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Hydrolyzable Tannins
A hydrolyzable tannin or pyrogallol-type tannin is a type of tannin that, on heating with hydrochloric or sulfuric acids, yields gallic or ellagic acids. At the center of a hydrolyzable tannin molecule, there is a carbohydrate (usually D-glucose but also cyclitols like quinic or shikimic acids). The hydroxyl groups of the carbohydrate are partially or totally esterified with phenolic groups such as gallic acid in gallotannins or ellagic acid in ellagitannins. Hydrolysable tannins are mixtures of polygalloyl glucoses and/or poly-galloyl quinic acid derivatives containing in between 3 up to 12 gallic acid residues per molecule. Hydrolyzable tannins are hydrolyzed by weak acids or weak bases to produce carbohydrate and phenolic acids. Examples of gallotannins are the gallic acid esters of glucose in tannic acid (C76H52O46), found in the leaves and bark of many plant species. Hydrolysable tannins can be extracted from different vegetable plants, such as chestnut wood ('' Castanea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyrogallol
Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a water-soluble, white solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomers of benzenetriols. Production and reactions It is produced in the manner first reported by Scheele in 1786: heating gallic acid to induce decarboxylation. Gallic acid is also obtained from tannin. Many alternative routes have been devised. One preparation involves treating ''para''-chlorophenoldisulfonic acid with potassium hydroxide, a variant on the time-honored route to phenols from sulfonic acids. When in alkaline solution, pyrogallol undergoes deprotonation of one or more phenolic groups. Such solutions absorb oxygen from the air, turning brown. This conversion can be used to determine the amount of oxygen in a gas sample, notably by the use of the Orsat apparatus. Polyhydroxybenzenes are relatively electron-rich. One manifestation is the easy C-acetylation of pyrog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |