Diphenylmethane-mediated transmethylation of methylbenzenes over H-zeolites

Despite their vital roles in the catalytic cycle for toluene disproportionation, diphenylmethane (DPM)-type compounds have never been directly detected or proved to be true reaction intermediates from experimental techniques. In this report, we provide unprecedented insights into the DPM-mediated reaction mechanism, by demonstrating the build-up of DPM species inside the zeolite pores and following their decomposition. It can be stated that, despite their bulkiness, (di)methylated DPM species may indeed be formed at high concentrations in the ZSM-5 channels when toluene is reacted. The dimethyl-DPM species are unstable when present in the zeolite voids and decompose under a concomitant evolution of xylene at 200 degrees C.     

Platinum-palladium catalysts in hydrogenation of methylbenzenes

Hydrogenation of benzene, toluene, o,m and p-xylene over Pt, Pd and Pt–Pd/Al₂O₃ catalysts has been studied. Experimental data show that when Pd is added to Pt catalysts, a decrease in activity and changes in selectivity occur. This is explained by the formation of electron-deficient and electrorich metallic species.

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, , -, - - Pt, Pd Pt–Pd/Al₂O₃. , Pd Pt . .

     

Oxidation of methylbenzenes by heteropoly compounds in solution

Conclusions heteropoly compounds in acetic acid solution oxidize methylbenzenes to form mixtures of aromatic alcohols, aldehydes, di- and polyarylmethanes. The reaction may be carried out catalytically in the presence of oxygen. Results were obtained indicating the formation of an intermediate radical-cation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheska, No. 5, pp. 1010–1017, May, 1984.     

Selenium-catalyzed oxidative halogenation

Organoselenides catalyze the oxidation of halides by H₂O₂. Furthermore, these selenides catalyze the transfer of oxidized halogens from N-halosuccinimides to olefins and ketones. Thus, organoselenides catalyze oxidative halogenation reactions including halolactonization, α-halogenation of ketones, and allylic halogenation. The ability of selenium to undergo reversible 2e⁻ oxidation-reduction chemistry facilitates halogenation through selenium-bound halogen intermediates.     

Formation of cation radicals from methylbenzenes on sulfated zirconia

The adsorption of methylbenzenes on sulfated zirconia has been studied by ESR. The catalyst is shown to possess acceptor sites capable to ionize methylbenzenes. The number of acceptor sites appeared to depend on the surface sulfur concentration. Oxygen is observed to strengthen the acceptor sites.     

Electrochemical halogenation of organic compounds

Data on the electrochemical chlorination, bromination, and iodination of organic compounds from various classes were summarized and systematized. The influence of the nature of the halogen and organic substrate on these processes was discussed. Data on the effects of the solvent, anode material, current density, and temperature on electrohalogenation were analyzed. The main tendencies of these reactions and their peculiarities as reactions of hydrogen substitution in the substrate were considered.     

Copper-catalyzed halogenation of arylboronic acids

In this Letter, a copper-catalyzed halogenation of arylboronic acids was described. This reaction tolerates a variety of functional groups, providing aromatic halides with good yields. It represents a facile and mild procedure to aryl halides.     

Allylic halogenation of unsaturated amino acids

A range of dehydro amino acid derivatives has been prepared and subjected to halogenation using either molecular bromine or chlorine, or NBS. Allylic halogenation of the unsaturated amino acid side chains occurs through radical bromination with NBS. The procedure is complementary to treatment with chlorine, which also affords allyl halides. This latter and unusual reaction is shown through a deuterium labelling study to proceed via an ionic mechanism. The choice of NBS or chlorine for allyl halide synthesis is shown to depend on the potential to avoid competing reactions, such as halolactonization of leucine derivatives with chlorine, and hydrogen abstraction and bromine incorporation at multiple sites on treatment of isoleucine derivatives with NBS. The synthetic utility of the allyl halides prepared in this study is indicated through the synthesis of a cyclopropyl amino acid derivative and the extension of the carbon skeleton of an amino acid side chain.     

