Alkylation of ethanolamines: An approach to a novel class of functional surfactants

Article abstract of DOI:10.1080/00397910802656109

Some monomeric and dimeric surfactants with functional head groups have been synthesized from di- and triethanolamine synthons. The treatment of alkyl bromide with triethanolamine resulted in simultaneous N-alkylation and O-alkylation products. However, with diethanolamine, N-alkylated products were obtained, which were further used to synthesize various double-tailed surfactants and gemini surfactants.

Full text of DOI:10.1080/00397910802656109

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Alkylation of Ethanolamines:
An Approach to a Novel Class of
Functional Surfactants
Bijay K. Mishra a , Partha Mukherjee a , Sukalyan
Dash b , Sabita Patel c & Hari N. Pati a
a Centre of Studies in Surface Science and
Technology, School of Chemistry, Sambalpur
University, Jyoti Vihar, India
b Department of Chemistry, University College of
Engineering, Burla, India
c Department of Chemistry, National Institute of
Technology, Rourkela, India
Published online: 16 Jun 2009.
To cite this article: Bijay K. Mishra , Partha Mukherjee , Sukalyan Dash , Sabita
Patel & Hari N. Pati (2009) Alkylation of Ethanolamines: An Approach to a Novel
Class of Functional Surfactants, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 39:14, 2529-2539, DOI:
10.1080/00397910802656109
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Synthetic Communications1, 39: 2529–2539, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802656109
Alkylation of Ethanolamines: An Approach to a
Novel Class of Functional Surfactants
Bijay K. Mishra,1 Partha Mukherjee,1 Sukalyan Dash,2
Sabita Patel,3 and Hari N. Pati1
1Centre of Studies in Surface Science and Technology, School of
Chemistry, Sambalpur University, Jyoti Vihar, India
2Department of Chemistry, University College of Engineering, Burla, India
3Department of Chemistry, National Institute of Technology,
Rourkela, India
Abstract: Some monomeric and dimeric surfactants with functional head groups
have been synthesized from di- and triethanolamine synthons. The treatment of
alkyl bromide with triethanolamine resulted in simultaneous N-alkylation and
O-alkylation products. However, with diethanolamine, N-alkylated products
were obtained, which were further used to synthesize various double-tailed
surfactants and gemini surfactants.
Keywords: Functional surfactants, gemini surfactants, Menschutkin reaction,
triethanolamine
INTRODUCTION
In the studies of cationic surfactants, alkyl trimethylammonium ions are
of significant importance because of the balanced point charge in the
head group, which helps in the formation of organized assemblies in both
aqueous and nonaqueous systems. The additional advantage in the
use of these oniums is the ease of the synthesis, which does not
need a complicated sequence of reaction and follow-up processes.[1]
Received October 23, 2008.
Address correspondence to Bijay K. Mishra, Center of Studies in Surface and
Technology, School of Chemistry, Sambalpur University, Jyoti Vihar 768 019,
India. E-mail: bijaym@hotmail.com
2529

2530
B. K. Mishra et al.
Incorporation of functionalities in these head groups can add
sophistication to organizations and also add applicability to the corre-
sponding surfactants.[2,3] Ethanolamines, a class of compounds with
enormous applications in chemical research on quaternization can easily
produce such functional head groups.
Triethanolamine (TEA) finds wide applications in the manufacturing
of household detergents and polishes, agricultural herbicides, pharma-
ceutical ointments, petroleum demulsifiers, synthetic resins, plasticizers,
adhesives, and sealants. It is also used in the preparation of fluids used
with water as lubricants[4] and also as anticorrosion reagents.[5,6]
A
mixture of TEA and a fatty acid in deionized water, under vigorous
stirring, affords a machining fluid, which can be applied in speeding
machines to ensure a clean machined surface.[7]
In the pioneering work of gemini surfactants (GSs), a class of
surfactants known to exhibit properties such as lesser critical micelle
concentration (cmc), greater efficiency in lowering the surface tension
of water and the interfacial tension between water and oil, and better
solubility in water than conventional monomeric surfactants, TEA ions
are the basic structural units.[8] GSs can be used to transfer pharmacolo-
gical agents into drug-carrying vesicles.[9–12] Recently, many studies con-
cerning the practical use of gemini molecules appeared in the literature,
showing that speculative interests were followed by practical applica-
tions, due to their unusual properties[13]: (i) lesser cmc and lesser C20
(the concentration at which a reduction of the surface tension of
20 mN=m is attained) values, (ii) better adsorption behavior at both the
air=water and the solid=water interfaces with respect to their monomers,
and (iii) tendency to form micelles of different shapes and dimensions
(i.e., spherical, rodlike, threadlike, vesicles), even at low concentration,
when compared with similar normal surfactants. Geminis are used as
promising surfactants in industrial detergents and have shown efficiency
in skin care products, antibacterial products, metal-encapped porphy-
razine and vesicle formation, construction of high-porosity materials,
antipollution protocols, analytical separations, nanoscale technology,
biotechnology, enhanced oil recovery, and paint additives.[14] These are
also used in the synthesis of new mesoporous zeolites for catalytic and
adsorption applications.[15] The use of transfection agents is necessary
to overcome difficulties associated with transferring high-molecular-
weight, negatively charged species across the (predominantly) negatively
charged cell membrane. This is generally accomplished through encapsu-
lation of DNA, for example, in cationic liposomes. The GSs are good
candidates to act as transfection agents because they are effective at
low concentrations, thus diminishing any toxic effect, and they possess
structural characteristics suitable for transfection of DNA. In particular,

