An investigation by means of correlation analysis into the mechanisms of oxidation of aryl methyl sulfides and sulfoxides by dimethyldioxirane in various solvents

Relative rate constants have been measured for the oxidation of aryl methyl sulfides and sulfoxides by dimethyldioxirane in acetone, in mixtures of acetone with aprotic co-solvents of both higher and lower relative permittivity, and in aqueous acetone mixtures. Correlation analyses of the effects of substituents in the different solvents show that, with one exception, reactions take place via a single step mechanism in which the formation of the new SO bond and the elimination of acetone occur concertedly. The exception was oxidation of the sulfides in aqueous acetone containing the highest proportion of water of those studied (20% v/v). Here, the behaviour of the reaction is consistent with a two-step mechanism in which the oxidant reversibly attacks the sulfide to form an open-chain sulfonium betaine that subsequently fragments to sulfoxide and acetone. There is no evidence for the participation of an intermediate dioxathietane as has been found in the case of sulfide oxidations by (trifluoromethyl)methyldioxirane in CH(2)Cl(2) and similar aprotic solvents. It is not justified to generalise a mechanism involving a betaine, with or without a derived dioxathietane, to the reactions of dimethyldioxirane in acetone.     

A General and Simple Synthesis of Phenylglyoxylic Esters via the Oxidation of Mandelic Esters with Ammonium Chlorochromate Adsorbed on Alumina

A general method for preparation of phenylglyoxylic esters by oxidation of mandelic esters with readily available ammonium chlorochromate adsorbed on alumina is described.     

Kinetic studies on the oxidation of aryl methyl sulfides and sulfoxides by dimethyldioxirane; absolute rate constants and activation parameters for 4-nitrophenyl methyl sulfide and sulfoxide

The oxidations of methyl 4-nitrophenyl sulfide and sulfoxide by dimethyldioxirane, in acetone and mixtures of acetone with water, methanol, acetonitrile and hexane, have been followed by UV-Vis spectroscopy to monitor the decay of the substrates. The data show that, under all the conditions studied, both oxidations obey second-order kinetics. Grunwald-Winstein and Kamlet-Taft analyses of the influence of solvents on the second-order rate constants have been used to obtain mechanistic information on the two reactions. Activation parameters for the two oxidations in acetone and aqueous acetone have been calculated from rate constants for reactions in the temperature range 283-313 K and compared with those from sulfide and sulfoxide oxidations with other oxidants. For sulfoxide oxidations in acetone and 1-20% v/v water in acetone, the results support a concerted nucleophilic displacement by sulfur of oxygen from dimethyldioxirane with the rate being dependent on the solvent's polarity. Sulfide oxidations in acetone and 1-5% v/v water in acetone also proceed by a concerted mechanism. However, in the most polar solvent system studied, 20% v/v water in acetone, the mechanism changes in favour of a two-step reaction involving a betaine intermediate. Importantly, the sulfide oxidation shows a different solvent dependence to that of the sulfoxide, with the rate of oxidation being determined by the hydrogen bond donor capacity and electron-pair donicity of the solvent.     

Synthesis of benzo[c]chromen-6-ones via novel cyclic aryl-Pd(II)-ester enolate intermediates

The examination of the palladium catalysed arylation reactions of mono-iodo derivatives of the phenyl and benzyl esters of benzoic acid, phenylacetic acid and dehydrocinnamic acid has resulted in the formation of benzo[c]chromen-6-ones, unexpected cinnamate and succinate products and diphenyl dimers. Many of these products can be rationalised as arising from novel cyclic ArPd(II)-enolate intermediates, formed by intramolecular C-H activation by ArPd(II).     

Identification of the products of oxidation of quercetin by air oxygen at ambient temperature

