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Sodium Dithionite Reduction of Nitroarenes Using Viologen as an Electron Phase-Transfer Catalyst
Koh Park, Kwanghee,Oh, Chang Hun,Joung, Won Kyou 충남대학교 기초과학연구소 1994 연구논문집 Vol.14 No.-
Various aromatic nitro compounds were reduced conveniently to the corresponding aniline derivatives with sodium dithionite using dioctyl viologen as an electron-transfer catalyst in dichloromethane-water two-phase system.
Solvent Effects on the Reactions of 1-Benzyl-1,4-dihydronicotinamide in Ethanol/Water Mixed Solvent
Koh Park, Kwanghee,Lee, Jae-Hun,Park, Joon Woo 충남대학교 기초과학연구소 1991 연구논문집 Vol.11 No.-
In conclusion, it has been shown that the reactions of BNAH exhibit the drastic solvent effects in ethanol/water mixed solvent. The results are interpreted in the framework of the existing mechanisms of the reactions. Futher studies on a variety of NADH analogs which is relevant to the mechanisms are currently underway. Acknowledgements. This work was supported by the Basic Science Research Institute Program of the Ministry of Education of the Republic of Korea and the Korea Science and Engineering Foundation.
Koh Park, Kwanghee,Oh, Chang Hun,Sim, Woo-Jeon 충남대학교 기초과학연구소 1995 연구논문집 Vol.15 No.-
Viologens (1.1'-dialkyl-4.4'-bipyridinium, V^2-) have been utilized as electron-transfer catalysts(ETC) for the reduction of various organic compounds. We have shown that various aromatic nitro compounds are reduced conveniently to the corresponding aniline derivatives with sodium dithionite using octyviologen(OcV^2-) as an ETC in a dichloromethane - water two-phase system, while aliphatic nitro compounds remain intact under the same reaction conditions.
Koh Park, Kwanghee,Han, Duhee,Shin, Daehyun 충남대학교 기초과학연구소 1987 연구논문집 Vol.7 No.-
Reduction of N-arylpyridinium compounds by NaBH_4 gave mixtures of the corresponding 1,2-dihydropyridine(major) and 1,4-dihydropyridine(minor), whereas similar reduction by Na_2S_2O_4 produced 1,4-dihydropyridines regioselectively. The proportion of 1,4-isomer in the product by NaBH_4 reduction appeared to increase with the electron-donating ability of N-aryl groups. When the N-aryl group is p-methylphenyl, p-ethylphenyl or p-methoxyphenyl, the 1,2-dihydropyridines in ethanol-water (4:1) solutions isomerized to the corresponding 1,4-dihydropyridines. N-(p-methylphenyl)-1,2-dihydropyridine and N-(p-ethylphenyl)-1,2-dihydropyridine in solid state also isomerized to the corresponding 1,4-dihydropyridines. The different behaviors of reduction among N-arylpyridiniums and isomerization of the reduction products depending on the substituent in N-aryl group were explained in terms of difference in the electronic effects of the substituents.
Koh Park, Kwanghee,Kim, Hong-Gid,Park, Joon Woo 충남대학교 기초과학연구소 1990 연구논문집 Vol.10 No.-
NADH analogs, 1-benzyl-3-substituted (X)-1,4-dihydropyridines 1-4(1:X-CONH_2;2:X=CSNH_2;3:X=COOCH_3;4:X=COCH_3) were synthesized. The second order rate constants for hydration reaction and oxidation reactions by Cu^2+, Fe(CN)_6^3- or methylacridinium iodide (MAI) of the compounds were determined. For all reactions investigated, the rate constants increased with decreasing electronegative character of the 3-substituents of 1,4-dihydropyridines: the decreasing order of the reaction rates was 2>1>3>4. However, the sensitivity of the reaction rates on the 3-substituents differed among the reactions. This was explained in view of mechanisms of the reactions.
Koh Park, Kwanghee,Lee, Jin Pyo,Park, Joon Woo 충남대학교 기초과학연구소 1994 연구논문집 Vol.14 No.-
Cyclodextrins are cyclic oligosaccharides which possess a hydrophobic cavity. They have attracted great attention as enzyme mimics because of their ability to form inclusion complexes with a variety of substrates and large kinetic effects on the reactions of the inclusates. Recently, efforts have been made into modifying cyclodextrins to enhance their kinetic effects. We have been interested in functionalized β-cyclodextrins(β-CDs). and have shown that there are differences in reactivity and enantioselectivity among functionalized β-CDs. Polyamine-functionalized β-CDs have metal-binding sites, and exhibit large metal ion effects on the binding affinity and reactivity of guest molicules. In this report, we present kinetics of the deacylation of m-nitrophenyl acetate in mono-6-deoxy-6[n-(2-aminoethyl)]amion-β-CD (CDen) and mono-6-deoxy-6-[N-(2-aminoethyl)-2-amionethyl]amino-β-CD (CD-dien) media in the presence and in the absence of divalent metal ions.