Alkylation of Ethanolamines
2531
through simple synthetic modifications, these compounds afford oppor-
tunities to tailor their structure for improving transfection efficiencies
that are not available with traditional surfactant or lipid systems.[16–21]
Despite voluminous work in the field of cationic surfactants contain-
ing an ammonium head group, the information regarding synthesis of
ethanolamine-based surfactants is limited.[22] The nucleophilicity of
amine and hydroxyl functions make the synthesis complicated. Herein
we have reported the synthesis of some TEA-based monomeric surfac-
tants with single and double alkyl hydrophobic tails and some novel
diethanolamine-based GSs having variation in hydrophobic chain length
and spacer length.
RESULTS AND DISCUSSION
The reaction achieved our objectives in getting quaternary ammonium
ion from a tertiary base stem with the Menschutkin reaction. Anticipat-
ing an easy approach for obtaining hexadecyl triethanolammonium
bromide, hexadecyl bromide was treated with TEA neat under reflux
condition and at the boiling temperature of alkyl bromide in a sealed
tube. The solid white mass obtained from the mixture of the two liquids,
in each case, exhibits a single spot in thin-layer chromatography (TLC).
The compound was found to be ionic and shows foaming behavior in
Scheme 1. a, R ¼ C6H13; b, R ¼ C8H17; c, R ¼ C10H21; and d, R ¼ C16H33.

2532
B. K. Mishra et al.
Scheme 2. R ¼ a, C16H33; b, C14H29; and c, C10H21.
aqueous medium. Neither the mass spectra nor the NMR spectral data
correspond to the expected product (2d). The infrared (IR) spectral data
with a strong CꢀO stretching frequency near 1000 cmꢀ1 in each case and
the significant decrease in nitrogen content in the molecule, when com-
pared to that in anticipated product, impelled us to propose an
O-alkylation along with N-alkylation during the reaction, affording
N-alkyl O-alkyl triethanolammonium bromide (3d) (Scheme 1). To see
the generality of this process, hexyl, octyl, and decyl bromides were trea-
ted with TEA, and similar results were obtained. However, on treatment
of hexadecyl bromide with diethanolamine (4), hexadecyldimethylammo-
nium bromide was obtained (5a), which on treatment with alkali resulted
in the corresponding tertiary amine (6a) (Scheme 2). In a subsequent
reaction, bromoethanol was treated with 6a to obtain a white mass,
which exhibited all spectral characteristics of hexadecyltriethanolammo-
nium bromide. The synthesis of the same compound was also achieved
by the treatment of hexadecyl amine with bromoethanol in the presence
of alkali, a procedure followed by Mitra et al. (Scheme 3).[22]
The formation of 3a–d may be attributed to an intermolecular
proton-transfer mechanism operating between two molecules of TEA.
The transfer may lead to the formation of an ion pair containing a
TEA ion and diethanolaminoethoxide (Scheme 4). In the presence of
alkyl bromide, the latter ion will give rise to both O- and N-alkylation,
and the former will be inert toward alkylation at N center.
The basicity difference of TEA and diethanolamine steers alkylation
to different sites. TEA, being more basic in nature, is capable of existing
Scheme 3. Formation of hexadecyltriethanolammonium bromide.

