Kinetics and Mechanism of the Oxidation of Some Thioacids by Butyltriphenylphosphonium Dichromate

2007 ◽  
Vol 32 (3) ◽  
pp. 119-129 ◽  
Author(s):  
K.M. Dilsha ◽  
Seema Kothari

The oxidation of thioglycollic, thiolactic and thiomalic acids by butyltriphenylphosphonium dichromate (BTPPD) in dimethylsulfoxide (DMSO) yielded the corresponding disulfide as the product. The reaction is first order with respect to BTPPD, however, second-order dependences of the rate were found on the concentrations of both the thioacid and hydrogen ions. The rate of oxidation of thiolactic acid (TLA) was determined in nineteen organic solvents. An analysis of the solvent effect by multiparametric equations indicated the cation-solvating power of the solvents to be most significant. A mechanism has been proposed involving the formation of a thioester in a pre-equilibrium, followed by its decomposition in the slow step.

2009 ◽  
Vol 34 (3) ◽  
pp. 199-209 ◽  
Author(s):  
Dinesh Pandey ◽  
Seema Kothari

The oxidation of DL-methionine (MT) by benzimidazolium dichromate (BIDC), in dimethyl sulfoxide, leads to the formation of the corresponding sulfoxide. The reaction is first order with respect to BIDC. Michaelis - Menten type kinetics were observed with respect to MT. The reaction is catalysed by hydrogen ions and the dependence is of the form kobs = k‘[H+]. The rate of oxidation of MT was determined in 19 organic solvents. An analysis of the solvent effect by solvatochromic equations indicated that though both the anion- and cation-solvating powers of the solvent contribute to the observed solvent effect, the role of cation-solvation is much the major. A suitable mechanism has been proposed.


1984 ◽  
Vol 62 (4) ◽  
pp. 729-735 ◽  
Author(s):  
John W. Bunting ◽  
Glenn M. Kauffman

The kinetics of disproportionation and ferricyanide ion oxidation of the 10-methylacridinium cation have been measured spectrophotometrically over the pH range 9–14 in.20% CH3CN – 80% H2O (v/v) and ionic strength 1.0 at 25 °C. Disproportionation is kinetically second-order in total acridine species. The pH–rate profile is consistent with the rate-determining reaction of one acridinium cation with the pseudobase alkoxide anion derived from a second acridinium cation. Ferricyanide ion oxidation is kinetically first-order in each of ferricyanide ion and total acridine species. The pH–rate profile requires three distinct pathways for the ferricyanide ion oxidation of the 10-methylacridinium cation. For pH < 9.7, rate-determining attack of ferricyanide ion on the neutral pseudobase predominates, while for pH > 12.8 the predominant oxidation pathway involves reaction of ferricyanide ion with the pseudobase alkoxide ion. Between pH 9.7 and 12.8, the major oxidation pathway involves initial disproportionation of the acridinium cation followed by ferricyanide ion oxidation of the 9,10-dihydro-10-methylacridine product. This latter route accounts for a maximum of 69% of the total ferricyanide ion oxidation at pH 11.1.


1970 ◽  
Vol 48 (23) ◽  
pp. 3613-3618 ◽  
Author(s):  
B. C. Hui ◽  
B. R. James

The kinetics of formation of mono- and dicarbonyl complexes in two successive stages by direct carbonylation of ruthenium(II) chlorides in dimethylacetamide solution have been studied at 65–80° and up to 1 atm CO by gas uptake techniques. Both stages are first order in ruthenium. Formation of the monocarbonyl is independent of CO pressure; dicarbonyl formation is first order in CO at low pressures with the order decreasing towards zero with increasing pressure, and shows an inverse chloride dependence from 0.1–2.0 M added chloride. For both stages, the data are consistent with a mechanism involving predissociation. A similar mechanism is suggested for the corresponding reactions in 3 M HCl solution which had been studied earlier and which showed overall second-order kinetics.Discussion on the related formation of molecular nitrogen complexes of ruthenium(II) is presented.


