Oxidation of alkylarenes to the corresponding acids using aqueous potassium permanganate by hydrodynamic cavitation

Oxidation of toluene using aqueous potassium permanganate was studied under heterogeneous condition in the presence of hydrodynamic cavitation and compared with the results of the reaction under acoustic cavitation. Various parameters, such as quantity of potassium permanganate, toluene to aqueous phase ratio, reaction time and cavitation parameters such as orifice plate, and pump discharge pressure were optimized. The reaction was found to be considerably accelerated at ambient temperature in the presence of cavitation. On comparison, it was found that when 1 kJ of energy was passed to the reaction mixture in the case of acoustic cavitation, the product obtained was 4.63 x 10(-6) mol, whereas when 1 kJ of energy was passed to the reaction mixture in the case of hydrodynamic cavitation the product obtained was 2.70 x 10(-5) mol. Hence, about six times more product would be obtained in the case of hydrodynamic cavitation than in the case of acoustic cavitation at same energy dissipation. It has been observed that further optimization is possible.     

Static foam destruction: role of ultrasound

High intensity ultrasonic vibrations were used for destabilizing the static foam structure. Ultrasonic horn as a source of ultrasonic vibration was used for the destruction of the foam. The effect of the ratio of the horn to the column diameter on the drainage and collapse rate of foam has been analyzed. Further, an empirical correlation for the initial foam collapse rate in the presence of ultrasonic horn has been developed in terms of the initial liquid hold-up, surface tension of the surfactant solution and the ratio of horn diameter to the column diameter. Efficiency of the ultrasonic horn is related to the position of the tip of the horn. Periodic supply of ultrasonic vibrations was found to be a more viable option than the continuous supply in terms of saving in energy and operating cost for defoaming using ultrasound.     

Low temperature recyclable catalyst for Heck reactions using ultrasound

The Heck reaction of iodobenzene with methyl acrylate in NMP as a solvent has been studied using Pd/C as a catalyst in the presence of ultrasound at room temperature. The ultrasound increased the rate of the reaction. The effect of base, solvent and recyclability of catalyst were studied in the presence of ultrasound and without ultrasound. The reaction only takes place in the presence of ultrasound. The catalyst could be recycled using HCOONa-ultrasound.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.     

Oxidation of alkylarenes using aqueous potassium permanganate under cavitation: comparison of acoustic and hydrodynamic techniques

Various alkylarenes were oxidized to the corresponding aryl carboxylic acids using aqueous potassium permanganate under heterogeneous condition in the presence of hydrodynamic cavitation and the results of the reaction have been compared with the acoustic cavitation in terms of their energy efficiency. The rate of reaction was determined for each reaction. In the oxidation of p-xylene, seven times more product could be obtained in the case of hydrodynamic cavitation than in the case of acoustic cavitation. The reaction was found to be considerably accelerated at ambient temperature.