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OH
OH
OH
Methanol
H
3
PW
12
O
14
N
2
= 30 bar,
468 K
O
O
O
O
O
HO
O
O
HO
HO
HO
OH
n
OH
OH
Methyl glucoside
Yield = 50-60%
Cellulose
+ Long-chain
alcohols
OH
OH
OH
Long-chain alcohols
O
O
HO
O
R
O
O
O
O
HO
Ionic liquid, 363 K,
Vacuum (40-400 mbar)
HO
HO
OH
OH
n
OH
Alkyl glucosides
surfactants
Cellulose
Scheme 31 Procedure for the transformation of cellulose into alkyl glucosides.
OH
OH
OH
OH
HO
HO
HO
HO
O
O
O
O
7
O
OH
OH
OH
O
O
O
OH
OH
OH
OH
N
7
N
OH
76% Selectivity
PS
PS-Im
0.5 eq.
Scheme 32 Sucrose etherification with epoxydodecane.
3.6 Ring opening of epoxides by carbohydrates on heterogeneous
catalysts
The base catalyzed synthesis of b-hydroxy ethers via ring opening of ep-
oxides is a useful tool for the synthesis of amphiphilic compounds de-
rived from sucrose or methyl-
D
-glucopyranoside.
91
Soluble bases such as
DMAP or tertiary amines are commonly used as homogeneous catalysts
for the reaction in water or a polar solvent such as DMSO. Heterogenized
catalytic systems have also been used. Sucrose etherification with the 1,2-
epoxydodecane was investigated using basic anion-exchange resins as
catalyst.
92
However, the recyclability of the catalyst was found to be
problematic (Scheme 32).
Using disaccharides such as sucrose, trehalose and isomaltose and 1,2-
epoxydodecane on an imidazole grafted polystyrene (PS-Im), the same
group has shown that good yields and chemoselectivities in mono-
hydroxyalkylethers were obtained, with major etherification at OH-2 in
the case of sucrose (Scheme 32).
93
Although the catalyst content needed
to be very high (0.5 eq vs substrate) to avoid epoxide side reactions, the
catalyst was found to be recyclable by simple filtration, allowing to pro-
duce non-ionic surfactants that exhibit similar foaming properties as
APGs or sucroesters.
4 Conclusion
The ecient etherification of carbohydrates remains a synthetic chal-
lenge. The Williamson reaction is unambiguously one of the most gen-
erally used chemical transformation and the recent literature evidences
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