Effect of Association on Nucleophilic Addition of (Meth)acrylic Aminoamides to Acrylic Acids in Aqueous Solutions

Article abstract of DOI:10.1134/S1070363218040059

Reactions of nucleophilic addition of N-(3-dimethylaminoalkyl)(meth)acrylamides to acrylic, N-acryloylaminoacetic, and 2-acrylamido-2-methylpropanesulfonic acid with the formation of betaines revealed an unusual dependence of the initial rate and equilibrium conversion on concentration of the reagents. The observed effects were explained by structural features of the reagents and the products.

Full text of DOI:10.1134/S1070363218040059

ISSN 1070-3632, Russian Journal of General Chemistry, 2018, Vol. 88, No. 4, pp. 641–645. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © О.А. Kazantsev, D.S. Baruta, D.М. Kamorin, K.K. Shirshin, А.P. Sivokhin, 2018, published in Zhurnal Obshchei Khimii, 2018,
Vol. 88, No. 4, pp. 556–560.
Effect of Association on Nucleophilic Addition
of (Meth)acrylic Aminoamides to Acrylic Acids
in Aqueous Solutions
О. А. Kazantseva, D. S. Barutaa, D. М. Kamorina, K. K. Shirshina,b*, and А. P. Sivokhina
a R.E. Alekseev Nizhny Novgorod State Technical University, ul. Minina 24, Nizhny Novgorod, 603950 Russia
*e-mail: kkshirshin@mail.ru
b N.I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia
Received October 26, 2017
Abstract—Reactions of nucleophilic addition of N-(3-dimethylaminoalkyl)(meth)acrylamides to acrylic,
N-acryloylaminoacetic, and 2-acrylamido-2-methylpropanesulfonic acid with the formation of betaines
revealed an unusual dependence of the initial rate and equilibrium conversion on concentration of the reagents.
The observed effects were explained by structural features of the reagents and the products.
Keywords: N-(3-dimethylaminoalkyl)metacrylamides, acrylic acid, N-acryloylaminoacetic acid, 2-acrylamido-
2-methylpropanesulfonic acid, betaines
DOI: 10.1134/S1070363218040059
Synthetic water-soluble polymers containing betaine
motifs are used as amphoteric thickeners [1],
flocculants [2], additives to paper and textile materials
[3], components of detergents and cosmetics [4].
Monomers for their preparation are synthesized in one
step by nucleophilic addition of tertiary amines to
acrylic acids: acrylic acid 1, N-acryloylaminoacetic
acid 2, 2-acrylamido-2-methylpropanesulfonic acid 3
[5–7].
amine fragment CH2CH2N(CH3)2 and differ by the
presence or absence of methyl substituents in positions
3 and 6 with respect to the amine nitrogen. Earlier, for
these compounds sharply different dependencies were
revealed of initial rates on starting concentrations of
the reagents for nucleophilic reactions with participa-
tion of amino groups: the quaternization with ethylene
chlorohydrin [10] or chloroacetic acid [11] by the
Menshutkin reaction.
R3N + СН2=СНСООН ⇄ R3N+СН2СН2COO–, (1)
The goal of the present work was to elucidate and
analyze the dependence of the initial rates and equilib-
rium conversions on the initial concentrations of the
reagents (at their constant ratio) in nucleophilic
addition reactions of amines 4–6 to acrylic acids 1–3 in
aqueous solutions. Amines 4–6 have pKa values of
9.23, 9.39, and 9.25 [12], practically the same sum of
induction constants of the substituents at nitrogen atom
Σσ* (0.1724, 0.1726, 0.1725), but different sum of
steric constants ΣRS: 4.72, 4.95, 5.31.
R3N + СН2=СНCONHCH2СООН
⇄ R3N+СН2СН2CONHCH2COO–,
(2)
(3)
R3N + СН2=СНCONHС(СН3)2CH2SО3Н
⇄ R3N+CH2CH2CONHС(СН3)2CH2SО3–.
