CH 3 C CCH 3
CH 3 C CH
Ag
+
CH 3 C C Ag
Ag
+
+ H +
No reaction
(Precipitate)
Terminal alkyne
Internal alkyne
4.5.5 Industrial uses of alkynes
Ethynes are industrially used as a starting material for polymers, e.g. vinyl
flooring, plastic piping, Teflon and acrylics. Polymers are large molecules,
which are prepared by linking many small monomers. Polyvinyl chloride,
also commonly known as PVC, is a polymer produced from the polymerization of vinyl chloride.
C
H CH
H 2 C CHCl
CH 2 CH
Cl n
Ethyne
+ HCl
Vinyl chloride
Polymerize
Poly(vinyl chloride)
PVC
4.5.6 Preparation of alkynes
Alkynes are prepared from alkyl dihalides via elimination of atoms or groups
from adjacent carbons. Dehydrohalogenation of vicinal- or geminal-dihalides is
a particularly useful method for the preparation of alkynes (see Section 5.4.5).
R C
H
H
C
X
X
R'
R C
X
H
C
H
X
R'
RC CR'
R
H
X
R'
or
Alkyne
NaNH 2
geminal or vicinal
Alkyl dihalide
NaNH 2
Metal acetylides or alkynides react with primary alkyl halides or tosylates to
prepare alkynes (see Sections 5.5.2 and 5.5.3).
RCH 2 Y
RCH 2 C CR'
R'C≡CMgX
R'C≡CNa or
Y = X or OTs
Alkyne
4.5.7 Reactions of alkynes
Alkynes are electron-rich reagents. The triple bond acts as a nucleophile,
and attacks the electrophile. Therefore, alkynes undergo electrophilic
110
CH4 ORGANIC FUNCTIONAL GROUPS
CH 3 C CH
Ag
+
CH 3 C C Ag
Ag
+
+ H +
No reaction
(Precipitate)
Terminal alkyne
Internal alkyne
4.5.5 Industrial uses of alkynes
Ethynes are industrially used as a starting material for polymers, e.g. vinyl
flooring, plastic piping, Teflon and acrylics. Polymers are large molecules,
which are prepared by linking many small monomers. Polyvinyl chloride,
also commonly known as PVC, is a polymer produced from the polymerization of vinyl chloride.
C
H CH
H 2 C CHCl
CH 2 CH
Cl n
Ethyne
+ HCl
Vinyl chloride
Polymerize
Poly(vinyl chloride)
PVC
4.5.6 Preparation of alkynes
Alkynes are prepared from alkyl dihalides via elimination of atoms or groups
from adjacent carbons. Dehydrohalogenation of vicinal- or geminal-dihalides is
a particularly useful method for the preparation of alkynes (see Section 5.4.5).
R C
H
H
C
X
X
R'
R C
X
H
C
H
X
R'
RC CR'
R
H
X
R'
or
Alkyne
NaNH 2
geminal or vicinal
Alkyl dihalide
NaNH 2
Metal acetylides or alkynides react with primary alkyl halides or tosylates to
prepare alkynes (see Sections 5.5.2 and 5.5.3).
RCH 2 Y
RCH 2 C CR'
R'C≡CMgX
R'C≡CNa or
Y = X or OTs
Alkyne
4.5.7 Reactions of alkynes
Alkynes are electron-rich reagents. The triple bond acts as a nucleophile,
and attacks the electrophile. Therefore, alkynes undergo electrophilic
110
CH4 ORGANIC FUNCTIONAL GROUPS