Pyridazines. LXXXIV. Studies on borohydride reduction of pyridazine compounds

Imidazo[1,2-b]pyridazine, s-triazolo[4,3-b]pyridazine and tetrazolo[1,5-b]pyridazine and some derivatives thereof were reduced with sodium borohydride to give the corresponding 5,6,7,8-tetrahydro derivatives. A mechanism for these reductions is proposed and reduction at the C₇-C₈ bond occurs before the reduction of the C₆? N₅ bond. Substituents at position 7 and/or 8 cause a significant decrease in the extent of reduction or lead to a 5,6-dihydro derivative by competitive attack at the 6 position.     

Microbial reduction of sulfur-containing ketones by Geotrichum sp.

Bioreduction of some β-carbonyl phenyl sulfides, sulfoxides and sulfones (1, 3, 5, 8, 11 and 13) by Geotrichum sp. was studied. Reduction of β-carbonyI phenyl sulfoxides (5 and 8) gave anti-Prelog sulfoxide alcohols. (S, Ss)-3-Chloro-1-phenylsulfinylpropan-2-ol (9) was obtained in high yield with 95% e. e. after recrystallization from methylene chloride-petroleum ether.     

The reduction mechanism of the CO group. Part 2. The electrochemical reduction of p-diacetylbenzene in aqueous medium

A detailed study of the electrochemical reduction of diacetylbenzene A in aqueous medium between H_o = −5 and pH 14 is presented. The reactants are strongly adsorbed, so that the reactions are of a surface nature. From H_o = −5 to pH 6, a global 2e⁻ reduction yielding an enediol-type intermediate occurs. Analysis using the theory of the square schemes with protonations at equilibrium shows that, up to pH 4, the reaction is controlled by the first electron uptake, the paths being successively H⁺e⁻ and e⁻H⁺. The elementary electrochemical surface rate constants are 9.6 × 10⁷ s⁻ and 1.2 × 10⁶ s⁻ for AH⁺ and A respectively. From pH 6 to 14, a le⁻ adsorption wave, corresponding to the formation of (a) monoradical(s), appears and is followed by a le⁻ wave due to the reduction of the radical(s). A dimerization occurs, due to the coupling A⁻ + AH, as in the case of the monocarbonyl compounds. The rate of this surface process, k_d = 5 × 10¹³ cm² mol⁻¹ s⁻¹, is markedly smaller than the rate of the homogeneous reaction obtained in alkaline ethanol by Savéant et al. for the coupling of the radicals of benzaldehyde, benzophenone and acetophenone.     

Oxygen reduction on polycobaltprotoporphyrin film: II. pH effect and the mechanism of oxygen reduction

The oxygen reduction kinetics on polycobaltprotoporphyrin (PCoPP) film has been examined with the rotating disc electrode technique in O₂-saturated solution of various pH. PCoPP film promotes the oxygen reduction process via two electrons to produce peroxide over wide pH range. When pH value of solution decreases, catalytic activity of PCoPP film increases. Possible catalytic mechanisms have been proposed for oxygen reduction.     

The reduction mechanism of the C=O group. Part 2. The electrochemical reduction of p-diacetylbenzene in aqueous medium

A detailed study of the electrochemical reduction of diacetylbenzene A in aqueous medium between H_o = −5 and pH 14 is presented. The reactants are strongly adsorbed, so that the reactions are of a surface nature. From H_o = −5 to pH 6, a global 2e⁻ reduction yielding an enediol-type intermediate occurs. Analysis using the theory of the square schemes with protonations at equilibrium shows that, up to pH 4, the reaction is controlled by the first electron uptake, the paths being successively H⁺e⁻ and e⁻H⁺. The elementary electrochemical surface rate constants are 9.6 × 10⁷ s⁻ and 1.2 × 10⁶ s⁻ for AH⁺ and A respectively. From pH 6 to 14, a le⁻ adsorption wave, corresponding to the formation of (a) monoradical(s), appears and is followed by a le⁻ wave due to the reduction of the radical(s). A dimerization occurs, due to the coupling A⁻ + AH, as in the case of the monocarbonyl compounds. The rate of this surface process, k_d = 5 × 10¹³ cm² mol⁻¹ s⁻¹, is markedly smaller than the rate of the homogeneous reaction obtained in alkaline ethanol by Savéant et al. for the coupling of the radicals of benzaldehyde, benzophenone and acetophenone.     

