Furfural formation from d-xylose: the use of different halides in dilute aqueous acidic solutions allows for exceptionally high yields.

Starting from the results achieved in a previous work on the effects of Cl(-) ions on furfural formation in aqueous acid solution [Marcotullio, G. et al., Green Chem.2010, 12, 1739], the general effect of different halides is addressed. Experimental results show the halides to influence at least two distinct steps in the reaction leading from d-xylose to furfural under acidic conditions, via different mechanisms. The nucleophilicity of the halides appears to be critical for the dehydration, but not for the initial enolization reaction. By combining different halides synergic effects become evident resulting in very high selectivities and furfural yields.