Synthesis and oxidation of thioglicosides underlain by neomenthanethiol,D-glucose,and D-fructose

Synthesis of sulfides proceeding from neomenthanethiol, 1,2-O-isopropylidene-α-D-glucofuranose and 2,3:4,5-di-O-isopropylidene-β-D-fructopyranose was performed to get 65 and 54% yield respectively. Oxidation of the sulfides afforded diastereomeric sulfoxides in the yields from 40 to 53%, and diastereomeric excess (de) up to 36%. After removing the isopropylidene protection from 1-deoxy-1-[(1S,2S,5R)-2-isopropyl-5-methylcyclohexylsulfanyl]-2,3:4,5-di-O-isopropylidene-β-D-fructopyranose a water-soluble sulfide was obtained.     

Kinetics and mechanism of the oxidation of some diols by benzyltrimethylammoniumtribromide

The kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers by benzyltrimethylammonium tribromide (BTMAB) have been studied in 3:7 (v/v) acetic acid-water mixture. The vicinal diols yield the carbonyl compounds arising out of the glycol bond fission while the other diols give the hydroxycarbonyl compounds. The reaction is first-order with respect to BTMAB. Michaelis-Menten type kinetics is observed with respect to diol. Addition of benzyltrimethylammonium chloride does not affect the rate. Tribromide ion is postulated to be the reactive oxidizing species. Oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of a kinetic isotope effect. The reaction exhibits substantial solvent isotope effect. A mechanism involving a glycol-bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidized by a hydride ion transfer to the oxidant, as are the monohydric alcohols.     

Evidence of esterification during the oxidation of some aromatic aldehydes by permanganate

Summary The permanganate ion oxidation of PhCHO in HClO₄ medium is first order in [MnO _inf4 ^sup- ], but of complex order with respect to [aldehyde] as well as [H⁺]. The influence of substituents on the reaction rate and mechanism has also been studied in 40% (v/v) aqueous AcOH and convincing evidence favours an ester formation mechanism. Thermodynamic values associated with 11 intermediate ester formation and the activation parameters associated with the disproportionation steps involved have been evaluated.     

Effect of substituents on the oxidation of some alkyl-aryl sulphoxides by chloramine-T

The oxidation rates of some substituted phenyl methyl sulphoxides with chloramine-T have been studied in alkaline and neutral media. OsO₄ is used as catalyst in alkaline medium where the meta and para substituents show no effect on the reaction rate. This is explained on the basis of isokinetic relationship. In both the media, the orthosubstituents show steric effect.     

Kinetics and mechanism of the oxidation of some thioacids by benzyltrimethylammonium dichloroiodate

The oxidation of thioglycolic, thiolactic, and thiomalic acids by benzyltrimethylammonium dichloroiodate (BTMAIC) to the corresponding disulfide dimer, is first-order with respect to each the thioacid and BTMAIC. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The reaction failed to induce polymerization of acrylonitrile. The reaction rate increases with the increase in the concentration of zinc chloride. Addition of benzyltrimethylammonium chloride enhances the reaction rate. Suitable mechanism has been proposed. © 1996 John Wiley & Sons, Inc.     

Laser-driven oxidation of some haloolefins

CW CO₂ laser-photosensitized (SF₆) oxidation of hexafluoropropene, chlorotrifluoroethene, l,l-dichlorodifluoroethene, 1,2-dichlorodifluoroethene and hexafluoro-1,3-butadiene with molecular oxygen at total pressure 13-26.5 kPa leads with all but the last to the formation of carbonyl halides. The distribution of these products suggests that the oxidation occurs via a cleavage of intermediary dioxetanes. The reactivities of the olefins towards oxygen at mean effective temperature 710 K are nearly equal.     

Titrimetric determination of some organic acids by xenon trioxide oxidation

Aqueous xenon trioxide in acidic or neutral solutions oxidises carboxylic acids quantitatively to carbon dioxide and water. Micro and semimicro amounts of carboxylic acids may be determined by the iodometric titration of the excess of xenon trioxide remaining in the reaction mixture. The optimum time and temperature for the reaction depend on the structure of the acid ; dicarboxylic and hydroxy-carboxylic acids react faster than corresponding monocarboxylic acids. Oxalic and polyhydroxy acids are oxidised within 20 min at room temperature while acetic, maleic, succinic, malonic acids require 2 hr at 40 degrees . Carboxylic acids in amounts less than 100 mug are determined with a coefficient of variation of 4%, which decreases to 1 % for amounts over 250 mug.     

