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.

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.

The kinetics and the mechanism of oxidative decarboxylation of benzilic acid by acidic permanganate (stopped-flow technique) — An autocatalytic study

2004 ◽  
Vol 82 (9) ◽  
pp. 1372-1380 ◽  
Author(s):  
Sairabanu A Farokhi ◽  
Sharanappa T Nandibewoor
Keyword(s):  
Activation Parameters ◽  
Oxidative Decarboxylation ◽  
Two Stage ◽  
First Order ◽  
First Order Kinetics ◽  
Stage Process ◽  
Benzilic Acid ◽  
Reaction Constants ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of the oxidation of benzilic acid by potassium permanganate in an acidic medium were studied spectrophotometrically. The reaction followed a two-stage process, wherein both stages of the reaction followed first-order kinetics with respect to permanganate ion and benzilic acid. The rate of the reaction increased with an increase in acid concentration. Autocatalysis was observed by one of the products, i.e., manganese(II). A composite mechanism involving autocatalysis has been proposed. The activation parameters of the reaction were calculated and discussed and the reaction constants involved in the mechanisms were calculated. There is a good agreement between the observed and calculated rate constants under different experimental conditions.Key words: oxidation, autocatalysis, benzilic acid, two-stage kinetics.

Catalytic deuterium exchange reactions with organics. XXIII. Deformylation during the deuteration of aromatic α-hydroxy acids and related compounds

1966 ◽  
Vol 19 (2) ◽  
pp. 211 ◽  
Author(s):  
GE Calf ◽  
JL Garnett
Keyword(s):  
Carboxylic Acid ◽  
Heavy Water ◽  
Mandelic Acid ◽  
Hydroxy Acids ◽  
Exchange Reactions ◽  
Catalyst Activation ◽  
Π Complex ◽  
Complex Adsorption ◽  
Benzilic Acid ◽  
Related Compounds

The transition-metal catalysed exchange of aromatic a-hydroxy acids with heavy water has been studied. Benzilic acid and its 00'-dichloro- and pp'-dimethyl derivatives simultaneously deformylate with the formation of the corresponding diary1 ketones. Mandelic acid and derivatives are stable under these conditions and only deuterate, whereas 9-hydroxyfluorene-9-carboxylic acid decomposes quantitatively to 9-fluorenol and 9-fluorenone. Benzhydrol decomposes appreciably to benzophenone. The effect of catalyst (soluble Fe, Co, Ni, Ru, Rh, Pd, Ir, and Pt chlorides versus insoluble oxides) and the method of catalyst activation (hydrogen, sodium borohydride, and self-activation) on the exchange and deformylation reactions have been studied. The results are interpreted in terms of a mechanism based on π-complex adsorption.

Analytical approach for transient photoconductivity in undoped a-Si:H

1995 ◽  
Vol 377 ◽  
Author(s):  
M. Goerlitzer ◽  
P. Pipoz ◽  
H. Beck ◽  
N. Wyrsch ◽  
A. V. Shah
Keyword(s):  
Steady State ◽  
Theoretical Model ◽  
Analytical Approach ◽  
Room Temperature ◽  
Free Electrons ◽  
Recombination Time ◽  
Sample Quality ◽  
Transient Photoconductivity ◽  
Light Intensities ◽  
Good Agreement

ABSTRACTTransient photoconductive response of undoped a-Si:H has been studied; the changes were analysed between two slightly different steady-state illumination conditions, at room temperature. A theoretical model is developed to describe transient photoconductivity; it yields good agreement with the measured curves for a whole range of light intensities. Numerical evaluations allows one to extract the recombination time of electrons. Comparison with steady-state photoconductivity yields a band mobility of free electrons between 0.1 and 6 cm2V−1s−1, depending upon sample quality.

Steady-State stress distributions in circumferentially notched bars subjected to creep

1982 ◽  
Vol 17 (3) ◽  
pp. 123-132 ◽  
Author(s):  
K D Al-Faddagh ◽  
R T Fenner ◽  
G A Webster
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Stress Index ◽  
Stress Distributions ◽  
Computer Solution ◽  
Time Intervals ◽  
Throat Region ◽  
Intermediate Time ◽  
State Stress ◽  
Good Agreement

The paper describes a procedure, based on a finite element method, for calculating directly the steady-state stress distribution in circumferentially notched bars subjected to creep without the need for obtaining solutions at intermediate time intervals. Good agreement is obtained with relevant approximate plasticity solutions and with numerical calculations which approach the steady-state over a period of time from the initial elastic stress distribution. Also, the procedure is equally applicable to primary, secondary, and tertiary creep, provided the variables of stress and time are separable in the creep law. Results obtained for a range of notch geometries and values of the stress index, n, are reported. It is found for each profile that a region of approximately constant effective stress, σ, independent of n, is obtained which can be used to characterise the overall behaviour of the notch throat region when a steady-state is reached sufficiently early in life. An approximate method for estimating the maximum equivalent steady-state stress across the notch throat is also presented which does not require a computer solution.

Coupling of Sloshing and Ship Motions

2003 ◽  
Vol 47 (03) ◽  
pp. 208-221 ◽  
Author(s):  
Olav F. Rognebakke ◽  
Odd M. Faltinsen
Keyword(s):  
Steady State ◽  
Transient Behavior ◽  
Frequency Domain Analysis ◽  
Ship Motions ◽  
Steady State Motion ◽  
Constant Coefficients ◽  
Incident Waves ◽  
Violent Sloshing ◽  
Different Levels ◽  
Good Agreement

The coupled effect between ship motions and sloshing is studied. Two-dimensional experiments of a hull section containing tanks filled with different levels of water excited in sway by regular waves have been conducted. Steady-state results are obtained for the sway amplitude. Even if violent sloshing occurs in the tanks, the steady-state motion is almost linear and sinusoidal with the frequency of the linear incident waves. This implies that higher-order harmonics of the sloshing force are filtered out by the system. Simulations of the modeled case are performed using a linear and a nonlinear sloshing model and mainly assuming linear external flow. For steady-state motion, a convolution formulation does not improve the results relative to using constant coefficients in the equation of motion. However, in order to properly model the transient behavior in an irregular sea, a convolution formulation must be included. The treatment of the retardation function for the external problem is discussed in detail. A good agreement between experiments and computations is reported. The calculated coupled motion is sensitive to the damping of the sloshing motion in a certain frequency range where the coupled sloshing and ship motions cause resonant ship motions. A quasilinear frequency domain analysis is used to explain this by introducing the sloshing loads as a frequency dependent spring.

scholarly journals Liquid Brine in Ice Shelves

1975 ◽  
Vol 14 (70) ◽  
pp. 125-136 ◽  
Author(s):  
R. H. Thomas
Keyword(s):  
Steady State ◽  
Heat Transport ◽  
Thermal Equilibrium ◽  
Transport Model ◽  
Percolation Model ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Brine Layer ◽  
Good Agreement

Holes drilled into thin areas of the Brunt Ice Shelf encounter a layer of liquid brine less than 1 m thick approximately at sea-level. Assuming the brine to be moving horizontally, analysis of its effects on thermal equilibrium gives an estimate of steady-state annual brine flow that is in good agreement with the value deduced from a percolation model. The effect of firn density on percolation rates is such that the slope of an active brine layer increases rapidly as ice thickness increases. However, the heat transport model predicts that brine layers are unlikely to be active in both very thick and very thin ice shelves.

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