J.C. Kuriacose

Cadmium sulfide with iridium sulfide and platinum sulfide deposits as a photocatalyst for the decomposition of aqueous sulfide

Abstract The in situ deposition of Pt and Ir on CdS during the photocatalytic decomposition of aqueous sulfide results in the formation of an effective bifunctional photocatalyst (MS/CdS/M, where MS is Pt or Ir sulfide and M is Pt or Ir) which is more active than CdS and metallized CdS. In situ metallization provides a convenient method for the preparation of metal- and metal-sulfide-deposited CdS. The order of reactivity for the in situ metallization of CdS in the case of the photocatalytic decomposition of aqueous sulfide is Rh > Pt > Ru = Ir > Co ≃ Ni ≃ Fe. Based on the observed results a mechanism for the photocatalytic decomposition of aqueous sulfide is proposed.

Ruthenium(III)-catalysed oxidation of secondary alcohols by N-methylmorpholine N-oxide (NMO)

Abstract A catalytic amount of RuCl3 in the presence of excess of N-methyl-morpholine N-oxide (NMO) in DMF oxidizes secondary alcohols to ketones. Spectral studies reveal the formation of a Ru(V)-oxo species which is formed in situ on adding N-oxide. The formation of Ru(V) has been established by cyclic voltammetric studies. The mechanism involves the formation of Ru(V)-oxo species in steady state concentrations from Ru(III) and NMO, and this in turn reacts with the substrate in the rate-determining step.

Reactions of the carbonate radical with aliphatic amines

Abstract Carbonate radicals react with aliphatic amines by a dual mechanism, viz. (i) hydrogen abstraction and (ii) electron transfer. The former is more probable with primary amines. Tertiary amines react via electron transfer. Both mechanisms may operate in secondary amines. Cyclic tertiary amines react with different rates and their relative reactivities are explained on the basis of the concept of Hoffmanns ‘through bond’ interaction.

Hydrogenation and transfer hydrogenation of d-fructose catalyzed by dichlorotris (triphenylphosphine) ruthenium (II)

Abstract d -Fructose is hydrogenated to d -glucitol and d -mannitol using RuCl 2 (PPh 3 ) 3 as catalyst at 100°C and atmospheric pressure. Besides hydrogenation, fructose undergoes transfer hydrogenation when propan-2-ol and butan-2-ol are used as solvents. Under an inert atmosphere (nitrogen), only transfer hydrogenation of fructose is observed in these alcohols. The rate of hydrogenation is comparable with transfer hydrogenation under similar reaction conditions. Cyclohexanol, benzyl alcohol, 1-phenylethanol and benzhydrol are also found to be good hydrogen donors for fructose reduction. Both hydrogenation and transfer hydrogenation yield glucitol and mannitol whose ratio is always 1:1. The catalyst is deactivated when hydrogen donors such as 2-methoxyethanol and tetrahydrofurfuryl alcohol are employed. The deactivation is attributed to the formation of an inactive ruthenium carbonyl complex, viz ., RuHCl (CO) (PPh 3 ) 3 . The hydrogen donating ability of these alcohols and their oxidation potentials are compared and the relative degrees of correlation are rationalized.

RuCl2(PPh3)3-catalyzed transfer hydrogenation of d-glucose

Glucose is transfer hydrogenated by propan-2-ol, butan-2-ol, cyclohexanol, benzyl alcohol, 1-phenylethanol, benzhydrol, 2-methoxyethanol and tetrahydrofurfuryl alcohol in the presence of RuCl2(PPh3)3 at 100 °C and atmospheric pressure. Mixed solvent systems such as dimethylacetamide-water and dioxane-water are utilized for this reaction. The major product from glucose is sorbitol, although glucono-1,5-lactone is invariably formed as a side product from a disproportionation reaction. When 2-methoxyethanol and tetrahydrofurfuryl alcohol are used as hydrogen donors, the catalyst undergoes permanent change to a hydridocarbonyl complex, which catalyzes only disproportionation of glucose. Glucose also acts as a good hydrogen donor when hydrogen acceptors such as cyclohexanone are introduced into the reaction system.

Reduction of nitrobenzene by dodecacarbonyl tri-iron under triphase conditions

Abstract Reduction of nitrobenzene to aniline by Fe3(CO)12 under triphase conditions has been investigated and the efficiency of the polymer-supported phase transfer agents compared. Reduction occurs under mild conditions and the isolation of the product is easier than in the homogeneous system. The yield of aniline is similar to that obtained in the Fe3(CO)12/Al2O3 system.

Reaction of the carbonate radical with substituted anilines

Rate constants for the reaction of carbonate radical with aniline and some parasubstituted anilines have been determined by the flash photolysis technique. Using σ+ para values the rate constants at pH 8.5 correlate very well with the Hammett equation yielding ρ= − 1. The carbonate radical oxidises aniline giving the anilino radical. The products so formed have been identified through studies under conditions of continuous irradiation.

Spectral evidence for the formation of active intermediates from RuCl3 and RuCl2(PPh3)3 with N-methylmorpholine N-oxide (NMO) and phenyliodosoacetate (PIA) as mild oxidants

Abstract Electronic, EPR and IR spectral evidence are given for the formation of the following active species: (1) ruthenium(VIII) in ruthenium(III)-PIA system, (2) ruthenium(V) oxo species in ruthenium(III)- N - oxide system, and (3) ruthenium(II)-phosphine oxide complex in ruthenium(II) N -oxide system. Cyclic voltammetric studies also suggest the formation of Ru(V) in ruthenium(III)- N -oxide system.

Kinetics and mechanism of RuCl2PPh3)3-catalyzed oxidation of sulfides by N-methylmorpholine N-oxide

Abstract Oxidation of dibutylsulfide, diphenylsulfide, methylphenylsulfide and dibenzylsulfide to the corresponding sulfoxides by N-methylmorpholine N-oxide (NMO) catalyzed by RuCl2(PPh3)3 in DMF solvent is reported. The reaction is first order in both catalyst and N-oxide. The order with respect to the substrate is variable, being zero at higher concentrations and fractional at lower concentrations. The order of reactivity observed for the substrates is as follows: dibutylsulfide ≈ dibenzylsulfide > methylphenylsulfide > diphenylsulfide. RuCl2(PPh3)3 oxidizes olefins to form epoxides at a slower rate. The order of reactivity observed for the two types of substrates parallels their nucleophilicity (sulfides > alkenes). Spectral studies indicate 1:1 complex formation between RuCl2(PPh3)3 and the sulfides. The active oxidant is the Ru(IV)oxo complex formed by the oxidation of Ru(II) by NMO.

Reaction of the phosphate radical with amines — A flash photolysis study

Rate constants for the reaction of phosphate radical with some aromatic and aliphatic amines have been determined by the flash photolysis technique. The products formed under conditions of continuous irradiation have been identified. In the case of an aromatic amine the major product is the azo compound while in the case of an aliphatic amine a carbonyl compound is formed.