Page 81 - Visions of the Future Chemistry and Life Science

70 D. J. MACQUARRIE

existing processes being far from ‘green’. Thus researchers have been
active in preparing analogous MTS structures containing titanium.
Results with these MTS materials have shown that these materials are
indeed capable of carrying out many of the desired reactions, but without
the limitations of size which hamper the zeolites. For example, one of the
important applications of titanium-containing zeolites is the hydroxyla-
tion of benzene to phenol (which is used as a precursor to antioxidants for
food and cosmetic use), and then further to hydroquinone, used in the
photography industry as a developer. Ti containing MTSs are known and
can carry out the same type of transformations as the corresponding
zeolite. Larger molecules such as naphthalenes, which cannot enter the
pores of the zeolites, can access the pores of the MTSs, and react in the
expected manner. One important target is Vitamin K3, a derivative of
naphthalene, formed by hydroxylation. Current practice still involves the
use of acidic chromium reagents which are used in large quantities, and
are highly toxic. Significant success has been reported with the use of Ti
containing mesoporous materials of this reaction type, and further
progress is expected (see Figure 4.7).
The organically modified versions of these materials have also been
investigated as catalysts. These materials have great potential, as the incor-
poration of organic groups will allow a much wider variety of materials to
be prepared, and thus a much wider range of applications can be investi-
gated. Simple amine (an example of a basic group, which will remove a
proton from a molecule, thus making it able to react in many ways) con-

Figure 4.7. Possibilities for the synthesis of Vitamin K3. The small pore titanium
zeolite TS-1 cannot fit the large naphthalene molecule into its pore system, and
thus is effective in this transformation. The larger titanium MTS material is
capable of interacting with the molecule, and the desired transformation can take
place.