UMM AL-QURA UNIVERSITYFACULTY OF MEDICINEDEP. OF BIOCHEMISTRY

بسم الله الرحمن الرحيم

OBJECTIVES: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.

ODORS:

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:

EXPERIMENT S: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.

ABDULLATIF TAHA ABDULLAMSC. BIOCHEMISTRY

QUESTIONS?