Nanostructural composite photocatalysts based on polycrystalline cadmium sulfide

The results of studies of new photocatalysts—composites of cadmium sulfide with nanoparticles or thin layers of copper(I), silver(I), mercury(I), copper(II), bismuth(III), antimony(III) and iron(III) sulfides—are reviewed. The optical and electrophysical characteristics, the ranges of photosensitivity, the nature of the increased activity and the peculiarities of the photocatalytic effects are discussed. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 22039 Kiev, Science Prosp., 31. Translated from Teoreticheskiya i éksperimental'naya Khimiya, Vol. 33, No. 5, pp. 306–321, September–October, 1997.     

Photoelectrochemical behavior of nanostructural composites based on polycrystalline cadmium sulfide

Nanostructural composites can be used as suspension electrodes; they are made by substitution cadmium(II) at the surfaces of CdS microcrystals for Cu(I, II), Fe(III), Bi(III), and Sb(III). Features are considered in the photoelectrochemical action mechanism of the various nanocomposites. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 79–82, March–April, 1999.     

Direct allylation of benzyl alcohols,diarylmethanols, and triarylmethanols mediated by XtalFluor-E

We report the direct allylation of benzyl alcohols, diarylmethanols and triarylmethanols mediated by XtalFluor-E using allyltrimethylsilane. The resulting allylated products are obtained in moderate to high yield.     

Visible light photoredox catalysed amidation of carboxylic acids with amines

A visible-light promoted photoredox catalysed, green one-pot approach for the amidation of carboxylic acids with amines has been developed for the synthesis of diverse aliphatic and aromatic amides. The proposed strategy is extendable also to biologically active amides and could represent a low-cost alternative to the common synthetic pathways. The developed strategy may hold great potential for a comprehensive display of biologically interesting peptide synthesis and amino acid modification.     

Aerobic oxidative esterification of benzyl alcohols with catalytic tetrabromomethane under visible light irradiation

We report a useful method for the facile synthesis of aromatic esters from benzyl alcohols with molecular oxygen and catalytic tetrabromomethane in alcohol under visible light irradiation with a fluorescent lamp. This is the first metal-free reaction using molecular oxygen as the terminal oxidant.     

Visible light mediated metal-free oxidative aromatization of 1,3,5-trisubstituted pyrazolines

The visible light mediated oxidation of 1,3,5-trisubstituted pyrazolines under metal-free conditions was developed. Various substituted pyrazolines were oxidized to pyrazoles by irradiation with visible light/sunlight. A plausible mechanism was proposed for the light mediated oxidation proceeding via formation of intermediates with electron rich C-3 positions and electron deficient C-5 positions. Correlation between the electronic effect induced by the aryl substituents and the rate of oxidation was studied by UV–vis spectroscopy. This correlation study supported the proposed mechanism. Electron withdrawing substituents at the 3-phenyl group and electron releasing substituents at the 5-phenyl group enhanced the rate of oxidation; whereas, electron donating substituents at the 3-phenyl group and electron withdrawing substituents at the 5-phenyl group reduced the rate.     

Oxidative amidation of benzyl alcohols with amino acid esters mediated by N-hydroxysuccinimide/phenyliodine diacetate

A simple protocol involving metal-free oxidative amidation of benzyl alcohols with amino acid esters has been presented. The amidation proceeds in a radical pathway unlike in conventional metal-mediated extrusion of dihydrogen. The method is advantageous in terms of metal-free conditions, nonexpensive commercial starting substrates. Also various substituents in the starting materials are tolerated and sterically hindered amino acid side chains could provide good yields of amide products.     

Oxidation of benzyl alcohols, benzyl halides, and alkylbenzenes with oxone

Oxidation of benzyl alcohols, benzyl halides, and alkylbenzenes to their corresponding oxidation products has been shown to be accomplished directly with oxone. The methodology that involves mere stirring/heating of the reactants and oxone in acetonitrile/water (1:1, v/v) is simple and practical, but is limited to substrates that do not contain sensitive functionalities and heteroaromatic rings.     

