HU193841B - Process for preparing 3,5,6-trichlor-2-hydroxy-benzoic acid - Google Patents

Abstract

3,5,6-Trichloro-2- hydroxy-benzoic acid is obtd. by the oxidn. of 3,5,6 trichloro-benzaldehyde with Ag2O. The aldehyde is obtd. from 2,4,5-tri-chloro-phenol by formulation. Silver oxide is regenerated via its nitrate, with alkalies.

Description

This application relates to a novel process for the preparation of 3,5,6-trichloro-2-hydroxybenzoic acid. The above compound is used as an intermediate of bis-2,4,5-trichloro, 6-carbopentoxyphenyl oxalate (CPPO) as an intermediate in a component of chemiluminescent compositions based on the peroxoxalate principle.

3,5,6-trichloro, 2-hydroxybenzoic acid is prepared according to the literature discussed in more detail below: 3,5-Dichloro-salicylic acid, obtained by direct chlorination of salicylic acid in 2060% fuming sulfuric acid and then further chlorinated to 3,5,6-trichloralsalicylic acid:

Thus, U.S. Patent No. 3,013,055. According to US patent, the chlorination process in fuming sulfuric acid at 80-90 ° C yields the target compound in 70% yield. No. 3,062,877, an improved version of this chlorination reaction. According to US patent, the same chlorination process can be carried out in the presence of 1 ppm of 1% iodine catalyst. An improved version of the pathway is disclosed in U.S. Patent No. 4,308,395. U.S. Pat. No. 4,123,125, according to which salicylic acid is chlorinated in sulfuric acid and then the sulfuric acid solution of the obtained 3,5-dichloralsalicylic acid is saturated by the addition of sulfuric trioxide. The compound is then further chlorinated in the presence of an iodine catalyst. The latter method provides the target compound with a production of over 90%.

A common feature of all variants of the processes described above is that the target compound is prepared by further chlorination of 3,5-dichlorosalicylic acid with elemental chlorine in the presence of a very aggressive solvent (oleum). The above chlorination processes can only be carried out with the utmost care in specially trained devices. A particular disadvantage of the above processes is that their by-products (a mixture of sulfuric and hydrochloric acid gas saturated with chlorine and hydrogen chloride gas) are very environmentally unfavorable.

A further disadvantage of the described processes is that the chlorination process is accompanied by constant by-reactions which result in the formation of various by-products in addition to the target compound. These by-products according to the studies of C.D. Dowd and D.B. Paul (Aust. J. Chem., 1984, p. 73-86) are chloranyl, trichloralsalicylic acid trimer, 2,3,5,6-tetrachlorohydroquinone and trichloralsalicylic acid polymer.

In the present invention, a process for the preparation of 3,5,6-trichloro-2-hydroxybenzoic acid has been developed, whereby the above compound can be obtained in high purity bypassing the chlorination process in very good yield.

The starting compound of the present invention is 3,5,6-trichloro, 2-hydroxybenzaldehyde which can be obtained from 2,4,5-trichlorophenol in the formylation reaction.

Any of the known 2 aromatic electrophilic formylation processes (Gatterman, Gatterman-Koch, Vilsmeier, Reimer-Tiemann, Duff syntheses) can be used to carry out the above reaction.

According to our method, 3,5,6-trichloro-2-hydroxybenzaldehyde can be converted almost quantitatively into the target compound by alkaline silver oxide precipitation from alkaline aqueous solution by alkalization from solution. The reaction shows particularly surprising selectivity for this oxidation process.

Other well-known reagents for the formation of -CHO-> COOH oxidation (chromates, oxygen, bichromates, etc.) do not perform this reaction. After filtering off the precipitated metal silver, the filtrate is acidified and then precipitated

3.5.6-Trichloro-2-hydroxybenzoic acid is filtered off. The metal silver formed as a by-product of the process is converted into silver nitrate with nitric acid, which can be reused.

Thus, by turning the silver, an economical method for the preparation of the above compound is obtained, since the process oxidant is practically nitric acid, which initiates the Ag -?

The following example illustrates our process without limiting the scope of protection.

Example:

Potassium hydroxide (g) was dissolved in water (200 ml) and then 3,5.5-trichloro-2-hydroxybenzaldehyde (22.5 g) and silver oxide (25 g) were freshly prepared in 38.5 g of silver nitrate. ml of aqueous solution of potassium hydroxide by means of a solution of 30 g of potassium hydroxide in 100 ml of water. The reaction mixture was heated to 100 ° C for 30 minutes and then held at this temperature for 15 minutes. The suspension is cooled to 20 ° C, the silver is filtered off and the precipitate is washed with 50 ml of 5% potassium hydroxide solution. The mother liquor and the washing liquid were adjusted to pH 2 with 10% hydrochloric acid at 25-30 ° C and the resulting suspension was stirred at 0 ° C for 2 hours. The precipitated crystals are then filtered off, the crystals are washed on the filter 2 times with 50 ml of ice water and dried under an infrared lamp.

Yield: 21.9 g of 3,5,6-trichloro-2-hydroxybenzoic acid (91%).

M.p. 207 ° C (liter: 207-8 ° C)

Elemental analysis: C M Cl

Theoretical 34.8 1.24 44.1

Found 39.9 1.30 44.0

TLC identification: Running solvent: CHCl ₃ 45 mL c-hexane 45 mL ethanol 5 mL acetic acid 5 mL

Layer: Kieselgel 60 F ,, ₅₄ (Merck) Visualization: UV (254 nm)

Rf values:

3.5.6 - trichloro, 2-hydroxybenzaldehyde: 0.85

3.5.6-trichloro, 2-hydroxybenzoic acid: 0.20

Claims (1)

A process for the preparation of 3,5,6-trichloro-2-hydroxybenzoic acid, wherein 3,5,6-tri-2193841 chloro-2-hydroxybenzaldehyde is prepared in a molar ratio of 3,5,6-trichloro-2-hydroxy. per liter of benzaldehyde, prepared in a manner known per se, by basing silver nitrate with 0.9-1.3 moles of silver oxide in an aqueous solution containing 0.9-3.0 moles of potassium hydroxide at 50-100 ° C for 5-60 minutes. oxidized, then precipitated and filtered from the reaction mixture) is converted into nitric acid with nitric acid in a known manner, reused in the process 5 is isolated after acidification of 3,5,6-trichloro, 2-hydroxybenzoic acid, preferably hydrochloric acid.