Chem 242 Spring 2008

Problem Set 5

Question 1. Predict the major product of the following reactions.

O Me O Me

a) Br2, FeBr3

Br

OH O Br 1) NaOH, b)

2) H2 (1 atm), Pt catalyst

OH Cl c) 1) HNO , H SO 3 2 4 Me Me NO 2) NaOH 2 O O

Me Me Me Me

d) SO3, H2SO4

SO3H Chem 242 Spring 2008

Question 2. Provide reagents that will accomplish the following transformations. Multiple steps may be needed.

1) acetyl chloride, AlCl a) 3 H3C 2) SO3/H2SO4 SO3H O

NH2 NO2 Br Br 1) H2 (1 atm), Pd catalyst b) 2) Br2 (no FeCl3 needed)

Br

Me

Me O Me

1) isobutyryl chloride, AlCl3 c) 2) Cl2, FeCl3

Cl

Me

Me Me Me OH

1) NaOH, Et–I d) 2) t-butyl chloride, AlCl3

OEt Chem 242 Spring 2008

Question 3. A student wanted to synthesize para-nitroaniline by nitration of aniline as shown below.

NH2 NH2

HNO3, H2SO4 + some ortho-product

NO2

a) Provide a mechanism for the formation of para-nitroaniline.

O O O H2SO4 N N N O OH O OH2 O

NH NH NH NH NH2 2 2 2 2

O

N O2N H O2N H O2N H O2N H

O NH2 HSO4

NO2

b) When the experiment was actually attempted, the reaction was very sluggish and the product mixture contained large amounts of meta-nitroaniline. Briefly explain the sluggish rate and the formation of meta-nitroaniline.

+ In strong acid, the amine will become protonated. An –NH3 group is stongly deactivating and meta-directing.

NH 2 NH3 fast reaction, slow reaction, ortho/para products HNO3, H2SO4 meta-products

<.001% >99.999% Chem 242 Spring 2008

Question 4. When styrene is treated with aqueous sulfuric acid, one of the major products is shown below. Provide a mechanism for this dimerization reaction.

Me

catalytic H+

protonate olefin

H+

Me Me 2nd olefin attacks benzene ring attacks carbocation carbocation (Friedel-Crafts rxn)

Me

HSO4 H elimination Me Chem 242 Spring 2008

Question 5. Provide a complete mechanism for the reaction shown below.

Me Me Me Me AlBr3 Me Br

AlBr 3 ionization Me & hydride Me Me AlBr shift Me Br 3 H Me

electrophilic attack (Friedel- Crafts alkylation)

– Br Me Me Me H Me Me Me Chem 242 Spring 2008

Question 6. Non-benzene aromatic compounds frequently show analogous reactivity to benzene. With this in mind, explain why the bromination of furan occurs at the observed position on the five-membered ring.

O O O Br2, FeBr3 Br

Br furan product not formed

O O Only 2 resonance forms, less stable Br H H Br + O " Br "

Br H H O H " Br+ " Br O O Br Br

Three resonance forms, more stable

O Br

product