Sucrose, telomerization

The reaction was first conducted with success on sucrose [82], The degree of substitution (DS) obtained was controlled by the reaction time. Thus, under standard conditions (0.05% Pd(OAc)2/TPPTS, NaOH (1 M)/iPrOH (5/1), 50 °C) the DS was 0.5 and 5 after 14 and 64 h reaction time, respectively. The octadienyl chains were hydrogenated quantitatively in the presence of 0.8-wt.% [RhCl(TPPTS)3] catalyst in a HjO-EtOH (50/10) mixture, yielding a very good biodegradable surfactant (surface tension of 25 mN m-1 at 0.005% concentration in water) [84]. Telomerization reaction was also conducted with success on other soluble carbohydrates such as fructose, maltose, sorbitol and /i-cyclodextrin. 

As compared to the esterification of sucrose, cataly tic etherification of sucrose provides another family of non-ionic surfactants that are much more robust than sucrose esters in the presence of water. Synthesis of sucroethers can be achieved according to two processes (1) the ring opening of epoxide in the presence of a basic catalyst and (2) the telomerization of butadiene with sucrose using a palladium-phosphine catalyst. 

The application of sucrose derivatives as surfactants, plastics, or polymers is attractive because this pure and cheap carbohydrate is a renewable polyfunctional starting material. The telomerization of sucrose (20) was initially reported by Hill et al. [11, 39] using a Pd(ll)/PPh3 catalytic system in an i-PrOH/H20 mixture (Fig. 13). 

Table 11 Telomerization of butadiene (1) with sucrose (20) in water-based solutions...

Sucrose (20) was also used for the reaction of telomerization with 1 [19, 49, 50]. Applying specific conditions, sucrose octadienyl ethers were obtained with an average degree of substitution of 4.7-5.3. These products are practically insoluble in water, clear or almost colorless, and present a viscosity of 1500-2000 cPs at 25°C [39]. These properties confer to these products the possibility of being employed as emulsifiers or defoaming agent [49]. Minimum surface tension of solution of substituted sucrose in water is 25-28 mN/m whatever the degree of substitution... 

DS < 1). However, this value is achieved for 1 g/L for the telomerized sucrose (DS = 0.4) and 0.1 g/L for the corresponding saturated compound. This was correlated with high foaming capability [20]. 

Other Alkyl Ethers. Sucrose has been selectively etherified by electrochemical means to generate a sucrose anion followed by reaction with an alkyl halide (21,22). The benzylation of sucrose using this technique gives 2-O-benzyl- (49%), T-O-benzyl- (41%), and 3 -O-benzyl- (10%) sucrose (22). The benzylation of sucrose with benzyl bromide and silver oxide in DMF also produces the 2-O-benzyl ether as the principal product, but smaller proportions of T- and 3 -ethers (23). Octadienyl ether derivatives of sucrose, intermediates for polymers, have been prepared by a palladium-catalyzed telomerization reaction with butadiene in 2-propanol—water (24). 

The telomerization of sucrose with butadiene was catalyzed in aqueous solution by palladium acetate and tppts (102). The sucrose conversion was about 96%, but octadienyl ethers of different degrees of alkylation were also formed. 

Alkyl ethers of sucrose have been prepared by reaction with long-chain alkyl halides to provide mixtures of regioisomers and products of different degree of substitution.82,83 A similar reaction with chloromethyl ethers of fatty alcohols provides formaldehyde acetals.84,85 Alkenyl ethers of various carbohydrates, and notably of sucrose, can also be obtained by palladium-catalyzed telomerization of butadiene (Scheme 6).86 88 Despite a low-selectivity control, this simple and clean alternative to other reactions can be carried out in aqueous medium when sulfonated phosphines are used as water-soluble ligands. 

K. Hill, B. Gruber, and K. J. Weese, Palladium catalyzed telomerization of butadiene with sucrose A highly efficient approach to novel sucrose ethers, Tetrahedron Lett., 35 (1994) 4541 1542. 

I. Pennequin, J. Meyer, I. Suisse, and A. Mortreux, A further application of TPPTS in catalysis Efficient sucrose-butadiene telomerization using palladium catalysts in water, J. Mol. Catal. A Chem., 120 (1997) 139-142. 

Hausoul et al. [60] also reported on telomerization with aldopentoses (D-xylose, L-arabinose), aldohexoses (D-glucose, D-mannose, D-galactose), ketohexoses (d-fructose, L-sorbose) and the disaccharides D-sucrose and cellobiose, using Pd/ TOMPP as catalyst without the addition of base in /V,/V-di methyl acetamide as the solvent (Fig. 15). The Pd/TOMPP combination had previously been shown to be highly active in the telomerization of various polyols (vide supra). Good conversion... 

Pennequin et al. [89, 106] observed a much-improved selectivity towards the mono- and di-telomers by using the TPPTS ligand in an aqueous phase with added isopropanol and NaOH. At a Pd loading of 0.40 mol% (relative to sucrose) with TPPTS (P/Pd = 3), a sucrose conversion of 73% was observed after 30 min, with a selectivity of 66% to the mono-telomer and 32% to the di-telomer. The group of Pinel also used Pd/TPPTS for the telomerization with sucrose in water, obtaining differently substituted sucrose telomers depending on the chosen reaction parameters [ 107]. 

Further work was done in the telomerization of butadiene with carbon dioxide yielding a a-lactone in good yields [116-118]. For the catalyst recycle the successive extraction of the product with 1,2,4-butanetriol was proposed and investigated in detail. Mortreux et al. studied the telomerization of butadiene with sucrose which could also be carried out efficiently in water-organic medium in the presence of Pd salt and TPPTS [119]. Mono- and dioctadienylether were selectively obtained using aqueous sodium hydroxide/isopropanol mixtures. 

The telomerization of sucrose has been studied more in depth. Using water alone as solvent, sucrose conversion was only 65% after 5 hours with 36% of mono and 48% of dioctadienyl compounds. The use of basic conditions (sodium hydroxide 1 M) resulted in a large increase of the catalytic activity for example, after only 26 minutes, 87% of sucrose was very selectively converted into octadienyl ethers with a higher average degree of substitution (DS = 2.4) (Scheme 11). Under these conditions, a turnover frequency of 5400 h could be observed after 20 min, at the maximum conversion rate. ... 

Scheme 11 Telomerization of butadiene with sucrose in basic aqueous medium.

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