JPS6314693B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing benzaldehydes. More specifically, the general formula is

[Formula] (wherein X represents H, Cl, Br, CN, or NO ₂ ) The methyl group of the compound (hereinafter referred to as toluenes) is chlorinated to produce one molecule of toluenes. Chlorinated products having an average of 1.0 to 2.0 chlorine atoms (hereinafter referred to as chlorinated toluene mixture)
The first step is to produce the chlorinated toluene mixture obtained in the first step, and the general formula is

[Formula] (wherein X represents H, Cl, Br, CN or NO ₂ ) A second step of producing a compound (hereinafter referred to as benzaldehydes) This invention relates to a method for producing benzaldehydes. Benzaldehydes are useful as raw materials for medicine, agriculture, dyes, fragrances, and other organic synthesis. Conventionally, many methods are known as methods for producing benzaldehydes. The method for producing benzaldehydes is as follows, taking benzaldehyde as an example. That is, the main methods for producing benzaldehyde include the direct oxidation method of toluene and the hydrolysis method of benzal chloride, and other known methods include methods using benzyl chloride, benzyl alcohol, and benzoyl chloride as raw materials.
However, these methods are not necessarily preferred methods. For example, regarding the direct oxidation method of toluene, a lot of research has been done on reaction conditions, catalysts, etc., but it is still not possible to selectively produce benzaldehyde, so benzoic acid or benzyl alcohol etc. are produced as by-products in large quantities. The reality is that. Much research has been conducted on catalysts and reaction conditions regarding methods for hydrolyzing benzal chloride. In this case, benzaldehyde can be produced in a relatively high yield by selecting the reaction catalyst and reaction conditions. However, in this case, there are considerable difficulties in producing benzal chloride itself. That is, the production of benzal chloride is usually carried out by thermal or photochlorination of toluene, but in this chlorination, there is a relationship between the degree of chlorination and the composition of the whole organism, as shown in the reference diagram. There is. That is, benzal chloride is obtained in the form of a mixture with benzyl chloride and benzotrichloride, and benzal chloride cannot be selectively synthesized. Therefore, in order to obtain benzal chloride, not only is separation operation such as distillation required from the mixture, but there are also drawbacks such as a low yield relative to toluene.
Therefore, the method for producing benzaldehyde by hydrolysis of benzal chloride cannot be said to have a high yield when using toluene as a starting material. Several methods have been known for a long time using benzyl chloride as a starting material, such as reacting it with dilute nitric acid or lead nitrate, reacting it with a hexamethylenetetramine solution, and oxidizing it with sodium dichromate after hydrolysis. It is being However, in this case as well, it is quite difficult to produce benzyl chloride. That is, in the synthesis of benzyl chloride by chlorination of toluene, benzyl chloride is obtained in the form of a mixture with benzal chloride and the like, as shown in the reference diagram, and benzyl chloride cannot be synthesized selectively. Therefore, not only is a separation operation required, but the yield is also low, as in the case of benzal chloride. In order to improve these drawbacks, the present inventors conducted intensive research on a new method for producing benzaldehyde, and found that the number of chlorine atoms in the methyl group of toluene (hereinafter referred to as the degree of chlorination) reached a certain number. chlorinated toluene mixture or halogen in the core, -
The present invention was completed by discovering that benzaldehydes can be produced in good yield by reacting a chlorinated toluene mixture containing CN or -NO ₂ with nitric acid under specific conditions. I've reached it. In the method of the present invention, in the chlorination reaction of the first step, the general formula

Toluenes 1 represented by [Formula] (wherein X represents H, Cl, Br, CN or NO ₂ )
A chlorinated toluene mixture in which an average of 1 to 2 chlorines are introduced into the methyl group is produced by reacting 1 to 2 moles of chlorine per mole, and the resulting chlorinated toluene mixture is directly used as is. Alternatively, the present invention relates to a method for producing benzaldehydes in high yield by carrying out a simple distillation and then reacting with nitric acid under specific conditions in a second step. According to the method of the present invention, a chlorinated toluene mixture containing benzyl chloride (or its nuclear substituted product) and benzal chloride (or its nuclear substituted product) as main components is reacted with nitric acid under specific conditions. Any of them can be a benzaldehyde. By limiting the degree of chlorination of toluenes to a specific range, the chlorinated toluene mixture can be directly used as a raw material for the oxidation reaction with nitric acid. The difficulty in procuring raw materials is solved in the method for producing benzaldehyde using raw materials. It is therefore possible to advantageously produce benzaldehydes. The chlorination of toluenes in the first step of the method of the present invention is usually carried out by bubbling chlorine in the liquid phase under irradiation with ultraviolet light, or by adding a radical generator such as benzoyl peroxide or azobisisobutyronitrile to the reaction solution. The reaction is carried out by adding chlorine to the liquid phase and bubbling chlorine into the liquid phase to carry out the reaction. In this case, it is not always necessary to use a reaction solvent, but it is of course possible to use a chlorinated hydrocarbon solvent such as carbon tetrachloride.
