Methanol spectroscopic studies

Formaldehyde is produced and sold as water solutions containing variable amounts of methanol. These solutions are complex equiUbrium mixtures of methylene glycol, CH2(OH)2, poly(oxymethylene glycols), and hemiformals of these glycols. Ultraviolet spectroscopic studies (13—15) iadicate that even ia highly concentrated solutions the content of unhydrated HCHO is <0.04 wt%. 

In-situ ATR-FTIR spectroscopic study of electro-oxidation of methanol and adsorbed CO at Pt-Ru alloy. J. Phys. Chem. B, 108, 2654-2659. 

Kunimatsu K. 1986. Infrared spectroscopic study of methanol and formic acid adsorbates on a platinum electrode Part I. Comparison of the infrared absorption intensities of hnear CO(a) derived from CO, CH3OH and HCOOH. J Electroanal Chem 213 149 157. 

Beden B, Hahn F, Juanto S, Lamy C, Leger JM. 1987a. Infrared spectroscopic study of the methanol adsorbates at a platinum electrode Part I. Influence of the bulk concentration of methanol upon the nature of the adsorbates. J Electroanal Chem 225 215-225. 

A. Fujii, S. Enomoto, M. Miyazaki, and N. Mikami, Morphology of protonated methanol clusters An infrared spectroscopic study of hydrogen bond networks of H+(CH30H)n (n 4 15). 

It is essential to understand the mechanisms of methanol oxidation including the adsorbate formation and removal. To this purpose, the electrochemical oxidation of adsorbed carbon monoxide (COad) and methanol was studied using electrochemical and two spectroscopic... 

H. A. Headlam and P. A. Lay, EPR spectroscopic studies of the reduction of chromium(VI) by methanol in the presence of peptides. Formation of long-lived chromium(V) peptide complexes, Inorg. Chem., 40 (2001) 78-86. 

A subsequent picosecond electronic absorption spectroscopic study of TPE excited with 266- or 355-nm, 30-ps laser pulses in cyclohexane found what was reported previously. However, in addition to the nonpolar solvent cyclohexane, more polar solvents such as THF, methylene chloride, acetonitrile, and methanol were employed. Importantly, the lifetime of S lp becomes shorter as the polarity is increased this was taken to be evidence of the zwitterionic, polar nature of TPE S lp and the stabilization of S lp relative to what is considered to be a nonpolar Sop, namely, the transition state structure for the thermal cis-trans isomerization. Although perhaps counterinmitive to the role of a solvent in the stabilization of a polar species, the decrease in the S lp lifetime with an increase in solvent polarity is understood in terms of internal conversion from to So, which should increase in rate as the S -So energy gap decreases with increasing solvent polarity. Along with the solvent-dependent hfetime of S lp, it was noted that the TPE 5ip absorption band near 425 nm is located where the two subchromophores— the diphenylmethyl cation and the diphenylmethyl anion—of a zwitterionic 5ip should be expected to absorb hght. A picosecond transient absorption study on TPE in supercritical fluids with cosolvents provided additional evidence for charge separation in 5ip. 

In the specific case of the tailed sapphyrin carboxylates 5 and 6, for which evidence of self-assembly was noted in the solid state (vide supra), H NMR spectroscopic studies carried out in 4-methanol, d-chloroform, and mixtures of the two solvents showed strong line broadening, and upfield shifts of the methylene tail peaks. Such findings are, of course, fully consistent with the proposed dimerization. Further, dilution experiments performed over a concentration range of 50 to 5 mM in these solvents showed little change in the spectra, indicating that the dimeric form prevails under these conditions, even in highly polar solvents. In the case of 6, the actual dimeric stoichiometry was confirmed by vapor pressure osmometry (VPO) measurements carried out in 1,2-dichloroethane. 

When finely divided silica is treated with methanol and then pyrolyzed, it becomes activated toward chemisorption of various gases341-343. Recent careful spectroscopic studies by Radzig and coworkers344-347 and by Razskazovskii et aZ.348,349 establish beyond reasonable doubt that the principal reactive sites are divalent silicons, (=Si—0)2 Si , silylene centers 350, which participate in a rich chemistry. 

Aprotic solvents mimic the hydrophobic protein interior. However, a functional artificial receptor for flavin binding under physiological conditions must be able to interact with the guest even in competitive solvents. As found by spectroscopic measurements with phenothiazene-labeled cyclene, the coordinative bond between flavin and Lewis-acidic macrocyclic zinc in methanol was strong enough for this function. Stiochiometry of the complex was proved by Job s plot analysis. Redox properties of the assemblies in methanol were studied by cyclic voltammetry which showed that the binding motif allowed interception of the ECE reduction mechanism and stabilisation of a flavosemiquinone radical anion in a polar solvent. As a consequence, the flavin chromophore switched from a two-electron-one-step process to a two-step-one-electron-each by coordination. 

Kreiter (67) first demonstrated by XH NMR spectroscopic studies the acidity of hydrogen atoms that are bonded at the a-C atom of alkoxy-(alkyl) carbene complexes. In CH3OD solution, in the presence of catalytic amounts of sodium methanolate, pen tacarbonyl[methoxy (methyl) car-bene cliromiumfO) exchanges for deuterium all hydrogen atoms of the methyl group that is situated next to the carbene carbon ... 

Adachi, D., Katsumoto, Y., Sato, H., and Ozaki, Y., Near-infrared spectroscopic study of interaction between methyl group and water in water-methanol mixtures, Appl. Spectrosc., 56, 357-361, 2002. 

In situ spectroscopic studies have identified a variety of species, such as formate, dioxymethylene, carbonate, and methoxide, to coexist under methanol synthesis conditions on Cu/ZnO-based catalysts [22, 23], Fourier transform infrared spectroscopy studies of CuZn-based catalysts under H2/C02 identified the presence of formate bound to both Cu and ZnO, whereas methoxide was found on ZnO only. Carbonates were found to form via C02 adsorption on ZnO [24] and partially oxidized Cu [23], and were quickly converted into formate via Cu-activated hydrogen. Upon exposure to CO mixtures, only zinc-bound formate was observed [22], The hydrogenation of these formates to methoxide is thought to be rate determining in methanol synthesis. 

The coadsorption and IR spectroscopic studies cited in this section indicate that surface formate is readily formed from C02 and H2 or from CO and H20 vapors. It appears that the reaction of CO and H2 to formate is considerably more difficult. Moreover, while both formate and methoxide have been detected in methanol decomposition over ZnO and in the synthesis over the Zn0/Cr203 catalysts, no positive evidence of these species has so far been gathered for the copper-based catalysts. 

Liddel U, Becker ED. Infra-red spectroscopic studies of hydrogen bonding in methanol, ethanol, and f-butanol. Spectrochem Acta 1957 10 70-84. 

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