We try to conduct derivatization of Leucine and Valine by reaction with BSTFA, using classical Gehrke method. But during the heating, a teflon lined cap cannot managed with autogenous pressure of acetonitrile vapors, and relieve pressure, so some amounts of derivatizated amino acids have lost, and there is no reproducibility in series.

How this problem can be solved? Steel autoclave? Or maybe anyone has conducted this reaction without acetonitrile, or at lower temperatures?