Indian Journal of Chemistry

Sect. A: Inorganic, Bio-inorganic, Physical, Theoretical & Analytical

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VOLUME 49A

NUMBER 9

September 2010

CONTENTS

Papers

 

1167

 

Theoretical studies on decomposition kinetics of CF3CF2O radical

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hari Ji Singh* & Bhupesh Kumar Mishra

 

 

 

Unimolecular decomposition reactions of CF3CF2O radical formed from CF3CHF2 have been investigated by ab initio quantum mechanical methods. Two most important channels of decomposition occurring via C-C bond scission and F-elimination have been considered. Calculations at G2(MP2) and G2M(CC,MP2) level of theories reveal that C-C bond scission
is the dominant pathway during the decomposition of
CF3CF2O radical.

 

 

 

1174

 

Catalytic combustion of diesel soot particles on potassium and sodium titanates

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

K Joseph Antony Raj & B Viswanathan*

 

 

 

Potassium and sodium titanates have been synthesized and their activity for oxidation of diesel soot particles evaluated by
TG-DTG. Soot oxidation carried out over K and Na titanates shows complete combustion of diesel soot at 415 ーC.

 

 

1182

 

Transesterification of propylene carbonate with methanol using Mg-Al-CO3 hydrotalcite as solid base catalyst

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C Murugan & H C Bajaj*

 

 

 

The catalytic activity of hydrotalcite samples with varying Mg/Al molar ratio is studied for transesterification of propylene carbonate with methanol. The catalyst exhibits very high TON (~280 mmol DMC/gcat) under optimized conditions. A plausible reaction mechanism is proposed.

 

 


 

1189

 

Synthesis, characterization and photocatalytic activity of alkaline earth metal doped titania

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Balaram Kiran Avasarala, Siva Rao Tirukkovalluri* & Sreedhar Bojja

 

 

 

Beryllium doped titania (Be2+傍iO2) with different percentages of Be2+ (0.25, 0.5, 0.75 and 1.0 wt %) have been synthesized and characterized. Anatase crystalline phase is observed both in synthesized TiO2 as well as in Be2+傍iO2. Degradation rate of monocrotophos by Be2+傍iO2 is found to be higher than by unsubstituted TiO2.

 

 

 

 

 

1197

 

Molecular and supramolecular structures of diethyltellurium diiodide and diethyltellurium bis(carboxylates)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Prakash C Srivastava*, Vikas Singh,
Shrinkhala Dwivedi & Ray J Butcher

 

 

 

The modification of supramolecular assembly present in (C2H5)2TeI2 by replacing iodines with carboxylate groups is demonstrated. The cooperative participation of intermolecular C(sp3)-H---O and C(sp2)-H---O hydrogen bonds in strengthening the supramolecular assemblies is discussed.

 

 

 

 

 

Notes

 

1206

 

Assessment of π-nucleophilicity of silyl enolates using philicity index

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sanjib Deuri & Prodeep Phukan*

 

 

 

Nucleophilic reactivities of silyl enol ethers and ketene silyl acetals have been studied using conceptual density functional theory based reactivity descriptors. While intramolecular reactivity towards elctrophilic attack is studied on the basis of local philicity index, the intermolecular reactivity is assessed using group philicity. Role of β-methyl substituents is found to be crucial for nucleophilic reactivity of these systems.

 

 

 

 

 

1212

 

CrOX -Y2O3 catalysts for vapor phase fluorination of dichlorodifluoromethane

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Wen-Zhi Jia, Li-Qiong Xing, Lin Qian, Xin Chen, Yue-Juan WangJi-Qing Lu, Ke-Feng Chen,
Xue-Liang Zhang & Meng-Fei Luo
*

 

 

 

A series of CrOx-Y2O3 catalysts has been tested for vapor phase fluorination of dichlorodifluoromethane for synthesis of tetrafluoromethane. Conversion of CCl2F2 to CClF3 is very fast, while that of CClF3 to CF4 is a rate-determining step.
Pre-fluorinated CrOX-Y2O3 catalyst calcined at 600 ーC (CrYF-6) is most active for the reaction, (CF4 yield 95%). Characterization results indicate that the catalytic activity depends on the coordination of active Cr species and Lewis acid sites.

