4
K. Harikumar, V. Rajendran / Ultrasonics Sonochemistry xxx (2013) xxx–xxx
isopropylbutane-1,4-diammonium dibromide by keeping other
experimental parameters are kept constant. The influence of the
amount of MPTC on the O-alkylation of 4-nitrophenol has been
studied by varying amount of MPTC from 0.2 to 1.0 g under ultra-
sound irradiation (40 kHz, 300 W). Apparent rate constants were
evaluated from the plot of ꢁln(1 ꢁ X) versus time. As shown in
Fig. 2, the rate of the reaction increased with increasing in the
amount of MPTC along with ultrasound irradiation (40 kHz,
300 W). The kapp values are linearly dependent on the amount of
multi-site phase-transfer catalyst. The increasing the kapp value is
attributed to the positive effect of ultrasound might be
enlarged [43].
[45]. The reason is that the number of reactant molecules which pos-
sess higher activation energy at a higher temperature and thus the
ultrasonic wave easily passes through the reactor [46,47]. The other
point is that the collision of the reactants at higher temperature is
also increased. Hence, the apparent rate constant is increased at
higher temperature. Arrhenius plots were made in Fig. 3 of ꢁlnkapp
against 1/T to get activation energy of 52.16 kJ molꢁ1
.
From the literature survey, the dehydrobromination of (2-
bromoethyl)benzene catalyzed by tetraoctylammonium bromide
(TOAB), an extraction mechanism was proposed [48] due to lower
Ea value (<43 kJ molꢁ1). In general, higher activation energy (more
than 43 kJ molꢁ1) suggest an interfacial mechanism [44,49]. The
activation energy for the heterogeneous ethylation of phenylacto-
nitrile was reported to be 63.64 kJ molꢁ1and for this an interfacial
mechanism was proposed [10]. Further, in the N-alkylation of pyr-
rolidine-2-one, the Ea (51.35 kJ molꢁ1) was reported by Sasson and
Bilman [50], and for this reaction they proposed an interfacial
mechanism. They concluded that the deprotonation of the sub-
strate takes place at the interphase and consequently the organic
anion is extracted and reacts in the bulk of the organic phase.
The rate-determining step in the process is the anion exchange
at the interphase. In our study, the observed Ea value is
52.36 kJ molꢁ1. Hence, we proposed an interfacial mechanism for
our present study [44,51,52].
7.3. Effect of the concentration of n-butyl bromide
To investigate the influence of n-butyl bromide (BB) on the
kinetics of synthesis of 1-butoxy-4-nitrobenzene under ultrasonic
irradiation condition (40 kHz, 300 W), the amount of BB was varied
from 0.2 to 1.0 g. In the presence and absence of ultrasound results
are shown in (Table 1). The data clearly indicates that the kapp va-
lue increases with increasing the amount of n-butyl bromide.
When the n-butyl bromide concentration increased, the probabil-
ity of finding the substrate with active-site of the catalyst and
ultrasound enhanced the rate of the reaction [43,44]. It may be
due to reduces the surface area between the aqueous and organic
phases, and hence more reactants collide to each other simulta-
neously we get higher kapp value.
7.5. Influence of amount of water
n-Butylation of 4-nitrophenol with n-butyl bromide as a limit-
ing agent under ultrasound condition (40 kHz, 300 W) was exam-
ined by varying the amount of water from 30 to 50 mL, under
standard reaction conditions. Apparent rate constants were ob-
tained from the plot of ꢁln(1 ꢁ X) against time. Generally, the vol-
ume of water directly affects both the concentration of potassium
carbonate in the aqueous phase and also generation of anions.
Therefore, the conversion (or the reaction rate) will be affected
by the volume of water. Fig. 4 shows the effect of the amount of
water on the rate of the reaction. On increasing the volume of
water, the concentration of alkali compound in aqueous solution
is decreases. This situation would dramatically reveal the hydra-
tion effect of the active catalyst [PhOꢁQ+] as the volume of water
changed from 30 to 50 mL. From the literature, the kinetic study
of the phase-transfer catalyzed etherification of 4,40-bis(chloro-
methyl)-1,10-biphenyl with phenol in an alkaline solution of potas-
sium hydroxide/organic solvent two-phase medium, similar
decrease in rate of the reaction on corresponding increase in vol-
ume of water was reported [53].
7.4. Effect of temperature
The effect of temperature on the reaction between
4-nitrophenol and n-butyl bromide was studied under otherwise
similar conditions. The temperature was varied from 30 to 80 °C.
The kinetic profile of the reaction is obtained by plotting
ꢁln(1 ꢁ X) versus time. It is obvious that the reactivity is increased
with an increase in the temperature along with ultrasonic effect
Effect of MPTC
45
40
With ultrasound
Without ultrasound
35
30
25
20
15
10
5
7.6. Effect of ultrasonic power
Ultrasonic irradiation is defines as acoustic waves with frequen-
cies in the 20–100 MHz range [24,54]. They create cavities gener-
ating locally high temperature and pressures [55–58] or strong
electric fields [56,58–60]. Ultrasound is known to accelerate
diverse types of organic reactions and it is established generous
reactions, which are otherwise slow due to poor mass transfer
are accelerated by sonication due to cavitation [57]. It has been re-
ported that a combination of PTC and ultrasound is often better
than either of the two techniques alone [58]. In such transfer of
species across the interface and ultrasound merely facilitates this
transfer, possibly by increasing the interfacial area across which
this transfer occurs.
To ascertain the influence of various ultrasonic frequencies on
the rate of n-butylation of 4-nitrophenol with same output power
of 300 W, the ultrasonic frequency was varied in the range of 28
and 40 kHz under otherwise similar conditions using MPTC as
the catalyst. Also we followed the reaction under silent condition.
0
0.2
0.4
0.6
0.8
1
1.2
MPTC (g)
Fig. 2. Effect of the amount of MPTC on the apparent rate constant: 0.5 g of
4-nitrophenol 20 g of K2CO3, 15 mL of H2O, 0.2 g of internal standard (biphenyl),
0.6 g of butyl bromide, 0.3 g of MPTC, 30 mL of chlorobenzene, 65 °C; ultrasound
conditions (40 kHz, 300 W).
Please cite this article in press as: K. Harikumar, V. Rajendran, Ultrasound assisted the preparation of 1-butoxy-4-nitrobenzene under a new multi-site
Harikumar, Kuppuswamy
