Alkoxide-to-hydroxide ion activity ratios in water-ethylene glycol and water-1-propanol systems

Abstract

The dissociation constants of water and alcohol, their ionic products as well the ionic product of the mixture, equilibrium constants of the 0H + ROH ± R0 + H20 equilibrium, and the alkoxide-to-hydroxide ion activity ratios were determined in water-ethylene glycol and water--1-propanol systems. The conditions of validity of Rochester's equation are discussed.In the alkaline region in water-alcohol mixtures, equilibrium establishes between the alkoxide and hydroxide ions according to Eq. (A), 0H + ROH ± R0 + H20 (A) characterized by the equilibrium constant K = a(H,O) a(R0)/[a(ROH) a(0H)].(1)The values of this constant in highly concentrated (virtually neat) alcohols are usually determined by 1H NMR spectroscopy' or by means of indicator colour changes2. For systems of dilute alcohols, use is made of the absorbance of the alkoxide ions3. An empirical equation4 has been suggested for the calculation of the constant in water-methanol systems; to other water-alcohol systems, however, this equation is inapplicable5. For water-methanol, water-ethanol and water-2-propanol systems over wide alcohol concentration regions, Murto6 attempted to calculate the equilibrium constants via concentrations of reaction products of parallel reactions. The problem can also be tackled by employing Gibbs transfer energies7. In this case, Eq. (2) (Rochester's equation) can be derived: log [Ksi -(KOHaoH) -kRO] = -koH . log Yh + log K20.(2) aH2O aH2OIn the water-methanol system, Eq.(2) is applicable over a wide alcohol concentraCollect.

Kinetics and Mechanisms of Reactions of Thiol, Thiono, and Dithio Analogues of Carboxylic Esters with Nucleophiles

“…In the alkaline solvolysis of N,N- diphenylthiobenzamide and 4-chloro N,N- dimethylthiobenzamide in water−ethanol mixtures, the order of OH - was found to vary from 1 to 2 with varying solvent composition. This was attributed to the formation of three tetrahedral intermediates in the reaction path: two arising from OH - attack (one monoanionic, 18 , and the other dianionic, 19 ) and one formed by EtO - attack ( 20 ) …”

“…This was attributed to the formation of three tetrahedral intermediates in the reaction path: two arising from OHattack (one monoanionic, 18, and the other dianionic, 19) and one formed by EtOattack (20). 80 The kinetics and mechanism of the hydrolysis of S-benzamides in aqueous solution promoted by AuCl 4and various amino-chlorogold(III) ions 81 and AuBr 4and Au(CN) 2 Br 2 -82 have been subjected to scrutiny. All these reactions proceed by desulfurization leading to the O-amide.…”