Reynold T. Iwamoto

Voltammetric evaluation of the stability of trichloride, tribromide, and triiodide ions in nitromethane, acetone, and acetonitrile

Abstract : The formation constants of trichloride, tribromide, and triiodide ions in acetonitrile and tribromide and triiodide ions in nitromethane and in acetone have been evaluated from electrochemical data. In addition, lower limits for the formation constant of the trichloride ion in acetone and in nitromethane have been calculated. The order of stability of the trihalides in these three aprotic solvents is Cl3(-) > Br3(-) > I3-, the reverse of that found in water. (Author)

References electrodes for voltammetry in acetonitrile

The saturated calomel electrode is the reference electrode in aqueous polarographic studies. Such is not the case, however, with nonaqueous polarographic studies. In particular acetonitrile has been used as the solvent for many polarographic studies with just as many reference electrodes. An attempt has been made to correct this unfortunate situation. Appropriate measurements have been made to evaluate the potential of the various reference electrode systems used in acetonitrile with respect to the aqueous saturated calomel electrode.

Complexes of copper(I) and silver(I) with acetonitrile in water, the lower alcohols, acetone, and nitroethane

Abstract The effect of solvent on the stability of acetonitrile complexes of copper(I) and silver(I) has been investigated. Small non-correlatable differences in stability are evident. Because of no major differences in the compatibility of the ligand, acetonitrile and the solvents, and the nearly identical potentials for the copper(I), copper(Hg) and for the silver(I), silver couples in the solvents examined, the general similarity of the stability constants of the copper(I) complexes and of the silver(I) complexes in the solvents used is not completely unexpected.

Characterization of the dimeric one-electron electrolytic reduction products of 1-alkylpyridinium ions in acetonitrile

Abstract A chemical-electrochemical approach for the determination of the positions of coupling in the dimeric one-electron reduction products of 1-alkylpyridinium ions in acetonitrile is described. The procedure involves the treatment of a solution of the dimeric species with an appropriate quinone followed by electrochemical examination of the resulting solution. For 1-alkylpyridinium ions without ring substituents, the dimer is concluded to be the 4,4′ coupled isomer, based on the formation in the cases of 1-methyl-, 1-ethyl-, and 1-benzylpyridinium ions of the 1,1′-dialkyl-4,4′-bipyridinium monocation radical species on treatment of the dimeric species with 1,4-benzoquinone. The characteristics, particularly the quantitative nature, of this tetrahydrobipyridine-quinone reaction have been examined.

Gold porphyrin complexes. Evidence for electrochemically inert gold (III)

Abstract Gold(III) tetraphenylporphine tetrachloroacurate, gold(III) etioporphyrin I tetrachloroacurate, and gold. (III) mesoporphyrin IX dimethylester acetate were synthesized and characterized by visible spectral and electrochemical (classical and cyclic voltammetry and coulometry) studies. The gold porphyrin complexes show spectral properties similar to those reported for other metalloporphyrins, except Mn and Mo, and electrochemical properties similar to those of metalloporphyrins with a stable central metal ion. Interestingly, in these gold complexes the tripositive metal ion is electrochemically inert.

Polarographic evidence for the stability of copper(I) ion in some non-complexing nonaqueous solvents

Abstract The polarographic behaviour of Cu(II) ion in methanol, ethanol, 1-propanol, 2-propnol, allyl alcohol, acetone, mesityl oxide, acetylacetone, acetic anhydride, nitromethane and pyridine is discussed. Stability of Cu(I) ion in a number of these solvents appears to be due to lower solvation energy of Cu(II) ion and not to higher solvation energy of Cu(I) ion than in water.

Synthesis of unsymmetrical 4,4′-dialkyl-2,2′-bipyridines

Abstract Conversion of 4,4′-dimethyl-2,2′-bipyridine to 4-hexadecyl-4′-methyl-2,2′-bipyridine, 4-heptadecyl-4′-methyl-2,2′-bipyridine, and 4,4′-diheptadecyl-2,2′-bipyridine by treatment with lithium diisopropylamine followed by an appropriate alkyl bromide is reported.

Chloro complexes of copper(II) and copper(I) in methanol, ethanol, 2-propanol, 2-butanol and acetone

Abstract The chloro complexes of copper(II) and copper(I) in methanol, ethanol, 2-propanol, 2-butanol, and acetone have been investigated by voltammetry. Log βCuCl2- values in the solvents in the order listed above are: 9.3, 12.3, 13.4, 14.1, and 19.2. For the copper(II) complexes, log βCucl+ in methanol is 4.9 and in ethanol,

Electrochemical behavior of copper ions and silver ion in hydracrylonitrile and some related nitriles

Abstract The electrochemical behavior of copper ions in hydracrylonitrile and related nitriles has been investigated. It is of interest to note that in hydracrylonitrile copper(II) ion is solvated by the nitrile group, whereas in I:I alcohol-nitrile mixtures, it is solvated by the hydroxyl group. This unusual situation appears to be due to the fact that hydracrylonitrile (dielectric constant, 65), I:I ethanol-acetonitrile mixture (dielectric constant, 32), and. I:I I-butanol-propionitrile mixture are polar solvent systems and, therefore, favor the more polar solvated form of copper(II) ion. This, in- hydracrylonitrile has the solvent molecules oriented with the nitrile group attached to copper(II) ion and the hydroxyl group sticking out and forming a polar outer sheath and in I:I alcohol-nitrile mixture has alcohol rather than nitrile molecules in the co-ordination sphere. Nitrile-solvated copper(II) ion with an outer sheath consisting only of alkyl groups behaves like a non-polar solute. In view of the absence of any solvent effect on the potentials of the copper couples in hydracrylonitrile, 3-butenenitrile, and in the alkoxypropionitriles, copper ions are most likely solvated by the trans conformer of these solvents. The effect of substituents in the 3-position in propionitrile i.e., on the basicity of the nitrile group on the potentials of the copper couples, is consistent with the influence of the substituents on other functional groups in different compounds. Except for the fact that silver(I) ion is reduced at potentials more positive than those at which copper(I) ion is reduced, the electrochemical reduction of silver(I) ion in hydracrylonitrile and related nitriles is similar to that of copper(I) ion.

Experimental and theoretical studies of Schiff base chlorophylls

Abstract— A protonated Schiff base of Ni (II)‐pyrochlorophyll a has been synthesized which exhibits a reversible bathochromic shift of 504 cm‐1 relative to Ni (II)‐pyrochlorophyll a. The magnitude of this shift lies between those observed for P700 and P680, the photoactive pigments of photosystems I and II in plants. Cyclic voltammetric measurements show that the protonated Schiff base is about 0.2 V more difficult to oxidize than its unprotonated form. These results suggest that a protonated Schiff base may be a better model for P680 than, as was originally assumed, for P700. In addition, the results of solvent and counterion effect studies show that microenvironmental perturbations in the neighborhood of the protonated Schiff base moiety are unlikely to induce further spectral shifts. Ab initio quantum mechanical calculations show a small hypsochromic shift rather than the observed bathochromic one, and the reasons for this discrepancy are discussed.