© 2009 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 82, No. 4, 509–513 (2009)
509
Accelerated Saponification of Methyl Dodecanoate with Aqueous
Sodium Hydroxide Solution in the Presence of Alcohols
in a Silicone Rubber Tube as a Flow-Type Reactor
Atsushi Kamiouji, Keiji Hashimoto, Hiroshi Kominami,* and Seishiro Ito
Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University,
Kowakae, Higashiosaka, Osaka 577-8502
Received October 31, 2008; E-mail: hiro@apch.kindai.ac.jp
Saponification of methyl dodecanoate with an aqueous sodium hydroxide solution in the absence and presence of
alcohols was studied using a tubular reactor made of silicone tube to elucidate effects of alcohol addition on the
saponification. The reaction rates of saponification were accelerated significantly when alcohols were dissolved in methyl
dodecanoate and the rates were increased in the order: without alcohol ¹ ethanol < propanol < butanol. The rates in all
cases obeyed the Nernst diffusion rate equation, and the values of apparent diffusion constant, ka, that were determined
from the slope of Nernst plots were increased in the above order, indicating that diffusion of sodium ion in the aqueous
solution into the mixture of methyl dodecanoate and alcohol was much easier than that to methyl dodecanoate without
alcohol. The values of ka increased with increase in the amount of butanol both in the tubular reactor and in a beaker
(batch system). The thickness of the diffusion layer, ¤, decreased with increase in the amount of butanol in the
saponification in the tubular reactor, suggesting that the increase in ka in the saponification in the presence of butanol in
the tubular reactor can be explained by decrease in values of ¤.
Development of novel technologies for a sustainable world
is needed to resolve serious environmental and energy prob-
lems. The substitution of organic solvents for water in organic
syntheses has attracted much attention from the point of view
of eco-friendly production of chemicals.1-4 A water solvent is
also very useful for practical use because water is safe, cheap,
and chemically stable. However, organic compounds are often
hydrophobic. Therefore, most studies on organic synthesis in a
water solvent have focused on the development amphiphilic
catalysts such as a phase-transfer catalyst,5,6 amphiphilic
catalyst-anchored polymers7-10 and a Lewis-acid catalysts that
are stable in water.11,12 An optimal catalyst is generally present
for each reaction and there is no catalyst that is almighty for
some reactions. It is hence essential for practical use to develop
an optimal catalyst for each reaction. Another way to apply a
water solvent to organic syntheses is the development of a
novel reactor having a large diffusion constant in a two-phase
reaction between a water solvent and hydrophobic reactant(s).
There have been some studies on a micro-reactor in the two-
phase reaction,13-16 but the high cost of the micro-reactor itself
limits its application to the production of expensive chemicals
such as medicinal chemicals, because the micro-reactor is made
by using advanced technologies and is used under a high
pressure. There have been few studies on novel reactors other
than a micro-reactor.
solution to the methyl esters was increased 300-500 times more
than those in a batch system.17,18
It is known that addition of a solubilizer such as an alcohol
to the reaction mixture of water and hydrophobic reagents often
promotes the reaction rate in a batch system. We attempted to
apply the tubular reactor to saponification of fatty acid methyl
esters with aqueous sodium hydroxide solution in the presence
of alcohols as a model of two-phase reaction and to elucidate
the effects of addition of alcohols on saponification in the
tubular reactor. It was found that the addition of alcohols
significantly increased the reaction rate of saponification in the
tubular reactor as well as in the batch-type reactor. In this paper,
we show that (1) the saponification of methyl dodecanoate with
sodium hydroxide (NaOH) in the presence of alcohols also
obeyed the Nernst diffusion rate equation and that its rate-
controlling step was diffusion of sodium cation into the mixture
of methyl dodecanoate and alcohol, (2) a larger apparent
diffusion constant was obtained in the presence of alcohols, and
(3) alcohols dissolved in methyl dodecanoate decreased the
thickness of the diffusion layer formed between the ester phase
and the aqueous phase.
Experimental
Materials.
Commercial and reagent-grade methyl dodec-
anoate, sodium hydroxide (NaOH), ethanol, propanol, butanol,
hexane, and biphenyl were used without further purification.
Distilled water was used as a solvent of NaOH. Commercial tubes
made of silicone rubber with an inner diameter of 1.7 mm were
supplied by ARAM Corporation, Osaka.
We have developed a long tubular reactor using a cheap and
mass-produced tube made of silicone rubber. We already
reported that saponification of some kinds of fatty acid methyl
ester with aqueous alkali hydroxide solution was accelerated
significantly by using a long tubular reactor and that the
apparent diffusion constant of alkali cation in the aqueous
Saponification.
In a typical run, NaOH (20 mmol) was
dissolved in 5.0 cm3 of distilled water. A peristaltic pump (Cole