Hydrogen bromide reaction with propene

A process, which uses propene bromohydrin as an intermediate, has been extensively studied as a route for the conversion of propene to propylene oxide [62, 63], The electrolyte is an aqueous solution of sodium bromide saturated with propene gas. An undivided flow cell fitted with a graphite anode is used. Overall, propylene oxide and hydrogen are generated in the sequence of cell reactions given in Scheme 2.3. 

Kharasch s earliest studies in this area were carried out in collab oration with graduate student Frank R Mayo Mayo performed over 400 experi ments in which allyl bromide (3 bromo 1 propene) was treated with hydrogen bromide under a variety of conditions and determined the distribution of the normal and abnormal products formed during the reaction What two prod ucts were formed Which is the product of addition in accordance with Markovmkovs rule Which one corresponds to addition opposite to the rule ... 

Evidence in support of a carbonium ion type of mechanism for low temperature polymerization was also obtained in an investigation of the kinetics of the homogeneous liquid phase polymerization of propene in the presence of aluminum bromide and hydrogen bromide at about —78° (Fontana and Kidder, 89). The rate of reaction is approximately proportional to the concentration of the promoter, no polymerization occurring in its absence. During the main portion of the reaction, the rate is independent of the monomer concentration toward the end, it decreases, due apparently to the low-concentration of the monomer, addition of more olefin resulting in an increase in the rate. It was concluded that the reaction involves an active complex, which may be regarded as a carbonium ion coupled with an anion ... 

The structure of allyl bromide (3-bromo-l-propene) is CH2=CHCH2Br. Its reaction with hydrogen bromide in accordance with Markovnikov s rule proceeds by addition of a proton to the doubly bonded carbon that has the greater number of attached hydrogens. 

Detailed studies of systems involving aluminium-based Lewis acids and hydrogen halides are scarce. Fontana and Kidder investigated the polymerisation of propene initiated by the pair aluminium bromideTiydrt n bromide. The cocatalytic role of the latter acid was clearly proved since no polymerisation could be detected in its absence. The dependence of the rate of polymerisation upon the cocatalyst concentration and the induction periods observed make this system similar to those in which stannic chloride induces the polymerisation of olefins in the presence of variable quantities of water (see Sect. IV-C-3-b). With relatively large quantities of added hydrogen bromide, addition of this acid to the mcmomer to give fso-propyl bromide must have constituted an important side reaction. 

The main products of the reaction are hydrogen bromide, propene and benzene, with smaller amounts of 1-bromopropene and 2-bromopropane. The mechanism requires the overall activation energy to be equal to that for the first step. While these two energies are very close for allyl bromide (estimates are 45.5 and 47.5 kcal.mole for reaction 1, and 45.4 kcal.mole" for the overall activation energy ), the C-Br bond dissociation energy of 65 kcal.mole for ethyl bromide is considerably greater than the overall activation energy of 53 kcal. 

Earlier we looked at the formation of 2-bromopropane when hydrogen bromide was added to propene, and also the formation of ethanol from ethene reacting with dilute sulphuric acid. Suggest what would be the product of the reaction between propene and dilute sulphuric acid. 

BROMO-l-PROPENE (106-95-6) Forms explosive mixture with air (flash point 30°F/—1°C). Heat and light can cause decomposition with fumes of hydrogen bromide. Violent reaction with strong oxidizers, strong acids. 

The maj or product that results in a reaction involving 1-propene with hydrogen bromide, in the presence of peroxides is ... 

Free-radical Reactions.—Publications have appeared dealing with the bidirectional addition of trifluoroiodomethane and hydrogen bromide across the C=C bond in the olefin CF3 CH CHMe, peroxide-initiated addition of 1,2-dibromotetrafluoroethane to ethylene, propene, and isobutene, the addition of pentafluoroiodoethane to 3,3,4,4-tetrafluorohexa-l,5-diene (see p. 29), peroxide-initiated cyclodimerization of 3,3,4,4-tetrafluoro-4-iodobut-l-ene (see p. 29), and telomers from tribromofluoromethane or tetrabromomethane and bromotrifluoroethylene as high-density fluids for gyroscope flotation. The telomerization of chloromethanes with tetra-fluoroethylene provides a measure of the relative reactivity for both chlorine and hydrogen abstraction by the CF2 CF2 radical. The chain-transfer... 

With hydrogen bromide (HBr), allyltrimethylsilane [CH2=CHCH2Si(CH3)3] yields 2-bromo-l-(trimethylsilyl)propane (Equation 10.91) however, with hydrogen chloride (HCl), the same substrate yields chlorotrimethylsilane and propene (Equation 10.92). This has led some observers to conclude that the reaction with hydrogen bromide (HBr) is not an ionic process beginning, for example, with proton transfer from HBr to the substrate, but rather that the reaction is a radical reaction (of hydrogen and bromine atoms), which simply adds in what appears to be a Markownikoff fashion as a result of stabilization by silicon (see Russell and Nagpal, 1961). 

The possible reaction products when propene reacts with hydrogen bromide... 

Yet another possibility is illustrated by the propene (or ethylene) dimerization catalyzed by 7r-l,l,3,3-tetraphenylallylnickel bromide (26) activated with ethylaluminum dichloride the isolation of considerable amounts of 1,1,3,3-tetraphenylpropene (27) from the reaction mixture suggests that a hydrogen atom has been transferred from the substrate olefin to the sterically hindered 1,1,3,3-tetraphenylallyl system under formation of 3 [Eq. (7)] (81). The subsequent formation of the HNiY species from 3 can then take place by insertion of a second propene molecule and /3-hydrogen elimination, as discussed above. 

It is well known that HBr adds on to propene to give isopropyl bromide (2.55) in accordance with the Markovnikov s rule. The reaction proceeds via a 2°-carbocation intermediate (the secondary carbocation being more stable than the primary carbocation) (Scheme 2.43). Normally, when a molecule HX adds to a carbon-carbon double bond, the hydrogen becomes attached to the carbon with the greatest number of hydrogens, and the X group becomes attached to the carbon with the fewest hydrogens. This is known as Markovnikov s rule (see section 2.1.2) (also see the addition of HCl to propene Scheme 2.4). 

The reaction is faster with electron-rich alkenes. The rate constants for addition of bromine to a series of alkenes were found to increase in the order ethene < propene < 2-butene isobutene < 2-methyl-2-butene. In other words, each methyl group that replaces a hydrogen atom on ethene increases reactivity. The addition of bromine to substituted ethenes in methanol with added sodium bromide can be correlated to the equation... 

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