Ammonium Chloride, an Effective Promoter of Catalytic Enantioselective Hydrogenation

5 Ammonium Chloride, an Effective Promoter of Catalytic Enantioselective Hydrogenation 

In a separate experiment, a very strong correlation between the concentration of ammonium chloride (up to around 500 ppm), on the one hand, and e.e. and conversion, on the other, was observed (Fig. 4.3) [27]. 

Data shown by circles in the figure correspond to percent conversion, as measured by liquid chromatography (LC). Data points marked by squares correspond to percent enantiomeric excess, as measured by LC of the areas under the peaks for the 1 -enantiomer of sitagbptin free base. Since solutions of ammonium chloride are 

This study illustrates the fact that many variables, some of them unexpected, may influence a sensitive chemical transformation. When the reaction involved represents the key step in a production process, as shown for the enantioselective hydrogenation of 13 to sitagliptin 1, optimization of the technological process requires the combined use of synthetic, analytical and physicochemical studies, often based on the serendipity and the imagination of the synthetic chemist. 

Hanefeld M, Xu L, Caria C, Williams-Herman D, Khatami H (2006) Diabetologia 49 2564-2571 

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