1978 ◽  
Vol 31 (12) ◽  
pp. 2581 ◽  
Author(s):  
PJ Nichols ◽  
MW Grant

13C Fourier-transform N.M.R. has been used to measure the rate of exchange of dimethyl sulfoxide with hexakis(dimethyl sulfoxide)nickel(II) cation. The parameters obtained, kex(25°C)(9.8�4.6) × 103 s-1, ΔH‡ 50�2 kJ mol-1 and ΔS‡ 0�4 J K-1 mol-1, are in excellent agreement with those of the most recent 1H N.M.R. study. The reaction between Ni(Me2SO)62+ and diethyldithiocarbamate (dtc-) gives only Ni(dtc)2. When dtc- is in excess, the rate of formation of Ni(dtc)2 is first order in Ni2+ and dtc-. The ionic-strength and temperature dependences of the second-order rate constants are consistent with the rate-determining formation of an unstable Ni(dtc)+ complex by an ID mechanism.


2003 ◽  
Vol 2003 (4) ◽  
pp. 182-183 ◽  
Author(s):  
Gamal Abdel-Whab Ahmed ◽  
Khalid Suliman Khairou ◽  
Refat Moustafa Hassan

The kinetics of oxidation of chitosan as polysaccharide by permanganate in aqueous perchlorate media at a constant ionic strength was found to have second-order overall kinetics and to be first-order in the concentration of both reactants, the results obtained showed that the reaction is acid catalysed.


2005 ◽  
Vol 83 (9) ◽  
pp. 1212-1221 ◽  
Author(s):  
W David Chandler ◽  
Zhao Wang ◽  
Donald G Lee

2-Propanol is oxidized by tetrapropylammonium perruthenate (TPAP) in a reaction that is second order in TPAP and first order in 2-propanol. One of the products, believed to be ruthenium dioxide, is an effective catalyst for the reaction, making it an autocatalytic process. The rate of oxidation is relatively insensitive to the presence of substituents. Primary kinetic deuterium isotope effects are observed when either the hydroxyl or the α hydrogen is replaced by deuterium. The only product obtained from the oxidation of cyclobutanol is cyclobutanone, indicating that the reaction is a two-electron process. Tetrahydrofuran is oxidized at a rate that is several orders of magnitude slower than that observed for 2-propanol, suggesting that the reaction of TPAP with alcohols may be initiated by formation of perruthenate esters. A tentative mechanism consistent with these observations is proposed.Key words: oxidation, alcohols, tetrapropylammonium perruthenate, reaction mechanism, autocatalysis.


1986 ◽  
Vol 64 (6) ◽  
pp. 1161-1169 ◽  
Author(s):  
Alan R. Katritzky ◽  
Bogumil Brycki

Evidence is presented to demonstrate that at the borderline between first-order reaction via nucleophilic trapping of intimate ion–molecule pairs and first-order reaction via the formation of free carbocations, both mechanisms proceed independently, without merging. Similarly at the borderline between first-order (rate-determining formation) and second-order (rate-determining nucleophilic attack) reactions of intimate ion–molecule pairs, both reactions again proceed independently.


1997 ◽  
Vol 36 (04/05) ◽  
pp. 315-318 ◽  
Author(s):  
K. Momose ◽  
K. Komiya ◽  
A. Uchiyama

Abstract:The relationship between chromatically modulated stimuli and visual evoked potentials (VEPs) was considered. VEPs of normal subjects elicited by chromatically modulated stimuli were measured under several color adaptations, and their binary kernels were estimated. Up to the second-order, binary kernels obtained from VEPs were so characteristic that the VEP-chromatic modulation system showed second-order nonlinearity. First-order binary kernels depended on the color of the stimulus and adaptation, whereas second-order kernels showed almost no difference. This result indicates that the waveforms of first-order binary kernels reflect perceived color (hue). This supports the suggestion that kernels of VEPs include color responses, and could be used as a probe with which to examine the color visual system.


