Stability constants of hydrazoic acid–tributyl phosphate complexes in hexadecane solution

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Abstract
The gas-chromatographic technique of elution by characteristic point (ECP) has been used to study the complexing of hydrazoic acid with tributylphosphate (TBP) in hexadecane solution. The study covered the temperature range, 298–338 K, with hydrazoic acid concentrations in solution up to 0.55 mol dm–3. The dilution–depletion theory previously advanced by the authors is shown, again, to accommodate the results very well and stability constants for the HN3–TBP complex in the range 40–100 dm3 mol–1 have been determined; the associated enthalpy and entropy are found to be –19 200 J mol–1 and –26.3 J mol–1 K–1, respectively. The results correlate well with those previously reported for HCl–TBP complexation and substantiate the description of HN3 as a halogenoid hydracid. The study further confirms the considerable utility of the relatively simple ECP technique in the study of strongly complexing systems at finite concentrations in solution.