 

 

 

Authors for correspondence are indicated by (*)

 

 

 

Indian Journal of Chemistry

Vol. 49A, September 2010, pp. 1167-1173

 

Theoretical studies on decomposition kinetics of CF 3 CF 2 O radical

Hari Ji Singh* & Bhupesh Kumar Mishra

Department of Chemistry, DDU Gorakhpur University , Gorakhpur 273 009, India

Email: hari_singh81@hotmail.com

Received 15 April 2010 ; revised and accepted 20 August 2010

The unimolecular decomposition reactions of CF 3 CF 2 O radical formed from hydrofluorocarbons, CF 3 CHF 2 in the atmosphere has been investigated using ab initio quantum mechanical methods. Two most important channels of decomposition occurring via C-C bond scission and F-elimination have been considered. Energetics calculations have been performed at G2(MP2) and G2M(CC,MP2) level of theories. The calculations reveal that C-C bond scission is the dominant pathway during the decomposition of CF 3 CF 2 O radical. Transition states have been searched on the potential energy surface of the decomposition reactions involved. Intrinsic reaction coordinate calculations have also been made. The analysis shows that transition states smoothly connect the reactant and products. The thermal rate constants for the decomposition reactions involved are evaluated using Canonical transition state theory utilizing the ab initio data at 298 K and 1 atm pressure.

Keywords : Theoretical chemistry, Decompositions, Hydrofluorocarbons, HFC-125, Canonical transition state theory, Intrinsic reaction coordinates

 

Indian Journal of Chemistry

Vol. 49A, September 2010, pp. 1174-1181

 

Catalytic combustion of diesel soot particles on potassium and sodium titanates

K Joseph Antony Raj & B Viswanathan*

National Centre for Catalysis Research, Indian Institute of Technology Madras , Chennai 600 036 India .

Email: bvnathan@iitm.ac.in

Received 4 May 2010 ; revised and accepted 13 August 2010

Potassium and sodium titanates have been synthesized and characterized, and, the activity for oxidation of diesel soot particles evaluated by TG-DTG. The XRD patterns, DRIFT spectra and XRF data reveal the formation of sodium and potassium titanates. The formation of K 2 Ti 2 O 5 and Na 16 Ti 10 O 28 phases are observed for K 2 O and Na 2 O loadings greater than 33 %. The BET-surface area and pore volume results show the non-porous characteristics of the materials. The soot oxidation characteristics of K and Na titanates show that the complete combustion of diesel soot can be obtained between 400 and 415 °C. Potassium and sodium titanates exhibit greater activity than the high surface area hydrated titania, showing the enhanced soot-catalyst contact characteristics of the titanates and also the ability of the catalysts to release active oxygen species. The results show that titania can be a suitable support for K and Na, particularly for the combustion of soot.

Keywords : Catalysts, Oxidations, Combustion, Diesel soot oxidation, Titania, Potassium titanate, Sodium titanate, Catalytic combustion

IPC Code: Int. Cl. 9 B01J21/00; C07B33/100

 

Indian Journal of Chemistry

Vol. 49A, September 2010, pp. 1182-1188

 

Transesterification of propylene carbonate with methanol using Mg-Al-CO 3 hydrotalcite as solid base catalyst

C Murugan & H C Bajaj*

Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute
Council of Scientific and Industrial Research (CSIR), G B Marg, Bhavnagar 364 021, Gujarat , India

Email: hcbajaj@csmcri.org

Received 18 June 2010; revised and accepted 17 August 2010

The catalytic activity of synthetic hydrotalcites of varying Mg/Al molar ratio from 2 to 5 has been investigated for the transesterification of propylene carbonate with methanol. The hydrotalcite with Mg/Al molar ratio of 5 at different calcination temperature has been characterized using FT-IR, P-XRD and surface area analyses. Under optimized conditions, the catalyst with Mg/Al molar ratio 5 shows highest propylene carbonate conversion (72 %) with 97 % dimethyl carbonate selectivity. The catalyst shows the highest TON (280 mmol DMC/g cat ) ever reported with heterogeneous catalysts. A plausible reaction mechanism has been proposed based on the results obtained.

