How do I convert benzoic acid to meta-fluorobenzoic acid in not more than 3 steps? I did it but the process was a little too long.
Here is my attempt
Two steps should be enough ;-)
Your product is an electron-deficient arene and $\ce{-NO2}$ is a decent nucleofuge. Try to replace it by fluorine in a nucleophilic aromatic substitution!
Your approach might be "three steps" according to some people. The last two reactions in your synthesis, converting the amine to the diazo salt followed by fluoridation, are usually done in the same reaction vessel with the diazo salt never isolated.
Your three steps would be:
$$\begin{aligned} 1.\ &\ce{->[\ce{HNO3}][\ce{H2SO4}]}\\ \\ 2.\ &\ce{->[\ce{Sn}][\ce{HCl}]}\\ \\ 3.\ &\ce{->[1)\ \ce{NaNO2,\ HCl}][2)\ \ce{HBF4}]} \end{aligned}$$