Kinetics of oxidation and comproportionation reactions involving an oxammonium ion,benzyl alcohol and methyltrioxorhenium(VII)

The reactions of 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinium N‐oxide, an oxammonium ion abbreviated R₂NO⁺, have been studied. The previously unreported triflate salt was used in this study because the anions of the usual chloride and bromide salts can themselves be oxidized. Reactions between R₂NO⁺ and alcohols produce ketones and aldehydes; the rate constant for PhCH₂OH is 4.4 × 10⁻³ L mol⁻¹ s⁻¹ in acetonitrile at 298 K. The immediate product is the hydroxylamine, R₂NOH, but its further comproportionation reaction with R₂NO⁺ yields the stable piperidinyl oxyl radical, R₂NO^·. The rate constant of this reaction is 1.78 × 10³ L mol⁻¹ s⁻¹ at 298 K. The possibility of using R₂NO⁺ and MTO as co‐catalysts for the oxidation of alcohols was explored, but the competitive rates are such that the resultant is not particularly attractive. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 381–385, 1999     

Kinetic study of the oxidation of alcohols by cetyltrimethylammonium permanganate

Kinetics of the oxidation of 2-propanol, 1-butanol, 2-butanol and 1-pentanol by cetyltrimethylammonium permangenate oxidant have been investigated. The reactions are autocatalytic, colloidal manganese dioxide as one of the reaction products has been identified as the auto-catalyst.

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2-, 1-, 2- 1- . . , , .

     

Kinetics and mechanism of the oxidation of substituted benzylamines by cetyltrimethylammonium permanganate

Oxidation of meta- and para-substituted benzylamines by cetyltrimethylammonium permanganate (CTAP) to the corresponding aldimines is first order with respect to both the amine and CTAP. Oxidation of deuteriated benzylamine (PhCD₂NH₂) exhibited the presence of a substantial kinetic isotope effect (k _H /k _D = 5.60 at 293 K). This confirmed the cleavage of an α-C-H bond in the rate-determining step. Correlation analyses of the rates of oxidation of 19 monosubstituted benzylamines were performed with various single and multiparametric equations. The rates of the oxidation showed excellent correlations in terms of Yukawa—Tsuno and Brown’s equations. The polar reaction constants are negative. The oxidation exhibited an extensive cross-conjugation, in the transition state, between the electron-donating substituents and the reaction centre. A mechanism involving a hydride-ion transfer from the amine to CTAP in the rate-determining step has been proposed.     

Water oxidation intermediates applied to catalysis: benzyl alcohol oxidation

Four distinct intermediates, Ru(IV)═O(2+), Ru(IV)(OH)(3+), Ru(V)═O(3+), and Ru(V)(OO)(3+), formed by oxidation of the catalyst [Ru(Mebimpy)(4,4'-((HO)(2)OPCH(2))(2)bpy)(OH(2))](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl) and 4,4'-((HO)(2)OPCH(2))(2)bpy = 4,4'-bismethylenephosphonato-2,2'-bipyridine] on nanoITO (1-PO(3)H(2)) have been identified and utilized for electrocatalytic benzyl alcohol oxidation. Significant catalytic rate enhancements are observed for Ru(V)(OO)(3+) (~3000) and Ru(IV)(OH)(3+) (~2000) compared to Ru(IV)═O(2+). The appearance of an intermediate for Ru(IV)═O(2+) as the oxidant supports an O-atom insertion mechanism, and H/D kinetic isotope effects support net hydride-transfer oxidations for Ru(IV)(OH)(3+) and Ru(V)(OO)(3+). These results illustrate the importance of multiple reactive intermediates under catalytic water oxidation conditions and possible control of electrocatalytic reactivity on modified electrode surfaces.     

