The synthesis of aryl iodides via arylthallium intermediates is highly prized in advanced regioselective organic synthesis. What intrinsic physical/thermodynamic property of the initial thallation ste

Question

The synthesis of aryl iodides via arylthallium intermediates is highly prized in advanced regioselective organic synthesis. What intrinsic physical/thermodynamic property of the initial thallation step ($Ar-H + Tl(OCOCF_3)_3$) provides its massive synthetic advantage over direct electrophilic halogenation?

Prashant Kotian · Accepted Answer

Correct answer: B. Thallation of arenes using thallium(III) trifluoroacetate is a highly reversible electrophilic aromatic substitution. Because the electrophile is exceptionally massive and bulky, ortho substitution suffers from severe steric hindrance. The reversibility of the reaction allows the system to equilibrate towards the most thermodynamically stable isomer, which is overwhelmingly the para-substituted arylthallium compound. Subsequent treatment with aqueous instantly replaces the thallium group with iodine, yielding pure para-iodo arenes with exquisite regiocontrol.

💡 Solution & Explanation

Practice 22,000+ questions like this