Keywords : Catalysts, Transesterification, Hydrotalcites, Carbonates, Magnesium, Aluminum

IPC Code: Int. Cl. 9 B01J21/02; B01J21/10; B01J27/232; C01F5/00; C01F7/00; C07B41/14

 

Indian Journal of Chemistry

Vol. 49A, September 2010, pp. 1189-1196

 

Synthesis, characterization and photocatalytic activity of alkaline earth metal doped titania

Balaram Kiran Avasarala a , Siva Rao Tirukkovalluri a * & Sreedhar Bojja b

a Andhra University , Department of Inorganic and Analytical Chemistry, Visakhapatnam , India

Email: raost@yahoo.com

b Indian Institute of Chemical Technology , Inorganic and Physical Chemistry Division, Hyderabad , India

Received 17 March 2010 ; revised and accepted 26 August 2010

The synthesis of beryllium doped titania (Be 2+ 傍iO 2 ) at different percentages (0.25, 0.5, 0.75 and 1.0 wt %) by sol-gel method and its characterization by XRD, UV-visible absorption spectroscopy, XPS, SEM and FT-IR techniques are reported. Diffraction peaks of anatase crystalline phase have been observed both in synthesized TiO 2 as well as in Be 2+ 傍iO 2 . Presence of Be 2+ ions in the TiO 2 structure causes significant absorption shift towards the visible region. FT-IR and XPS data show the interstitial presence of Be 2+ ion in TiO 2 . The photocatalytic efficiency of the synthesized Be 2+ 傍iO 2 and unsubstituted TiO 2 has been evaluated by the degradation of monocrotophos pesticide under visible light irradiation, wherein the degradation rate of MCP by Be 2+ 傍iO 2 is found to be higher than by unsubstituted TiO 2 . This may be attributed to the more efficient electron-hole creation in Be 2+ 傍iO 2 in visible light, as compared to unsubstituted TiO 2 which can be excited only by UV irradiation. The effect of dopant concentration, p H, catalyst dosage and pollutant concentration have been studied for obtaining optimal degradation conditions.

Keywords: Catalysts, Photocatalysts, Titania, Beryllium

 

Indian Journal of Chemistry

Vol. 49A, September 2010, pp. 1197-1205

 

Molecular and supramolecular structures of diethyltellurium diiodide and diethyltellurium bis(carboxylates)

Prakash C. Srivastava a, *, Vikas Singh a , Shrinkhala Dwivedi a & Ray J Butcher b

