A-hydroxyl-o>

Solomon et al. [203] developed a technique allowing the terminal aminoxyl to be replaced by a hydroxyl function. With this aim, they reacted the terminal aminoxyl containing oligomer with acetic acid catalyzed by zinc. Pradel et al. [218] achieved the synthesis of hydroxy-telechelic polybutadiene by applying the methodology of Solomon et al. to a-hydroxyl/o-aminoxyl polybutadiene (the synthesis was presented earlier) at 80 °C. After 2 h, they obtained a quantitative reduction of the aminoxyl functions evidenced by ll NMR (Scheme 38). The average hydroxyl functionality of oligobutadiene was 2.06. 

Scheme 4. Synthetic strategy for a-hydroxyl-o)-methoxycarbonyl asymmetric telechelic PIBs.

Carboxylic acids contain at least one carboxyl functional group (COOH), which in turn is composed of a carbonyl (C=0) and a hydroxyl (O—H) group. A carboxylate (COO ) is the salt of a carboxylic acid formed after deprotonation of carboxyl group. Carboxyl and carboxylate functional groups exist widely in biological systems, such as in amino acids, fatty acids and drug moleucles. 

Oxide Chlorides. Zirconium oxide dichloride, ZrOCl2 -8H2 0 [13520-92-8] commonly called zirconium oxychloride, is really a hydroxyl chloride, [Zr4(OH)g T6H2 0]Clg T2H2O (189). Zirconium oxychloride is produced commercially by caustic fusion of zircon, followed by water washing to remove sodium siUcate and to hydrolyze the sodium zirconate the wet filter pulp is dissolved in hot hydrochloric acid, and ZrOCl2 -8H2 O is recovered from the solution by crystallization. An aqueous solution is also produced by the dissolution and hydrolysis of zirconium tetrachloride in water, or by the addition of hydrochloric acid to zirconium carbonate. 

Pyrazoles, isoxazoles and isothiazoles with a hydroxyl group in the 3-position (491 Z = NR, O, S) could isomerize to 3-azolinones (492). However, these compounds behave as true hydroxy derivatives and show phenolic properties. They give an intense violet color with iron(III) chloride and form a salt (493) with sodium hydroxide which can be O-alkylated by alkyl halides (to give 494 R = alkyl) and acylated by acid chlorides (to give 494 R = acyl). 

In the endoplasmic reticulum of eukaryotic cells, the oxidation of the terminal carbon of a normal fatty acid—a process termed ch-oxidation—can lead to the synthesis of small amounts of dicarboxylic acids (Figure 24.27). Cytochrome P-450, a monooxygenase enzyme that requires NADPH as a coenzyme and uses O, as a substrate, places a hydroxyl group at the terminal carbon. Subsequent oxidation to a carboxyl group produces a dicarboxylic acid. Either end can form an ester linkage to CoA and be subjected to /3-oxidation, producing a... 

Of particular value, was the reagent s ability to oxidize a hydroxyl group attached directly to a furanoid ring (6, 7, 46), as is illustrated by the conversion of l,2 5,6-di-0-isopropylidene-a-D-glucofuranose into l,2 5,6-di-0-isopropylidene-a-D-n o-hexofuranos-3-ulose (1). The follow-... 

Glycosides are formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide, or monosaccharide residue, and a second compound that may—or may not (in the case of an aglycone)—be another monosaccharide. If the second group is a hydroxyl, the O-glycosidic bond is an acetal link because it results from a reaction between a hemiacetal group (formed from an aldehyde and an —OH group) and an-... 

All of these results support the o-hydroxylation hypothesis, but they do not prove it. No o-hydroxy nitrosamine or a derivative of one has ever been isolated as a metabolite of any nitrosamine. Nevertheless, a-hydroxylation is an attractive working hypothesis and it seems to account for... 

Smith, C., Mitchinson, M.A., Aruoma, O. and Halliwell, B. (1992). Stimulation of lipid peroxidation and hydroxyl radical generation by the contents of human atherosclerotic lesions. Biochem. J. 286, 901-905. 

The reaction endothermicity establishes a minimum for the activation energy whereas abstraction of a hydrogen atom from carbon is a feasible step in a chain process, abstraction of a hydrogen atom from a hydroxyl group is unlikely. Homolytic cleavage of an O-H bond is likely only if the resulting oxygen radical is stabilized, such as in phenoxy radicals formed from phenols. 

---