Conversion of Benzal Halides to Benzaldehydes in the Presence of Aqueous Dimethylamine

Abstract

Aqueous dimethylamine is an efficient reagent for the conversion of a variety of benzal halides to their corresponding benzaldehydes. Studies indicate that aqueous dimethylamine significantly accelerates aldehyde formation from benzal halide precursors, as compared to the use of water alone. Indeed, these reactions are routinely completed in one hour or less, depending upon substrate substitution. Desired products can be isolated in pure form, and in high yield, but silica gel filtration is often necessary to remove baseline contaminants. The method represents a novel, economical approach to acquire pure, substituted benzaldehydes from commercially available, or easily prepared starting materials.

Theoretical considerations on the hydrolysis of 2‐dichloromethylbenzimidazole

“…There are two possible ways for the intermediate 3b to react: first of them, in agreement to the results obtained for intermediates 1b-2b, when benzimidazole-2-carboxaldehyde should be obtained, and second, according to the behavior of 2-substituted benzimidazole derivatives [3], when dimerization of intermediate 3a occurs and a pentacyclic structure is obtained (see Fig. 2).…”

“…With these considerations one could propose the synthesis of benzimidazole-2-carboxaldehyde under milder reaction conditions like the reaction of aromatic dihalogenomethyl derivatives with aqueous solution of secondary aliphatic amines [3].…”

Reaction of benzal bromides in water/dioxane system for easy access to benzaldehydes and 2-formylbenzonitriles (2-cyanobenzaldehydes)

“…27,28 Under the described conditions, the hydrolysis was also effective in the synthesis of the benzaldehyde and of other monosubstituted benzaldehydes bearing different substituents ( Table 2). All pure products were isolated in very high yields from the workup without any further chromatographic purification, the results being somewhat better than or comparable with those reported in the literature.…”

“…2,19 On the other hand, the transformation of gem-dihalo compounds (benzal halides) into benzaldehydes is quite a common method. [20][21][22][23][24][25][26][27][28][29][30] In this case solvolytic displacement of halogen with successive replacement by hydroxyl followed by formal loss of HBr to generate the corresponding aldehyde, is favored by resonance stabilization offered by the aromatic ring. 29 Figure 2.…”

“…All pure products were isolated in very high yields from the workup without any further chromatographic purification, the results being somewhat better than or comparable with those reported in the literature. 27,28 Only the dibromide bearing the strongly electron-withdrawing nitro group was less reactive, and unreacted starting material was recovered (Entry 4).…”