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Hydrolysis
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
As with nucleophilic substitution reactions, rates of dehydrohalogenation reactions will be dependent on the strength of the C-X bond being broken in the elimination process. Accordingly, it is expected that the ease of elimination of X will follow the series Br > Cl > F. The relative reactivities of Br and Cl toward elimination is evident from the hydrolysis product studies of l,2-dibromo-3-chloropropane (DBCP: Burlinson et al., 1982). DBCP has been used widely in this country as a soil fumigant for nematode control and has been detected in groundwaters (Mason et al., 1981) and subsoils (Nelson, et al., 1981). Hydrolysis kinetic studies demonstrated that the hydrolysis of DBCP is first order both in DBCP and hydroxide ion concentration above pH 7. Below pH 7, hydrolysis occurs via neutral hydrolysis; however, the base-catalyzed reaction will contribute to the overall rate of hydrolysis as low as pH 5. Product studies performed at pH 9 indicate that transformation of DBCP occurs initially by E2 elimination of HBr and HCl (Figure 2.4).
Chemical Destruction
Published in Domenic Grasso, Hazardous Waste Site Remediation, 2017
Dehydrohalogenation is the likely form of elimination in the dechlorination process. Dehydrohalogenation is the removal of a hydrogen from the carbon adjacent to the halide, as well as the removal of the halide to form a double bond.
Advanced Risk-Based Biodegradation Study Using Environmental Information System and the Holistic Macroengineering Approach
Published in Donald L. Wise, Debra J. Trantolo, Edward J. Cichon, Hilary I. Inyang, Ulrich Stottmeister, Remediation Engineering of Contaminated Soils, 2000
Stergios Dendrou, Basile Dendrou, Mehmet Tumay
Dehydrohalogenation is an elimination reaction in which a halogen is removed from one carbon atom, followed by the subsequent removal of a hydrogen atom from an adjacent carbon atom. In this two-step reaction, an alkene is produced. Removal of a halogen decreases the oxidation state of the compound, but the loss of a hydrogen atom increases it. This results in no external electron transfer, and there is no net change in the oxidation state of the reacting molecule. Contrary to the patterns observed for hydrolysis, the likelihood that dehydrohalogenation will occur increases with the number of halogen substituents. Specifically, monohalogenated aliphatics apparently do not undergo dehydrohalogenation, unlike CA and polychlorinated alkanes, which have been observed to undergo dehydrohalogenation under normal conditions.
Effect of substitution on dissociation kinetics of C2H5X, (X = F, Cl, Br and I): A theoretical study
Published in Molecular Physics, 2021
Nitin R. Gulvi, Priyanka Patel, Parimal J. Maliekal, Purav M. Badani
In the present section, we have executed electronic structure calculations to estimate the effect of the substitution on pyrolysis of C2H5X (X = F, Cl, Br, and I). The unimolecular decomposition of C2H5X could result in the molecular elimination reaction (dehydrohalogenation = HX) or C–X bond dissociation reaction (dehalogenation). It must be noted here that, no transition state structures could be located for C–X bond dissociation reaction. Hence, this type of reaction is termed as the loose reaction throughout the manuscript [63]. The energy required for such eliminations were estimated by the difference in total energies of products and reactants [64]. Figure 2(a) and Table S7 of supplementary information, depict the C–X bond dissociation energy of C2H5X (X = F, Cl, Br and I). From the Table S7 (of supplementary information), it is seen that the energies predicted by QCISD(T)/6-311G**//BMK/6-311G** level of theory are in close agreement with the experimental reported values, as compared to the other level of theory. Hence, the further estimations were performed using the energies that were obtained at same level of theory. The reactions involved in the dehalogenation of ethyl halide are as follows: Our calculations based on energy consideration, suggests C–F bond dissociation energy (BDE) as 100.29 kcal mol−1, while dechlorination of ethyl chloride takes place with 74.76 kcal mol−1. The energy needed to break C–Br bond is observed to be lower than C–Cl (by 10.80 kcal mol−1) and higher than C–I (by 12.07 kcal mol−1) bond. Hence, the energy required for dehalogenation of C2H5X (X = F, Cl, Br, and I), was found in the following order of C–F > C–Cl > C–Br > C–I. This trend can be attributed to the fact that the C–X bond length increases from C–F to C–I (see Figure 1).