Sodium acetoacetaldehyde was prepared by formylation of acetone with ethyl formate, using sodium ethoxide in ether. A major impurity always present in our sodium acetoacetaldehyde was 10-40 mol% sodium formate, which was easily deteded by NMR and was also confirmed by IR analysis. The presence of sodium formate as a contaminant leads to the generation of hydrogen bromide due to oxidation of sodium formate by bromine (eq l). 6