Solvent-free reactions using cetyltrimethylammonium permanganate and cetyltrimethylammonium dichromate-cis-1,2-dihydroxylation of alkenes,oxidation of alcohols and regeneration of aldehydes and ketones from oximes

Cetyltrimethylammonium permanganate (CTAP) and cetyltrimethylammonium dichromate (CTAD) have been known to be good oxidizing agents in organic solvent media. This homogeneous solution phase procedure itself is a useful advantage over oxidation reactions carried out employing inorganic manganese salts (e.g., KMnO₄) or chromium salts (e.g., Kr₂Cr₂O₇) performed under heterogeneous conditions. Now we have found that oxidation reactions using CTAP or CTAD do not require a solvent medium, and can be performed under completely solvent-free conditions. We have carried out 1,2-dihydroxylation of olefins with CTAP, oxidation of alcohols to aldehydes/ketones with CTAD, and regeneration of aldehydes and ketones from their oxime derivatives using either reagent, essentially under solid phase conditions. The results are excellent. As a dihydroxylating agent the CTAP is so good that it should be able to replace the highly toxic and expensive OsO₄ for this reaction.     

Reactivity of an adsorbed Ru(VI)-oxo complex: oxidation of benzyl alcohol

The phosphonated ruthenium complex, [Ru(tpy-PO(3)H(2))(OH(2))(3)](2+) (1) (tpy-PO(3)H(2) = 4'-phosphonato-2,2':6',2' '-terpyridine), was synthesized and attached to glass|ITO or glass|ITO|TiO(2) electrodes. After attachment to the metal oxide surface through the phosphonate linkage, 1 can be oxidized (either chemically or electrochemically) to the reactive Ru(VI)-dioxo complex, glass|ITO|[((HO)(2)OP)tpy)RuVI(O)(2)(OH(2))](2+), which remains attached to the surface. The attached Ru(VI) complex reacts with benzyl alcohol through mechanisms similar to those proposed for the solution analog. More specifically, Ru(VI) is reduced in a stepwise fashion to Ru(IV) and then finally to Ru(II). The reduction of Ru(VI) is accompanied by a rate-limiting insertion to the C-H bond of benzyl alcohol, followed by solvolysis of the aldehyde hydrate. In addition, the surface-bound Ru(VI) acts as an electrooxidation catalyst which carries out approximately 130 (2e(-)) turnovers before deactivation.     

Kinetics of oxidation of benzyl alcohol by sodium N-chloro-p-toluenesulfonamide

The kinetics of oxidation of benzyl alcohol and substituted benzyl alcohols by sodium N-chloro-p-toluenesulfonamide (chloramine-T, CAT) in HClO₄ (0.1–1 mol/dm³) containing Cl^? ions, over the temperature range of 30–50°C have been studied. The reaction is of first order each with respect to alcohol and oxidant. The fractional order dependence of the rate on the concentrations of H⁺ and Cl^? suggests a complex formation between RNCl^? and HCl. In higher acidic chloride solution the rate of reaction is proportional to the concentrations of both H⁺ and Cl^7hyphen;. The observed solvent isotope effect (k/k) is 1.43 at 30°C. The reaction constant (p = ?1.66) and thermodynamic parameters are evaluated. Rate expressions and probable mechanisms for the observed kinetics have been suggested.     

A novel lipopathic Cr(VI) oxidant for organic substrates: Kinetic study of oxidation of benzyl alcohol

A novel lipopathic oxidizing agent, cetyltrimethylammonium dichromate, was used for oxidation of benzyl alcohol in various organic solvents and in surfactant systems. The reaction kinetics was investigated with change in [acid], [substrate], [oxidant], [surfactant], and temperature. The rate constant values led to propose that the reaction occurs in a reversed micellar system produced by the oxidant, akin to an enzymatic environment. The rate variation with variation in [surfactant] and solvent isotope effect suggest that the path of reaction to be through the formation of an ester complex, the decomposition of which is the rate‐determining step. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 651–656, 2006     

