2,4-Dichlorophenols

In addition to the Hquid—Hquid reaction processes, there are many cases in both analytical and industrial chemistry where the main objective of separation is achieved by extraction using a chemical extractant. The technique of dissociation extraction is very valuable for separating mixtures of weakly acidic or basic organic compounds such as 2,4-dichlorophenol [120-83-2] and 2,5-dichlorophenol [583-78-8] which are difficult to separate by... 

Amino-4,6-dichlorophenol. This compound (11) forms long white needles from carbon disulfide, and aggregate spheres from benzene. It sublimes at 70—80°C (8 Pa = 0.06 mm Hg) and decomposes above 109 °C. It is freely soluble in benzene and carbon disulfide, and is sparingly soluble in petroleum ether, water, and ethanol. The free base is unstable and the hydrochloride salt (mp 280—285°C, dec) is employed commercially. 

Industrial production is by reduction of the corresponding nitrophenol with iron or hydrazine (167,168). 2-Amino-4,6-dichlorophenol finds important use as an azo-dye intermediate (see Azo dyes). 

The reductive dechlorination of chlorinated aromatics is more compHcated in that the initial dechlorination of more highly chlorinated compounds may be either chemical or enzymatic, eg, PGP, whereas the dechlorination of less chlorinated compounds or dechlorinated products is typically enzymatic. For example, the first dechlorination of 2,4-dichlorophenol (ortho position) can occur either chemically or enzymatically the second dechlorination (para position) is enzymatic (eq. 10). 

Other compounds that have shown promising properties in vitro against E. histolytica are niridazole (10), tinidazole (11, Fasigyn, Simplotan), gossypol (12), bithionol [(13), 2,2 -thiobis(4,6-dichlorophenol)], and pimaricin (14, Natamycia [7681-93-8]). The chemotherapy of amebiasis has been reviewed (9). 

Dichlorophenols. Among all the dichlorophenols, C H Cl O, it is 2,4-dichlorophenol that is produced in greatest quantity. 2,4-Dichlorophenol is used in manufacturing 2,4-dichlorophenoxyacetic acid [94-75-7] (2,4-D) and 2-(2,4-dichlorophenoxy)propionic acid [720-36-5] (2,4-DP). Industrially, 2,4-dichlorophenol can be obtained by chlorinating phenol, -chlorophenol, o-chlorophenol, or a mixture of these compounds in cast-iron reactors. The chlorinating agent may be chlorine or sulfuryl chloride in combination with a Lewis acid. For example ... 

Chlorination with SO2CI2, which is favorable to the para isomer at the monochlotination stage, gives an excellent yield of 2,4-dichlorophenol. Startiag with (9-chlorophenol, it is possible to attain a selectivity for 2,4-dichlorophenol of 98%, if chlotination is carried out ia Hquid SO2 at low temperature (20). 2,6-Dichlorophenol is also used as an iatermediate. It is obtained by chlotinatiag o-chlorophenol ia the presence of a catalytic quantity of an amine, with or without a solvent medium (21,22), giving a yield of 90%. 

In the chlorination of 2,4-dichlorophenol it has been found that traces of amine (23), onium salts (24), or triphenylphosphine oxide (25) are excellent catalysts to further chlorination by chlorine ia the ortho position with respect to the hydroxyl function. During chlorination (80°C, without solvent) these catalysts cause traces of 2,4,5-trichlorophenol ( 500 1000 ppm) to be transformed iato tetrachlorophenol. Thus these techniques leave no 2,4,5-trichlorophenol ia the final product, yielding a 2,4,6-trichlorophenol of outstanding quaUty. The possibiUty of chlorination usiag SO2CI2 ia the presence of Lewis catalysts has been discussed (26), but no mention is made of 2,4,5-trichlorophenol formation or content. 

Chlorination of 2,6-dichlorophenol by chlorine at 70°C gives a yield of only 85%. Fifteen percent of the mixture is made up of 2,4,5,6,6-pentachloro-2-cyclohexen-l-one, the formation of which can be explained by the foUowiag mechanism ... 

Effects in Animals. The LD ia rats for all light chlorophenols, irrespective of the administration route, ties between 130 and 4000 mg/kg body weight. The toxicity of these compounds ia order of increasing strength is tetrachlorophenols > monochloropheno1 s > dichlorophenols > trichlorophenols when the chlorophenol is administered either orally or by subcutaneous iajection. 

Dow produces 2,4-dichlorophenol chiefly for a captive market ia the United States and Bra2il. 

In addition to the use of 2,4-dichlorophenol in the synthesis of 2,4-D herbicides (acid 2,4-D, acid 2,4-DP, acid 2,4-DB), it is also found in the selective post-emergence herbicide, diclofop-methyl [51338-27-3] (61) and as a selective pre-emergence herbicide, oxadia2on [19666-30-9] (62). A postemergence herbicide is appHed between the emergence of a seedling and the maturity of a crop plant. 

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