The chlorination reaction is usually carried out at a reaction temperature of 50°C to 160°C, but the actual reaction temperature is appropriately selected depending on the presence or absence of a solvent, its type, and the type of toluene to be chlorinated. Further, the timing of the chlorination reaction is appropriately determined depending on the method of blowing chlorine gas depending on the reaction apparatus. In the chlorination reaction of the method of the present invention, alkylene polyamine, benzamide, triallyl phosphate, etc. may be added as necessary to suppress the formation of undesirable impurities. The chlorination reaction can be carried out either batchwise or continuously. What is important in the above chlorination reaction is the molar ratio of chlorine and toluene to be reacted, and this is because a chlorinated toluene mixture having an average of 1 to 2 chlorine atoms in the methyl group per molecule of toluene is produced. For this purpose, it is necessary to react 1 to 2 moles of chlorine per mole of toluene. Since the reaction between toluenes and chlorine can be carried out almost quantitatively, an amount of chlorine substantially equal to the amount corresponding to the desired average degree of chlorination of the chlorinated toluene mixture or a slight excess of chlorine is added to the toluene. A chlorinated toluene mixture having the desired average degree of chlorination can be obtained by reacting with chlorinated toluene. The second step of the method of the present invention is a step in which the chlorinated toluene mixture produced in the first step is mixed with nitric acid and reacted. The chlorinated toluene mixture used in the second step usually does not require any special purification or separation operations, but if there are many tars and other byproducts generated during the chlorination reaction, these byproducts may be removed. Therefore, it is preferable to perform distillation or the like. Note that it is also possible to hydrolyze the chlorinated toluene mixture before reacting with nitric acid, and then react with nitric acid. The concentration of nitric acid when carrying out the second step of the method of the present invention is generally 0.5 to 12 wt%, preferably 2
~8wt%. If the concentration of nitric acid is high, carboxylic acids tend to be produced as by-products, which is not preferable. Furthermore, when the concentration of nitric acid is low, the reaction efficiency is poor and economical efficiency is lost, which is not preferable. The reaction temperature in the second step is usually 70~70°C at normal pressure.
It is 105℃. In the case of pressurization, the temperature is 100 to 130°C, depending on the magnitude of the pressure. The preferred reaction temperature is the reflux temperature at which the reaction mixture of the raw materials chlorinated toluene mixture and nitric acid aqueous solution is refluxed under normal pressure, and is usually around 100°C or slightly higher. However, these temperatures may vary slightly depending on the concentration of nitric acid and the types or relative amounts of reactants. The amount of nitric acid used in the chlorinated toluene mixture is generally 0.2 to 10 mol, preferably 1.0 to 6.0 mol, per 1 mol of the chlorinated toluene mixture. The amount of nitric acid used is determined appropriately depending on the substance to be reacted, its composition, and reaction conditions.
Generally, when the average degree of chlorination of the chlorinated toluene mixture is low, good results can be obtained by increasing the amount of nitric acid, and when the average degree of chlorination is high, decreasing the amount of nitric acid can be obtained. Is possible. When carrying out the second step of the method of the present invention, it is not necessary to use a catalyst, but using a catalyst accelerates the reaction and shortens the reaction time.
Using a catalyst is a preferred embodiment. In this case, the catalysts include vanadium pentoxide, ammonium metavanadate, sodium metavanadate,
Vanadium compounds such as vanadium chloride and vanadyl sulfate are preferred from the viewpoint of effectiveness. The amount of catalyst added varies depending on the type of catalyst, the composition of the chlorinated toluene mixture, or the concentration of nitric acid, but is usually 0.001 to 0.10 parts by weight per 1 part by weight of the chlorinated toluene mixture. Note that mineral acids such as hydrochloric acid and sulfuric acid can also be used as catalysts. In this case, the amount of catalyst is 0.01 to 1 part by weight of the chlorinated toluene mixture.
It is 1.5 parts by weight. A conventional separation method is used to separate the target product from the reaction product. That is, the reaction product can be removed by cooling the reaction mixture after the completion of the reaction and separating the crystallized crystals, separating the liberated oil, or adding an organic solvent to the reaction product to extract it. Benzaldehydes can be separated from The benzaldehydes separated in this way include by-product carboxylic acid compounds, but
These acidic substances can be removed by washing with a dilute alkaline aqueous solution. Since the benzaldehydes obtained in this way are of high purity, they can be used as they are, but if necessary, the purity can be further increased by ordinary purification methods such as distillation or recrystallization. I can do it. Furthermore, free carboxylic acid can be recovered from the alkaline washing solution of the reaction product. Example 1 First step 368 g of toluene was placed in a photoreactor with an internal volume of 600 ml, which was equipped with a thermometer, a stirrer, a chlorine blowing pipe, a reflux condenser that also served as exhaust, and a light irradiation device using a high-pressure mercury lamp.
