Starch telomerization

To prepare more hydrophobic starches for specific applications, the partial substitution of starch with acetate, hydroxypropyl, alkylsiliconate or fatty-acid ester groups has been described in the literature. A new route, however, consists of grafting octadienyl chains by butadiene telomerization (Scheme 3.9) [79, 82, 83], The reaction was catalyzed by hydrosoluble palladium-catalytic systems prepared from palladium diacetate and trisodium tris(m-sulfonatophenyl)phosphine (TPPTS). 

Fig. 3.4 Modification of starch by butadiene telomerization. Influence of the catalyst mass and temperature on the degree of substitution (DS).

Keywords Hydrophobic starch, Octadienyl ether, Palladium, Surfactant, Telomerization, Water catalyzed reaction... 

Fig. 15 Influence of the temperature on the degree of substitution for the telomerization of butadiene with starch...

Table 12 Influence of the presence of i-PrOH on the telomerization of butadiene (1) with starch (21)...

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]. 

Fig. 23 Viscosity profiles of (a) native starch, (b) Native starch heated up at 50°C for 24 h. (c) Telomerized starch with DS = 0.055. (d) Telomerized starch with DS = 0.1. Dotted line. temperature profile...

Some properties of substituted starches were determined [55]. The viscosity of telomerized starches (DS < 0.1) was evaluated by heating a suspension of the material in water for 15 min (Fig. 23). 

The surface polarity of telomerized starches was determined by the contact angle technique. The surface free energy of the solid was measured from the contact angles of a drop of various probe liquids with the surface of a starch tablet (Table 16). 

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]. 

There are a number of unique challenges in telomerization with starch for a suitable hydrophobicity, only a very low degree of substitution (<0.1) is required. While this means that lower catalyst activity can be acceptable, the catalyst must still be active at low 1,3-butadiene concentrations. In addition, starch may gelatinize at elevated temperatures, thus losing its desired properties. Furthermore, starch is practically insoluble in water at room temperature, making efficient interaction between the catalyst and starch difficult. 

Table 6 Influence of surfactant on the telomerization with starch at low 1,3-butadiene concentrations [110]...

Donze U, Pinel C, Gallezot P, Taylor PL (2002) Palladium-catalyzed telomerization of butadiene with starch. Adv Synth Catal 344 906-910... 

Mesnager J, Quettier C, Lambin A, Rataboul F, Pinel C (2009) Telomerization of butadiene with starch under mild conditions. ChemSusChem 2 1125-1129... 

Some natural polymers have also been used as support for Schiff base ligands. A starch support has also been used as support for a PyBox. A telomerized starch 96 [91] presenting a final double bound reacted with a thiol-PyBox in the presence of AIBN (Scheme 45) to form the corresponding immobilized PyBox. [92] Although the Ru-97 complex exhibited lower activity (up to 44% after the third reuse) and selectivity (trans/cis 76/24 with 50% ee for the... 

In order to avoid the use of an organic co-solvent with aqueous mixtures, telomerization of butadiene with starch has been performed in pure water in the presence of surfactants.The best activity was achieved using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant. Using the system [(7i-allyl)Pd(TPPMS)2]/CTAB/Na2S04/CTAB (TPPMS = (m-sulfonatophenyl)-diphenylphosphine monosodium salt) in... 

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