Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part II. Oxidation in Acidic Medium. A Comparison with the HOBr – Oxalic Acid Reaction

1971 ◽  
Vol 49 (4) ◽  
pp. 654-659 ◽  
Author(s):  
Judith M. Pink ◽  
Ross Stewart
Keyword(s):  
Steady State ◽  
Oxalic Acid ◽  
Acidic Medium ◽  
Mandelic Acid ◽  
Reaction Path ◽  
Oxidative Decarboxylation ◽  
Hydroxy Acids ◽  
Bromine Water ◽  
Acid Reaction ◽  
Ph Range

The oxidative pattern of α-hydroxy acids by acidic bromine water is shown to be similar to the oxalic acid – bromine water reaction. In both cases HOBr is the oxidant and the undissociated form of the organic acid is required for reaction to occur. The rate law −d[HOBr]/dt = k[HOBr][hydroxy acid] is observed for oxidations carried out in the presence of Ag+ ion in the pH range 2–5. Below that pH bromination occurs. Bell-shaped pH-rate profiles are obtained for the oxidations of benzilic, mandelic, and 2-hydroxy-2-methylpropanoic acids. The calculated rates, based on a steady state treatment of a reaction path involving a hypobromite intermediate (R2COBrCO2H) are in agreement with the observed values and with the observation that the rates of oxidation of mandelic acid in D2O and H2O are the same.

Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part I. Oxidation in Neutral and Alkaline Medium

1971 ◽  
Vol 49 (4) ◽  
pp. 649-653 ◽  
Author(s):  
Judith M. Pink ◽  
Ross Stewart
Keyword(s):  
Steady State ◽  
Kinetic Study ◽  
Oxidation Rate ◽  
Mandelic Acid ◽  
Oxidative Decarboxylation ◽  
Hydroxy Acids ◽  
Bromine Water ◽  
Benzilic Acid ◽  
Hydroxylic Proton ◽  
Good Agreement

A kinetic study of the oxidative decarboxylation of α-hydroxy acids by bromine water shows that above pH 6 Br2 is a much more significant oxidant for these compounds than is HOBr, and that OBr− is virtually inert. The rate law – d[oxidant]/dt = k[oxidant][substrate] is observed and the oxidation pattern differs from that of alcohols in that the α-hydrogen is not involved in the reaction.All the compounds studied (benzilic, mandelic, and 2-hydroxy-2-methylpropanoic acids) exhibit bell-shaped pH-rate profiles with maxima at about pH 8. A mechanism is proposed involving the attack of Br2 (or HOBr) at the carboxylate site concurrently with base-catalyzed loss of the hydroxylic proton. A steady state treatment based on this mechanism yields calculated rates in good agreement with the observed values. Furthermore, the same parameters predict the rates observed at lower pH in the presence of added excess bromide. The Br2 oxidation rate is greater than the HOBr rate by a factor of 60 for benzilic acid, 37 for 2-hydroxy-2-methylpropanoic acid, and 10 for mandelic acid.

Mandelic acid and phenyllactic acid “Reaction Sets” for exploring the kinetics and mechanism of oxidations by hydrous manganese oxide (HMO)

2019 ◽  
Vol 21 (6) ◽  
pp. 1038-1051
Author(s):  
Xiaomeng Xia ◽  
Alan T. Stone
Keyword(s):  
Physicochemical Properties ◽  
Manganese Oxide ◽  
Mandelic Acid ◽  
Heterogeneous Reactions ◽  
Hydroxy Acids ◽  
Medium Effects ◽  
Phenyllactic Acid ◽  
Hydrous Manganese Oxide ◽  
Acid Reaction

Two hydroxy acids reaction sets are used to explore the kinetics, the role of physicochemical properties, and medium effects of the heterogeneous reactions on hydrous manganese oxide (HMO) surface.

Electrolytic reduction of o-nitrobenzyl thiocyanate in buffered solutions on mercury

1985 ◽  
Vol 50 (1) ◽  
pp. 33-41 ◽  
Author(s):  
Jaromír Hlavatý
Keyword(s):  
Acidic Medium ◽  
Reaction Path ◽  
Electrolytic Reduction ◽  
Buffer System ◽  
Height Ratio ◽  
Preparative Electrolysis ◽  
Clear Explanation ◽  
Ec Mechanism ◽  
Controlled Potential

The o-nitrobenzyl thiocyanate (I) behaves differently on the DME and on a large mercury pool electrode. Polarography did not give a sufficiently clear explanation of the reaction mechanism, only the preparative experiments yielded useful results. Whereas polarographic curves in solutions of Britton-Robinson buffer system with 50% by vol. ethanol exhibit two cathodic waves within the pH region 1-12, corresponding according to their height ratio to an uptake of 4 e and 2 e respectively, the controlled potential preparation electrolysis (CPE) and coulometry results indicate a more complicated reaction path. In the CPE carried out at the concentration of I 1 . 10 -2 mol/l the electroreductive splitting of CH2-SCN occurs as the first step. Nitrobenzyl radicals so formed react in the follow-up dimerization resulting in dibenzyl or toluene structures. Simultaneously or at a later stage the completion of the electrolytic reduction of the nitro group proceeds to the hydroxylamino group. In solution of 9 > pH > 1 the CPE of nitro compound I takes place by an ECEC mechanism yielding dibenzodiazocine III, its N-oxide IV and 2,2'-dimethylazoxybenzene (V). In course of preparative electrolysis in strongly acidic medium 2-amino-benzo(l,3)-thiazine-l-oxide (II) is formed by an EC mechanism.

