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Alcohol oxidation reaction kinetics

It was seen when analyzing the kinetic data for alcohol oxidation reactions that the catalytic action of nickel oxide is due to a mediator mechanism. Higher oxide forms interact with the adsorbed organic species and oxidize them. In the following step the higher oxide forms are regenerated by electrochemical oxidation of lower oxide forms. [Pg.545]

The oxidation of alcohols to aldehydes and ketones is one of the most common and well-studied reactions in organic chemistry [1], Many of these processes require organic or metal oxidants. It is much more desirable to find systems that utilize oxygen and a catalyst to perform alcohol oxidation, because of the environmental and economic benefits. A number of important advances have been made in this area, as described in the preceding section (IV.1.1.6). Recently, several groups have developed enantioselective aerobic alcohol oxidations, enabling kinetic resolution of secondary alcohols [2]. [Pg.393]

The stepwise reduction of NO2 to NO occurs at standard reduction potentials very close to the standard potential for the reduction of O2 to H2O (Table 15.1, Eqs. (15.1-15.3)). This relationship implies that NO cocatalysts are able to capture nearly the full thermodynamic driving force of O2 as a terminal oxidant [4]. This favorable feature, together with the kinetically facUe oxidation of NO to NO2 (Table 15.1, Eq. (15.4)), contributes to the effectiveness of NO -based cocatalysts in aerobic oxidation reactions. Depending on the reaction conditions, NO2 can equilibrate with other nitrogen oxide species, such as N2O4, and NO, which could also serve as catalytically relevant oxidants in NO -catalyzed aerobic alcohol oxidation reactions (Eq. (15.5)) [5]. [Pg.239]

Abstract The faster kinetics of the alcohol oxidation reaction in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel, and palladium, makes the alkaline direct alcohol fuel cell a potentially low-cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. In this work an overview of catalysts for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol, and ethylene glycol, formed by these materials, is presented. [Pg.89]

In direct alcohol fuels cells (DAFCs), some simple organic molecules such as methanol, ethanol, formic acid, and ethylene glycol are used as alternative fuels. Besides the slow kinetics of ORR in the cathode, the slow alcohol oxidation reaction on Pt is another major contribution to low DAFC performance. [Pg.751]

Chapter 1 discusses the current status of electrocatalysts development for methanol and ethanol oxidation. Chapter 2 presents a systematic study of electrocatalysis of methanol oxidation on pure and Pt or Pd overlayer-modified tungsten carbide, which has similar catalytic behavior to Pt. Chapters 3 and 4 outline the understanding of formic acid oxidation mechanisms on Pt and non-Pt catalysts and recent development of advanced electrocatalysts for this reaction. The faster kinetics of the alcohol oxidation reaction in alkaline compared to acidic medium opens up the possibility of using less expensive metal catalysts. Chapters 5 and 6 discuss the applications of Pt and non-Pt-based catalysts for direct alcohol alkaline fuel cells. [Pg.752]

However, the kinetics of alcohol oxidation reaction (AOR) is sluggish and Pt is considered as the best electrocatalyst for oxidation of alcohols in acid medium [9,10]. The electrocatalysis of AOR involves a multi-electron transfer and multi-step mechanism with formation of many... [Pg.453]

Since the transition state for alcohol oxidation and ketone reduction must be identical, the product distribution (under kinetic control) for reducing 2-butanone and 2-pentanone is also predictable. Thus, one would expect to isolate (R)-2-butanol if the temperature of the reaction was above 26 °C. On the contrary, if the temperature is less than 26 °C, (S)-2-butanol should result in fact, the reduction of... [Pg.208]

The complex Pd-(-)-sparteine was also used as catalyst in an important reaction. Two groups have simultaneously and independently reported a closely related aerobic oxidative kinetic resolution of secondary alcohols. The oxidation of secondary alcohols is one of the most common and well-studied reactions in chemistry. Although excellent catalytic enantioselective methods exist for a variety of oxidation processes, such as epoxidation, dihydroxy-lation, and aziridination, there are relatively few catalytic enantioselective examples of alcohol oxidation. The two research teams were interested in the metal-catalyzed aerobic oxidation of alcohols to aldehydes and ketones and became involved in extending the scopes of these oxidations to asymmetric catalysis. [Pg.84]

