Kinetics, isotope rate effect, and mechanism of dehydrobromination of cis-1,2-dibromoethylene with triethylamine in dimethylformamide

Formation kinetics of an amino carboxy type merostabilized free radical

“…Dioxindole was prepared by the reduction of isatin with sodium dithionite in aqueous solution as described by Marschalk.13 3,5,5-Trimethyl-2-morpholinone was obtained previously from the disproportionation of radical 4.2 jV-Methylisatin (6). /V-Methylisatin was prepared by the reaction of the sodium salt of isatin with methyl iodide using a procedure analogous to that described by Heller.11 The product, recrystallized from water, melted at 129-131 °C (lit.14 mp 134 °C) and gave the following spectral absorptions: NMR (CDCI3) 3.30 (s, 3 H), 6.8-7.3 (m, 2 H), and 7.5-7.8 ppm (m, 2 H); mass spectrum m/e (rel intensity) 161 (28), 133 (10), 125 (19), 104 (23), and 77 (12).…”

Alkylidenecarbenes, Alkylidenecarbenoids, and Competing Species: Which Is Responsible for Vinylic Nucleophilic Substitution, [1 + 2] Cycloadditions, 1,5-CH Insertions, and the Fritsch−Buttenberg−Wiechell Rearrangement?

“…Therefore, 359 and 361 either were not formed or decayed too rapidly by elimination of KCl. The latter possibility would be in accord with the fast β-elimination of other unsaturated acyclic intermediates, , including β-halogenoalkenyl anions which require 140 some rehybridization for halide expulsion.…”

“…There-i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .fore, 359 and 361 either were not formed or decayed too rapidly by elimination of KCl. The latter possibility would be in accord with the fast β-elimination of other unsaturated acyclic intermediates,326,327 including β-halogenoalkenyl anions which require 140 some rehybridization for halide expulsion. The decarboxylation of13 C-labeled (*) 356 produced mixtures 319 of the isotopomers 350 and 351 in the ratio 81:19 from (E)-356 via (Z)-357 but in a 23:77 ratio from (Z)-356 (not shown) via (E)-357.…”

Reductive Elimination of Chlorinated Ethylenes by Zero-Valent Metals

“…Although dehydrohalogenation does occur for haloethylenes (48)(49)(50), it requires extreme conditions in homogeneous solution. Thus, the second-order rate constant for OHreaction with TCE in water at 25 °C is 1.8 × 10 -7 M -1 s -1 (51), yielding a half-life at pH 7 of 10 6 years.…”

“…Cipollone et al . () have speculated this arises through the sequential hydrogenolysis of tetrachloroethylene (PCE) to trichloroethylene (TCE), dichloroethylenes (DCEs), and then vinyl chloride (VC), followed by VC dehydrohalogenation to acetylene: Although dehydrohalogenation does occur for haloethylenes ( − ), it requires extreme conditions in homogeneous solution. Thus, the second-order rate constant for OH - reaction with TCE in water at 25 °C is 1.8 × 10 -7 M -1 s -1 (), yielding a half-life at pH 7 of 10 6 years.…”