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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,Lee, Hai-Whang Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.3
The nucleophilic substitution reactions of (2R,4R,5S)-(+)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $5.0^{\circ}C$. The anilinolysis rate of 3 involving a cyclic five-membered ring is considerably fast because of small negative value of the entropy of activation (${\Delta}S^\neq=-2cal\;mol^{-1}\;K^{-1}$) over considerably unfavorable enthalpy of activation (${\Delta}H^\neq=18.0\;kcal\;mol^{-1}$). Great enthalpy and small negative entropy of activation are ascribed to sterically congested transition state (TS) and bulk solvent structure breaking in the TS. A concerted $S_N2$ mechanism with a backside nucleophilic attack is proposed on the basis of the secondary inverse deuterium kinetic isotope effects, $k_H/k_D$ < 1.
Kinetics and Mechanism of the Anilinolysis of 1,2-Phenylene Phosphorochloridate in Acetonitrile
Barai, Hasi Rani,Lee, Hai-Whang Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.9
The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $-15.0^{\circ}C$. The studied substrate of 1,2-phenylene phosphorochloridate is cyclic five-membered ring of phosphorus ester, and the anilinolysis rate of 1 is much faster than its acyclic analogue (4: ethyl phenyl chlorophosphate) because of extremely small magnitude of the entropy of activation of 1 compared to 4. The Hammett and Bronsted plots exhibit biphasic concave upwards for substituent X variations in the nucleophiles with a break point at X = 3-Me. The values of deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) change from secondary inverse ($k_H/k_D$ < 1) with the strongly basic anilines to primary normal ($k_H/k_D$ > 1) with the weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the transition state (TS) variation from a predominant backside attack to a predominant frontside attack, in which the reaction mechanism is a concerted $S_N2$ pathway. The primary normal DKIEs are substantiated by a hydrogen bonded, four-center-type TS.
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>
Barai, Hasi Rani,Lee, Hai Whang Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.11
The kinetic studies on the reactions of ethyl methyl (2) and ethyl propyl (4) chlorothiophosphates with X-pyridines have been carried out in acetonitrile at $35.0^{\circ}C$. The free energy correlations with X show biphasic concave upwards with a break point at X = H (2) and 3-Ph (4), respectively. A stepwise mechanism with a rate-limiting leaving group expulsion from the intermediate is proposed based on the magnitudes of selectivity parameters for both substrates. The considerably large values of ${\beta}_X$ = 1.50(2) and 1.44(4) with strongly basic pyridines and relatively small values of ${\beta}_X$ = 0.43(2) and 0.36(4) with weakly basic pyridines are interpreted as a change of the attacking direction of the X-pyridines from a frontside to a backside attack toward the chloride leaving group.
Barai, Hasi Rani,Lee, Hai-Whang Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.7
Kinetic studies for the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-pyridines have been carried out in dimethyl sulfoxide at 85.0 $^{\circ}C$. The Hammett and Br$\"{o}$nsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H, while those for substituent Z variations in the leaving groups are linear. The negative sign of the cross-interaction constant (${\rho}_{XZ}$) implies that the reaction proceeds through a concerted mechanism for both the strongly and weakly basic pyridines. The magnitude of ${\rho}_{XZ}$ (= -0.35) for the strongly basic pyridines is greater than that (${\rho}_{XZ}$ = -0.15) for the weakly basic pyridines, indicating a change of the nucleophilic attacking direction from frontside for the strongly basic pyridines to backside for the weakly basic pyridines. The early transition state is proposed on the basis of the absence of positive deviations from both the Hammett and Br$\"{o}$nsted plots for the strong ${\pi}$-acceptor, X = 4-Ac, and small values of ${\rho}_{XZ}$ and ${\beta}_X$.
Barai, Hasi Rani,Lee, Hai-Whang Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.3
The nucleophilic substitution reactions of (2R,4R,5S)-(+)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide with X-pyridines are investigated kinetically in acetonitrile at $5.0^{\circ}C$. The free energy relationships for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ac. Unusual positive $\rho_X$ (= +4.73) and negative ${\beta}_X$ (= -0.75) values are obtained with the weakly basic pyridines, and rationalized by the isokinetic relationship with isokinetic temperature at $t_{ISOKINETIC}=39.3^{\circ}C$. 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 on the basis of greater magnitudes of selectivity parameters ($\rho_X$ = -6.15 and ${\beta}_X$ = 1.11) with the strongly basic pyridines compared to those ($\rho_X$ = 4.73 and ${\beta}_X$ = -0.75) with the weakly basic pyridines.