Wyniki wyszukiwania - BazTech

Ograniczanie wyników

1 Polish Journal of Chemistry

1 2006

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: phosphazene

Sortuj według:

Ogranicz wyniki do:

tert-Butylimino-tris(dimethylamino)phosphorane as a Proton Acceptor in the System of Reaction of 1-Nitro-1-(4-nitrophenyl)alkanes in THF

Wisłocka I., Nowak I., Jarczewski A.

Polish Journal of Chemistry

2006

Vol. 80, nr 12

2017-2029

Unexpectedly the reaction of deprotonation of carbon acids with phosphazene bases occurred very slowly. The kinetic study of the proton transfer reactions between C-acids of the series of nitroalkanes with increasing bulk of R = H, Me, Et, i-Pr substituents as 4-nitrophenylnitromethane (1), 1-nitro-1-(4-nitrophenyl)ethane (2), 1-nitro-1-(4-nitrophenyl) propane (3), 2-methyl-1-nitro-1-(4-nitrophenyl)propane (4) and the tert-butylimino-tris(dimethylamino)phosphorane (5) named P1-t-Bu phosphazene is elaborated. The reactions have been studied in THF under pseudo-first-order conditions. The product of the proton transfer reactionwith P1-t-Bu in THF appeared to be associated into ion pairs. The equilibrium constants range from >100000 to 11.8 decreasing along with growing bulk of alkyl substituent in the reacting C-acid. The second order rate constants (k2H) are rapidly declining: 9360, 2.31, 0.66, 0.09 dm3 mol–1 s–1for 1, 2, 3, and4 respectively, and could not be accounted for the small values of the enthalpies of activation HH = 6.1, 18.0, 20.7 and 11.1 kJ mol–1. The reactions show negative and relatively large values of the entropies of activation SH = –149.7, –176.5, –178.7, –227.8 J mol–1 deg–1. The primary deuterium kinetic isotope effects are large showing tendency of reverse relation towards steric hindrance of the reacting C-acids, kH/kD = 15.8, 13.6, 13.2 for 1,2, and 3, respectively. The results have been discussed in terms of the influence of steric effects brought by the bulk of alkyl substituents in the C-acid and the base on formation of the transition state. Also the influence of traces of residual water present in the reaction system has been taken into consideration.