The sodium borohydrirle reduction of N-iminopyridinium ylides. I. Synthesis of N-imino-1,2,3,6-tetrahydropyridines

Reaction of arylsulfonyl, pyridylearbonyl and arylalkylhydrazines 2 with 2,4-dinitrophenyl-pyridinium chloride 1 affords N-iminopyridinium ylides 3. The sodium borohydride reduction of ylides 3 to N-imino-1,2,3,6-tetrahydropyridines is described.     

Electrochemical reduction of some methanofullerenes. On the mechanism of the retro-Bingel reaction

The reactions of electrochemical reduction of methanofullerenes bearing phosphonate and alkoxycarbonyl groups at theexo-carbon atom were studied. The mechanism of the retro-Bingel reaction as the cleavage of two C−C bonds between the C(61) atom and the fullerene shell accompanied by electrochemical electron transfer was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 426–429, March. 2000.     

Electrochemical reduction of cinoxacin. The unexpected formation of an isatin derivative

The electrochemical reduction of cinoxacin (I) has resulted, via a series of chemical and electrochemical steps, in the formation of an indole dione III.     

Pyrrole reduction: The zinc/acid reduction of octahydrocarbazoles

The stereo- and regiochemical course of the zinc/acid reduction of 1,2,3,4,5,6,7,8,-octahydrocarbazole is strongly influenced by experimental conditions and by the nature of the N-substituent.     

The wolff-kishner reduction of 2-acetonyl pyrazines and pyridines. A novel rearrangement

Wolff-Kishner reduction of 1-(6-methylpyrazin-2-yl)-2-propanone leads to the formation of 2-isopropyl-6-methylpyrazine ( 2a ), in addition to the expected 6-methyl-2-n-propylpyrazine. The by-product 2a is suggested to arise via a spirocyclopropylidene aza-anion, which serves as a conduit between the initial less-stable secondary 1-(2-pyrazinyl)-2-propyl carbanion and the more stable primary 2-(2-pyrazinyl)-1-propyl carbanion. Similar results were observed for the 1-(3-methylpyrazin-2-yl) and 1-(6-methylpyridin-2-yl)-2-propanones. The extent of by-product formation diminished in the pyridine ring system. Electrophilic activation of the ring appears essential since the benzene analog phenylacetone gave no detectable cumene under identical reaction conditions.     

Indolopyridines containing a bridgehead heteroatom. 12. Synthesis and reduction of 12-arylidene-5,6-dihydroindolo[2,1-a]isoquinolinium trifluoroacetates

Condensation of 5,6-dihydroindolo[2,1-a]isoquinoline with aromatic aldehydes in trifluoroacetic acid afforded 12-arylidene-5,6-dihydroindolo[2,1-a]isoquinolinium trifluoroacetates. Hydrogenolysis of these salts on rhenium heptasulfide at elevated temperature and hydrogen pressure yielded indolo[2,1-a]isoquinolines, while reduction with sodium borohydride gave 12-arylmethylindoloisoquinolines. Photoluminescence was found for some indolo[2,1-a]isoquinolines.     

Polyelectrolytes containing dihyronicotiamide I. Electrostatic effect on the reduction in aqueous solution

Reduction of charged or uncharged substrates by a copolymer of N-(p-vinylbenzyl)-1,4-dihydronicotinamide and sodium styrene-p-sulfonate (PNAH) in aqueous solutions was investigated. Electrostatic interaction of PNAH with charged substrates led to a far more effective reduction of crystalviolet (CV) and a far less effective reduction of potassium ferricyanide (FeC) than the monomer model [N-benzyl-1,4-dihydronicotinamide (BNAH)] system. In the PNAH-CV system, in particular, a rapid reduction occurs by a first-order process because of the remarkable concentration effect of the polymer. Furthermore, this reduction was not appreciably affected by an added salt, suggesting the presence of hydrophobic interaction between PNAH and CV.     

