. . "Preferred possibilities for use are 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, which can also be employed in the presence of phase transfer catalysts such as, for example, triethylbenzylammonium chloride, tetrabutylammonium bromid" . . . . . . .