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Elimination Reactions

Elimination Reactions. When a bromoalkane is warmed with dilute aqueous alkali it undergoes a substitution reaction to produce the corresponding alcohol.

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Elimination Reactions

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  1. Elimination Reactions • When a bromoalkane is warmed with dilute aqueous alkali it undergoes a substitution reaction to produce the corresponding alcohol. • If however it is added to a hot,concentrated solution of an alkali in ethanol it undergoes an elimination reaction to form an alkene as shown in Figure 1038.

  2. Elimination Reactions • In the case of the elimination reaction, the hydroxide ion reacts with the ethanol to produce the ethoxideion as follows: • Ethoxideion is a stronger base and weakernucleophile than the hydroxide ion and so favours the elimination reaction, as does the higher temperature and concentration. • The ethoxide ion acts as a base and removes the hydrogen ion from the carbon next to the halogen as shown in Figure 1039.

  3. Elimination Reactions • The overall reaction is therefore the elimination of hydrogen bromide from the bromoalkane. • Note that if the halogen is in the middle, rather than at the end of the hydrocarbon chain then the elimination can occur in more than one direction, hence a mixture of products may result. • Hence, as shown in Figure 1040 below, two different alkenes are produced when 2-bromobutane is heated with alcoholic solution of potassium hydroxide:

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