prov:value
| - These are of the general formulae (VI) and (VII) ##STR10## where R??, R?? and R?? are identical or different and are each alkyl, for example of 1 to 5 carbon atoms, preferably methyl or ethyl, aryl, such as phenyl, or aralkyl, such as benzyl, or a radical ##STR11## where R??, R?? and R?? are identical or different and are each hydrogen, OH, halogen, eg. chlorine or bromine, alkyl, for example of 1
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