Effect of reactant association on addition of tertiary amines to acrylic acid in aqueous solutions

Article abstract of DOI:10.1134/S1070427206100144

The formation of betaines by the reaction of tertairy amines (N,N-dimethyl-N-2-hydroxyethylamine, N,N-dimethylaminoethyl methacrylate, N-methylmorpholine, N,N-dimethylaminopropionitrile, 1,4-diazabicyclo[2.2.2] octane) with acrylic acid in aqueous solutions in a wide concentration range was studied. The concentration effects observed were interpreted taking into account the association of the starting reagents. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S1070427206100144

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 10, pp. 1629 1633.
Original Russian Text A.P. Malyshev, K.V. Shirshin, O.A. Kazantsev, A.P. Sivokhin, I.V. Zhiganov, A.E. Kuznetsov, 2006, published in Zhurnal
Prikladnoi Khimii, 2006, Vol. 79, No. 10, pp. 1650 1654.
Pleiades Publishing, Inc., 2006.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Effect of Reactant Association on Addition
of Tertiary Amines to Acrylic Acid in Aqueous Solutions
A. P. Malyshev, K. V. Shirshin, O. A. Kazantsev, A. P. Sivokhin,
I. V. Zhiganov, and A. E. Kuznetsov
Dzerzhinsk Polytechnic Institute, Nizhni Novgorod State Technical University, Dzerzhinsk,
Nizhni Novgorod oblast, Russia
Received January 24, 2006
Abstract The formation of betaines by the reaction of tertairy amines (N, N-dimethyl-N-2-hydroxyethyl-
amine, N, N-dimethylaminoethyl methacrylate, N-methylmorpholine, N, N-dimethylaminopropionitrile,
1,4-diazabicyclo[2.2.2]octane) with acrylic acid in aqueous solutions in a wide concentration range
was studied. The concentration effects observed were interpreted taking into account the association of
the starting reagents.
DOI: 10.1134/S1070427206100144
Carboxy betaines are components of many cosmetics
and pharmaceutical preparations [1]. In many cases, it
is appropriate to prepare -betains in a single step by
nucleophilic addition of tertiary amines to the acti-
vated C=C bond in acrylic acid. Water is a convenient
solvent for such reactions [2]. Previously, we have
examined the reaction of a series of trialkylamines
with acrylic acid in dilute and moderately concentrated
aqueous solutions [3, 4]. From the practical viewpoint,
it is appropriate to use as high concentrations of reac-
tants as possible; however, specific features of betaine
formation from amines and acrylic acid in concen-
trated aqueous solutions have not been studied yet.
In this study, we examined the effect of reactant
association on the nucleophilic addition of tertiary
amines to AA to give betaines:
+
CH2 CHCOOH + NRR R
RR R NCH2CH2COO ,
where NRR R" = (CH3)2NCH2CH2OH (DMAE),
(CH3)2NCH2CH2OCOC(CH3) CH2 (DMAEM),
(MeM), (CH ) N(CH ) CN (DMAPN),
O
H3C N
3 2
2 3
N(CH2CH2)3N DABCO.
As amines we chose compounds containing, along
with the reacting amino group, additional N- and
O-containing functional groups: N, N-dimethyl-N-2-
hydroxyethylamine (DMAE), N, N-dimethylamino-
ethyl methacrylate (DMAEM), N-methylmorpholine
(MeM), N, N-dimethylaminopropionitrile (DMAPN),
asnd 1,4-diazabicyclo[2.2.2]octane (DABCO). The ad-
ditional functional groups considerably increase the
solubility of amines and their salts in water, which
allowed syntheses in aqueous solutions in a wide
concentration range. Furthermore, according to [10],
the energies of intermolecular associative interactions
involving hydroxy, etser, ether, nitrile, and amino
groups are essentially different. Therefore, we ex-
pected that comparison of the activities of polyfunc-
tional amines in the betaine formation would furnish
additional information on the effect of these interac-
tions on the reaction in question.
Recent papers give more and more indications that
(meth)acrylic monomers in aqueous soilutions tend to
form stable molecular associates which can strongly
affect the chemical properties of these compounds.
In particular, studies of the hydrolysis of aminoalkyl
and hydroxyalkyl methacrylates (N, N-dimethylamino-
ethyl and 2-hydroxyethyl methacrylates) have shown
that the association of the monomers results in ab-
normal acceleration or inhibition of the reaction in
concentrated solutions [5, 6]. Another consequence
of the association of amine-containing (meth)acrylic
esters or amides in water is the possibility of spon-
taneous radical polymerization under certain condi-
tions [7, 8]. A study of the radical homopolymeriza-
tion of acrylic acid (AA) in aqueous solutions also
revealed a significant effect of the monomer self-as-
sociation on the rate constant of chain propagation [9].
1629

