Friedel-Crafts Reaction for Detecting Arenes

Anhydrous aluminum chloride reacts vigorously with water, even the moisture on your hands, producing fumes of hydrogen chloride that are highly corrosive if inhaled. Do not allow aluminum chloride to come in contact with your skin. If it does, immediately flood the affected area with water. Because aluminum chloride is a powdery solid that can easily become airborne, weigh and transfer it into the reaction flask in the hood. 

Preparation Sign in at www.cengage.coin/login to Read the MSDSs for the chemicals used or produced in this procedure. 

In a dry Pyrex test tube held almost horizontally, heat about 100 mg of anhydrous aluminum chloride until the material has sublimed to 3 or 4 cm above the bottom of the tube (Fig. 25.5). Allow the tube to cool until it is almost comfortable to touch then add about 20 mg of a solid, or 1 drop of a liquid, down the side of the tube, followed by 2 or 3 drops of chloroform. The appearance of a bright color ranging from red to blue where the sample and chloroform come in contact with the aluminum chloride is a positive indication of an aromatic ring. 

Cool the contents of the test tube in an ice-water bath and cautiously add a few milliliters of cold water to hydrolyze the aluminum salts. Flush the resulting aqueous layer down the drain, and place the organic layer in the container for halogenated organic liquids. 

Two types of derivatives are used to characterize aromatic hydrocarbons and aryl halides. These are prepared by nitration (Eq. 25.33) and side hain oxidation (Eq. 25.34). 

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