Gadde Ramachandraiah

Environmentally benign chlorination and bromination of aromatic amines, hydrocarbons and naphthols

A simple and efficient procedure for chlorination and bromination of aromatic amines, hydrocarbons and naphthols by the action of aqueous hydrohalic acid and hydrogen peroxide is described. This environmentally clean and safe procedure involves in situ generation of the active halogen and its uncatalyzed reaction with the substrates in this study.

An alternative method for the regio- and stereoselective bromination of alkenes, alkynes, toluene derivatives and ketones using a bromide/bromate couple

Mixtures of NaBr and NaBrO3 in two different ratios have been used for highly stereoselective bromination of alkenes and alkynes, and regioselective bromine substitution at the α-carbon of ketones and at the benzylic position of toluene derivatives. The reactions were conducted in an aqueous acidic medium under ambient conditions. The solid reagents were prepared from the intermediate obtained in the “cold process” of bromine manufacture and are stable, non-hazardous and inexpensive to prepare. This procedure provides an efficient and practical alternative to conventional procedures using liquid bromine directly or indirectly.

Eco-friendly and versatile brominating reagent prepared from a liquid bromine precursor

Facile bromination of various organic substrates has been demonstrated with a 2 : 1 bromide:bromate reagent prepared from the alkaline intermediate of the conventional bromine recovery process. The reagent is acidified in situ to generate HOBr as the reactive species, which effects bromination. Aromatic substrates that have been successfully brominated under ambient conditions without use of any catalyst include phenols, anilines, aromatic ethers and even benzene. Non-aromatic compounds bearing active methylene group were monobrominated selectively with the present reagent and olefinic compounds were converted into the corresponding bromohydrins in moderate yields. By obtaining the present reagent from the liquid bromine precursor, the twin advantages of avoiding liquid bromine and producing the reagent in a cost-effective manner are realised. When coupled with the additional advantage of high bromine atom efficiency, the present protocol becomes attractive all the way from “cradle to grave”.

Synthesis and characterization of some ruthenium(V) oxo complexes of the Schiff base, bis(salicylaldehyde)-o-phenylenediamine, with appended Cl−, imidazole and 2-methylimidazole: the first examples of stable oxo complexes via direct oxygenation

Abstract Oxygenation of ruthenium(III) Schiff base complexes of the composition K[Ru III (Saloph)Cl 2 ] and [Ru III (Saloph)XCl] (Saloph=bis(salicylaldehyde)- o - phenylenediamine; X=imidazole (Im), 2-methylimidazole (2-MeIm)) with molecular oxygen gives the oxo derivatives of the composition, [Ru V (Saloph)X- (O)] + (X=Cl, Im or 2-MeIm). The oxo complexes were also synthesized by the reaction of [Ru III - (Saloph)XCl] with PhIO or H 2 O 2 . The complexes thus obtained were characterized by analytical data, molar conductance, magnetic susceptibility, spectroscopic and electrochemical methods. Kinetics of the oxygenation reaction have also been investigated.

A new, environment friendly protocol for iodination of electron-rich aromatic compounds

A new environment friendly procedure for effective aromatic iodination is presented. A mixture of potassium iodide and potassium iodate is used in the presence of an acid for in situ iodination of aromatic compounds.

Electrolytic synthesis of succinic acid in a flow reactor with solid polymer electrolyte membrane

This paper describes the galvanostatic synthesis of succinic acid from maleic acid in an ion exchange membrane flow cell. The electrolysis was carried out at stainless steel, lead and copper cathodes under variable conditions of current density and substrate concentration. Depending upon the experimental conditions, the yield of succinic acid varied from 95 and 99% with a coulombic efficiency of 80–99%. The product was characterized by various physicochemical techniques, viz. 1H-NMR, IR and UV–Visible spectroscopy and elemental analysis. The operational conditions giving maximum yield of product were identified. The mechanism of electrochemical reduction of maleic acid and advantages of using a catholyte without supporting electrolyte are discussed.