Alkylation of Ethanolamines
2533
Scheme 4. Ion pair formation of triethanolamine.
in the ion pair form, and both O- and N-sites are alkylated, whereas
diethanolamine is alkylated only at nitrogen center.
The N-alkylated products from diethanolamine have been used as
the synthon components of some novel tertiary amines. The quaternary
diethanolammonium bromides, on treatment with alkali, resulted in
alkyldiethanolamines. These bases with decyl, tetradecyl, and hexadecyl
chains produce foams in water upon shaking. These compounds also
form a condensed monolayer on water surface.
The tertiary bases (6a–c) further provide scope of synthesizing some
double-tailed surfactants. On Menschutkin reaction with alkyl bromides,
the bases afforded quaternary compounds (7a–g) (Scheme 5). A C16C10
double-tailed quaternary diethanolammonium compound (7c) could be
obtained by treating C16 tertiary base with C10 alkyl bromide and sepa-
rately by treating C10 tertiary base with C16 alkyl bromide. The products
in both the cases have superimposed spectral characteristics, and the
melting points are the same. These compounds also produce foam in
water and can form a condensed monolayer on water surface. Among
the synthesized double-tailed ethanolammonium salts, the C16C6 dietha-
nolammonium bromide (7a) is soluble in water in hot conditions but
reappears up on cooling.
The tertiary bases (6a–c) were used as the synthon components for
the synthesis of some GSs (8a–g). With dibromoalkanes, the tertiary
bases undergo Menschutkin reaction to afford cationic functional GSs,
where the cationic onium ions are separated by flexible spacers
Scheme 5. a, R ¼ C16H33, R1 ¼ C6H13; b, R ¼ C16H33, R1 ¼ C8H17; c, R ¼ C16H33,
R1 ¼ C10H21; d, R ¼ C16H33, R1 ¼ C14H29; e, R ¼ C16H33, R1 ¼ C16H33; f,
R ¼ C10H21, R1 ¼ C10H21; and g, R ¼ C10H21, R1 ¼ C16H33.

2534
B. K. Mishra et al.
Scheme 6. a, R ¼ C16H33, n ¼ 2; b, R ¼ C16H33, n ¼ 3; c, R ¼ C16H33, n ¼ 4; d,
R ¼ C16H33, n ¼ 5; e, R ¼ C14H29, n ¼ 6; f, R ¼ C16H33, n ¼ 4; g, R ¼ C10H21,
n ¼ 4.
(Scheme 6). When the spacers are small, there is a decrease in hydropho-
bicity, leading to water solubility. The GSs with hexadecyl alkyl chains
and n ¼ 2 (6a) and n ¼ 3 (6b) spacers are water soluble, whereas the GS
with n ¼ 4 (6c) spacer is soluble in hot water, and they aggregate beyond
concentration range 3 ꢁ 10ꢀ4 to 5.6 ꢁ 10ꢀ4 M forming, probably,
micelles. The critical concentration, termed cmc, is found to be much less
than the cmc of CTAB. The GS with n ¼ 6 (6d) spacer, however, is water
insoluble.
Thus a novel class of functional surfactants and the corresponding
GSs have been strategically synthesized to open up a new horizon in
the area of surfactant systems.
EXPERIMENTAL
Diethanolamine, TEA, alkyl bromides, and dibromoalkanes are of
Sisco research-grade (India) and have been used without further purifica-
tion. Methanol, ethanol, acetonitrile, ethylacetate, cetyl amine, and
bromoethanol (Merck, India) were purified by distillation before use.
Synthesis of N-Hexadecyltriethanolammonium Bromide (2)
A
mixture of bromoethanol (0.081 mol) and n-hexadecyl amine
(0.027 mol) in 3:1 molar ratio was refluxed for 24 h followed by dropwise
addition of 2.7 M NaOH on a water bath. The reaction mixture was
extracted with chloroform, and the organic layer was dried over
anhydrous sodium sulfate. Chloroform was removed by evaporation in
air, and the solid mass thus obtained was desiccated. The mass was
recrystallized from methanol=ethylacetate solvent to obtain a white com-
pound: yield 40%; mp 115ꢂC; 1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88
(t, 3H), 1.25–1.34 (br, m, 26H), 1.83 (br, 2H), 3.18–3.23 (br, 2H),
3.35–3.49 (br, 6H), 4.08 (br, 6H). CHN clculated: C, 58.15%; H,

