4 system was first quantified by van Helden and Verkade (Rec. Trav. Chim. 73, 53 (1954)). By nitration and acid hydrolysis in dilute hydrochloric acid, after separation by steam distillation, they obtained a content of 52% p-nitroxylidine and 27% o-nitroxylidine. The yield of nitration and hydrolysis was 45.5%.

Nolting and Witt (Ber. 18, 2664 (1885)) mention the nitration of p-xylidine in the HNO ₃ -H ₂ SO _{4 system} and report that p-nitroxylidine was also obtained as a route through the acetylderivative. Other details are not given. Another process for the preparation of 2,5-dimethyl-4-nitroaniline is protected by MS. AO 166 147. Starting from 2-p-toluenesulfonylamino-1,4-xylene, which is nitrated in the form of a suspension by nitric acid in an aqueous medium at a temperature of from 50 to 90 ° C, respectively. in the presence of 0.1 to 20% CH 3 COOH. Subsequent hydrolysis affords 2,5-dimethyl-4-nitroaniline. This tosylation route makes it possible to prepare 2,5-dimethyl-4-nitroaniline from p-xylidine by tosylation, nitration and detosylation in a total yield of 78.6%.

The latter route gives a relatively high yield of the desired p-nitroxylidine, but currently the limiting factor for the industrial process is the lack of p-toluenesulfonyl chloride. Due to the inhibition of saccharin production by classical chlorosulfonation of toluene, a permanent lack of p-toluenesulfonyl chloride can be expected in the future. Thus, from a perspective point of view, the amount of p-toluenesulfonyl chloride waste is unable to satisfy the needs of 2,5-dimethyl-4-nitroaniline.

It is an object of the present invention to provide a process which does not require p-toluenesulfonyl chloride. To solve this problem, the acetylation pathway from p-xylidine (acetylation, nitraoe, hydrolysis) and direct nitration of p-xylidine were studied. It has now been discovered by systematic study of both routes that 2,5-dimethyl-4-nitroaniline can be prepared according to the conditions of the invention in technically pure form by direct nitration of p-xylidine with the same result as the acetylderivative (Table 1).

Table no

Comparison of nitration selectivity of differently acylated 2,5-dimethylaniline.

Acyl Nitration system Temperature P-nitro-a-o ratio · -nitroisomer Tosyl hno ₃ / h ₂ o Mp 50-90 ° C Almost exclusively p-nitro Acetyl hno ₃ / h ₂ sat ₄ 5-10 ° C 60 to 65/35 to 40 Free amine hno ₃ / h ₂ sat ₄ 0-5 ° C 65/35

In addition to 2,5-dimethyl-4-nitroaniline and 2,5-dimethyl-6-nitroaniline, the formation of one more nitrosomer was found by thin-layer chromatography below the NMR sensitivity level. A theoretical amount of nitric acid is sufficient for complete nitration;

Thus, the selectivity of nitration does not change at all when 2,5-dimethylaniline is nitrated. in the acetylated form or as the free amine in the form of the sulfate. This is related to the distribution of electron density in individual positions. The protonated amino group significantly reduces the electron density, especially at the o- and β-position to this group. Both m-positions to the protonated amino group have the relatively highest electron density. However, one m-position is occupied by a methyl group and the other is spherically shielded by an adjacent methyl group. However, the decrease in the electron density in the nucleus by protonation is compensated by the positive induction effect of both methyl groups, including the possible hyperconjugation of the hydrogen bonds of the methyl substituents. This interaction of all influences causes no significant change in the distribution of nitrosomers between the protonated free amine and the acetylated form.

This principle was used in the development of technology. According to the invention, the p-xylidine is dissolved in sulfuric acid followed by nitration with a nitration mixture HNO ₃ -H ₂ SO ₄ at a temperature of 0 to 30 ° C, preferably 5 to 10 ° C. After nitration, the reaction system is diluted with water and separated by 2,5-dimethyl-4-nitroaniline in technically pure form.

The process is also based on the further recognition that p-nitroxylidine can be separated from o-nitroxylldine to an appropriate extent in an acidic medium to a satisfactory degree. NMR showed that the p-nitroisomer is only slightly soluble and the o-nitroisomer exhibits an order of magnitude higher solubility. Thus, it is sufficient to work with such an amount of sulfuric acid during nitration which, when diluted to 20 to 50% by weight. upon completion of the nitration, guarantees the separation of o-nitroxylidine so that only p-nitroxylidine is separated. Thus, the O-nitroxylidine enters the effluent stream of dilute sulfuric acid. The amount of sulfuric acid required is between 7 and 12 wt. parts per 1 part of p-xylidine. Preferably a ratio of 7 to 8: 1 is used, i.e. the lowest satisfactory ratio. After washing rezultuje technically pure 2 _F 5-dimethyl-4-nitroaniline as a 33-37% aqueous paste, which contains in the dry state of at least 95 and p-nitro isomer. Thin layer chromatography showed the presence of the o-nitro isomer to an insignificant extent. The melting point of the dry matter is in the range of 140 to 145 ° C. The yield is in the range of 60 to 63% based on the p-xylidine employed.