负载型Pd-Ni双金属纳米颗粒在无溶剂苯甲醇氧化中有效抑制甲苯的生成

醇类化合物的选择性氧化是实验室和工业应用中一类重要的官能团转化反应.以分子氧为氧化剂,在液相无溶剂条件下温和氧化符合绿色化学的要求.负载型Pd基催化剂因其优异的催化活性而在该反应中得到广泛应用.但是,单金属Pd催化剂对反应目标产物醛类化合物的选择性还有待提高.例如,在苯甲醇液相无溶剂氧化中,甲苯是在单金属Pd催化剂上的主要副产物.针对这一问题,除了对载体进行改性和修饰外,开发双金属Pd基催化剂也是一种有效的选择性调控策略.虽然已有的Pd-Au双金属催化剂可以在一定程度上降低甲苯的选择性,但是在较高温度和较高转化率下仍然难以控制甲苯的大量生成.本文采用固相合金化法合成了负载型Pd-Ni双金属纳米颗粒.该方法首先以硝酸镍为镍的前驱体浸渍介孔二氧化硅,然后负载钯纳米颗粒.在高温固相还原条件下,作为种子的钯纳米颗粒和镍通过原子迁移和生长,形成Pd-Ni双金属纳米颗粒.扫描透射电镜、能量色散X射线光谱、X射线衍射和X射线光电子能谱等表征证实了Pd-Ni双金属纳米颗粒的生成.上述催化剂用于苯甲醇液相无溶剂氧化,催化结果显示Ni的加入可以抑制副产物甲苯的生成,并且随Ni负载量增加,甲苯的选择性(在80%等转化率下)由22.6%(单金属Pd)降低至1.6%(双金属Pd1Ni20).尽管Ni的加入降低了单金属Pd的活性,但是由于提高了目标产物苯甲醛的选择性,醛的最终产率得到提升.进一步催化研究表明,Ni的加入可以抑制无氧氛围下甲苯的生成,说明Ni可以抑制歧化反应和降低表面氢浓度.这种作用可归结于Pd-Ni双金属的协同效应.该效应得到了CO吸附的傅里叶变换漫反射红外光谱和密度泛函理论研究的证实.双金属的几何效应和电子效应均减弱了苯甲醇在双金属纳米颗粒表面的解离吸附和相互作用,导致苯甲醇的吸附减弱,同时C–O键断裂不易进行.另外,由于Ni的亲氧性,双金属纳米颗粒表面有利于氧的吸附,降低吸附氢的浓度,减少C–H键生成,从而抑制甲苯的生成.     

(N-Benzyl-bis-N',N'-salicylidene)-cis-1,3,5-triaminocyclohexane copper(II): a novel catalyst for the aerobic oxidation of benzyl alcohol

Reaction of Cu(BF(4))(2).6H(2)O with the N(3)O(2) donor ligand H(2)L (where H(2)L = N-benzyl-N',N'-di-tert-butyl-disalicyl-triaminocyclohexane) results in the formation of a novel Cu(II)L complex, 1. X-Ray crystallography of it shows the Cu(II) centre coordinated by two phenolate oxygens and two imine nitrogens in a distorted square plane with an elongated bond to the amine nitrogen (2.512 A) in the axial position. EPR spectroscopy gives g values of g(1) = 2.277, g(2) = 2.100, g(3) = 2.025, and A(1) = 15.6 mT which are consistent with the distorted square pyramidal coordination environment determined from the X-ray structure. UV/visible and electrochemical analysis of shows that it undergoes two reversible processes assigned to the successive oxidation of the phenolate oxygens to phenoxyl radicals, the first at E((1/2)) = 0.89 V (DeltaE = 81 mV, vs. Ag/AgCl) and the second at E((1/2)) = 1.13V (DeltaE = 84 mV, vs. Ag/AgCl). Chemical oxidation results in the formation of a species, assigned as [1](+)(.) which is EPR silent due to antiferromagnetic coupling between the Cu(II) centre and the bound phenoxyl radical. The oxidised species catalyses the oxidation of benzyl alcohol to benzaldehyde.     

