Fluorine, Iodine, & Hydrogen Replacement

Balz-Schiemann:

$$\begin{aligned}\text{Ar-N}_2^+\text{Cl}^- + \text{HBF}_4 \longrightarrow \text{Ar-N}_2^+\text{BF}_4^- \downarrow \xrightarrow{\Delta} \text{Ar-F} + \text{BF}_3 \uparrow + \text{N}_2 \uparrow \end{aligned}$$

Iodine Introduction: 

$$\text{Ar-N}_2^+\text{Cl}^- + \text{KI} \longrightarrow \text{Ar-I} + \text{KCl} + \text{N}_2 \uparrow$$

Reductive Deamination:

$$\begin{aligned}\text{Ar-N}_2^+\text{Cl}^- + \text{H}_3\text{PO}_2 + \text{H}_2\text{O} \longrightarrow \text{Ar-H} + \text{H}_3\text{PO}_3 + \text{HCl} + \text{N}_2 \uparrow\end{aligned}$$

Notation:

• $$\text{H}_3\text{PO}_2$$ = Hypophosphorous acid (phosphinic acid); Ethanol ($$\text{CH}_3\text{CH}_2\text{OH}$$) can also serve as the reducing agent for this deamination step.