It was shown that in aqueous, alcohol solutions or
without solvent such reactions proceed under mild
conditions and are not accompanied by side
transformations [5–9]. For the presence of vinyl groups
in betaines formed by reactions (1)–(3) to be active in
radical polymerization, as starting amines, (meth)
acrylic monomers with sterically non-hindered tertiary
amino groups can be used, like N-(3-dimethylamino-
propyl)acrylamide 4, N-(3-dimethylaminopropyl)metha-
crylamide 5, N-(1,1-dimethyl-3-dimethylaminopropyl)-
acrylamide 6 [9]. Compounds 4–6 contain the same
The addition of amines to electron-deficient C=C
bonds is known to increase with the nucleophilicity of
amine and steric accessibility of its reaction center
[8, 13]. However, because of the reaction of neutral-
lization, amines and carboxylic acids, when
simultaneously present in aqueous solutions, exist in
various equilibrium forms: as unbound molecules,
641

642
KAZANTSEV et al.
х, %
v0×104, mmol g–1 s–1
τ, min
с0, mmol/g
Fig. 1. Dependence of conversion of acids (1–3) 1, (4) 2,
(5) 3 on time in the reactions with amines 4–6. Initial
concentration of amine, mmol/g: (1–3) 3.0, (4, 5) 1.0.
Fig. 2. Effect of initial concentrations of the reagents on
the initial rates of addition of amines 4–6 to acid 1.
contact and solvent-separated ion pairs, dissociated
ions. The equilibria between these forms depend on
initial concentrations of the reagents, ionic strength of
the solutions, and other factors. Binding of molecules
of the reagents to salts sharply decreases the acid
activity and nucleophilic properties of the amino
group, which is converted to the ammonium one [13].
The transfer of proton to the negatively charged
α-carbon atom of the activated alkene, finalizing the
nucleophilic addition, can also follow different routes.
As a result, as was shown by the example of addition
of pyridine to acid 4 [14], adequate kinetic equation
must include several different reaction rates, with the
understanding that a set of constant values calculated
for certain conditions can be unsuitable for the other
conditions (for example, for the increase of
concentration of the reagents from 0.05 to 1.0 М).
Therefore in this work as a criterion of the influence of
initial concentrations of amines 4–6 having very
similar structure of the amine reaction center on the
kinetics of their addition to acids 1–3 we have chosen
readily measurable experimental parameters: initial
rates and attained equilibrium conversion.
compounds 4–6 strongly differ by manifestation of
concentration effects.
Figure 1 shows typical kinetic curves, which
demonstrate that reactions (1)–(3) in the systems under
investigation reach the equilibrium in 1–3 h.
Based on the kinetic curves extrapolated to zero
time the initial reaction rates were determined at
different concentrations of the reagents with their
constant ratio (Figs. 2, 3). In doing so, unusual
concentration plots were obtained. In dilute solutions
(concentration of the reagents up to 1.0 mmol/g), the
initial rates of addition of amines 4–6 to acids 1–3 are
slightly different. However, with the increase of initial
concentrations of the reagents, the activity of amines
becomes substantially different, the difference being
dependent on the range of concentrations. For
example, in concentration of 1.5 mmol/g, amine 5
shows the least activity as compared to 4 and 6, at
с0 3.0 mmol/g it shows the highest activity, and at
с0 ~4.0 mmol/g the rate of addition of amine 5 is
intermediate between those of 4 and 6.
