Abstract

Manoj Kumar and B.R. Singh

DOI : http://dx.doi.org/10.13005/ojc/300269

Thermodynamic protonation constants of dimethyl barbituric acid [DMBA], Diphenyl barbituric acid [DPBA], di-o-tolyl barbitiuric acid[D-O-TBA], di-m-tolyl barbituric acid [D-m-TBA], di-p-tolyl, barbituric acid [D-p-TBA], di-o-xylyl barbituric acid [D-o-XBA], di-m-xylyl barbituric acid [ D-m-XBA], di-p-xylyl barbituric acid [D-p-XBA], di-α napthyl barbituric acid [D-α-NBA] and di-p-anisyl barbituric acid [D-p-ABA] have been determined in different mole fraction of deoxane [ 0.175 – 0.350 ] at 20, 30, and 40  0.10⁰C. The thermodynamic protonation constant [ ] values do not vary linearly with reciprocal of dielectric constant of medium, but a plot of pk^T_a versus the mole fraction of dioxane is linear at all given temperatures. The mean ionic radii are  for barbiturates ions, being in the region of 2.12 – 2.72 A⁰, slightly increases with dioxane percentages. The values of ΔG⁰, Δ H⁰ and  Δ S⁰ have been evaluated. The effect of temperature as well as medium effect are briefly discussed.

Thermodynamic; protonation; dimethyl barbituric acid

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