Active nickel-based reduction of organic compounds

The reducing system NiCl₂·2H₂O—Li—arene_cat (cat is catalyst) was proposed for use to reduce a wide range of organic compounds, including alkenes, alkynes, carbonyl compounds, imines, halogenated derivatives, sulfonates, aromatic compounds, hydrazines, azo and azoxy compounds, N-oxides, and nitrones. The degree of reduction can be controlled for some substrates. Deuterium can be incorporated in the reaction products using nickel chloride deuteriohydrate. Nitrones, N-alkoxyamides, and acyl azides are also reduced with the Li—arene_cat system containing no nickel salt.     

Studies of the electrochemical reduction of some dinitroaromatics

The electrochemical reduction of a series of dinitroaromatics, along with one trinitro compound, has been investigated at a glassy carbon electrode in N,N-dimethylformamide. The separation between the two standard potentials for the reduction, E°₁ − E°₂, has been determined and discussed in terms of the structures of the compounds. cis-4,4′-Dinitrostilbene was shown to undergo redox-catalyzed isomerization to the trans isomer. This was demonstrated with partial controlled potential electrolysis followed by chromatographic analysis of the solution. It was also found that redox-catalyzed isomerization could adequately account for the voltammetric behavior. The anion radicals of 3,5-dinitropyridine and 1,3,5-trinitrobenzene undergo reversible dimerization reactions. The rate and equilibrium constants for the dimerization were determined by simulation of the voltammograms of these two compounds and also by simulation of the voltammograms obtained with solutions from the one-electron controlled potential reduction, that is, solutions of the dimer. The equilibrium constants for dimerization were also determined by electron paramagnetic resonance spectroscopy.     

Integration points for the reduction of boundary conditions

An analysis of a method for the numerical evaluation of the integral is presented. The method introduces a change of variable, x = x(q), with the property that d ⁿx/dqⁿis zero at x = a, x = b for n = 0, 1, 2,... N, where N is an integer to be chosen. The Euler-Maclaurin formula shows that the resulting integral in the variable q is ideally suited for numerical integration, using equally spaced points and equal weights in q-space. Examples are given for various integrals which occur in quantum chemistry and applications to more than one dimension are discussed.This paper was presented during the session on numerical integration methods for molecules of the 1970 Quantum Theory Conference in Nottingham. It has been revised in the light of the interesting discussion which followed.     

Biomimetic and microbial reduction of nitric oxide

The biomimetic reduction of nitric oxide (NO) to nitrous oxide (N₂O) by dithiothreitol in the presence of cyanocobalamin and cobaltcentered porphyrins has been investigated. Reactions were monitored directly using Fourier Transform Infrared (FTIR) Spectroscopy vapor-phase spectra. Reaction rates were twofold faster for the corrin than for the cobalt-centered porphyrins. The stoichiometry showed the loss of two molecules of NO per molecule of N₂O produced. We have also demonstrated that the facultative anaerobe and chemoautotroph,Thiobacillus denitrificans, can be cultured anoxically in batch reactors using NO as a terminal electron acceptor with reduction to elemental nitrogen (N₂). We have proposed that the concentrated stream of NO_x, as obtained from certain regenerable processes for the gas desulfurization and NO_x removal, could be converted to N₂ for disposal by contact with a culture ofT. denitrificans. Four heterotrophic bacteria have also been identified that may be grown in batch cultures with succinate, yeast extract, or heat and alkali pretreated sewage sludge as carbon and energy sources and NO as a terminal electron acceptor. These areParacoccus dentrificans, Pseudomonas denitrificans, Alcaligens denitrificans, andThiophaera pantotropha.     

