Generally,
EPDA is produced through the chemical reactions of epichlorohydrin (ECH)
with neodecanoic acid (NDA), and three typical synthetic processes have
been developed according to the published literatures and patents (seeScheme 1 ).10 The first preparation method is
carried out by using the alkali metal salt of NDA. The specific
operations can be summarized as: (1) NDA reacts with sodium hydroxide
aqueous solution to generate neodecanoate, (2) then the salt solution is
dripped into the reactor with ECH heated reflux in it. This
organic-aqueous reaction system has high viscosity and low interfacial
tension because the neodecanoate, whose chemical structure consists of a
polar head and a hydrophobic tail, can function as a surfactant. Hence,
the emulsification can be rather serious for this system. Besides, the
alkaline environment can cause the hydrolysis of ECH to produce
dichloropropanol and glycerol, leading to the waste of reactant and
posing difficulties for waste water treatment. The second synthetic
process is
based
on the largely excessive use of ECH, the by-product dichloropropanol can
be converted into ECH and recycled through the reaction with alkalis.
However, the atom economy is poor,
and the relatively low purity of EPDA increases the cost in the
downstream purification processes.
At present, the two-step process is the most widespread path for EPDA
production, including the initial acidolysis ring-opening reaction of
ECH with neodecanoic acid to produce chlorohydrin ester intermediate
(EPDA-M), and the following ring-closure step by alkali treatment. The
acidolysis reactions of ECH with organic acids can be catalyzed by a
series of nitrogenous catalyst11-13 and complexes of
transition metal14, 15. Tetramethylammonium chloride
(TMAC) has been recognized as a high-performance catalyst because of its
high catalytic activity and ease of separation and
recovery.16 The significant advances have been made to
explore the catalytic mechanism and the interaction effect between TMAC
and the reactants17, providing theoretical support for
process optimization. The following ring-closure reaction by
dehydrochlorination is a relatively mature process involved in some
practical industrial applications, such as the production of propylene
oxide through the chlorohydrin approach18, 19 and the
production of ECH from dichloropropanol (DCP)20, 21.
The advantages, including the mild conditions applied in the whole
process, the high conversion of neodecanoic acid and high selectivity
towards EPDA, determine the great applicability of this two-step
process. However, there are few researches to optimize the process
conditions. Besides, the complete catalytic reaction pathways and the
mechanism to explain the formation of the side product dichloropropanol
(DCP) are still not clear. The lack of these studies leads to the
unclarity of the strategies to improve the effective utilization rate of
ECH and reduce the organic waste.
The essential objective of this work is to optimize the two-step
production process of EPDA catalyzed by TMAC in batch condition.
Moreover, some reliable experiments are conducted to verify the
catalytic mechanism of the main acidolysis reaction and demonstrate the
side reactions, as well as its occurrence conditions and control
methods. Hopefully, the study methods and the obtained mechanisms can be
successfully applied for other production processes of glycidyl eaters,
such as glycidyl acrylate and glycidyl methacrylate.
Experiment
Reagents and materials
All reagents used in the experiments were classified as analytical grade
and purchased from commercial reagent company. Neodecanoic acid was
purchased from Shanghai Ethyl Chemical Co., LTD, with the purity of 99%
tested by titration. The rest of chemicals were routinely used in our
laboratory, and all purchased from Aladdin Chemistry Co., LTD. The
purities of all reagents could meet the experimental requirements, hence
the further purification steps were not required.
Experimental procedures