Polysaccharides, telomerization

Palladium-Catalyzed Telomerization of Butadiene with Polyols From Mono to Polysaccharides... 

Abstract The telomerization of butadiene with alcohols is an elegant way to synthesize ethers with minimal environmental impact since this reaction is 100% atom efficient. Besides telomerization of butadiene with methanol and water that is industrially developed, the modification of polyols is still under development. Recently, a series of new substrates has been involved in this reaction, including diols, pure or crude glycerol, protected or unprotected monosaccharides, as well as polysaccharides. This opens up the formation of new products having specific physicochemical properties. We will describe recent advances in this field, focusing on the reaction of renewable products and more specifically on saccharides. The efficient catalytic systems as well as the optimized reaction conditions will be described and some physicochemical properties of the products will be reported. 

This reaction is environmental friendly since it produces no salt, provides a 100% atom efficiency, and can be performed in water to fulfill some green chemistry principles. In this review, we wish to focus on the telomerization of mono and polysaccharides. As an introduction, recent results achieved with several polyols will be summarized. 

It was shown from data summarized previously that telomerization of butadiene can occur with a large range of alcohols including reduced saccharides as well as mono- and disaccharides. It is of interest to extend such a reaction to much more complicated substrates such as polysaccharides (21) (Fig. 14). In that case, a low degree of substitution (average number of ether chains per glucose unit) is sufficient to modify deeply the physical properties of the organic polymer [51]. 

The catalyzed telomerization of butadiene has been applied to other polysaccharides such as inulin (22) (Fig. 20) which is a polyfructose extracted from Jerusalem artichokes (tuber) or from chicory (roots). This soluble polymer is easily telomerized under mild conditions and the degree of substimtion is also dependent on the reaction conditions [20] (Fig. 20). 

Hydrogenation of the lateral chain of telomerized polysaccharides (starch, inulin) has been carried out using homogeneous RhCl(TPPTS)3 complex (0.8%) at40°C under 30 atm. H2 in H20/EtOH (5/1) mixture. Both terminal and substimted double bonds were successively hydrogenated [59]. 

Starch is an abundant, inexpensive polysaccharide that is readily available from staple crops such as com or maize and is thus is mostly important as food. Industrially, starch is also widely used in papermaking, the production of adhesives or as additives in plastics. For a number of these applications, it is desirable to chemically modify the starch to increase its hydrophobicity. Starch modification can thus prevent retrodegradation improve gel texture, clarity and sheen improve film formation and stabilize emulsions [108], This may, for example, be achieved by partial acetylation, alkyl siliconation or esterification however, these methods typically require environmentally unfriendly stoichiometric reagents and produce waste. Catalytic modification, such as the palladium-catalyzed telomerization (Scheme 18), of starch may provide a green atom-efficient way for creating chemically modified starches. The physicochemical properties of thus modified starches are discussed by Bouquillon et al. [22]. 

The previous section illustrates that the polysaccharide components of lignocellu-losic biomass provide ample opportunities for the telomerization reaction to convert (hemi-)cellulose-derived renewable building blocks such as saccharides, sugar alcohols and polyols into valuable bulk chemicals. The third key component of... 

Bouquillon S, Muzart J, Pinel C, Rataboul F (2010) Palladium-catalyzed telomerization of butadiene with polyols from mono to polysaccharides. Top Curr Chem 295 93-119... 

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