Koh Park, Kwanghee,Kang, Byung-Kue 충남대학교 기초과학연구소 1995 연구논문집 Vol.15 No.-
Kinetic studies of the deacylation reactions of p-and m-nitrophenyl ester of (R or S)-α-methoxyphenylacetic acid were performed in β-CD, mono-6-deoxy-6-[N-(2-aminoethyl)]amino-β-CDen)and mono-6-deoxy-6-[N-(2-aminoethyl)-2-aminoethyl]amino-β-CD) (β-CDdien) media. The binding constants (K) of the substrates to the hosts and the rate constants (k_φ^CD)for the complexed substrates were determined, (k_φ^CD) values are highly dependent on the hosts and the substrates, whereas differences in K values among them are modest. The p-nitrophenyl esters show larger acceleration by β-CDen and β-CDdien than the corresponding m-isomers, while the m-isomers are more reactive than the p-isomers in β-CD media. This is taken as an indication that the amino groups attached to the primary side of β-CD participate in the deacylation reaction.
Micellar and Metal Ion Effects on the Reactions of 1,4-Dihydronicotinamide
Koh Park, Kwanghee,Suh, Jee Hee,Park, Joon Woo 충남대학교 기초과학연구소 1989 연구논문집 Vol.9 No.-
1.4-Dihydronicotinamides are widely investigated, mainly as model compounds of the coenzyme NADH. While NADH and its model compounds can reduce various functionalities they are known to be unstable in aqueous medium and undergo acid catalyzed hydration reaction. Thus most NADH mimic reductions of organic substrates have been performed in non-aqueous media. For efficient NADH reductions in biological systems which is obviously aqueous, there must be some mechanisms which retard the hydration reaction and accelerate the reduction reactions. This can be achieved by the interations of the coenzyme with the NADH-dependent dnzymes and substrates. The catalysis of metal ions is necessary for reduction reactions in alcohol dehydrogenases that require NADH as a cofactor. Similarly, it mimic reductions in non-aqucous media. The sufactant micelles are extensively utilized as enzyme mimetic system. It was reported that the micelles greatly affect the hydration reaction of NADH model compounds. The reactions of NADH model compounds in surfactant micellar solutions containing metal ions would mimic the reactions in biological systems more colsely. In this communication, we wish to report the micellar and metal ion effects on the reduction of 2.2.2-trifuoroacetophenone(TFA) by 1-benzyl-1.4-dihydronicontinamide (BNAH) and the hydration of BNAH.
Koh Park, Kwanghee,Moon, Gyeoung Un,Kwon, Ki-Sung 충남대학교 기초과학연구소 1988 연구논문집 Vol.8 No.-
The reaction between 1-benzyl-3-carbamoyl-1,4-dihydropyridine (BNAH) 1 and various 1-arylpyridinium salts 2, and the reaction between 1-(4-methylphenyl)-1,4-dihydropyridine 4b and 1-aryl-3-carbamoylpyridinium (1-arylnicotinamide) salts 5 were carried out. The extents of reaction in equilibrium were estimated by nmr integration data. The equilibrium constants for the reactions, K, and the standard Gibbs free energy changes for the reduction of the pyridinium slats to the corresponding 1,4-dihydropyridines ΔG°′ were evaluated. The Hammett plot of log K for the reaction between 1 and 2, and ΔG°′ against σ_p of the substituents in 1-aryl moiety shows linear correlation with the reaction constant ρ of 9.4 (for log K vs σ_p) and -54.5 KJ/mole (for ΔG°′ vs σ_p). It was found that 1-aryl-1,4-dihydropyridines have much higher reducing power than the corresponding 1-aryl-1,4-dihydronicotinamides, and the power is affected greatly by the electron-withdrawing ability of the substituents in aryl group. The reaction were utilized for preparation of 1,4-dihydropyridines bearing highly electron-withdrawing groups such as 4-nitrophenyl and 2,4-dinitrophenyl, which could not be obtained by conventional dithionite reduction of the corresponding pyridinium salts due to the base-labile nature of the salts.