Russian Journal of Applied Chemistry, Vol. 77, No. 3, 2004, pp. 427 429 Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 3,
004, pp. 434 436.
Original Russian Text Copyright
2
2004 by Danov, Kolesnikov, Efremov, Mezhenin.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Kinetics of Hydroxyethylation of Dimethylamine
S. M. Danov, V. A. Kolesnikov, R. V. Efremov, and D. Yu. Mezhenin
Dzerzhinsk Branch, Nizhni Novgorod State Technical University, Dzerzhinsk, Nizhni Novgorod oblast, Russia
Received October 6, 2003
Abstract The kinetics of hydroxyethylation of dimethylamine with oxirane was studied in the temperature
interval 20 50 C at the oxirane : dimethylamine molar ratio of 1 : 3. The influence exerted on the reaction
rate by the reaction product, dimethylethanolamine, was examined.
Dimethylethanolamine (DMEA), hydroxyethylation
product of dimethylamine (DMA), is widely used in
basic organic synthesis, as solvent in paint-and-varnish
production, and as a component of cleansing, degreas-
ing, preserving, hydraulic, and cutting fluids.
tive hydroxyethylation. After completion of the sub-
stitution, at temperatures above 110 C, the reaction
decelerated again, and above 150 C it almost fully
stopped. However, at 70 100 C the reaction contin-
ued after substitution completion, yielding polyoxy-
ethylated products. This phenomenon was explained
by Sorokin and Shode [6 8]. They reported on forma-
tion of minor amounts of quaternary ammonium bases
which catalyze successive hydroxyethylation as effi-
ciently as do, e.g., alkali metal alcoholates. However,
quaternary ammonium bases are unstable and decom-
pose above 100 C with the regeneration of the tertiary
amine.
DMEA is synthesized in industry by liquid-phase
hydroxyethylation of DMA. At one of the enterprises,
the synthesis is performed in a coaxial-pipe reactor at
8
0 175 C, pressure of 5 6 MPa, and DMA : oxirane
(OX) molar ratio of 3 : 1.
However, the quality of the DMEA produced is
poor, because the conditions in the reactor are far
from being optimal. Because of inefficient heat ex-
change, the temperature in the reactor rises to 175 C,
whereas the available papers recommend much lower
synthesis temperatures.
It is also known that, in DMA hydroxyethylation,
formation of the desired DMEA is accompanied by
side reactions such as formation of dimethylamino-
ethoxyethanol (DMAEE), isomerization of oxirane
into acetaldehyde, and dimerization and polymeriza-
tion of oxirane [9]. The resulting products can under-
go further transformations.
In this work we studied the kinetics of DMA hy-
droxyethylation with the aim to obtain data required
for optimizing the reactor design and operation con-
ditions. It is known that, in the absence of proton
donors, amines do not react with oxirane or react very
slowly [1]. Lebedev and Smirnova [2 5] studied the
reaction of oxirane with various amines manometri-
cally. They found that proton donors (water, alcohol,
phenols, acids) accelerate the reaction and that the
reaction follows the first-order kinetic equation. The
amino alcohol formed in the reaction also acts as a
proton donor, causing an autocatalytic effect. The
reaction follows the Brønsted relationship, and for
each type of proton donors the logarithms of the rate
Preliminary experiments showed that the side reac-
tions were insignificant at 20 60 C and DMA : oxi-
rane molar ratio of 3 : 1. This ratio is used in the com-
mercial synthesis, and therefore we chose it in our
kinetic experiments.
The reaction rate was evaluated from accumulation
of DMAE in the reaction mixture, monitored chroma-
tographically. Figure 1 shows the kinetic curves of
DMEA formation at various temperatures.
constants correlate with the pK values.
a
It is seen that the kinetic curves are S-shaped,
which is typical of autocatalytic reactions. The DMEA
formed in the process can donate protons activating
the oxirane molecule. To confirm the occurrence of
autocatalysis, we performed some experiments at
30 C with addition of DMEA to the starting mixture.
The results are shown in Fig. 2.
In experiments without catalysts, in agreement with
data of [1], no reaction initially occurred; the induc-
tion period became shorter with increasing tempera-
ture, but fully disappeared only at 230 C. After the
end of the induction period, the reaction rate sharply
grew, and the nitrogen atom underwent fast and selec-
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070-4272/04/7703-0427 2004 MAIK Nauka/Interperiodica