a Department of Chemistry, Lucknow University , Lucknow 226 007, India

Email: pcsrivastava31@rediffmail.com

b Department of Chemistry, Howard University, Washington DC20059, USA

Received 8 January 2010 ; revised and accepted 29 July 2010

Diethyl tellurium bis(carboxylates) ( C 2 H 5 ) 2 TeR ¢ 2 (R' = C 6 H 5 OCO, 4-NO 2 C 6 H 4 OCO, 3,5-(NO 2 ) 2 C 6 H 3 OCO, C 6 H 5 CH=CHOCO, 4-OCH 3 C 6 H 4 OCO) have been synthesised from the metathetical reactions of diethyl tellurium diiodide (C 2 H 5 ) 2 TeI 2 and corresponding silver salts and characterized by IR, 1 H, 13 C and 125 Te NMR spectroscopy. The structures of (C 2 H 5 ) 2 TeI 2 , (C 2 H 5 ) 2 Te(C 6 H 5 OCO) 2 , (C 2 H 5 ) 2 Te(4-NO 2 C 6 H 4 OCO) 2 , (C 2 H 5 ) 2 Te{3,5-(NO 2 ) 2 C 6 H 3 OCO} 2 , (C 2 H 5 ) 2 Te(C 6 H 5 -CH=CHOCO) 2 and (C 2 H 5 ) 2 Te(4-OCH 3 C 6 H 4 OCO) 2 have been established by single crystal X-ray diffraction studies. The structures of these complexes (the immediate environment about tellurium is that of distorted trigonal bipyramidal geometry with a stereochemically active electron lone pair) are described in the context of their ability to generate intermolecular Te---I and Te---O secondary bonds and C( sp 2 )-H---O and C( sp 3 )-H---O hydrogen bonds leading to the formation of zig-zag ribbons, stairs, dimeric, trimeric, tetrameric and extended supramolecular assemblies. The modification of supramolecular assembly present in the precursor (C 2 H 5 ) 2 TeI 2 by replacing the iodines with carboxylate groups is demonstrated and the cooperative participation of intermolecular C( sp 2 )-H---O and C( sp 3 )-H---O hydrogen bonds in strengthening the supramolecular assemblies is discussed.

Keywords : Coordination chemistry, Tellurium, Carboxylates, C-H---O hydrogen bonds, Supramolecular associations

IPC Code: Int. Cl. 9 C07C395/00

 

Indian Journal of Chemistry

Vol. 49A, September 2010, pp. 1206-1211

 

Assessment of p-nucleophilicity of silyl enolates using philicity index

Sanjib Deuri & Prodeep Phukan*

Department of Chemistry, Gauhati University , Guwahati 781 001, Assam , India

Email: pphukan@yahoo.com

Received 2 April 2010 , revised and accepted 20 August 2010

A study on the nucleophilic reactivity of silyl enol ethers and ketene silyl acetals has been carried out using conceptual density functional theory based reactivity descriptors. Silyl enolates having substituents of both electron releasing and electron withdrawing nature at various key positions of the molecules have been considered for the study. While intramolecular reactivity towards elctrophilic attack is studied on the basis of local philicity index, the intermolecular reactivity is assessed using group philicity. Role of ゚-methyl substituents are found to be crucial for nucleophilic reactivity of these systems.

Keywords : Theoretical chemistry, Density functional calculations, Silylenolates, Nucleophilicity, Philicity index, Group philicity

 

Indian Journal of Chemistry

Vol. 49A, September 2009, pp. 1212-1216

 

CrO X -Y 2 O 3 catalysts for vapor phase fluorination of dichlorodifluoromethane

Wen-Zhi Jia a , Li-Qiong Xing a , Lin Qian a , Xin Chen a , Yue-Juan Wang a , Ji-Qing Lu a , Ke-Feng Chen b ,
Xue-Liang Zhang b & Meng-Fei Luo a, *

a Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry , Zhejiang Normal University , Jinhua 321004, China

Email: mengfeiluo@zjnu.cn

b Zhejiang Qu Hua Fluor-Chemistry Company Limited, Quzhou 324004, China

Received 3 May 2010 ; revised and accepted 20 August 2010

A series of CrO x -Y 2 O 3 catalysts has been prepared using a deposition-precipitation method and tested for vapor phase fluorination of dichlorodifluoromethane (CCl 2 F 2 ) for synthesis of tetrafluoromethane (CF 4 ). A comparative study using CCl 2 F 2 and CClF 3 as the reactants for the fluorination reaction reveals that the conversion of CCl 2 F 2 to CClF 3 is very fast, while that of CClF 3 to CF 4 is a rate-determining step. Pre-fluorinated CrO X -Y 2 O 3 catalyst calcined at 600 °C (CrYF-6) is found to be the most active for the reaction, (CF 4 yield 95%) and is stable during the testing period for the fluorination reaction. The characterization results indicate that the catalytic activity depends on the coordination of active Cr species and Lewis acid sites.

Keywords : Catalysts, Fluorination, CrO x -Y 2 O 3 catalysts, Acidity, Lewis acidity, Oxides, Chlorofluorocarbons

IPC Code: Int. Cl. 9 B01J23/26; C07B39/00