Hydroxyl reaction with ethanol, aqueous

Aldehydes and ketones undergo methylenation in 50-85% yield on reaction with either 1 or 2 (2 equiv.) in THF aldehydes react much more rapidly than ketones. Reactions with 1 can also be conducted in ethanol or aqueous THF at -70°, but reagent 2 is much less effective in the presence of ethanol or water. Both reagents are useful for methylenation of substrates contaming hydroxyl groups. Methylenation of o-hydroxybenzaldehyde with 1 in anhydrous THF proceeds in 76% yield. 

Cleavage of 2,3-epoxy halidesA zinc-copper couple, prepared by sonication of zinc powder and Cui in aqueous ethanol, cleaves epoxy halides to a radical that rearranges to an allylic alcohol. Since the epoxy halide is prepared by epoxidation of an allylic alcohol (m-chloroperbenzoic acid) followed by reaction with P(ChH5)3 and CBr4, the reaction effects 1,3-transposition of the hydroxyl group. 

Other derivatives can be prepared by reaction of the alcohol with an acid anhydride. For example, phthalic or 3-nitrophthalic anhydride (I mol) and the alcohol (Imol) are refluxed for half to one hour in a non-hydroxylic solvent, e.g. toluene or alcohol-free chloroform, and then cooled. The phthalate ester crystallises out, is precipitated by the addition of low boiling petroleum ether or is isolated by ev toration of the solvent. It is recrystallised from water, 50% aqueous ethanol, toluene or low boiling petroleum ether. Such an ester has a characteristic melting point and the alcohol can be recovered by acid or alkaline hydrolysis. 

With regard to the composition of the electrical effects, values of pj for the sets studied are reported in Table XIV. The sets in which the hydroxyl group is the reaction site generally exhibit a Pr value of about 39. The cis-3-substituted acrylic acids show a p value of 39 in aqueous solution. The value of 71 obtained in 50% aqueous ethanol seems too large. 

Reaction of 1-nitropropane with glutaraldehyde in aqueous ethanol in the presence of sodium hydroxide yields a mixture of two products, the major component of which, lr-ethyl-l-nitrocyclohexane-2c,6f-diol (98), can be isolated in 36% yield ). Acid-catalyzed acetylation converts (98) into the di-O-acetate, hydrogenation yields the corresponding amine, which has been characterized as the hydroacetate, N-acetate and triacetate. Configurational assignments followed from NMR data, which clearly showed the steric non-equivalence of the two hydroxyl groups vicinal to the tertiary center. 

The gamma-radiation-induced oxidation of 2-propanol has been investigated. Acetone and hydrogen peroxide are the principal products and arise via a chain reaction in aqueous acid solutions at high concentrations of 2-propanol. In neutral solutions of 2-propanol and in solutions of methanol and ethanol, no such chain reactions are observed. The reasons for this are discussed along with the implications of the results for the hydroxyl radical yield in water radiolysis. 

Although the radiation-induced oxidation of ethanol has been fully in-- vestigated (2, 22, 23), little work has been published on the oxidation of other alcohols. In connection with a project concerned with the relative rates of hydroxyl radical reactions using 2-propanol as reference solute, it was thought desirable first to investigate the radiation chemistry of 2-propanol-oxygen solutions both in aqueous solution and pure 2-propa-nol. The results of this investigation are presented here. 

For the modification of silica with aminosilanes, the liquid phase procedure is usually applied. Only few studies have described the vapour phase APTS modification.6,7 The modification proceeds in three steps, (i) A thermal pretreatment of the silica determines the degree of hydration and hydroxylation of the surface, (ii) In the loading step, the pretreated substrate is stirred with the silane in the appropriate solvent, (iii) Curing of the coating is accomplished in a thermal treatment. On industrial scale ethanol/water is used as a solvent, on lab-scale an organic solvent is used. The reasons for this discrepancy is the increased control on the reaction processes, possible in an organic solvent. This will be clarified by the discussion of the modification mechanism in aqueous solvent and the effect of water in the different modification steps. 

Alternatively, the use of higher temperatures [117] or ultrasonic waves in water/THF (5 1) mixtures were shown to allow the coupling reaction without aluminum powder [100]. When the aldehyde contained a free hydroxyl group, then the reaction under sonication became very rapid and efficient [103]. When applied to carbohydrates, this sono-allylation proceeded with high threo selectivity and allowed the preparation of higher-carbon complex sugars directly in aqueous ethanol without protection (Scheme 25) [118]. In this case also sonication can be replaced by heating the reaction mixture for 2 h under reflux [119]. 

The key contribution to this problem again came from Bunnett s school. Bunnett and Randall (1958 see also Bunnett, 1959) found that the reaction of N-methylaniline with l-fluoro-2,4-dinitrobenzene is subject to general base catalysis by acetate ions in ethanol solution and by hydroxyl ions in aqueous dioxane. The detailed kinetic results are consistent with competition of mechanisms (25b) and (25c) with mechanism (25a). 

---