Propyl bromide

Does the lower energy radical intermediate lead to the lower energy product Compare energies for 1-propyl bromide and 2-propyl bromide to tell. 

Two reactants. In the preparation of n-hexane, 61 5 g. of n-propyl bromide were treated with 23 g. of sodium and 18 0 g. of n-hexane were ultimately isolated. 

It is evident from the equation that the sodium is used in excess. Actually 61 5 g. of n-propyl bromide is 0 5 gram mol this will react with 0 5 gram atom or 11-5 g. of sodium, so that 100 per cent, excess was actually employed. The theoretical yield of n-hexane will be 0-25 gram mol or 21-5 g., since 2 mols of n-propyl bromide give 1 mol of n-hexane. The actual yield was 18 g., hence the percentage yield is (18/21-5) X 100 = 84 per cent. 

Cool the mixture and decant the solution from the sodium bromide wash the salt with two 20 ml. portions of absolute alcohol and add the washings to the main solution. Distil off the alcohol, which contains the slight excess of n-propyl bromide used in the condensation, through a short fractionating column from a water bath. The residue A) of crude ethyl n-propylacetoacetate may be used directly in the preparation of methyl n-butyl ketone. If the fairly pure ester is required, distil the crude product under diminished pressure and collect the fraction boihng at 109-113727 mm. (183 g.) (R). 

The fact that n-butylbenzene can be prepared in reasonable yield by the action of sodium upon a mixture of bromohenzene and n-butyl bromide can be partly explained on the assumption that n-butyl bromide reacts with phenyl-sodium more rapidly than does bromobenzene. It is interesting to note that n-butylbenzene can be prepared either from benzylsodium and n-propyl bromide or from phenylsodium and n-butyl bromide (Section VI,29). 

The experimental details for mono-M-propylanillne are as follows. Reflux a mixture of 230 g. of aniline and 123 g. of n-propyl bromide for 8-10 hours. Allow to cool, render the mixture alkafine, and add a solution of 150 g. of zinc chloride in 150 g. of water. Cool the mixture and stir after 12 hours, filter at the pump and drain well. Extract the thick paste several times with boiling light petroleum, b.p. 60-80° (it is best to use a Soxhlet apparatus), wash the combined extracts successively with water and dilute ammonia solution, and then dry over anhydrous potassium carbonate or anhydrous magnesium sulphate. Remove the solvent on a water bath, and distil the residue from a Claisen flask with fractionating side arm (well lagged). Collect the n-propyl-aniline at 218-220° the yield is 80 g. Treat the pasty solid zincichloride with an excess of. sodium hydroxide solution and steam distil 130 g. of pure aniline are recovered. 

The formation of alkylbenzenes, largely free from unaaturated compounds, provides another interesting application of organosodium compounds. Thus pure M-butylbenzene is readily obtained in good yield from benzyl sodium and n-propyl bromide. Benzyl-sodium is conveniently prepared by first forming phenyl-sodium by reaction between sodium and chlorobenzene in a toluene medium, followed by heating the toluene suspension of the phenyl-sodium at 105° for about 35 minutes ... 

Substitution can take place by the S l or the 8 2 mechanism elimination by El or E2 How can we predict whether substitution or elimination will be the principal reac tion observed with a particular combination of reactants The two most important fac tors are the structure of the alkyl halide and the basicity of the anion It is useful to approach the question from the premise that the characteristic reaction of alkyl halides with Lewis bases is elimination and that substitution predominates only under certain special circumstances In a typical reaction a typical secondary alkyl halide such as iso propyl bromide reacts with a typical Lewis base such as sodium ethoxide mainly by elimination... 

FIGURE 8 11 When a Lewis base reacts with an alkyl halide either substitution or elimination can occur Sub stitution (Sn2) occurs when the Lewis base acts as a nu cleophile and attacks carbon to displace bromide Elimi nation (E2) occurs when the Lewis base abstracts a pro ton from the p carbon The alkyl halide shown is iso propyl bromide and elimi nation (E2) predominates over substitution with alkox ide bases... 

The rearrangement of carbonium ions that readily occurs according to the thermodynamic stabiUty of cations sometimes limits synthetic utility of aromatic alkylation. For instance, the alkylation of ben2ene with / -propyl bromide gives mostly isopropylben2ene (cumene) much less... 

The rate of acetolysis of t-butyl bromide relative to that of i-propyl bromide at 25°C is 10 - , whereas the rate of acetolysis of 2-methyl-2-adamantyl bromide relative to that of 2-adamantyl bromide is 10 ... 

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