SYNTHESIS OF ALCOHOLS FROM HALOALKANES

To avoid competition between substitution and ehmination, we can select a nucleophilic oxygen source that is not a strong base. One such source is the ethanoate ion (acetate ion). It is a weaker base than the hydroxide ion because ethanoic acid (acetic acid) is a stronger acid than water. It will displace a hahde such as bromide ion in an Sj 2 process. The resulting ester can then be cleaved by aqueous base in a process called saponification to give the desired alcohol. 

We will discuss the details of the mechanism of this second reaction, a nucleophihc acyl substitution, in Chapter 20. At present, we will only note that the nucleophilic hydroxide ion cleaves the carbonyl carbon—oxygen bond, and that a competing elimination reaction does not occur. Although the equation may look hke a typical nucleophihc substitution reaction in which hydroxide ion displaces the ethanoate ion, the reaction does not occur by way of an S 2 mechanism. The ether oxygen atom (shown in red) of the ester remains bonded to the alkyl group. In general, attack of nucleophiles on esters occurs at the carbonyl carbon atom, not at the sp -hybridized carbon atom of the alkyl group. 

Write the structures of the products of the reaction of (S)-2-bromooctane with sodium acetate followed by hydrolysis with hydroxide ion. What is the configuration of each compound  

An Sj 2 reaction gives a product with inverted configuration with respect to the reactant. The ester formed has the R configuration. The hydrolysis reaction does not occur at the chiral center, and thus the configuration of the alcohol is the same as for the ester. 

Which of the two compounds should react faster with sodium acetate in DMF, c - or tram-4-methyl-1 -chlorocyclohexane  

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