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

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2 Answers 2


Two steps should be enough ;-)

  1. Nitrate benzoic acid. In J. Chem. Educ., 1967, 44, 464 (DOI), the authors added benzoic acid to fuming nitric acid at 0 °C. 3-nitrobenzoic acid is the major isomer (~ 75%). Recrystallize from ethanol.

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!

  1. In the case of 4-nitrobenzoic acid, the transformation to 4-fluorobenzoic acid has been described to work with a yield of >95% in a room temperature reaction using DMSO as a solvent and anhydrous tretrabutylammonium fluoride (TBAF) as the reagent. (DOI)
  • $\begingroup$ but here the NO2 group will be in resonance with the ring, therefore how can you you remove it so easily? $\endgroup$
    – Prakhar
    Jul 16, 2016 at 3:49

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:

$$\begin{aligned} 1.\ &\ce{->[\ce{HNO3}][\ce{H2SO4}]}\\ \\ 2.\ &\ce{->[\ce{Sn}][\ce{HCl}]}\\ \\ 3.\ &\ce{->[1)\ \ce{NaNO2,\ HCl}][2)\ \ce{HBF4}]} \end{aligned}$$


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