. This reaction can be carried out in an organic solvent. The organic solvent includes e.g. aromatic hydrocarbons such as toluene, benzene and chlorobenzene, aliphatic esters such as ethyl acetate, propyl acetate and butyl acetate, ethers such as diethyl ether, diisopropyl ether and tetrahydrofuran, halogenated hydrocarbons such as dichloromethane and dichloroethane, and alcohols such as methanol, ethanol and isopropanol. These can be used 