prov:value
| - Suitable groups represented by R1, R2, R3 and R4 may be selected from hydrogen, halogen atom such as fluorine, chlorine, bromine or iodine; perhaloalkyl particularly, perfluoro(C1-C6)alkyl such as fluoromethyl, difluoromethyl, trifluoromethyl, trifluoroethyl, fluoroethyl, difluoroethyl, mono or polyhalo substituted methyl, ethyl, propyl, butyl, pentyl or hexyl groups and the like; hydroxy, thio, a
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