TY - JOUR
T1 - Kinetic and theoretical considerations in the hydrolysis of iminocarbonates
AU - Katzhendler, Jehoshua
AU - Goldblum, Amiram
AU - Ringel, Israel
PY - 1988
Y1 - 1988
N2 - Analysis of the pH-rate profiles for the hydrolysis of 4-methyl-2-(N- phenylimino)-1,3-dioxolane (1) and 2-[N-(p-fluorophenyl)imino]-4-phenyl-1,3- dioxolane (2) together with product distribution of compounds (1)-(5) and pK values estimated for the various ionic forms T0, T+, T±, and T- of the tetrahedral intermediates, enables the determination of the reactivity of the tetrahedral intermediates along their reaction pathways. At pH <6, the only products formed are the amine and the carbonate (C-N fission) and at pH >6 C-O bond fission increases to form carbamates. The transition point corresponds to pK values of 9.2 and 8.5 for compounds (1) and (2), respectively. It is proposed that in acidic solution C-N bond fission proceeds via T+ ⇌ T+ → P while at a moderate pH this bond fission proceeds via a proton-switch mechanism T0 → T±. At pH > 11 the only product produced is the hydroxycarbamate (C-O fission) via its anionic intermediate T-. Mono- and gem-dimethyl substituted iminocarbonates T- undergo two modes of ring-opening. Employing MNDO/H calculations the relative stability (ΔHF) of the intermediates and their formed products was predicted and correlated with actual experimental product distribution.
AB - Analysis of the pH-rate profiles for the hydrolysis of 4-methyl-2-(N- phenylimino)-1,3-dioxolane (1) and 2-[N-(p-fluorophenyl)imino]-4-phenyl-1,3- dioxolane (2) together with product distribution of compounds (1)-(5) and pK values estimated for the various ionic forms T0, T+, T±, and T- of the tetrahedral intermediates, enables the determination of the reactivity of the tetrahedral intermediates along their reaction pathways. At pH <6, the only products formed are the amine and the carbonate (C-N fission) and at pH >6 C-O bond fission increases to form carbamates. The transition point corresponds to pK values of 9.2 and 8.5 for compounds (1) and (2), respectively. It is proposed that in acidic solution C-N bond fission proceeds via T+ ⇌ T+ → P while at a moderate pH this bond fission proceeds via a proton-switch mechanism T0 → T±. At pH > 11 the only product produced is the hydroxycarbamate (C-O fission) via its anionic intermediate T-. Mono- and gem-dimethyl substituted iminocarbonates T- undergo two modes of ring-opening. Employing MNDO/H calculations the relative stability (ΔHF) of the intermediates and their formed products was predicted and correlated with actual experimental product distribution.
UR - http://www.scopus.com/inward/record.url?scp=37049068424&partnerID=8YFLogxK
U2 - 10.1039/P29880001653
DO - 10.1039/P29880001653
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AN - SCOPUS:37049068424
SN - 1472-779X
SP - 1653
EP - 1660
JO - Journal of the Chemical Society, Perkin Transactions 2
JF - Journal of the Chemical Society, Perkin Transactions 2
IS - 9
ER -