2017 ◽  
Vol 9 (3) ◽  
pp. 17-30
Author(s):  
Kelly James Clark

In Branden Thornhill-Miller and Peter Millican’s challenging and provocative essay, we hear a considerably longer, more scholarly and less melodic rendition of John Lennon’s catchy tune—without religion, or at least without first-order supernaturalisms (the kinds of religion we find in the world), there’d be significantly less intra-group violence. First-order supernaturalist beliefs, as defined by Thornhill-Miller and Peter Millican (hereafter M&M), are “beliefs that claim unique authority for some particular religious tradition in preference to all others” (3). According to M&M, first-order supernaturalist beliefs are exclusivist, dogmatic, empirically unsupported, and irrational. Moreover, again according to M&M, we have perfectly natural explanations of the causes that underlie such beliefs (they seem to conceive of such natural explanations as debunking explanations). They then make a case for second-order supernaturalism, “which maintains that the universe in general, and the religious sensitivities of humanity in particular, have been formed by supernatural powers working through natural processes” (3). Second-order supernaturalism is a kind of theism, more closely akin to deism than, say, Christianity or Buddhism. It is, as such, universal (according to contemporary psychology of religion), empirically supported (according to philosophy in the form of the Fine-Tuning Argument), and beneficial (and so justified pragmatically). With respect to its pragmatic value, second-order supernaturalism, according to M&M, gets the good(s) of religion (cooperation, trust, etc) without its bad(s) (conflict and violence). Second-order supernaturalism is thus rational (and possibly true) and inconducive to violence. In this paper, I will examine just one small but important part of M&M’s argument: the claim that (first-order) religion is a primary motivator of violence and that its elimination would eliminate or curtail a great deal of violence in the world. Imagine, they say, no religion, too.Janusz Salamon offers a friendly extension or clarification of M&M’s second-order theism, one that I think, with emendations, has promise. He argues that the core of first-order religions, the belief that Ultimate Reality is the Ultimate Good (agatheism), is rational (agreeing that their particular claims are not) and, if widely conceded and endorsed by adherents of first-order religions, would reduce conflict in the world.While I favor the virtue of intellectual humility endorsed in both papers, I will argue contra M&M that (a) belief in first-order religion is not a primary motivator of conflict and violence (and so eliminating first-order religion won’t reduce violence). Second, partly contra Salamon, who I think is half right (but not half wrong), I will argue that (b) the religious resources for compassion can and should come from within both the particular (often exclusivist) and the universal (agatheistic) aspects of religious beliefs. Finally, I will argue that (c) both are guilty, as I am, of the philosopher’s obsession with belief. 


2009 ◽  
Vol 74 (1) ◽  
pp. 43-55 ◽  
Author(s):  
Dennis N. Kevill ◽  
Byoung-Chun Park ◽  
Jin Burm Kyong

The kinetics of nucleophilic substitution reactions of 1-(phenoxycarbonyl)pyridinium ions, prepared with the essentially non-nucleophilic/non-basic fluoroborate as the counterion, have been studied using up to 1.60 M methanol in acetonitrile as solvent and under solvolytic conditions in 2,2,2-trifluoroethan-1-ol (TFE) and its mixtures with water. Under the non- solvolytic conditions, the parent and three pyridine-ring-substituted derivatives were studied. Both second-order (first-order in methanol) and third-order (second-order in methanol) kinetic contributions were observed. In the solvolysis studies, since solvent ionizing power values were almost constant over the range of aqueous TFE studied, a Grunwald–Winstein equation treatment of the specific rates of solvolysis for the parent and the 4-methoxy derivative could be carried out in terms of variations in solvent nucleophilicity, and an appreciable sensitivity to changes in solvent nucleophilicity was found.


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