Arylphosphonic acids. I. Substituent effects on their first and second dissociations

Abstract

, 1729 (1987) Thermodynamic pK1 and pK2 values of 36 arylphosphonic acids have been determined. The pK values of the tneta and para compounds are correlated well by the a " parameter, suggesting that there is little conjugation between the phosphonic group and the aromatic ring; the p values of the first and second dissociations are 0.923 and 1.140, respectively. The -P03H-group itself appears to be electron donating, contrary to earlier literature reports. The effect of ortho groups has been examined using multivariate analysis; the steric component of the proximity effect is acid weakening and has a larger effect on the second dissociation than on the first, presumably because a greater change in degree of solvation accompanies the second dissociation than the first.K. NAGARAJAN, KEVIN P. SHELLY, R. R. PERKINS et Ross STEWART. Can. J. Chem. 65, 1729 (1987). On a dtterrnint les valeurs des pKI et pKz thermodynamiques de 36 acides arylphosphoniques. On a pu ttablir une bonne corrklation entre les valeurs des pK des composts meta et para et le parametre a"; ce resultat suggkre qu'il existe peu de conjugation entre le groupement phosphonique et le cycle aromatique; les valeurs de p pour les premiere et deuxieme dissociations sont respectivement 0,923 et 1,140. Contrairement i ce qui a pu &tre publie anttrieurement, le groupement -P03HF semble &tre Clectrodonneur. Faisant appel a une analyse multi-variable, on a aussi examint I'effet des groupements en ortho; la composante stkrique de l'effet de proximitt a pour effet de diminuer l'aciditt et cet effet est plus important sur la deuxieme dissociation que sur la premiere; ce resultat est probablement caust par le fait que le changement dans le degrt de solvatation qui accompagne la deuxikme dissociation est plus important que celui qui accompagne la premikre.[Traduit par la revue] Introduction As part of a study of general acid and general base catalysis of protolytic reactions we have prepared a series of arylphosphonic acids, ArP03H2, and examined the effectiveness of the three catalytic species, ArP03H2, ArPO3HP, and AI-PO~'-, on the enolization of acetone (1); the present paper deals with the acid dissociation constants of the first two of these species.There are a number of reports in the literature of the effect of substituents on the pK1 and pK2 values of arylphosphonic acids, most notably those of Jaff6 et al. (2, 3) and of Nuallain (4). We are particularly concerned with proximity effects in prototropic reactions and we needed pK data for ortho, meta, and para derivatives. The data of Jaff6 et al. include such compounds but the pK values are not thermodynamic values; the data of Nuallain, which are much less extensive, have been corrected for ionic strength effects but include only two ortho compounds. Since we needed a set of self-consistent pK values for our catalytic work we have measured the first and second dissociation constants of a considerable number of arylphosphonic acids and corrected them to the standard state. The effects of substituents on t...

Proton dissociation properties of arylphosphonates: Determination of accurate Hammett equation parameters

“…As a consequence, the Hammett equations of arylphosphonic acids reported before might describe the correlation between substituents and pKa values less accurately. Therefore, here we report the pKa values of several arylphosphonic acids measured by highly accurate methods (differential pH-metric titration, NMR-pH titration), compare the results with in silico predicted values (cpKa) and those measured by Nagarajan et al [26] based on the goodness of the correlation (R 2 , s) and the mean absolute error (MAE) of the compared pKa values, and determine a more accurate Hammett equation for arylphosphonic acid derivatives.…”

Fluorescent Arylphosphonic Acids: Synergic Interactions between Bone and the Fluorescent Core

“…[35][36][37][38][39] In addition, the pKa 2 of phenylphosphonic acid (PhPO 3 H 2 )i s7 .44, giving PhPO 3 2À a À2c harge under physiological pH. [40] Therefore, the use of phosphonic acid metal-binding unit(s)totarget biologically significant divalent metal ions offers highly sensitive and pH-independent metal probesw orkingn ear physiological pH. Bisphosphonates have been previously attached to cyanine( Osteosense)a nd fluoresceinm oieties with long aliphatic hydrocarbon side chains to label target calcification with green or near infrared fluorescence.…”

Photoluminescent lead(II) coordination polymers stabilised by bifunctional organoarsonate ligands

“…This reaction behaviour and the consequent lower tendency to bridge metal centers than corresponding phosphonate ligands can be interpreted in light of their p K a values. According to the literature, the p K a values of phenylphosphonic acid are 1.86 and 7.51 [89], and the p K a values of phenylarsonic acid are 3.8 and 8.5 [90], suggesting that the 2nd deprotonation event occurs more readily for phosphonic acids than that for the arsonic acids. Despite the fact that arsonate anions can also adopt a variety of potential coordination modes, their ability as complexing agents has not yet been fully explored.…”