Biasing Divergent Polycyclic Aromatic Hydrocarbon Oxidation Pathway by Solvent-Free Mechanochemistry

Area of Science:

• Organic Synthesis
• Chemical Reactivity
• Mechanochemistry

Background:

• Controlling reaction selectivity is crucial in modern organic synthesis.
• Divergent reactivity control of reagents under varying conditions is less explored than selectivity.
• Polycyclic aromatic hydrocarbons (PAHs) and periodic acid (H5IO6) are common reagents.

Purpose of the Study:

• To investigate the divergent reactivity of periodic acid with PAHs.
• To demonstrate the influence of reaction conditions (solution vs. mechanochemical) on product outcome.
• To explore the potential of mechanochemistry in controlling chemical pathways.

Main Methods:

• Solution-based reactions of PAHs with periodic acid.
• Solvent-free mechanochemical reactions using ball-milling.
• Control experiments to verify reaction pathways.
• Mechanistic studies including in situ crystalline phase analysis.

Main Results:

• Solution conditions yielded C-H iodination products.
• Solvent-free mechanochemical conditions yielded C-H oxidation quinone products.
• Products from each condition were not intermediates of the other.
• Mechanistic studies revealed a crystalline-to-crystalline phase change in periodic acid under ball-milling.

Conclusions:

• Mechanochemistry can completely switch reaction pathways.
• A polymeric hydrogen-bond network of periodic acid in the solid state influences reactivity.
• This work unmasks hidden reactivity of chemical reagents through mechanochemistry.