To identify organic compounds from their odors and the colors of their reaction products.
Many organic compounds give characteristic odors as follows: Pleasant odor: ethers, esters. Pungent odor: carboxylic acids, acetic acid, acid chloride, acid anhydride, acetic anhydride and amines: pyridine. Phenolic odor: many phenols and derivatives of salicylic acid. Almond odor: benzaldehyde, benzonitrile and nitrobenzene.
Many organic compounds give characteristic colors of their reaction products. The above odors and colors help in identification of at least classes of organic compounds. Colors of Reaction Products:
Test for Halides: Add 2 ml. of AgNO3 to 1 ml. of methyl iodide and shake. A yellow precipitate of AgI is formed in the cold. Test for Alcohols: Add 3 ml. of KI and 10 ml. of NaOCl to 0.5 ml. of ethanol and warm gently. Fine yellow crystals of iodoform separate. Test for Ethers: Add a few crystals of iodine to 3 ml. of diethyl ether. Iodine dissolved in the ether giving a brown color.
Test for Aldehydes: Add 3 drops of NaOH to 3 ml. of AgNO3 in a test tube. Add ammonia solution drop by drop until the precipitate of silver oxide is almost re-dissolved and then add 3 drops of formaldehyde. A silver mirror is formed. Test for Ketones: Add 1 ml. of sodium nitroprosside to 0.5 ml. acetone in a test tube. Add NaOH in excess; a red coloration is produced. Test for Carboxylic Acids: Add NaOH to FeCl3 solution in a test tube untill a small permanent precipitate of Fe(OH)3 is produced. Use the filtrate as neutral FeCl3 solution. Place 0.5 g of acetic acid in a test tube and add slight excess of NH3 solution until just alkaline to litmus paper. Add a piece of unglazed porcelain and boil until NH3 is removed and then cool. To the solution so obtained add a few drops of neutralized FeCl3 solution; A deep red coloration is produced.
Test for Esters: To a few drops of ethyl acetate add 0.2 g hydroxylamine- hydrochloride and about 5 ml. of NaOH and gently boil for 1-2 min. cool and acidify with HCl and then add a few drops of FeCl3 solution. A violet or deep red-brown color develops immediately. Test for Acid chloride: Acidify 2 ml. of AgNO3 with HNO3 and then add acetyl chloride solution drop by drop with shaking. A white precipitate of AgCl is produced. Test for Nitrobenzene: To a very dilute solution of nitrobenzene (1%) in a test tube, add few drops of FeCl3 solution. A reddish coloration is produced. Test for Phenol: To a very dilute solution of phenol (1%) in a test tube, add a drop of FeCl3 solution. A violet coloration is produced.