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Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols in experiments. It is a weak acid, which can lose H + ions in solution. The nonionized phenolphthalein molecule is colorless and the double deprotonated phenolphthalein ion is fuchsia. Further proton loss in higher pH occurs slowly and leads to a colorless form.
Upon reduction, the very intense pink color of the cationic form of phenolphthalein fades to a faint yellow color. It is this form of phenolphthalein that is present in Kastle–Meyer test kits. In order to generate the intense pink color indicative of a positive test, the reduced phenolphthalein must be oxidized back to its normal, colored form.
Oxidative phenol couplings, however, often suffer from over-oxidation, especially since the intended coupled product is more oxidizable (has a lower oxidation potential) than the starting material. In such cases, the catalyst can be quenched or poisoned by engaging in off-cycle redox processes with the product.
Phenol oxidation with hypervalent iodine reagents leads to the formation of quinone-type products or iodonium ylides, depending on the structure of the phenol. Trapping of either product is possible with a suitable reagent, and this method is often employed in tandem with a second process.
The direct oxidation of benzene (C 6 H 6) to phenol is possible, but it has not been commercialized: C 6 H 6 + O → C 6 H 5 OH. Nitrous oxide is a potentially "green" oxidant that is a more potent oxidant than O 2. Routes for the generation of nitrous oxide however remain uncompetitive. [26] [23] [25]
The Dakin oxidation. The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde (2-hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide (H 2 O 2) in base to form a benzenediol and a carboxylate. Overall, the carbonyl group is oxidised, whereas the ...
The enzyme works by catalyzing the o-hydroxylation of monophenol molecules in which the benzene ring contains a single hydroxyl substituent to o-diphenols (phenol molecules containing two hydroxyl substituents at the 1, 2 positions, with no carbon between). [3] It can also further catalyse the oxidation of o-diphenols to produce o-quinones. [4]
The Elbs persulfate oxidation is the organic reaction of phenols with alkaline potassium persulfate to form para-diphenols. [1] The reaction is generally performed in water at room temperatures or below, using equimolar quantities of reagents. The Elbs persulfate oxidation. Several reviews have been published. [2] [3] [4]