Jochanan Blum

Palladium-catalyzed decomposition of aqueous alkali metal formate solutions

Abstract Aqueous sodium and potassium formate solutions undergo catalytic decomposition, under mild conditions, into molecular hydrogen and hydrogen carbonate in the presence of palladium on carbon. Both the formate and water hydrogen atoms are involved in the process and undergo fast exchange. Some kinetic and mechanistic features of the decomposition reaction are reported.

Reversible ion-pair extraction in a biphasic system. application in transition metal-catalyzed isomerization of allylic compounds

Abstract A two-liquid-phase catalysis is described in which aqueous metal halides of Group VIII are used for the isomerization of water-insoluble allylic compounds. With the aid of quaternary ammonium or phosphonium salts, the metal catalyst is extracted into the reagent-containing phase and returned to the aqueous layer by lipophilic anions upon completion of the catalytic process.

Alkyne hydration promoted by RhCl3 and quaternary ammonium salts

Abstract Ion pairs generated from RhCl 3 and quaternary ammonium salts were shown to promote the addition of water to carbon-carbon triple bonds. Terminal alkynes were found to form exclusively ketones. The reaction proved to take place in wet THF, as well as under phase transfer conditions. Under the latter conditions the rhodium catalyst could be recovered as NaRhCl 4 in the aqueous phase by addition of aqueous NaClO 4 . Kinetic studies with 1-octyne and phenylacetylene revealed that the rate of hydration depends on the concentrations of the alkyne, water, rhodium and quaternary ammonium salt. The observed activation energy values of 14.2 and 12.8 kcal mol −1 for the hydration of 1-octyne and phenylacetylene, respectively, indicate that these reactions are both chemically and diffusion controlled.

Catalytic hydrogenation of olefins, acetylenes and arenes by rhodium trichloride and aliquat-336 under phase transfer conditions

Abstract The ion pair formed from aqueous rhodium trichloride and aliquat-336 in dichloroethane catalyzes hydrogenation of a variety of unsaturated compounds. Aromatics are reduced to cyclohexane derivatives under exceedingly mild conditions.

Mutagenicity of phenanthrene and phenanthrene K-region derivatives.

Phenanthrene and 9 K-region derivatives, most of them potential metabolites of phenanthrene, were tested for mutagenicity by the reversion of histidine-dependent Salmonella typhimurium TA1535, TA1537, TA1538, TA98 and TA100 and the rec assay with Bacillus subtilis H17 and M45. The strongest mutagenic effects in the reversion assay were observed with phenanthrene 9,10-oxide, 9-hydroxyphenanthrene and N-benzyl-phenanthrene-9,10-imine. Interestingly, the mutagenic potency of the arene imine was similar to that of the corresponding arene oxide. This is the first report on the mutagenicity of arene imine. The mutagenic effects of all these phenanthrene derivatives were much weaker than that of the positive control benzo[a]pyrene 4,5-oxide. Even weaker mutagenicty was found with cis-9,10-dihydroxy-9,10-dihydrophenanthrene and with trans-9,10-dihydroxy-9-10-dihydrophenanthrene. The other derivatives were inactive in this test. However, 9-10-dihydroxyphenanthrene and 9,10-phenanthrenequinone were more toxic to the rec- B. subtilis M45 strain than to the rec+ H17 strain. This was also true for phenanthrene 9,10-oxide and 9-hydroxyphenanthrene, but not with the other test compounds that reverted (9,10-dihydroxy-9,10-dihydrophenanthrenes; N-benzyl-phenanthrene 9,10-imine; benzo[a]pyrene 4,5-oxide) or did not revert (phenanthrene, 9,10-bis-(p-chlorophenyl)-phenanthrene 9,10-oxide, 9-10-diacetoxyphenanthrene) the Salmonella tester strains. Although the K region is a main site of metabolism and although all potential K-region metabolites were mutagenic, phenanthrene did not show a mutagenic effect in the presence of mouse-liver microsomes and an NADPH-generating system under standard conditions. However, uhen epoxide hydratase was inhibited, phenanthrene was activated to a mutagen that reverted his- S. typhimurium. This shows that demonstration of the mutagenic activity of metabolites together with the knowledge that a major metabolic route proceeds via these metabolites dose not automatically imply a mutagenic hazard of the mother compound, because the metabolites in question may not accumulate in sufficient quantities and therefore the presence and relative activities of enzymes that control the mutagenically active metabolites are crucial. N-Benzyl-phenanthrene 9.10-imine was mutagenic for the episome-containing S. typhimurium TA98 and TA100 but not for the precursor strains TA1538 and TA1535. This arene imine would therefore be useful as a positive control during routine testing to monitor in the former strains the presence of the episome which is rather easily lost.