Sodium arenetellurolate-catalyzed reduction of nitroalkanes to oximes

Treatment of aliphatic nitro compounds with NaBH₄ in alkaline ethanol in the presence of a catalytic amount of diaryl ditelluride at 25°C for 5–20 h produces the corresponding oximes, generally as a mixture of E/Z isomers, in fair to good yields. Arenetellurolate anion (ArTe⁻) generated in situ is suggested to be the active species for the reduction.     

Electrochemical reduction of nitrotetralones

The electrochemical reduction of three nitrotetralone derivatives by tast and differential pulse polarography and cyclic voltammetry in a wide pH range was studied. In aqueous media, the reduction of mono- and dinitrotetralone follows the general pattern of reduction of aromatic nitro compounds: the nitro group is reduced in a four-electron step to a hydroxylamine group. However, in mixed media this reduction differs from that of other nitrobenzenes, due to the fact that the formation of the nitroradical anion was not observed. The reduction of the acetoxy derivative was studied only at alkaline pH, because it suffered acid hydrolysis. The ionization pK of the protonatable groups were polarographically obtained.     

Alkaloid studies. VI. lithium aluminum hydride reduction of apoyohimbine and the synthesis of 3,4,5,6-tetradehydroyohimbane-16-methanols

Catalytic reduction of apoyohimbine ( 1 ), prepared from yohimbine and thionyl chloride in pyridine, gives methyl yohimbane-16α-carboxylate ( 2 ) after equilibration with methoxide. LAH reduction of 2 or β-yohimbine O-tosylate ( 3 ) gives yohimbane-16α-methanol ( 4a ). LAH reduction of 1 affords yohimbane-16α-carboxaldehyde ( 5 ), yohimb-16-ene-16-methanol ( 6a ) and yohimbane-16β-methanol ( 7a ). Structural assignments 6a and 7a are confirmed by mass spectral measurements. Pmr spectra of 4a, 6a and 7a and their O-acetates 4b, 6b and 7b are discussed. LAH reduction of apo-α-yohimbine ( 8 ) affords alloyohimb-16-ene-16-methanol ( 9 ). Dehydrogenation of 4a with palladium black and maleic acid gives 3,5,4,5,6-tetradehydroyohimbane-16α-methanol ( 10 ) iodide, and 7a gives 3,4,5,6-tetradehydroyohimbane-16β-methanol ( 11 ) iodide and picrate. Properties of 10 and 11 differ from those of melinonine E.     

Drag reduction experiments with very large pipes

Various substances have been tested in the laboratory for their suitability as flow enhancers in aqueous solutions. The following maximum drag reductions (%) were obtained with pipes of 14 mm diameter and a Reynolds number of 10⁵: Na-carboxy methylcellulose (32), hydroxyethyl cellulose (42), cetyltrimethylammonium chloride/-naphthol (74; Re=10⁴), polyethylene oxide (76), K-polyphosphate/Na-pyrophosphate (77), polyacrylamide (80). The tested, partially hydrolysed polyacrylamide which was produced by a special process was found to be not only extremely effective and highly resistant to shear degradation but also unaffected by the salt content, the temperature and the water spoilage. Experiments were therefore made with this material on an industrial scale, that is to say with pipes up to 750 mm in diameter and 3200m in length. Whilst in the laboratory (pipes up to 14 mm in diameter) drag reductions were measured according to the Virk asymptote, the results obtained with large pipe diameters were lower. At diameters ranging from 300 to 750 mm a maximum drag reduction of 65% (at a concentration of 30 ppm PAAM and a constant wall shear stress of 50 Pa) has been obtained independently of the diameter.Symbols c concentration - d diameter - FE (as index) flow enhancer - k roughness - l length - n degree of polymerization - p pressure drop - r radius - Re Reynolds number - T temperature - v velocity - w (as index) water - drag reduction - friction factor - kinematic viscosity - density - wall shear stress Dedicated to Prof. Dr. R. Bonart on the occasion of his 60th birthday