19. Reactions of Aromatics: EAS and Beyond

The following are all substitution reactions, two of which we study in later chapters. With no knowledge of mechanism, what would you expect the ratio of products to be for each reaction, based on a random statistical distribution?

(b) Replacing a hydrogen (H) with bromine (Br):

Propose a mechanism for the aluminum chloride–catalyzed reaction of benzene with chlorine.

Styrene (vinylbenzene) undergoes electrophilic aromatic substitution much faster than benzene, and the products are found to be primarily ortho- and para-substituted styrenes. Use resonance forms of the intermediates to explain these results.

When bromine is added to two beakers, one containing phenyl isopropyl ether and the other containing cyclohexene, the bromine color in both beakers disappears. What observation could you make while performing this test that would allow you to distinguish the alkene from the aryl ether?

Phenol reacts with three equivalents of bromine in CCl₄ (in the dark) to give a product of formula C₆H₃OBr₃. When this product is added to bromine water, a yellow solid of molecular formula C₆H₂OBr₄ precipitates out of the solution. The IR spectrum of the yellow precipitate shows a strong absorption (much like that of a quinone) around 1680 cm^–1. Propose structures for the two products.

Propose a mechanism for the bromination of ethoxybenzene to give o- and p-bromoethoxybenzene.

Predict the major products of the following reactions.

(a) toluene + excess Cl₂ (heat, pressure)

What products are obtained from the reaction of the following compounds with one equivalent of Br₂, using FeBr₃ as a catalyst?

a.

What is the major product(s) of each of the following reactions?

a. bromination of p-methylbenzoic acid

What products are obtained from the reaction of the following compounds with one equivalent of Br₂, using FeBr₃ as a catalyst?

b.

What is the major product(s) of each of the following reactions?

b. chlorination of o-benzenedicarboxylic acid

Why isn’t FeBr₃ used as a catalyst in the first step of the synthesis of 1,3,5-tribromobenzene?

Bromination of phenol or aniline does not require the use of a Lewis acid catalyst and often results in trihalogenation. Why?