DE1144256B - Process for the preparation of 2, 3, 6-trichlorobenzoic acid - Google Patents

Description

GERMAN

PATENT OFFICE

N 20683 IVb / 12 ο

REGISTRATION DATE: OCTOBER 17, 1961

NOTICE
THE REGISTRATION
ANDOUTPUTE
EDITORIAL: FEBRUARY 28, 1963

processed into a product with this acid

2,3,6-Trichlorobenzoic acid is a known herbicidal agent. The commercially available 2,3,6-trichlorobenzoic acid contains not only isomeric trichlorobenzoic acids but also tetrachlorobenzoic acids, e.g. B. 2,3,5,6-tetrachlorobenzoic acid. These isomeric tri- and tetrachlorobenzoic acids have a significantly lower herbicidal effect than 2,3,6-trichlorobenzoic acid. In addition, the presence of these components leads to undesirable difficulties in those cases where a selective action is required, e.g. B. in combating sticky herb and chicken intestines in cereals. The technical commercial product containing about 60 percent by weight of 2,3,6-trichlorobenzoic acid cannot be produced in a simple manner
a higher salary
will.

According to the invention, 2,3,6-trichlorobenzoic acid is obtained by allowing chlorine to act on 2,3-dichloro-6-nitrobenzonitrile ^{at 200 to 230 ° C. and saponifying the 2,3,6-trichlorobenzonitrile obtained.}

The proposed procedure, in which the nitro group is replaced by chlorine, is surprising high yields of 2,3,6-trichlorobenzonitrile practically approaching the theoretical value high purity, that of the herbicide 2,3,6-trichlorobenzoic acid used on a large scale in practice can be saponified.

The 2,3,6-trichlorobenzonitrile can be used to convert such into 2,3,6-trichlorobenzoic acid Nitriles can be converted into carboxylic acids in a known manner or in a similar manner, e.g. B. by Exposure to a base or a mineral acid. The nitrile is first converted into the carboxamide and then converted to the carboxylic acid. It is particularly advantageous to mix the nitrile with alcoholic Lye, e.g. B. caustic soda or potassium hydroxide to convert into the corresponding carboxamide, which is converted into carboxylic acid with nitrosylsulfuric acid. This method gives a good yield of an almost pure product.

The 2,3,6-trichlorobenzonitrile can be prepared from 2,3-dichloro-6-nitrobenzonitrile by introducing chlorine into the molten starting material until no more nitrous vapors escape. In the case of continuous operation, molten 2,3-dichloro-6-nitrobenzonitrile and chlorine are preferably passed in countercurrent through a reaction device with inert packing. The reaction is carried out between 200 and 23O ⁰ C.

Process for the preparation of 2,3,6-trichlorobenzoic acid

Applicant:

N. V. Philips' Gloeilampenfabrieken, Eindhoven (Netherlands)

Representative: Dipl.-Ing. H. Zoepke, patent attorney, Munich 5, Erhardtstr. 11

Claimed priority: Netherlands of October 20, 1960 (No. 257 082)

Harmannus Koopman, Weesp (Netherlands), has been named as the inventor

2
example

a) Chlorine was introduced into 500 g of 2,3-dichloro-6-nitrobenzonitrile at a temperature of 200 to 205 ^° C. until no more nitrous vapors escaped. The duration was about 2 hours. The product crystallized after cooling and consisted of practically pure 2,3,6-trichlorobenzonitrile. Yield: 460 g (97%) 2,3,6-trichlorobenzonitrile. Melting point 118 to 121 ^° C. The 2,3-dichloro-6-nitrobenzonitrile, which is a new substance, had been prepared from 2,3,4-trichloronitrobenzene by reaction with cuprocyanide in the presence of pyridine.

b) A mixture obtained by adding a solution of 36 g of potassium hydroxide in 40 cm ^{3 of} water to a solution of 34.4 g of 2,3,6-trichlorobenzonitrile in 200 cm ^{3 of} ethanol was refluxed for 4 hours . After the ethanol was then distilled off under reduced pressure, the residue was neutralized with concentrated hydrochloric acid while cooling in ice. The resulting crystals of 2,3,6-trichlorobenzamide were filtered off with suction, washed with water and dried. Yield: 34.8 g (93%). The 2,3,6-trichlorobenzamide was dissolved in 155 ml of concentrated sulfuric acid; the resulting solution was cooled to 1O ⁰ C and a solution of 14 g sodium nitrite in 40 ml of water is between 10

309 537.416

and 20 ° G was added dropwise. The mixture was slowly warmed to 50 to 60 ⁰ C. After the relatively vigorous evolution of gas that occurred, the mixture was heated to 110 ° C. for a further 20 minutes. When pouring onto blocks of ice, 2,3,6-trichlorobenzoic acid crystallized out. This was separated and washed with cold water. Yield: 25 g (71%).

The 2,3,6-trichlorobenzonitrile can in known Way to be processed into an acaricide preparation.

Claims (1)

PATENT CLAIM: Process for the preparation of 2,3,6-trichlorobenzoic acid, characterized in that chlorine is introduced into 2,3-dichloro-6-nitrobenzonitrile at 200 to 230 ⁰ C until nitrous vapors are no longer formed, the reaction mixture is cooled and that 2,3,6-trichlorobenzonitrile obtained in this way is saponified by methods known per se via 2,3,6-trichlorobenzamide to give 2,3,6-trichlorobenzoic acid. 3 »557/416 2.6Ϊ