How is using thiamine as a catalyst rather than cyanide an application of green
chemistry?
PROCEDURE
To a six inch test tube was added thiamine hydrochloride (0.65 g), followed by water (2
mL). The mixture was gently shaken until homogeneous, and then ethanol (7.5 mL)
was added. Finally, sodium hydroxide (10%, 1.5 mL) was added and the mixture was
gently stirred to ensure complete mixing.
Benzaldehyde (3.8 mL) was then added at room temperature in one portion with gentle
stirring. The pH of the resulting reaction mixture was determined and adjusted to >10
by dropwise addition of 10% sodium hydroxide. The reaction mixture was then partially
submerged in a 65 °C water bath2 and the progress of the reaction was periodically
monitored by TLC analysis.
Once TLC analysis indicated that the reaction was complete, the reaction mixture was
cooled to approximately room temperature, and then chilled in an ice-water bath. The
resulting precipitate was collected by vacuum filtration and air-dried. The crude product
was purified by recrystallization from hot ethanol (8 mL ethanol/g crude product)
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