(4.0 mol) was charged, the contents were heated to 95°C, and chlorine gas was blown in while stirring and under light irradiation. Shortly after chlorine injection, a rise in temperature was observed along with the generation of hydrogen chloride. 142g/hr (2.0mol/hr) while maintaining the reaction temperature at 100℃ and irradiating with light.
The introduction of chlorine was continued for 3 hours at a rate of . Almost no chlorine was detected in the gas being discharged, and the chlorine injected had almost completely reacted. After 3 hours of reaction, chlorine injection was stopped after 426 g (6.0 mol) of chlorine had been blown into the reactor, and dry nitrogen gas was passed through the reaction solution to remove hydrogen chloride and chlorine gas from the system. The reaction product thus obtained was 558 g. When the reaction product was analyzed by gas chromatography, its composition was 1 mol% toluene, 48 mol% benzyl chloride, 46 mol% benzal chloride, 3 mol% benzotrichloride, and 1 mol% other.
It was in mol%. The average degree of chlorination of the reaction solution was 1.5. 2nd step: 49.3 g of the chlorinated toluene mixture obtained in the 1st step (corresponding to 0.343 mol when calculated as an average degree of chlorination of 1.5) into two three-necked flasks equipped with a thermometer, stirrer, and reflux condenser. and 3wt% nitric acid 1440
1.5 g of vanadium pentoxide were charged, and the mixture was heated to an elevated temperature while stirring, and the reaction was carried out under reflux for 5 hours. After the reaction mixture was cooled and the oily portion was separated, 100 ml of toluene was added to the aqueous layer for extraction twice. The oily part and the extract were combined and the toluene was distilled off.
The remaining oil was distilled. By this method 111~
34.1 g of a fraction at 114° C./100 mmHg was obtained. When this substance was analyzed by infrared absorption spectrum, it was confirmed that it was benzaldehyde. The purity as determined by gas chromatography was 99.4%. The yield of benzaldehyde based on the raw material toluene is 90.4%. Example 2 First step 368 g (4.0 mol) of toluene was placed in the same photoreaction device as used in the first step of Example 1, and the reaction temperature was maintained at 100°C as in the first step of Example 1. The chlorination reaction was carried out by blowing chlorine under light irradiation. Chlorine injection is 114g/hr (1.6mol/
hr), and the reaction was continued for 3 hours. 341
After blowing in chlorine (4.8 mol), the blowing of chlorine was stopped, and hydrogen chloride and chlorine gas in the system were removed by passing dry nitrogen gas to obtain 523 g of a reaction solution. Gas chromatographic analysis of this product revealed that it contained 67 mol% of benzyl chloride, 27 mol% of benzal chloride, 4 mol% of toluene, and 2 mol% of others. The average degree of chlorination was 1.2. 2nd step Into the same reactor as in the 2nd step of Example 1, 61.0 g of the chlorinated toluene mixture obtained in the 1st step (degree of chlorination
(equivalent to 0.457 moles when calculated as 1.2), 1440 g of 4wt% nitric acid, and 1.8 g of ammonium metavanadate.
I prepared it. This mixture was heated to an elevated temperature while stirring, and the reaction was carried out under reflux for 6 hours. After the reaction was completed, the same treatment as in the second step of Example 1 was carried out, and 43.6 g of benzaldehyde fraction was obtained by distillation. As a result of gas chromatography analysis, the purity was 99.3%. The yield of benzaldehyde based on toluene as a raw material is equivalent to 88.3%. Example 3 First step 368 g (4.0 mol) of toluene was placed in the same photoreactor as used in the first step of Example 1, and
As in the first step, the reaction temperature was maintained at 100 °C,
A chlorination reaction was carried out by blowing chlorine under light irradiation. Chlorine injection is 142g/hr (2.0mol/hr)
The reaction was continued for 3.6 hours. When 7.2 moles of chlorine had been blown into the system, the chlorine injection was stopped and dry nitrogen gas was passed through the system to remove hydrogen chloride and chlorine gas, yielding 606 g of a reaction solution. Gas chromatography analysis of this material revealed that the composition was 27 mol% benzyl chloride, 66 mol% benzyl chloride, and benzotrichloride.
