prov:value
| - Preferred examples of R.sup.4 and R.sup.5 are hydrogen and hydrocarbon residues such as alkyl groups, e.g. methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and n-hexyl, alkoxyphenyl groups, e.g. methoxyphenyl and ethoxyphenyl, alkylphenyl groups, e.g.tolyl and ethylphenyl, aryl groups, e.g. phenyl, chlorophenyl and nitrophenyl, aralkyl groups, and derivatives thereof, furyl, and pyridyl.Ar.sup.
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