Method for preparing CLT acid (2-amino-4-methyl-5-chlorobenzene sulfonic acid) by continuous catalytic hydrogenation reduction

Abstract

The invention provides a method for preparing CLT acid (2-amino-4-methyl-5-chlorobenzene sulfonic acid) by continuous catalytic hydrogenation reduction. The 2-amino-4-methyl-5-chlorobenzene sulfonic acid (CLT acid) can be prepared from a water solution of 2-nitro-4-methyl-5-chlorobenzenesulfonic acid by adopting a continuous catalytic hydrogenation reduction method. According to the method provided by the invention, the loss of a catalyst caused by frequent filtration during the intermittent reaction process can be effectively reduced, and the internal circulating utilization of the catalyst can be realized to prolong the service life of the catalyst; and simultaneously, when the CLT acid is prepared by continuous catalytic hydrogenation reduction according to the method, the volume of a reaction kettle is smaller, the reaction stability is good, the dechlorination of a product is lower, the selectivity is high, and byproducts are fewer.

Description

technical field [0001] The invention relates to the field of organic chemical synthesis, in particular to a method for preparing CLT acid through continuous catalytic hydrogenation reduction. Background technique [0002] CLT acid, also known as 2-amino-4-methyl-5-chlorobenzenesulfonic acid, is an important red organic pigment intermediate, mainly used in the manufacture of organic pigments Jinguanghong C, rubber scarlet LG and Lithol scarlet, etc. , which are widely used in the formulation of inks, paints and coatings, and in the coloring of plastics and rubber. At present, the synthesis method of CLT acid used at home and abroad is basically the toluene sulfonation method, that is, the finished product of CLT acid is obtained after toluene sulfonation, chlorination, nitration, reduction, acid analysis, pressure filtration and drying. [0003] For the reduction process of CLT acid, the iron powder reduction process is widely used at home and abroad at present. A large amou...

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Problems solved by technology

At present, there are many research reports on the preparation of CLT acid by catalytic hydrogenation reduction. There are mainly the following methods: 1. Using Pd / C as a catalyst, a batch reaction method is used in a high-pressure hydrogenation reactor to carry out catalytic hydrogenation reduction preparation CLT acid, the method has the following problems: (1) the volume of the reactor is relatively large, resulting in higher equipment investment

(2) The reaction stability is poor, the product dechlorination is high, the selectivity is low, resulting in more by-products

(3) There is a large loss of catalyst active components and a short catalyst life, resulting in high catalyst costs; 2. Using Pt / C as a catalyst, a batch reaction method is used in a high-pressure hydrogenation reactor for catalytic hydrogenation reduction to prepare CLT acid , the method has the following problems: (1) The volume of the reactor is relatively large, resulting in high equipment investment

(2) Although the catalytic hydrogenation reduction effect is very good when Pt / C is used as the catalyst, the dechlorination of the product is low, but because the market price of CLT acid is only 25,000-28,000 yuan / ton, and the price of Pt / C is relatively high, In the batch reaction mode, the loss of catalyst active components is large, resulting in high catalyst costs

3. Utilize granular carbon-supported or Al2O3-supported Pt-type catalysts, in a fixed-bed reactor, adopt the mode of continuous feeding, continuous discharging and continuous feeding of hydrogen to carry out continuous catalytic hydrogenation reduction to prepare CLT acid, This method has the following problems: (1) The reaction temperature and pressure are high, and the requirements for the material and pressure resistance level of the equipment are also high, resulting in high investment in equipment

(2) The fixed bed reactor has high requirements on the purity of the raw materials, otherwise, due to too many impurities in the material, it will easily cause the poisoning and failure of the granular catalyst, which will cause a large risk in large-scale production and is difficult to control. In addition, due to the purity of the CLT acid nitro material Not very high, so not suitable for continuous catalytic hydrogenation reduction to prepare CLT acid

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