Volumetric and viscometric studies on L-ascorbic acid, nicotinic acid, thiamine hydrochloride and pyridoxine hydrochloride in water at temperatures (288.15–318.15) K and at atmospheric pressure

Apparent molar volumes V2,ϕ, apparent molar isentropic compressibilities KS,2,ϕ and viscosity B-coefficients have been determined for L-ascorbic acid, nicotinic acid, thiamine hydrochloride and pyridoxine hydrochloride in water at temperatures (288.15–318.15) K from density, speed of sound and viscosity measurements, respectively. Partial molar volumes V2o and partial molar isentropic compressibilities KS,2o at infinite dilution, and viscosity B-coefficients have been calculated from the corresponding data. The partial molar expansibilities VEo(VEo=(∂V2o/∂T)P), second order derivative (∂2V2o/∂T2)P and solvation number (Sn) have been calculated. Both volumetric and viscometric studies indicate that nicotinic acid acts as structure promoter where as other vitamins act as structure destroyer. The transition state theory has been used to calculate the activation free energy for viscous flow.

Apparent molar volume, V2,ϕ (a), apparent molar isentropic compressibilities, KS,2,ϕ (b) as a function of molality of L-ascorbic acid in water at different temperatures: ♦, 288.15 K; ■, 298.15 K; Δ, 308.15 K; and ●, 318.15 K.Figure optionsDownload as PowerPoint slideHighlights
► V2o, KS,2o and B-coefficients have been determined in water for the studied vitamins.
► Negative KS,2o values tend to become positive at higher temperature.
► Results indicate that only nicotinic acid acts as structure maker.