Ultrasound assisted the preparation of 1-butoxy-4-nitrobenzene under a new multi-site phase-transfer catalyst – Kinetic study

doi:10.1016/j.ultsonch.2013.07.016

Ultrasonics Sonochemistry

Volume 21, Issue 1, January 2014, Pages 208-215

https://doi.org/10.1016/j.ultsonch.2013.07.016 Get rights and content

Highlights

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A new multi-site phase-transfer catalyst was used for the preparation of 1-butoxy-4-nitrophenol.
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Different frequency of ultrasound irradiation was tested.
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A suitable reaction mechanism was proposed for this reaction.

Abstract

In the present research work deals with the preparation of 1-butoxy-4-nitrobenzene was successfully carried out by 4-nitrophenol with n-butyl bromide using aqueous potassium carbonate and catalyzed by a new multi-site phase-transfer catalyst (MPTC) viz., N¹,N⁴-diethyl-N¹,N¹,N⁴,N⁴-tetraisopropylbutane-1,4-diammonium dibromide, under ultrasonic (40 kHz, 300 W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40 kHz, 300 W) in a batch reactor, it shows that the overall reaction greatly enhanced with ultrasound irradiation than without ultrasound. The present study provides a method to synthesize nitro aromatic ethers by ultrasound assisted liquid–liquid multi-site phase-transfer catalysis condition.

Graphical abstract

In this work, a detailed kinetic investigation of n-butylation of 4-nitrophenol with n-butyl bromide under a new multi-site phase-transfer catalyzed reaction is reported. The reaction was carried out in bi-phase medium at 65 °C under ultrasonic condition.

Introduction

As the chemical reactants reside in immiscible phases, phase-transfer catalysts have the ability to carry out the heterogeneous reactions by one of the reactants penetrating from its normal phase (generally aqueous phase) to the organic phase where the reaction take place, which gives a high conversion and selectivity for the desired product under mild reaction conditions [1]. Ever since Jarrouse [2] found that quaternary onium salts as an effective catalyst for enhancing the two-phase reaction, this methodology occupies an unique niche in organic synthesis and it is a commercially matured discipline with over 600 applications [3], [4], [5], [6], [7] covering a wide spectrum of industries such as pharmaceuticals, agrochemicals, dyes, perfumes, flavours, specialty polymers, pollution control, etc. As the application of phase-transfer catalysts (PTC) grew, much effort was placed on the development of phase-transfer catalysts with higher catalytic efficiency. To this end, researchers have developed “multi-site” phase-transfer catalysts (MPTC) for much higher activity than normal phase-transfer catalysts. Recently, the catalytic behaviour of multi-site phase-transfer catalysts have been attracted much attention, due to the fact that multiple molecules of the aqueous reactant can be carried into the organic phase once a reaction cycle, thus the catalytic efficiency is enhanced [8], [9], [10], [11], [12].

Currently, a new analytical and process experimental techniques which are environmental being techniques viz., ultrasound and microwave irradiation have become immensely popular in promoting various organic reactions [13], [14], [15], [16], [17]. Ultrasound irradiation is a transmission of a sound wave through a medium and is regarded as a form of energy enhance the rate of the reaction due to mass transfer and effective mixing [18], [19], [20].

The effect of ultrasonic energies in organic syntheses (homogeneous and heterogeneous reactions) has been boosted in recent years [21], [22], [23], [24], [25], [26], [27]. Sonication of multiphase systems accelerates the reaction by ensuring a better contact between the different phases [28], [29]. Further, ultrasound irradiation also increase the reaction rate and avoid the use of high reaction temperatures [30]. These days this environmental benign technology is combined with phase-transfer catalysts (PTC) with primary objective of optimizing reaction conditions [31], [32], [33].

Our interest was entered on first time evaluating the influence of ultrasound in association with multi-site phase-transfer catalyst (MPTC) on the synthesis of 1-butoxy-4-nitrobenzene from 4-nitrophenol with n-butyl bromide (BB) under heterogeneous condition. Since, the kinetic study of O-alkylation of 4-nitrophenol using n-butyl bromide under controlled MPTC reaction conditions will be interesting and challenging, we followed the kinetic study using a newly synthesized multi-site phase-transfer catalyst (MPTC) viz., N¹,N⁴-diethyl-N¹,N¹,N⁴,N⁴-tetraisopropylbutane-1,4-diammonium dibromide, as a catalyst under ultrasonic condition (40 kHz; 300 W). Further, to the best of our knowledge, there is no literature reports’ regarding n-butylation of 4-nitrophenol under MPTC–ultrasonic irradiation condition.

Section snippets

Chemicals

All reagents, including 4-nitrophenol, n-butyl bromide, potassium carbonate, benzene, toluene, chlorobenzene, biphenyl and other reagents are synthesis guaranteed grade (GR) chemicals and were used as received without further purification.

