Abstract

Manoj Kumar¹, P. P. Vishvakarma² and Seema Singh¹

DOI : http://dx.doi.org/10.13005/ojc/310258

Thermodynamic deprotonation constants [ pK_a^T"> ] of dimethyl thiobarbituric acid [DMTBA], diphenyl thiobarbituric acid [DPTBA], di-o-tolyl thiobarbituric acid[DOTTBA], di-m-tolyl thiobarbituric acid [DMTTBA], di-p-tolyl, thiobarbituric acid [DPTTBA], di-o-xylyl thiobarbituric acid [DOXTBA], di-p-xylyl thiobarbituric acid [ DPXTBA],  di-α naphthyl thiobarbituric acid [DANTBA] and di-β-naphthyl thiobarbituric acid [DBNTBA] have been determined in different mole fraction of dioxane [ 0.175 – 0.350 ] at 20, 30, and 40 15±">  0.10⁰C. The plot of the thermodynamic deprotonation constant [pK_a^T">  ] versus the mole fraction of dioxane is linear at all the given temperatures. The mean ionic radii 15(r±)">  for thiobarbiturate ions, being in the region of 2.10 – 2.70 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;deprotonation constants;thiobarbituric acid

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