On pulse radiolysis of N2O saturated aqueous solutions of atropine, an optical absorption band (
max at 320 nm,e=2.81·103 dm3·mol–1·cm–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·108 dm3·mol–1·s–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·109 dm3·mol–1·s–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e
was found to react with atropine forming a transient band with
max at 310 nm (=3.55·103 dm3·mol–1). Its decay was also second order with a rate constant of 1.64·109 dm3·mol–1·s–1. The bimolecular rate constant for the reaction of e
with atropine as estimated from the decay of e
absorption at 720 nm is 3.9·109 dm3·mol–1·s–1. Specific one-electron oxidizing and reducing agents (such as Cl
, Tl2+, SO
and (CH3)2COH, CO
, respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e
was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·109 and 3.2·109 dm3·mol–1·s–1, respectively.
Authors:Mohan T. Hosamani, Narasimha H. Ayachit, and D. K. Deshpande
Thermodynamic parameters, like, change of activation energy for dipole orientation (ΔG*), enthalpy (ΔH*), and entropy (ΔS*) of activation in the case of binary-, ternary-, etc. mixtures of polar molecules in pure liquid phase or in dilute solution phase in a non polar solvent helps in drawing certain quantitative conclusions regarding their relaxation behavior as to whether a single component is responsible for observed microwave absorption or a cooperative phenomenon (average) by all the dipoles of the mixture contribute to it. Dielectric relaxation behavior of polar molecules in a non-polar solvent, or mixtures of these substances at different microwave frequencies and over a range of temperatures and concentrations give a method of determining these quantities. Such an experimental investigation on verity of systems is necessary to draw quantitative conclusions regarding the system of the molecules which are not studied so as to examine if the results obtained are in favor or against the general conclusions already arrived at, in other systems. With this in view, systematic dielectric measurements in a range of temperatures are carried out at a single microwave frequency on a single weight fraction in benzene of the four substituted indoles, namely, 5-Bromoindole, 5-Fluoroindole, 2,3-Dimethylindole, 2,5-Dimethylindole and on binary (1:1) mixtures of 2,5-Dimethylindole + 5-Bromoindole and 2,3-Dimethylindole + 5-Fluoroindole in benzene as solvent at different temperatures. The results are presented and discussed.
Authors:Rajesh Kumar, H. Pant, V. Sharma, Sadhana Mohan, and S. Mahajani
A radiotracer study was carried out in a trickle bed reactor (TBR) independently filled with two different types of packing
i.e., hydrophobic and hydrophilic. The study was aimed at to estimate liquid holdup and investigate the dispersion characteristics
of liquid phase with both types of packing at different operating conditions. Water and H2 gas were used as aqueous and gas phase, respectively. The liquid and gas flow rates used ranged from 0.83 × 10−7–16.67 × 10−7 m3/s and 0–3.33 × 10−4 m3 (std)/s, respectively. Residence time distribution (RTD) of liquid phase was measured using 82Br as radiotracer and about 10 MBq activity was used in each run. Mean residence time (MRT) and holdup of liquid phase were
estimated from the measured RTD data. An axial dispersion with exchange model was used to simulate the measured RTD curves
and model parameters (Peclet number and MRT) were obtained. At higher liquid flow rates, the TBR behaves as a plug flow reactor,
whereas at lower liquid flow rates, the flow was found to be highly dispersed. The results of investigation indicated that
the dispersion of liquid phase is higher in case of hydrophobic packing, whereas holdup is higher in case of hydrophilic packing.