Vinyl chloride
Vinyl chloride
The simplest
unsaturated alcohol is vinyl alcohol, CH2=CHOH. This is, however, unknown; all
attempts to prepare it result in the formation of acetaldehyde (together with a
small amount of ethylene oxide), e.g., vinyl bromide on treatment with silver
oxide in boiling water gives acetaldehyde.
CH2=CHBr + ‘AgOH’ ⟶ AgBr + [CH2=CHOH] ⟶ CH3CHO
Although vinyl
alcohol itself is unknown, many of its derivatives have been prepared, and are
quite stable. These derivatives may be prepared by the interaction between
acetylene and the other reactant in the presence of a suitable catalyst. e.g.,
vinyl chloride:
C2H2 +
HCl (Hg2+) ⟶ CH2=CHCl
Vinyl chloride
is manufactured by the thermal decomposition of ethylene dichloride at
600-650oC:
ClCH2CH2Cl ⟶ CH2=CHCl + HCl
Vinyl chloride
and bromide are conveniently prepared in the laboratory by heating ethylene
dichloride and dibromide, respectively, with ethanolic potassium hydroxide:
BrCH2CH2Br +
KOH (ethanol) ⟶ CH2=CHBr + KBr
+ H2O
Many of the
vinyl compounds are used to make plastics. Vinyon, which is a thermoplastic, is
a copolymer of vinyl chloride and vinyl acetate.
The halogen
atom in vinyl halides is not reactive; vinyl halides do not undergo the usual
double decomposition reactions of the alkyl halides. Vinyl chlorides and
bromides readily form Grignard reagents in tetrahydrofuran as solvent and they
react with lithium to form lithium compounds which undergo the usual reactions:
The reaction
for the unreactivity of the halogen atom is not clear. Some believe it is to be
due to resonance through which the halogen atom acquires some double-bond
character, and is thereby more strongly bound to the carbon atom due to the
shortening of the C-CL bond:
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