Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

Summary.  The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism. Received December 30, 1999. Accepted (revised) March 6, 2000     

Kinetics of the Oxidative Degradation of rac-Serine by Aqueous Alkaline Permanganate

Summary.  The kinetics of the oxidation of rac-serine by permanganate in aqueous alkaline medium was studied spectrophotometrically. The reaction showed first order kinetics in permanganate ion concentration and an order less than unity in rac-serine and alkali concentration. Increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation reaction proceeds via an alkali-permanganate species which forms a complex with rac-serine. The latter decomposes slowly, followed by a fast reaction between a free radical of rac-serine and another molecule of permanganate to give the products. There is a good agreement between the observed and the calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism. Received October 15, 1999. Accepted (revised) December 15, 1999     

Kinetics and Mechanism of Permanganate Oxidations of Isosorbide in Different Acidic Media

The oxidation kinetics of isosorbide (S) by potassium permanganate in both perchloric and sulfuric acid solutions was investigated spectrophotometrically at a constant ionic strength of 2.0 mol·dm^?3 and at 25 °C. In both acids, the oxidation reactions showed a first-order dependence on \([{\text{MnO}}_{4}^{ - }]\), apparent a less than unit-order dependence with respect to [S] and a fractional-second-order dependence with respect to [H⁺]. Variation of either the ionic strength or dielectric constant of the reactions media did not significantly affect the oxidation rates. In both acids, the final oxidation product of isosorbide was identified by both spectroscopic and chemical tools as the corresponding monoketone derivative, namely (1S,4S,5R)-4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. Under comparable experimental conditions, the oxidation rate of isosorbide in perchloric acid was lower than that in sulfuric acid. The oxidation mechanism describing the kinetic results was proposed and the rate law expression was derived. The activation parameters of the second-order rate constants were computed and are discussed.     

Electrochemical,Chemical and Enzymatic Oxidations of Phenothiazines

The oxidation of several phenothiazine drugs (phenothiazine, promethazine hydrochloride, promazine hydrochloride, trimeprazine hydrochloride and ethopropazine hydrochloride) has been carried out in aqueous acidic media by electrochemical, chemical and enzymatic methods. The chemical oxidation was performed in acetic acid with hydrogen peroxide or in formate buffers using persulfate. The enzymatic oxidation was performed in acetate or ammonium formate buffer by the enzyme horseradish peroxidase in the presence of H₂O₂. Molecules with, in the lateral chain, two carbon atoms (2C) separating the ring nitrogen and the terminal nitrogen, showed two parallel oxidation pathways, that is (i) formation of the corresponding sulfoxide and (ii) cleavage of the lateral chain with liberation of phenothiazine (PHZ) oxidized products (PHZ sulfoxide and PHZ quinone imine). Molecules with three carbon atoms (3C) separating the two nitrogens were oxidized to the corresponding sulfoxide. The chemical oxidation of all the studied molecules by hydrogen peroxide resulted in the corresponding sulfoxide with no break of the lateral chain. Oxidation by persulfate yielded, for the 3C derivatives, only the corresponding sulfoxide, but it produced cleavage of the lateral chain for the 2C derivatives. The origin of the distinct oxidation pattern between 2C and 3C molecules might be related to steric effects due to the lateral chain. The data are of interest in drug metabolism studies, especially for the early search. In the case of 2C phenothiazines, the results predict the possibility of an in vivo cleavage of the lateral chain with liberation of phenothiazine oxidized products which are known to produce several adverse side effects.     

Mechanistic and spectroscopic investigations of oxidative degradation of aspirin by aqueous alkaline permanganate

The kinetics of oxidation of aspirin (ASP) by permanganate in alkaline medium at a constant ionic strength of 0.06 mol dm⁻³ was studied spectrophotometrically using a rapid kinetic accessory. The reaction between permanganate and aspirin in alkaline medium exhibited 1:4 stoichiometry (aspirin: permanganate). The reaction was of first order in [permanganate ion] and had less than unit order in both [ASP] and [alkali]. A decrease in the dielectric constant of the medium decreased the rate of reaction. The effect of added products and ionic strength of the reaction medium have been investigated. The oxidation reaction in alkaline medium has been shown to proceed via a permanganate–aspirin complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies. A suitable mechanism is proposed. The reaction constants involved in the different steps of the mechanism were derived. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also determined.     

Diterpene chemistry : Transformations of 8(17), 14-labdadien-13-ol—Part 2

Aqueous permanganate oxidation of 8(17)-labden-13-ol gave two novel oxidation products by functionalisation of an unactivated carbon atom. The structures have been confirmed by degradative studies and a mechanism to account for their formation is proposed.     

