Separation of Diastereomers

Although diastereomers are in general easy to separate under normal or reversed-phase chromatographic conditions, it often happens, especially when the chiral centres are located far away from each other, that it is not always easy to separate these compounds. When we are confronted with such a problem, we always investigate the possibilities of micro-crystalline cellulose triacetate or tribenzoate and the physically coated derivatized polysaccharides. We have experienced that this approach can be a solution in many cases. An example of such a separation is described in the next example.

A racemic alcohol was derivatized with optically pure (1S)-camphor sulfonic acid chloride. It was not possible to separate the obtained diastereomers under normal-phase conditions on bare silica or amino-modified silica. Under the reversed-phase conditions which we generally apply in our laboratories it was not possible to separate the isomers. We did some experiments on different derivatized polysaccharide phases. On a 50 x 4.6 mm i.d. Chiralpak AD (amylose 3,5-dimethylphenyl carbamate) using ethanol as the eluent, the diastereomers were very well separated. Because with pure ethanol the retention factors were relatively high, the effect of the addition of acetonit-rile was investigated. A few chromatograms of these experiments are depicted in Figure 5. Using a mixture of 95 vol% ethanol and 5 vol% acetonitrile, it was easy to isolate a large pure amount of both dias-tereomers.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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