nol; an ester such as ethyl acetate, propyl acetate, butyl acetate or ethyl propionate; a carboxylic acid such as acetic acid or propionic acid; water; or a mixture of solvents mentioned above, and is preferably a halogenated hydrocarbon or a carboxylic acid, and particularly preferably dichloromethane, chloroform, dichloroethane or acetic acid) at a temperature between ???20??? C. and 150??? C. (