Oxidation of Arylthiourea by Cetyltrimethylammonium Dichromate

With a view to investigate the oxidation behaviors of cetyltrimethylammonium dichromate on multifunctional groups, some arylthioureas were subjected to oxidation, both in neutral and in acidic conditions. In neutral conditions, the products were found to be a mixture of corresponding urea and isonitrile. In acidic conditions, the products were corresponding ureas only. A probable mechanism was proposed for the formation of the product, wherein the first step involves coupling of –NH₂ and –SH of one molecule to the –NH₂ and –SH of another molecule, respectively, which is followed by removal of nitrogen and sulfur. The microwave irradiation resulted in great yield of isonitrile than urea in neutral conditions.

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Selective Oxidation of Arylaldoximes by Cetyltrimethylammonium Dichromate to Arylaldehydes and Arylnitriles

Aldoxime is converted into corresponding nitrile derivative on treatment with cetyltrimethylammonium dichromate.     

Selective Oxidation of Alcohols Using Benzyldimethyltelluronium Dichromate

Selective oxidation of benzylic, allylic, and saturated secondary alcohols to the corresponding aldehydes or ketones by benzyldimethyltelluronium dichromate is described.     

Oxidation of Antitubercular Drug Isoniazid by a Lipopathic Oxidant,Cetyltrimethylammonium Dichromate: A Mechanistic Study

The oxidation of an antitubercular drug isoniazid by a lipopathic oxidant cetyltrimethylammonium dichromate (CTADC) in a nonpolar medium generates isonicotinic acid both in the presence and the absence of acetic acid. The conventional UV–vis spectrophotometric method is used to study the reaction kinetics. The occurrence of the Michaelis–Menten–type kinetics with respect to isoniazid confirms the binding of oxidant and substrate to form a complex before the rate‐determining step. The existence of the inverse solvent kinetic isotope effect, k(H₂O)/ k(D₂O) = 0.7, in an acid‐catalyzed reaction proposes a multistep reaction mechanism. A decrease in the rate constant with an increase in [CTADC] reveals the formation of reverse micellar–type aggregates of CTADC in nonpolar solvents. In the presence of different ionic and nonionic surfactants, CTADC forms mixed aggregates and controls the reaction due to the charge on the interface and also due to partition of oxidant and substrate in two different domains. High negative entropy of activation (ΔS^? = –145 and –159 J K^?1 mol^?1 in the absence and presence of acetic acid) proposes a more ordered and highly solvated transition state than the reactants. Furthermore, the solvent polarity‐reactivity relationship reveals (i) the presence of less polar and less ionic transition state compared to the reactants during the oxidation, (ii) differential contribution from nonpolar and dipolar aprotic solvents toward the reaction process, and (iii) the existence of polarity/hydrophobic switch at log P = 0.73. A suitable mechanism has been proposed on the basis of experimental results. These results may provide insight into the mechanism of isoniazid oxidation in hydrophobic environment and may assist in understanding the drug resistance in different location.     

Kinetics and Mechanism of Cetyltrimethylammonium Bromide Catalyzed N-Bromosuccinimide Oxidation of D-Mannose in Acidic Medium

The kinetics and mechanism of N-bromosuccinimide (NBS) oxidation of D-mannose in the absence and presence of cetyltrimethylammonium bromide (CTAB) in acidic media have been studied under the condition [D-mannose]_T ? [NBS]_T at 40°C. Under the kinetic conditions, both the slower uncatalyzed and faster catalyzed paths go on. Both the paths show the fractional and first order dependence on [D-mannose] and [NBS]_T, respectively. The rate decreased with increase in acidity. Neither succinimide (NHS) nor Hg(II) influenced the reaction rate. Activation parameters of the reactions were determined by studying the reaction at different temperatures (30–50°C). The influence of salts on the reaction rate was also studied. CTAB accelerates the reactions and the observed effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. In the reaction, approximately 1 mole of NBS oxidized one mole of D-mannose. A reaction scheme of the oxidation of D-mannose by NBS was found to be in consistent with the rate law and the reaction stoichiometry.     

