. "is usual to employ an alkali or alkaline-earth metal hydroxide, preferably an alkali metal hydroxide such as especially sodium hydroxide or potassium hydroxide, and magnesium hydroxide.A sodium substituted tetraphenylborate, such as sodium tetrakis [3,5-bis(trifluoromethyl)phenyl]borate is employed in a particularly preferred manner.The substituted tetraphenylborate salt is used in the reaction in" . . .