Introduction of oxygen functions and their reactions

It has been stressed that the presence in a benzene derivative of two bulky substituents, such as chlorines ortho with respect to the reaction site may cause severe steric hindrance. As expected, the perchloroaryl carboxylic acids are not esterified by Meyer s acid-catalysed procedure either, although their methyl esters are readily prepared with diazomethane (Riera, 1961). In general, the synthesis of alkyl esters is successfully performed by acylation of alcohols with the overcrowded acid chlorides, the latter being obtained smoothly from the corresponding acids with thionyl chloride. 

Polyesterification and polyamidation (77) have also been effected with perchloroaromatic bifunctional components (Ballester, 1979). (Acylating components tetrachloroterephthaloyl dichloride, 4,4 -dichloroformyl-octachlorobiphenyl. Substrates tetrachlorohydroquinone, tetrachloresorci- 

Because of steric shielding, the hydrolysis of aromatic chlorinated esters and amides cannot be carried out under normal conditions, not even with the Hammett-Newman method, i.e. treatment with concentrated sulphuric acid and then with water. For comparison, the hydrolysis of highly hindered esters, such as ethyl mesitoate, can readily be performed in concentrated sulphuric acid (Treffers and Hammett, 1937 Newman et al., 1945). Hydrolysis of the perchlorinated esters can be effected with oleum in excellent yields. (To perform that of perchloroamides, hot (160°C) oleum is required (Ballester et al., 1978b).) It is assumed that the mechanism of hydrolysis for perchloroesters with oleum is analogous to that proposed by Newman, i.e. 

Treatment of / -methoxyheptachlorostyrene with oleum affords / -hydroxy-heptachlorostyrene. The hydrolysis of a,/ -dimethoxyhexachlorostyrene by means of concentrated sulphuric acid gives a//-/ -ethoxyhexachloroaceto-phenone (Ballester et al., 1980e) total hydrolysis can be accomplished with oleum. It is noteworthy that hydrolytic oxidation results from the direct treatment of dimethoxyhexachlorostyrene with oleum, 4-methoxytetra-chlorobenzoic acid being the product (79). 

NUCLEOPHILIC AROMATIC SUBSTITUTIONS WITH HYDROXIDE AND ALKOXIDE IONS 

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