62
Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain
4
4.1 Synthesis of Substituted Fatty
Acids
Common substitution reactions on the aliphatic
chain, for instance chlorination, take place with
almost statistical distribution of the chlorine
atoms on the fatty acid alkyl chain. Only the
methylene groups directly adjacent to the carboxyl group are somewhat shielded from the
electrophilic attack of the chlorine radicals by
the I-effect of the COOH substituent. The result
is a mixture of chlorinated fatty acids that can be
converted into hydroxyl- or amino-substituted
fatty acids (. Fig. 4.1).
However, this reaction sequence is only
industrially useful if it is possible to carry out
chlorination more regioselectively. One approach
is the Hell–Volhard–Zelinsky reaction, in which
chlorination is carried out in chlorosulfonic acid
as a solvent and a strong radical scavenger prevents statistical chlorination: The α-chloro fatty
acid is formed selectively.
Some further substitution reactions at the
fatty alkyl chain are listed in . Table 4.1.
In particular, the regioselective sulfonation of
the α-methylene group might gain greater industrial significance. Sulfonation of fatty acid methyl
esters with sulfur trioxide and air produces the
Chapter Timetable
5 We briefly discuss the chemistry of the
saturated fatty acid alkyl chain.
5 Much more versatile is the chemistry of
the C=C double bond of unsaturated
fatty acid compounds. Here you will
get to know the possibilities of using
C–O and C–C linkages to derive new
functionalized or branched molecules.
5 The selective hydrogenation of C=C
double bonds is also discussed.
In addition to reactions at the carboxyl group, a
fatty acid can also undergo reactions at the alkyl
chain (or alkylene chain). The chemical attack
can take place at different positions:
5 At any non-activated methylene group, e.g.
at the CH 2 groups of the carbon atoms C3 to
C17 of stearic acid,
5 At the terminal methyl group (C18),
5 On the methylene group (C2) which is next
to the carboxyl group,
5 At the carbon atom of a C=C double bond
(e.g. C9 and C10 of oleic acid),
5 At the methylene group allyl to the C=C
double bond (C8 and C11 of oleic acid).
COOH
+ Cl 2
- HCl
COOH
Cl
+ 2 NH 3
- NH 4 Cl
COOH
NH 2
+ H 2 O
- HCl
COOH
OH
. Fig. 4.1 Substitution reactions at the saturated fatty acid alkyl chain
. Table 4.1 Substitution reactions at the saturated fatty alkyl chain
Reaction
Reagents
Products
Sulfochlorination
SO 2 , chlorine
Sulfochlorides
Sulfoxidation
SO 2 , oxygen
Sulfonic acids
Chlorophosphonylation
PCl 3 , oxygen
Phosphonic acid dichlorides
Fluorination
HF, electrochemical
Perfluoro fatty acids
Sulfonation
SO 3 , air
α-Sulfofatty acids and their esters
Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain
4
4.1 Synthesis of Substituted Fatty
Acids
Common substitution reactions on the aliphatic
chain, for instance chlorination, take place with
almost statistical distribution of the chlorine
atoms on the fatty acid alkyl chain. Only the
methylene groups directly adjacent to the carboxyl group are somewhat shielded from the
electrophilic attack of the chlorine radicals by
the I-effect of the COOH substituent. The result
is a mixture of chlorinated fatty acids that can be
converted into hydroxyl- or amino-substituted
fatty acids (. Fig. 4.1).
However, this reaction sequence is only
industrially useful if it is possible to carry out
chlorination more regioselectively. One approach
is the Hell–Volhard–Zelinsky reaction, in which
chlorination is carried out in chlorosulfonic acid
as a solvent and a strong radical scavenger prevents statistical chlorination: The α-chloro fatty
acid is formed selectively.
Some further substitution reactions at the
fatty alkyl chain are listed in . Table 4.1.
In particular, the regioselective sulfonation of
the α-methylene group might gain greater industrial significance. Sulfonation of fatty acid methyl
esters with sulfur trioxide and air produces the
Chapter Timetable
5 We briefly discuss the chemistry of the
saturated fatty acid alkyl chain.
5 Much more versatile is the chemistry of
the C=C double bond of unsaturated
fatty acid compounds. Here you will
get to know the possibilities of using
C–O and C–C linkages to derive new
functionalized or branched molecules.
5 The selective hydrogenation of C=C
double bonds is also discussed.
In addition to reactions at the carboxyl group, a
fatty acid can also undergo reactions at the alkyl
chain (or alkylene chain). The chemical attack
can take place at different positions:
5 At any non-activated methylene group, e.g.
at the CH 2 groups of the carbon atoms C3 to
C17 of stearic acid,
5 At the terminal methyl group (C18),
5 On the methylene group (C2) which is next
to the carboxyl group,
5 At the carbon atom of a C=C double bond
(e.g. C9 and C10 of oleic acid),
5 At the methylene group allyl to the C=C
double bond (C8 and C11 of oleic acid).
COOH
+ Cl 2
- HCl
COOH
Cl
+ 2 NH 3
- NH 4 Cl
COOH
NH 2
+ H 2 O
- HCl
COOH
OH
. Fig. 4.1 Substitution reactions at the saturated fatty acid alkyl chain
. Table 4.1 Substitution reactions at the saturated fatty alkyl chain
Reaction
Reagents
Products
Sulfochlorination
SO 2 , chlorine
Sulfochlorides
Sulfoxidation
SO 2 , oxygen
Sulfonic acids
Chlorophosphonylation
PCl 3 , oxygen
Phosphonic acid dichlorides
Fluorination
HF, electrochemical
Perfluoro fatty acids
Sulfonation
SO 3 , air
α-Sulfofatty acids and their esters