CN109928951A - The preparation method of 2- isopropyl thioxanthone - Google Patents

Abstract

The present invention relates to a kind of preparation methods of photoinitiator 2- isopropyl thioxanthone, more particularly to 2-(4- isopropyl thiophenyl) benzoic acid carries out ring closure reaction under the conditions of reflux dewatering and prepares 2- isopropyl thioxanthone.This method has many advantages, such as using the concentrated sulfuric acid is few, environmental pressure is small, product appearance is good.

Description

The preparation method of 2-isopropylthioxanthone

technical field

The invention relates to a preparation method of a photoinitiator 2-isopropylthioxanthone, in particular to the preparation of 2-isopropylthioxanthone by ring-closing reaction of 2-(4-isopropylphenylthio)benzoic acid under reflux dehydration conditions Propylthioxanthone.

Background technique

2-Isopropylthioxanthone is a high-efficiency free-radical type II photoinitiator, suitable for light-curing materials composed of unsaturated polyester and acrylic monomers, and can be used in colorless or colored UV-curable inks, wood Furniture, decorative coatings, adhesives, coatings for automotive metal parts, optical fiber manufacturing, printed luminous materials, etc. It acts as a sensitizer when used with a cationic photoinitiator, and can also be used as a photosensitizer to enhance the curing performance of Photoinitiator 907.

According to the different raw materials used, at present, the preparation method of 2-isopropylthioxanthone that can be industrially produced mainly includes:

1. Use 2,2'-dithiodiphenylcarboxylic acid and cumene as raw materials: prepare 2-isopropylthioxanthone (CN1220666) in the next step catalyzed by concentrated sulfuric acid; or in a multi-step reaction, 2,2'-Dithiodiphenylcarboxylic acid is first converted into 2-chlorothiobenzoyl chloride by reaction, and then reacted with cumene to prepare 2-isopropylthioxanthone (CN1461302);

2. Using o-chlorobenzoic acid (CN101570534, CN101817812, CN101830887) or o-aminobenzoic acid (CN102174036) or o-chlorobenzonitrile (CN2013106571115) as raw materials, react with 4-isopropyl thiophenol to prepare intermediate 2-( 4-isopropylphenylthio) benzoic acid, then ring-closing reaction under the catalysis of concentrated sulfuric acid to prepare 2-isopropylthioxanthone:

The main disadvantage of method 1 is that the product produced is a mixture of 2-isopropylthioxanthone and 4-isopropylthioxanthone, of which 4-isopropylthioxanthone is less reactive and therefore less mixed Pure thioxanthone has good activity. Method 2 therefore has a short route to prepare pure 2-isopropylthioxanthone, which has great advantages, but still has shortcomings. First of all, concentrated sulfuric acid is both a catalyst and a solvent, and the production of water in the reaction process will affect the catalytic effect of concentrated sulfuric acid, so the amount of concentrated sulfuric acid is very large, resulting in a large amount of waste acid, and the pressure of sewage treatment is high; secondly, the product has poor appearance and color. darkened.

SUMMARY OF THE INVENTION

The purpose of the present invention is to avoid the problems in the prior art and provide a process method for preparing 2-isopropylthioxanthone with less concentrated sulfuric acid, low environmental pressure and good product appearance.

In order to overcome the steps of method 2, there are two improvement ideas: one is to increase the organic solvent and reduce the amount of concentrated sulfuric acid; the other is to ensure the catalytic effect of the concentrated sulfuric acid and take away the water produced by the reaction from the reaction system. Moreover, the added organic solvent can also carry water at the same time, which solves two problems at the same time, preferably a solvent that is convenient for post-processing and insoluble in water.

According to the above thinking, the specific operation steps of the technology of the 2-isopropylthioxanthone preparation method provided by the invention:

1) Dissolve 2-(4-isopropylphenylthio)benzoic acid in an organic solvent,

2) Add catalyst, heat for reflux and water separation,

3) After the reaction is completed, add water to quench the reaction;

The organic solvent is selected from cyclohexane, methylcyclohexane, and dichloroethane; the catalyst is selected from concentrated sulfuric acid.

