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Hasi Rani Barai,이해황 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.2
The nucleophilic substitution reactions of Y-aryl methyl (8) and Y-aryl propyl (10) chlorothiophosphates with X-pyridines are studied kinetically in acetonitrile at 35.0 ºC. The Hammett and Brönsted plots with X in the nucleophiles for both substrates exhibit biphasic concave upwards with a break region between X = 3-Me and H. The obtained values of the cross-interaction constants (ρχγ ) are negative with 8 while positive with 10 despite the same free energy correlations with X for both substrates. A stepwise mechanism with a rate-limiting bond formation is proposed with 8, whereas a stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed with 10 based on the sign of ρχγ , negative and positive with 8 and 10, respectively. A frontside nucleophilic attack is proposed with strongly basic pyridines based on the considerab- ly great magnitudes of ρχ and βχ values while a backside attack is proposed with weakly basic pyridines based on the relatively small magnitudes of ρχ and βχ for both substrates.
Hasi Rani Barai,Ehtesham Ul Hoque,이미진,이해황 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
The kinetic studies on the reactions of O-methyl (1), O-propyl (3) and O-isopropyl (4) phenyl phosphonochloridothioates with substituted anilines and deuterated anilines have been carried out in acetonitrile at 55.0 oC. A concerted SN2 mechanism is proposed for the anilinolyses of 1, 3 and 4. The anilinolysis rates of the phosphonochloridothioates are predominantly dependent upon the steric effects over the inductive effects of the two ligands. The deuterium kinetic isotope effects (DKIEs; kH/kD) are primary normal with 1 and 3, while secondary inverse with 4. Primary normal and secondary inverse DKIEs are rationalized by frontside and backside nucleophilic attack transition state, respectively. The DKIEs of the phosphonochloridothioates do not have any consistent correlations with the two ligands.
Barai, Hasi Rani,Banerjee, Arghya Narayan,Bai, Fan,Joo, Sang Woo Elsevier 2018 Journal of industrial and engineering chemistry Vol.62 No.-
<P><B>Abstract</B></P> <P>A hybrid electrochemical microelectrode is fabricated with a simple and cost-effective sono-chemical method, which consists of anodized titania nanotube arrays covered with manganese oxide nanostructures (nanorods+nanoparticles mixed morphology). The modification of the surface of the highly porous titania nanotube arrays with high-surface-area manganese oxide nanomaterials leads to considerable increment in the surface roughness of the composite electrode, which manifests high active surface sites of the electrode, and hence, leads to excellent electrochemical properties of the hybrid samples. The cyclic voltammetry and galvanostatic charge–discharge characterizations depict considerably improved electrochemical performance with high areal capacitance values. The areal capacitance of the composite electrode is obtained around 65mFcm<SUP>−1</SUP> @ 1.0mVs<SUP>−1</SUP> scan rate, which is more than 160 times higher than the control electrode (TNT, 0.4mFcm<SUP>−1</SUP> @ 1.0mVs<SUP>−1</SUP> scan rate). The composite electrode also depicts high capacity retention with only 4% decrement in the capacitance value over 2500 cycles. Also the composite electrode reveals almost 65 times increment in the power density for a mere 2 times decrement in the energy density. This high cyclic stability along with excellent energy-power performance indicates very good applicability in practical charge storage devices. The electrochemical impedance spectroscopic studies showed near-ideal capacitive performance with very low charge transfer resistance. This superior supercapacitive performance of the hybrid electrode is due to the combinatorial effect of electric double-layer capacitance of TNT and pseudocapacitance of MO as well as high active surface sites of the electrode for higher utilization of the active material. Therefore, this simple and low-cost technique to fabricate hybrid microelectrode with superior electrochemical properties can be very useful for high-performance supercapacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A hybrid electrode is fabricated by a simple cost-effective sono-chemical method. </LI> <LI> It leads to considerable increment in the surface roughness to high active sites. </LI> <LI> Its high active surface sites leads to its excellent electrochemical properties. </LI> <LI> Very high areal capacitance of TNT-MO is obtained with high rate-capability. </LI> <LI> Excellent cycling life depicts TNT-MO very promising electrode for high-rate charge/discharge operations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kinetics and Mechanism of the Anilinolysis of Aryl Ethyl Isothiocyanophosphates in Acetonitrile
Hasi Rani Barai,어디까리,이해황 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.6
The nucleophilic substitution reactions of Y-aryl ethyl isothiocyanophosphates with substituted X-anilines and deuterated X-anilines were investigated kinetically in acetonitrile at 75.0 oC. The free energy relationships with X in the nucleophiles exhibited biphasic concave downwards with a break point at X = H. A stepwise mechanism with rate-limiting bond formation for strongly basic anilines and with rate-limiting bond breaking for weakly basic anilines is proposed based on the negative and positive ρXY values, respectively. The deuterium kinetic isotope effects (DKIEs; kH/kD) changed gradually from primary normal with strongly basic anilines, via primary normal and secondary inverse with aniline, to secondary inverse with weakly basic anilines. The primary normal and secondary inverse DKIEs were rationalized by frontside attack involving hydrogen bonded, four-center-type TSf and backside attack involving in-line-type TSb, respectively.