The shapes of the initial rate dependences on
concentration for reactions of amines 4–6 are also
different. In the case of amine 5, the curve has a
clearly expressed maximum, for 6 the maximum is
smoothed (although corresponds to approximately the
same concentration, 3.0–3.5 mmol/g). The dependence
of the rate of addition of amine 4 on concentration has
Judged from practical equity of the values of pKa
and Σσ* of amines 4–6 and only small variation of
steric hindrances ΣRS, their activity in nucleophilic
addition reactions with the same electron-deficient
alkenes must be similar. However, the experimental
results have shown that as in the Menshutkin reaction
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EFFECT OF ASSOCIATION ON NUCLEOPHILIC ADDITION
643
v0×104, mmol g–1 s–1
х, %
с0, mmol/g
с0, mmol/g
Fig. 3. Effect of initial concentrations of unsaturated acids
on the initial rates of addition of amine 5 to acids (1) 2 and
(2) 3.
Fig. 4. Effect of initial concentration of the reagents on the
equilibrium conversion for addition of amines (1–3) 4–6 to
acid 1.
an S-shaped form with sharp increase of the rate in the
concentration interval 1.0–3.5 mmol/g.
for carrying out the process up to deep conversion
(Figs. 4, 5). Therewith in all five systems the growth of
с0 values first gives rise to a substantial shift of the
equilibrium toward the product formation, the
equilibrium conversion increases 1.5–6.5 times.
However, in three systems, with further increase in the
initial concentrations of the reagents a decrease in
equilibrium conversions was detected. Most clearly it
was manifested in system 5–1, where the initial
concentration of the reagents could be increased up to
We have also compared the concentration effects in
the addition of amine 5 to acids 1–3. The products of
reactions (2) and (3) are, respectively, methacrylic
carboxy- and sulfobetaines with two monosubstituted
amide groups. Acids 2 and 3 at an equimolar ratio of
the reagents are inferior in activity in the addition of
amines to acid 1, therefore, their reactions were
performed with excess of amines. It is worth noting,
that, when using acids 2 and 3 at с0 > 2 mmol/g, the
homogeneity of the systems was violated. In view of
this, the effect of initial concentrations of the reagents
was investigated in more narrow intervals than in
reaction with acid 1.
х, %
It turned out that for the addition of amine 5 to acid
2 the concentration dependence of the initial rate
passes through a maximum, and there is an interval of
initial concentrations of the reagents in which v0 first
sharply increases and then quickly decreases. The
maximally reached initial rates correspond to much
lower values of с0 than in the case of addition of amine
5 to acid 1 (1.5 as compared to 3.5 mmol/g). For the
system 5–3, the maximum on the plot v0–f(с0) is
lacking and monotonous growth of the initial rate close
to linear is observed.
с0, mmol/g
As follows from the data on equilibrium conver-
sions reached in all investigated systems, the effect of
the total initial concentration of the reagents is retained
Fig. 5. The effect of initial concentrations of unsaturated
acids on equilibrium conversions in addition of amine 5 to
acids (1) 2 and (2) 3.
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KAZANTSEV et al.
4 mmol/g with retention of homogeneity of the system.
In other cases, the highest initial concentrations were
as low as 2 mmol/g (5–2, 5–3) or 3 mmol/g (4–1, 6–1);
note that for acrylic aminoamides the reason for such
limitation was not the violation of homogeneity but
spontaneous polymerization of the monomers
occurring when the conversion reached > 20% in
solutions with higher с0 (even when concentration of
the inhibitor of radical polymerization, hydroquinone,
was substantially increased).
of factors determining the kinetic specific features of
the reactions can be alteration of accessibility of the
reaction centers connected with the structure of the
associates. Therefore, the formation of associates may
either favor or prevent the contact between the reaction
centers. The model of formation in concentrated
aqueous solutions of ammonium salts of vinyl type of
monomeric associates favoring the reactions with
participation of the С=С bonds was first suggested
rather long ago on the basis of the data on spontaneous
polymerization [19]. Occurring of spontaneous
polymerization in some systems we investigated is also
indicative of a possibility of formation of similar
associates in them.
