To
308 g. (2.1 moles) of phosphorus pentoxide (reagent grade) in a
3-l. round-bottomed flask is added
174 g. (2 moles) of finely powdered, dry isobutyramide (Note
1). The flask is tightly stoppered, and the two dry solids are thoroughly mixed by shaking. The flask then is attached to a
water-cooled condenser set for downward distillation; a
500-ml. suction flask connected to the condenser by a
rubber stopper is a convenient receiver. A
calcium chloride tube is attached to the side arm of the receiver, and the receiver is surrounded by crushed ice. The reaction flask is heated for 8–10 hours in an electrically heated
oil bath maintained at 200–220°. The nitrile starts to distil almost at once. The reaction mixture becomes a thick, brown syrup which foams considerably toward the end of the distillation. The time of reaction may be cut to 1–2 hours by connecting the distillation system to an aspirator and intermittently removing the nitrile under reduced pressure (Note
2). Very little additional nitrile can be obtained by further heating of the reaction mixture.
The contents of the receiver are transferred to a
500-ml. modified Claisen flask,
10–15 g. of phosphorus pentoxide is added (Note
3), and the product is distilled from an oil bath held at 145–155°. After only a few drops of fore-run, the main fraction distils at 99–102°/740 mm. The yield is
96–120 g. (
69–86%). The product is colorless when first distilled but acquires a yellow tint after standing a few days. If it is again distilled from
phosphorus pentoxide or Drierite, it boils at
101–103° and remains colorless;
n25D 1.3713.