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Electrocyclic versus homolytic decompositions of peroxides: Solvent and phase effects
Author(s) -
Hiatt R.,
Rahimi P. M.
Publication year - 1978
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550100205
Subject(s) - homolysis , chemistry , acetone , solvent , solvent effects , peroxide , medicinal chemistry , photochemistry , radical , organic chemistry
Abstract The thermal decomposition of isopropyl peroxide in solvents is shownto be a competition between unimolecular homolysis ( k r ) and an electrocyclic reaction yielding H 2 plus acetone ( k H ). The value of k H increases markedly with increasing solvent polarity: PhCH 3 < i ‐PrOH < MeOH < H 2 O. Log k H correlates linearly with E t (or Z ). The effect on k r is similar but less pronounced. Log k r 's for both i ‐Pr 2 O 2 and t ‐Bu 2 O 2 are shown to correlate with the molar solubility parameter δ. The negligible contribution of the electrocyclic reaction to thermal decompositions of peroxides in the vapor phase is thus not due to peculiar behavior of that reaction, which clearly has a polartransition state. It is argued that the transition state for unimolecular homolysis has no polar character despite the apparent sensitivity of homolysis rates to solvent polarity.