3205-31-0Relevant articles and documents
Kinetics of α-(2,6-Dimethylphenl)vinyllithium: How to Control Errors Caused by Inefficient Mixing with Pairs of Rapidly Competing Ketones
Knorr, Rudolf,Knittl, Monika,Behringer, Claudia,Ruhdorfer, Jakob,B?hrer, Petra
, p. 2843 - 2854 (2017/03/23)
Kinetic studies are a suitable tool to disclose the role of tiny reagent fractions. The title compound 2 reacted in a kinetic reaction order of 0.5 (square root of its concentration) with an excess of the electrophiles ClSiMe3, 1-bromobutane (n-BuBr), or 1-iodobutane (n-BuI) at 32 °C in Et2O or in hydrocarbon solvents. This revealed that the tiny (NMR-invisible) amount of a deaggregated equilibrium component (presumably monomeric 2) was the reactive species, whereas the disolvated dimer 2 was only indirectly involved as a supply depot. Selectivity data (relative rate constants κobs) were collected from competition experiments with the faster reactions of 2 in THF and the addition reactions of 2 to carbonyl compounds. This provided the rate sequences of Et2C=O > dicyclopropyl ketone > t-Bu-C(=O)-Ph > diisopropyl ketone ? t-Bu2C=O > ClSiMe3 > n-BuI > n-BuBr ≈ (bromomethyl)cyclopropane (but t-Bu2C=O 3 in THF only) and also of cyclopropanecarbaldehyde > acetone ≥ t-Bu-CH=O. It is suggested that a deceivingly depressed selectivity (1 obs A/kB), caused by inefficient microscopic mixing of a reagent X with two competing substrates A and B, may become evident toward zero deviation from the correlation line of the usual inverse (1/T) linear temperature dependence of ln κobs.
