Page 602 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Synthesis of Reactants and Intermediates for Polymers 565

OH
CH 3 CH 2
CH 3 H C CH 3
3
CH 3
O 2 CH 2 (17.27)
O +

Ethylbenzene Propylene Propylene Styrene
oxide
Vinyl chloride, formerly obtained from acetylene, is now produced by the transcatalytic process
where chlorination of ethylene, oxychlorination of the byproduct hydrogen chloride, and dehydro-
chlorination occur in a single reactor.

Cl

H C CH 2 + H Cl + O 2 H 2 O + Cl H Cl +
2
Cl CH 2 (17.28)
Ethylene Hydrogen 1,2-Ethylene Vinyl
chloride chloride chloride
Vinyl chloride is also produced by the direct chlorination of ethylene and the reaction of acety-
lene and hydrogen chloride (Equation 17.29). The hydrogen chloride generated in the chlorination
of ethylene can be employed in reaction with acetylene, allowing a useful coupling of these two
reactions (Equation 17.30). Today, most vinyl chloride is produced from reaction of ethylene and
chlorine forming ethylene dichloride. The ethylene dichloride is heated under pressure resulting in
its decomposition to vinyl chloride and hydrogen chloride (Equation 17.29).
Cl

.
H C CH 2 + Cl Cl Cl Cl + H Cl (17.29)
2
CH 2
Cl
HC CH + H Cl (17.30)

CH 2
Vinylidene chloride, or 1,1-dichloroethene, is produced by the pyrolysis of 1,1,2-trichloroethane
o
at 400 C in the presence of lime or base (Equation 17.31). Since both vinylidene chloride and vinyl
chloride are carcinogenic, their concentrations must be kept low. It was widely used to form poly-
mer, mainly poly(vinylidene chloride), which formed the basis for a cling wrap called Saran warp.
Research suggested that Saran wrap may pose a health danger by leaching when microwaved.
Because of this, most cling wrap formulations have changed to polythene.

Cl Cl
Cl
H C + H Cl
2
Cl
Cl
1,1,2-Trichloroethane Vinylidene chloride (17.31)

9/14/2010 3:43:24 PM
K10478.indb 565 9/14/2010 3:43:24 PM
K10478.indb 565