19497-26-8Relevant articles and documents
Kinetic study of the reactions of various types of C-acids with amine bases in acetonitrile. An unusual effect of common BH+ cation on the rate constants
Galezowski, Wlodzimierz,Grzeskowiak, Iwona,Jarczewski, Arnold
, p. 1042 - 1049 (2007/10/03)
The rates of proton transfer reactions between C-acids of different types such as 1-(4-nitrophenyl)-1-nitroalkanes, 4-nitrophenylcyanomethanes, and 2,4,6-trinitrotoluene, and organic bases such as 1,1,3,3-tetrametylguanidine, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), and tri-n-butylamine have been measured in acetonitrile at pseudo-first-order conditions. A general equation for the rates of proton transfer reactions between C-acids and bases with product existing in two forms, ions and ion pairs, has been derived and its applicability tested. The equation works well except for reactions of 1-(4-nitrophenyl)-1-nitroalkanes with guanidines for which the second-order rate constant is diminished with concentration of guanidinium cation, while tetrabutylammonium salts accelerate the reactions. Possible reasons for this are discussed.
Entropy barriers to proton transfer
Meot-Ner, Michael,Smith, Sean C.
, p. 862 - 869 (2007/10/02)
Proton transfer between sterically hindered pyridines and amines proceeds through locked-rotor, low-entropy intermediates. The reactions exhibit slow kinetics (efficiencies of 0.1-0.0001) and large negative temperature coefficients (up to k = CT-8.7). The rates become slower and the temperature dependencies steeper with increasing steric hindrance. The observations are reproduced by a multiple complex-switching RRKM model that allows several alternative complexes to be rate controlling: a series of loose complexes, a locked-rotor tight complex that occurs before the formation of a hydrogen-bonded complex, and a complex located at the central barrier. The rate-limiting transition state shifts from the loose to the tight and central-barrier complexes with increasing temperature. The model suggests that at elevated temperatures, above 1000 K, ion-molecule reactions will become slow even for unhindered, small reactants. Ion kinetics may then become similar to neutral radical kinetics.