Sugar-based hydrotropes: preparation, properties and applications - Carbohydrate Chemistry: Chemical and Biological Approaches - page 59

Fig. 7 Classical and catalytic routes to glycerol-based hydrotropes. 50,51-56,58

Fig. 8 Classical and catalytic routes to isosorbide-based hydrotropes. 58,59,62

achieved with higher selectivity towards the monobutyl ethers, obtained
as a mixture of isomers (Fig. 7). 58
Liu et al. also performed the direct dehydration/alkylation of sorbitol
under the same conditions to access the monobutyl ethers of

isosorbide 58 (Fig. 8).
Monoethers of isosorbide are attractive bio-based hydrotropes 35,36,59-64
due to the increasing availability of isosorbide that is readily obtained by
the double dehydration of sorbitol. The development of ecient access to
monosubtituted isosorbide to provide amphiphilic species is thus of
great interest. As isosorbide (1,4 : 3,6-dianhydro-D-glucitol) has two
non-equivalent hydroxyl groups, two positional isomers with different
physico-chemical properties (see next section) can be obtained. OH-2
(exo-orientation with respect to the fused rings) is more accessible,
whereas OH-5 (endo-orientation) is more acidic because it is involved in
an intramolecular hydrogen bond with the oxygen atom of the neigh-
bouring tetrahydrofuran ring, which drives the selectivity towards one or
the other isomer depending on the reaction conditions (Fig. 8). The
preparation of monoethers of isosorbide can be performed under
classical Williamson conditions, with the drawbacks already mentioned
above. Alternatively, isosorbide monooctadienyl ethers could be prepared
eciently by the Pd-Catalyzed telomerisation of butadiene 62 (Fig. 8). The
reaction can be performed either in neat water or using catalytic amounts