Oxidation of quercetin by air oxygen takes place in water and aqueous ethanol solutions under mild conditions, namely in moderately-basic media (pH approximately 8-10) at ambient temperature and in the absence of any radical initiators, without enzymatic catalysis or irradiation of the reaction media by light. The principal reaction products are typical of other oxidative degradation processes of quercetin, namely 3,4-dihydroxy-benzoic (proto-catechuic) and 2,4,6-trihydroxybenzoic (phloroglucinic) acids, as well as the decarboxylation product of the latter--1,3,5-trihydroxybenzene (phloroglucinol). In accordance with the literature data, this process involves the cleavage of the gamma-pyrone fragment (ring C) of the quercetin molecule by oxygen, with primary formation of 4,6-dihydroxy-2-(3,4-dihydroxybenzoyloxy)benzoic acid (depside). However under such mild conditions the accepted mechanism of this reaction (oxidative decarbonylation with formation of carbon monoxide, CO) should be reconsidered as preferably an oxidative decarboxylation with formation of carbon dioxide, CO2. Direct head-space analysis of the gaseous components formed during quercetin oxidation in aqueous solution at ambient temperature indicates that the ratio of carbon dioxide/carbon monoxide in the gas phase after acidification of the reaction media is ca. 96:4%. Oxidation under these mild conditions is typical for other flavonols having OH groups at C3 (e.g., kaempferol), but it is completely suppressed if this hydroxyl group is substituted by a glycoside fragment (as in rutin), or a methyl substituent. An alternative oxidation mechanism involving the direct cleavage of the C2-C3 bond in the diketo-tautomer of quercetin is proposed.     

Einsatz der Isotachophorese zur quantitativen Bestimmung von Hippurs?ure, Phenylglyoxyls?ure und Mandels?ure im Urin von Styrol-exponierten Personen

Ohne Zusammenfassung

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Quantitative determination of hippuric, phenylglyoxylic, and mandelic, acid in urine of styrene-exposed persons by isotachophoresis

     

The oxidation of organic substances by compounds of tervalent manganese-I Oxidation of mandelic acid, ethylene glycol, glycerol and d-mannitol by the pyrophosphate complex of manganese(III) and by manganese(III) sulphate

The oxidation of mandelic acid, ethylene glycol, glycerol and d-mannitol by the pyrophosphate complex of manganese(III) and with manganese(III) sulphate was studied. It was shown that benzaldehyde is formed by oxidation of mandelic acid, which undergoes no further oxidation. In the case of ethylene glycol, glycerol and d-mannitol the reactions do not follow a simple course and therefore are not of analytical utility. The effect of acidity and time on the course of the reactions was found and a procedure for the indirect titrimetric determination of mandelic acid with both reagents proposed.     

Ion-pair chromatography of acidic drug metabolites and endogenic compounds.

Liquid-liquid chromatographic systems based on ion-pair partition with silica microparticles as the support for the stationary phase have been used for the separation of anionic compounds of biochemical and pharmacological interest. A high separating efficiency can be obtained with both aqueous and organic mobile phases and the retention is easily regulated by the nature and the concentration of the quaternary ammonium counter ion, present in the aqueous phase. The influence of the composition of the liquid phases on the selectivity and separating efficiency has been studied, as well as equilibration methods and the stability of the systems. Examples are given of separations of sulphonamides, barbiturates, glucuronic and sulphuric acid conjugates of steroidal compounds and phenols glycine conjugates of carboxylic acids (hippuric, nicotinuric and salicyluric acid) and anionic metabolites of biogenic amines (indoleacetic, benzoic, mandelic and phenylacetic acid derivatives).     

Application d'un reactif sulfovanadique en milieu acetique anhydre a l'etude analytique de quelques acides α-carbonyles ou α-hydroxyles

(Application of a vanadium(V) reagent in anhydrous acetic acid to the determination of some α-carbonyl or α-hydroxyl carboxylic acids). The reagent is prepared from vanadium pentoxide and sulfuric acid in anhydrous acetic acid medium. The oxidation kinetics of various α-carbonyl (glyoxylic, pyruvic, phenylglyoxylic) and α-hydroxyl (glycolic, lactic, mandelic, gluconic) acids are described. A study of the reaction stoichiometry shows that the immediate reaction, corresponding to the consumption of 2–9 mol V(V) mol^?1 of acid, depending on the acid, is useful quantitatively, except for lactic acid which gives a slow non-stoichiometric reaction.     