Autocatalytic Oxidation of Thiamine Hydrochloride (Vitamin B1) by Permanganate in Aqueous Sulfuric Acid Medium: A Kinetic and Mechanistic Study

The reaction kinetics of autocatalytic oxidation of thiamine hydrochloride (vitamin B₁) by the permanganate ion in aqueous sulfuric acid medium has been investigated spectrophotometrically under the pseudo–first‐order condition at 25°C. The observed stoichiometry is 6:5 in terms of the mole ratio of permanganate ions and thiamine hydrochloride. Formation of products was confirmed by UV–vis, IR, GC‐MS, and NMR spectral data. Usually in the permanganate oxidation–reduction reactions, one of the products, Mn²⁺ autocatalyzes the reaction, but in the present investigation the autocatalytic effect is due to the (4‐methyl–thiazol‐5‐yl) acetic acid, a product formed from the oxidation of vitamin B₁, which is a rare case. The added Mn²⁺ does not have any significant effect on the rate of reaction. The reaction is first order with respect to both permanganate and thiamine hydrochloride concentrations. An increase in the sulfuric acid concentration decreases the rate of reaction. A composite scheme and rate laws were proposed. The activation parameters with respect to the slow step and reaction constants involved in the mechanism were determined and discussed.     

Oxidation of Benzyl Ethers via Phase Transfer Catalysis

A convenient procedure for the oxidation of benzyl ethers to benzoate esters is reported. Potassium permanganate in dichloromethane with phase transfer catalysis by triethylbenzylammonium chloride (TEBAC) affords products regiospecifically in fair to excellent yields.     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

 The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism.     

Efficient Oxidation of Alcohols with Potassium Permanganate Adsorbed on Aluminum Silicate Reagent

Summary. A new reagent, potassium permanganate adsorbed on aluminum silicate, suitable for the oxidation of primary and secondary alcohols to the corresponding carbonyl compounds is described.     

An Efficient Selective Oxidation of Alcohols with Potassium Permanganate Adsorbed on Aluminum Silicate under Solvent-free Conditions and Shaking

Summary. A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported.     

Solid Phase Derivatizations in HPLC: Polymeric Permanganate Oxidations of Alcohols and Aldehydes in HPLC-SPR

Abstract

On-line or off-line oxidations of various alcohols, aldehydes, and ketones can now be performed in conjunction with high performance liquid chromatography (HPLC), utilizing a newly developed polymeric permanganate solid phase reactor (SPR). These derivatization reactions are compatible with most reversed phase and normal phase solvents for HPLC separations, and many of these oxidations can be accomplished in real-time, on-line, at or above room temperature. Such HPLC-SPR approaches for chemical modifications and derivatizations of various oxidizable analytes provide a useful and quite practical newer approach for the HPLC-ultraviolet (UV) detection of appropriate analyte species. Difference chromatography, often with improved UV detection, can be used to confirm the suspected presence of a particular oxidizable analyte in a complex sample matrix. All of these solid phase derivatizations utilize conventional, commercially available HPLC instruments and accessories. These HPLC-SPR oxidation methods for chemical derivatization have also been applied to certain real world samples, in order to demonstrate the overall value and applicability of such analytical approaches.     

Alcohol Oxidations Using Reduced Polyoxovanadates

A full account of our recently communicated room temperature alcohol oxidation using reduced polyoxovanadates (r‐POV s) is presented. Extensive optimizations revealed optimal conditions employing 0.02 equiv. of r‐POV catalyst Cs₅(V₁₄As₈O₄₂Cl), 5 equiv. tert‐butyl hydrogen peroxide (^t BuOOH ) as the terminal co‐oxidant, in an acetone solvent for the quantitative oxidation of aryl‐substituted secondary alcohols to their ketone products. The substrate scope tolerates most aryl substituted secondary alcohols in good to quantitative yields while alkyl secondary and primary activated alcohols were sluggish in comparison under similar conditions. Catalyst recyclability was successful on a 1.0 mmol scale of starting alcohol 1‐phenylethanol. The oxidation was also successfully promoted by the V^IV /V^V mixed valent polyoxovanadate (POV ) Cs₁₁Na₃Cl₅(V₁₅O₃₆Cl). Finally, a third POV , Cs_2.64(V₅O₉)(AsO₄)₂, was investigated for catalytic activity using our established reaction protocol, but proved ineffective as compared to the other two r‐POV catalysts. This study expands the field of POM ‐mediated alcohol oxidations to include underexplored r‐POV catalysts. While our catalysts do not supplant the best catalysts known for the transformation, their study may inform the development of other novel oxidative transformations mediated by r‐POV s.     

Polarographic determination of methyl methacrylate

The permanganate oxidation of methyl methacrylate in weakly acidic solution yields methyl pyruvate. Hydroxylamine hydrochloride is used for destroying the excess of permanganate. At the same time it is consumed for oximation of the pyruvate, and the resulting oxime is determined polarographically. The reaction scheme of permanganate oxidation of methyl methacrylate is suggested and optimum working conditions are found both for permanganate oxidation and for polarographic determination. The method is used for the determination of vapours of methyl methacrylate in the air, for industrial hygiene purposes.     

