Benzaldehyde reactions with chromium chloride

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,... 

Oxidation of the trihydroxypropyl compound 7 or the aldehydes 38 and 40 with chromium trioxide in acetic acid or 50% sulfuric acid furnishes the 3-carboxylic acids, which readily decarboxylate to the 3-unsubstituted compounds at their melting points. " In contrast, the 3-methyl-l-phenyl compoimd is not appreciably attacked by chromiiun trioxide, potassium permanganate, or selenium dioxide. Chromyl chloride oxidation of 7 does not give the aldehyde 38 but apparently provides the tetraflavazolyl ether 41. The inertness of the 3-methyl group is emphasized by its stability toward bromine and its lack of reaction with benzaldehyde." ... 

The ability of the anhydrous chiomiuin(n) ion to reduce vinyl halides and provide alkenylchromium compounds which participate in aldehyde addition reactions was first described by Takai and cowoik-ers. Treatment of 2-iodopropene (173) and benzaldehyde with anhydrous chromium(II) chloride in DMF afforded allylic alcohol (174) in quantitative yield (equation 62). ... 

To a flask was added 200 mg chromium(II) chloride (1.63 mmol, 2.5 eq.) then 2.5 mL THF was added under vigorous stirring. After a few minutes, 229 mg benzaldehyde (2.16 mmol, 3.0 eq.) and 156.3 mg 3,7-dimethyl-l-bromo-oct-2,6-diene (0.72 mmol, 1.0 eq.) were added. The resulting mixture was stirred for 3 h at 55" C, and the reaction was quenched with brine. The aqueous layer was extracted three times with diethyl ether, and the combined organic fractions were washed twice with brine, dried over MgS04, and concentrated in vacuo. The residue was purified by silica gel column chromatography using diethyl ether as the eluent, to afford 64% 2,6-dimethyl-l-phenyl-2-vinyl-hept-5-en-l-one as a colorless oil, in a yield of 64%, Rf = 0.64 (hexane/EtOAc, 98 2). 

The kinetics of the chromyl chloride oxidation of the carbon-carbon double bond of styrene have been examined using stopped-flow spectrophotometry/ the product being a chromyl chloride-styrene adduct. The rate is first order with respect to each reactant and a linear free-energy relationship (Hammett correlation) has been shown to hold for a variety of substituted groups. The data are consistent with a mechanism involving electrophilic attack by the chromium(vi) species on the double bond to yield the adduct, which decomposes on hydrolysis to give phenylacetalde-hyde and benzaldehyde as the major reaction products ... 

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