1630
MALYSHEV et al.
EXPERIMENTAL
The reaction of AA with tertiary amines was per-
formed at 50 C and equimolar ratio of the reactants.
Hydroquinone (0.5 wt % relative to AA) was added to
the reaction mixtures to prevent radical polymeriza-
tion. The reactant concentrations in aqueous solution
1
were varied from 1 to 6 mmol g (with DABCO, the
1
maximal concentration was 3 mmol g ; at higher
concentrations, the system became heterogeneous).
Addition of tertiary amines to AA was monitored
by a decrease in the concentration of the C=C bonds
determined by bromide bromate titration. The spe-
cific viscosity of the reactants was measured with
an Ubbelohde viscometer (dc 0.34, 0.56, and 0.73 mm;
25 C). The 1H NMR spectra were recorded on a
Varian Gemini-300 Fourier spectrometer (300 MHz),
solvent D2O, reference DMSO.
Fig. 1. Variation of the reactant concentration c with time
Amine: (1) DMAPN, (2) DABCO, (3) DMAE,
(4) DMAEM, and (5) MeM; the same for Figs. 2, 3,
.
and 5.
3-(N, N-Dimethyl-N-hydroxyethylammonio)prop-
ionate. To 18.2 g of a 76% solution of AA in water,
containing 0.07 g of hydroquinone, we added 17.1 g
of DMAE. The resulting mixture was heated at 50 C
for 5 h. After the reaction completion, water was
distilled off in a vacuum, and the residue was washed
with acetone. The product was vacuum-dried (20
40 C, 2 mm Hg) to constant weight. Yield 24.8 g
(80.1%). The product contained no C=C bonds and no
acid groups.
Found, %: N 8.58.
Calculated, %: N 8.70.
1H NMR spectrum, , ppm: 3.34 3.39 ( CH2N+);
2.85 (CH3N+); 2.55 2.64 ( CH2OH, CH2COO ).
The addition of amines to AA is an equilibrium
reaction throughout the examined range of initial con-
centrations of the reactants. Figure 1 shows typical
kinetic curves of consumption of the reactants at their
high concentrations. Figures 2a and 2b show the de-
pendences of the equilibrium conversion and initial
reaction rate on the initial reactant concentration.
The following trends can be revealed. As the initial
1
concentrations are raised in the range 0 1.5 mmol g
for amines containing no oxygen (DMAPN, DABCO),
the equilibrium conversion sharply increases, reaches
a maximum (88 95%) at the initial concentration of
1
about 2.5 mmol g , and does not noticeably change
with further increase in the concentration.
A different pattern is observed with the oxygen-
containing amines. In the experiments with DMAE,
the equilibrium conversion monotonically grows with
Fig. 2. (a) Equilibrium conversion X and (b) initial reaction
rate v vs. the reactant concentration c.
0
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 10 2006

