a reflux ratio of 10 1 the main fraction is collected at a rapid distillation rate when the vapor no longer reaches the head of the column the distillation is considered finished collection of a final fraction is necessary only if the original p phenoxybenzoyl chloride contained significant amounts of impurities other than p phenoxybenzaldehyde and its derivatives the clear colorless distillate is transferred to clean 500 ml wheaton glass bottles or 1 gal amber bottles which have been dried in an oven at 110 u00b0 c for 1 hour and cooled in a dessicator the bottles are blanketed with dry nitrogen capped with polyethylene lined caps sealed with parafilm and stored at room temperature the distillation produces about 15 17 kg of main fraction plus about 1 kg of recyclable forecut for a total yield of about 80 90 in a small vial about 200 mg 12 drops of crude p phenoxybenzoyl chloride is dissolved in about 2 ml of trifluoroacetic acid to this yellowish brown solution is added three drops of 5 wt acenaphthene dichloromethane solution the vial is swirled to mix the contents thoroughly and the color is immediately observed negative test the color of the solution is yellowish brown indicating that no p phenoxybenzaldehyde or its derivatives are present positive test the color of the solution is green or blue green indicating that p phenoxybenzaldehyde or its derivatives are still present this procedure describes the absorbancy index as test used to determine the aldehyde content of acid chlorides chemically it is based on the conversion in the presence of concentrated sulfuric acid and of acid halide of the aldehyde or its derivatives to a colored species which can be detected spectrophotometrically where the acid chloride is a liquid for example p phenoxybenzoyl.