Oxidation of Cyclohexanol and Cyclohexanone by Monochromate Ions in Organic Solvents and on Solvent Free Microwave Irradiation under Phase Transfer Catalysis - A Comparative Study

Oxidation of cyclohexanol and cyclohexanone were carried out by acidified monochromate ions in ethyl acetate and toluene under phase transfer catalysis and also in solvent free condition under microwave irradiation. The extraction of monochromate ions from aqueous medium to organic phase was carried by employing various phase transfer catalysts in the presence of mineral acids. The effect of [catalyst] and [mineral acid] on extraction of monochromate from aqueous phase to organic phase was also studied. The product obtained, namely adipic acid obtained with both reactants was characterized by its melting point and infrared spectral technique. The reaction was over within 15 min with more than 85% yield at a temperature of 323 K under microwave irradiation where as it gave around 70% yield at 353 K within 150 min under phase transfer catalysis condition. The enhanced reaction rate and high yield of product substantiate the application of phase transfer catalytic technique under microwave irradiation for organic synthesis. A suitable mechanism for the oxidation of substrates by monochromate under phase transfer catalysis is also suggested.

Study of Buchwald-Hartwig reaction with catalysts based on monovalent copper

Many natural substances and drugs includes N-aryl-substituted heterocycles. These substances can be synthesized in various conditions, one of which is the amination of Buchwald-Hartwig. In this reaction formation of N-substituted anilines was observed as the resalt of the interaction between aryl halides and tin amides in palladium catalysis condition. It was discovered by Buchwald and Hartwig in 1994. In 1996, toxic amides of tin and P(o-Tol)3 were replaced by amines and chelating diphosphines. Due to high yields and good reproducibility, Buchwald-Hartwig amination is the attractive method for producing aromatic amines. Currently, this amination is carried out with triphenylphosphine palladium complexes. The main drawback of these catalysts is the high cost and toxicity. In this regard, work is underway to replace these catalysts on copper containing. Currently using complexes of monovalent copper with the following chelating agents: diamines, amino acids, 1,10-phenanthroline, diols. In this work, we studied the reaction of C-N cross-combination using a catalytic system based on a complex of monovalent copper and 1-ethylbenzimidazole. The efficiency of this catalytic system is compared with the copper – L proline system described in the literature. It is shown that the use of copper – 1-ethyl-benzimidazole system can reduce the synthesis time from forty hours to twelve. It is established that the presence of the acceptor substituent in the substrate increase the yield of the product in the Buchwald-Hartwig reaction. Indole was used as a substrate. Arylation was carried out by iodobenzene, o-iodotoluene and p-iodnitrobenzen.

Ultrasonically Promoted Synthesis of Ethyl 2-(naphthalen-2-yloxy)acetate in Solid-Liquid Heterogeneous Phase Transfer Catalysis Condition

<p>In this paper, the synthesis of ethyl 2-(naphthalen-2-yloxy)acetate from β-naphthol and ethyl 2-bromoacetate under ultrasound and catalyzed by quaternary ammonium salt in solid-liquid heterogeneous condition was described. Trace amount of water play a major role in this solid-liquid reaction. The reaction follows pseudo first order rate law. The apparent rate constant of the organic phase reaction was obtained form the experimental data. The combination of small amount of tetrabutylammonium bromide (TBAB) and ultrasound (k_app = 25.22×10^-3min^-1) shows several fold enhanced rate of the reaction than the conventional operation (k_app = 6.42×10^-3min^-1for TBAB only). The rate constant increases (0.05 to 0.3 g) with increase in the concentration of catalyst (from k_app = 10.12×10^-3min^-1to k_app = 34.46×10^-3min^-1). The other kinetic effects such as, effect of agitation speed, kind of frequency of ultrasound, kind of various quantity of K₂CO₃, quantity of water, temperature, different quaternary ammonium salts, solvents and volume of organic solvents on the conversion of ethyl 2-bromoacetate and apparent rate constant were investigated in detail and rational explanations are provided. Copyright © 2016 BCREC GROUP. All rights reserved</p><p><em>Received: 4^th November 2015; Revised: 13^rd January 2016; Accepted: 16^th January 2016</em></p><p><strong>How to Cite:</strong> Abimannan, P., Rajendran, V. (2016). Ultrasonically Promoted Synthesis of Ethyl 2-(naphthalen-2-yloxy)acetate in Solid-Liquid Heterogeneous Phase Transfer Catalysis Condition. <em>Bulletin of Chemical Reaction Engineering &amp; Catalysis</em>, 11 (3): 273-283 (doi:10.9767/bcrec.11.3.567.273-283)</p><p><strong>Permalink/DOI:</strong><a href="http://doi.org/10.9767/bcrec.11.3.567.273-283"> http://doi.org/10.9767/bcrec.11.3.567.273-283</a></p>

Thermal Debromination of Waste Printed Circuit Boards by Iron-Based Catalyst

Pyrolysis appears to be a promising route allowing all-components recovery of the high value of potentially accessible products from waste printed circuit boards (WPCBs). However, bromine-containing pyrolysis oil must be dehalogenation, otherwise it will be a strong impact on thermal treatment. In the present study, an effective and environmental-friendly process using tri-iron tetroxide sorbent (Fe-O) to simultaneously degrade brominated epoxy resin from WPCBs was developed in pyrolysis process. The results show that brominated epoxy resins can be quickly decomposed under catalysis condition. Bromide concentration in pyrolysis oil decreases with the increase of the content of Fe-O. It can transfer the bromine from the gas phase and liquid phase to solid phase. When adding proportion to 1:1, bromine concentration of pyrolysis oil decreased by up to 98.2%. Fe-O can promote the decomposition of complex structure of benzene compounds to substance with simple structure. This study produces halogen free liquid products to recycle.

Microwave-Assisted Improved Regioselective Synthesis of 12H-Benzopyrano[3,2-c][1]benzopyran-5-ones by Radical Cyclisation

Two new effective methodologies have been adopted for the preparation of 4-(2′-bromobenzyloxy)benzopyran-7-ones 3(a–h). In the first methodology, 4-hydroxy[1]benzopyran-2-ones 1(a–d) was alkylated with 2-bromobenzyl bromide 2a or 2-bromo-5-methoxy benzyl bromide 2b under phase transfer catalysis condition using lithium hydroxide/tetrabutyl ammonium bromide in N,N-dimethylformamide at 40–50°C and in the second method the microwave irradiation protocol has been exploited by simply mixing of 4-hydroxy[1]benzopyran-2-ones 1(a–d) with 25% excess of 2-bromobenzyl bromide 2a or 2-bromo-5-methoxy benzyl bromide 2b. A catalytic amount of TBAB and potassium carbonate were added and irradiated in an open Erlenmeyer flask in a microwave oven for 4–10 min. The tributyltin-hydride-mediated radical cyclisation of 3(a–h) was carried out under microwave irradiation to generate 12H-benzopyrano[3,2-c][1]benzopyran-5-ones 4(a–h) in 78–88% yield and in this technique yields were significantly improved and reaction time was shortened compared to the previously reported conventional radical cyclisation method.