Organic Process Research & Development 2002, 6, 829−832
Evaluation of Kinetic Parameters from the Synthesis of Triaryl Phosphates
Using Reaction Calorimetry
Carlos F. Pinto Machado e Silva and Joa˜o F. Cajaiba da Silva*
UniVersidade Federal do Rio de Janeiro - UFRJ, Centro de Tecnologia, Instituto de Qu´ımica, Po´lo de Xistoqu´ımica,
21494-900, Rio de Janeiro, Brazil
Scheme 1
Abstract:
Triaryl phosphates were prepared by a “one-pot” methodology
through the reaction of sodium phenoxides with phosphorus
oxychloride. This system can be described as a semi-batch
reaction, where the phenoxides were synthesized inside the
reactor and a solution of phosphorus oxychloride in toluene
was added continuously through a pump. These highly exo-
thermic reactions were performed in a Mettler RC-1 reaction
calorimeter. The aim of this work was to evaluate the reaction
rate and the reaction rate constant through the study of the
rate of heat release. Although the phenoxides react almost
immediately with phosphorus oxychloride, it was possible to
notice the slight differences among the sodium phenoxides
studied. The phenoxide bearing an electron-donating group
(methoxy) was the most reactive, and the one bearing an
electron-withdrawing group (nitro) was the least reactive one.
The reactions could be considered to be feed-controlled. It was
demonstrated that the reaction temperature does not affect the
reaction rate and reaction rate constant in the same way that
the feed rate of the phosphorus oxychloride does.
Experimental Section
Toluene (0.8 L) was introduced manually in the RC-1
reactor vessel at room temperature (27 °C). The reaction
medium was stirred at 150 rpm during the experiment.
Phenol (0.25 mol) was added, and the reaction temperature
was raised to 30 °C. A solution of 5.75 g (0.25 mol) of
sodium dissolved in 100 mL of methanol was added. The
difference between the jacket and the reaction temperatures
(Tj - Tr) was set to 20 °C to remove all the methanol-
toluene azeotrope (64 °C) by distillation. The distillation
continued until the temperature reached toluene’s boiling
point (110 °C). A volume of toluene equal to the distilled
volume of azeotrope (250 mL, in average) was added to the
reactor after the distillation was finished. This procedure was
necessary to ensure that the reaction mass could be consid-
ered as a constant throughout all the experiments to compare
different values of reaction enthalpies. To determine the total
heat-transfer coefficient U and the heat capacity of the
reaction medium Cp, a set of temperature ramps and
calibrations was performed.
Introduction
The triaryl phosphates are thermically stable compounds
and can be used in different industrial applications suchas
plastifiers, lubricants, hydraulic fluids, and flame retardants.1
They can be obtained by a “one-pot” synthesis through
the reaction of phenoxides with phosphorus oxychloride2 as
shown in Scheme 1.
The main purpose of this work was to apply a mathemati-
cal model to obtain an estimation of the kinetic constants
and reaction rates through the interpretation of calorimetric
data from the triaryl phosphate synthesis.
During a period of 5 min, 170 mL of a 0.5 M solution of
phosphorus oxychloride in toluene was added to the reactor
through a pump. In each experiment, 0.083 mol of phos-
phorus oxychloride was added (144 g). A final set of U and
Cp determinations was carried out.
Discussion
The classic methods for the evaluation of kinetic constants
are based mainly on following the concentration profiles
through the reaction by chromatographic techniques.3 The
implementation of these techniques would be very difficult
in this case, since the reaction of phenoxides and phosphorus
oxychloride is extremely fast, taking place almost im-
mediately when the reagents are mixed.
A mass balance for a semi-batch reactor was used to
obtain an expression for the reaction rate constant (k). The
synthesis reactions were carried out in a Mettler RC-1
reaction calorimeter. A complete description of this reactor
can be found in the literature.4
The obtained data from reaction calorimetry are based
on the heat flow, which is calculated from the overall heat-
transfer coefficient, the wetted area and the temperature
difference between the reactor wall and the fluid circulating
through the vessel jacket.5
Fax: 55 21 25900990.
(1) Quin, L. D. A Guide to Organophosphorus Chemistry; John Wiley & Sons
Inc.: New York, 2000.
(2) Da Silva, J. F. C.; Nakayama, H. T.; Neto, C. C. Phosphorus Sulfur 1997,
131, 71-82.
(3) Levenspiel, O. Chemical Reaction Engineering; Wiley: New York, 1972.
(4) Crevati, A.; Mascarello, F.; Lenthe, B.; Minder, B.; Kikic, I. Ind. Eng.
Chem. Res. 1999, 38, 4629-4633.
(5) Leggett, D. J. Thermochim. Acta 2001, 367/368, 351-365.
10.1021/op025554w CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/16/2002
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