19497-26-8Relevant academic research and scientific papers
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.
Solvent effects on the ground and excited states proton transfer in 4-methyl-2,6-diformylphenol: Aprotic solvents
Roy, R.,Mukherjee, S.
, p. 20 - 24 (2007/10/02)
The interaction of 4-methyl-2,6-diformylphenol (MFOH) with tributylamine and trioctylamine in different aprotic solvents has been studied quantitatively by means of electronic absorption and fluorescence spectroscopy with special attention to proton transfer at different temperatures.The acid-base interaction leads to different types of complexes, depending upon the dielectric constant of the solvents.In cyclohexane, dioxane or tetrahydrofuran hydrogen-bonded ion pair is formed, whereas a solvent-separated ion pair is formed in acetonitrile by the addition of amine inthe ground state.The large Stokes-shifted band in the fluorescence specrum of this compound in the 530 nm region is attributed to the tautomer generated by intramolecular proton transfer in the excited state.In the presence of an amine the sharp band at 445 nm region in cyclohexane, dioxane and tetrahydrofuran has been assigned to the schiff base and the band at 520 nm in acetonitrile to the hydrogen-bonded ion pair.Some thermodynamic data have been evaluated and 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.
