4088 Batiha et al.
Asian J. Chem.
TABLE-1
BOILING TEMPERATURE OF TERTIARY AMINES
such a structure increases sharply due to the neighborhood
with ammonium nitrogen atom, which is apparently the main
cause of acceleration of the acylation reaction in the presence
of tertiary amines. Thus, amines play the role of intermediate
carriers of acyl groups.
Based on preliminary kinetic studies, benzoic acid and
tertiary amine hydrochloride (NR·HCl) released during the
hydrolysis of benzoyl chloride did not influence the rate of
the studied reaction. Hence, stage (III) practically does not
occur.Accordingly, the hydrolysis reaction of benzoyl chloride
in the presence of tertiary amines can be presented by the
following scheme:
Tertiary amine
Pyridine
2-methyl pyridine
2,6-Dimethyl pyridine
Quinoline
b.p. (ºC)
114.5
127.0
143.0
124.1
Pressure, mm Hg
760
745
760
18
For the treatment of acidic compounds, a solvent of
dioxane (pure grade) shaken with 50 % aqueous NaOH was
used. After separation from alkali, dioxane was boiled for 6 h
with sodium metal and then distilled on a column at atmos-
pheric pressure (Tb = 100.5 ºC at P = 757 mm Hg). The water
content, which was determined by gas-liquid chromatography,
was 0.107 %. In all experiments, only freshly prepared dioxane
and water were used.
The study of hydrolysis kinetics reaction of benzoyl
chloride was carried out in an oven at a temperature of 298.15
0.01 ºC. Kinetic experiment began with the preparation of
working solutions of reagents in dioxane. Working solution
of benzoyl chloride was prepared in one pycnometer and water
with catalyst was in another.
C6H5COCl + NR3 + H2O → C6H5COOH + R3N·HCl(IV)
As follows from the Scheme (IV), hydrogen chloride
released during the process binds the tertiary amine. In this
regard, the concentration of tertiary amine in the reaction
mixture will be changed over time.
Kuritsin10 studied the kinetics of the hydrolysis reaction
of benzoyl chloride in dioxane containing 1 to 3 mol/L of
water. He found that the reaction obeys the laws of first-order
reaction. The kinetic equation for the reaction (IV) is:
d(c0,bc − x)
After the preparation of working solutions, 5 mL of
benzoyl chloride was poured into reaction flasks. Then, water
was added to flasks and the solution was stirred. The moment
of water addition was considered to be the beginning of the
reaction. In the all experiments, the initial concentration of
benzoyl chloride and water in dioxane were 0.005 and 1 mol/L,
respectively, while the concentration of catalyst was in the
range of 0.005-0.02 mol/L.
−
= kob (c0,bc − x)·(c0,ta − x)
(1)
dτ
where, c0,bc and c0,ta are the initial concentrations of benzoyl
chloride and tertiary amine, respectively; x is the change in
concentration of benzoyl chloride to time τ; kob is the observed
rate constant, which can be calculated as follows:
kob = k0c0,H O
(2)
2
Since in all the kinetic experiments the initial concentration
The reaction propagation was observed by monitoring the
change of unreacted benzoylchloride in the reaction sample.
The reaction was determined using diethylamine toluene
solution. The reaction was stopped using diethylamine toluene
solution. Since diethylamine is a strong base and many times
more reactive than water, it almost instantly connects unreacted
benzochloride. Excess diethylamine was titrated with a solution
of hydrogen chloride in isopropyl alcohol. As an indicator,
bromophenol blue dissolved in isopropyl alcohol was used.
of water c0,H O >> c0,ta and c0,bc [eqn. (2)], the rate constant (k)
of reaction (IV) is referred to a single concentration of water.
Therefore, from eqn. (1), it follows that:
2
c0,bc (c0,ta − x)
c0,ta (c0,bc − x)
1
kob
=
ln
(3)
τ(c0,ta − c0,bc
)
or
x
kob
=
(4)
τ·c0,bc (c0,bc − x)
if the kinetic experiment c0,bc = c0,ta.
RESULTS AND DISCUSSION
As an example, the rate constants, which were calculated
by using eqn. (3) in one of the kinetic experiments are listed
in Table-2. From the data listed in Table-2, the rate constants
are approximately constant in the range of degrees of conversion
of 11 to 55 %.
Once again, the constancy of kobs values with time
confirms that the benzoic acid and tertiary amine hydrochloride
formed during the hydrolysis do not influence the rate of the
studied reaction.
EXPERIMENTAL
Purifications of benzoyl chloride, tertiary amines and
dioxane were carried out by the method described byVorobuv
et al.11. Kinetic experiment and analysis of mixture reaction
was adopted from Shebanova and Ivanova12.
Benzoyl chloride (chemically pure grade) was distilled
under vacuum [boiling temperature (Tb) of 65 ºC at pressure
(P) of 6 mm Hg]. Water was twice distilled at atmospheric
pressure. The first distillation was carried out by adding
KMnO4 (Tb = 99.8 ºC at P = 756 mm Hg). Tertiary amines:
pyridine (pure grade), 2-methyl pyridine (pure grade), 2,6-
dimetilpiridin (pure grade), quinoline (pure grade) were dried
by solid potassium hydroxide and then distilled. Pyridine was
distilled at atmospheric pressure, while 2-methyl pyridine, 2,6-
dimethyl pyridine were distilled under reflux at atmospheric
pressure. Quinoline was distilled under a vacuum. Boiling
temperature of tertiary amines are listed in Table-1.
The arithmetic means of the reaction (I) rate constants at
various concentrations of benzoyl chloride and tertiary amine
in the reaction mixture are listed in Table-3.
As in Shebanova and Kulibaba13, we have carried out many
kinetic experiments in which tribenzylamine was injected as
an acceptor of hydrogen chloride. In this case, the catalyst
concentration remained constant in the reaction mixture. In
the presence of tribenzylamine, the kinetic rate equation takes
the form: