Oxidation of methanol and ethanol

Bartlett and Cotman found that the kinetics of oxidation of methanol obeyed the rate equation 

The reaction is faster than the spontaneous decomposition of peroxodisulphate, so Bartlett and Cotman proposed a chain mechanism involving sulphate radical-ions and the CH2OH radical. Kolthoff et al. showed that allyl acetate inhibits the reaction, and reduces the rate to that observed in the absence of methanol. They pointed out that if the inhibition is explained on the basis of Bartlett and Cotman s mechanism, the predicted rate equation does not include the methanol concentration. This difficulty was resolved by Edwards et al., who showed that in the absence of oxygen the reaction is zero-order with respect to methanol. They proposed the following mechanism (similar to that originally proposed by Bartlett and Cotman) 

For long chains (the observed chain length is 100 at 70 °C and initial [SjOl ] = 10 M) the stationary state approximation gives 

Note that a different termination step from that in the 2-propanol oxidation is responsible for the rate being independent of the substrate concentration. The absence of in equation (41) predicts the same rate for CD3OH. The observed isotope effect ( h/ d) is 1 3 which can reasonably be ascribed to a secondary effect on or an inverse effect on k (Edwards et aV ). 

In the oxidation of ethanol, the order with respect to peroxodisulphate is again three-halves and the mechanism is considered to be the same as that proposed for methanol, but the oxidation is complicated by inhibition due to the product, acetaldehyde (Edwards et If sufficient acetaldehyde is added to the reac- 

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Biological oxidation of methanol and ethanol in the body produces the corresponding aldehyde followed by the acid. At times the alcoholics, by mistake, drink ethanol, mixed with methanol also called denatured alcohol. In the body, methanol is oxidised first to methanal and then to methanoic acid, which may cause blindness and death. A methanol poisoned patient is treated by giving intravenous infusions of diluted ethanol. The enz5mie responsible for oxidation of aldehyde (HCHO) to acid is swamped allowing time for kidneys to excrete methanol. 

Oxidation of ethylene to ethylene oxide (T=25(MOOOC) Oxidation of methanol and ethanol to acetaldehyde formaldehyde (T=246-378°C)... 

C.T. Hable and M.S. Wrighton, electrocatal3dic oxidation of methanol and ethanol A comparison of platinum-tin, and platinum-ruthenium catalyst particles in a conducting polyaniline matrix, Langmuir, 9, 3284—3290 (1993). 

Preparation and characterization of PANI/NiO nanocomposite using various surfactants, e.g., polyvinyl alcohol and hydroxypropylcellulose, were reported by Aleahmad et al. [230]. PANl and NiO were electro-codeposited from aniline and NiSO through cyclic voltammetric scans at controlled acidity leading thus to the formation of PANI/NiO composite film [231]. The stability of NiO in the composite films against acidic environments was found to be enhanced in comparison with the corresponding stability of pure NiO. Electrochemical catalytic behavior of PANl/NiO composite film was demonstrated by the catalytic oxidation of methanol and ethanol. Multicolored electrochromic thin films of... 

Figures 21.4 and 21.5 present examples of PMRs with photocatalytic membranes. The PMR shown in Fig. 21.4 was applied for photocatalytic oxidation of methanol and ethanol in the gaseous phase (Tsuru et al, 2003,...

Schematic diagram of a PMR withTiOj/a-AIjO, photocatalytic membrane for photocatalytic oxidation of methanol and ethanol in gaseous phase. MFM, mass flowmeter T, thermocouple GC, gas chromatograph BL, black light (adapted fromTsuru etal., 2003 Tsuru eta ., 2006). 

Suffredini HB, Tricoli V, Vatistas N, Avaca LA (2006) Electro-oxidation of methanol and ethanol using a Pt-Ru02/C composite prepared by the sol-gel technique and supported on boron-doped diamond. J Power Sources 158(1) 124—128... 

Oliveira Neto A, Franco EG, Arico E, Linardi M, Gonzalez ER (2003) Electro-oxidation of methanol and ethanol on Pt-Ru/C and Pt-Ru-Mo/C electrocatalysts prepared by Bdnnemann s method. J Eur Ceram Soc 23 2987-2992... 

Neto AO, Dias RR, Tusi MM, Linardi M, Spinace EV (2007) Electro-oxidation of methanol and ethanol using PtRu/C, PtSn/C and PtSnRu/C electrocatalysts prepared by an alcohol-reduction process. J Power Sources 166 87-91... 

Even though several methods have been devised for the oxidation of methanol and ethanol to formaldehyde and acetaldehyde, with the subsequent polarographic determination of these aldehydes, none of them has yet been widely accepted. The nonreproducibility of the oxidation, volatility of both alcohols and aldehydes formed, the reactivity and polymerization of the aldehydes and the kinetic character of the wave of formaldehyde, seem to be the main reasons for this situation. 

Biallozor S, Kupniewska A, Jasulaitene V. Electro-oxidation of methanol and ethanol on poly(3,4-ethylenedioxythiophene) with dispersed Pt, Pt+Sn and Pt+Pb particles. Fuel Cells 2003 3 8-14. 

Wang, W., Zhang, H., Lin, G., and Xiong, Z. Study of Ag/Lao.6Sro.4Mn03 catalysts for complete oxidation of methanol and ethanol at low concentrations. Appl Catal B Environ. 2000, 24, 219-232. 

Koyama,K., Matsuoka,M., Tsutsumi,S. The homolytic methoxylation and ethoxylation of olefins by the anodic oxidation of methanol and ethanol. Bull. Chem, Soc. Japan 40, G1 (1967). 

Electrochemical studies have been performed in acidic medium by Kadirgan et al. [61], who have evaluated the activity of Pt-Pd/ C nanoparticles in the electro-oxidation of methanol and ethanol. Chronoamperometry investigation conducted at 0.45 V vs. ERH showed that Pt and Pd have a synergistic effect, which increases the catalytic activity of the catalyst two or threefold as compared to that of pure Pt (Pt/C Etek). This effect was attributed to a change in the electron density of platinum, responsible for the weakening of the Pt—CO bond and the consequent decrease in its poisoning rate. 

In the case of methanol and ethanol oxidation (as well as other small organic molecules) strongly adsorbed intermediate is considered to be COads, hence, the understanding of CO electrocatalytic oxidation presents a basis for the understanding of electrocatalytic oxidation of methanol and ethanol. A key role in the understanding of the electrocatalysis of CO oxidation is played by surface science, which provides crucial information on the nature of CO interaction with electrocatalytic surfaces. 

Taylor PH, Cheng Li, Dellinger B. The influence of nitric oxide on the oxidation of methanol and ethanol. Combust Flame 1998 115 561—7. 

To understand the various phenomena take place during electro-oxidation of methanol and ethanol on Pt-black surface, Verma et al. (2005e) studied half-cell using cyclic voltammetry. Fig. 8 shows the cyclic voltammograms with and without the fuel (methanol and ethanol) in 1 M KOH solution at the scan rate of 50 mV s". In the forward scan, ethanol electro-oxidation shows a prominent peak at 0.03 V as compared to electro-oxidation of methanol, which shows a broad plateau from -0.4 V to 0.6 V. It implies that Pt-black electode catalyst is more active in the case of ethanol than methanol for electro-oxidation. During reverse... 

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