The method for preparing 2-isopropylthioxanthone provided by the invention is characterized in that the amount of concentrated sulfuric acid is selected from 1-3 times of the amount of 2-(4-isopropylphenylthio)benzoic acid. A large amount of concentrated sulfuric acid is conducive to speeding up the reaction rate, but if the amount is too large, the color of the product is not good, and if the amount of sulfuric acid is too small, the reaction time needs to be prolonged for a long time, which affects the production cycle and production capacity.

The method for preparing 2-isopropylthioxanthone provided by the invention is characterized in that the amount of the organic solvent is selected from 1.5-10 times the weight of 2-(4-isopropylphenylthio)benzoic acid. Different types of solvents have different dosages. The principle is that it can not only dissolve or completely dissolve the reaction raw materials in the state of reflux, but also ensure that the water produced by the reaction can be completely separated when the water is refluxed. The amount of solvent should not be too much, which will affect the production capacity.

Initially, the inventors preferred solvent and organic solvent with water agent to be toluene and xylene. First of all, their boiling points are high enough to ensure sufficient reaction temperature; secondly, they can dissolve the intermediate 2-(4-iso-iso) in a hot state. propylphenylthio) benzoic acid; again their water carrying capacity is very good, see Table 1.

Table 1 The formation of binary azeotrope between toluene, xylene and water

However, during the experiment, the inventor found that when using toluene or xylene as solvent and water-carrying agent, a new side reaction, sulfonation reaction, would occur, which would not only affect the appearance of the product, but also could not obtain a product with a qualified appearance. ; And the by-product benzenesulfonic acid produced by the side reaction will cause the post-treatment emulsification to be very serious, and a large amount of water needs to be added to make the stratification obvious, and the environmental pressure is large. Therefore neither toluene nor xylene are good solvents for this reaction.

The inventor abandoned toluene and xylene with good water-carrying effect, and looked for non-benzene-based, water-insoluble solvents. First, non-benzene-based solvents can avoid sulfonation side reactions, and insoluble in water can facilitate post-processing, because the use of water-soluble solvents Or when the solvent is miscible with water, the solvent needs to be recovered first, and then the water-insoluble solvent is added for extraction, which not only consumes kinetic energy, but also causes cross-contamination of the solvent.

After experiment and exploration, the inventor found that the choice of solvent cyclohexane, methylcyclohexane or dichloroethane can not only promote the reaction well, but also effectively take out the water generated by the reaction during the reaction process; and post-treatment There will be no emulsification, the post-processing is simple, and the most important thing is that the appearance of the product prepared by the reaction is very good.

In the preparation method of 2-isopropylthioxanthone provided by the invention, the raw material 2-(4-isopropylphenylthio)benzoic acid can be conveniently prepared, and 2-(4-isopropylphenylthio)benzoic acid There have been many literature reports on the preparation of sodium benzoate, such as CN101570534, CN101817812, CN101830887, US4902826, etc., all of which are prepared by reacting sodium 2-(4-isopropylphenylthio)benzoate under alkaline conditions, and then obtained by acidification.

The preparation method of 2-isopropylthioxanthone provided by the invention reduces the consumption of concentrated sulfuric acid from about 10 times in the prior art to 3 times or less, reduces the consumption of concentrated sulfuric acid, and also reduces the amount of extraction and quenching. The amount of water used in the reaction reduces the waste acid water in the post-treatment. After the acid water is separated, the organic phase is washed twice, and the water phase after the secondary water washing can be directly applied to the extraction and quenching of the next batch of reactions. The amount of water used in the extraction and quenching reaction is selected from 1-2 times the quality of the concentrated sulfuric acid. It can be well layered without adding too much water, and the waste acid water obtained with this amount of water can also be used to acidify 2-( 4-isopropylphenylthio) sodium benzoate, then generate 2-(4-isopropylphenylthio) benzoic acid and a substantially saturated sodium sulfate solution, purify sodium sulfate by cooling and crystallization, and use it for sales, thereby obtaining low salt content. Therefore, the environmental pressure of post-treatment is not large.

The advantages of the method for preparing 2-isopropylthioxanthone provided by the invention are:

(a) the consumption of concentrated sulfuric acid is small, saving cost;

(b) the acid water obtained by post-processing is used for the preparation of raw materials, and pure by-product sodium sulfate can be prepared, and the environmental pressure is small;

(c) The appearance of the prepared product is good.

Specific examples:

In order to illustrate the present invention more clearly, the following non-limiting examples are used to further illustrate.