Mononuclear bis(dimethylglyoximato)ruthenium(III) complexes with different appended axial groups: highly efficient catalysts for water oxidation

Abstract Mononuclear ruthenium( III ) complexes [Ru(H-dmg) 2 XY] n ( n = −1, when X = Y = Cl − or ClO 4 − n = 0 when X = Cl − and Y = imidazole or 2-methylimidazole) were used as catalysts in water oxidation to molecular oxygen by electrolytic and chemical methods. The evolved oxygen in both methods was measured at atmospheric pressure (30 °C) using a specially-designed gas volumetric apparatus. The maximum turnover number of the above complexes (mol O 2 evolved per mole complex per hour) are reported.

Complexes of Ru(III) with aminopolycarboxylic acids and their interaction with molecular oxygen to form Ru(IV)-μ-peroxo complexes

The interaction of Ru(III) with IMDA, HEDTA, EDTA, PDTA, CDTA and DTPA was studied by potentiometric and spectrophotometric methods at 25°C and 0.10 M ionic strength. Experiments were carried out under nitrogen and oxygen atmospheres. Evidence for the formation of dioxygen complexes in these systems is presented. Stability constants for the different species existing in each of the systems were calculated using a computer programme. Ru(III) forms very strong complexes with aminopolycarboxylic acids, which then interact with molecular oxygen to form a series of μ-peroxo and μ-hydroxo-μ-peroxo complexes.

Dioxygen affinities of some ruthenium(III) schiff base complexes

Abstract The synthesis and dioxygen affinities of some ruthenium(III) Schiff base complexes in DMF solution in the presence of different axial bases are reported. The ligands used are bis(salicylaldehyde)ethylenediimine (salen), bis(salicylaldehyde)diethylenetriimine (saldien), bis(picolinaldehyde)- o -phenylenediimine (picoph), bis(picolinaidehyde)ethylenediimine (picen) and bis(picolinaldehyde)diethylenetriimine (picdien). The axial ligands employed are chloride (Cl − ), imidazole (Im) and 2-methylimidazole (2-MeIm). From the oxygenation constants it is found that electron donating substituents on the Schiff bases increase the affinity for dioxygen. Equilibrium dioxygen uptake measurements at 278, 288 and 303 K provide values of Δ H ° and Δ S ° of oxygenation that fall in the range − 6.1 to −13.3 kcal mol − 1 for Δ H ° and − 10 to − 31 cal deg − 1 mol − 1 for Δ S °. The dioxygen adducts of Ru III were characterized by electrochemistry, UV–vis, IR and EPR techniques as Ru IV superoxo complexes.

Formation of a rhodium(II) monohydrido complex derived from wilkinson's complex RhCl(PPh3)3 in the interlamellar spaces of montmorillonite and catalytic hydrogenation of cyclohexene

Abstract The interaction of molecular hydrogen with [Rh(PPh 3 ) 3 ] + ( 1a ) “immobilized” in the interlamellar spaces of montmorillonite resulted in the formation of a monohydrido complex, [Rh II H(PPh 3 ) 3 ] ( 2a ), characterized by electrochemical data of the clay-loaded electrode, IR, EPR and hydrogen absorption studies. Heterogenized homogeneous catalytic hydrogenation of cyclohexene catalysed by 1a was investigated in the temperature range 283–313 K. The order of reaction with respect to cyclohexene and hydrogen concentration is fractional and first order with respect to catalyst concentration. Thermodynamic parameters Δ H 0 and Δ S 0 corresponding to the formation of the monohydrido species were found to be 18 kcal mol −1 and 61 e.u., respectively. The activation enthalpy, Δ H ‡ , and entropy, Δ S ‡ , for the hydrogenation of cyclohexene by the Rh II —H complex in clay are more negative by about 2 kcal mol −1 and 7 e.u. compared to Wilkinsons catalyst, RhCl(PPh 3 ) 3 ( 1 ), in homogeneous solution.