Bromination of p-bromophenol. I. Kinetics and mechanism in acetic acid medium
About: This article is published in Australian Journal of Chemistry.The article was published on 1968-01-01. It has received 6 citations till now. The article focuses on the topics: Acetic acid.
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TL;DR: The second-order and third-order rates of electrophilic bromination of various donors follow complex kinetics which include both first-and secondorder dependences on bromine, especially in the less polar solvents as discussed by the authors.
Abstract: The rates of electrophilic bromination of various donors follow complex kinetics which include both first-order and second-order dependences on bromine, especially in the less polar solvents. The second-order rate constant ks and the third-order rate constant kt are evaluated for alkene bromination in carbon tetrachloride, and they are compared to those already listed for the electrophilic brominations of substituted styrenes, arenes, and metal carbonyls in the extant literature. Despite the varying magnitudes of the second– and third-order rate constants for these diverse donors (and in different solvents), the ratio log(ks/kt) is remarkably invariant. The mechanistic implication of this unique observation is discussed in the context of charge transfer interactions which are common to the activated complexes in the electrophilic brominations of various donors.
11 citations
TL;DR: This chapter focuses on electrophilic aromatic substitution and reviews the literature published prior to 1969, and discusses the kinetic evaluation of complex formation.
Abstract: Publisher Summary This chapter focuses on electrophilic aromatic substitution and reviews the literature published prior to 1969. In general, kinetics studies fall into two classes: those aimed at determining the reaction mechanism and those that utilize the reaction to determine substituent effects in electrophilic aromatic substitution. The chapter also discusses the kinetic evaluation of complex formation. Kinetic studies are of little value to determine the extent of complex formation in the reaction path of electrophilic substitution. Unless the formation of the complex is rate-determining, the kinetic form is independent of complex formation. In addition, the influence of complex formation on reaction rates only comes from the factors that lead in the first place to complex formation. Substituent effects are inadequate for showing the extent of complex formation; however, when they indicate similar effects on substitution and complex formation, they provide evidence that the latter is a pathway of the former.
5 citations
TL;DR: In this article, a composite rate expression involving Br2 and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.
Abstract: Hydrogen bromide is known to inhibit the bromination of aromatic substrates (ArH), either by fixing up bromine as HBr3 or ArH as ArH · HBr. However, there is catalysis by HBr in the bromination of mesitylene in acetic acid. The bromination of o-xylene in acetic acid in the dark is found to be autocatalytic, and the reaction is overall third order, first order in o-xylene with the orders in Br2 and HBr depending on the concentrations. A composite rate expression involving Br2 and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.
1 citations
TL;DR: In this paper, variable orders in bromine and p-nitrophenol have been observed on varying the concentrations of reactants for the bromination of aromatic substrates.
Abstract: Bromination of aromatic substrates like p-bromophenol, anisole, etc. by molecular bromine in acetic acid follows the rate expression, Rate=k[ArH][Br2]+k′[ArH][Br2]2. For the bromination of p-nitrophenol in acetic acid, variable orders in bromine and p-nitrophenol have been observed on varying the concentrations of reactants. A rate expression of the type, Rate=k[ArH][Br2]+k′[ArH][Br2]2+k″[ArH]2[Br2] has been proposed. The observations conform to a general mechanism for bromination provided a bromine molecule, a substrate molecule or solvent molecules can be the electrophile in the rate determining step, depending upon the conditions employed for the reaction.
1 citations
01 Sep 1970
TL;DR: In this article, the kinetics of bromination of anisole and a less reactive substrate like p-nitrophenol were investigated in acetic acid medium with iodine added to accelerate the reaction.
Abstract: The kinetics of bromination of a reactive substrate like anisole and a less reactive substrate likep-nitrophenol has been investigated in acetic acid medium with iodine added to accelerate the reaction. The effective catalyst has been shown to be iodine bromide. The experimental results obtained from a study of the phenomenon of catalytic maximum in these reactions are in good agreement with the theoretical expectations.
1 citations