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A dry sample is collected with a swab or filter paper. A few drops of alcohol, then a few drops of phenolphthalein, and finally a few drops of hydrogen peroxide are dripped onto the sample. If the sample contains hemoglobin, it will turn pink immediately upon addition of the peroxide, because of the generation of phenolphthalein. A positive ...
Phenolphthalein does not directly participate in this process; instead, it acts as an external source of electrons. In its reaction with hydrogen peroxide, the heme center of hemoglobin behaves as a peroxidase, reducing the peroxide to water. This activity depletes hemoglobin of electrons that are, in turn, re-supplied by the phenolphthalein.
The Dakin oxidation can occur in mild acidic conditions as well, with a mechanism analogous to the base-catalyzed mechanism. In methanol, hydrogen peroxide, and catalytic sulfuric acid, the carbonyl oxygen is protonated (14), after which hydrogen peroxide adds as a nucleophile to the carbonyl carbon, forming a tetrahedral intermediate (15).
Dialkyl peroxides, e.g., dicumyl peroxide, are synthesized by addition of hydrogen peroxide to alkenes or by O-alkylation of hydroperoxides. Diacyl peroxides are typically prepared by treating hydrogen peroxide with acid chlorides or acid anhydrides in the presence of base: [1] H 2 O 2 + 2 RCOCl → (RCO 2) 2 + 2 HCl H 2 O 2 + (RCO) 2 O → ...
Such applications have largely been replaced by methods using phenolphthalein/hydrogen peroxide and luminol. The popular dye congo red is derived from benzidine. Related 4,4’-benzidines
Solution: The main components of a universal indicator, in the form of a solution, are thymol blue, methyl red, bromothymol blue, and phenolphthalein. This mixture is important because each component loses or gains protons depending upon the acidity or alkalinity of the solution being tested. It is beneficial to use this type of universal ...
For materials containing more than 1.0 percent but not more than 7.0 percent hydrogen peroxide, the available oxygen content (O a) is not more than 0.5 percent, when determined using the equation: O a = 16x = where for a material containing k species of organic peroxides:
At pH = 10, phenol and phenolate are in approximately 1:1 proportions. The phenoxide anion (aka phenolate ) is a strong nucleophile with a comparable to the one of carbanions or tertiary amines. [ 3 ]