JPS63218651A - Production of benzonitriles - Google Patents

Abstract

PURPOSE:To economically obtain the titled compound of good quality useful as medicines without using expensive chemicals, by thermally reacting benzoic acids with urea in a molten state using cobalt acetate and boric acid together as a catalyst. CONSTITUTION:Benzoic acids are thermally reacted with urea in a molten state to afford benzonitriles. In the process, cobalt acetate and boric acid are used together as a catalyst. The cobalt acetate is preferably added in an amount of about 0.1-5wt.%, particularly about 0.3-3wt.% expressed in terms of cobalt acetate tetrahydrate. the boric acid is preferably added in an amount of about 0.1-5wt.%, particularly about 0.3-3wt.% expressed in terms of orthoboric acid. The reaction is carried out at >=about 160 deg.C, particularly about 180-210 deg.C in the former stage thereof and the temperature is increased to >=220 deg.C, preferably 230-280 deg.C in the latter stage thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing the corresponding benzonitriles from benzoic acids at low cost without using expensive chemicals.

Benzonitriles are compounds useful as raw materials for medicines, agricultural chemicals, dyes, pigments, etc., and it is desired to develop an economical production method for producing benzonitriles with good purity.

(Prior art) A method for producing benzonitriles by adding urea to benzoic acids and heating is known (Japanese Unexamined Patent Application Publication No. 1983-1999).
32758).

This method converts benzoic acids into benzonitriles in a single reaction step without using solvents, chlorinating agents, dehydrating agents, etc., and is superior in that benzonitriles can be produced by simple and inexpensive means. ing.

However, if phosphoric acid or phosphate salts are used as a catalyst to promote the reaction in this method, deposits that are difficult to remove will be generated on the reactor wall, which is disadvantageous for industrial use. found. Further, when boric acid, ammonium borate, or the like is used as a catalyst, the activity as a catalyst is rather weak, and cobalt borate has the problem of being difficult to obtain industrially.

That is, since the conventional techniques have the above-mentioned problems, it is an object of the present invention to provide a significantly improved means for producing benzonitriles that is industrially practicable and inexpensive.

[Means and effects for solving the problems] Therefore, the present inventors have developed a method that can synthesize benzonitriles in one step reaction using inexpensive raw materials, which are easily available industrially, We conducted extensive research with the aim of finding a highly active catalyst that does not generate deposits on the reactor wall.

As a result, it was discovered that all of the above requirements were satisfied by using cobalt acetate and boric acid together as catalysts, and the present invention was completed.

That is, the present invention provides a method for producing benzonitriles by subjecting benzoic acids and urea to a heating reaction in a molten state, which is characterized in that cobalt acetate and boric acid are used together as catalysts. It is.

The method of the present invention will be specifically explained below.

First, the benzoic acids used in the present invention include benzoic acid itself, benzoic acids in which the benzene nucleus is substituted with an alkyl group such as a methyl group or tertiary butyl group, benzoic acids in which a halogen such as chlorine or bromine is substituted, Examples include those substituted with an alkoxy group such as ]-oxy group, and those substituted with a plurality of these substituents.

Urea is used in an amount of about 1 to 3 times, particularly about 1.01 to 1.5 times, by mole relative to these benzoic acids. Although the entire amount of urea may be initially charged into the reactor together with benzoic acids, it is also preferable to continuously supply molten urea as the reaction progresses.

In the present invention, in addition to benzoic acids and urea, cobalt acetate ζboric acid is further added as a catalyst to the reactor.

The amount of cobalt acetate added is approximately 0.1 to 5% as cobalt acetate tetrahydrate, particularly 0.3% based on benzoic acids.
About 3% by weight is preferable.

The amount of boric acid added is preferably about 0.1 to 5% by weight, particularly about 0.3 to 3% by weight as orthoboric acid based on benzoic acids.

As a catalyst, it is necessary to use cobalt acetate and boric acid together; adding each of them alone will not
Sufficient promoting effect cannot be obtained. Furthermore, even if boric acid is used in combination with other cobalt compounds such as basic cobalt carbonate,
After all, the promoting effect is not sufficient.

The reaction temperature needs to be at least higher than the melting point of the mixture of benzoic acids and urea, but it is usually appropriate to keep it at about 160°C or higher, especially in the range of about 180 to 210°C, for several hours in the first half of the reaction.

In the first stage of the reaction at a relatively low temperature, benzoic acids react with urea and are mainly converted into benzamides. Urea reacts with benzoic acids and converts into amide groups, ammonia, and carbon dioxide gas, and also undergoes self-condensation and self-decomposition, producing some non-volatile and volatile by-products.

The reaction mixture, which has almost completely been converted into benzamides in the first half of the reaction, is usually heated for about 1 to 10 hours at a temperature of 220° C. or higher, preferably 230 to 280° C., in the latter half of the reaction. Roughly converts benzamides into benzonitriles. In this case, the boiling point of the target benzonitrile is usually 200 to 280°C.
Therefore, it is best to adopt a so-called reactive distillation method in which the produced benzonitriles are reacted with by-product water while being pumped out of the reactor under slightly reduced pressure as the case may be, in order to shift the reaction equilibrium to the product side and reduce the production It is advantageous in that it allows substances to be isolated without thermal deterioration.