This reaction can be used as a kinetic test to determine which radicals predominate in an alcohol oxidized under given conditions. If hydroxyperoxide radicals predominate, the... [Pg.294]

The reaction rate is half-order in palladium and dimeric hydroxides of the type shown are very common for palladium. The reaction is first order in alcohol and a kinetic isotope effect was found for CH2 versus CD2 containing alcohols at 100 °C (1.4-2.1) showing that probably the (3-hydride elimination is rate-determining. Thus, fast pre-equilibria are involved with the dimer as the resting state. When terminal alkenes are present, Wacker oxidation of the alkene is the fastest reaction. Aldehydes are prone to autoxidation and it was found that radical scavengers such as TEMPO suppressed the side reactions and led to an increase of the selectivity [18],... [Pg.332]

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. [Pg.51]

DMFCs and direct ethanol fuel cells (DEFCs) are based on the proton exchange membrane fuel cell (PEM FC), where hydrogen is replaced by the alcohol, so that both the principles of the PEMFC and the direct alcohol fuel cell (DAFC), in which the alcohol reacts directly at the fuel cell anode without any reforming process, will be discussed in this chapter. Then, because of the low operating temperatures of these fuel cells working in an acidic environment (due to the protonic membrane), the activation of the alcohol oxidation by convenient catalysts (usually containing platinum) is still a severe problem, which will be discussed in the context of electrocatalysis. One way to overcome this problem is to use an alkaline membrane (conducting, e.g., by the hydroxyl anion, OH ), in which medium the kinetics of the electrochemical reactions involved are faster than in an acidic medium, and then to develop the solid alkaline membrane fuel cell (SAMFC). [Pg.5]

The structural, spectroscopic and electrochemical properties of oxoruthenate (IV) complexes have been summarised, and a representative compilation of kinetic parameters for their oxidation reactions with alcohols, alkanes and alkenes presented [20],... [Pg.70]

The kinetics of secondary alcohol oxidation has been investigated with various reactants. When 2-octanol is oxidized with acetone solvent in the presence of excess reactant, the reaction is first-order with respect to H2O2 and zero-order with respect to the alcohol. Typical results are presented in Fig. 21. [Pg.300]

The [3-hydroxy amines are a class of compounds falling within the generic definition of Eq. 6A.6. When the alcohol is secondary, the possibility for kinetic resolution exists if the Ti-tartrate complex is capable of catalyzing the enantioselective oxidation of the amine to an amine oxide (or other oxidation product). The use of the standard asymmetric epoxidation complex (i.e., T2(tartrate)2) to achieve such an enantioselective oxidation was unsuccessful. However, modification of the complex so that the stoichiometry lies between Ti2 (tartrate) j and Ti2(tartrate)1 5 leads to very successful kinetic resolutions of [3-hydroxyamines. A representative example is shown in Eq. 6A.11 [141b,c]. The oxidation and kinetic resolution of more than 20 secondary [3-hydroxyamines [141,145a] provides an indication of the scope of the reaction and of some... [Pg.273]

C kinetic isotope effects (KIEs) of four cinnamyl alcohol oxidations have been determined by 13C NMR spectroscopy using competition reactions with reactants at natural 13C abundance. Primary 13C KIEs of the Pd(II)-catalysed oxidation and of the MnC>2 oxidation are similar ( 1.02) and indicate the C—H bond cleavages to be the irreversible and rate-limiting steps in the respective reactions. Low primary 13C KIEs in Swern and Dess-Martin oxidations, however, indicate that the initial C—H bond breakings and proton transfers are not the irreversible steps in these mechanisms, which control the rate.284... [Pg.124]


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See also in sourсe #XX -- [ Pg.453 ]




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