Thermodynamics of proton ionization in dilute aqueous solution. XIII. .DELTA.G.deg.(pK), .DELTA.H.deg., and .DELTA.S.deg. values for proton ionization from several methyl- and ethyl-substituted aliphatic carboxylic acids at 10, 25, and 40.deg.

Abstract

A calorimetric study has been made of proton ionization in dilute aqueous solution from aliphatic carboxylic acids a t 10, 25, and 40" (13 acids) and at 25" (3 acids). Values of A S " are calculated by combining the resulting AH" values with AGO values obtained from the literature or determined from potentiometric o r calorimetric measurements. The trends in AGO, AH", and ASo are described by an electrostatic model, and deviations from this model are taken as a measure of nonelectrostatic substituent effects for carboxylic acids.his study was undertaken as part2 of a program

Extent of Proton Transfer in the Transition States of the Reaction Catalyzed by the .DELTA.5-3-Ketosteroid Isomerase of Comamonas (Pseudomonas) testosteroni: Site-Specific Replacement of the Active Site Base, Aspartate 38, by the Weaker Base Alanine-3-sulfinate

“…Following the argument presented in the Appendix, it is found that £,£,£, £ ' =-L2-Í- In eq 3 r is the ratio of the acid dissociation constants of ASI and D residues, while the rate constants on the right side have the significance given in eq 1. When the rate constants measured by Hawkinson et al (1991b) are employed and r is taken to be 562 [ / = 2.75 (Oae & Kunieda, 1977;Christensen et al, 1970)], we calculate from eq 3 that ß = 0.75. The values of £4 and £5 which were used to obtain this result are the lower limits for these rate constants determined by Hawkinson et al However, if £4 and £5 are increased while their ratio is maintained at 3, the value of ß obtained from eq 3 is unchanged.…”

Temperature dependence of density of polymer gels: Effects of ionizable groups in copoly(N-isopropylacrylamide/acrylic acid or sodium acrylate)–water systems

“…We then calculate K (¼K w / K a ) from Eq. (3) by using the value of pK a (¼4.84 AE 0.2) [28] for this acid and K w [29]. Next, either [H þ ] (or Table 1 Representative experimental values for n(gel)(T ), r p (gel)(T ), r s (gel), and m p / m(gel) for copoly[NIPA(1 À x)/HAc(x)] and copoly[NIPA(1 À x)/NaAc(x)] networks and water (first batch)…”

Determination of Carboxylic Acid Dissociation Constants to 350 °C at 23 MPa by Potentiometric pH Measurements

“…Solid circles represent the experimental data from this study at 23 MPa. The other symbols represent ○, Sue et al at 23 MPa; ◇, Fisher and Barnes 9 ; ▵, Oscarson et al 8 ; □, Mesmer et al 6 ; and +, Christensen et al at saturation vapor pressure. Solid and dashed lines represent the calculated results from eq 19 and from the revised HKF equation of state 29 at 23 MPa.

2 Dissociation constants of propanoic acid.

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“…9 In contrast, some studies have been carried out for propanoic and butanoic acids up to 225 °C10-13 and for pentanoic and hexanoic acids up to 60 °C. 12,14 No measurements have been carried out at higher temperatures.…”

“…Knowledge of the dissociation constants of carboxylic acids at hydrothermal conditions has long been a basis for understanding not only fundamental physical and chemical phenomena but also organic and inorganic reaction mechanisms in several applications. − Many studies have been carried out on the dissociation of aqueous ethanoic acid up to 400 °C and 32 MPa by measurements of potentiometry, , calorimetry, and electrical conductivity . In contrast, some studies have been carried out for propanoic and butanoic acids up to 225 °C − and for pentanoic and hexanoic acids up to 60 °C. , No measurements have been carried out at higher temperatures.…”