Accordingly, the present invention provides a process for the preparation of 2,5-dimethyl-4-nitroaniline, wherein the undissolved p-xylidine in concentrated sulfuric acid is treated with a nitration mixture in a molar ratio of nitric acid: p-xylidine = 1.0 to 1.1: 1 and at a weight ratio of sulfuric acid: p-xylidine of 7 to 12: 1 at 0 to 30 ° C, and the 2,5-dimethyl-4-nitroaniline formed is precipitated upon dilution in water to give 20 to 50% by weight of sulfuric acid.

According to the invention, it is possible to start with p-xylidine of both pure and technical products prepared by hydrogenation from nitroxylene. Sulfuric acid can be used in a concentrated (96-100%) standard grade and nitric acid in either concentrated (65-66%) or fuming (98%) grade.

The advantage of the invention is the simplicity of the technology. The acetylation of p-xylidine, followed by drying of the intermediate and re-hydrolytic cleavage of the acetyl group, is omitted.

The simplification is a saving of investment costs, since the technology requires, besides the raw material containers, only a nitration reactor and a dilution slurry with an aqueous paste separation device. Material savings are 25% over acetylation technology. Overall, the technology according to the invention is better obtainable in terms of raw material and equipment, with lower material costs.

A certain disadvantage is the relatively high consumption of p-xylidine, since about 1/3 of this raw material leaves the technology in the form of a solution of o-nitroxylidine in diluted H ₂ SO ₄ in the β-p-nitroisomer mixture.

Examples

Example 1

The reactor was charged with 1,769 g of 96% sulfuric acid and charged gradually

363.6 g (3 mol) of p-xylidine such that the temperature did not exceed 40 ° C. The suspension was stirred until the p-xylidine was completely dissolved in sulfuric acid.

Prior to the actual nitration, the nitration mixture was prepared by mixing 293 g of 65.8% HNO4 and 1140 g of 96% H2SO4 while cooling with water so that the temperature of the mixture was 20-25 ° C.

The contents of the reactor were cooled to 0 ° C with ice and the nitration mixture was metered so quickly that the temperature of the reaction system was between 0 and 5 ° C. After the nitration mixture was dispensed, the system was stirred at 0-5 ° C for 1 h. The syrupy liquid was poured into 8,110 g of water so quickly that the temperature did not exceed 50-60 ° C. The precipitated p-nitroxylidine suspension was cooled with water to 20 ° C and the aqueous p-nitroxylidine paste was separated by suction and washed with 20 L of water until the reaction to sulfuric acid was lost.

838 g of an aqueous paste of 2,5-dimethyl-4-nitroaniline with a content of 37.0% nitro compound were obtained. 10 408 g of waste dilute sulfuric acid containing 27.0% H ₂ SO ₄ and 1.6% nitroxylidines and 20 138 g of wash water containing 1.7% H ₂ SO ₄ and 0.10% nitroxylidines were discarded. The yield was

62.2% of the product based on the p-xylidine employed.

Example 2

68.1 kg of 96% sulfuric acid were charged to the nitrator. Then 14.0 kg of p-xylidine (0.115 5 kmol) were metered in such that the temperature of the reaction mixture did not exceed 40 ° C. The contents were stirred for 2 h until the p-xylidine dissolved.

In a weighing container, a nitration mixture was prepared by mixing 44 kg of 96% sulfuric acid and 11.4 kg of 65% nitric acid at a maximum temperature of 5 ° C.

In the nitrator, the solution of p-xylidine in sulfuric acid was cooled to 0 ° C and the nitration mixture was forced so quickly that the nitration temperature was in the range of 0 to 5 ° C. After completion of dosing, the system was stirred for 1 h.

312 kg of water was charged to the control boiler and the nitrator content was started with stirring so that the dilution temperature did not exceed 60 ° C. The suspended 2,5-dimethyl-4-nitroaniline suspension was cooled to 20 ° C and pressurized to a frame filter press. The product was washed with 2,500 L of water until loss of the acid reaction.

36.3 kg of an aqueous paste were obtained containing 31.7% of 2,5-dimethyl-4-nitroaniline, which in turn indicated a yield of 60.0% based on the p-xylidine employed.

The waste sulfuric acid had a concentration of 25.8% H 2 SO 4 and contained 1.3% nitroxylidines.

Claims (1)

SUBJECT OF THE INVENTION A process for the preparation of 2,5-dimethyl-4-nitroaniline by nitration of p-xylidine with an HNO-HLSO system characterized in that to the dissolved p-xylidine in a molar ratio of HNO 2: p-xylidine = 1.0-1.1: 12: 1 at a reaction temperature of 0 to 30 ° C, and the resulting precipitate by dilution in water to form a concentrated I 2 SO 4 by weight with a nitration mixture and a weight ratio I 2 SO 4: p-xylidine of 7 to 2,5-dimethyl- The 4-nitroaniline is nitrated with 20 to 50% sulfuric acid.