11.15%20Preparation%20of%20Alkenylbenzenes

1
11.15Preparation of Alkenylbenzenes

• dehydrogenation
• dehydration
• dehydrohalogenation

2
Dehydrogenation

• industrial preparation of styrene
• 11,800,000,000 lbs. produced in U.S. in 1999.

630C
ZnO
H2
3
Acid-Catalyzed Dehydration of Benzylic Alcohols
KHSO4
heat

H2O
(80-82)
4
Acid-Catalyzed Dehydration of Benzylic Alcohols
KHSO4
heat
(80-82)
5
Dehydrohalogenation
NaOCH2CH3
ethanol, 50C
(99)
6
11.16Addition Reactions of Alkenylbenzenes

• hydrogenation
• halogenation
• addition of hydrogen halides

7
Hydrogenation
(92)
8
Halogenation
Br2
CH
CH2
Br
Br
(82)
9
Addition of Hydrogen Halides
(75-84)
10
Addition of Hydrogen Halides

via benzylic carbocation
11
Free-Radical Addition of HBr
HBr
peroxides
12
Free-Radical Addition of HBr
HBr
peroxides
CH
CH2Br

via benzylic radical
13
11.17Polymerization of Styrene
14
Polymerization of Styrene
polystyrene
15
Mechanism

RO
16
Mechanism

RO
H2C
CHC6H5

17
Mechanism

RO
H2C
CHC6H5

18
Mechanism

RO
H2C
CHC6H5
19
Mechanism

RO
H2C
CHC6H5
H2C
CHC6H5

20
Mechanism

RO
H2C
CHC6H5
H2C
CHC6H5

21
Mechanism

RO
H2C
CHC6H5
H2C
CHC6H5
22
Mechanism

23
Mechanism

24
Mechanism