Column 25 cm long, carrying XE-60-L-valine-s-a-phenylethylamide, operated at 180 C Courtesy of Angew, Chem,(ref26)

Figure 41. The Separation of Some b. Hydroxy Acids as their O-(isopropyl-Carbamoyl) Isopropylamides.

Temperature stable chiral stationary phases can also be prepared from the polar polysiloxane OV-225 by converting the cyano group into Chirasil-Val type polymers. Saeed et al., (25 ) hydrolyzed the cyano groups on the OV-225 and the carboxy groups so formed coupled with vailine-t-butylamide by the amino group. K nig et al., (26) synthesized a modified form of the same polymer containing (R) - or (S) - a - phenylethylene as an additional chiral component. This stationary phase became known commercially as XE-60-L-valine-S-a-phenylethylamide. The separation of racemic b-hydroxy acids as their O-(isopropyl-carbamoyl)isopropylamides on this stationary phase is shown in figure 41.

K nig et al., (27 ) also reduced the cyano groups of the polar polysiloxane OV-225 to the amine and then coupled it with N-acyl-L-valine via the carboxyl group. This material was also used extensively for chiral separations.