prov:value
| - The process as claimed in claim 3, wherein, in said formula I, R11, R12 and R13 are identical or different and are a hydrogen atom, a halogen atom, a C1 -C4 -alkyl group, a CF3 group, a C6 -C8 -aryl group, a pentafluorophenyl group, a C1 -C4 -alkoxy group, a C2 -C4 -alkenyl group, a C7 -C10 -arylalkyl group, a C8 -C12 -arylalkenyl group or a C1 -C12 -alkylaryl group, or R11 and R12 or R11 and R13,
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