5.5 mol%, other 1.5 mol%, the average degree of chlorination is
It was 1.8. 2nd step Into the same reactor as in the 2nd step of Example 1, 71 g of the chlorinated toluene mixture obtained in the 1st step (degree of chlorination: 1.8
(equivalent to 0.460 mol) and 4wt% nitric acid
I prepared 1440g. This mixture was heated to an elevated temperature while stirring, and the reaction was carried out under reflux for 12 hours. After the reaction was completed, the same treatment as in the second step of Example 1 was carried out,
43.2 g of benzaldehyde fraction was obtained by distillation. The yield of benzaldehyde based on toluene, the raw material, is equivalent to 87%. Example 4 First step 380 g (3.0 mol) of p-chlorotoluene was placed in the same photoreactor as used in the first step of Example 1, and the reaction temperature was raised to 130 mol in the same manner as in the first step of Example 1. The chlorination reaction was carried out by blowing chlorine into the solution while maintaining the temperature at 0.degree. C. and irradiating it with light. Chlorine blowing is 106
g/hr (1.5 mol/hr), and the reaction was continued for 3.0 hours. When 4.5 moles of chlorine had been blown into the reactor, the chlorine blowing was stopped, and the same procedure as in Example 1 was carried out to obtain 527 g of a reaction solution. Gas chromatography analysis of this material revealed that the composition was 2 mol% p-chlorotoluene, 48 mol% 4-chlorobenzyl chloride, 46 mol% 4-chlorobenzyl chloride, and 4 mol% others.
The average degree of chlorination of p-chlorotoluene was 1.5. Second step: Into the same reactor as in the second step of Example 1, add 81.3 g of the chlorinated mixture of p-chlorotoluene obtained in the first step.
(Equivalent to 0.456 moles when calculated as a degree of chlorination of 1.5)
1,440 g of 5 wt % nitric acid and 2.4 g of vanadium pentoxide were charged, and the mixture was heated to an elevated temperature with stirring, and the reaction was carried out under reflux for 6 hours. After cooling the reaction mixture and separating the crystals, 100 ml of toluene was added to the solution and extracted twice. The crystal part and the extract were combined and toluene was distilled off, and the residue was distilled to obtain 48 g of a fraction having a temperature of 100 to 102°C/20 mmHg. As a result of infrared absorption spectrum analysis,
It was confirmed that it was p-chlorobenzaldehyde. The yield of p-chlorobenzaldehyde based on the raw material p-chlorotoluene was equivalent to 73.9%. Example 5 First step 380 g (3.0 mol) of o-chlorotoluene was placed in the same photoreactor as used in the first step of Example 1.
The reaction temperature was adjusted in the same manner as in the first step of Example 1.
Maintained at 130℃ and blown chlorine under light irradiation,
A chlorination reaction was carried out. Chlorine blowing is 106
g/hr (1.5 mol/hr), and the reaction was continued for 3.6 hours. After blowing in 5.4 moles of chlorine, the blowing of chlorine was stopped, and the same treatment as in Example 1 was carried out to obtain 558 g of a reaction solution. Gas chromatographic analysis of this product revealed that o-chlorotoluene was 0.5 mol%, o-chlorobenzyl chloride was 28 mol%, o-chlorobenzal chloride was 67 mol%, o-chlorobenzotrichloride was 3 mol%, and others were 1.5 mol%. The average degree of chlorination with respect to o-chlorotoluene was 1.8. 2nd step In the same reactor as in the 2nd step of Example 1, 64.7 g of the chlorinated mixture of o-chlorotoluene obtained in the 1st step was added.
(Equivalent to 0.343 moles when calculated as a degree of chlorination of 1.8)
1,440 g of 3 wt % nitric acid and 2.0 g of vanadium pentoxide were charged, and the mixture was heated to an elevated temperature with stirring, and the reaction was carried out under reflux for 6 hours. The reaction mixture was cooled, 200 ml of toluene was added thereto to separate the oil phase, and 100 ml of toluene was added to the aqueous solution portion for two extraction operations. After combining the first oily part and the extract and distilling off the toluene, the remaining part was distilled, resulting in 36g of distillate at 107-110℃/30mmHg.
I got it. As a result of infrared absorption spectrum analysis,
It was confirmed to be o-chlorobenzaldehyde. The o-chlorobenzaldehyde yield based on the raw material o-chlorotoluene was 73.5%.

Claims (1)

[Claims] 1. By chlorinating the methyl group of a compound whose general formula is represented by [Formula] (wherein X represents H, Cl, Br, CN, or NO ₂ ),
The first step is to produce a chlorinated product having 2.0 chlorine atoms, and the chlorinated product obtained in the first step is reacted with nitric acid to obtain the general formula [formula] (where X is H, Cl , Br, CN or NO ₂ ).