Compare the color of this solution with the yellow observed when the original compound is tested with ferric chloride in the presence of acid to assure the color is due to the formation of ferric hydroxamate complex. Some acids will give a positive test. To 2 mL of a 1 M hydroxylamine hydrochloride solution in propylene glycol is added 1 drop or 30 mg of the compound dissolved in a minimum amount of propylene glycol. Add 1 mL of 1 M potassium hydroxide and the mixture is boiled gently for 2 min. Positive Test A red to violet color constitutes a positive test.
Yellow colors indicate negative tests, and brown colors or precipitates are indeterminate.
Some sterically hindered amides fail to react. To prepare the sulfonyl chloride from the sulfonic acid, combine 5 drops of thionyl chloride and 100 mg of the sulfonic acid in a test tube and heat in boiling water for 1 min. Allow the test tube to cool. To the test tube, 0.5 mL of a saturated solution of hydroxylamine hydrochloride in methanol is added. A drop of acetaldehyde is added.