4.5.1 Solvent selection
The selection of a proper solvent is crucial in any (photo)chemical
reaction. Here, this is even more significant as the solvent should play
a role in different process steps. First, it should be able to
solubilize the cyclooctene (both cis - and trans -) and the
sensitizer. Also, the solvent has to be transparent at the required
wavelength, 245 nm. On the other hand, it should not dissolve the
packing powders
(AgNO3/silica).
If AgNO3 dissolves, the trans -complex will not be
collected in packed bed and there is no separation of thetrans -isomer from the cis -isomer. This means that there is
no equilibrium shift in the direction of the trans -isomer.
Considering the features mentioned, n-hexane or cyclohexane seem to be
proper choices. Cyclohexane has a higher boiling point than n-hexane.
Since to desorb trans -cyclooctene from
AgNO3/SiO2 there is an elution step
needed which is not included in this process design. Therefore, as the
solvent of this process, n-hexane is preferred. Also, in order to
increase the solubility of cis and trans -cyclooctene 1%
of diethyl ether is added. It is worth mentioning that diethyl ether
dissolves AgNO3, so it is recommended not to increase
the ratio of diethyl ether to n-hexane to more than 5:95 (volume ratio).