Therefore, in all five investigated systems strong
concentration effects are revealed. When analyzing the
reasons of these effects it is necessary to underline
sharp differences in the addition of aminoamides with
the same structure of the amine reaction center to acid
1, as well as the fact that in the investigated systems
both the reagents and the products have potential
centers for associative interactions. It is well known
that the amine, acidic, and amide groups are active in
formation of hydrogen bonds; the presence of charged
ammonium, carboxylate and sulfonate groups must
cause strong ionic interactions in the reagents and
products. The studied aminoamides were earlier shown
to actively form associates in aqueous solutions [15],
the effect of association on physical properties of the
solutions being notably different.
The obtained results show that the occurrence of
reactions (1)–(3) with participation of amines 1–3 is
strongly affected by associative interactions depending
on the structure of the reagents. With increased initial
concentrations, the role of noncovalent pre-reaction
interactions increases. At low conversion the main
factor is association of the reagents, while at high
conversion the association of the products of the
reaction makes its contribution. This determines the
differences in concentration effects measured for the
initial rates and for equilibrium conversions of
reactions (1)–(3).
This allows a conclusion that the concentration
effects in reactions (1)–(3) are due to associative
interactions with participation of the reagents. In recent
years more and more data appear in the literature that
under certain conditions such interactions may play an
important role in the kinetics of homogeneous liquid-
phase reactions with participation of the reagents
capable of association. This allowed developing, in
particular, adequate kinetic models for some reactions
of alcohols [16, 17]. The method of simulation had
shown [18] that the rate constants for the reactions in
liquid-phase systems capable of association may
increase or decrease with concentration of the
associated reagents depending on the equilibrium
constant and the ratio of the rate constants for free and
associated molecules. In the case of participation in
association of not only the reagents but also the
reaction products, the concentration dependences at a
deep conversion may differ from those for initial rates.
EXPERIMENTAL
Acid 1 (“Acrylate” Ltd.), amine 4, and acid 3
(Aldrich) were used without additional purification.
Acid 2 and amine 1 were synthesized by the Schotten-
Baumann reaction from acryloyl chloride and
aminoacetic acid or N,N-dimethylpropanediamine [12,
20]. Amine 3 was prepared by the Ritter reaction using
the described procedure [21].
The addition of amines 4–6 to acid 1 was
performed at 50°С with an equimolar ratio of the
reagents; the reaction of amine 5 with acid 3, at 70°С
and molar ratio of the reagents 1.5 : 1.0; the reaction of
amine 5 with acid 3, at 50°С and the ratio of 1.2 : 1.0.
Initial concentrations of the reagents varied from
0.5 mmol/g to maximally possible (up to the limit of
solubility or carrying the reaction in mass). To exclude
radical polymerization of the monomers, hydroquinone
(0.5% of the monomer) was introduced to the reaction
mixtures. The degree of conversion in reactions (1)–(3)
was calculated from variation of concentration of the
С=С bonds, which was determined by bromide-
bromate titration.
The obtained results are indicative of this very
behavior in the investigated systems. Note also that
association may affect not only redistribution of the
electron density in the molecules of the reagents,
which determines the variation of their reactivity. One
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EFFECT OF ASSOCIATION ON NUCLEOPHILIC ADDITION
645
Compd., 1998, vol. 370, no. 4, p. 547. doi 10.1002/
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calculated from Eqs. (4) and (5) using the Galkin–
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(σA)i
n
σ* = Σ –—— ,
(4)
(5)
ri2
i=1
Ri2
RS = 30log 1 – nΣ —— .
4ri2
i=1
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where (σА)i denotes the ability of the ith atom of the
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Taft’s scale of inductive constants; inductive effect of
alkyl substituents was taken to be zero), Ri is the
covalent radius of the ith atom, Å, ri is the distance of
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ACKNOWLEDGMENTS
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This work was performed with the financial support
from the Ministry of Education and Science (State
contract 10.2326.2017/PCh) and the Program of
development of R.E. Alekseev Nizhny Novgorod State
Technical University.
17. Stul’, B.Ya. and Chesnokov, B.B., Kinet. Catal., 2002,
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