. . . . "able and in the case where compounds of the formula (VI) are employed, alkali metal and alkaline earth metal oxides, hydroxides and carbonates, such as sodium hydroxide, potassium hydroxide, magnesium oxide, calcium oxide, sodium carbonate, potassium carbonate and calcium carbonate, each of which can also be employed in the presence of phase-transfer catalysts, e.g. triethylbenzylammonium chloride" . . . . .