Chemistry Reference
In-Depth Information
TABLE 4.11. The cmc's of Typical Sodium Alkylbenzene-
sulfonate Surfactants
Temperature (
C)
Alkylbenzene Group
cmc (mM)
p-Hexyl
75
37
p-Heptyl
75
21
p-Octyl
60
15
o-Octyl
55
19
p-Nonyl
75
6.5
p-Decyl
50
3.8
p-Dodecyl
30
1.2
p-Tetradecyl
75
0.66
p-1-Methyldecyl
35
2.53
p-1-Methyldodecyl
35
0.72
p-1-Methyltetradecyl
40
0.31
p-1-Methylhexadecyl
50
0.13
fied, have been reported, however (Table 4.12). It can be seen that the cmc values
for the straight-chain esters follow the Klevens relationship, although the value of
B is slightly smaller than that found for single-chain surfactants. As might be
expected, the cmc's for the branched esters of equal carbon number occur at higher
concentrations.
As mentioned above, the addition of a benzene ring to the hydrophobic chain has
an effect on the cmc similar to the addition of 3.5 -CH
2
- groups. Since many nat-
ural fatty acids serve as starting materials for synthetic surfactant manufacture, it is
of interest to know what effect might be expected from the presence of ethylenic
unsaturation in the chain. Some data for the cmc's of saturated and unsaturated fatty
acid analogs are given in Table 4.13. As can be seen, the presence of a single double
bond in the chain increases the cmc by as much as a factor as 3-4 compared to the
saturated compound. In addition to the electronic presence of the double bond, the
isomeric configuration (cis or trans) will have an effect, with the cis isomer usually
TABLE 4.12. The cmc's of Typical Surfactants Containing
Two Hydrophobic Groups (Not Branched)
Surfactant
cmc (mM)
Sodium di-n-butylsulfosuccinate
200
Sodium di-i-butylsulfosuccinate
200
Sodium dipentylsulfosuccinate
53
Sodium dihexylsulfosuccinate
12.4
Sodium dioctylsulfosuccinate
6.8
(C
8
H
17
)
2
(CH
3
)
2
N
þ
Cl
26.6
(C
10
H
21
)
2
(CH
3
)
2
N
þ
Cl
2.0
(C
12
H
25
)
2
(CH
3
)
2
N
þ
Cl
0.18