Example 1: Preparation of 2-(4-isopropylphenylthio)benzoic acid

120.3g (0.79mol) o-chlorobenzoic acid, 120g (0.79mol) 4-isopropyl thiophenol, 68.0g (1.70mol) sodium hydroxide were heated to 80°C and stirred for 0.5 hours, 520mL of toluene was added, and heated Reflux dehydration, after removing 14 mL of water. The obtained solution was protected with nitrogen, sealed and pressurized at 1 MPa, heated to 210 ° C, reacted for 10 hours, cooled and cooled, desolvated to recover toluene, adjusted to pH 2 with dilute hydrochloric acid or dilute sulfuric acid, suction filtered, and dried to prepare 204 g of 2-(4-isopropylphenylthio)benzoic acid, mp 149-151°C.

Example 2: Preparation of 2-isopropylthioxanthone

Take 136.2g (0.50mol) of 2-(4-isopropylphenylthio)benzoic acid and dissolve it in 250mL of dichloroethane, slowly add 125.0g of 98% sulfuric acid (1.25mol) dropwise in a water bath, after 30min dripping, slowly Heating to raise the temperature, dehydration under reflux, monitoring the reaction by TLC or liquid phase according to the amount of separated water, after the reaction is complete, add 150 mL of water to the temperature, stir for 30 min, stand for stratification, separate the organic phase, and the acid water phase for later use. The organic phase was washed with 150 mL of water, and then the solvent was recovered by distillation. The residue was recrystallized with 250 mL of absolute ethanol to obtain 114.5 g of a pale yellow solid, namely 2-isopropylthioxanthone, with a content of 99.4%.

Example 3: Preparation of 2-isopropylthioxanthone

Take 136.2g (0.50mol) of 2-(4-isopropylphenylthio)benzoic acid and disperse it in 400mL of cyclohexane, slowly add 125.0g of 98% sulfuric acid (1.25mol) dropwise in a water bath, drop after 30min, slowly heat The temperature was raised, refluxed and dehydrated, and the reaction was monitored by TLC or liquid phase according to the amount of separated water. After the reaction was complete, 150 mL of water was added to the temperature, stirred for 30 min, left to stand for stratification, and the organic phase was separated, and then washed with 150 mL of water, and then the solvent was recovered by distillation. The product was recrystallized with 250 mL of anhydrous ethanol to obtain 115.8 g of a pale yellow solid, namely: 2-isopropylthioxanthone, with a content of 99.3%.

Example 4: Preparation of 2-isopropylthioxanthone

Take 136.2g (0.50mol) of 2-(4-isopropylphenylthio)benzoic acid and dissolve it in 250mL of dichloroethane, slowly add 75.0g of 98% sulfuric acid (0.75mol) dropwise in a water bath, after 30min dripping, slowly Heating and heating, dehydration under reflux, monitoring the reaction according to the amount of separated water or TLC or liquid phase, after the reaction is complete, add 75 mL of water to the temperature, stir for 30 min, stand for stratification, separate the organic phase, wash with 75 mL of water, and then distill and recover the solvent , the residue was recrystallized with 250 mL of absolute ethanol to obtain 113.2 g of a pale yellow solid, namely: 2-isopropylthioxanthone, with a content of 99.0%.

Example 5: Preparation of 2-isopropylthioxanthone (application of waste acid solution)

120.3g (0.79mol) o-chlorobenzoic acid, 120g (0.79mol) 4-isopropyl thiophenol, 68.0g (1.70mol) sodium hydroxide were heated to 80°C and stirred for 0.5 hours, 520mL of toluene was added, and heated Reflux dehydration, after removing 14 mL of water. The obtained solution was protected with nitrogen, sealed and pressurized 1MPa, heated to 210 ° C, reacted for 10 hours, cooled down, desolvated and recovered toluene, and the pH of the reaction solution was adjusted to 2 with the acid water separated from Example 2, and the pH of the reaction system was maintained. The temperature is about 40°C, suction filtration and drying to prepare 200g of 2-(4-isopropylphenylthio)benzoic acid. The filtrate was cooled to 0°C, suction filtration was performed again, and dried naturally to obtain 145 g of sodium sulfate decahydrate.

