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Vadodara, India

Pulla S.,University of Arkansas at Little Rock | Ramidi P.,University of Arkansas at Little Rock | Jarvis B.L.,University of Arkansas at Little Rock | Munshi P.,Rubamin Laboratories Ltd | And 5 more authors.
Greenhouse Gases: Science and Technology | Year: 2012

We report a study on the effect of substituents on the activity of chlorostannoxane catalysts in coupling epoxides and carbon dioxide for cyclic carbonate synthesis. All butyl-substituted (1a) chlorostannoxane was found to yield cyclic carbonates in high turnover number (TON 2340) at 300 psi CO 2, 130 °C in 2 h. All the reactions were performed under solvent-free conditions in the presence of a Lewis base which acts as a co-catalyst. The activity was found to change with change in the substituents on the catalysts. The effect of change in substituents was studied with respect to variation in essential parameters, such as time, temperature, pressure, and difference in catalyst to co-catalyst ratio. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd. Source


Ramidi P.,University of Arkansas at Little Rock | Sullivan S.Z.,University of Arkansas at Little Rock | Gartia Y.,University of Arkansas at Little Rock | Munshi P.,Rubamin Laboratories Ltd | And 5 more authors.
Industrial and Engineering Chemistry Research | Year: 2011

We have studied an ionic Cr V(O) complex of a cyclic amido ligand (1) for cyclic carbonate synthesis using epoxide and carbon dioxide (CO 2) as starting materials. Lithium salt of 1 (Li1) showed a high turnover number (TON) of 2950 at 180 °C and 450 psig CO 2 pressure. Reactions were run under solvent-free conditions and in the presence of a Lewis base, which acts as a cocatalyst. Important reaction parameters such as pressure, temperature, and variation of cocatalyst to catalyst ratio were studied in order to obtain optimum reaction conditions. Besides the obvious effect of the anionic Cr V on the catalytic activity, the cation of the complex has a profound effect on the overall catalytic activity of the complex. The effect is most significant when the cation is Li +. In order to probe the effect of cation and particularly of Li + on the catalytic activity, several Cr V(O) complexes were synthesized with various cations. Both inorganic (Na +, K +) and organic cations ((Ph) 4P +, (Bu) 4N +) were used to synthesize the complexes and eventually to understand the effect of the cations. The activity dropped to almost half (TON 1500) for the complexes with cations of Na + (Na1), K + (K1), (Ph) 4P + (PPh 41), and (Bu) 4N + (Bu 4N1), indicating the significant role of Li + on the overall catalytic activity of Li1. Addition of a calculated amount of Li salt to the complexes with larger cations restores the catalytic activity to the same level as that of Li1, thus reinforcing the role of Li +. We have attempted to correlate the high activity of Li + compared to larger cations based on its relatively higher Lewis acidity. Charge densities (Z eff/volume) of all inorganic cations indicate that Li + has the highest charge density and thus the highest Lewis acidity, which in turn helps in producing the high catalytic activity of the complex. A probable mechanism signifying the role of Li + and ably supported by ab initio theoretical calculations is presented. © 2011 American Chemical Society. Source


Beckman E.J.,University of Pittsburgh | Munshi P.,University of Pittsburgh | Munshi P.,Rubamin Laboratories Ltd | Munshi P.,Reliance Industries Ltd.
Green Chemistry | Year: 2011

A reversible CO 2 carrier (RCC) has been developed to perform carboxylation of ketone to β-ketoester under ambient CO 2 pressure and temperature. RCC has been synthesized by immobilizing 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) on methylhydrosiloxane support and reacting with CO 2 with 100% degree of functionalisation. RCC is found to be recyclable and shows retention of activity in 5 recycles. CO 2 absorption under ambient temperature and desorption at 120°C renders the material suitable for carrying out carboxylation reactions at 25°C with excellent yields. The yield of the reaction can reach up to 100% with TON 200 in 4 h. The extent of the reaction primarily depends upon enol content of the substrate. β-Ketoacid produced during the reaction can be isolated and converted to its corresponding methyl ester derivative by reacting with methyl iodide. © 2011 The Royal Society of Chemistry. Source


Munshi P.,University of Pittsburgh | Munshi P.,Rubamin Laboratories Ltd | Beckman E.J.,University of Pittsburgh | Padmanabhan S.,Reliance Industries Ltd.
Industrial and Engineering Chemistry Research | Year: 2010

As disclosed in preceding studies [Munshi and Beckman Ind. Eng. Chem. Res. 2009, 48, 1059-1062 and Beckman and Munshi US Patent 7,271,286, 2007], aluminum chloride is superior among Lewis acids in making p-toluic acid from toluene and 6.9 MPa CO 2 offering 80% stoichiometric yield, with respect to Al 2Cl 6, and 98% selectivity at 80 ° 18 h. Attempts to improve the efficiency resulted in the finding that H+ exchange between HCl and T0l-COOAl2Cl5 is the key step in making the reaction catalytic. Introduction of a base complemented by a fluorinated solvent can only bring Al 2Cl 6into catalytic cycle, provided pKa[TolCOOH] > pKa[BH+] > PKa[HCl]. Efficiency of the reaction depends upon the nature of the fluorinated solvents and reaction parameters employed. Turnover number of 7.87 for p-toluic acid in 6 h is obtained employing 2.68 mmol quinoxaline, 15 mL 1,3,5-tris(trifluoromethyl)benzene, and 2.68 mmol of Al 2Cl 6 nd CO 2 at a pressure of 6.9 MPa CO 2 and 100 ° C.The base and fluorinated solvent could be recyclable and reused. © 2010 American Chemical Society. Source


Ramidi P.,University of Arkansas at Little Rock | Munshi P.,Rubamin Laboratories Ltd | Gartia Y.,University of Arkansas at Little Rock | Pulla S.,University of Arkansas at Little Rock | And 3 more authors.
Chemical Physics Letters | Year: 2011

The synthesis of cyclic carbonates from CO2 and epoxides catalyzed by alkali metal halides (MX) in combination with a Lewis base (LB) is reported here. The unique synergistic effect between MX and LB has been observed at an optimum mole ratio of 1:1. High turnover frequency (TOF, h-1) indicates that an increase in the reaction efficiency of up to 40 times is obtained by comparison with the reaction carried out using only MX. The activity of MX primarily falls in the order of alkali metal ion's Lewis acidity. The optimum conditions for this solventless reaction were 130 °C and 2 MPa of CO2 pressure. © 2011 Elsevier B.V. All rights reserved. Source

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