| http://www.w3.org/ns/prov#value | - A starting material for carrying out the process of the present invention is a compound of the formula (I) as defined above, wherein R1, R2, R3 and R4 can be the same or different, and represent H, a halogen such as fluorine, chlorine, bromine or the like, or an alkyl group of from 1 to about 10 carbon atoms wherein, when at least one of R1, R2, R3 or R4 is halogen, at least one of remaining R1, R
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