Alcohols methanol oxidation

The mechanism of the simplest alcohol (methanol) oxidation on Pt has been studied for several decades as it is the only alcohol that does not need the C-C bond breaking for a full oxidation to CO2. However, it can be seen that the number of electrons per molecule of alcohol increases from 6 tol2 when exchanging methanol with ethanol as the fuel. Under standard conditions, AG° = 1,325 kJ/mol and standard... 

Esters of the homologous acids are prepared by adding silver oxide in portions rather than in one lot to a hot solution or suspension of the diazo ketone in an anhydrous alcohol (methyl, ethyl or n-propyl alcohol) methanol is generally used and the silver oxide is reduced to metallic silver, which usually deposits as a mirror on the sides of the flask. The production of the ester may frequently be carried out in a homogeneous medium by treating a solution of the diazo ketone in the alcohol with a solution of silver benzoate in triethylamlne. 

Butyl alcohol is employed as a feedstock in Japan to make methyl methacrylate monomer. In one such process (26), the alcohol is oxidized (in two steps) to acryHc acid, which is then esterified with methanol. In a similar process (27), /-butyl alcohol is oxidized in the presence of ammonia to give methacrylonitrile [126-98-7]. The latter is hydrolyzed to methacrjiamide [79-39-0] which then reacts with methanol to yield methyl methacrylate [80-62-6]. 

Secondary alcohols are oxidized at room temperature to ketones in high yields by HOCl generated in situ from aqueous NaOCl and acetic acid (109,110). Selective oxidation in the presence of a primary alcohol is possible. In methanol, aldehydes are oxidized to methyl esters (110). Under the proper conditions, alcohols can be esterified with HOCl forming isolable alkyl hypochlorites. 

Liver alcohol dehydrogenase (ADH) is relatively nonspecific and will oxidize ethanol or other alcohols, including methanol. Methanol oxidation yields formaldehyde, which is quite toxic, causing, among other things, blindness. Mistaking it for the cheap... 

These are diamagnetic 16 electron species (reaction in methanol or 2-meth-oxyethanol gives OsH(CO)Cl(PR3)2, presumably because the alcohol is oxidized to an aldehyde that can be a source of CO) (Figure 1.65). These... 

A few results have been reported on the oxidation of cyclohexanol by acidic permanganate In the absence of added fluoride ions the reaction is first-order in both alcohol and oxidant , the apparent first-order rate coefficient (for excess alcohol) at 25 °C following an acidity dependence k = 3.5-1-16.0 [H30 ]sec fcg/A , depends on acidity (3.2 in dilute acid, 2.4 in 1 M acid) and D2o/ H20 is f-74. Addition of fluoride permitted observation of the reaction for longer periods (before precipitation) and under these conditions methanol is attacked at about the same rates as di-isopropyl ether, although dioxan is oxidised over twenty times more slowly. The lack of specificity and the isotope effect indicates that a hydride-ion abstraction mechanism operates under these conditions. (The reactivity of di-isopropyl ether towards two-equivalent oxidants is illustrated by its reaction with Hg(II).) Similar results were obtained with buffered permanganate. 

OH/oxide species. At potentials anodic of 1 V, incomplete oxidation of formaldehyde to formic acid is activated, while methanol oxidation is almost completely hindered. This reflects an easier oxidation of the C-H group in the aldehyde than in the alcohol. For the negative-going scan, where the COadouble-peak stmcture in the current efficiency. 

Although the complete mechanism for each of the previously described reactions is not known, substantial details have been worked out. First, it is clear that Ti is incorporated into the framework of the silicalite structure. Too much Ti (more than about 2.5%) in the preparation steps forms nonframework TiOz crystallites, which decompose H202. Second, the rate enhancement due to methanol suggests a tight association at the Ti active site as shown in Fig. 6.8.37,38 This is supported by the fact that methanol oxidizes much more slowly than other alcohols.47 This tight coordination of methanol is proposed to increase the electrophilicity of the Ti-coordinated H202 and facilitate oxygen transfer to the alkene.31... 

The same group, in a previous work, reported on the realization of a hybrid anode electrode [197]. An appreciable improvement in methanol oxidation activity was observed at the anode in direct methanol fuel cells containing Pt-Ru and Ti02 particles. Such an improvement was ascribed to a synergic effect of the two components (photocatalyst and metal catalyst). A similar behavior was also reported for a Pt-Ti02-based electrode [198]. Another recent study involved the electrolysis of aqueous solutions of alcohols performed on a Ti02 nanotube-based anode under solar irradiation [199]. 

A different system has been described by Pierre and co-workers in 1998 (207). They showed that the electrochemically one-electron oxidized Complex G (Fig. 31) electrocatalyses, in the presence of KOH, the oxidation of primary alcohols (methanol, ethanol, 1-propanol, and 1-butanol) to the corresponding aldehydes >30 turnovers were observed. 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

Reactions alcohols, 29 36-49 adsorption, 29 36-37 clean surfaces, 29 37-38 ethanol oxidation, 29 44—48 methanol oxidation, 29 38-44 oxidation on copper and silver, 29 38-48 oxidation reaction, silver, 29 48-49 base-catalyzed, of hydrocarbons, 12 117 free radical mechanism in, of hydrogen peroxide, 4 343... 

A Ni metal complex is also effective for methanol oxidation [128]. The intermediary aldehydes (95) are isolable by employing a two-phase system in 30 86% yields (Scheme 35) [129]. Under basic conditions, secondary alcohols are readily oxidized into the corresponding ketones [130]. 

Oxidation of Alcohols in a Direct Alcohol Fuel Cell The electrocatalytic oxidation of an alcohol (methanol, ethanol, etc.) in a direct alcohol fuel cell (DAFC) will avoid the presence of a heavy and bulky reformer, which is particularly convenient for applications to transportation and portable electronics. However, the reaction mechanism of alcohol oxidation is much more complicated, involving multi-electron transfer with many steps and reaction intermediates. As an example, the complete oxidation of methanol to carbon dioxide ... 

Type 4A sieves. The pore size is about 4 Angstroms, so that, besides water, the ethane molecules (but not butane) can be adsorbed. Other molecules removed from mixtures include carbon dioxide, hydrogen sulphide, sulphur dioxide, ammonia, methanol, ethanol, ethylene, acetylene, propylene, n-propyl alcohol, ethylene oxide and (below -30°) nitrogen, oxygen and methane. The material is supplied as beads, pellets or powder. 

Methanol is oxidized to formaldehyde and dimethyl formate. Under the experimental conditions, neither formic acid nor its esters were detected. The other primary alcohols are oxidized to give aldehydes and, in a subsequent reaction, carboxylic acids. Acetals and esters are also formed. Profiles of the reaction products in the oxidation of l-propanol are shown in Fig. 19. 

The simplest alcohol, methanol, is commonly known as wood alcohol, because it was once obtained by heating wood in the absence of air, a process that also produced charcoal. Now methanol is synthesized from methane in natural gas. Methanol itself has a relatively low toxicity. However, methanol is oxidized (metabolized) in the liver to formaldehyde and then to formic acid, both of which are much more toxic. 

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