Quinoline Skraup’s synthesis

Sulphuric acid is the condensing agent used. The reaction might be compared with the preceding reaction and with Skraup s quinoline synthesis (see p. 165). 

REACTION SKRAUP S QUINOLINE SYNTHESIS Example Quinoline... 

Quinoline is a colorless liquid, b.p. 239°, with a characteristic odor. It possesses the properties of a tertiary amine base forming salts as pyridine does. It is present with the latter in coal tar and in bone oil but is usually not obtained from these sources being prepared by Skraup s synthesis. 

The classical method of quinoline synthesis involves Skraup s procedure. " However, it requires a large amount of H2SO4 at elevated temperature and the reaction often becomes violent. 

Scheme 7. The classical Skraup quinoline synthesis (a) and Fukuyama s modified approach (b) using /V-aryl-AZ-sulfonylaminopropionaldehydes (56).

Doebner-von Miller reaction is a variant of the Skraup quinoline synthesis (page 509). Therefore, the mechanism for the Skraup reaction is also operative for the Doebner-von Miller reaction. The following mechanism is favored by Denmark s mechnistic study using C-labelled a,P-unsaturated ketones. ... 

On the other hand molybdenum species, due to their Lewis acidity, catalyse mainly the condesation reactions similar to those proposed in the mechanism o-f the acid catalysed Skraup s synthesis o-f quinolines -from aldehydes and anilines ... 

Quinoline, Leucoline chinoletne 1 -benzazine benzo[b]pyridine. CJf,N mol wt 129.15. C 83.69%, H 5.46%. N 10.85%. Occurs in small amounts in coal tar. Prepd by the Skraup synthesis by heating aniline with glycerol and nitrobenzene in presence of sulfuric acid Clarke, Davis, Org. Syn. coll vol. I, 478 (Ind ed., 1941) 478 alternate syntheses Manske, Chem. Rev. 30, 113 (1942) Berg -strom, ibid. 35, 150 (1944). Process based on the interaction of aniline with acetaldehyde and a formaldehyde hemiacetal Cislak, Wheeler. U-S. pat. 3,020,281 (1962 to Reilly Tar A Chem.). Toxicity data Smyth etal. Arch. Ind. Hyg. Occup. Med. 4, 119 (1951). 

Skeletal rearrangement s. Rearrangement, skeletal Skraup quinoline ring synthesis... 

The formation of quinolines by irradiation in alcohols has been known from Ciamieian s times actually, the components for a Skraup synthesis are generated in situ by photoredox processes. A dedieated system has been devised, based on an arenesulfonic acid functionalized mesoporous silica decorated with titania. The examination has been extended to various nitrobenzenes and different Ti02 catalysts, and shown to be quite general, though with a different product distribution. Platination of the catalyst reduced the imine function and directed the process toward N-allqrlation. The related reaction leading to benzimidazoles from o-nitroanilines has been likewise optimized from the preparative point of view. ... 

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