Synthesis of Nicotinic Acid by Potassium Dichromate Oxidation

IntroductionNicotinic acid,whose IUPAC name is 3-pyridine formic acid,also known as Vitamine B5,ismainly used as an additive in food,drink andforage industry[1— 3 ] .In medical practice,it is usedto cure pellagra and other relative vitaminedeficiency illness. It is also an intermediate for thesynthesis of important medicines and chemicalmaterials[1,4] . In China,the demand of nicotinicacid is very big. However,there are manyproblems in the current preparation methods ofnicotinic acid,such…     

Quinolinium Dichromate Oxidation of Diols: A Kinetic Study

Quinolinium dichromate (QDC) in water oxidizes vicinal and nonvicinal diols to the corresponding alpha-hydroxy carbonyl compound. The rate is proportional to the concentrations of diol, oxidant and hydrogen ions, and the reactions proceed almost twice as fast in D(2)O than in H(2)O. These data can be correlated with a mechanistic pathway involving the intermediate formation of a chromate ester, which undergoes decomposition to give the product.     

Efficient Oxidation of Hantzsch 1,4-Dihydropyridines with Nicotinium Dichromate

A convenient method for the oxidation of various 4-substituted Hantzsch 1,4-dihydropyridines with nicotinium dichromate (NDC) in refluxing acetonitrile is reported. The yields obtained are excellent.     

重铬酸钾电化学合成反应表观动力学

针对重铬酸钾传统生产技术存在的高污染、高消耗等问题,研究了用电化学合成绿色技术.由在自制电解槽中以铬酸钾为原料电化学合成重铬酸钾的反应动力学实验,测得不同反应条件下的动力学数据.结果表明,电化学合成反应过程表现为拟零级反应动力学特征.建立了电化学合成反应表观动力学方程和阳极电解液体积随转化率的变化方程,求得了动力学参数...     

Comparing Dichromate Oxidation and Size Exclusion Chromatography of Dissolved Carbohydrates

Standardised methods are used to characterise the pulp or cellulosic material for its alkali resistance and alkali solubility. Today, pulp is usually characterised by its solubility in sodium hydroxide. The characterisation test was based on the treatment of pulp with sodium hydroxide solution of a defined concentration, according to a specified procedure. The dissolved organic matter was then determined by dichromate oxidation. The results obtained by size exclusion chromatography showed that both the amount and the molecular weight of the dissolved carbohydrates vary when investigating solubility and α-cellulose content of pulps. The results show further that S₁₈ values obtained by dichromate oxidation are overestimated when characterising pulps containing higher amounts of hemicellulose and/ or short chain cellulose, compared with results obtained by the SEC method. On the contrary, S₁₀ values are overestimated when determined by dichromate oxidation in higher alpha pulps.     

Kinetics and Mechanism of Styrene Oxidation Using Transition Metal Substituted Dodecatungstophosphate

Tetraalkylammonium (TAA) salts of transition metal substituted dodecatungstophosphate, (TAA)5PW11O39.H₂O (where TAA = (C₂H₅)4N (TEA), (C3H7)4N (TPA), and (C₄H9)4N (TBA), and M = Mn ₂+ , Fe ₂+ and Co₂ ) catalyzed the oxidation of styrene with H₂O₂ at 353 K. Except for the Mn ₂+ salt, other TAA salts were found to be active and gave mainly benzaldehyde and styrene oxide products. Among the catalyst tested, TBA (tetrabutylammonium) salt of Co ₂+ was more active in styrene oxidation. Kinetics of TBA-PW11CoO₃₉ catalyzed oxidation of styrene have been investigated and mehanism for oxidation of styrene has been proposed.     

重铬酸烟酰胺的合成及其选择性氧化作用

吡啶及季铵[1,2]的重铬酸盐是由醇制备醛和酮的优良的氧化剂,此类氧化剂的氧化反应具有反应条件温和、选择性强,产率较高等优点.然而,所有这些氧化反应须在有机溶剂中进行,而且氧化剂用量大大超过醇[3],价格昂贵.本文报道一种新型氧化剂重铬酸烟酰胺盐,可以在水溶液中进行氧化反应,且亦能表现出上述优良氧化剂的特点.重铬酸烟酰胺是较稳定的水溶性氧化剂,其制备方便、安全、易于保存,是一种可广泛使用的氧化剂.     

