Aromatic Nitration pre-lab lecture Chemistry 2412L Aromatic Nitration pre-lab lecture

Nitration of Toluene Reactions on substituted benzenes result in three possible isomers: ortho, meta, and/or para Consider the nitration of toluene:

Nitration of Toluene This reaction is an example of an electrophilic aromatic substitution The H2SO4 donates a H+ to HNO3 which results in the formation of NO2+ and H2O The nitronium ion (NO2+) is electrophilic and reacts with the toluene nucleophile A substitution reaction occurs: NO2+ substitutes for one of the H’s on toluene

Nitration of Toluene The ease or difficulty of a nitration reaction depends on the substituent(s) already present on the aromatic compound Electron-donating groups (activators) facilitate the nitration Electron-withdrawing groups (deactivators) hinder the nitration Consult your textbook (Wade) to determine if –CH3 is and activator or a deactivator.

Nitration of Toluene The major isomers formed in the reaction also depend on the substituent(s) already present on the aromatic compound Some groups are ortho,para-directors, and the ortho and para products are the major products Some groups are meta-directors, and the meta product is the major product Consult your textbook (Wade) to determine if –CH3 is an o,p-director or a m-director.

Nitration of Toluene In this experiment, you will perform the nitration of toluene, and use GC to analyze the product mixture that results.

Gas Chromatography Review the gas chromatography technique (discussed in CHEM 2411L) What determines the order of elution of the products? How do you determine the percent of each product in the mixture? What do you predict the major product(s) will be for the nitration of toluene?

Procedure Notes At the end of the reaction and work-up, your nitrotoluene product(s) will be dissolved in a small volume of ether (1-2 mL) Use this solution to analyze your product mixture using Gas chromatography IR spectroscopy

Safety Notes Concentrated sulfuric acid and concentrated nitric acid can cause burns on contact with the skin. Particular care must be taken in measuring and handling these reagents. Clean up any spills immediately (consult your instructor). Should any acid get on you, wash quickly and thoroughly with cold water and then with soap and water. Wear safety goggles! Aromatic nitro compounds are generally toxic and some may cause contact dermatitis. Avoid contact with any of the products. Diethyl ether is highly flammable. There should be no flames in the room. Do not work near a hotplate or other heating device.