Carbon-14 and tritium isotope effects in Hofmann degradation of quaternary amines
At the time we started the following studies there were only a few measureDlents of isotope effects in E2 reactions of the Hofmann elimination type. Saunders and Aspergerl have found that substitution of 34S for 32S in the + base-catalysed elimination reaction of C6H5CH2CH2S(CH3)2Brresults in a negligible kinetic isotope effect, indicating that the activation process in the r ate-delermining step involves practically no stretching of the C-S bond in the transition state. Later, Saunders and Edison2 determined the deut•:!rium isotope effects for E2 eliminations on compounds of the type + + CaH5CDzCHzX with X = S(CH3)2 and X = N(CHs)3. Rodnett and Flynn3 measured the isotope effect for trimethyl-(p-nitro-ßphenethyl-ß-T)-ammonium iodide and found kH/kT = 7·4 ± 2·8. Shiner and Smith4 degraded trimethyl-ethyl-ß-D3-ammonium hydroxide and obtained the value kH/kn = 3·9 ± 0·5 at 137°. A few months ago Ayrey, Bourns et al.5 published the measurements of nitrogen isotope effects for ethyl-trimethylammonium-15N hydroxide and trimethyl-ß-phenethylc=,:mmonium-15N hydroxide. We cletermined the carbon-14 and tritiumisotope effects for the following <tuarternary ammonium hydroxides: + (CH3)NR, OH(1) R = 14CH2CH3 (II) R = _l4CH2CHzCHs (III) R = 14CHzCHzCaH4N02(p) ~IV) R = 14C(CHs)s (V) R = CH2 14CH2CHs (VI) R = -CHTCHzCHa (VII) R = -CH2CHTCH3 (VIII) R = -CH2CH2CH2T (IX) R = -CH2CH2T (X) R = -CH2CHTCaH4N02(P) +oc ß (CHs)3NCH2CH2+ B--+ (CHs)aN + CH2=CH+ HB