Bromination of ethane

Example 12.1. Calculate the enthalpy for each step in the bromination of ethane b>... 

Why would the bromination of ethane to ethyl bromide be a more efficient synthesis than the bromination of hexane to 1-bromohexane ... 

A comparison of chlorination and bromination reveals that bromination is generally a much slower process than chlorination. To understand why, we must take a closer look at the individual propagation steps. We will compare AH of each propagation step for the chlorination and bromination of ethane ... 

Energy diagrams for the two propagation steps of radical chlorination and radical bromination of ethane. 

The relative rates of reaction of ethane toluene and ethylbenzene with bromine atoms have been measured The most reactive hydrocarbon undergoes hydrogen atom abstraction a million times faster than does the least reactive one Arrange these hydrocarbons in order of decreasing reactivity... 

In the presence of catalysts, trichloroethylene is readily chlorinated to pentachloro- and hexachloroethane. Bromination yields l,2-dibromo-l,l,2-trichloroethane [13749-38-7]. The analogous iodine derivative has not been reported. Fluorination with hydrogen fluoride in the presence of antimony trifluoride produces 2-chloro-l,l,l-trifluoroethane [75-88-7] (8). Elemental fluorine gives a mixture of chlorofluoro derivatives of ethane, ethylene, and butane. 

In this structure, five halogen atoms— three fluorines, one chlorine, and one bromine atom— replace five of the six hydrogen atoms of ethane. 

The substantial difference in the heats of reaction of ethane, ethene, and ethyne with bromine is reflected in a very important practical consideration in handling ethyne (acetylene), namely its thermodynamic stability relative to solid carbon and hydrogen gas. Unlike ethane, both ethene and ethyne can be shown from bond energies to be unstable with respect to formation of solid carbon and gaseous hydrogen ... 

A new recyclable ditribromide reagent, 1,2-dipyridiniumtribromide-ethane, has been synthesized and used for the bromination of several aromatic compounds.130... 

When a 0.20 mol mixture of ethane, ethylene and acetylene is passed through ammoniacal CU2CI2 solution, 7.6 grams of precipitate is formed. The remaining mixture is passed through bromine solution and 8 grams of bromine is used up. How many moles of ethane were there in the original mixture ... 

An alirraative course for the reaction of bromine with ethane couM result in tbe formation of bromomethane. ... 

The literature references to this work are a little complicated, and are as follows preliminary note giving brief description of complete research, reference 8 study of the reaction CH3 + HBr -> CH4 + Br, reference 7 study of the bromination of methane, reference 266, and of ethane, reference 6. 

These reactions involve lithiation of l,3-dithiole-2-thione 103 with lithium diisopropylamide (LDA) followed by reactions of the resulting carbanions with various electrophiles. Thus, the direct lithiation and subsequent bromina-tion of l,3-dithiole-2-thione 103 allowed a selective preparation of mono- and dibrominated derivatives in 80% yields. For instance, the reaction of 103 with LDA (lequiv), followed by treatment with 1,2-dibromotetrachloro-ethane, produced monobrominated derivative 104, whereas the reaction of 103 with excess of LDA (3 equiv) led to the isolation of dibrominated derivative 105 (Scheme 5) <2006T8152>. Earlier attempts at bromination of 103 using, for example,/i-toluenesulfonyl bromide <2001JMC2181> or 1,2-dibromotetrachlorethane <2001JMC1570> yielded mixtures of mono- and dibrominated derivatives in low yields (25-30%). 

Use the data in Table 5.3 to calculate AH for the reaction of ethane vi itb chlorine, bromine, and iodine ... 

Khazaei, A., Vaghei, R. G., Karkhanei, E. Bromination of organic allylic compounds by using N,N -dibromo-N,N -1,2-ethane diyi bis(2,5-dimethyl benzene sulfonyl)amine. Synth. Common. 2002, 32, 2107-2113. 

There are instances in which the mode of fission and therefore reaction mechanism changes with the environment or experimental conditions. This can be illustrated with the dissociation of hexaphenyl-ethane, the bromination of bromobenzene, and the reactions of diazonium ions ... 

The simplest method for the synthesis of m-brominated phenolics is the bromination of o- and p-substituted phenolics. As shown in the following equations, mesitol was brominated to give 3-5 dibromomesitol (8). The o-substituted tetramethyl bisphenol gave tri- and tetra-brominated compounds (9). Similar substitution occurs with the o-substituted tetramethyl bisphenol ethane (10). 

To obtain predominantly bromoethane, use a large excess of ethane relative to the bromine. Statistically, the bromine is more likely to encounter an ethane molecule than a bromoethane. 

Bromination of alkanes follows the same mechanism as chlorination, mechanism for the monobromination of ethane... 

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