Oxidation Etard

ESCHWEILER - CLARKE Amne methylation 111 ETARD Oxidation 112 Evans 266... 

A9(l 1 )-Estrone methyl ether, 84-85 Etard oxidation, 62 Ethanalation, 73 Ethanolamine, 146 Ether cleavage, 7 Ethoxyacetyl chloride, 137 N-Ethoxycarbonylazepine, 103 N-Ethoxycarbonyl-2-ethoxy-l,3-dihydroquin-oline(EEDQ), 137 Ethoxyketene, 137-138 Ethylamine, 186 Ethyl azidoformate, 138 Ethylbenzene, 328 Ethylbenzenes, 15 Ethyl bromide, 159 Ethyl bromoacetate, 26, 28, 236 Ethyl 4-bromocrotonate, 236 Ethyl bromocyanoacetate, 237 Ethyl chlorodiazoacetate, 222... 

Obtained in 70% yield from CrOj and TiCU in CH2CI2 with ultrasound irradiation for 2.5 h. It can be used in the Etard oxidation or converted into Cr02(0Bu >2 and the cyclic chromate of 2,5-dimethylpentane-2,5-diol for other oxidations. 

Benzaldehyde.—The aldehydes of the aromatic seiies may also be obtained by the oxidation of a methyl side-chain with chromium oxychloride. The solid brown product, C,H,.CH.)(CrO,CL)2, formed by adding C1O2CIJ to toluene, dissolved in carbon bisulphide, is decomposed with water, and benzaldehyde sepaiates out (Etard). Other methods for pie-paring aromatic aldehydes are (i) the Fiiedel-Crafts reaction, in which a mixture of carbon monoxide and hydrogen chloride aie passed into the hydrocaibon in presence of aluminium chloride and a little cuprous chloride,... 

The name Etard reaction is often applied to any oxidation with chromyl chloride, for example, oxidation of glycols (19-7) and Alkenes (19-10). 

The effect of solvent upon k2 has been reported , and it was concluded that the activated complex is not sufficiently polar to be called ionic . The oxidations of toluene and triphenylmethane exhibit primary kinetic deuterium isotope effects of 2.4 and ca. 4 respectively. No isotopic mixing occurred during formation of the Etard complex from a mixture of normal and deuterated o-nitrotoluene . The chromyl chloride oxidation of a series of substituted diphenylmethanes revealed that electron-withdrawing substituents slow reaction while electronreleasing groups have the opposite effect, the values ofp andp being —2.28 + 0.08 and —2.20 + 0.07 respectively . ... 

Oxidation of Arylmethanes - Electrochemical Alternative Routes to the Etard Reaction... 

Etard reagents (chromyl chloride and some derivatives) suffer from the problem that occasionally they can exhibit a lack of selectivity and low yields. They are useful in the selective oxidation of aromatic side-chains to a carbonyl group, aldehyde or ketone but in many instances, the formation of the initial complex is slow and yields are low because of difficulties in the work-up which lead to undesired over-reaction. Attempts have been made to solve the problems by the use of sonication [134]. A simple preparation of the liquid reagent was proposed and the Etard reaction itself together with the hydrolytic step were conducted under sonication, with some success (Scheme 3.25). 

Etard reaction org chem Direct oxidation of an aromatic or heterocyclic bound methyl group to an aldehyde by utilizing chromyl chloride or certain metallic oxides. a tar re,ak-sh3n ... 

H.H.Franck et al, ZAnorgChem 232,109 (1937) CA 31,5289 4)M.A.Bredig, JPhys Chem 46,816,818(1942) CA 37,1918(1943) Thorium Dicarbide, THC, solid, d 8.96 at 18°. Was prepd by Moissan Etard on heating in an electric furnace a mixt of powdered thorium oxide and sugar-charcoal made into a paste with turpentine. Other methods of prepn are given in Ref 3 Refs l)Beil 1, 914I 2)H.Moissan ... 

Stoichiometric oxidations may also lead to aldehydes from methyl-substituted arenes. Chromyl chloride applied in the classical Etard reaction843 forms a 2 1 insoluble adduct with the possible structure 101. The aldehyde is isolated after treatment with water ... 

Reaction XC1. (a) Oxidation of Aromatic Hydrocarbons to Aldehydes by the action of Chromyl Chloride in Carbon Disulphide Solution. (Etard.) (A. Ch., [5], 22, 225.)—In this reaction the hydrocarbon and chromyl-chloride are both dissolved in carbon disulphide, and the solutions carefully mixed. An explosive intermediate compound is precipitated, and this is separated and decomposed with water to give the aldehyde. The yields are very good, but the method is not often used owing to the inconvenience of working with carbon disulphide and the dangerous nature of the intermediate compounds. 

Chromyl chloride converts the aromatic methyl group into an aldehyde this reaction is known as the Etard reaction h For example, toluene can be oxidized to benzaldehyde. 

Triethanolamine (TEOA) is added to tbe initial reaction mixture to reduce [RuCbpy) ] as it is generated thus the back reaction (producing [Ruibpy) ] and is I etarded. The reduced methylviologen MV reduces water to hydrogen in the presence of collodial platinum and is oxidized back to thereby completing... 

Chromyl chloride, Cr202Cl2, a dark-red liquid (mp -96.5 °C, bp 117 °C, d 1.911), is prepared from chromium trioxide or sodium dichromate, hydrochloric acid, and sulfuric acid [665]. The reagent is used in solutions in carbon disulfide, dichloromethane, acetone, tert-butyl alcohol, and pyridine. Oxidations with chromyl chloride are often complicated by side reactions and do not always give satisfactory yields. The mechanism of the oxidation with chromyl chloride, the Etard reaction, is probably of free-radical nature [666]. Complexes of chromyl chloride with the compounds to be oxidized have been isolated [666, 667, 668]. 

Oxidations with chromyl chloride (Etard reaction) of aromatic compounds with longer chains are not always suitable because the reactions result in more than one product [673]. 

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