Reimer-Tiemann synthesis

THE REIMER-TIEMANN SYNTHESIS SALICYLALDEHYDE FROM PHENOL AND CHLOROFORM 1... 

There are, in addition, a number of methods by which the aldehyde group is introduced into an aromatic ring for example, the Reimer-Tiemann synthesis of phenolic aldehydes (Sec. 24.12). 

Phenolic aldehydes can be obtained by the Duff reaction, in which the phenol is heated with urotropine, boric acid, and glycerol for 30 minutes at 150-160° 857 the yields are not high (15-20%), but the procedure is simpler and less time -consuming than the Reimer-Tiemann synthesis the products are the ortho-derivatives. Dialkylanilines can be formylated in the same way,858 but here the products are the para-aldehydes. 

The reaction of phenol with chloroform and alkali (dichlorocarbene) at 65 to 70 °C gives salicylaldehyde (Reimer-Tiemann synthesis), from which coumarin is produced by reaction with acetic anhydride and sodium acetate at 135 to 155 °C (Perkin reaction). Coumarin is used as a perfume and fragrance. 

The formylation of a phenol 1 with chloroform in alkaline solution is called the Reimer-Tiemann reaction. It leads preferentially to formation of an ortho-formylated phenol—e.g. salicylic aldehyde 2 —while with other formylation reactions, e.g. the Gattermann reaction, the corresponding /jara-formyl derivative is obtained as a major product. The Reimer-Tiemann reaction is mainly used for the synthesis of o-hydroxy aromatic aldehydes. 

Crafts alkylation and acylation (Section 22-4E and 22-4F), the Gattermann-Koch reaction for preparation of aldehydes from arenes and carbon monoxide (Section 22-4F), and the Kolbe-Schmitt, Reimer-Tiemann, and Gattermann reactions for synthesis of acids and aldehydes from arenols (Section 26-1E). 

Another example of minimizing the reaction steps necessary for synthesis is the direct conversion of cresols into hydroxybenzaldehydes, replacing the Reimer-Tiemann reaction in which phenol is reacted with chloroform in the presence of KOH. Hydroxybenzaldehydes are used in pharmaceuticals, perfumes, and colors. In the direct oxidation cresols are reacted with oxygen in the presence of Cu/Co/C catalysts forming the salicylaldehyde [49]. 

The classical synthesis of vanillin from eugenol or isoeugenol was developed in 1896 and it remained the preferred method for about 50 years. Vanillin is now prepared industrially in large amounts by the Reimer-Tiemann reaction, starting with... 

Treatment of a phenol with chloroform (trichloromethane) in the presence of hydroxide ion results in the synthesis of a 2-hydroxybenzalde-hyde through C-formylation. Dichlorocarbene, CCl2, is generated by the action of base on chloroform and this highly reactive electrophile then attacks the phenoxide. The mechanism of the Reimer-Tiemann reaction, is given in Scheme 4.12. 

REIMER TIEMANN Phenol formylation 314 REISSERT-GROSHEINTZ FISCHER Cyanoamme reaction 315 REPPE Acetylano reaction 3t6 von RICHTER Aromatic carboxylalion 317 von RICHTER - WIDMAN - STOERMER Cmndme synthesis 3t8 RILEY Selenaim dioxide oxidation 319 Rimmi 4... 

From Phenols by CCI4.—The Reimer-Tiemann reaction for the synthesis of hydroxy aldehydes (p. 659) is ... 

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