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Chapter 23: Problem 590

Suggest a mechanism for the steps in the synthesis of phenolphthalein.

Short Answer

Expert verified
The synthesis of phenolphthalein involves a series of reactions, beginning with the formation of phenoxide ion by reacting phenol with a strong base (NaOH or KOH). The phenoxide ion, as a strong nucleophile, attacks the electrophilic carbon atom of one carbonyl group in the phthalic anhydride molecule to form an ester linkage and generate an intermediate molecule. A second alkoxide ion is formed by introducing another molecule of phenol and reacting it with a strong base. This second alkoxide ion then attacks the remaining carbonyl group in the intermediate molecule, forming another ester linkage and producing the phenolphthalein molecule.

Step by step solution

01

Starting materials

Phenolphthalein can be synthesized from the reaction of phenol and phthalic anhydride in the presence of a strong base (usually sodium hydroxide or potassium hydroxide). Step 2: Formation of alkoxide ion
02

Formation of alkoxide ion

The phenol reacts with the strong base (NaOH or KOH) to form a phenoxide ion. The base abstracts the acidic hydrogen from phenol, resulting in the phenoxide ion and a water molecule. Phenol acts as an acid and the strong base as the base. The reaction is as follows: \[ Phenol + NaOH \rightarrow Phenoxide\, ion + H_2O \] Step 3: Nucleophilic attack
03

Nucleophilic attack

The phenoxide ion, being a strong nucleophile, attacks the electrophilic carbon atom of one carbonyl group in the phthalic anhydride molecule. This step forms the ester linkage between the phenol and phthalic anhydride and generates an intermediate molecule. \[ Phthalic\, anhydride + Phenoxide\, ion \rightarrow Intermediate \] Step 4: Formation of second alkoxide ion
04

Formation of second alkoxide ion

We need to introduce another molecule of phenol and convert it into a phenoxide ion in a similar manner as in Step 2. This is done by reacting phenol with another equivalent of strong base (NaOH or KOH). Step 5: Nucleophilic attack by the second alkoxide ion
05

Nucleophilic attack by the second alkoxide ion

The second phenoxide ion (generated in step 4) reacts with the intermediate molecule from step 3 and attacks the remaining carbonyl group. This step forms another ester linkage, similar to the one formed in step 3, and produces the phenolphthalein molecule. \[ Intermediate + Phenoxide\, ion \rightarrow Phenolphthalein \] In conclusion, phenolphthalein is synthesized through a series of reactions including the formation of phenoxide ions and nucleophilic attacks on the phthalic anhydride molecule by these ions.

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Most popular questions from this chapter

How much difference in physical properties would you expect for o-and \(p\) -cyanophenol isomers? Explain.

Write structures for each of the following names: (a) m-cresol (b) 3 -hydroxybenzenesulfonamide (c) 3 -chloro-1, 2 -benzoquinone (d) o-methoxyphenol (e) \(\mathrm{p}(\mathrm{t}-\) tolyl \()\) azophenol (f) benzyl pheny 1 ether (g) \(3-\) (o-hydroxy phenyl pentanoic acid) (h) 2 -methoxy-1, 4 -naphthoquinone

(a) Why is phenol \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\) a stronger acid than an alcohol? (b) Would para-acetylphenol be a stronger or weaker acid than phenol? (c) Would 2, 4 -dinitrophenol be a stronger or weaker acid than \(p\) -nitrophenol? Draw contributing structures to support the answers.

Outline all steps in the synthesis from toluene of: (a) p-cresol via diazotizatiori; (b) p-cresol via thallation; (c) m-cresol via diazotizatiori; (d) m-cresol via thallation.

Outline a synthesis of cumene from cheap, readily available hydrocarbons. Then synthesize phenol from cumene.
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