TLC

The other method of identification and purification is through TLC.  Two plates were run, one with a comparison of the crude product with the starting material and another with the final, pure product compared to the starting material.  Because the starting material is less polar, than the expected product as it is a keytone, it will have a larger Rf value because it travels farther up the silica gel plate as it has less interactions with the plate.  The product of the reduction has an alcohol group and therefore more polarity.  As a result, the product is expected to have a smaller Rf value.  In the TLC of the crude 1,2-diphenylethane-1,2-diol, the filter paper of the TLC chamber was likely in contact with the right side of the plate causing the co-spot of starting material and crude product to travel inward. Despite this factor, the results of the TLC were still conclusive.  The spot of just the crude product’s Rf is 0.7708 and there no spot above it indicating there is no remnant starting material.  The Rf of the crude product is also similar to the Rf (0.7917) found in the co-spot of the starting material and the crude product.  In the TLC of the second plate comparing the starting material and the recrystallized pure product, 1,2-diphenylethane-1,2-diol, the results showed a slightly lower Rf value of 0.6808 of just the pure product and 0.7021 of co-spot.  Based on these lower numbers, the recrystallization process must have removed some nonpolar impurities from the solvent.  It also revealed the presence of some of the starting material in the pure product as seen by second higher spot with the Rf of 0.8936 which is consistent with the other starting material spots of the first lane (Rf= 0.8936) and the co-spot (Rf= 0.9149).  Based on the TLC, the final product is 1,2-diphenylethane-1,2-diol with some residual starting material in it causing the lower melting point as well as the second, higher spot of starting material.