From 5-Hydroxymethylfurfural (HMF) to Polymer Precursors: Catalyst Screening Studies on the Conversion of 1,2,6-hexanetriol to 1,6-hexanediol

1,6-hexanediol (1) is an important polymer precursor for the polyester industry. In this paper, exploratory catalyst screening studies on the synthesis of 1 from 1,2,6-hexanetriol (2) are described via two different routes. The latter is available by a two-step procedure from 5-hydroxymethylfurfural (HMF, 3), a promising bio-based platform chemical. In the first approach, the direct catalytic hydrodeoxygenation of 2 to 1 with heterogeneous catalysts and molecular hydrogen was explored. Best results were obtained using a Rh-ReOx/SiO2 catalyst in water (180 A degrees C, 80 bar H-2, 20 h reaction time), leading to full conversion of 2 and 73 % selectivity to 1, the main byproduct being 1,5-hexanediol (4). In a second approach, 2 was first converted to tetrahydropyran-2-methanol (2-THPM, 5) in quantitative yield using triflic acid as catalyst (125 A degrees C, 30 min). Various catalysts were explored for the subsequent ring opening/hydrodeoxygenation of 5 to 1 using a hydrogenation protocol and the best results were obtained with a Rh-ReOx/SiO2 catalyst, viz. 96 % selectivity to 1 at 26 % conversion (120 A degrees C, 80 bar H-2, 20 h)