Dissolve 136.2g (0.50mol) of 2-(4-isopropylphenylthio)benzoic acid prepared above in 250mL of dichloroethane, slowly add 125.0g of 98% sulfuric acid (1.25mol) dropwise in a water bath, dropwise for 30min After completion, slowly heat up and dehydrate, monitor the reaction according to the amount of separated water, TLC or liquid phase, after the reaction is complete, drop the temperature and add 150 mL of water, stir for 30 min, stand for stratification, separate the organic phase, and then wash with 150 mL of water, then The solvent was recovered by distillation, and the residue was recrystallized with 250 mL of absolute ethanol to obtain 115.7 g of a pale yellow solid, namely: 2-isopropylthioxanthone, with a content of 99.3%.

Example 6: Preparation of 2-isopropylthioxanthone

Take 136.2g (0.50mol) of 2-(4-isopropylphenylthio)benzoic acid and dissolve it in 300mL of toluene, slowly add 125.0g of 98% sulfuric acid (1.25mol) dropwise in a water bath, after 30min dripping, slowly heat up, Reflux dehydration, monitor the reaction according to the amount of separated water, TLC or liquid phase. After the reaction is complete, add 150 mL of water to the temperature, stir for 30 min, and let it stand for 4 h. No stratification at all. Another 150 mL of water was added, and there was still a small part of the emulsified middle layer, and the emulsified layer was also divided into the water phase together. The separated organic phase was washed with 150 mL of water, and then the solvent was recovered by distillation, and the residue was recrystallized with 250 mL of absolute ethanol to obtain 95.4 g of a yellow-brown solid, namely: 2-isopropylthioxanthone, with a content of 98.8 %.

Example 7: Preparation of 2-isopropylthioxanthone

Dissolve 136.2 g (0.50 mol) of 2-(4-isopropylphenylthio) benzoic acid in 300 mL of toluene, slowly add 200.0 g of 98% sulfuric acid (2.00 mol) dropwise in a water bath, drop after 30 min, slowly heat up, Incubate the reaction at 60°C and monitor the reaction by TLC or liquid phase. After the reaction is complete, drop to room temperature, add 600 mL of water, stir for 30 min, stand for stratification, and there is a slight emulsification intermediate layer, and the emulsified layer is also divided into the water phase. The separated organic phase was washed with 200 mL of water, and then the solvent was recovered by distillation, and the residue was recrystallized with 250 mL of absolute ethanol to obtain 101.8 g of a dark yellow solid, namely: 2-isopropylthioxanthone, with a content of 98.7 g %.

Example 8: Preparation of 2-isopropylthioxanthone (concentrated sulfuric acid as solvent)

Take 496.8 g of concentrated sulfuric acid (270 mL), stir and cool down to about 10 °C with an ice-water bath, and add 136.2 g (0.50 mol) of 2-(4-isopropylphenylthio)benzoic acid to the concentrated sulfuric acid in batches over 2 h. After the reaction is completed, pour it into 600 mL of ice water, stir for 30 min, add 300 mL of toluene for extraction, let stand for stratification, separate the organic phase, wash the organic phase with 200 mL of water, and then distill the solvent to recover the residue. It was recrystallized with 250 mL of absolute ethanol to obtain 100.0 g of a dark yellow solid, namely: 2-isopropylthioxanthone, with a content of 98.7%.

The product prepared by each embodiment, its yield, appearance, sulfuric acid consumption, sulfuric acid waste water situation are shown in Table 2.

Table 2

Claims (3)

1. a preparation method of 2-isopropylthioxanthone preparation method, operation step comprises: 1) Dissolve 2-(4-isopropylphenylthio)benzoic acid in an organic solvent; 2) Add concentrated sulfuric acid, heat to reflux and separate water; 2) After the reaction is completed, add water to quench the reaction; The organic solvent in step 1) is selected from cyclohexane, methylcyclohexane, and dichloroethane. 2. 2-isopropylthioxanthone preparation method according to claim 1 is characterized in that the consumption of vitriol oil is selected from 1-3 of the amount of 2-(4-isopropylphenylthio) benzoic acid substance times. 3 . The method for preparing 2-isopropylthioxanthone according to claim 1 , wherein the consumption of the organic solvent is selected from 1.5-10 times the weight of 2-(4-isopropylphenylthio)benzoic acid. 4 .