A reliable method by ultra‐performance liquid chromatography coupled with tandem mass spectrometry to quantify and confirm simultaneously the presence of solvent metabolites in workers' urine

Ultra‐performance liquid chromatography coupled with tandem mass spectrometry was used for the biological monitoring of workers occupationally exposed to solvents. The method was developed using a triple quadrupole to investigate the relevant urinary metabolites of styrene, namely mandelic acid and phenylglyoxylic acid. The method provides quantitative and qualitative data to give additional assurance about the nature of the contaminant analyzed in workers' urine. A full scan and a product ion scan were acquired within the chromatographic peak acquired in MRM. For the two metabolites, the repeatability was 96%, the precision ≥97%, and the accuracy ≥93 ± 3%. The quantitative performances were not influenced by the inclusion of simultaneous full scan acquisition as compared to a usual quantitative approach. Footprints of each substance of interest were obtained at each injection, and full scan data can be interrogated for the presence of interferences and other contaminants. The method developed has been submitted to random real samples from both non‐occupationally and occupationally exposed workers. The urines of non‐occupationally exposed workers were all free of mandelic acid, phenylglyoxylic acid and putative interferences showing the high selectivity of the method. However, the urines of occupationally exposed workers were robustly quantified. The levels of mandelic acid and phenylglyoxylic acid ranged between 0.2 and 9 mM, and the footprints of each metabolite and structural information were acquired in parallel with the quantitative results, thus providing unquestionable data about the nature of the contaminant and the levels reported. The combination of qualitative information acquired simultaneously with quantitative results provides the structural information needed in case of questions, without any harmful effect on the robustness and throughput of the quantitative analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

毛细管胶束电动色谱在扁桃酸合成中的应用

扁桃酸是药物中间体,可以苯甲醛为原料在相转移催化剂作用下合成制得.为了选择最佳合成条件,提高扁桃酸的转化率,需要对合成过程中各组分的含量进行快速测定,及时指导最优合成条件的选择.产品扁桃酸中可能含有未反应的苯甲醛和副产品苯甲酸、苯甲醇等杂质.以往采用非水溶剂酸碱滴定分析法测定产品中扁桃酸的含量,但当产品中有苯甲酸等酸性物质存在时,会使测定结果偏高.由于待测样品中组分扁桃酸、苯甲酸酸性使沸点较高,     

Application de reactions d'hydroalumination en synthese organique: obtention d'α-alkyl α-hydroxyesters par addition enantioselective de tetraalkylaluminates AU phenylglyoxalate de (−) menthyle.

Using tetraalkylaluminates prepared via hydroalumination in THF of various vinyl compounds resulted in selective addition to the keto group of phenylglyoxylic acid (?) menthyl ester. Not only simple alkyl groups but also functionalized alkyl groups were added. By this way, a variety of α-substituted mandelic acid (?) menthyl esters were obtained with diastereomeric excesses close to 70%.     

Photolysis of dimethyldioxirane

Phosphorescence of methyl acetate formed by isomerization of electron-excited dimethyldioxirane is observed upon excitation at the wavelength of the absorption band of dimethyldioxirane in acetone at 77 K. The quantum yield of the photodecomposition of dimethyldioxirane at 296 K is equal to 13.1±0.7 mol Einstein⁻¹. The high quantum yield of photolysis is evidence for the chain mechanism of decomposition of dimethyldioxirane. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 938–941, May, 1997.     

Efficient Photodecarboxylation of Trifluoromethyl-substituted Phenylacetic and Mandelic Acids

A total of eight CF₃-substituted phenylacetic and mandelic acids are shown to undergo efficient photodecarboxylation (PDC; Φ = 0.37–0.74) in basic aqueous solution to give the corresponding trifluoromethyltoluenes or trifluoromethylbenzyl alcohols. The products are consistent with the almost exclusive formation of benzylic carbanions that subsequently react with water, with minor amounts (≤5%) of radical-derived products detected. Quenching studies indicate that the reaction likely proceeds from the singlet excited state. This work demonstrates that the CF₃ group greatly facilitates the excited state ionic PDC of phenylacetic acids.     

