Hydrogen bonds methanol-water mixture

The solvation dynamics following charge-transfer electronic excitation of diatomic solutes immersed in a methanol-water mixture provides a direct window on the molecular changes occurring upon solvent substitution. The solvation response of the mixtures is separated into methanol and water contributions in order to elucidate the role played by each molecular species on the solvation dynamics. Significandy different responses for the two solutes are found and related to the fact that the solute with the smaller site diameters is a much better hydrogen (H)-bond acceptor than the larger diameter solute (Skaf and Ladanyi, 1996). 

M. S. Skaf, T. Fonseca and B. M. Ladanyi, Wave-vector-dependent dielectric relaxation in hydrogen-bonding liquids a molecular-dynamics study of methanol, J. Chem. Phys., 98 (1993) 8929-45 B. M. Ladanyi and M. S. Skaf, Wave vector-dependent dielectric relaxation of methanol-water mixtures, J. Phys. Chem., 100 (1996) 1368-80 M. S. Skaf, Molecular dynamics simulations of dielectric properties of dimethyl sulfoxide Comparison between available potentials, J. Chem. Phys., 107 (1997) 7996-8003. 

HDS catalysts generally consist of (heterogeneous) Mo or W sulfides on alumina supports. However, Bianchini et al. described a two-step procedure for HDS of thiophenes by the hydrogenolysis of thiols, followed by the desulfurization of the thiols by applying their zwitterionic rhodium(I) complex, [Rh(sulphos((cod)] (see previous section) [17]. This complex is soluble in polar solvents, such as methanol and methanol-water mixtures, but not in hydrocarbons. Benzo[b]thiophene was chosen as substrate since it is one of the most difficult thiophene derivatives to degrade. Under the mild reaction conditions of the two-step process, the benzene rings of the (di)benzothiophenes were not affected. In the absence of a base, the double bond of benzo[b]thiophene was hydrogenated, while in the presence of a base (NaOH) 2-ethylthiophenolate was the major product (Scheme 1). 

Ebukuro, T., Takami, A., Oshima, Y, et al. (1999). Raman spectroscopy studies on hydrogen bonding in methanol and methanol/water mixtures under high temperature and pressure, J. Supercrit. Fluid, 15, pp. 73-78. 

A series of new chiral furan derivatives has also been published demonstrating the utility of both the CB-DM and CB-RSP to separate based on steric bulk in simple methanol/water mixtures [12], This technique of steric repulsion as a mechanism was also demonstrated for the separation of 16 racemic dihydrofuroflavones with a similar complementary effect for the CB-DM and CB-RSP [13], Another example of this useful combination of steric bulk and hydrogen bonding mechanism for the CB-RSP can be found in the publication cited for the separation of 12 chiral dihydrobenzofurans [14]. 

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