Schwarzenbach

The coordination of bidentate ligands is generally more efficient than expected on the basis of the binding affinity of monodentate analogues. This is referred to as the chelate effect. For reviews, see (a) Schwarzenbach, G. Helv. Chim. Acta, 1952, 35, 2344 (b) reference 75. 

The data refer to various temperatures between 18 and 25°C, and were compiled from values cited by Bjerrum, Schwarzenbach, and Sillen, Stability Constants of Metal Complexes, part II, Chemical Society, London, 1958, and values taken from publications of the lUPAC Solubility Data Project Solubility Data Series, International Union of Pure and Applied Chemistry, Pergamon Press, Oxford, 1979-1992 H. L. Clever, and F. J. Johnston, J. Phys. Chem. Ref Data, 9 751 (1980) Y. Marcus, Ibid. 9 1307 (1980) H. L. Clever, S. A. Johnson, and M. E. Derrick, Ibid. 14 631 (1985), and 21 941 (1992). 

The utility of complexation titrations improved following the introduction by Schwarzenbach, in 1945, of aminocarboxylic acids as multidentate ligands capable of forming stable 1 1 complexes with metal ions. The most widely used of these new ligands was ethylenediaminetetraacetic acid, EDTA, which forms strong 1 1 complexes with many metal ions. The first use of EDTA as a titrant occurred in... 

B. Gilg, H. MuUer, and K. Schwarzenbach. Paper presented Advances in Stabili tion and Controlled Degradation of Polymers, New Paltz, N.Y., June... 

Benzyl chloromethyl ketone has been prepared by the reaction of diazomethane with phenylacetyl chloride. The method of Clibbens and Nierenstein, in which one equivalent of diazomethane is added to the acyl chloride and the chloromethyl ketone obtained directly, could not be duplicated by Bradley and Schwarzenbach or by the submitters. 

Characterised by conversion to the acridine salt by addition of alcoholic acridine (l.lg in 50mL), filtering off the yellow salt and recrystallising from H2O. The salt has m 215°(dec), A- ax 259nm (e 15,400) in H2O. [Baddiley and Todd J Chem Soc 648 1947, 582 1949, cf LePage Biochem Prep 1 1 I949 Martell and Schwarzenbach Helv Chim Acta 39 653 7956]. 

It has been recrystd from H2O (fine needles) and is freely soluble in boiling H2O. Crysts also from H2O by addition of acetone. Purified by chromatography on Dowex 1 (in formate form), eluting with 0.25M formic acid. It was then adsorbed onto charcoal (which had been boiled for 15min with M HCI, washed free of chloride and dried at 100°), and recovered by stirring three times with isoamyl alcohol/H20 (1 9 v/v). The aqueous layer from the combined extracts was evaporated to dryness under reduced pressure, and the product was crystallised twice from hot H2O. [Morrison and Doherty Biochem J19 433 7967]. It has A-max 259nm (e 15,400) in H2O at pH 7.0. [Alberty et al. J Biol Chem 193 425 7957 Martell and Schwarzenbach Heh Chim Acta 39 653 7956]. The acridinium salt has m 208° [Baddiley and Todd J Chem Soc 648 1947 Pettit Synthetic Nucleotides, van Nostrand-Reinhold, NY, Vol 1 252 1972 NMR Sarma et al. J Am Chem Soc 96 7337 1974 Norton et al. J Am Chem Soc 98 1007 1976 IR of diNa salt Miles Biochem Biophys Acta 27 324 1958],... 

Schwarzenbach, J. and Gill, K.F. (1979) System Modelling and Control, Edward Arnold, London. 

P. Karrer,G. Schwarzenbach, andG.E. Vizinger, Helv. Chim. Acta,20,72(1937). 

Probably the most satisfactory model with which to explain the chelate effect is that proposed by G. Schwarzenbach If L and L-L are present in similar concentrations and are competing for two coordination sites on the metal, the probability of either of them coordinating to the first site may be taken as equal. However, once one end of L-L has become attached it is much more likely that the second site will be won by its other end than by L, simply because its other end must be held close to the second site and its effective concentration where it matters is therefore much... 

Saturated solutions of some reagents (T) 829 Schoniger oxygen flask see Oxygen flask Schwarzenbach classification 53 Screened indicators 268 Sebacic acid 469 Secondary pH standards 831 Selective ion meters 567 Selectivity coefficient, 559 in EDTA titrations, 312 in fluorimetry, 733 of analytical methods, 12 Selenium, D. of as element, (g) 465 Semi-log graph paper 572 Sensitivity (fl) 834, (fu) 732 Separation coefficient 163, 196 Separations by chromatographic methods, 13, 208. 233, 249... 

With the usual type of dibasic acid the equilibrium constant for the second step is always smaller than that for the first (Kx>K2)y but the diazonium ion represents another kind of acid in which the second constant is greater than the first (K2 > Kf), Schwarzenbach (1943) was the first to discover analogous abnormal acid-base equilibria and he explained under what circumstances the phenomenon can occur (for a historical account of Schwarzenbach s work see Zollinger, 1992). 

For pioneering studies on these constants see Bartlett (1934, pKa) and Schwarzenbach and Witt-wer (1947, for KE). 

So far only a start has been made (mainly by G. E. K. Branch and G. Schwarzenbach) on the problem of correlating the acidity or basicity of a substance with its resonating electronic structure. It should be possible to develop the theory of molecular structure to such an extent as to permit the reliable prediction of the behavior of substances with respect to this property and other physical and chemical properties. 

Schl Schwarzenbach, G., Heller, J. Helv. Chim. Acta 34 (1951) 576. 

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