Reaction of methyl acrylate with N,N-dimethylethanolamine in the presence of a titanium alkoxide

Article abstract of DOI:10.1134/S1070427212110079

The kinetic features were examined for transesterifi cation of methyl acrylate with N,N-dimethylethanolamine in the presence of tetra(N,N- dimethylaminoethyl) titanate at different molar ratios of the reactants and at temperatures within 50-80 C, as well as for side reactions of Michael addition at 95-125 C. The major parameters governing the selectivity of the synthesis of N,N-dimethylaminoethyl acrylate were determined.

Full text of DOI:10.1134/S1070427212110079

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 11, pp. 1676−1680. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © P.A. Demidov, I.A. Lavrent’ev, V.V. Potekhin, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 11, pp. 1766−1770.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Reaction of Methyl Acrylate with N,N-Dimethylethanolamine
in the Presence of a Titanium Alkoxide
P. A. Demidova, I. A. Lavrent’evb, and V. V. Potekhinb
aSt. Petersburg State Institute of Technology (Technical University), St. Petersburg, Russia
e-mail: demidov@himtek.ru
b“Khimtek Inzhiniring” Closed Joint-Stock Company, St. Petersburg, Russia
Received July 26, 2012
Abstract—The kinetic features were examined for transesterification of methyl acrylate with N,N-dimethyletha-
nolamine in the presence of tetra(N,N-dimethylaminoethyl) titanate at different molar ratios of the reactants and at
temperatures within 50–80°C, as well as for side reactions of Michael addition at 95–125°C. The major parameters
governing the selectivity of the synthesis of N,N-dimethylaminoethyl acrylate were determined.
DOI: 10.1134/S1070427212110079
N,N-Dimethylaminoethyl acrylate (DMAEA), the
product of transesterification of methyl acrylate with
dimethylethanolamine (DMEA), serves as a raw material
in synthesis of water-soluble polymers having broad-
spectrum applicability (as flocculants, fragrances, and
extractants).
ence of titanium alkoxides have not yet been examined.
Here, we report results that can aid in further optimization
of the reactor design and operation.
EXPERIMENTAL
We used methyl acrylate [99.7%, TU (Technical Speci-
fications) 2435-003-52470063–2003], DMEA (99.3%,
TU 2423-004-78722668–2010), DMAEA (99.9%,
Arkema), methanol [99.5%, GOST (State Standard)
6995–77], and titanium tetraisopropylate (99.7%, TU
2423-008-50284764–2006]. The catalyst was prepared by
the technique described in [6]. For synthesis of Michael
adducts we used the procedure from [7].
The DMAEA synthesis reaction involves an equilib-
rium process and, consequently, requires withdrawing
the resultant methanol from the reaction medium for the
equilibrium to be shifted towards the target product.
Commercially, the transesterification reaction is con-
ducted in an ester production apparatus, comprised of a
continuously stirred tank reactor coupled with a rectifying
column which receives the gas stream to be separated
from methanol, at elevated temperatures (100–140°C),
atmospheric or reduced pressure (40–80 kPa), in the
presence of a homogeneous catalyst and a polymerization
inhibitor. The initial methyl acrylate is used in a 2–3-fold
molar excess with respect to DMEA [1–3].
The reactions were carried out in a metal reactor
equipped with a jacket, a thermometer, a stirrer, and a
sampler. Temperature control was achieved via circulation
of the coolant (PMS-100 silicone fluid) through the reac-
tor jacket and a LOIP LT-300 thermostatic bath. All the
starting chemicals, including the inhibitor (phenothiazine,
0.2%), were introduced into the reactor and heated to the
desired temperature; the warm-up period was no longer
than 5 min. In the transesterification experiments, the
catalyst was introduced into the reaction mixture heated
to the desired temperature; prior to analysis, the catalyst
was removed from the transesterification samples by
precipitation as hydrous titania, and this was followed
by filtration of the solution.
As known [4], transesterification of methyl acrylate
with DMEA involves, along with the main reaction of
DMAEA formation, side Michael reactions (addition
of alcohols at the vinyl group). The selectivity of the
process is governed primarily by the choice of catalysts,
among which neutral catalysts, organotitanium [5, 6] and
organotin [1, 3] compounds, have received widespread
application. The kinetic features and mechanism of trans-
esterification of methyl acrylate with DMEA in the pres-
1676

