Show how you would convert aniline to the following compounds. (a) fluorobenzene (b) chlorobenzene

Verified step by step guidance

1. Step 1: Convert aniline to benzene diazonium chloride by treating it with NaNO2 and HCl at 0-5°C.
2. Step 2: For fluorobenzene, perform the Schiemann reaction by treating the benzene diazonium chloride with HBF4 to form benzene diazonium tetrafluoroborate, then heat to release N2 and form fluorobenzene.
3. Step 3: For chlorobenzene, perform the Sandmeyer reaction by treating the benzene diazonium chloride with CuCl to replace the diazonium group with a chlorine atom.
4. Step 4: Purify the products using standard organic purification techniques such as distillation or recrystallization.
5. Step 5: Confirm the structures of the final products using spectroscopic methods such as NMR or IR spectroscopy.

Key Concepts

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This mechanism is crucial for converting aniline to halogenated derivatives like fluorobenzene and chlorobenzene. The aromatic ring's electron density attracts electrophiles, allowing for the substitution to occur while maintaining the aromaticity of the compound.

Reactivity of Aniline

Aniline, an aromatic amine, is more reactive than benzene due to the electron-donating effect of the amino group (-NH2). This increased reactivity facilitates the electrophilic substitution reactions, making it easier to introduce halogens onto the aromatic ring. Understanding how the amino group influences the reactivity and orientation of substitution is essential for predicting the products formed during the conversion.

Halogenation Reagents

The conversion of aniline to fluorobenzene and chlorobenzene requires specific halogenation reagents. For chlorination, reagents like chlorine gas (Cl2) in the presence of a catalyst (e.g., FeCl3) are commonly used. For fluorination, more reactive reagents such as fluorine gas (F2) or electrophilic fluorinating agents are necessary due to the high reactivity of fluorine. Knowing the appropriate reagents and conditions is vital for successful halogenation.