EFFECT OF REACTANT ASSOCIATION ON ADDITION OF TERTIARY AMINES TO ACRYLIC ACID 1631
Inductive ( *) and steric (Rs) constants of substituents R, R , R" in the starting amines (N* is the reaction center)
*
Amine
NRR R"
Rs
DMAE
DMAEM
MeM
DABCO
DMAPN
(CH3)2N*CH2CH2OH
(CH3)2N*CH2CH2OCOC(CH3)=CH2
CH3N*(CH2CH2)2O
0.20
0.5
0.67
5.83
6.33
6.23
4.43
6.02
N*(CH2CH2)3N
(CH3)2N*CH2CH2C N
0.8
the initial solution concentration (with a minor de-
viation from linearity) and reaches almost 100% at
the maximal concentration (actually, for neat re-
actants without solvent). With DMAEM and MEM,
the equilibrium conversion first increases in the ini-
tial concentration, passes through a maximum, and
then sharply decreases at concentrations exceeding
actions of reactant molecules with the formation of
various associates.
Therefore, the next step of our study was concerned
with the association of amines in aqueous solutions in
the presence of acids. In these experiments, AA was
replaced with acetic acid to preclude betaine forma-
tion. We obtained the viscosity concentration de-
pendences (VCDs) for solutions of amine acetates
(Fig. 3). It is known [14] that the occurrence and fea-
tures of intermolecular interactions in solutions can
be judged from the VCDs. Pronounced deviations
of the VCDs from the linearity, observed with all
the amines, suggest the occurrence of the association.
Figure 3 shows that the VCDs of the salts of all
the amines except DABCO exhibit pronounced max-
ima. According to [14, 15], maxima in the viscosity
isotherms correspond to the formation of stable com-
plexes in the system. To evaluate the relative capa-
bility of the amine salts for association, we cal-
1
3.2 mmol g .
The dependences of the initial rates on the re-
actant concentration also vary with the amine struc-
ture. This dependence is approximately linear with
DMAE, passes through a pronounced maximum with
MeM, is close to exponential with DMAEM, and is
S-shaped with DMAPN and DABCO.
It has been shown previously [3, 4] that, in dilute
solutions at approximately equimolar reactant ratio,
the relative activity of various tertiary amines in re-
actions with AA is determined by the steric acces-
sibility and nucleophilicity of the nitrogen atom. To
evaluate these parameters for the amines examined in
*
this study, we used the inductive ( ) and steric (Rs)
constants of substituents, calculated according to
[11, 12]. These procedures were developed for sys-
tems with a four-coordinate carbon atom as a reaction
center. However, previous studies of N-alkylation
of tertiary amines have shown that this approach also
gives adequate results when applied to systems with
a nitrogen atom as reaction center [13].
The constants listed in the table show that the
amines chosen are similar in the steric accessibility
and nucleophilicity of the reaction centers. Therefore,
in accordance with the previously developed concepts,
the amines should not essentially differ in the reactiv-
ity toward AA. Thus, the concentration effects ob-
served cannot be interpreted in terms of the traditional
concept of nucleophilic reactions of amines. We attri-
bute the abnormal dependences of the initial rate of
betaine formation and equilibrium conversion on the
initial reactant concentration to intermolecular inter-
Fig. 3. Specific viscosity of aqueous solutions of amine
acetates at 25 C vs. the concentration c.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 10 2006

1632
MALYSHEV et al.
and steric accessibility of reaction centers in the iso-
lated molecules, but strongly differ in the tendency
toward association in the presence of acids. In this con-
text, it is reasonable to assume that the factor respon-
sible for significant differences in the betaine forma-
tion kinetics is the effect of the association on the local
concentration, accessibility, and reactivity of active
centers of the reactants. Our results show that the as-
sociation can both accelerate and inhibit the reaction.
In particular, it is known [16] that form linear ag-
gregates alcohols in aqueous solutions. It is reasonable
to assume that DMAE or its salt, containing a hydroxy
group, also tend to form such associates. Apparently,
the local concentration of the reactants in such as-
sociates increases, which facilitates their reaction.
As a result, the concentration, initial rate, and equilib-
rium conversion proportionally increase.
Fig. 4. Determination of
sociation factor
and
for calculating the as-
2
1
.
Shibalovich et al. [17] measured the surface tension
of aqueous solutions of DMAEM and its salts and
showed that these compounds exhibit surface activity
even in relatively dilute solutions. Hence, associ-
ates of micellar rather than linear type are more prob-
able for DMAEM salts. It should be noted that,
1
at concentrations less than 1.8 mmol g (relatively
dilute solutions), the dependences of the specific vis-
cosity and reaction rate on the amino ester concentra-
tion are approximately linear. At concentrations ex-
1
ceeding 2 mmol g , both the viscosity of the reaction
mixtures and the initial reaction rate sharply increase,
i.e., the association of the starting amine salts favora-
bly affects the betaine formation. A sharp decrease in
the equilibrium conversion in highly concentrated
1
solutions (>3.5 mmol g ) is apparently due to forma-
tion in the course of the reaction of stable heteroasso-
ciates of the starting reactants and betaines, in which
the mutual arrangement of the unchanged amino
groups and C=C bonds is unfavorable for the reaction.
Fig. 5. Association factor at 25 C vs. the concentration
of amine acetates, c.
culated the association factor
of deviation of the VCD from the linearity:
reflecting the extent
Data for the MeM AA system show that, in this
case, the reaction rate and viscosity of the system
grow virtually linearly as the reactant concentration
1
= (
2)/
,
2
is raised to 2 mmol g , and in the concentration
1
1
range 2 4 mmol g the growth accelerates. With
where
is the actual specific viscosity of an amine
is the specific
a further increase in the concentration, the initial rate,
equilibrium conversion, and viscosity sharply de-
crease. This fact may be due to the formation in high-
ly concentrated solutions of stable homoassociates of
the starting amine salts and heteroassociates of amine
salts with the forming betaines, with the mutual ar-
rangement of the amino group and C=C bond in these
associates being unfavorable for the reaction.
salt at a1 given concentration, and
2
viscosity at the same concentration, estimated by
extrapolation of the initial linear portion of the VCD
(Fig. 4).
Figure 5 shows the dependences of on the amine
salt concentration. It is seen that DABCO and DMAE
show the strongest tendency toward association, and
DMAEM and DMAPN, the weakest tendency. Thus,
the amines chosen are similar in the nucleophilicity
With DABCO and DMAPN containing no oxygen
atoms, the molecular packing in the homo- and
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 10 2006

