prov:value
| - 1 to 12 carbon atoms, chosen from amongst alkyl, aryl, aralkyl, alkylaryl and cycloalkyl radicals, the best results being obtained if R' is chosen from amongst the alkyl radicals containing from 2 to 6 carbon atoms, X is a halogen chosen from amongst fluorine, chlorine, bromine and iodine, the best results being obtained if X is chlorine, and m is any number such that 0<m???3 and preferably such
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