The flavor of beer can be tainted by a trace contaminant, called ortho-bromophenol. To reduce the incidents of contamination, beer manufacturers have used certified beer flavor standards to train professional beer tasters to recognize the flavor of ortho-bromophenol. Preparing these certified standards requires pure samples of ortho-bromophenol. Propose a synthesis of ortho-bromophenol starting from phenol. (Org. Synth. 1934, 14, 14.)

Choose from the reagents below.

A. dilute NaOH

B. conc. fuming, 1 mol H2SO4

C. HBr

D. Br2, FeBr3

E. Zn

F. Dilute H2SO4

G. HNO3

H. Hcl

I. Br2

conc. fuming, 1 mol H2SO4

Dilute NaOH

Br2

Dilute H2SO4

Explanation:

The  synthesis of ortho-bromophenol follows the reaction sequence shown in the image attached.

First of all, the phenol is sulphonated using concentrated sulphuric acid at 100°C.  Carrying out the reaction at 100°C ensures that the para-isomer predominates. Lower temperatures favour the formation of the ortho isomer. Dilute sodium hydroxide is added before the addition of bromine.

Bromine molecule is then added. The incoming electrophile now attaches to the ortho position. Dilute acid is  added at 100°C to remove the -SO3H thereby obtaining the Ortho-bromophenol

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