Relative oxidation rates alcohols

Figure 3. Relative oxidation rates of various methoxyl-substituted benzyl alcohols, measured by oxygen consumptionAnin. (veratryl alcohol = 100). No oxidation of the lower four alcohols was detected.

Figure 4. Relative oxidation rates of various aromatic alcohols. Para-hydroxyl substitution eliminates substrate oxidation.

RELATIVE RATE OF OXIDATION OF ALCOHOLS BY SO AND OH RADICAL, RESPECTIVELY... 

Oxygen uptake during substrate oxidation was measured with a Clark oxygen electrode (Rank Brothers, Cambridge, U.K.) at room temperature with 1 mM substrate in 0.25 mM sodium tartrate buffer, pH 3.0 (3 mL). Rates are expressed relative to veratryl alcohol oxidation. 

A characteristic of catalysis processes is that a variety of compounds may catalyse a particular reaction, but only one or two of these catalysts show enough selectivity, activity and stability to warrant use in an industrial process. Selectivity is the ability of a catalyst to increase the relative rate of formation of a desired product when two or more competing reactions may occur. For modification of the direction of a reaction, mixed catalysts consisting of two compounds both with moderate to good catalytic activity have been developed. For example, the vapour phase oxidation of alcohols to aldehydes and ketones involves a mixed a- Fe203/ M0O3 catalyst rather than a single oxide. 

Overoxidation with permanganate is always a problem, but the relative reaction rates are very much a function of the pH of the reaction mixture and, in basic solution, potassium permanganate oxidizes unsaturated groups more rapidly than it oxidizes alcohols ... 

The oxidation of substituted /3-benzoylpropionic acids by PFC follows the Hammett relation with a negative reaction constant. A possible mechanism for the oxidation has been discussed.5 The oxidation of maleic, fumaric, crotonic, and cinnamic acids by PCC is of first order with respect to PCC and the acid. The oxidation rate in 19 organic solvents has been analysed by Kamlet s and Swain s multiparametric equations. A mechanism involving a three-centre transition state has been postulated.6 The relative reactivity of bishomoallylic tertiary alcohols toward PCC, to yield substituted THF products via the tethered chromate ester, is dependent only on the number of alkyl groups. This observation suggests a symmetrical transition state in this intramolecular Cr(VI)-alkene reaction.7 Mechanisms have been proposed for the oxidation of 2-nitrobenzaldehyde with PBC8 and of crotonaldehyde with tetraethylammonium chlorochromate.9... 

Table III. Relative Rate Results for the CAN Oxidation of Alcohols 6a-6e...

RELATIVE RATES OF OXIDATION OF ALCOHOLS WITH CHROMIC... 

Alcohol is usually imbibed in liquid forms such as beer, wine, brandy, and hard liquor, etc. The type of alcohol commonly consumed is known as ethanol. It is rapidly and efficiently absorbed into the bloodstream from the stomach, small intestine, and colon. Recent studies have suggested that women have a more efficient absorption than men. In the bloodstream, alcohol is distributed to all parts of the body, including the fetus(es) of pregnant women. Alcohol is metabolized in the liver and converted to acetaldehyde by the action of alcohol dehydrogenase (ADH) and other oxidizing agents at a relatively constant rate. 

Laccase, in contrast to GOase, does not mediate the aerobic oxidation of alcohols in vivo, but in the presence of a variety of electron mediators, notably TEMPO, is able to catalyze alcohol oxidations in vitro (47,50). Recent kinetic and EPR studies (58) have established the mechanistic details of TEMPO/laccase-catalyzed oxidations of alcohols and provided insights into reasons for the relatively low rates of conversion and the need for high loadings of TEMPO. This provides a sound basis for further improvement of the synthetic utility of this system, e.g., by stabilizing the laccase via immobilization and/or the use of more stable TEMPO derivatives. 

Polmer-snpported IBX Reagents. Two different phenoxide linked polymer-based IBX reagents have been developed. The silica supported reagent (Poly-IBX) is used in THE The oxidation rate increases relative to DMSO as solvent. The primary alcohol in the cyclohexanol may be oxidized preferentially, and thus avoid formation of the cyclohexanone expected from the secondary alcohol (eq 8). This selectively is retained even with a threefold... 

Formation of an aldehyde such as 17 in the presence of a powerful oxidizing agent such as chromium(VI) is usually followed by rapid oxidation of 17 to the corresponding carboxylic acid, pentanoic acid (18). In other words, Jones s oxidation of simple aldehydes usually gives the carboxylic acid as the major product. If the reaction mixture is heated, overoxidation to the carboxylic acid is even more rapid. The fact that the Jones reagent rate of oxidation of alcohol to aldehyde is fast can be used to an advantage, and when acetone is used as a solvent, the rate of oxidation of aldehyde to acid is relatively slow. Acetic acid (ethanoic acid) serves a similar role in many oxidations. 

Generally, isolated olefinic bonds will not escape attack by these reagents. However, in certain cases where the rate of hydroxyl oxidation is relatively fast, as with allylic alcohols, an isolated double bond will survive. Thepresence of other nucleophilic centers in the molecule, such as primary and secondary amines, sulfides, enol ethers and activated aromatic systems, will generate undesirable side reactions, but aldehydes, esters, ethers, ketals and acetals are generally stable under neutral or basic conditions. Halogenation of the product ketone can become but is not always a problem when base is not included in the reaction mixture. The generated acid can promote formation of an enol which in turn may compete favorably with the alcohol for the oxidant. 

The facile and selective oxidation of both primary and secondary hydroxy groups with certain nucleotides led Pfitzner and Moffatt (48) to explore the scope of the carbodiimide-methyl sulfoxide reagent with steroid and alkaloid alcohols. Relatively minor differences were apparent in the rate of oxidation of epimeric pairs of 3- and 17- hydroxy steroids whereas the equatorial lLx-hydroxyl group in several steroids was readily oxidized under conditions where the axial epimer was unreactive [cf. chromic oxide oxidation (51)]. 

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