Alkylation of Ethanolamines
2535
10.57%; N, 3.08%. Found: C, 58.13%; H, 10.64%; N, 3.08%. MS m=z
calcd.: 374.62; found: 374.2.
Synthesis of N-Hexadecyldiethanolammonium Bromide (5a)
A
mixture of diethanolamine (6.6 mM) and hexadecyl bromide
(0.0066 mol) in 1:1 ratio in 20 mL methanol–acetonitrile solvent mixture
(30:70) was refluxed for 48 h on a water bath. The solvent was evaporated
on a water bath followed by cooling up to 5ꢂC to obtain a milky white
mass. It was washed with ether several times to remove any trace of
the hexadecyl bromide and recrystallized from methanol=ethyl acetate
mixed solvent to obtain a white crystalline product (5a): yield 90%; mp
85ꢂC; 1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (t, 3H), 1.18–1.35
(br, m, 26H), 1.81 (br, 2H), 3.54 (br, 2H), 3.67 (br, 4H), 4.03 (br, 4H),
8.77 (br, s). CHN calculated: C, 58.52; 10.80; N, 3.41. Found: C, 58.66;
H, 11.03; N, 3.30. Mass (m=z): calc.: 330; found: 330.
By following this procedure, 5b was synthesized (reflux time: 44 h,
yield 90%, mp 62–65ꢂC). The same procedure was also followed for the
synthesis of 5c (reflux time: 50 h, yield 76%, mp 27–32ꢂC). Compound
5b was crystallized from methanol=ethyl acetate.
Synthesis of N-Hexadecyldiethanolamine (6a)
Hexadecyldiethanolammonium bromide (5a: 0.005 mol) was dissolved in
30 mL water followed by addition of 30 ml 2 N ammonia. The solution
was transferred to a separating funnel and was extracted with 20-mL
portions ether three to four times. The ethereal layers were collected, eva-
porated to dryness in air, and kept in the desiccator to obtain the desired
tertiary amine (6a) in solid state; yield 70%; mp 49–51ꢂC; IR: 3301.70
(-OH), 2920.95 (-CH), 2851.91 (-CH), 1043.90 (-CO), 876.96 (-C-C),
721.77 (-C-C) cmꢀ1
;
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (t,
3H), 1.26 (bs, 28H), 2.52 (m, 2H), 2.66 (t, 4H), 3.6 (t, 4H); mass (m=z):
329.57 (calc.); (Mþ þ 1) 330.6; (Mþꢀ1) 328.8 (found).
Following the same procedure, tetradecyldiethanolamine (6b) and
decyldiethanolamine (6c) were synthesized from diethanolamine and
corresponding alkyl bromides respectively.
Compound 6b: Yield 75%; waxy solid; IR: 3333.87 (-OH), 2923.98
(-CH), 2853.52 (-CH), 1367.21 (-CN), 1045 (-CO), 877.44 (-C-C),
721.08 (-C-C) cmꢀ1
3H), 1.25 (bs, 22H), 1.45 (m, 2H), 2.52 (t, 2H), 2.65 (t, 4H), 3.61 (t, 4H).
;
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (t,
Compound 6c: Yield 70%; waxy solid; IR: 3333.98 (-OH), 2925.57
(-CH), 2854.59 (-CH), 1044.41 (-CO), 876.86 (-C-C), 722.34 (-C-C) cmꢀ1
;

