To convert m-ethylaniline to m-ethylfluorobenzene, it should be treated with nitrous acid followed by .

Explanation:

In this reaction, we must exchange the amino group () for a fluorine atom (). Also, the first step in this reaction is the addition of nitrous acid.

We must remember that the amino group in the presence of nitrous acid produces a diazonium salt. The group is a very good leaving group and many benzene derivatives can be produced from this intermediate (see figure 1).

If what we want is to bond a fluorine atom we must use to be able to produce m-ethylfluorobenzene (see figure 2).

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