EFFECT OF REACTANT ASSOCIATION ON ADDITION OF TERTIARY AMINES TO ACRYLIC ACID 1633
heteroassociates is favorable, according to the exper-
imental data, for the betaine formation. Therefore,
with an increase in the initial concentration to above
2. Suminov, S.I. and Kost, A.N., Usp. Khim., 1969,
vol. 38, no. 11, pp. 1933 1963.
3. Kazantsev, O.A., Doctoral Dissertation, Yaroslavl,
1
1.0 1.5 mmol g , the initial reaction rate and vis-
1998.
cosity of the mixture demonstrate virtually synchro-
nous accelerated growth, without a decrease in
the equilibrium conversion.
4. Le Berre, A. and Delacroix, A., Bull. Soc. Chim. Fr.,
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et al., Zh. Prikl. Khim., 2003, vol. 76, no. 7,
pp. 1150 1153.
CONCLUSIONS
6. Kazantsev, O.A., Shirshin, K.V., Sivokhin, A.P.,
et al., Zh. Prikl. Khim., 2003, vol. 76, no. 8,
pp. 1333 1335.
(1) The effect of the initial reactant concentration
on the nucleophilic addition of tertiary amines to
acrylic acid in aqueous solutions was examined.
7. Kazantsev, O.A., Kuznetsova, N.A., Shirshin, K.V.,
et al., Vysokomol. Soedin., Ser. A, 2003, vol. 45,
no. 4, pp. 572 580.
(2) With an increase in the initial reactant con-
centration, the initial reaction rate grows linearly
(N, N-dimethyl-N-2-hydroxyethylamine), exponential-
ly (N, N-dimethylaminoethyl methacrylate), in the
S-shaped mode (N, N-dimethylaminopropionitrile, 1,4-
diazabicyclo[2.2.2]octane), or passes through a max-
imum followed by a sharp decrease (N-methylmor-
pholine).
8. Kazantsev, O.A. and Shirshin, K.V., Polymer, 2004,
vol. 45, no. 15, pp. 5021 5029.
9. Lazhik, I., Beuermann, S., and Buback, M., Macro-
molecules, 2003, vol. 36, no. 25, pp. 9355 9363.
10. Irzhak, V.I., Korolev, G.V., and Solov’ev, M.E.,
Usp. Khim., 1997, vol. 66, no. 2, pp. 179 200.
11. Galkin, V.A., Cherkasov, A.R., Sayakhov, R.D., et al.,
(3) With an increase in the initial reactant concen-
tration, the equilibrium conversion monotonically
grows to reach maximal values (N, N-dimethyl-N-
hydroxyethylamine, N, N-dimethylaminopropionitrile,
1,4-diazabicyclo[2.2.2]octane) or passes through a
maximum followed by a sharp decrease (N, N-dimeth-
ylaminoethyl methacrylate, N-methylmorpholine).
Zh. Obshch. Khim., 1995, vol. 65, no. 4, pp. 458 468.
12. Galkin, V.A., Sayakhov, R.D., and Cherkasov, R.A.,
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protsessom (Solvent as a Means To Control a Chem-
ical Process), Fialkov, Yu.Ya., Ed., Leningrad: Khi-
miya, 1990.
(4) Salts of tertiary amines in aqueous solutions
tend to form associates; their structure determines
the course of the reaction of betaine formation.
15. Arutyunyan, R.S., Grigoryan, V.V., Egoyan, R.V.,
et al., Arm. Khim. Zh., 1988, vol. 41, no. 6,
pp. 323 327.
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