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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 oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate (gem-diol, R-CH(OH) 2) by reaction with water. Thus, the oxidation of a primary alcohol at the aldehyde level without further oxidation to the carboxylic acid is possible by performing the reaction ...
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]
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.
Other large scale aldehydes are produced by autoxidation of hydrocarbons: benzaldehyde from toluene, acrolein from propylene, and methacrolein from isobutene. [ 6 ] [ 7 ] In the Wacker process , oxidation of ethylene to acetaldehyde in the presence of copper and palladium catalysts, is also used.
Benzyl chloride is prepared industrially by the gas-phase photochemical reaction of toluene with chlorine: [3] C 6 H 5 CH 3 + Cl 2 → C 6 H 5 CH 2 Cl + HCl. In this way, approximately 100,000 tonnes are produced annually. The reaction proceeds by the free radical process, involving the intermediacy of free chlorine atoms. [4]
Phenylmethanediol is an organic compound that is a geminal diol, the hydrate of benzaldehyde. It is a short-lived intermediate in some chemical reactions, such as oxidations of toluene [2] and benzaldehyde [3] and the reduction of benzoic acid. [4]