Journal of the Iranian Chemical Society
Volume:5 Issue: 4, October 2008

The use of palladium catalysts for the oxidation of alcohols to aldehydes and ketones in the presence of various types of reoxidants is well known. Recently, the advantages of using molecular oxygen as the oxidant in the Pd-catalyzed oxidation of alcohols have been explored. The aim of this review is to provide an overview on the most important homogeneous palladiumcatalyzed aerobic oxidation of alcohols without a co-catalyst during last decade until the end of 2007.

The addition of dimethyl acethylendicarboxylate (DMAD) to thiosemicarbazone and guanylhydrazone of aldehydes afforded compoundes which were characterized to be new substituted imidazoles. Their structures were determined by 1H NMR, IR, mass spectra and elemental analyses.

Poly [N-(2-aminoethyl) acrylamido] trimemethyl ammonium chloride was prepared and used as an effective heterogeneous phase-transfer catalyst. This modified polyacrylamide catalyzed nucleophilic displacement of alkyl halides for easy preparation of alkyl thiocyanates, alkyl cyanides, alkyl azides, and alkyl aryl ethers in high yields and short reaction times in organic and aqueous media under two-phase and triphase conditions. The catalyst can be recovered and reused several times.

Treatment of thiosalicylic acids with p-halotoluene in concentrated sulfuric acid gave 1-halo-9H-thioxanthen-one 3 and its isomer 4 in high yields. Aromatic nucleophilic substitutions of the resulted 1-halo-9H-thioxanthen-9-ones with O-, N- and Snucleophiles are studied in a comparative manner, and various new O-, N- and S-substituted 9H-thioxanthen-9-ones are obtained.

An efficient, simple and green procedure for N-alkylation of azaheterocycles by quaternary ammonium salts in the presence of K2CO3 under microwave irradiation is described. Using this method, N-alkyl derivatives of azaheterocycles are obtained in good to excellent yields and short reaction times.

A new and simple approach to the analysis of pericyclic reactions based on combination of the interaction of HOMO-LUMO molecular orbitals and Huckel-Mobius aromaticity concept in transition state is reported. This approach seems to be more powerful than the Woodward-Hoffmann approach which appears to be limited to reactions with sufficiently high symmetry, and the Huckel-Mobius that use the non-participating lowest basis set (Ψ1). One important impact of the current approach is its capability in addressing the photochemical concerted reactions.

Methyltriphenylphosphonium peroxydisulfate (MTPPP) was synthesized by treating methyltriphenylphosphonium bromide with potassium peroxydisulfate in aqueous solution. This reagent was used as a suitable and efficient reagent for the cleavage of oximes, phenylhydrazones and 2,4-dinitro phenylhydrazones to their corresponding carbonyl compounds under non-aqueous condition.

The effect of a series of metal oxides on synthesis of diethyl 1-hydroxyphosphonates under solvent free condition was studied and the results showed that calcium oxide was the most efficient reagent than the others for preparation of the title compounds.

A simple, rapid and efficient method for the preparation of benzoxazoles, benzimidazoles and oxazolo[4,5-b]pyridines from the reaction of orthoesters with o-aminophenols, o-phenylenediamine and 2-amino-3-hydroxypyridine in the presence of silica sulfuric acid under heterogeneous and solvent-free conditions is reported. The significant features of this method are short reaction times, high yields of the products, mild reaction conditions, solvent free reaction, cheapness, non-toxicity and reusability of the catalyst.

A new heterogeneous catalyst prepared by immobilization of MO2(acac)2 on Mobil Catalytic Material, MCM-41, is reported. This catalyst, MoO2(acac)2-MCM-41, was successfully applied for efficient epoxidation of olefins with tert-BuOOH in 1,2-dichloroethane as solvent. The catalyst was characterized by elemental analysis, FT-IR, UV-Vis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). This catalyst can be reused several times without significant loss of its catalytic activity.

In this study the ability of Cercis siliquastrum L. leaves for the adsorption of Pb(II), Cu(II) and Ni(II) ions were studied. The effects of different parameters such as contact time of biosorbent and sorbents, pH of metal solution, and initial metal ion concentration on the biosorption were investigated. The maximum sorption of all metals were carried out in pH 4. Increasing the initial metal concentration in lower values caused a steep growth in biosorption, which was not observed in higher values. In the optimum sorption condition, the affinity of the leaves to metal ions was in the order of Pb(II)>Cu(II)>Ni(II). The biosorption of the metal ions were studied by Langmuir and Freundlich adsorption isotherm models. It was observed that the data were fitted very well to Langmuir adsorption isotherm model. According to the obtained correlation coefficient values, Freundlich model could predict Pb(II) and Cu(II) adsorption adequately but it was not suitable for Ni(II) sorption. Experimental data were exploited for kinetic evaluations related to the sorption process. According to our results, second-order kinetic provided a good description of biosorption for the tested metals with regression correlation coefficients more than 0.9998 for all the sorbate-sorbent systems.

A mild and efficient method for trimethylsilylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by tetrabutylammonium bromide is reported. The method is highly chemoselective for the o-protection of primary and secondary alcohols in the presence of amines, thiols and tertiary alcohols.

A mixture of ethyl acethylenecarboxylate, various aryl aldehydes and aminoacetaldehyde dimethyl acetal in the presence of silica gel were converted to N-ethyldimethyl acetal-1,4-dihydropyridines using microwave irradiation with good yields.

A simple and efficient method has been developed for the synthesis of �±-aminophosphinic acids from hypophosphorus acid under solvent "free conditions using microwave irradiation. �±-Aminophosphinic acids were obtained in high yield under mild conditions by reaction of hypophosphorus acid with aldehydes in the presence of amines under microwave irradiation.

Various types of aromatic and aliphatic sulfides are selectively oxidized to the corresponding sulfoxides in good to excellent yields using 30% H2O2 in the presence of catalytic amounts of N-bromosuccinimide (NBS) in buffered aqueous acetonitrile solution (pH =7.00). The results showed that acid sensitive functional groups such as double bonds, and O,O-acetals remained intact under the described reaction conditions

The mild and efficient oxidation of a variety of organic functional groups with a twin catalyst/oxidant, bis(phenanthroline)silver(II) peroxydisulfate, [Ag(phen)2]S2O8, is reported. This reagent shows high selectivity and the type of obtained products and the extent of oxidation are strongly dependent to the type of the functional groups and oxidant/substrate molar ratios.

Room temperature Rap-Stoermer condensation of �±-haloacetophenone with various 2-hydroxyarylaldehydes mediated by KF/Al2O3 resulted in sole formation of good to excellent yields of various substituted benzofurans in the absence solvent or extra stimulant.

An innovative route to preaper a number of variously substituted α-aminophosphonate is presented. The protocol avoids the use of any catalyst, organic solvents, and dry reaction conditions. The synthesis of α-aminophosphonates in the present study represents a three-component reaction in which no intermediate formation of either an imine or α-hydroxy phosphonate was observed.