Natsuki Yamashita

Electroreductive synthesis of oligosilanes and polysilanes with ordered sequences

Abstract The stepwise elongation of SiSi or SiGe chain was achieved by the electroreductive cross-coupling reaction of chlorohydrosilanes with dichlorooligosilanes using magnesium electrodes. The electroreductive cross-coupling reaction of chlorodimethylsilane ( 1 ) with dichlorodiphenylsilane ( 2 ) or dichlorodiphenylgermane ( 4 ), for instance, gave 1,3-dihydro-1,1,3,3-tetramethyl-2,2-diphenyltrisilane ( 3 ) or bis(hydrodimethylsilyl)germane ( 5 ) in good yield. Compounds 3 and 5 were readily transformed to the corresponding 1,3-dichlorotrisilane ( 6 ) and bis(chlorosilyl)germane ( 7 ), respectively. The electroreductive polymerization of the resulting dichlorooligosilanes using magnesium electrodes in tetrahydrofuran was successfully applied to the synthesis of sequence-ordered polysilanes.

Electroreduction of aliphatic esters using new paired electrolysis systems

Electroreduction of aliphatic esters to form 2-alkoxytetrahydrofurans was achieved by using a new paired electrolysis system, that consists of the cathodic reduction of aliphatic esters and the anodic oxidation of the solvent (THF). It was also found that the presence of magnesium ion in the electrolyte promoted the electroreduction of aliphatic esters remarkably. In fact, the electroreduction of aliphatic esters was found to proceed toward 2-alkoxytetrahydrofurans by using a platinum cathode and anode in the presence of anodically dissolved magnesium ions.

Electroreduction of aromatics using magnesium electrodes in aprotic solvents containing alcoholic proton donors

Abstract Regioselective electroreduction of the aromatics, including methoxybenzenes, by using LiClO4 as a supporting electrolyte in an aprotic solvent (THF) containing alcoholic proton donors such as t-BuOH was successfully achieved to afford the corresponding 1,4-cyclohexadienes regioselectively in high yield. The electrolysis can be performed under constant current conditions at ambient temperature. The effect of electrode materials was remarkable, that is, the use of Mg electrodes gave the best result. Moreover in the presence of t-BuOD instead of t-BuOH, the deutrated 1,4-cyclohexadienes were obtained in high deuterium incorporation at 1- and 4-positions. A direct electron transfer to the aromatics is unlikely, and it is reasonable that the solvated Li(0), which is generated by the cathodic reduction of LiClO4, is intermediately involved in the electron transfer with being assisted by the anodically generated Mg2+ as an electron transfer catalyst.

Radical Copolymerizability of Acrylamide Derivatives with Methyl Vinyl Ketone

Abstract Radical copolymerization of methyl vinyl ketone (MVK, M1) with acrylamide (AAm) and its derivatives, such as methacrylamide (MAAm) and N,N′ -dimethylacrylamide (DMAAm), was carried out in dioxane or ethanol using α,α - azobisisobutylonitrile as the initiator at 60°C under vacuum. The monomer reactivity ratios found in dioxane were as follows: ri = 1.06, r2 = 6.41 for the MVK-AAm system; r1 = 0.29, r2 = 3.05 for the MVK-MAAm system; and r1 = 0.95, r2 = 0.26 for the MVK-DMAAm system. The n and r2 values obtained in ethanol were as follows: r1 = 0.88, r2 = 1.18 for the MVK-AAm system; and r1 = 0.37, r2 = 2.04 for the MVK-MAAm system. Q2 and e2 values of AAm derivatives in dioxane were estimated to be 3.03 and 1.04 for MAAm and 2.15 and 1.11 for DMAAm, respectively. The Q2 and e2 values of MAAm in ethanol were estimated to be 2.67 and 1.21, respectively. Based on these results, the alternating copolymerizability depends on the interaction of monomer-monomer, and the strong solvent effect depends on t...

Anionic Copolymerizations of Acrolein with Methyl Vinyl Ketone and Acrylamide by Imidazole

Abstract The anionic copolymerizations of acrolein (AL) with methyl vinyl ketone (MVK) and acrylamide (AAm) in the presence of imidazole (Im) as an initiator have been studied in tetrahydrofuran at 0°C. The AL-MVK copolymers were found to be composed of vinyl polymer with one Im group attached and having an aldehyde and a carbonyl side chain. The monomer reactivity ratio was determined from a Fineman-Ross plot as r1 = 2.02 and r2 = 0.06. On the other hand, the AL-AAm copolymer were found to be composed of polymer units of 1,2 and 1,4 addition polymerization of AAm. These observations might be explained by the intermolecular hydrogen transfer mechanism of AAm. The polymerization mechanisms were discussed on the basis of these copolymerization results.