Instrumentation

FT-IR Spectra were recorded on a Brucker-Tensor 27 FT-IR spectrophotometer. ¹H NMR and ¹³C spectra were recorded on a Bruker 400 and 100 MHz respective using TMS as an internal standard. Gas chromatography was carried out using a GC-Varian 3700 model.

Ultrasonic process equipment

Ultrasonic energy is transmitted to the process vessel through the liquid medium, usually water in the tank. For safety purpose, the sonochemical reactor consisted of two layers stainless steel body. The sonochemical reactor configuration used in the present work is basically an ultrasonic bath. The internal dimension of the ultrasonic cleaner tank is 48 × 28 × 20 cm with liquid holding capacity of 5 L. Two types of frequencies of ultrasound were used in these experiments, which are 28 and 40 kHz with

Synthesis of a new MPTC

A mixture of 4 g of N-ethyl-N-isopropylpropan-2-amine, 3.5 mL of 1,4-dibromobutane, and 60 mL of ethanol was placed in a 250 mL three necked round-bottomed Pyrex flask. The reaction mixture was refluxed in the nitrogen atmosphere for 48 h. The solvent and excess 1,4-dibromobutane were completely removed under vacuum and onium salt, i.e. N¹,N⁴-diethyl-N¹,N¹,N⁴,N⁴-tetraisopropylbutane-1,4-diammonium dibromide (MPTC, Scheme 1) was washed with n-hexane (3 × 20 mL). The white solid MPTC (hygroscopic) was

Synthesis of 1-butoxy-4-nitrobenzene under mechanical stirring

To the mixture of K₂CO₃ (20 g, 0.1449 mol) in water (15 mL) and the newly synthesized MPTC (0.6 g, 1.2658 × 10⁻³ mol), 4-nitrophenol (0.5 g, 3.5 × 10⁻³ mol) was added under overhead stirring to generate the phenoxide anion. Then n-butyl bromide (0.5913 g, 4.3 × 10⁻³ mol) in chlorobenzene (40 mL) was added slowly. The reaction mixture was heated at 65 °C for 6 h with vigorous stirring. The crude product was isolated by simple extraction with diethyl ether (3 × 25 mL). The organic layer was collected and the solvent

Reaction mechanism and kinetic model

For synthesizing 1-butoxy-4-nitrobenzene compound, the overall reaction of 4-nitrophenol and n-butyl bromide (BB) was catalysed by the newly prepared MPTC (Q⁺Br⁻) in the aqueous alkaline (K₂CO₃) bi-phase medium and is represented in Scheme 2. The reaction is carried out under MPTC assisted ultrasonic irradiation condition. In the current investigation the kinetics was followed in the presence of an excess amount of 4-nitrophenol and by fixing n-butyl bromide as limiting agent. The main reason

Results and discussion

The reaction was conducted on a 150 mL three-necked Pyrex round-bottom flask which permits agitating the solution, inserting the water condenser to recover organic reactant and taking samples and feeding the reactants. This reaction vessel was suspended at the centre of the sonicator. A known quantity of chlorobenzene (30 mL, solvent), potassium carbonate (20 g, 0.1447 mol), 0.2 g biphenyl IS, (internal standard) were introduced into the reactor. Then, 0.5 g of 4-nitrophenol (3.6 × 10⁻³ mol) and 0.4 g of

Mechanism

Generally mechanism [41], [67], [68] for basic anion initiated PTC reactions are classified into two types viz.: (i) Starks extraction mechanism and (ii) Maksoza interfacial mechanism. In the extraction mechanism is more likely to be part of reactions when they depend agitation speed only up to certain level (300 rpm) and there after the rate will be constant factor. Also the energy of activation calculated from the Arrhenius plot will be below 45.36 kJ mol⁻¹, on the other hand, if the reaction in

Conclusion

In the present study, the rate of the reaction was controlled to study the kinetic aspects of the formation of the 1-butoxy-4-nitrobenzene from 4-nitrophenol and n-butyl bromide under ultrasonic–MPTC condition. The apparent reaction rates were observed to obey the pseudo-first order kinetics, performing the reaction in ultrasonic condition resulted in shorter reaction time, selectivity, high yield, etc. The reaction mechanism and the apparent rate constants were obtained from the experimental

Acknowledgements

The authors would like to thank the University Grants Commission, New Delhi, India for financial support for this research work. We also thank The Pachaiyappa’s Trust, Chennai, Tamil Nadu 600 030, India and Sri Chandrashekarendra Saraswathi Viswa Mahavidyalaya, Deemed University, Enathur, Kanchipuram, Tamil Nadu 631 561, India, for their grant of permission to do this research work.

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Ultrasound assisted the preparation of 1-butoxy-4-nitrobenzene under a new multi-site phase-transfer catalyst – Kinetic study

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Instrumentation

Ultrasonic process equipment

Synthesis of a new MPTC

Synthesis of 1-butoxy-4-nitrobenzene under mechanical stirring

Reaction mechanism and kinetic model

Results and discussion

Mechanism

Conclusion

Acknowledgements

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