may be optionally substituted with one or more halogen atoms, and wherein if the aryl group is phenyl or naphthyl then the phenyl or naphthyl may be optionally substituted with C1 -C4 alkyl, up to C4 alkenyl or C1 -C4 alkoxy, provided that at least one of R3, R4 and R5 is a methyl group substituted with one, two or three halogen atoms; and (3) a solvent. 8.