Kinetics and Mechanism of the Pyridinolysis of Ethylene Phosphorochloridate in Acetonitrile
Barai, Hasi Rani,Lee, Hai-Whang Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.12
The nucleophilic substitution reactions of ethylene phosphorochloridate (2) with X-pyridines are investigated kinetically in acetonitrile at $-20.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. Unusual positive ${\rho}_X$ (= +2.49) and negative ${\beta}_X$ (= -0.41) values are obtained with the weakly basic pyridines, and rationalized by the isokinetic relationship with isokinetic temperature at $t_{ISOKINETIC}=6.6^{\circ}C$. The pyridinolysis rate of 2 with a cyclic five-membered ring is forty thousand times faster than its acyclic counterpart (3: diethyl chlorophosphate) because of great positive value of the entropy of activation of 2 (${\Delta}S^{\neq}$ = +49.2 eu) compared to negative value of 3 (${\Delta}S^{\neq}$ = -44.1 eu) over considerably unfavorable enthalpy of activation of 2 (${\Delta}H^{\neq}=28.4\;kcal\;mol^{-1}$) compared to 3 (${\Delta}H^{\neq}=6.3\;kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed.
Kinetics and Mechanism of the Anilinolysis of Aryl Ethyl Isothiocyanophosphates in Acetonitrile
Barai, Hasi Rani,Adhikary, Keshab Kumar,Lee, Hai Whang Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.6
The nucleophilic substitution reactions of Y-aryl ethyl isothiocyanophosphates with substituted X-anilines and deuterated X-anilines were investigated kinetically in acetonitrile at $75.0^{\circ}C$. The free energy relationships with X in the nucleophiles exhibited biphasic concave downwards with a break point at X = H. A stepwise mechanism with rate-limiting bond formation for strongly basic anilines and with rate-limiting bond breaking for weakly basic anilines is proposed based on the negative and positive ${\rho}_{XY}$ values, respectively. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) changed gradually from primary normal with strongly basic anilines, via primary normal and secondary inverse with aniline, to secondary inverse with weakly basic anilines. The primary normal and secondary inverse DKIEs were rationalized by frontside attack involving hydrogen bonded, four-center-type TSf and backside attack involving in-line-type TSb, respectively.
Barai, Hasi Rani,Hoque, Md. Ehtesham Ul,Lee, Mijin,Lee, Hai Whang Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
The kinetic studies on the reactions of O-methyl (1), O-propyl (3) and O-isopropyl (4) phenyl phosphonochloridothioates with substituted anilines and deuterated anilines have been carried out in acetonitrile at $55.0^{\circ}C$. A concerted $S_N2$ mechanism is proposed for the anilinolyses of 1, 3 and 4. The anilinolysis rates of the phosphonochloridothioates are predominantly dependent upon the steric effects over the inductive effects of the two ligands. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are primary normal with 1 and 3, while secondary inverse with 4. Primary normal and secondary inverse DKIEs are rationalized by frontside and backside nucleophilic attack transition state, respectively. The DKIEs of the phosphonochloridothioates do not have any consistent correlations with the two ligands.