A Comparison between Kinetic Parameters from the Synthesis of Tris(p-nitrophenyl)phosphite and Tris(p-nitrophenyl)phosphate Using Reaction Calorimetry

Article abstract of DOI:10.1021/op034100b

Tris(p-nitrophenyl)phosphite was prepared by a modification of a "one-pot" methodology developed for the preparation of triaryl phosphates. This exothermic reaction was performed in a Mettler RC-1 calorimeter. The principal aim of this work was to compare the reactivity of phosphorus trichloride and phosphorus oxychloride in their reactions with sodium p-nitrophenoxide. The reaction rate and the reaction rate constant for the synthesis of tris(p-nitrophenyl)phosphite were evaluated and compared to the obtained values for the tris(p-nitrophenyl)-phosphate synthesis. Phosphorus trichloride was found to react faster than phosphorus oxychloride, but the reaction with the phosphorus oxychloride proved to be more exothermic.

Full text of DOI:10.1021/op034100b

Organic Process Research & Development 2003, 7, 954−956
A Comparison between Kinetic Parameters from the Synthesis of
Tris(p-nitrophenyl)phosphite and Tris(p-nitrophenyl)phosphate Using Reaction
Calorimetry
Rafael C. Seiceira, Carlos F. P. Machado e Silva, Luciana R. M. Esteva˜o, 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
Abstract:
and -20.29 kJ, respectively. The percentages of the total
heat released from these reactions, expressed as heat conver-
sion, are shown in Figure 1.
Tris(p-nitrophenyl)phosphite was prepared by a modification
of a “one-pot” methodology developed for the preparation of
triaryl phosphates. This exothermic reaction was performed in
a Mettler RC-1 calorimeter. The principal aim of this work
was to compare the reactivity of phosphorus trichloride and
phosphorus oxychloride in their reactions with sodium p-
nitrophenoxide. The reaction rate and the reaction rate constant
for the synthesis of tris(p-nitrophenyl)phosphite were evaluated
and compared to the obtained values for the tris(p-nitrophenyl)-
phosphate synthesis. Phosphorus trichloride was found to react
faster than phosphorus oxychloride, but the reaction with the
phosphorus oxychloride proved to be more exothermic.
The synthesis of tris(p-nitrophenyl)phosphate is more
exothermic than the synthesis of tris(p-nitrophenyl)phosphite,
but the heat conversion curve shows clearly that, for a
specified value of time, the percentage of the total heat
released is higher for the reaction of sodium p-nitrophenoxide
with PCl3 than for the reaction using POCl3, indicating that
the reaction synthesis of the phosphite should be faster.
To verify this observation, the reaction rate and the
reaction rate constant k for the tris(p-nitrophenyl)phosphite
synthesis was estimated using the expressions 1 and 2,
respectively.2
-RAV ) NA0 dX/dt
(1)
(2)
Introduction
dX
Vr
A modification of a “one-pot” methodology developed
for the preparation of triaryl phosphates1 was applied to the
synthesis of tris(p-nitrophenyl)phosphite through the reaction
of sodium p-nitrophenoxide with phosphorus trichloride.
The main purpose of this work was the comparison of
the reactivity of phosphorus trichloride with that of phos-
phorus oxychloride in relation to sodium p-nitrophenoxide
and to check if the mathematical model developed for the
evaluation of the kinetic parameters from the synthesis of
triaryl phosphates2 could be applied to this synthesis.
k )
dt
(1 - X)[FB0t - NA0X/3]
The terms dX/dt, (1 - X), and NA0X/3, from eq 2, were
calculated from the points in the conversion curves. All the
data were obtained in intervals of 4 s, so that the term dX/dt
was calculated by dX/dt ) (Xi+1 - Xi)/4. These results are
summarized in Table 1.
The total heat transfer coefficients were nearly the same
for both reactions. The intervals presented in Table 1
correspond to the values measured before and after the
additions of PCl3 and POCl3. The rate of dissipative flow
was greater than the rate of heat production. The graphs
showing these observations are shown as Supporting Infor-
mation.
The reaction rate constant for the phosphite synthesis
(kphosphite) was 4 times greater than the reaction rate constant
for the phosphate synthesis (kphosphate). If these values
correspond to the real behavior of the studied reactions, the
addition of a solution containing the same molar proportion
of PCl3 and POCl3 over a suspension of sodium p-nitro-
phenoxide would furnish the phosphite and phosphate in
yields of 80% and 20%, respectively. This experiment was
performed, and the crude product, a mixture of tris(p-
nitrophenyl)phosphite and tris(p-nitrophenyl)phosphate, was
analyzed by 31P NMR; the percentage area of tris(p-
nitrophenyl)phosphite and tris(p-nitrophenyl)phosphate sig-
nals in the 31P NMR were 77.6 and 22.4%, respectively.
These results are in very good agreement with the predicted
values of kphosphite and kphosphate given by the mathematical
Discussion
The synthesis reactions were carried out in a Mettler RC1
reaction calorimeter where kinetic evaluations based in the
heat flow can be estimated in a noninvasive in-situ way.3
The irreversible second-order reactions applied to the
synthesis of tris(p-nitrophenyl)phosphite and tris(p-nitro-
phenyl)phosphate are outlined in Scheme 1.
Following the methodology showed in Scheme 1, tris(p-
nitrophenyl)phosphite and tris(p-nitrophenyl)phosphate were
obtained in 87% and 95% yields, respectively. The enthalpy
for the reactions of sodium p-nitrophenoxide with 175 mL
of 0.5 molar solutions of PCl3 and POCl3 were -14.59 kJ
* Corresponding author. Fax: 55 21 25900990. E-mail: cajaiba@iq.ufrj.br.
(1) Cajaiba da Silva, J. F.; Nakayama, H. T.; Neto, C. C. One-pot synthesis of
a triaryl phosphates: a reaction calorimetry approach. Phosphorus, Sulfur
Silicon Relat. Elem. 1997, 131, 71-82.
(2) Machado e Silva, C. F.; Cajaiba da Silva, J. F. Org. Process Res. DeV.
2002, 6, 829-832.
(3) Crevati, A.; Mascarello, F.; Lenthe, B.; Minder, B.; Kikic, I. Ind. Eng.
Chem. Res. 1999, 38, 4629-4633.
954
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10.1021/op034100b CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/09/2003

