Aldehydes aromatic, preparation

GATTERMANN ALDEHYDE SYNTHESIS. Preparation of aldehydes of phenols, phenol ethers, or heterocyclic compounds hy treatment of the aromatic substrate with hydrogen cyanide and hydrochloric acid in the presence of Lewis acid catalysts. 

STEPHEN ALDEHYDE SYNTHESIS. Preparation of aldehydes from nitriles by reduction with stannous chloride in ether saturated with hydrochloric acid. The intermediate aldimine salts have to be hydrolyzed. The best results are obtained in the aromatic series. 

Aromatic aldehydes are prepared by passing carbon monoxide and dry hydrogen chloride through an ether or nitrobenzene solution of an aromatic hydrocarbon in the presence of a catalyst, commonly aluminum chloride with cuprous chloride as a carrier. The process is illustrated by the synthesis of p-tolualdehyde (51%). A convenient procedure for obtaining an equimolar mixture of anhydrous hydrogen chloride and carbon monoxide consists in dropping chlorosulfonic acid on formic acid, viz.,... 

Vilsmeier and Haack found that the reagent forms a 1 1 complex with phosphoryl chloride and that this attacks an aromatic compound of adequate reactivity to give a product hydrolyzed by water to an aromatic aldehyde. They prepared p-dimethyl-aminobenzaldehyde, but did not record full details ... 

Removal of the acetaldehyde by distillation shifts the equilibrium to the right The formation of semicarbazones (III) is a reaction common to all aldehydes. For preparative reasons we have only described reactions involving aromatic aldehydes, since these afford semicarbazones which crystallise very readily (eqn. 2) ... 

Aromatic Aldehydes. The preparation of aromatic aldehydes from benzene or monoalkyl and polyalkyl aromatic compounds by means of carbon monoxide and hydrogen chloride has been reviewed by Crounse (19). 

Another procedure involving IBX and ball milling could be effected, namely deprotection of dithianes 46 to prepare aldehydes (Scheme 6.16). Both aromatic and aliphatic aldehydes were prepared by Mai [ 10] employing this reaction protocol in high yield within 45 min to 1.5h, using the oxidation procedure described for IBX oxidation of alcohols to aldehydes (Z1O2 jar and ball, in Retsch MM 200 mill). 

Pd-catalyzed decarbonylation of aldehydes has been well-known. Also, Pd-catalyzed hydrofonnylation of alkenes to fonn aldehydes was reported, althongh the major reaction was hydrogenation to give alkanes. Aromatic aldehydes are prepared by the carbonyla-tion of aryl halides in the presence of H2 or other hydrides. Thus, Pd catalyzes both formation and decarbonylation of aldehydes (Scheme 10). 

Kurihara reported imidazomethyl phosphonates 35 as another HWE-type reagents. The 35 reacted readily with various aldehydes and ketons in the presence of t-BuOK to produce ( )-vinylimiazoles 36 in good to excellent yields. The reactions of 35 with all substrates, aliphatic aldehydes, aromatic and heteroaromatic aldehydes, provided substituted ( )-vinylimidazoles. The synthetic utility of the reagent 35 was demonstrated by the efficient preparation of few histamine H3 ligands (37) by simple hydrogenation of intermediate 36. 

Acid chlorides can be reduced to aldehydes either by catalytic hydrogenation or by reaction with a metal hydride. In both cases, the reagent and the reaction conditions are selected to avoid the further reduction of the aldehyde. The conversion of an acid chloride to an aldehyde can be carried out by the Rosenmund reduction, which uses hydrogen gas and a modified palladium catalyst. The palladium catalyst is altered to prevent further reduction of the aldehyde. To prepare the catalyst, the palladium is treated with quinoline, an aromatic heterocyclic amine, and is heated with sulfhr. 

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

For the preparation of oximes, pheuylhydrazones and p nitrophenyl-hydrazones (where applicable), see under Aromatic Aldehydes, Section IV,135,4-d. 

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