inert with respect to the reactants and immiscible with water; for this purpose, it is possible to use, in particular, aromatic hydrocarbons, especially alkylbenzenes such as toluene or xylene, and, where appropriate, to add a dehydrating agent such as, for example, para-toluenesulphonic acid; it is preferable to work at the refluxing temperature of the solvent or solvent mixture used; the imines