Decarbonylation and dehydrogenation of carbohydrates

Abstract

Carbohydrates, especially aldose or ketose sugars, including those whose carbonyl group is masked by hemi-acetal or hemi-ketal formation, are decarbonylated by heating the feed carbohydrate together with a transition metal complex in a suitable solvent. Also, primary alcohols, including sugar alditols are simultaneously dehydrogenated and decarbonylated by heating a mixture of rhodium and ruthenium complexes and the alcohol and optionally a hydrogen acceptor in an acceptable solvent. Such defarbonylation and/or dehydrogenation of sugars provides a convenient procedure for the synthesis of certain carbohydrates and may provide a means for the conversion of biomass into useful products.

We claim: 
     
       1. A process for the decarbonylation of an aldose or kitose sugar, each of said sugars having unprotected alcohol moieties, comprising the steps of: (a) dissolving said sugar in a solution containing a transition metal complex decarbonylation agent, selected from the group consisting of chlorotis(triphenylphosphine)rhodium, dichlorotetrakis(triphenylphosphine) dirhodium, chlorotris(diphenylmethylphosphine)-rhodium, [Rh(Ph 2  PCH 2  CH 2  PPH 2 ) 2  ] + , and mixtures thereof, and a suitable aprotic, polar solvent free of CO-donating impurities, under an inert atmosphere; and   (b) heating the carbonyl-free solution containing the dissolved sugar which results from step (a) for a time sufficient to effect decarbonylation of said sugar while maintaining said inert atmosphere.   
     
     
       2. The method of claim 1 wherein the decarbonylation process is conducted under nitrogen. 
     
     
       3. The process of claim 1, wherein said aldose sugar is selected from the group consisting of glucose, arabinose, glyceraldehyde, 2-deoxyribose, glucoheptose and glycol aldehyde. 
     
     
       4. The process of claim 1 wherein said ketose sugar is selected from the group consisting of fructose and 1,3-dihydroxyacetone. 
     
     
       5. The process of claim 1 wherein said sugar is an unprotected sugar existing predominantly in the form of a hemi-acetal or a hemi-ketal. 
     
     
       6. The process of claim 1 wherein the resulting mixture is heated to a temperature in the range of from about 75° C. to about 150° C. 
     
     
       7. The process of claim 1 wherein said suitable solvent is selected from the group consisting of polar amide solvents. 
     
     
       8. The process of claim 7 wherein said solvent is selected from the group consisting of N-methyl-2-pyrrolidinone and dimethylacetamide.