Influence of Nucleophiles on the High Temperature Aqueous Isomerization of cis- to trans-Cinnamic Acid

Article abstract of DOI:10.1021/jo00075a034

The rate of isomerization of cis- to trans-cinnamic acid in water at 195 deg C was monitored as a function of added nucleophile.The expected nucleophile addition products were not observed but could be synthesized and, when subjected to the reaction conditions, rapidly converted to trans-cinnamic acid.Deuterium labeling studies indicated that proton abstraction was not the rate-determining step, that the α-deuterium of α,β-dideuterio-cis-cinnamic acid was rapidly exchanged for an α-hydrogen atom without loss of the cis geometry, and that some direct isomerization of cis- to trans-cinnamic acid occured without the loss of vinyl deuterium atoms.The isomerization appears to involve an addition-elimination mechanism in the case of HO(1-) and HS(1-) ions, with the former more effective.Anthrahydroquinone ion was quite effective, meaning that it was a superior nucleophile or was promoting reactions by another mechanism (possibly electron tranfer chemistry).The results have bearing on the rate-determining step in one of the delignification mechanisms occurring during the pulping of wood.