Electrophilic amination of methylbenzenes with sodium azide in trifluoromethanesulfonic acid

Russian Journal of Organic Chemistry -     

Visible-light-induced halogenation of aliphatic CH bonds

Alkyl halides are of particular interests in the areas of pharmaceutical, agrochemical, and material sciences. Direct CH halogenation has been recognized as the most efficient method for the introduction of halogen atoms into organic molecules. This Digest paper highlighted some of the most recent and significant developments in the visible light-promoted halogenation of aliphatic CH bonds.     

Enzymatic halogenation of pyrazoles and pyridine derivatives

Pyrazole, 1-methylpyrazole and 3-methylpyrazole are chlorinated by the enzyme chloroperoxidase from Caldariomyces fumago, in the presence of potassium chloride and hydrogen peroxide at pH 2.7, yielding the corresponding 4-chloro derivatives in good yields. A 4H-pyrazole is proposed as an intermediate in this reaction. 2-Aminopyridine was converted regiospecifically by the same enzyme into 2-amino-3-chloropyridine, and 8-hydroxyquinoline gave its 5,7-dibromo-derivative in very good yield when bromide ion was used as the halide substrate.     

Thermochemical studies on the halogenation of tetraphenyllead

The bromination and iodination of tetraphenyllead and the corresponding triphenyllead halides have been studied in a solution calorimeter and the enthalpies of formation of the crystalline solids Ph₃PbBr, Ph₂PbBr₂, Ph₃PbI, and Ph₂PbI₂ have been derived. Values for the gas phase have been calculated using enthalpies of sublimation derived from vapourpressure measurements. The PbBr and PbI bond energy terms have been derived.     

Electrochemical halogenation of 4-hydroximino-2,2,6,6-tetramethylpiperidine

Electrochemical chlorination and bromination of 4-hydroximino-2,2,6,6-tetramethylpiperidine were studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1808–1810.Original Russian Text Copyright © 2004 by Kashparova, Kagan, Zhukova.     

Stereospecific halogenation of ethyl methyl phosphorothioic acid

Tetramethyl-α-halogenoenamines are useful reagents for the stereospecific conversion of phosphorothioic acids to the corresponding phosphoryl halides.     

Silver-catalyzed decarboxylative halogenation of carboxylic acids

Decarboxylative halogenation of carboxylic acids catalyzed by silver carbonate is reported. ortho-Nitrobenzoic acids react with copper(II) chloride or bromide in DMF/DMSO at 130-140 °C leading to the corresponding aryl halides in moderate to good yields.     

Photochemical reaction of 1- and 2-naphthalenecarbonitrile with some methylbenzenes

1- and 2-Naphthalenecarbonitriles (1- and 2-NN) photochemically react with 1,2,4,5,-tetramethylbenzene (4) (but not with lower homologues). The products are 1,1'-(1,2-ethane-diyl)bis-(2,4,5-trimethylbenzene) (5) and 3-hydroxy-1-naphthalenecarbontrile with 1-NN and 5 and 1,2-dihydro-2-naphthalenecarbonitrile with 2-NN. The reaction involves electron transfer to the NN singlet excited state followed by proton transfer. 4-Methylbenzyl-(1-cyano-4-naphthyl)methyl ether (9) and the corresponding trimethylbenzylderivative 10, which contain donor and acceptor chromophores linked together, were prepared and found to show enhanced excimer emission but no photochemical reactivity, 1- and 2-NN react with 1-methoxy-4-methylbenzene (but not with the 3-isomer) analogously as with 4, but in this case small amounts of benzylated 1,2-dihydro-1-naphthalenecarbonitriles and 1,4-dihydro-2-naphthalenecarbonitriles are also formed. The mechanism is discussed in comparison with the corresponding reaction of 1,4-naphthalenecarbonitrile.