Unraveling the surface reactions during liquid-phase oxidation of benzyl alcohol on Pd/Al2O3: an in situ ATR-IR study

The palladium-catalyzed liquid-phase reaction of benzyl alcohol to benzaldehyde was investigated in the presence and absence of oxygen by attenuated total reflection infrared (ATR-IR) spectroscopy. The 5 wt % Pd/Al2O3 catalyst was fixed in a flow-through ATR-IR cell serving as a continuous-flow reactor. The reaction conditions (cyclohexane solvent, 323 K, 1 bar) were set in the range commonly applied in the heterogeneous catalytic aerobic oxidation of alcohols. The in situ ATR-IR study of the solid-liquid interface revealed a complex reaction network, including dehydrogenation of benzyl alcohol to benzaldehyde, decarbonylation of benzaldehyde, oxidation of hydrogen and CO on Pd, and formation of benzoic acid catalyzed by both Pd and Al2O3. Continuous formation of CO and its oxidative removal by air resulted in significant steady-state CO coverage of Pd during oxidation of benzyl alcohol. Unexpectedly, benzoic acid formed already in the early stage of the reaction and adsorbed strongly (irreversibly) on the basic sites of Al2O3 and thus remained undetectable in the effluent. This observation questions the reliability of product distributions conventionally determined from the liquid phase. The occurrence of the hydrogenolysis of the C-O bond of benzyl alcohol and formation of toluene indicates that Pd was present in a reduced state (Pd0) even in the presence of oxygen, in agreement with the dehydrogenation mechanism of alcohol oxidation.     

Kinetic study of oxidation of N‐(α‐methylbenzylidene) anilines by dimethyldioxirane

A kinetic study of the oxidation of substituted N‐(α‐methylbenzylidene) anilines by dimethyldioxirane was investigated using a UV/VIS spectrophotometer. Oxaziridines and nitrones were formed as intermediates, and in the excess of dimethyldioxirane corresponding carbonyl compounds, nitrosobenzene or nitrobenzene, were formed quantitatively. The kinetic data were used in the equation for the formation of oxaziridines and nitrones as an intermediate and further oxidation to the corresponding acetophenones and nitrosobenzene. Hammett ρ values were determined for compounds p‐substituted on the aromatic ring attached to the carbon atom of the imino group, and it was found that these substituents have very little effect on the oxidation reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 492–497, 2007     

Human urine certified reference material CZ 6009: creatinine,styrene metabolites (mandelic acid and phenylglyoxylic acid)

The reference material was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to styrene. The concentrations of mandelic acid (MA), phenylglyoxylic acid (PGA), and hippuric acid (HA) in urine were determined by three modes of high-performance liquid chromatography (HPLC). For isochronous stability testing the urinary mandelic acid and phenylglyoxylic acid concentrations were followed over a 24-month period for a preliminary batch by use of HPLC. No changes of the concentration values were found. The creatinine concentration was stable for more than five years. Standard Reference Material NIST 914a Creatinine was used for traceability purposes for creatinine. Pure chemicals MA and PGA were used for traceability purposes. Control material ClinChek-Urine Control (Recipe) was analyzed simultaneously. The mean values of MA and PGA compare well with the means and fall within the control range of control samples. Results from homogeneity, stability, and traceability testing were evaluated using the statistical program ANOVA. The certified values and their uncertainties were evaluated from the results of interlaboratory comparisons, and homogeneity and stability tests. The values are unweighed arithmetical averages of accepted results and their uncertainties are combined uncertainties (coverage factor=1).Abbreviations MA Mandelic acid - HA Hippuric acid - PGA Phenylglyoxylic acid - 3-HBA 3-Hydroxybenzoic acid - ANOVA Analysis of variance - CV Coefficient of variance - NIST National Institute of Standards and Technology - HPLC High-performance liquid chromatography     

Iodide-catalyzed reductions: development of a synthesis of phenylacetic acids

A new convenient and scalable synthesis of phenylacetic acids has been developed via the iodide catalyzed reduction of mandelic acids. The procedure relies on in situ generation of hydroiodic acid from catalytic sodium iodide, employing phosphorus acid as the stoichiometric reductant.     

Catalytic method for obtaining 2-aryl-substituted imidazolines

2-Arylimidazolines were synthesized catalytically on KU-2 ion-exchange resin by condensation of esters of aromatic acids (benzoic, phenylacetic, anthranilic, salicylic, and 3,5-di-tert-butylsalicylic) with ethylenediamine. From 30 to 48% of the diamide is formed in addition to the corresponding imidazolines in the condensation of the esters of benzoic and phenylacetic acids with ethylenediamine. The condensation of the esters of salicylic and 3,5-di-tert-butylsalicylic acids with ethylenediamine gave quantitative yields of the monoamide, which is dehydrated to 2-arylimidazoline during vacuum distillation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 383–385, March, 1972.