prov:value
| - Compound as claimed in claim 1, wherein R1 and R2 each independently is hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or tert-butyl, X is a hydrogen atom, a fluorine, chlorine, bromine or iodine atom, a nitro, methyl, methoxy, ethyl, ethoxy, n-propyl, n-propoxyl, isopropyl, isopropoxy or n-, iso-, sec- or tert-butyl or -butoxy group, a and n each independently is 1 or 2, Y is a
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