Maria Luiza Ambros von Holleben

A selective reduction of α,β-unsaturated ketones

Abstract A selective hydrogenation of carbon-carbon double bond of α,β-unsaturated ketones are obtained when a mixture of limonene, α,β-unsaturated ketone and 10% Pd/C is refluxed with vigorous stirring for 15–45 min. The best results are obtained when a molar ratio limonene:α,β-unsaturated ketone of 3:1 and 4 molar % palladium/ketone are used. The stereoselectivity is similar to the results obtained when H 2 and Pd/C have been used in neutral solvent.

Experimental and theoretical study on the reactivity of the R-CN/H2O2 system in the epoxidation of unfunctionalized olefins

A reatividade da acetonitrila, tricloroacetonitrila, benzonitrila, m-clorobenzonitrila, 3-cianopiridina, 1-naftonitrila e 9-antracenonitrila na geracao in situ do respectivo acido peroxicarboximidico foi estudada por calculos de OM, utilizando o metodo AM1, e experimentalmente na epoxidacao do cicloexeno e R-(+)-limoneno. Os resultados experimentais mostraram que a reatividade do sistema Cl3CCN/H2O2 foi semelhante ao MCPBA na epoxidacao de olefinas nao-funcionalizadas, quando o solvente utilizado foi uma mistura bifasica CH2Cl2/H2O.

Very efficient epoxidation of 1,4-polybutadiene with the biphasic system methyltrioxorhenium (MTO)-CH2Cl2/H2O2

The biphasic system methyltrioxorhenium (MTO)-H2O2/CH2Cl2 was studied in the epoxidation of polybutadiene and the results showed that this system presents a high selectivity and the extension of epoxidation (10–50%) can be modulated by the amount of oxidant added, without significant change in the molecular weight of the polymer.

Ativação do peróxido de hidrogênio para a epoxidação de olefinas não-funcionalizadas

A general overview about the more useful activating agents of the hydrogen peroxide in the epoxidation of unfunctionalized alkenes, focusing mechanistic proposals. Moreover, reactivity and stereochemistry, including the stereogenic effect of the hydroxyl group is presented.

Hydrogenation of styrene-butadiene rubber by hydrogen transfer from limonene

The heterogeneous catalytic transfer hydrogenation of styrenebutadiene rubber (SBR) by the use of limonene as hydrogen source and as solvent in the presence of Pd/C as catalyst has been studied. The influence of the heating time on the reduction and on the structure of the donor was studied. Partial hydrogenations of the olefinic bonds of SBR are obtained when a mixture of limonene, SBR and 10% Pd/C is refluxed with vigorous stirring for 50–200 minutes.

Methods of cyclization of some δ-diketones

Abstract Three methods of cyclizing δ-diketones where the β- and γ-carbons form part of a ring system were studied: 1) strong base in protic media; 2) strong aqueous acid biphasic with apolar solvent; 3) alumina with saturated hydrocarbons. General limits were established for each method and a system validated for preparative scale cyclization without isomerization of an external double bond.

Métodos para a hidrogenação de ligações olefínicas em polímeros

The broad variety of hydrogenation methods of polydienes is presented. Homogeneous and heterogeneous catalysis are reviewed emphasizing also hydrogen transfer from donor compounds.