Preferred examples of the solvents which may be employed in the reactions include ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and xylene; ethers such as ethyl ether, tetrahydrofuran and dioxane; halogenated hydrocarbons such as chlorobenzene, chloroform, tetrachloromethane and dichloroethane; tertiary amines such as triethylamine, pyridine and dimethylani