Reactions of halogens with hydrogen halides. Studies in the Cl₂ + HBr system

Abstract

The following net processes occur in a system containing chlorine and hydrogen bromide :(1)These reactions have been followed spectrophotometrically in a gas phase stopped flow apparatus. The first two reactions are strongly surface catalyzed on untreated glass or quartz, but are much slower if the cell surface has been covered with silicone and photochlorinated. Rates in such systems are first order in each reactant, and comparable limiting rate constants have been obtained in cells with different methods of preparing the surfaces and with different surface-to-volume ratios. These experimental rate constants must be equal to or greater than those of the homogeneous bimolecular reactions. Then limiting rate constants at 35°C in liters per mole per second are kl 5 0.8, kz 2 15, and k3 5 0.04. Reactions of HI with (212, Br2, and IC1 are all much faster than reaction (2).These observations and those of other diatomic molecule reactions can be rationalized if halogen and hydrogen halide molecules react through a transition state in which the hydrogen atom is near the center of a triangle of three halogen atoms.

Kinetics of the bromine catalyzed elimination of HCl from 1,1,1‐trichloroethane

“…This would imply that if klc is lo4 to lo5 M-' s-l then k6 would be lo8' to 108.5 M-1 s-These are not unreasonable values for these rate constants [16,20,21]. However, even 30 torr of HBr, the lowest pressure of HBr added, would be at least 100 times the steady state pressure and would completely quench the autocatalysis.…”

An investigation on the reaction mechanism of the F2+Cl2→2ClF using the B3LYP method

“…Many experimental studies and quantum chemical calculations have been performed to reveal the mechanism of the reactions between halogens and halides 1–9. For example, an experimental investigation has been carried out on the reaction between Cl 2 and Br 2 and showed that the reaction happens through a bimolecular process 1, 2. The reaction F − +HCl→HF+Cl − was studied at the MP4/6‐31G* level and the rate constants at different temperatures were evaluated with the trajectory method 7.…”

Thermal rate constants, energy dependence and isotope effect for laser initiated halogen--hygrogenhalide reactions

“…A crucial piece of missing information is the shape of the potential surface for the approaching reagnets which is the determining factor 2 for the total reaction rate. 3 The purpose of this work is to provide a better understanding of the characteristic features of the entrance valley by investigating the temperature variation of the rate, the energy dependence of the reaction and the relative rates for two competing isotopically substituted reactions.…”