34253-18-4Relevant articles and documents
MECHANISM OF ESTER AMINOLYSIS IN APROTIC MEDIA AND SPECIFIC SOLVENT EFFECTS
Nagy, Otto B.,Reuliaux, Victor,Bertrand, Nicole,Mensbrugghe, Anne Van Der,Leseul, Jean,Nagy, Janos B.
, p. 1055 - 1074 (2007/10/02)
The n-butylaminolysis of nitro-substituted 4'-nitrophenyl benzoates and cinnamates as well as of phenylacetates in aprotic solvents is governed by a kinetic law implying higher order terms in nucleophile.It is shown that the attacking nucleophile forms a n-? type molecular complex with the substrate before reaching the transition state in the subsequent kinetic step.This molecular complex is a true reaction intermediate as evidenced by the observed negative activation enthalpy.Other nucleophile molecules intervene as general base catalysts.Tertiary amines also catalyse the reaction.Their catalytic activity is linearly related to their hydrogen bond forming ability and it is not a direct function of their proton basicity.By varying the nucleophile structure, an excellent Broensted relationship could be obtained for the first time in aprotic media, the β of which confirms that the catalytic collapse of tetrahedral intermediate is the rate determining step.The reaction of cinnamates turns out to be less sensitive to structural changes of the substrate than is the reaction of benzoates as shown by the corresponding Hammet ? values.The electronic effects of 2-nitro groups are strongly solvent dependent.Once more, it is established that whenever specific solvent effects (?-donor or n-donor ability) are present, they dominate the overall effect.A general reaction mechanism is proposed which not only explains the various roles played by the nucleophile but also accounts successfully for the great variety of kinetic schemes observed in aprotic media.