Polymerizabilities of Several Polar Vinyl Monomers by Imidazole

Abstract Polymerizabilities of several polar vinyl monomers in the presence of imidazole (Im) have been studied in CDC13 and CD3OD by NMR spectra. Acrylic acid formed a bimolecular adduct with Im as the initial adduct, while methacrylic acid was not obtained, On the other hand, methyl acrylate, methyl methacrylate (MMA), acrylamide (AAm), and acrylonitrile formed the initial adduct between Im and monomer, respectively. In these monomers, AAm and MMA gave each polymer in tetrahydrofuranat room temperature. The number-average molecular weight ([Mbar]n) of AAm polymers was determined to be in the range of 1000 to 1500, and the [Mbar]n of MMA polymers was found to be in the range of 2500 to 4500, The rate of polymerization Rp was expressed by the equations Rp = k[Im][AAm] and Rp = k[Im] [MMA]2, respectively. The activation energy ER was obtained by Arrheniusss plots as ER(AAm) = 9.6 kcal/mol and ER(MMA) = 3.8 kcal/mol. These polymerization mechanisms are discussed on the basis of these results.

Magnesium and lanthanide ions promoted electrochemical coupling of aliphatic esters and tetrahydrofuran for the synthesis of acetals

Electroreduction of aliphatic esters in THF was found to be promoted by the catalytic amount of porphine–magnesium(II) complexes and afforded 2-alkoxytetrahydrofuran derivatives, the coupling products between alkoxide anions formed by the electroreduction of aliphatic esters and THF cation generated by the anodic oxidation of the solvent (THF). In this reaction, chlorophyll a extracted from Trifolium repens L was remarkably effective. In addition, lanthanide metal(III) ions such as samarium trichloride were also found to be effective for the electroreduction of aliphatic esters.

Preparation of novel modified electrode by anodic oxidation of carbon fiber with radical NO3 and its application to the selective reduction of acetophenone

Abstract Modification of the surface of carbon fiber (CF) with hydroxyl groups was attained by the indirect oxidation of CF with radical NO 3 generated by the anodic oxidation of NO 3 − . This modified CF electrode showed quite interesting selectivity in the electroreduction of acetophenone.

Hydrogen transfer polymerization mechanism of acrylamide induced by propagating polyacrolein anion

Abstract In order to investigate the interaction between acrolein (AL) and acrylamide (AAm) on anionic copolymerization, the homopolymer-izabilities of AL in the presence of several p-substituted phenyl-acetamides such as p-nitroacetanilide, p-chloroacetanilide, acet-anilide, and p-methylacetanilide were investigated in tetrahydro-furan at 0°C using imidazole as an anionic catalyst. A linear co-relation was obtained by Hammett′ s equation as described by log R /R = 0.28σ. This result suggests that the homopolymeriz- P Po ability of AL is influenced by the structure of the amide compound. An increase of the additive propionamide (PAm) on the homopolym-erization of AL induced by the pyridine-water initiation system increased the polymerization rate R; however, it decreased the intrinsic viscosity [η] of poly-AL. From the measurement of infrared spectroscopy and elementary analysis, the presence of a chain transfer reaction between the poly-AL anion and PAm was found. These results support the presence of in...

Electroreduction of aliphatic esters by using alkali metal ion–crown ether complexes as mediators

The electroreduction of methyl decanoate (1) by using alkali metal ion-free Bu4NClO4 as a supporting electrolyte and platinum as anode and cathode was carried out in the presence of several kinds of alkali metal ion sources. The use of Bu4NClO4 as a supporting electrolyte without alkali metal ions gave only a trace amount of the reduced product. The addition of 0.05 equiv. of LiClO4 or NaClO4 into this electroreduction system gave the reduction product, 2-alkoxytetrahydrofurans 5 in ca. 20% yield. In this electrolysis, the ligand effect of the alkali metal ion sources was remarkably noted, that is, the electroreduction using sodium ion–crown ether complexes, especially, sodium ion—the polymeric crown ether ligands such as poly(vinylbenzo-15-crown-5-co-styrene) complex, greatly increased the efficiency of the electroreduction. It is plausible that alkali metal (0) species are electrogenerated from alkali metal ions and react as active reductants to reduce the aliphatic esters and the mediatory system is established in this electrolysis system.