A Three‐Phase Emulsion/Solid‐Heterogenization Method for Transport and Catalysis

We describe a method for the heterogenization of (catalytic) reactions, which eliminates the need for organic solvents. The method relies on a novel multiphase transport concept, namely on the transport of hydrophobic substrates to an entrapped catalyst, and the transport of the resulting product from the catalyst-entrapping environment back into the bulk. The general idea is as follows: A catalyst is entrapped inside a hydrophobically modified porous sol-gel matrix; the hydrophobic substrate for that catalyst forms an emulsion in water in the presence of a suitable surfactant; and the powdered catalytic sol-gel material is dispersed in that emulsion. Upon contact of the surfactant with the hydrophobic interface of the sol-gel matrix, it reorients and spills the substrate into the pores of the matrix, where the catalyst is entrapped. The catalytic process takes place there, and the product is extracted out by the same transport vehicle, namely by the emulsifying surfactant; then the emulsion is broken, and the product separated. We term this whole process the EST (emulsion±solid transport) process, and have demonstrated it (following a detailed search for optimal conditions) with the [CH3(C8H17)3 N][RhCl4] catalyzed hydrogenation of chalcone and cisstilbene, in which the solid is a partially alkylated SiO2 sol-gel matrix within which the catalyst is entrapped, and where the emulsifying surfactant is cetyl(trimethylammonium) p-toluenesulfonate. Heterogenization of homogeneous catalytic procedures has been of central interest in the field of catalysis. Several heterogenization methods have been developed[1] which can be classified into the following categories: Covalent-bond immobilization of the catalyst on supports such as inorganic matrices,[2] organic-polymer solids,[3] organic±inorganic composites,[4] and recently also on dendrimers[5] and liquid±liquid biphasic systems[6] in which the catalyst is in one phase and the product is in the other. Recent examples of such systems are fluorinated biphasic catalytic systems[7] and ionic liquids.[8] Other methods include supported liquid-phase catalysis (SLPC), which is based on immobilizing the catalyst within a thin liquid film on a high surface area support[9] and physical immobilization of the catalysts within porous supports, which requires no covalent bonding and which retains the homogeneous catalyst in its native structure. Sol-gel catalysis has been COMMUNICATIONS

Dichlorobis(triphenylphosphine)nickel-catalyzed cross-coupling of aryl chlorides with intramolecularly stabilized group 13 metal alkylating reagents

Abstract The intramolecularly stabilized alkyl and aryl aluminum complexes 1 , 4 and 11 , as well as the indium compounds 6 , 9 and 10 cross-couple with a variety of chloroarenes at 80°C in the presence of NiCl 2 (PPh 3 ) 2 to give selectively the respective alkylated arenes in high yields. Addition of organic or inorganic bases lowers the reaction temperature to 50°C.

One-pot sequences of reactions with sol-gel entrapped opposing reagents. Oxidations and catalytic reductions

An oxidant and a reducing catalyst are placed in a single pot without destroying each other, but are still capable of carrying out useful reactions, simultaneously. The oxidant, pyridinium dichromate, and an H2-reduction catalyst, RhCl[P(C6H5)3]3, were entrapped in separate sol-gel matrices, and with these entrapped reagent and catalyst, three different flow-chart sequences of one-pot redox reactions were carried out—up to four reactions in one pot—without their mutual destruction and with no need for separation steps.

Sol–gel entrapped chiral rhodium and ruthenium complexes as recyclable catalysts for the hydrogenation of itaconic acid

Abstract Chiral Ru–BINAP, Rh–DIOP and Rh–BPPM complexes have been physically entrapped in sol–gel matrices. The resulting materials are recyclable leach-proof catalysts for enantioselective hydrogenation of itaconic acid. Chiral methylsuccinic acid of o.p. up to 78% is obtained. The complexes, including the water insoluble Ru–BINAP derivatives, react both in organic and in aqueous media.

Comparison between homogeneous and sol-gel-encapsulated rhodium-quaternary ammonium ion pair catalysts

The ion pairs RhCl3/Aliquat 336® and RhCl3/[Me3N(CH2)3Si(OMe)3]Cl were entrapped in SiO2 sol-gel matrices, and used as catalysts for isomerization of allybenzene, disproportionation of 1,3-cyclohexadiene, hydrogenation of alkenes, alkynes, arenes, nitriles and nitro-compounds, and for hydroformylation of CC double bonds. The immobilized ion pairs proved to be stable, leach-proof and recyclable. Occasionally the catalytic efficiency dropped upon recycling, owing to pore blockage but the activity could be restored by treatment with boiling water. The performances of the sol-gel-entrapped ion pairs were compared with those of the homogeneous RhCl3/Aliquat 336 catalyst. In most cases the immobilized catalysts proved superior to their homogeneous version.