| Étard reaction | |
|---|---|
| Named after | Alexandre Léon Étard |
| Reaction type | Organic redox reaction |
| Identifiers | |
| Organic Chemistry Portal | étard-reaction |
TheÉtard reaction is achemical reaction that involves the directoxidation of anaromatic orheterocyclic boundmethyl group to analdehyde usingchromyl chloride.[1][2][3] For example,toluene can be oxidized tobenzaldehyde.
It is named for the French chemistAlexandre Léon Étard (5 January 1852,Alençon – 1 May 1910).
The reaction mechanism proceeds via anene reaction withchromyl chloride, forming the precipitated Étard complex. The Étard complex is then decomposed by a [2,3]sigmatropic rearrangement underreducing conditions to prevent further oxidation to a carboxylic acid. Reducing conditions for the decomposition of the Étard complex are provided by saturated aqueoussodium sulphite. Typical solvents for the reaction includecarbon disulfide,dichloromethane,[4]chloroform, andcarbon tetrachloride, with carbon tetrachloride being the most common. To obtain a highly purified aldehyde product, the Étard complex precipitate is often purified before decomposition in order to prevent reaction with any unreacted reagent. The reaction is normally carried out for a few days to several weeks and the yields are high.[5][6]
The Étard reaction is most commonly used as a relatively easy method of convertingtoluene intobenzaldehyde. Obtaining specific aldehyde products from reagents other than toluene tends to be difficult due to rearrangements. For example,n-propylbenzene is oxidized topropiophenone,benzyl methyl ketone, and several chlorinated products, with benzyl methyl ketone being the major product.[7][8] Another example arises from the Étard reaction of trans-decalin which results in a mixture of trans-9-decalol, spiro [4.5]decan-6-one, trans-1-decalone, cis-1-decalone, 9,10-octal-1-one, and1-tetralone.[9]
Other oxidation reagents likepotassium permanganate orpotassium dichromate oxidize to the more stable carboxylic acids.
Oxidation oftoluene tobenzaldehyde is quite a useful conversion. Benzaldehyde is routinely used for its almond flavor. The aldehyde is comparatively reactive and readily participates inaldol condensations. Benzaldehyde can serve as a precursor for various compounds, including dyes, perfumes, and pharmaceuticals. For example, the first step in the synthesis ofephedrine is condensation of benzaldehyde withnitroethane[citation needed]. Additionally, benzaldehyde is instrumental in the synthesis ofphentermine.[10] Unlike other oxidising agents (like KMnO4 or CrO3 etc.), chromyl chloride doesnot oxidise aldehyde to carboxylic acid.