We demonstrate the efficient and direct transformation of a range of low value substrates, such as lignocellulose and algal biomass, into significantly higher value chemicals, including low molecular weight reducing saccharides, 5-(hydroxymethyl)furfural, furyl hydroxymethyl ketone and furfural. This is based on a systematic study of ZnCl₂·nH₂O (n = 2.5–4.5), in particular the role of the molecular formula (the amount of H₂O) on its activity in the catalytic transformation of cellulosic materials into value added small molecules. The study includes various model transformations based on refined saccharides and applies the new insights to the highly selective transformation of raw biomass.