112642-90-7Relevant articles and documents
Les dialkoxy-2,2 ethanals, synthons difonctionnels a deux carbones : preparation par acetalisation du glyoxal et quelques applications en synthese
Stambouli, Abdelhamid,Hamedi-Sangsari, Farid,Amouroux, Roger,Chastrette, Francine,Blanc, Alain,Mattioda, Georges
, p. 95 - 100 (2007/10/02)
Known for a long time, 2,2-dialkoxy ethanals had to be prepare by rather tedious indirect pathways since monoacetalization of glyoxal was unknown.We discovered that it is possible to acetalize only one of the glyoxal functions using a great excess of alcohol, in the presence of an active enough catalyst.With careful monitoring of the reaction, 50 to 70 percent yield of monoacetals is obtained.The monoacetal is formed much quicker than the diacetal and the maximum yield is rather quickly obtained; with further elimination of water, diacetalization proceeds at the expense of the monoacetal.Depending on azeotropic compositions and boiling points, one of the following methods is used: 1.General method: 40 percent aqueous glyoxal (1 mol), alcohol (10 mol), catalyst (0.01 to 0.1 equivalent) and solvent are refluxed with azeotropic water extraction.The monitored (GC) reaction is stopped at the most favourable moment. 2.Method without solvent, convenient for unreactive alcohols, such as i-butanol: water is evaporated from glyoxal solution (1 mol); the residue, alcohol (10 mol) and catalyst are refluxed with water azeotropic extraction. 3.Method without solvent and without water azeotropic extraction: dehydrated glyoxal (1 mol) is refluxed with alcohol (10 mol) and catalyst.This method is the most convenient for methanol and ethanol.This sample and inexpensive preparation of 2,2-dialkoxy ethanals prompted us to perform syntheses of difunctional molecules otherwise only tediously accessible, since easily obtained functionalized acetals can be hydrolysed to functionalized aldehydes which constitute interesting synthons.Hydride or catalytic reduction as well as organometallic reactions lead to alcohols, further hydrolysed into 2-hydroxy aldehydes or oxidized to give way finally to α-ketoaldehydes for which this method provides a general synthetic pathway.From the oximes, prepared by classical methods, nitriles and amines can be obtained.Starting directly from the aldahydes, amines may be prepared by hydrogenation in the presence of ammonia or amines.The reaction of 2,2-dialkoxy ethanals with amides provides hydroxy and alkoxy acetal amides.The Cannizzaro reaction was also investigated; the same reactivity is displayed by formaldehyde and glyoxal monoacetals.Other reactions, among which Wittig and Wittig-Horner, are presently being studied in our laboratory.
