The term phenyl lower alkyl as used herein may include phenyl alkyl groups having 1 to 6 carbon atoms in the alkyl moiety such as benzyl, ??-phenethyl, ??-phenethyl, 3-phenylpropyl, 4-phenylbutyl, 2-methyl-2-phenylethyl, 2-methyl-3-phenylpropyl and the like.