A new selective route to 5-hydroxymethylfurfural from furfural and furfural derivatives over microporous solid acidic catalysts

Hydroxymethylation of furfural and its 1,3 dithiolane derivative with aqueous formaldehyde was performed in a batch mode in the presence of dealuminated mordenites as catalysts, at 363 K. Starting from furfural, the selectivity to 5-hydroxymethylfurfural is about 30% whatever the catalysts. However, the selectivity can rise up to 50% if an organic co-solvent is used for simultaneous extraction of 5-hydroxymethylfurfural from the aqueous phase. The low selectivity to 5-hydroxymethylfurfural was attributed to the weak reactivity of furfural resulting from the deactivation of the position 5 on the furan ring due to the electron-withdrawing character of the aldehyde group. The direct consequence of this deactivation is that the main reaction is the fast addition of formaldehyde to the aldehyde group of furfural, leading to resins. However, the unfavorable electronic effect can be bypassed by protection of the aldehyde via a thioacetal function with now an electron-donating character. In this way, hydroxymethylation of the 1,3-dithiolane derivative of furfural is easily achieved to yield the corresponding 1,3-dithiolane derivative of 5-hydroxymethylfurfural. The latter aldehyde can then be easily recovered by deprotection of the thioacetal function. (Résumé d'auteur