46012-02-6

Upstream product

• 87-86-5 Pentachlorophenol 
• 71-50-1 acetate 
• 83193-04-8 2,2-difluoroacetate 

Downstream Products

• 87-86-5 Pentachlorophenol 
• 83193-04-8 2,2-difluoroacetate 

Relevant academic research and scientific papers

Proton transfers among oxygen and nitrogen acids and bases in DMSO solution

Rate constants for the proton-transfer reactions between conjugate acids and bases of several amines, phenols, carboxylic acids, and the solvated proton in DMSO-d6 at 20 °C have been determined by the use of NMR line-shape analysis. Equilibrium constants for the same reactions are obtained from the pKa's of the acids in dimethyl sulfoxide, some of which have been reported in earlier work and the rest obtained in the present work by use of Bordwell's indicator techniques. All of the reactions have rale constants considerably below expected diffusion-controlled limits for the proton transfers in the thermodynamically favorable direction, and several of the reactions, including the identity reactions of carboxylic acids, have kinetic deuterium isotope effects, kH/kD, between 0.8 and 1.3. For reactions of N,N-dimethylbenzylammonium ion with several phenoxides, carboxylates, and solvent, the rate constants for transfers in the unfavorable directions show a reasonable Bronsted correlation with β ≈ 1 and a reasonably constant reverse rate constant of ≈3 × 106 M-1 s-1. The data clearly indicate that the proton-transfer step is not rate-limiting in these reactions. Most likely, desolvation is involved in the rate-limiting steps, but the rate constants are not simple functions of acidities as might have been expected if hydrogen bonding of acid to solvent were the major factor involved in the solvation Other factors, particularly dispersion interactions of solvent with solutes, are discussed. We suggest that the formation of an acid-base complex with proper orientation to allow contact between the proton and the basic site is rate-determining and involves desolvation along with detailed steric interactions of the acid-base pair.

Thermodynamics of Proton Transfer in Phenol-Acetate Hydrogen Bonds with Large Proton Polarizability and the Conversion of Light Energy into Chemical Energy in Bacteriorhodopsin

Phenol-acetate solutions in CCl4 are studied by IR spectroscopy as a function of the pKa of the phenols.The (I) Ar-OH...-OC Ar-O-...HOC (II) hydrogen bonds formed show large proton polarizability as indicated by continua in the IR spectra.The percent proton transfer (PT) increases from the p-cresol-acetate to the pentachlorophenol-acetate system from 0percent to 56percent.The Gibbs free energy, ΔG0PT, values of the PT equilibria at 295 K are determined as well as the standard enthalpy values, ΔH0PT, and the standard entropy values, ΔS0PT.These data are given in Table II.The shape of the intensity of the continuum as a function of the ΔH0PT value changes.In the classical approximation the average difference between the two minima of the proton double-minimum potential is given by ΔH0PT.With the decreasing amount of ΔH0PT, i.e., decreasing degree of asymmetry, the intensity of the continua decreases at higher and increases at lower wavenumbers.This result is in good agreement with the predictions from calculated line spectra.In the photocycle of bacteriorhodopsin a tyrosine-aspartate hydrogen bond is probably of importance for the conversion of light energy into chemical energy.On the basis of the obtained data it is shown that 9.5 kJ/mol can be converted into chemical energy due to a proton transfer induced by a local electrical field in a Tyr-Asp hydrogen bond.Furthermore, if the Ar-O-...HOC structure is broken afterwards by a conformational change, at least 25 kJ/mol of conformational energy is converted.Thus, altogether 34.5 kJ/mol of Gibbs free energy may be converted into chemical energy and stored by these processes.

HYDROGEN BONDING AND PROTON TRANSFER IN HYDRIDO-BIS-PHENOLATE COMPLEXES IN ACETONE

The homoconjugation, (ArO)2H-, and heteroconjugation, Ar'O- HOAr, (where Ar is aromatic) with proton transfer have been determined in acetone at 298 K.Tetra-alkylammonium phenolates were titrated with a variety of phenols to given ho