Video Transcript
Fill in the blank. Phenol reacts with concentrated
nitric acid in the presence of concentrated sulfuric acid, forming blank acid. (A) Phthalic, (B) salicylic, (C)
citric, (D) picric, (E) benzoic.
In this question, our starting
molecule is phenol. Phenol is an aromatic molecule that
contains a benzene ring. When we draw the structure of
phenol, we do not normally include the hydrogen atoms that are bonded to the carbon
atoms in the benzene ring. Phenol tends to undergo
substitution reactions with other reagents, where these hydrogen atoms are
substituted for some other group.
If the reagent concerned is
concentrated nitric acid, we get substitutions of the hydrogen atoms in positions
two, four, and six on the benzene ring. We also see that concentrated
sulfuric acid is included here. This is present as a catalyst. So for this particular reaction,
nitro groups are substituted for hydrogen atoms at positions two, four, and six. The product is therefore named
2,4,6-trinitrophenol. The common name for this molecule
is picric acid. Historically, it was used as a high
explosive. Although picric acid does not
contain an easily identifiable acidic group, we find that the hydroxy group in this
molecule can release a proton. This does not happen to any great
extent, so picric acid is a weakly acidic molecule.
Phthalic acid, salicylic acid,
citric acid, and benzoic acid all contain carboxylic acid functional groups, which
picric acid does not. So picric is the correct
answer.