In addition, if the heating temperature is set to 220°C or higher from the initial stage of the reaction,
Benzoic acids can be converted to benzonitriles without accumulating benzamides in the reaction system, but at high temperatures, urea tends to distill out of the system, self-decompose, and self-condensate, so the required amount of urea to be charged is This is not a very preferable operating method because as the amount of benzoic acid increases, unreacted benzoic acids and benzonitriles tend to leak out of the system, leading to a decrease in the yield and purity of the target substance.

The benzonitriles distilled from the reactor have sufficient purity and can normally be used as raw materials for medicines, agricultural chemicals, dyes, pigments, etc. However, small amounts of benzamides, benzoic acids, Since it contains ammonium carbonate and water, it can be purified to a high purity product by distilling it again or recrystallizing it.

On the other hand, the residue remaining in the reactor contains the unreacted benzoic acids and benzamides as well as the catalyst that remains active, so by newly adding benzoic acids and urea, the The synthesis reaction of benzonitriles can also be carried out repeatedly without re-adding the catalyst.

(Example〕 The present invention will be specifically described below with reference to Examples.

Example 1 In a glass reactor equipped with a stirrer and a distillation tube, 70 parts of ○-chlorobenzoic acid, 29.5 parts of urea (1.1 times the mole of o-chlorobenzoic acid), and four cobalt acetate bottles were added. 1.4 parts of the salt (2% by weight based on 0-chlorobenzoic acid) and 1.4 parts of Orthoform M were heated to 200°C for 4 hours. The composition of the reaction mixture at this point was O-chlorobenzamide 82.7
The weight percentage was 2.5% for 0-chlorobenzonitrile, 1.3% for O-chlorobenzoic acid, and 13.5% for others.

Subsequently, the temperature was raised to 240° C. or higher, and the resulting 0-chlorobenzonitrile was distilled out from the distillation tube together with by-product water under slightly reduced pressure, while heating and stirring was continued for 9 hours. The composition of 57.6 parts of the condensed distillate was 90.7% O-chlorobenzonitrile, 1.3% O-chlorobenzamide, 1.2% O-chlorobenzoic acid, and 6.8% others. . The composition of 9.2 parts of reactor residue was 51 parts of 0-chlorobenzoic acid.
．． 9%, 0-chlorobenzamide 3.8%, 0-chlorobenzonitrile 10.7%, and others 33.6%.

In addition, when the distillate is redistilled, the purity is 99.7% and the melting point is 4.
51.2 parts of 0-chlorobenzonitrile at 3-44°C were obtained. The consistent isolation yield of purified 0-chlorobenzonitrile from 0-chlorobenzoic acid was 83.2%.

Example 2 In Example 1, O-toluyl was substituted for O-chlorobenzoic acid! When 60.8 parts were used and reacted under the same conditions, purified o-tolunitrile with a purity of 99% or more was obtained in an isolated yield of 81.0%.

Example 3 When 67.9 parts of p-methoxybenzoic acid was used instead of 0-chlorobenzoic acid in Example 1 and the reaction was carried out under the same conditions, purified p-methoxybenzonitrile with a purity of 99% or more was obtained. 1q was obtained with an isolated yield of 72.5%.

Comparative Example 1 When the reaction was carried out under the same conditions as in Example 1 without adding cobalt acetate/shibonsalt, a purified product with a purity of 99% or more was obtained.
-The isolated yield of chlorobenzonitrile was only 28.5%.

Comparative Example 2 When the reaction was carried out under the same conditions as in Example 1 without adding orthoboric acid, the isolated yield of purified O-chlorobenzonitrile with a purity of 99% or more was only 62.0%.

Comparative Example 3 In Example 1, 0.6 part of basic cobalt carbonate was used in place of cobalt acetate/tetrasalt and the reaction was carried out under the same conditions, resulting in purified O-chlorobenzonitrile with a purity of 99% or more. The isolated yield was only 69.5%.

Comparative Example 4 When the reaction was carried out under the same conditions as in Example 1 using 1.4 parts of phosphoric acid instead of cobalt acetate tetrasalt and orthoboric acid, purified O-chlorobenzonitrile with a purity of 99% or more was obtained. was obtained with an isolated yield of 81.3%, but a white H film-like deposit was observed on the wall of the glass reactor used.

It was difficult to wash off this deposit using various solvents.

(Effects of the Invention) The method of the present invention has made it possible to economically produce benzonitriles of good quality without using expensive chemicals.

Claims (1)

[Claims] A method for producing benzonitriles by subjecting benzoic acids and urea to a heating reaction in a molten state, the method comprising using cobalt acetate and boric acid together as catalysts.