X is a halogen atom such as hydrogen, fluorine, chlorine, bromine and iodine; straight-chain, branched or cyclic alkyl having 1 to 4 carbon atoms such as methyl, ethyl, propyl and butyl; alkoxycarbonyl having 2 to 5 carbon atoms such as methoxycarbonyl, ethoxycarbonyl and butoxycarbonyl; benzoyl; alkoxycarbonylalkyl having 3 to 9 carbon atoms such as methoxycarbonylmethyl, ethoxycarbonylmethyl, bu