Halogen- and N-haloimide-promoted homo- and heterocoupling of alpha-(N-carbamoyl)alkylcuprates and alpha-(alkoxy)alkylcuprates

Both homo- and mixed lithium di-alpha-(heteroatom)alkylcuprates readily dimerize upon addition of halogens (e.g., I(2), Br(2)) or N-halosuccinimides to afford the coupled products in excellent yields. Higher yields result when the requisite alpha-(heteroatom)alkyllithium reagents are generated via deprotonation rather than by transmetalation of the corresponding stannanes. Mixed lithium dialkyl- or alkyl(aryl)cuprate reagents containing one alpha-(heteroatom)alkyl ligand and one simple alkyl or aryl ligand give significantly lower yields of coupled product. Low enantioselectivity has been achieved in the oxidative coupling of lithium (n-Bu)(2-pyrrolidinyl)cuprate.     

Enzymatic oxidation of cadmium and lead metals photodeposited on cadmium sulfide

Cadmium and lead metals deposited on CdS particles are shown to act as substrates--electron donors for enzymes, hydrogenase from Thiocapsa roseopersicina (HG), NAD-dependent hydrogenase from Alcaligenes eutrophus (NLH), and ferredoxin:NADP oxidoreductase (FNR) from Chlorella in the formation of hydrogen, NADH and NADPH, respectively. Adsorption of the enzyme on the surface of the metallized CdS particle is required for enzymatic oxidation of metal. The maximum rates for the formation of hydrogen and NADH catalyzed by hydrogenase and NAD-dependent hydrogenase with metals as electron donors are comparable with the rates obtained for these enzymes using soluble substrates. Kinetic analysis of the enzymatic oxidation of cadmium metal has revealed that the rate decreases mainly due to the formation of a solid product, which is supposed to be Cd(OH)2. The deceleration of lead oxidation catalyzed by hydrogenase proceeds at the expense of the inhibitory effect of the formed Pb2+. The enzymatic oxidation of electrochemically prepared cadmium metal is also shown. Based on these results, a new mechanism of action of the enzymes involved in anaerobic biocorrosion is proposed. By this mechanism, the enzyme accelerates the process of metal dissolution through a mediatorless catalysis of the reduction of the enzyme substrate.     

Dual-function of alcohols in gold-mediated selective coupling of amines and alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100?% in excess methanol.     

Photoredox catalyzed C-P bond forming reactions-visible light mediated oxidative phosphonylations of amines

A visible light mediated, carbon-phosphorus bond forming reaction has been developed. With the use of a readily available photoredox catalyst, α-amino phosphonates were obtained in good yields under mild reaction conditions.     

Photocatalytic syntheses of azoxybenzene by visible light irradiation of silica-coated cadmium sulfide nanocomposites

Photoirradiation (lambda= 436 nm) of a deaerated 2-propanol aqueous solution containing nitrobenzene and rhodium-loaded silica-coated cadmium sulfide nanoparticles produced azoxybenzene with relatively high selectivity (68%), the photocatalytic activity being enhanced with a decrease in the size of the semiconductor particle core.     

Glycosides of benzyl and salicyl alcohols from Alangium chinense

From the water-soluble fraction of the dried leaves of Alangium chinense, three new glycosides, benzyl alcohol beta-D-glucopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 6)]-beta-D-glucopyranoside, 2'-O-beta-D-glucopyranosylsalicin, and 2'-O-beta-D-glucopyranosyl-6'-O-beta-D-xylopyranosylsalicin were isolated along with seven known glycosides. The structures of the new compounds were determined by spectroscopic and chemical means.     

Transition-metal-free oxidative amidation of benzyl alcohols with amines catalyzed by NaI: a new method for the synthesis of benzamides

A simple, inexpensive, and efficient method for the synthesis of benzamides via the reaction of benzyl alcohols and amine hydrochloride salts in the presence of NaI as a green catalyst is described. Various derivatives of benzamide were synthesized in moderate to good yields using this method.     

Electrochemical acylation and alkylaminocarbonylation of amines and alcohols

Electrochemical acylation and ethylaminocarbonylation of amines and alcohols are performed by anodic oxidation of the hydroxamic acids and N-ethyl-N′hydroxyurea, respectively, in acetonitrile at a glassy-carbon electrode.     

Carbon dioxide reduction under visible light: a comparison of cadmium sulfide and titania photocatalysts

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Ruthenium catalyzed synthesis of secondary or tertiary amines from amines and alcohols

Unsymmetrical secondary and tertiary amines are prepared by the ruthenium catalyzed reaction of alcohols with amines, which provides highly efficient method for synthesis of cyclic amines.