Toyokichi Kitagawa

Voltammetric study of protonated 1,10-phenanthroline cation transfer across the water/nitrobenzene interface

Abstract The ion transfer of 1,10-phenanthroline (phen) across the water/nitrobenzene interface has been studied in the pH range 1–7 by electrochemical methods, adding phen to the aqueous phase or to the organic (nitrobenzene) phase. Current-scan polarography at an ascending water electrode and potential-scan cyclic voltammetry at a stationary plane electrode were used. With each addition, an anodic wave caused by the transfer of a protonated phen (Hphen + ) from the aqueous to the organic phase was observed. Here a detailed mechanism of the ion transfer is proposed by considering branch diffusions of phen species from the interface to either bulk phase by which the Hphen + transfer producing the anodic wave is depressed. With the addition of phen to the aqueous phase, the wave became deformed, noisy and steep, and finally separated into two waves as the phen concentration was increased and the pH was decreased. This is probably caused by the interfacial adsorption of Hphen + . The adsorption phenomenon is also discussed with the aid of electrocapillary curves.

Mass transfer of acetylacetone, ethylene glycol mono-n-butyl ether and ethylene glycol monophenyl ether across water-carbon tetrachloride and water-chloroform interfaces

Abstract The interfacial mass transfer kinetics of acetylacetone (acac), ethylene glycol mono- n -butyl ether (EGBE) and ethylene glycol monophenyl ether (EGPE) across water-carbon tetrachloride (Ccl 4 ) and water-chloroform (CHCl 3 ) interfaces were studied by stirring the two phases at various speeds, maintaining a quiescent interface with a constant area. In the analysis of data, two rate-determining steps consisting of a diffusion toward the interface and a mass exchange between the interface and bulk phases are considered. It is shown that the transfer of EGBE and EGPE in both CHCl 3 and Ccl 4 systems is controlled by the diffusion step even at high stirring speeds, whereas the transfer of acac in Ccl 4 is controlled by the interfacial exchange step at high stirring speeds. An irreversible transfer has been also observed in the EGBE and EGPE systems at low stirring speeds.

Transfer of trifluoroacetylacetone across a water/1,2-dichloroethane interface

Abstract The ion transfer of 1,1,1-trifluoroacetylacetone (HTAA) across a water/1,2-dichloroethane interface has been studied at various pH values, using current-scan polarography at the ascending water electrode, and a cathodic wave caused by the transfer of TAA − from the aqueous to the organic phase has been observed. Experiments have been carried out with two different types of addition of HTAA; one is the addition to the organic phase and the other to the aqueous phase. Although the anodic wave appears with both additions, the limiting current and the half-wave potential depend on the pH differently. Their dependences have been ascribed to the following: (1) the slow keto-enol tautomerization rate of HTAA; (2) the existence of TAA 2− hydrate anion; (3) some branch diffusions from the interfacial region to the bulk phase. The p K a2 value of HTAA has been determined to be 9.2.

Electrochemical reduction of rhenium(V) dithiocarbamate complexes trans-Re2O3(S2CNR2)4 in nonaqueous media

Abstract The electrochemistry for the reduction of tetrakis(dialkyl- and diphenyldithiocarbamato)-μ-oxodioxodirhenium complexes trans -Re 2 O 3 (S 2 CNR 2 ) 4 (R = methyl, ethyl, propyl, butyl and phenyl) was investigated in seven nonaqueous solvents. The complexes underwent a reversible reduction involving one- electron at a platinum electrode to [Re 2 O 3 (S 2 CNR 2 ) 4 ] − , which decomposed with the cleavage of the μ-oxo bridge to form ReO(S 2 CNR 2 ) 2 , R 2 CNS 2 − and other rhenium complexes. The redox potential E o ′ of [Re 2 O 3 (S 2 CNR 2 ) 4 ] 0/− couples and the stability of the reduction product [Re 2 O 3 (S 2 CNR 2 ) 4 ] − depend on the R group. The E o ′ are appreciably solvent-dependent. The difference in E o ′ with solvents could be interpreted in terms of the solubility parameters.

Electrochemistry of arylimido rhenium(V) dithiocarbamate complexes [{Re(NR)(S2CNR′2)2}2O] in N,N-dimethylformamide

The electrochemistry of tetrakis(N,N-diethyl- and N,N-diphenyldithiocarbamato)bis(arylimido)-μ-oxo-dirhenium complexes, [{Re(NR)(S2CNR′2)2}2O], where R=phenyl, p-tolyl, p-chlorophenyl and p-methoxyphenyl, has been studied in N,N-dimethylformamide. The [{Re(NR)(S2CNR′2)2}2O] complexes undergo a quasireversible one-electron reduction followed by the cleavage of the μ-oxo bond (ReORe) including the release of one dithiocarbamate ligand from the complex. The redox potential for the [{Re(NR)(S2CNR′2)2}2O]0/− couple and the stability of the reduction products depend on R and R′. Linear correlations have been obtained between the redox potential of the diethyl- and diphenyldithiocarbamate complexes and the Hammett p-substituent constant of the aryl moiety. The diphenyldithiocarbamate complexes are easier to reduce by 170 mV than the corresponding diethyldithiocarbamate complexes. The weaker π-bonding of RNRe causes the imido complexes to be more difficult to reduce than the corresponding oxo analogues [{ReO(S2CNR′2)2}2O]. The oxidation of [{Re(NR)(S2CNR′2)2}2O] is an irreversible one-electron process but the oxo analogues exhibit ill-defined voltammograms.

Rhenium complexes containing an η2-thiocarbamoyl group: synthesis, electrochemistry, and crystal structure of [Re(S2CNEt2)2(SCNEt2)(PPh3)]ClO4

A new redox couple of rhenium complexes, [ReIII(S2CNEt2)2(SCNEt2)(PPh3)] and [ReIV(S2CNEt2)2(SCNEt2)(PPh3)]ClO4, has been isolated and electrochemically characterized; the η2-co-ordination of the N,N-diethylthiocarbamoyl group in the latter has been confirmed by X-ray analysis.

Anodic oxidation of tyrosine at carbon paste electrode.

チロシンは0.7N~2.3Nの硫酸酸性中で,+1.0V(対SCE)に半ピーク電位をもつ良好な酸化波を示し,多量フェニルアラニン中のチロシンが,直線走査ボルタメトリーにより精度よく定量できた.遷移時間定数630,log(√τ-√t)/√τ対Eのプロットは直線となり,完全な不可逆酸化反応である.定電位電解,ポーラログラフィーにより電極反応について考察した.

Fundamental studies of carbon paste electrode

水銀溶出電位より陽電位で日常分析に使用しうる電極としてカーボンペースト電極を用い,フェロシアン化カリウム,フェリシアン化カリウム,オルトジアニシジンおよび過マンガン酸カリウムの電極反応をクロノポテンシオメトリーおよびボルタメトリーを用いて,白金電極の場合と比較検討した.白金電極表面の酸化などの影響もなく,ほぼ理論式と一致する結果を得,電極面積は±3%以内で幾何学的断面積と一致した.水銀溶出電位より陽電位で,日常分析に用いうる指示電極としてカーボンペースト電極を用い,その基礎的な検討を行なった.著者らはこの電極を用い,主として分析化学的に有用な有機試薬について,その電極反応機構を検討しており,EDTA類縁化合物の陽極酸化反応について興味ある知見を得ている.上述の基礎的な検討をもとにして得た結果を次報に報告する.