To 108 g. (0.72 mole) of piperonal in a 3-l. round-bottomed flask is added, in portions of 20 to 30 g., 454 g. (2.18 moles) of fresh phosphorus pentachloride. The reaction is vigorous at first, and the flask is kept cold with ice; moisture must be excluded. After about half of the pentachloride has been added the reaction becomes sluggish and cooling is unnecessary. The entire addition requires about thirty minutes. The resulting green or blue liquid containing undissolved pentachloride is heated very gently over a flame for about sixty minutes to expel hydrogen chloride. From the turbid, light brown liquid thus formed, volatile material is removed on a steam bath under the reduced pressure of a water pump. This operation takes about thirty minutes. The contents of the flask are then poured into 5 l. of cold water contained in a 12-l. round-bottomed flask (Note 1). A milky oil is formed which rises and sinks in the water and, after about thirty minutes, becomes solid. After standing overnight, the mixture is boiled gently for three hours. The brown solution, containing a little tar, is cleared with charcoal and evaporated under reduced pressure to about 700 cc., when the aldehyde begins to separate. The solution is allowed to stand overnight at about 0°; a large crop of crystals separates, is collected on a filter, and washed with a little water. The product is purified by recrystallization from three times its weight of water. It melts at 153–154°, with decomposition, and weighs 61 g. (61 per cent of the theoretical amount).