Secondary alcohols with an adjacent methyl group are oxidized to methyl ketones by iodine bleach.
Add four drops or 0.1 g of unknown to a test tube. Add 5 mL of dioxane, and shake until unknown dissolves. Add 1 mL of 10% NaOH solution, and then slowly add the iodine-potassium iodide solution with shaking, until a slight excess yields a definite dark color of iodine. Heat the mixture to 60oC.The addition of iodine is continued until the dark color is not discharged by 2 minutes of heating at 60oC. Add a few drops of 10% NaOH solution to discharge iodine color. Now fill the test tube with water and let stand for 15 minutes. Filter the precipitate and check the melting point; iodoform melts at 119-121oC.
Iodine-potassium iodide solution: Add 20.0 g of potassium iodide and 10.0 g of iodine to 80.0 mL of water and stir until the reaction is complete.
Formation of solid iodoform (yellow) is a positive test.
Test will not be positive if the R group is a di-ortho substituted aryl group.
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