Branching-First: Synthesizing C-C Skeletal Branched Biobased Chemicals from Sugars

© 2018 American Chemical Society. A novel strategy to biobased chemicals with a branched carbon skeleton is introduced. Hereto, small sugars, such as 1,3-dihydroxyacetone, are coupled catalytically to obtain branched C6 sugars, such as dendroketose, in high yield at mild conditions. By bringing this branching step up front, at the level of the sugar feedstock (branching-first), new opportunities for the synthesis of useful chemicals arise. Here, we show that the branched sugar can be efficiently valorized into (i) new branched polyols and (ii) short branched alkanes. The first route preserves most of the original sugar functionality by hydrogenation with Ru/C and renders access to branched polyols with three primary alcohol groups. These molecules are potentially interesting as plasticizers, cross-linkers, or detergent precursors. The second valorization route demonstrates a facile hydrodeoxygenation of the branched sugars toward their corresponding branched alkanes (e.g., 2-methylpentane). The highest alkanes yields (>65 mol % C) are obtained with a Rh/C redox metal catalyst in a biphasic catalytic system, following a HDO mechanism. In the short term, commercial integration of these monobranched alkanes, in contrast to branched polyols, is expected to be straightforward because of their drop-in character and well-known valuable octane booster role when present in gasoline. Accordingly, the branching-first concept is also demonstrated with other small sugars (e.g., tetroses) enabling the production of branched C6-C8 sugars and thus also branched C5-C8 alkanes after HDO.status: publishe

Branching-First: Synthesizing C–C Skeletal Branched Biobased Chemicals from Sugars

A novel strategy to biobased chemicals with a branched carbon skeleton is introduced. Hereto, small sugars, such as 1,3-dihydroxyacetone, are coupled catalytically to obtain branched C₆ sugars, such as dendroketose, in high yield at mild conditions. By bringing this branching step up front, at the level of the sugar feedstock (<i>branching-first</i>), new opportunities for the synthesis of useful chemicals arise. Here, we show that the branched sugar can be efficiently valorized into (i) new branched polyols and (ii) short branched alkanes. The first route preserves most of the original sugar functionality by hydrogenation with Ru/C and renders access to branched polyols with three primary alcohol groups. These molecules are potentially interesting as plasticizers, cross-linkers, or detergent precursors. The second valorization route demonstrates a facile hydrodeoxygenation of the branched sugars toward their corresponding branched alkanes (e.g., 2-methylpentane). The highest alkanes yields (>65 mol % C) are obtained with a Rh/C redox metal catalyst in a biphasic catalytic system, following a HDO mechanism. In the short term, commercial integration of these monobranched alkanes, in contrast to branched polyols, is expected to be straightforward because of their drop-in character and well-known valuable octane booster role when present in gasoline. Accordingly, the <i>branching-first</i> concept is also demonstrated with other small sugars (e.g., tetroses) enabling the production of branched C₆–C₈ sugars and thus also branched C₅–C₈ alkanes after HDO