Triazolines 24. Permanganate-catalyzed low temperature thermolysis of 5-(4-pyridyl) substituted 1,2,3-triazolines

Potassium permanganate oxidation of 1-aryl-5-(4-pyridyl)-1,2,3-triazolines I in a benzene-water two-phase system using the phase-transfer catalyst tetrabutylammonium chloride yields the corresponding 1H-1,2,3-tri-azoles II . However, when the reaction is run in a single phase in anhydrous benzene alone, the products are not triazoles, but imines III that can normally be obtained only by high-temperature thermolysis of the tri-azolines. The presence of both potassium permanganate and tetrabutylammonium chloride to yield the benzene soluble tetrabutylammonium permanganate ion pair appears essential for imine formation, although only in catalytic amounts. Thus a reaction pathway is proposed, which involves the initial coordination of the pyridyl nitrogen with the manganese atom of the permanganate ion leading to IV , followed by loss of nitrogen and regeneration of the permanganate ion via the dihydropyridine intermediates, V and VI , to yield the enamine VII , which tautomerizes to the imine III . Supportive evidence for the formation of IV is derived from the failure of 1,5-diaryl- and l-aryl-5-(3-pyridyl)triazolines to yield the respective imines; they lack the structural requirements necessary to comply with the proposed mechanism, and are recovered unchanged. Unlike the high temperature pyrolysis, the permanganate catalyzed low temperature thermolysis reactions provide cleaner products in better yields. Thus, the low temperature thermolysis may afford a route for the synthesis of clean samples of l-arylimino-l-ethyl-4-pyridines, especially when the triazolines are on hand.     

Permanganate Oxidation of Ambrein and the Absolute Configuration of Dihydro-γ-ionone (Supplement and Rectification)

Compounds 2 to 7 were identified among the products obtained from ambrein ( 1 ) by potassium permanganate oxidation; (+)-dihydro-γ-ionone ( 3 ) was shown to have the S-configuration.     

Permanganate oxidation of alkenes. Substituent and solvent effects. Difficulties with MP2 calculations

The permanganate oxidation of alkenes has been studied both experimentally and computationally. Transition state structures were located for the reaction of permanganate ion with a variety of monosubstituted alkenes at the B3LYP/6-311++G** level. Although the calculated activation energy for the reaction with ethene was reasonable, the calculated effect of substituents, based on the energies of the reactants, was much larger than that experimentally found. This was shown to be due to the formation of an intermediate charge-dipole complex which led to the transition state. Reaction field calculations found the complex to disappear in a high dielectric constant medium, and the range of activation energies for the reaction in solution became quite small. MP2 calculations were carried out in order to have a comparison with the DFT results. MP2-MP4 gave unusual results for calculations on permanganate ion as well as chromate ion and iron tetraoxide. They also gave markedly unreasonable results for the activation energy of the reaction of permanganate with ethane. CCSD/6-311++G** calculations gave satisfactory results for permanganate ion and chromate ion. At this level of theory, the reaction of permanganate with ethene was found to have a very early transition state, when the bond lengths of the reactants just began to change. The reaction was calculated to be very exothermic (-69 kcal/mol), and this was confirmed via calorimetry. The rates of permanganate oxidation of allyl alcohol and acrylonitrile were determined, and they had similar reactivities. The kinetics and the products of the reaction of permanganate with crotonate ion were examined in some detail.     

Evidence of competitive mechanisms during oxidation of CS(2)N(-)(3) by permanganate ion in alkaline solution

The oxidation of the 1,2,3,4-thiatriazole-5-thiolate ion, CS(2)N(-)(3), by permanganate ions in alkaline medium has been investigated over a wide range of oxidant concentrations. With a moderate excess of permanganate ion a 17-electron reaction takes place, yielding sulphate, nitrogen and carbon dioxide. With a high permanganate concentration the pseudohalide undergoes a 26-electron reaction yielding sulphate, carbon dioxide and nitrite as final products. These two different stoichiometries arise from the existence of competitive mechanisms and the ratio C(MnO(-)(4))/C(CS(2)N(-)(3)) will determine the course of the reaction.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of hydrazine

Oxidation of liydrazine in alkaline solutions with KmnO₄, gives inaccurate results both in the presence of absence of telluric acid. The titration curve is characterized by two inflections.Titration of KmnO₄ with hydrazine gives good results in the presence of Ba⁺² ions and 0.75–1NNaOH (when MnO₄^- gives MnO₂^-) or in the presence of 0.5–2.5N NaOH only (when MnO₄ gives MnO₂).Hydrazine could be estimated by oxidation with KMn0₄ either in the presence of Ba⁺² ions or telluric acid, after which the excess permanganate is back titrated with monovalent thallium. The alkalinity is Kept at 1N NaOH.     

Capillary electrophoretic determination of lignin degradation products obtained by permanganate oxidation

A new capillary electrophoretic (CE) technique was developed for the separation of lignin degradation products after permanganate oxidation, yielding information about quality and quantity of various linkages in the lignin molecule. This CE method is a promising alternative to existing gas chromatographic (GC) methods. An advantage in comparison with GC is the short separation time and the fact that the oxidation products (aromatic acids) can be analyzed without derivatization. The selectivity and sensitivity of CE combined with UV detection is adequate and makes it suited for fast routine characterization of lignins. If necessary, the CE method can be coupled with electrospray ionization mass spectrometry in order to make a clear assignment of the peaks.