prov:value
| - R1, R2, R3, and R4 are the same or different and each is a hydrogen atom, a hydroxy, a halogen atom, an alkoxy, a mercapto, an alkylthio, a nitro, a cyano, a carboxy, an alkoxycarbonyl, an aryloxycarbonyl, an acyl, an alkyl optionally substituted by
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