Phenols hydrogen bonding with solvent

The same effect is typical of the reactions of alkoxyl radicals with phenols, that is, these reactions are much slower in solvents capable of forming hydrogen bonds with O—H and N—H groups [50]. MacFaul et al. [50] proposed a universal scale for correlating the reactivities of phenols and the hydrogen-bonding abilities of solvents. 

Phenoxides undergo O-alkylation in solvents such as DMSO, DMF, ethers, and alcohols. In water and trifluoroethanol, however, extensive C-alkylation occurs.54 These latter solvents form particularly strong hydrogen bonds with the oxygen atom of the phenolate... 

The 17r<7 states also dominate the photoinduced processes in hydrogen-bonded chromophore-solvent clusters. The photoinduced hydrogen transfer reaction is experimentally and computationally well documented in clusters of phenol and indole with ammonia [14,16,32], There is no clear evidence for the existence of an excited-state proton transfer process in these systems [14], The same conclusion applies to bi functional chromophores solvated in finite clusters, such as 7HQ-ammonia and 7HQ-water clusters [15]. In future work, the photochemistry of larger and biologically relevant chromophores (such as tyrosine, tryptophan, or the DNA bases) should be investigated in a finite solvent environment. 

Recently, the use of sulfolane solvent allowed better kinetic control of the oxidation chain, with an increase of the selectivity to 80% or greater, at ca 8% benzene conversion. The by-products were catechol (7%), hydroquinone (4%), 1,4-benzo-quinone (1%) and tar (5%) [53, 54]. According to these authors, a rather stable complex, formed by hydrogen bonding with sulfolane, promoted desorption and hindered the re-adsorption of phenol, protecting it from consecutive oxidation (Equation 18.7). Actually, the rate of oxidation of phenol in the presence of sulfolane was only 1.6 times that of benzene, while it was 10 times higher in the presence of acetone. 

Polyamide precoated plates are currently used for the separation of phenols and phenolic compounds (i.e., anthocyanins, anthoxanthines, anthroquinone derivatives, and flavones) using solvents of different elution strength (DMF > formamide > acetone > methanol > water). Such eluents and solutes compete for the hydrogen bonds with the peptide groups of the polyamide. 

Purified elastin has a pale yellow color and a bluish fluorescence in uv light. Resists acid and alkaline hydrolysis. Practically insol in a wide range of hydrogen-bond-breaking solvents at temps up to 100° and swells, but does uot dissolve, in phenolic solvents. It appears practically impossible to bring elastin into oln except by hydrolytic reagents capable of rupturing peptide bonds. Elastin is one of only a few polymeric substances which, in the presence of water, exist in a form with rubber-Like extensibility and low modulus of elasticity. Enzymes which dissolve fibers of the insol protein... 

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