Stability constants have been measured for the formation of 1 :1 cornplexes between eight divalent metal ions and six carboxylate anions. For each anion the stabilities of the cornplexes follow the order Pb2+ > CuZ+ > CdZ+ > Znz+ > NiZ+ -CoZ+ > CaZ+ -MgZ+. The stabilities of the complexes with each metal ion are directly related to the basicities of the anions, and little or no bidentate chelation occurs between these metal ions and acetoxyacetic acid or N-acetylglycine. Canadian Journal of Chemistry, 48, 1654 (1970)In connection with another studv, we wished to hkuerin~ental Procedure --compare stability constants for 1 : 1 complex formation between various divalent metal ions and carboxylate anions. While stabilities of metal ion -acetate complexes have been well studied (I), comprehensive data are not available for complexes involving other carboxylate anions. The data that are available come from a number of different sources, and are often not directly comparable since widely differing conditions of temperature and ionic strength have been used in their determination. In particular, we were interested in the possibility that N-acetylglycine and acetoxyacetic acid might act as bidentate ligands when entering into complex formation with some bissociation constants of the carboxylic acids and stability constants of the 1 :1 metal-carboxylate complexes were determined by potentiometric titration at 30" and ionic strength 0.4. The ionic strength was adjusted with suitable concentrations of sodium nitrate.An aqueous solution (40ml) containing the metal nitrate (0.1 M ) and carboxylic acid (0.01 M ) was titrated with one equivalent (ten aliquots; each 0.4 ml) of potassium hydroxide solution (0.1 M). The pH of the solution was noted, after the addition of each aliquot of alkali, on a Corning Model 12 p H Meter, which had been previously standardized against 0.05 M potassium hydrogen phthalate solution (error in p H reading 20.002). The titration was carried out in a waterjacketed reaction vessel, thermostated at 300, and nitrogen was continuously bubbled through the solution.Acid dissociation constants were determined by a divalent ions. Such bidentate complex for-similar titration in the absence of divalent metal ions. we wish to report stability constants, which and the dissociation constant of the carboxylic acid.Hence at each point in the titration, a value for the were measured under constant experimental con-stability constant ditions, for the formation of 1 :1 complexes between eight divalent metal ions (lead, cadmium,copper, zinc, nickel, cobalt, calcium, and mag-for the formation of a 1 :1 complex could be calculated. nesium) and the anions of six carboxylic acids AllSreported values for log K are averages of 7-10 values, (acetic, benzoic, formic, chloroacetic, and a&-and the reported error is the greatest deviation from this oxyacetic acids and N-acetylglycine).value. Since the stabilities of these complexes are quite low, Experimentalrelatively large concentrations of the metal ions were Metal Salts requ...

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Abstract:The acidity and ket-no1 tautomerism of a series of symmetrical P-diketones (RCOCH2COR (1): R = methyl (a), phenyl (b), 3-pyridinyl (c), 4-pyridinyl(4, 3-(N-methy1)pyridinio (e), and 4-(Nrnethy1)pyridinio ( f ) ) and two series of unsymmetrical P-diketones (RCOCH2COCH, (7a-7fi and RCOCH,COC6H5 (8a4f )) have been investigated in aqueous solution at 25°C and ionic strength 0.1. Values of p K 2 were measured spectrophotometrically, and the acidities of the enols ( p m were obtained from the analysis of the pH dependence of the buffer catalysis for the general acid-catalyzed protonation of the enolate conjugate bases. These data in tum allowed the calculation of the acidities of the keto tautorners (p@) and the equilibrium constants for enolization (K, = [Enoll/ [Keto]). In general, KE is greater for the symmetrical ketones (1) than for the corresponding R-substituted unsymmetrical ketones (7 and 8). K, is much more sensitive to the nature of the R substituent in these three series of P-diketones than in the corresponding series of P-keto esters and amides. Correlations between for 8 and 7 combined with the known acidities of the corresponding P-keto esters and arnides provide the first accurate estimates of the acidities of dirnethyl malonate (pKa = 13.0) and malonarnide (pKa = 12.5) in aqueous solution.Key words: acidity, tautomerisrn, P-diketones. (8a4f)). On a rnesuri les pKaq spectrophotomCtriquement et on a dCterminC les acidids des Cnols ( p e ) par une analyse de la relation entre la dCpendance sur le pH de la catalyse du tampon sur la protonation par catalyse acide gCnCrale des bases conjuguCes Cnolates. Ces donnCes permettent ensuite de calculer les aciditCs des cCto-tautomtres et les constantes d9Cquilibre de 1'Cnolisation (KE = [Bnol:~/[~~tone]). En gCnCral, la valeur de KE est plus grande pour les cCtones symCtriques (1) que pour les cCtones non symttriques correspondantes substituies pardes groupes R (7 et 8). La valeur de KE est beaucoup plus sensible la nature du substituant R dans ces trois sCries de P-dicttones que dans les sCries correspondantes de P-cCtoamides. Des corrClations entre les valeurs des des composCs 7 et 8 cornbinCes avec les aciditCs connues des p-cktoesters et P-cCtoamides correspondants foumissent les prernisres Cvaluations prCcises des aciditks du malonate de dimCthyle (pKa = 13,O) et du malonarnide (pKa = 12,5) en solution aqueuse.

Equilibrium constants and the rates of ketone-enolate ion equilibration have been measured for the deprotonation of eight 3-(X-phenylacetyl)pyridines 1 (pKa 13.2 for X = H), ten 4-(X-phenylacetyl)pyridines 2 (pKa 12.2 for X = H), nine 1 -methyl-3-(X-phenylacetyl)pyridinium cations 3 (pK, 10.32 for X = H), and ten l-methyl-4-(X-phenylacetyl)pyridinium cations 4 (pKa 9.02 for X = H) in aqueous solution at 25 'C and ionic strength 0.1. The pKa values for each of these series of ketones are closely correlated with the pKa values for the corresponding ring-substituted phenols. Pseudo-first-order rate constants for deprotonation of both series of neutral ketones (1, 2 ) are strictly proportional to hydroxide ion concentration in the range pH 11-13, and second-order rate constants ( k o~) for hydroxide ion catalyzed deprotonation have been evaluated. The pseudo-first-order rate constants ( k d ) for deprotonation of both series of N-methyl cations (3,4) are subject to hydroxide ion catalysis (second-order rate constant koH) but display kinetic saturation effects consistent with kinetically controlled hydroxide ion addition to the carbonyl group of the ketone. In basic solution this addition competes with the thermodynamically more favorable enolate ion formation. These four series of ketones (1-4) display quite different linear Bransted plots (log koH vs pKa), with relative reactivities at constant pKa being in the order 4 < 3 < 2 < 1. The 4-NO2 and 4-CN substituents in all four series of ketones, and also 4 with X = W H 3 , show negative deviations from these Bransted relationships. These deviations, and also the relative reactivities for 1-4, can be traced to imbalances in both a-electron delocalization and solvent reorganization in the transition states relative to the enolate ion products. Bransted a values cover the range 0.66-0.76 and vary in the order