Catalytic cross coupling reactions

Transistion metal catalyzed cross coupling reactions are among the most versatile methods for establishing new carbon-carbon bonds. Nevertheless, (Csp3-Csp2) coupling features several synthetic problems i.e. the correct choice of the nature of electrophile and nucleophile or the appearance of homocoupling products. In this work Kumada type cross coupling reactions of alkyl Grignard reagents with different types of aromatic electrophiles were investigated. Transition metal compounds of the general formula {MCl2[Ph2P(CH2)1-3PPh2]} (M = Pd, Ni, Fe) are versatile precatalysts for the coupling of cyclohexyl Grignard reagents with either fluorinated bromobenzene or bromothiophene derivatives, catalytic activity of the precatalysts depends on the diphosphane ligands and increases in the order dppm < dppe < dppp, if cyclohexyl Grignard solutions without any additives are used, the catalytic activity of the precatalysts depends on the transition metal and increases in the order Fe < Ni < Pd. The addition of lithium salts to the Grignard solutions leads to an enhancement of activity for all precatalysts. The effect is most pronounced for iron precatalysts which upon addition of LiBr show an activity that is well comparable to that of palladium complexes under the same reaction conditions

Micellar and Polymer Catalysis in the Kinetics of Oxidation of L-lysine by Permanganate Ion in Perchloric Acid Medium

Kinetics of oxidation of L-lysine by permanganate ion in a perchloric acid medium was investigated to explore the order of the reaction with respect to&nbsp; oxidant and substrate and to study the catalytic behaviour of sodium lauryl sulphate (SLS) and polyethylene glycol (PEG). The reaction was found to be&nbsp; first-order with respect to the oxidant and the substrate and zero-order with respect to hydrogen ion. Changes in the sodium sulphate concentration&nbsp; produce a non-significant variation in the rate of the reaction. SLS and PEG were found to catalyze the reaction. Surfactant catalysis was modelled by&nbsp; Piszkiewicz’s cooperativity model, while polymer catalysis was explained with the help of the Benesi-Hildebrand equation. The temperature dependence&nbsp; of the rate of the reaction was elucidated, and activation parameters were obtained. Interestingly, the reaction was found to possess positive activation&nbsp; entropy indicating the dissociative nature of the transition state and outer-sphere electron transfer mechanism. A mechanism of the reaction that is&nbsp; supported by the experimental findings was suggested.&nbsp

The Catalytic Influence of Polymers and Surfactants on the Rate Constants of Reaction of Maltose with Cerium (IV) in Acidic Aqueous Medium

Kinetics of the reaction of maltose with cerium ammonium sulfate were analyzed spectrophotometrically by observing the decrease of the absorbance of cerium (IV) at 385 nm in the presence and absence of polyethylene glycols (600, 1500, and 4000) and polyvinylpyrrolidone (PVP), in addition to anionic micelles of sodium dodecyl sulfate (SDS), cationic micelles of cetyltrimethylammonium bromide (CTAB) and non-ionic micelles of Tween 20 surfactants. Generally, there is little literature about using the polymers (PEGs and PVP) as catalysts in the oxidation-reduction reactions. Therefore, the major target of this work was to investigate the influence of the nature of polymers and surfactants on the oxidation rates of maltose by cerium (IV) in acidic aqueous media, as well as employing the Piszkiewicz model to explain the catalytic effect. The kinetic runs were derived by adaptation of the pseudo first-order reaction conditions with respect to the cerium (IV). The reaction was found to be first-order with respect to the oxidant and fractional-order to maltose and H2SO4. The reaction rates were enhanced in the presence of polymer and micellar catalysis. Indeed, the surfactants were found to work perfectly close to their critical micelle concentrations (CMC). Electrostatic interaction and H-bonding appear to play an influential role in binding maltose molecules to polymer/surfactant micelles, while oxidant ions remain at the periphery of the Stern layer within the micelle