First, 150 mL of toluene was added to a flask equipped with a stirrer and an internal thermometer. Under stirring conditions, 0.09 g (0.08 x 10^-3 mol) of the (R,R)-VO salen complex from Example 1 and 21.1 g (0.15 mol) of freshly prepared 2-chlorobenzaldehyde were added sequentially. Subsequently, 10.1 g (0.375 mol) of hydrocyanic acid was added all at once. The resulting dark green homogeneous solution was stirred for 24 h at room temperature in a closed apparatus. The conversion was analyzed by gas chromatography (GC) to be 98% and the enantiomeric excess (ee) value of (S)-2-chloromandelate cyanohydrin was 73%.