scholarly journals Production and Characterization of Esterase in Lantinus tigrinus for Degradation of Polystyrene

2013 ◽  
Vol 62 (1) ◽  
pp. 101-108 ◽  
Author(s):  
LUBNA TAHIR ◽  
MUHAMMAD ISHTIAQ ALI ◽  
MUHAMMAD ZIA ◽  
NAIMA ATIQ ◽  
FARIHA HASAN ◽  
...  
Keyword(s):  
Acidic Medium ◽  
Specific Activity ◽  
Mineral Salt Medium ◽  
Tween 80 ◽  
Synthetic Polymers ◽  
Ftir Analysis ◽  
Polystyrene Film ◽  
Biological Degradation ◽  
Ph Range

Polystyrene is considered stable to biological degradation. Lantinus tigrinus isolated from wood sample produced esterase in growth medium under normal conditions. However, acidic medium, 37 degrees C temperature, presence of tween 80; and urea and yeast extract in mineral salt medium enhance the production of esterase and specific activity. Purified esterase was active at broad pH range and 45 degrees C. FTIR analysis confirmed that esterase produced by Lantinus tigrinus effectively degraded polystyrene film and broke macromolecules down to non-toxic molecules. This study concludes that the presence of Lantinus tigrinus at dumping sites can be exploited for waste management containing high molecular weight synthetic polymers.

scholarly journals Kinetics and Correlation Analysis of Reactivity in the Oxidation of Some α-Hydroxy Acids by Benzimidazolium Dichromate

2018 ◽  
Vol 43 (3-4) ◽  
pp. 300-314
Author(s):  
Dinesh Panday ◽  
Teena Kachawa ◽  
Seema Kothari
Keyword(s):  
Solvent Effect ◽  
Mandelic Acid ◽  
Bond Cleavage ◽  
Hydroxy Acids ◽  
Cyclic Transition ◽  
Hydride Ion ◽  
Rate Determining Step ◽  
Reaction Constant ◽  
Cyclic Transition State ◽  
Hydride Ion Transfer

Kinetic and mechanistic studies of the oxidation of mandelic acid and nine monosubstituted mandelic acids by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide are discussed with an emphasis on correlation of structure and reactivity. The reactions were of first order with respect to BIDC. However, Michaelis-Menten type kinetics were observed with respect to hydroxy acids. The reactions are catalysed by protons. The deuterium isotope effect for the oxidation of mandelic acid ( kH/ kD = 5.91 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. An analysis of the solvent effect showed that the role of cationsolvation is major. The reaction showed an excellent correlation with the Hammett σ values, the reaction constant being negative. Based on the kinetic data, analysis of the solvent effect and results of structure-reactivity correlation along with some non-kinetic parameters, a mechanism involving rate-determining oxidative decomposition of the complex through hydride-ion transfer via a cyclic transition state to give the corresponding oxoacid is suggested.

Radiolysis of aqueous chloroform solutions

1970 ◽  
Vol 48 (2) ◽  
pp. 271-276 ◽  
Author(s):  
B. J. Rezansoff ◽  
K. J. McCallum ◽  
R. J. Woods
Keyword(s):  
Oxalic Acid ◽  
Formic Acid ◽  
Hydroxyl Radicals ◽  
Ph Effect ◽  
Hydrogen Ions ◽  
Γ Radiation ◽  
High Ph ◽  
Hydrated Electrons ◽  
Presence And Absence ◽  
Ph Range

Saturated aqueous chloroform solutions (0.07 M) with pH ranging from 0.8 to 12.6 have been irradiated with 60Co γ-radiation in the presence and absence of air. G(Cl− + ClO−) increases with increasing pH in the pH range 1–3 (aerated solutions) or 3–6 (deaerated solutions) and again at pH greater than 10.5. The variation in yield from aerated solutions in the region pH 1–3 is attributed to competition between chloroform and hydrogen ions for hydrated electrons. However, such competition cannot account for the pH effect observed in deaerated solutions between pH 3 and 6. Increased yields from both aerated and deaerated solutions at high pH are attributed to the formation of O− by reaction of hydroxyl radicals and hydroxide ions. Formic acid and oxalic acid have been identified as minor products when aerated chloroform solutions are irradiated.

ChemInform Abstract: Use of Vanadate. Oxidative Decarboxylation of α-Hydroxy Acids.

ChemInform ◽  
1988 ◽  
Vol 19 (22) ◽  
Author(s):  
H. DUTTA ◽  
B. HAZRA ◽  
A. BANERJEE ◽  
S. BANERJEE
Keyword(s):  
Oxidative Decarboxylation ◽  
Hydroxy Acids
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