2536
B. K. Mishra et al.
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (t, 3H), 1.26 (bs, 14H), 1.47
(m, 2H), 2.55 (t, 2H), 2.68 (t, 4H), 3.63 (t, 4H).
Synthesis of Hexadecylhexyldiethanolamonium Bromide (7a)
A mixture of hexadecyldiethanolamine (6a: 0.0036 mol) and hexyl
bromide (0.0036 mol) was heated neat in an oil bath in a sealed tube in
1:1 molar ratio at 140–150ꢂC for 53 h. A dark solid was obtained, which
was washed with ether several times until the product became white. The
product was crystallized from 1:1 methanol–ethylacetate mixture to
obtain hexadecylhexyldiethanolammonium bromide (7a); yield 42%; mp
137ꢂC; IR ¼ 3333.67 (OH), 2924.5 (CH), 2852.3 (CH), 1372.58 (CN),
1
1305.71 (CN), 1075.46 (CO), 875.4 (C-C) cmꢀ1; H NMR (400 MHz,
CDCl3): d=ppm ¼ 0.88 (6H), 1.2–1.39 (32H), 1.89 (4H), 2.88–2.97 (4H),
3.21–3.46 (4H), 4.09 (2H), 4.5 (2H); mass (m=z): 414.73 (calc.), 414.60
(found).
The same procedure was adopted for the synthesis of hexadecyloctyl-
diethanolammonium bromide (7b) and hexadecyldecyldiethanol ammo-
nium bromide (7c). TLC: 7a, ethyl acetate—single spot; 7b, no suitable
eluent; 7c, 1:1 mixture of methanol and ethyl acetate—single spot.
1
Compound 7b: Reaction time 89 h; yield 35%; mp 185ꢂC; H NMR
(400 MHz, CDCl3): d=ppm ¼ 0.88 (6H), 1.25–1.33 (36H), 1.92 (4H),
2.95 (4H), 3.48 (4H), 3.98 (2H), 4.37 (2H).
1
Compound 7c: Reaction time 76 h; yield 35%; mp 180ꢂC; H NMR
(400 MHz, CDCl3): d=ppm ¼ 0.88 (6H), 1.2–1.33 (40H), 1.92 (4H),
2.93–3.01 (4H), 3.5 (4H), 3.98 (2H), 4.35 (2H).
Synthesis of GSs from Hexadecyldiethanolamine and
Dibromoethane (8a)
A mixture of hexadecyldiethanolamine (6a: 0.0015 mol) and 1,2-dibromo
ethane (0.00075 mol) was heated neat in an oil bath in a sealed tube in a
2:1 molar ratio at 140ꢂC for 30 h. A brownish black solid was obtained,
which was washed with ether several times to remove unreacted hexade-
cyldiethanolamine and dibromo ethane. A solid white mass was obtained,
which was recrystallized from methanol=ethyl acetate (8a); yield 32%; mp
60ꢂC; IR: 3329.73 (-OH), 2919.26 (-CH), 2851.55 (-CH), 1074.43 (-CO),
1
722.25 (-C-C) cmꢀ1; H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (6H),
1.26–1.34 (56H), 1.82 (4H), 3.2–3.5 (8H), 3.6–3.9 (4H), 4.0–4.23 (8H).
By using this procedure, the GSs (8b–g) have been synthesized with
suitable alkyl bromides and dibromo alkanes.

Alkylation of Ethanolamines
2537
Compound 8b: Reflux time: 57 h; yield 20%; mp 128ꢂC; IR: 3369.07
(-OH), 2919.53 (-CH), 2851.76 (-CH), 1111.91 (-CO), 723.80 (-C-C) cmꢀ1
;
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (6H), 1.255 (56H), 1.34 (2H),
1.85 (4H), 2.95 (8H), 3.5 (4Ha), 4.0 (4Hb), 4.5 (4H).
Compound 8c: Reflux time: 28 h; yield 30%; mp 222–224ꢂC; IR:
3331.48 (-OH), 2920.19 (-OH), 2851.76 (-OH), 1075.60 (-CO), 721.94
(-C-C) cmꢀ1
1.24–1.67 (60H), 3.43 (8H), 3.56 (8H), 3.81 (8H).
;
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.86 (6H),
Compound 8d: Reflux time: 56 h; yield 18%; mp 143ꢂC.
Compound 8e: Reflux time: 50 h; yield 40%; mp 152–155ꢂC; IR:
3438.50 (-OH), 2919.90 (-CH), 1111.88 (-CO), 1261.69 (-CN), 723.80
(-C-C) cmꢀ1
;
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (6H), 1.25
(56H), 1.32 (8H), 1.93 (4H), 2.95 (8H), 3.5 (4Ha), 4.0 (4Hb), 4.3 (4H).
Compound 8f: Reflux time: 54 h; yield 72%; mp 145–148ꢂC; IR: 3392.73
(-OH), 2919.56 (-CH), 2851.77 (-CH), 1111.77 (-CO), 867.90 (-C-C), 723.58
(-C-C) cmꢀ1
;
1H NMR (400 MHz, CDCl3): d=ppm ¼ 0.88 (6H), 1.25
(44H), 1.31 (8H), 1.94 (4H), 2.92–2.99 (8H), 3.5 (4H), 4.0 (4H), 4.37 (4H).
Compound 8g: Reflux time: 96h; yield 70%; mp 136–139ꢂC; IR:
3389.58 (-OH), 2924.14 (-CH), 2854.12 (-CH), 1370.08 (-CN), 1114
(-CO), 871.79 (-C-C), 723.58 (-C-C) cmꢀ1; H NMR (400MHz, CDCl3):
1
d=ppm ¼ 0.88 (6H), 1.25 (28H), 1.34 (8H), 1.95 (4H), 2.9–2.98 (8H), 3.48
(4H), 4.0 (4H), 4.38 (4H).
ACKNOWLEDGMENT
B. K. M. thanks the Board of Researchers in Nuclear Sciences, Bhaba
Atomic Research Center (BARC), Mumbai, for financial assistance
through a research project.
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