| Abstract
| - A spectroscopic and kinetic study of the reaction of methyl β-methylthio-α-nitrocinnamate (4-SMe) withmorpholine, piperidine, and hydroxide ion in 50% DMSO/50% water (v/v) at 20 °C is reported. Thereactions of 4-SMe with piperidine in a pH range from 10.12 to 11.66 and those with morpholine at pH12.0 are characterized by two kinetic processes when monitored at λmax (364 nm) of the substrate, but byonly one process when monitored at λmax (388) nm of the product. The rate constants obtained at 388 nmwere the same as those determined for the slower of the two processes at 364 nm. These rate constantsrefer to product formation, whereas the faster process observed at 364 nm is associated with the loss ofreactant to form an intermediate. In contrast, for the reaction of 4-SMe with morpholine at pH 8.62 therates of product formation and disappearance of the substrate were the same, i.e., there is no accumulationof an intermediate. Likewise, the reaction of 4-SMe with OH- did not yield a detectable intermediate.The factors that allow the accumulation of intermediates in certain SNV reactions but not in others arediscussed in detail, and structure−reactivity comparisons are made with reactions of piperidine andmorpholine with other highly activated vinylic substrates.
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