Biocatalytic oxidation of benzyl alcohol to benzaldehyde via hydrogen transfer

Various types of biocatalysts like oxidases, alcohol dehydrogenases, and microbial cells were tested for the oxidation of benzyl alcohol. Oxidases in combination with molecular oxygen led to low conversion. Alcohol dehydrogenases and microbial cells were tested in a hydrogen transfer reaction employing acetaldehyde, chloroacetone, and acetone as hydrogen acceptor. Excellent conversion (95%) could be achieved employing lyophilised cells of Janibacter terrae DSM 13953 at a substrate concentration of 97 mM.     

Correlation analysis of structure and reactivity in the oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate

The oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate (BBCP), leading to the corresponding benzaldehydes is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the alcohols. The oxidation of a,a-dideuteriobenzyl alcohol indicated the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzyl alcohols were correlated in terms of Charton's triparametric LDR equation whereas ortho- substituted benzyl alcohols were correlated with a four parametric LDRS equation. The results of correlation analyses point to an electron-deficient reaction center in the transition state. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 9–16, 1997.     

Kinetics and mechanism of the oxidation of benzyl alcohol by potassium chlorochromate

The kinetics of the oxidation of benzyl alcohol by potassium chlorochromate, KCrClO₃, has been studied in dimethyl sulfoxide-dichloromethane medium. The reaction is catalyzed by acid. The effects of temperature and solvent composition were studied and activation parameters evaluated. Probable mechanisms are discussed.

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, KCrClO₃, . . . .

     

Kinetic study of the ruthenium(VI)‐catalyzed oxidation of benzyl alcohol by alkaline hexacyanoferrate(III)

The kinetics of the Ru(VI)‐catalyzed oxidation of benzyl alcohol by hexacyanoferrate(III), in an alkaline medium, has been studied using a spectrophotometric technique. The initial rates method was used for the kinetic analysis. The reaction is first order in [Ru(VI)], while the order changes from one to zero for both hexacyanoferrate(III) and benzyl alcohol upon increasing their concentrations. The rate data suggest a reaction mechanism based on a catalytic cycle in which ruthenate oxidizes the substrate through formation of an intermediate complex. This complex decomposes in a reversible step to produce ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in a slow step. The theoretical rate law obtained is in complete agreement with all the experimental observations. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 421–429, 2002     

Efficient oxidation of benzyl alcohol with heteropolytungstate as reaction-controlled phase-transfer catalyst

A series of heteropolytungstates has been synthesized and utilized as catalysts to catalyze oxidation of benzyl alcohol with aqueous hydrogen peroxide.The results indicated that three of these catalysts showed the properties of reaction-controlled phase- transfer catalysis,and they had excellent catalytic ability to the oxidation of benzyl alcohol.No other by-products were detected by gas chromatography.Once the hydrogen peroxide was consumed completely,the catalyst precipitated from solvent,and the results of the catalyst recycle showed that the catalyst had high stability.     

Kinetics and mechanism of oxidation of ethanol,isopropanol and benzyl alcohol by chromium(VI) in perchloric acid medium

Chromium(VI) oxidation of some alkanols has been studied in perchloric acid medium. The reactions are first order with respect to [substrate] and [HCrO₄^-]. The order with respect to [H⁺]is between 1 and 2 for all the reactions. The activation parameters of the reactions have been calculated. A mechanism consistent with the above facts has been suggested. An attempt has been made to correlate the rate of the reactions with the structure of the substrates.     

Kinetics and mechanism of the oxidation of selenium(IV) by permanganate

Summary The oxidation of selenium(IV) by permanganate has been studied kinetically in acid, neutral and alkaline media. The reaction exhibits unit-order dependence on selenium(IV) and permanganate in all the three media. Manganese(VI) retards the reaction in alkaline medium. The rate-limiting step is the same in all the three media, but the stoichiometry is different, being 2:1 in alkaline medium, 2:3 in neutral medium and 2:5 in acid medium. Evidence has been obtained for a one electron-transfer in the rate-determining step.