6
58
J Surfact Deterg (2012) 15:657–661
Nevertheless, the synthesis and surface activities of such
carboxylic amidobetaine surfactants have not been repor-
ted. In order to compare the effect of the nature of
hydrophilic headgroups, and to correlate the aqueous
solution properties with a hydrophobic length, we report in
this preliminary work the synthesis, Krafft temperature and
surface activities of three amidobetaine surfactants with an
ultra-long monounsaturated tail, alkyl dimethyl amidopro-
pyl betaine (UCnDAB, n = 18, 22, and 24).
It is necessary to point out that the intermediate
UC18AMPM has a relatively better water solubility, and
the purified product was not obtained although several
different solvents were used for purification. Thus this
intermediate was directly used for further reaction without
any treatment.
In the second step, the obtained intermediates
UCnAMPM (n = 18, 22, and 24) were quaternized using
sodium chloroacetate with a molar ratio of 1:1.25 in a
mixture solvent mixture of ethanol and water (V/V = 5:1).
The reactants were refluxed at 79 °C for about 12 h; the
final mixture was evaporated off under reduced pressure,
then mixed with ethyl acetate and filtered. The filter cake
was repeatedly washed with ethyl acetate and purified by
chromatography on a silica gel column using dry ethanol as
a mobile phase to remove the unreacted sodium chloro-
As depicted in Scheme 1, the series of monounsaturated
ultra-long-chain amidobetaine surfactants UCnDAB
(
n = 18, 22, and 24) were prepared by a two-step process
from oleic acid, erucic acid, and nervonic acid, respec-
tively. The detailed synthesis and characterizations of each
intermediate and final surfactant can be found in the
Electronic Supplementary Material (ESM) of the present
article; here we just give a general protocol.
acetate and the by-product NaCl.
1
UC18DAB: H NMR (300 MHz, CDCl ): 0.87 (t,
In the first step, the tertiary amine intermediate (UCn-
AMPM) was prepared following our previously reported
pathway [16, 18], but with some modifications in this work.
The ultra-long-chain fatty acids (UCnFA) were directly
reacted with N,N-dimethyl-1,3-propanediamine (DMPDA)
3
J = 4.78 Hz, 3H), 1.25 (m, 20H), 1.60 (m, 2H), 2.00 (m,
6H), 2.21 (t, J = 7.23 Hz, 2H), 3.23 (s, 6H), 3.33-3.35
(m, 2H), 3.70-3.77 (m, 2H), 3.81(s, 2H), 5.30-5.38 (m,
?
2H), 8.01 (br, 1H). ESI HRMS: Calc., 425.3743 (M ? H );
(
molar ratio of 1:1.5) without additional solvents, and NaF
Found, m/z = 425.3751.
1
UC22DAB: H NMR (300 MHz, CDCl ): 0.86 (t,
was used as a catalyst. The reaction mixture was refluxed at
3
1
55–160 °C under an Ar atmosphere for 10 h, during
J = 6.48 Hz, 3H), 1.24 (m, 28H), 1.55 (m, 2H), 1.96-2.00
(m, 6H), 2.17 (t, J = 6.86 Hz, 2H), 3.23 (m, 8H), 3.64 (m,
2H), 3.93 (s, 2H), 5.27-5.37 (m, 2H), 8.06 (br, 1H). ESI
which the by-product H O was absorbed continuously by
2
Al O placed in a solvent still-head distillation apparatus.
2
3
?
When the reaction was terminated, the slurry products were
washed with cold mixture solvent of acetone and water
HRMS: Calc., 481.4369 (M ? H ); Found: m/z =
481.4378.
1
UC24DAB: H NMR (300 MHz, CDCl ): 0.87 (t,
(
V/V = 15:1) to remove the catalyst and residuals, then
3
filtered and washed repeatedly with the same solvent until
no DMPDA was found by the thin-layer chromatography.
The purified products were dried under a vacuum to obtain
the intermediates, UCnAMPM (n = 18, 22, and 24).
J = 6.60 Hz, 3H), 1.25 (m, 32H), 1.56 (m, 2H), 1.99 (m,
6H), 2.18 (t, J = 4.52 Hz, 2H), 3.24 (m, 8H), 3.67-3.92
(m, 2H), 3.97 (s, 2H), 5.32-5.35 (m, 2H), 7.97 (br, 1H).
?
ESI HRMS: Calc., 509.4682 (M ? H ); Found: m/z =
509.4688.
1
UC22AMPM: m. p. 33-34 °C; H NMR (300 MHz,
CDCl ): 0.88 (t, J = 6.54 Hz, 3H), 1.26 (m, 28H),
No residual sodium chloroacetate was detected in all of
the final products with ionic chromatography, and no pre-
3
1
7
3
.57-1.68 (m, 4H), 1.98-2.02 (m, 4H), 2.13 (t, J =
.62 Hz, 2H), 2.22 (s, 6H), 2.37 (t, J = 6.33 Hz, 2H),
.30-3.36 (m, 2H), 5.29-5.39 (m, 2H), 6.88 (br, 1H).
cipitates were found when adding AgNO aqueous solution
3
into the surfactant solutions, indicative of the absence of
by-product NaCl.
1
UC24AMPM: m. p. 42-43 °C; H NMR (300 MHz,
CDCl ): 0.87 (t, J = 6.6 Hz, 3H), 1.25 (m, 32H),
Water solubility of surfactants is a primary criterion
when considering its practical use. The Krafft temperature
3
1.59-1.66 (m, 4H), 1.98-2.01 (m, 4H), 2.14 (t, J =
7.62 Hz, 2H), 2.22 (s, 6H), 2.37 (t, J = 6.38 Hz, 2H),
3.29-3.35 (m, 2H), 5.29-5.39 (m, 2H), 6.92 (br, 1H).
(T ) is generally used to characterize the solubility of
K
ionic surfactants. Normally, the saturated long-chain
Scheme 1 The synthesis
O
O
O
protocol for the ultra-long-chain
monounsaturated amidobetaine
surfactants UCnDAB (n = 18,
NaF/Al2O3
Ar
ClCH2COONa
O-
+
H2N
N
N+
R
N
H
N
R
N
H
R
OH
O
2
2, and 24)
(UCnFA)
(DMPDA)
(UCnAMPM)
(UCnDAB)
for UCnFA (n=18, 22, and 24),RCOOH =
(CH2)n-11COOH
1
23