P. Zalupski, M. Jensen, A. W. Herlinger
Aug 1, 2005
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Journal
Journal of Solution Chemistry
Abstract
Bisphosphonic acids are powerful metal chelating reagents with a wide spectrum of applications. A series of partial ester derivatives of bisphosphonic acids was synthesized in order to investigate the physico-chemical changes induced by partial protection of the acid groups. The acid dissociation constants K1 and K2 for a homologous series of short-chain aqueous-soluble dibasic bisphosphonic acids, i.e., the P,P′-diethyl methylene-, ethylene- and propylene-bisphosphonic acid partial esters, H2DEt[MBP], H2DEt[EBP] and H2DEt[PrBP], respectively, were determined by potentiometric titration and 31P NMR spectrometry. All three diethyl esters are rather acidic with pK1 < 1.2 and pK2 < 2.2. The influence of the separation between the phosphonate groups on ligand acidity and successive pKa values is rationalized in terms of solvation, inductive and electrostatic effects.