| prov:value
| - methyl or phenyl, and X??? may be an anion such as hydroxide, sulfate, hydrogen sulfate, hydrogen carbonate, carbonate, a halide, preferably chloride, or an alcoholate of the formula OR, in which R may be C6-C14-aryl or C7-C12-aralkyl, preferably phenyl. [0048] Preferred catalysts are tetraphenylphosphonium chloride, tetraphenylphosphonium hydroxide, and tetraphenylphosphonium phenolate, with tetr
|