Figure 1. Heat conversion for the reactions of sodium p-nitrophenoxide with PCl3 (phosphite) and POCl3 (phosphate).
Scheme 1
Table 1. Calculated parameters for systems studied at
45 °C
Experimental Section
General. Infrared spectra were recorded on a Nicolet 740
FTIR spectrophotometer. H NMR and 31P NMR spectra
1
total heat transfer reaction rate
heat of
constant, k reaction rate reaction
(L/mol s) (kJ/kg)
dX/dt (s-1
coefficient, U
were recorded on a Brucker HC200 at 200 and 81 MHz,
respectively. CDCl3 was used as solvent, and chemical shits
were expressed in δ (ppm) units using TMS as internal
reference for 1H spectra and H3PO4 (85%) as external
reference for 31P.
product
(W/m2 K)
)
I
II
143.4-137.5
127.3-133.8
81.97 ( 10 0.281 ( 0.004 -14.10
20.81 ( 10 0.200 ( 0.004 -19.55
Tris(p-nitrophenyl)phosphite. Toluene (0.8 L) was
manually introduced into the RC-1 reactor vessel at 25 °C.
The reaction mixture was stirred during the experiment at
150 rpm using an anchor agitator. p-Nitrophenol (34.7 g)
was added, and the reaction temperature was raised to 30
°C. A solution of 5.75 g (0,25 mol) of sodium in 100 mL of
methanol was added. The excess methanol was removed as
a toluene-methanol azeotrope (64 °C) by distillation until
the temperature reached toluene’s boiling point (110 °C).
The reaction volume was completed to 0.8 L by the addition
of 0.2 L of toluene. 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 per-
formed. The reaction temperature was kept at 45 °C, and
then, 170 mL of a 0.5 M solution of phosphorus trichloride
in toluene was added to the reactor through a pump, during
model as expressed in eq 2. This result validates the
mathematical model used to evaluate the kinetics of the
studied reactions.
Conclusions
(1) Tris(p-nitrophenyl)phosphite was successfully pre-
pared using the one-pot methodology developed for the
synthesis of triaryl phosphates.
(2) Phosphorus trichloride was found to react approxi-
mately 4 times faster with sodium p-nitrophenoxide than with
phosphorus oxychloride, as expressed by the 31P NMR
results. These experimental values were in total agreement
with the predicted values indicated by the reaction rate
constants kphosphite and kphosphate furnished by the mathematical
model used.
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NA0 ) the initial number of mols of A in the reactor
NA0 ) number of mols of A that react until time t
NAOX ) number of mols of B that react until time t
a period of 5 min. A final set of U and Cp determinations
was carried out. Toluene was removed by distillation. The
resulting mixture of solids (sodium chloride and tris(p-
nitrophenyl)phosphite) was washed with water to remove the
sodium chloride. After drying, the product was obtained in
87% yield, mp 171-172 °C (lit.4 170-171 °C).
Tris(p-nitrophenyl)phosphate. The unique modification
in the previous procedure was the addition of a phosphorus
oxychloride solution instead of the phosphorus trichloride
solution. The product was obtained in 95% yield, mp 153-
156 °C (lit.5 153-155 °C).
X
R
T
) gas constant
) temperature (°C)
Tr
t
) reaction temperature (°C)
) time (seconds)
U
Vr
X
Xi
) global heat-transfer parameter (W m-2 K-1
)
) reaction volume (L)
) molar conversion of compound A
) fraction of heat release at time i
NOMENCLATURE
C
) concentration (mol L-1
) heat capacity of reacting mixture at constant pressure (J kg-1
K-1
) density (kg/dm3)
)
Acknowledgment
Cp
We thank Capes for the financial support.
)
d
Supporting Information Available
dX/dt ) rate of heat release (s-1
)
31P NMR of tris(p-nitrophenyl)phosphite, tris(p-nitro-
phenyl)phosphate, and their mixture. Graphs showing that
the heat dissipative flow is greater than the rate of production
of heat for the synthesis of tris(p-nitrophenyl)phosphite and
tris(p-nitrophenyl)phosphate. This material is available free
of charge via the Internet at http://pubs.acs.org.
FB0t ) number of mols of B added until time t
RA
k
) reaction rate
) reaction rate constant for a second-order reaction (L‚mol-1
s-1
)
Ni
) number of mols of i in the reactor at any given moment t
(4) Moffatt, J. I. G.; Khorana, H. G. J. Am. Chem. Soc. 1957, 79, 3741-3746.
(5) Kosolapoff, G. M.; MAIER, L. Organic Phosphorus Compounds; J.
Wiley: New York, 1972; Chapter 13, p 163.
Received for review July 21, 2003.
OP034100B
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