REACTION OF METHYL ACRYLATE
1677
Chromatographic analysis was carried out on a Tsvet
800 gas-liquid chromatograph [SE-30 column, 10 m ×
0.2 mm, a flame ionization detector, carrier gas (nitro-
gen) flow rate 200 ml min–1, evaporator and detector
temperature 180°C]. The chromatograph temperature
programming scheme was as follows: isothermal period
200 s at 60°C; temperature rise rate 20 deg s–1 to 200°C;
isothermal period 300 s; temperature rise rate 25 deg s–1
to 240°C; isothermal period 300 s.
Dimethylaminoethyl acrylate is formed by the reaction:
O
CH3
N
CH
CH3
CH2
CH2
OH
+
O
C
CH CH2
3
CH3
CH3
O
C
(1)
N
CH2
CH2
O
CH CH2
+
CH33 OH.
CH
CH3
(a)
The kinetic features of the transesterification reaction
were examined at different molar excesses of methyl
acrylate with respect to DMEA, catalyst concentrations,
and temperatures. The reaction rate was monitored by
measuring the amount of DMAEA accumulated in the
reaction system. Figure 1 presents the kinetic curves of
the target reaction.
We found that the reaction rate linearly varies with the
catalyst concentration.As shown in [8] for transesterifica-
tion of methyl benzoate with butanol, the reaction order
with respect to the catalyst depends on its concentration,
which fact was associated in that study with the tendency
to associate, exhibited by titanium alkoxides.At the same
time, titanium alkoxides derived from amino alcohols do
not form associates [9], which finding agrees well with
our data.
(b)
As the reaction model we took that based on the outer-
sphere transesterification mechanism (see the scheme).
This mechanism is described by the formal kinetic equa-
tion
(c)
r1 = ccat(k1cMAcDMEA – k–1cMeOHcDMAEA),
where ccat, cDMAEA, cMA, cMeOH, and cDMEA are the molar
concentrations of the catalyst, DMAEA, methyl acrylate,
methanol, and DMEA, respectively, and k1 and k–1, rate
constants of the forward and backward reactions, respec-
tively, l2 mol–2 h–1.
Fig. 1. Kinetic curves of transesterification. (A) Yield of
DMAEA based on DMEA, %, and (t) time, h. (a) Сatalyst
The activation energies of the forward and backward
reactions are 76 ± 5 and 46 ± 5 kJ mol–1, respectively.
The reaction is endothermic, with the heat effect ΔQ =
–30 kJ mol–1.
сoncentration 0.1 M, temperature 70°C. Methyl acrylate:DMEA
molar ratio: (1) 1 : 1, (2) 2 : 1, and (3) 3 : 1. (b) Catalyst con-
centration 0.1 M, methyl acrylate:DMEA molar ratio 3 : 1. T,
°C: (1) 50, (2) 60, (3) 70, and (4) 80. (c) Methyl acrylate:DMEA
molar ratio 3:1, temperature 70°C. Catalyst concentration, M:
(1) 0.05, (2) 0.1, and (3) 0.2.
Along with the main reaction of DMAEA formation,
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 11 2012

1678
DEMIDOV et al.
Scheme 1.
OCH3
O
CH
CH2
CH2
Ti[OR]4
+
CH
C
CH
C
O
Ti[OR]4 (fast),
2
OCH3
OCH3
OCH3
CH2
CH2
O
Ti[OR]4
Ti[OR]4
+
ROH
O Ti[OR]4 (slow),
CH
CH
C
CH
C
OR H
OR
C
OCH3
CH2
O
Ti[OR]4
+
CH3OH (slow),
O
CH2
CH
O
C
OR H
OR
CH
CH2
(fast).
C
CH2
Ti[OR]4
+
O
Ti[OR]4
CH
C
CH
2
OR
(adducts II and IV) proceeds to a negligible extent; forma-
tion of these compounds in the reaction medium is due
to transesterification of adducts I and III with DMEA.
Adduct I is formed by the reaction
side Michael reactions [7] and transesterification reac-
tions proceed, resulting in formation of esters with the
general formula
O
O
R
O
CH2
CH2
C
CH3
OH
+
CH3
O
C
CH CH2
O
R'
O
C
where R=CH2CH2N(CH3)2.
, (2)
CH3,
CH3
O
CH2
CH2
O
For Michael adducts, see table.
and adduct III, by the reaction
Addition of alcohols at the vinyl group of DMAEA
O
CH3
CH CH2
CH2 CH2
R'
+
CH3
O
N
C
CH2
CH2
OH
CH3
O
CH3
(3)
N
O
CH2
CH2
CH3.
C
O
CH3
Michael adducts
Adduct
The rate of accumulation of Michael adducts is affect-
ed by the basicity of the medium [7]; titanium alkoxides
do not give β-alkoxypropionic esters [6].
R
I
CH3–
CH3–
CH3–
The kinetic features of the reactions leading to ad-
ducts I and III were examined at different temperatures
and molar ratios of the reactants (methanol : methyl
acrylate : DMEA for adduct I and methyl acrylate :
DMEA for adduct III). The reaction rate was monitored
by measuring the amount of the products accumulated in
II
(CH3)2NCH2CH2–
CH3–
III
IV
(CH3)2NCH2CH2–
(CH3)2NCH2CH2–
(CH3)2NCH2CH2–
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 11 2012

