Hydroxyl oxidizing capacity

Oxidation became an important atmospheric reaction on Earth once molecular oxygen (O2) from photosynthesis had reached sufficiently high levels. This O2 could then photodissociate in the atmosphere to give oxygen atoms, which combine with O2 to form ozone (O3). When O3 absorbs UV light at wavelengths less than 310 nm, it produces excited oxygen atoms (0( D)) which can attack water vapor to produce the hydroxyl free radical (OH). It is the hydroxyl radical that, above all, defines the oxidative capacity of our O2- and... 

Aldehydes are emitted directly into the atmosphere from a variety of natural and anthropogenic sources and are also formed in situ from the atmospheric degradation of volatile organic compounds (VOCs). The atmospheric fate of aldehydes is controlled by photolysis and reaction with hydroxyl (OH) or nitrate (NO3) radicals and, in the case of unsaturated compounds, reaction with ozone (Atkinson, 1994). The photolysis of aldehydes is of particular importance because it is a source of free radicals in the troposphere, and thus may significantly influence the oxidizing capacity of the lower atmosphere (Finlayson-Pitts and Pitts, 1986). 

The conversion of cholesterol into bile acids represents the most obvious example of the high capacity of the liver to convert lipid-soluble material into excretable water-soluble products. In principle, the reactions in the formation of bUe acids are very similar to those generally involved in the metabolism and detoxication of various lipids and drugs hydroxylations, oxidations, and conjugations. In contrast to detoxication reactions, however, some of the reactions are highly specific and at least one of the hydroxylations is subject to metabolic control. In view of the importance of the rate of elimination of cholesterol in diseases such as atherosclero-... 

In spite of the fact that the atmosphere is composed predominantly of relatively inert molecules such as N2 and O2, it is actually a rather efficient oxidizing medium. One reason for the atmosphere s oxidizing capacity arises because the atmosphere contains minute amounts of very reactive molecular fragments, called free radicals. The most important free radical in the chemistry of the troposphere is the hydroxyl (OH) radical, which reacts with nearly every molecular species in the atmosphere. In addition, the atmosphere contains trace amounts of species less reactive than free radicals but nonetheless reactive enough to attack a variety of airborne compounds. Ozone (O3) is one important oxidizer, which also participates in the formation of the hydroxyl radical. 

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

Antioxidant capacities of common individual curcuminoids were determined in vitro by phosphomolybdenum and linoleic acid peroxidation methods. Antioxidant capacities expressed as ascorbic acid equivalents (pmol/g) were 3099 for curcumin, 2833 for demethoxycurcumin, and 2677 for bisdemethoxycurcumin at concentrations of 50 ppm. The same order of antioxidant activity (curcumin > demethoxycurcumin > bisdemethoxycurcumin) was observed when compared with BHT (buty-lated hydroxyl toluene) in linoleic peroxidation tests. The antioxidant activity of curcumin in the presence of ethyl linoleate was demonstrated and six reaction products were identified and structurally characterized. The mechanism proposed for this activity consisted of an oxidative coupling reaction at the 3 position of the curcumin with the lipid and a subsequent intramolecular Diels-Alder reaction. ... 

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