Alcohol from halogenoalkanes

An important method for preparing alkenes involves the elimination (an El or E2 mechanism) of HX from halogenoalkanes, RX (Section 5.3.2). Alcohols (ROH) can also be converted into alkenes by activating the OH group (e.g. by protonation or conversion into a tosylate) to make this into a better leaving group (Section 5.2.2). 

In case of the direct reaction of the natural oil or lower alkyl ester of natural fatty acid and the amine the reaction method for producing the amide derivatives is as follows That is, about 1 mol of the said oils and 1 to 100 equivalent mols of the said amines are mixed in the absence or presence of solvents such alcohols as methanol, ethanol or the like, such aromatic hydrocarbons as benzene, toluene, xylene or the like, such halogenoalkanes as methylene chloride, chloroform, carbon tetrachloride or the like, and such alkenes or alkanes as petroleum ether, benzene, gasoline, ligroin or cyclohexane, such ethers as tetrahyrofuran, dioxane and the like, or a mixture thereof, and the mixture is subjected to the reaction in the absence or presence of catalyst amount or equimolar amount to the amine of an auxiliary agent of condensation, such as alkoholate of alkali metal, i.e. lithium, methylate, lithium ethylate, sodium methylate, sodium ethylate, potassium-t-butylate and the like, or acidic auxiliary agents, i.e. p-toluenesulfonic acid and the like, thereby to yield the amide derivatives. In this reaction, a formal alcohol may be removed from the reaction system. 

The planar nature of the intermediate means that when the carbocation from an optically active halogenoalkane is attacked by a nucleophile from either side (with equal probability), a mixture of the two enantiomers of the alcohol is obtained (Figure 20.78). This gives a 50 50 racemic mixture of the two optical isomers. The planar shape of carbocations has been confirmed experimentally by X-ray diffraction (Chapter 4). 

Y. Kubota, M. Kodaka, T. Tomohiro, H. Okuno, Formation of cyclic urethanes from amino alcohols and carbon dioxide using phosphorus(III) reagents and halogenoalkanes, J. Chem. Soc. Perkin Trans. I (1993) 5-6. 

The alcohol is heated under reflux (see apparatus on page 219) with the reactants to make the halogenoalkane. The halogenoalkane made can then be distilled off from the reaction mixture and collected as oily droplets under water (Figure 17.4). 

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