Oxidation of Substituted Benzyl Alcohols by Quinoxalinium Dichromate. A Kinetic Study

Summary. Quinoxalinium dichromate (QxDC) oxidizes benzyl alcohol and substituted benzyl alcohols smoothly in dimethyl sulfoxide (DMSO) and in the presence of acid to the corresponding aldehydes. The reaction has unit dependence on each of the alcohol, QxDC, and acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electron-withdrawing groups retard the reaction, and the rate data obey Hammetts relationship. The reaction constant was –1.09±0.01 at 303K. Oxidation of ,-dideuteriobenzyl alcohol indicated the presence of a substantial primary kinetic isotope effect (k_H/k_D=6.78 at 303K). The reaction failed to induce the polymerization of acrylonitrile. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The analysis of the dependence of the kinetic isotope effect on temperature indicated that the reaction involves a symmetrical cyclic transition state. A suitable mechanism is proposed.     

Microwave-assisted Oxidation of Alcohols and Polyarenes with Cetyltrimethylammonium Bromochromate

An efficient and mild methodology for oxidation of alcohols and polyarenes was described using cetyltrimethylammonium bromochromate (CTMABC) under microwave irradiation. Primary and secondary alcohols and polyarenes could be selectively oxidized under microwave irradiation into the corresponding aldehydes and ketones in high yields and short reaction time, using commercially available and magnetically retrievable oxidative material (CTMABC).     

Dawson-型磷钼钒杂多酸盐相转移选择催化氧化苯甲醇合成苯甲醛反应研究

以Dawson型磷钼钒杂多酸盐为相转移催化剂，用过氧化氢水溶液为氧化剂，研究了苯甲醇液相选择氧化制苯甲醛的反应．系统考察了催化剂的类型、催化剂用量、反应温度和反应时间等因素对反应的影响．结果表明：(Cpry)6HP2Mo17VO62／H2O2／H2O是一可循环使用的苯甲醇选择氧化制苯甲醛的高效环境友好催化剂体系，适宜的反应条件为，催化剂用量2μmol，H2O2 10mmol，反应温度80℃，反应时间8h．     

Oxidation of Substituted Benzyl Alcohols by Quinoxalinium Dichromate. A Kinetic Study

Quinoxalinium dichromate (QxDC) oxidizes benzyl alcohol and substituted benzyl alcohols smoothly in dimethyl sulfoxide (DMSO) and in the presence of acid to the corresponding aldehydes. The reaction has unit dependence on each of the alcohol, QxDC, and acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electron-withdrawing groups retard the reaction, and the rate data obey Hammetts relationship. The reaction constant was –1.09±0.01 at 303K. Oxidation of ,-dideuteriobenzyl alcohol indicated the presence of a substantial primary kinetic isotope effect (k_H/k_D=6.78 at 303K). The reaction failed to induce the polymerization of acrylonitrile. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The analysis of the dependence of the kinetic isotope effect on temperature indicated that the reaction involves a symmetrical cyclic transition state. A suitable mechanism is proposed.     

Kinetic Features of the Oxidation of Aliphatic Dialdehydes by Quinolinium Dichromate1

Kinetic data on the rates of quinolinium dichromate oxidation of glyoxal and glutaraldehyde are determined and discussed with reference to aldehyde hydration equilibria. The effect of variations in solvent composition and temperature are studied. The solvent effect is analyzed. Kinetic results support a pathway via a rate-determining oxidative decomposition of a chromate ester of an aldehyde hydrate. A cyclic transition state is suggested; being a Hückel-type system (4n + 2), this is an allowed process.     

Oxidation of Alcohols with a New Neutral System of Potassium Dichromate in Dimethylformamide

A new and convenient procedure for the preparation of aldehydes and ketones by the oxidation of the corresponding primary and secondary alcohols with a neutral potassium dichromate-dimethylformamide system is described.