REACTION OF METHYL ACRYLATE
1679
(a)
(a)
(b)
(b)
(c)
Fig. 3. Kinetic curves of Michael addition reaction for adduct
III. (A) Methanol conversion, %, and (t) time, h. (a) Temperature
105°C. Methyl acrylate:DMEA molar ratio: (1) 2 : 1, (2) 1 : 1,
(3) 1 : 2, and (4) 4 : 1. (b) Methyl acrylate:DMEA molar ratio
2 : 1. T, °C: (1) 95, (2) 105, (3) 115, and (4) 125.
for DMAEA against 4.52 for DMEA [10, 11]).
The kinetics of accumulation of the products is ad-
equately described by the equation
r1 = kiKbcMA ROH
c
= ki'cDMEAсМАсROH,
Fig. 2. Kinetic curves of Michael addition reaction for adduct
I. (A) Methanol conversion, %, and (t) time, h. (a) DMEA con-
centration 0.5 M, temperature 105°C. Methanol:methyl acrylate
molar ratio: (1) 1 : 2, (2) 1 : 1, and (3) 2 : 1. (b) Methanol:methyl
acrylate molar ratio 1:2, temperature 105°C. DMEA concen-
tration, M: (1) 0.2, (2) 0.5, and (3) 1.0. (c) Methanol:methyl
acrylate molar ratio 1 : 2, DMEA concentration 0.5 M. T, °C:
(1) 95, (2) 105, (3) 115, and (4) 125.
where ki is the rate constant of ith reaction, and cROH
cMA, and cDMEA, concentrations of the alcohol, methyl
acrylate, and DMEA, respectively.
,
The activation energies of reactions (2) and (3) are
83 ± 5 and 70 ± 5 kJ mol–1, respectively.
Based on the kinetic features of the target and side reac-
tions examined, we propose the following mathematical
model of the process:
the reaction system. The examinations were carried out
under conditions of pseudo-zero-order kinetics to avoid
the interference from consecutive reactions. Figure 2
shows the kinetic curves of formation of adduct I, and
Fig. 3, those for adduct III.
dcDМEА
– –——— = сcat(k1cMA DМEА
c
dt
– k–1cMeOH DМАEА
c
) + k3сМАc2DМEА
,
The rate of accumulation of products in the presence
of DMAEA is by an order of magnitude lower compared
to DMEA because of a low basicity (pKb at 25°C is 5.4
Fairly close activation energies of the main and side
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 11 2012

1680
DEMIDOV et al.
reactions suggest that the selectivity of transesterification
of methyl acrylate with DMEA is weakly affected by
temperature variation. Methanol occurring in the reac-
tion medium not only decelerates the DMAEAformation
but also leads to accumulation of adduct I. Therefore, to
enhance the selectivity of the process, methanol needs
to be efficiently withdrawn from the reaction system. To
reduce the yield of adduct III, it is necessary to increase
the titanium alkoxide : DMEA molar ratio.
cess will be the higher, the more efficient the withdrawal of
methanolandthehigherthecatalyst:dimethylethanolamine
molar ratio.
ACKNOWLEDGMENTS
This study was financially supported by Khimtek
Inzhiniring Closed Joint-Stock Company.
REFERENCES
CONCLUSIONS
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 11 2012