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The Étard reaction is a chemical reaction that involves the direct oxidation of an aromatic or heterocyclic bound methyl group to an aldehyde using chromyl chloride. [1] [2] [3] For example, toluene can be oxidized to benzaldehyde. It is named for the French chemist Alexandre Léon Étard (5 January 1852, Alençon – 1 May 1910).
Benzaldehyde (C 6 H 5 CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is among the simplest aromatic aldehydes and one of the most industrially useful. It is a colorless liquid with a characteristic almond -like odor , and is commonly used in cherry -flavored sodas . [ 5 ]
The reaction is usually carried out in two steps in the same pot: partial oxidation is effected with TEMPO and hypochlorite, then chlorite is added to complete the oxidation. Only primary alcohol oxidation is observed. In conjunction with Sharpless dihydroxylation, this method can be used to generate enantiopure α-hydroxy acids. [19]
Toluene may also be brominated by treating it with HBr and H 2 O 2 in the presence of light. [31] C 6 H 5 CH 3 + Br 2 → C 6 H 5 CH 2 Br + HBr. Benzoic acid and benzaldehyde are produced commercially by partial oxidation of toluene with oxygen. Typical catalysts include cobalt or manganese naphthenates. [32]
In the classic example, benzaldehyde is converted to benzoin (PhCH(OH)C(O)Ph). [3] The benzoin condensation was first reported in 1832 by Justus von Liebig and Friedrich Wöhler during their research on bitter almond oil. [4] The catalytic version of the reaction involving cyanide was developed by Nikolay Zinin in the late 1830s. [5] [6 ...
Benzyl alcohol is produced industrially from toluene via benzyl chloride, which is hydrolyzed: . C 6 H 5 CH 2 Cl + H 2 O → C 6 H 5 CH 2 OH + HCl. Another route entails hydrogenation of benzaldehyde, a by-product of the oxidation of toluene to benzoic acid.
The process, which is catalyzed by platinum supported by aluminium oxide, is exemplified in the conversion methylcyclohexane (a naphthene) into toluene (an aromatic). [2] Dehydrocyclization converts paraffins (acyclic hydrocarbons) into aromatics. [3] A related aromatization process includes dehydroisomerization of methylcyclopentane to benzene:
When 17 O-labelled benzaldehyde reacts with carbonyl oxides, the label ends up exclusively in the ether linkage of the ozonide. [14] There is still dispute over whether the molozonide collapses via a concerted or radical process; this may also exhibit a substrate dependence.