Kinetics and mechanism of the oxidation of some organic sulfides by morpholinium chlorochromate

The oxidation of organic sulfides by morpholinium chlorochromate (MCC) resulted in the formation of the corresponding sulfoxides. The reaction is first order with respect to both MCC and the sulfide. The reaction is catalyzed by toluene‐p‐sulfonic acid (TsOH). The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain's equation showed that both the cation‐ and anion‐solvating powers of the solvents play important roles. The correlation analyses of the rate of oxidation of 34 sulfides were performed in terms of various single and multiparametric equations. For the aryl methyl sulfides, the best correlation is obtained with Charton's localized‐delocalized‐resonance and localized‐delocalized‐resonance‐steric equations. The oxidation of alkyl phenyl sulfides exhibited a very good correlation in terms of the Pavelich–Taft equation. The polar reaction constants are negative, indicating an electron‐deficient sulfur center in the rate‐determining step. A mechanism involving formation of a sulfonium cation intermediate in the slow step has been proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 65–72, 2009     

Kinetics and mechanism of oxidation of some alcohols by osmium tetroxide

Spectrophotometric studies of the kinetics of oxidation of 2-methylpropan-1-ol and 2-butanol by an alkaline solution of osmium tetroxide have been reported. A first-order dependence to osmium tetroxide was observed. A first-order dependence to both 2-methylpropan-1-ol and alkali at low concentration tends to zero order at higher concentrations. In the case of 2-butanol, first-order kinetics is exhibited with respect to 2-butanol but first-order kinetics observed at lower concentrations of alkali decrease at higher concentrations. A negligible ionic strength effect of the medium was observed. Activation parameters have been computed. A suitable mechanism in conformity with our kinetic observations has been suggested.     

Kinetic study of the oxidation of some catecholamines by digital simulation of cyclic voltammograms

Electrochemical oxidation of some catecholamines such as dopamine ( 1 ), L ‐dopa ( 2 ), and methyldopa ( 3 ) has been studied in various pH values, using cyclic voltammetry. The results indicate participation of catecholamines ( 1–3 ) in intramolecular cyclization reaction to form the corresponding o‐quinone derivatives ( 1d–3d ). In various pHs, based on ECE mechanism, the observed homogeneous rate constants (k_obs) of cyclization reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital‐simulated results. Also, the cyclization rate constants (k_cyc) were calculated using microscopic acidic dissociation constant of ammonium groups. The significant differences in electrochemical behavior, k_obs and k_cyc, of L ‐dopa ( 2 ) and methyldopa ( 3 ) with dopamine ( 1 ) are due to the effects of the side chain carboxyl group. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 17–24, 2005     

Chemical oscillators based on the oxidation of Mn(II) by some halogens

Chemical oscillators based on the oxidation of Mn(II) ions by bromine or chlorine in NaH₂PO₄–NaOH buffer solutions in a CSTR (continuous-flow stirred tank reactor) are described. The oscillations correspond to the two alternating processes. The first process is the oxidation of Mn(II) by HOBr or HOCl to Mn(IV) and the second one is of a micro-heterogeneous nature, consisting of the reduction of Mn _c ⁴⁺ and Mn _c ³⁺ centers on the surface of colloids (MnO₂)_col by halides.     

Kinetics and mechanism of oxidation of some aryl alcohols by acid bromate

The kinetics of oxidation of some substituted benzyl alcohols as well as the unsubstituted one by bromate ion in hydrochloric acid medium has been suggested. The results indicate that the reaction takes place by way of intermediate ester formation. Methoxy compounds react at much faster rates than the corresponding nitro substituted derivatives. The thermodynamic values associated with the equilibrium step and also for the slow step have been evaluated. A mechanism consistent with the experimental observations has been suggested.     

Evidence of protonation during the oxidation of some aryl alcohols by permanganate in perchloric acid medium and mechanism of the oxidation processes

The oxidation of benzyl alcohol and methoxy-, chloro-, and nitro- substituted benzyl alcohols by permanganate has been studied in aqueous and acetic acid medium in presence of perchloric acid. The reaction is first-order in [MnO₄^?] and [XC₆H₄CH₂OH], but the order is complex with respect to [H⁺]. Different thermodynamic parameters have been evaluated. The reaction occurs through the protonation of alcohol in a fast preequilibrium followed by a slow rate-determining oxidation step. A two-electron transfer oxidation step has been suggested for benzyl alcohol and chloro- and nitro- substituted alcohols, while the oxidation of methoxy compounds involves a one-electron transfer via a free-radical mechanism. © 1995 John Wiley & Sons, Inc.     

Mechanism of oxidation of some aliphatic ketones by N-bromosuccinimide in acidic media

Kinetics of the oxidation of methyl n-propyl ketone and methyl isobutyl ketone by N-bromosuccinimide (NBS) have been studied in perchloric acid media in presence of mercuric acetate. A zero order dependence to N-bromosuccinimide and a first order dependence to both ketones and hydrogen ion concentrations have been observed. Sodium perchlorate, mercuric acetate and succinimide additions have negligible effect while methanol addition has a positive effect on the reaction rate. A solvent isotope effect (k₀D₂O/K₀H₂O = 2.3-2.7 and 2.4-2.8 for MeCOn.pr and MeCoi-Bu, respectively) has been observed at 35°. Kinetic investigations have revealed that the order of reactivity is methyl n-propyl ketone > methyl isobutyl ketone. Various thermodynamic parameters have been computed and corresponding 1,2-diketones were found to be the products. A suitable mechanism in conformity with the above observations has been proposed.     

Kinetics and mechanism of oxidation of some aliphatic esters by sodium N-bromo-p-toluenesulfonamide

The kinetics of oxidation of methyl, ethyl, n-propyl, isopropyl, and n-butyl acetates to acetic acid and the corresponding aldehyde by the title oxidant in aqueous HCl medium at 40°C has been studied. The reaction shows first-order with respect to [oxidant] and fractional orders in [H⁺] and [ester]. An isokinetic relationship was observed with β = 374 K indicating enthalpy as the rate controlling factor. Attempts have been made to arrive at a linear free energy relationship through the Taft treatment. Electron releasing groups in the ester moiety increase the rate with ρ* = ?9.88. A two-pathway mechanism, consistent with the observed kinetic data, has been proposed. © 1993 John Wiley & Sons, Inc.     

Kinetic determination of some inorganic and organic compounds by oxidation with iodate

Sulphite (5.0 × 10^?1?5.0 × 10^?3 M), ascorbic acid and other compounds are oxidized by potassium iodate in dilute sulphuric acid; the production of iodide is monitored by an iodide-selective electrode. The time needed for a 40-mV potential change is inversely proportional to concentration. For sulphite (1.0 × 10^?5?1.0 × 10^?4 M), selectivity is improved by sweeping the sulphur dioxide formed in acidic EDTA-containing solution into the iodate solution.     

Photo-induced oxidation of some organic carbonyl compounds by vanadium(V)

The oxidation of pyruvic acid, levulinic acid, acetaldehyde, isobutyraldehyde and acetylacetone by vanadium(V) in aqueous solution on illumination with visible light is described. Pyruvic acid undergoes oxidation much more rapidly than does levulinic acid ; both give acetic acid. Acetaldehyde is more rapidly oxidized than is isobutyraldehyde, the former giving formic acid, and the latter, formic acid and acetone. Acetylacetone is converted into acetic acid. The oxidations are rapid and quantitative and may be used for the estimation of these carbonyl compounds.     

Kinetics and mechanism of the oxidation of some vicinal and non-vicinal diols by tetrabutylammonium tribromide

Kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers, by tetrabutylammonium tribromide (TBATB) has been studied. The vicinal diols yield products arising out of glycol-bond fission, while the non-vicinal diols produce the hydroxycarbonyl compounds. The reaction is first-order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to diols. The reaction fails to induce the polymerization of acrylonitrile. There is no effect of tetrabutylammonium chloride on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of any primary kinetic isotope effect. Values of solvent isotope effect, k(H₂O)/k(D₂O), at 288 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutan-1-ol are 3.41, 0.98 and 1.02 respectively. A mechanism involving a glycol-bond fission has been proposed for the oxidation of vicinal diols. Non-vicinal diols are oxidised by a hydride-transfer mechanism, as they are monohydric alcohols.     

Kinetics and mechanism of the oxidation of some aliphatic ketones by n-bromoacetamide in acidic media

Kinetics of the oxidation of methyl ethyl ketone (MEK) and diethyl ketone (DEK) by N-bromoacetamide (NBA) have been studied in perchloric acid media in the presence of mercuric acetate. A zero order dependence to NBA and a first-order dependence to both ketones and H⁺ have been observed. Acetamide, mercuric acetate and sodium perchlorate additions have negligible effect while addition of acetic acid has a positive effect on the reaction rate. A solvent isotope effect (K₀D₂O/k₀H₂O = 2.–.4 and 2.2-2.5 for MEK and DEK, respectively) has been observed at 40°. Kinetic investigations have revealed that the order of reactivity is MEK > DEK. The rates were determined at four different temperatures and the activation parameters were evaluated. The main product of the oxidation is the corresponding 1,2-diketone. A suitable mechanism consistent with the above observations has been proposed.