**Synthetic Applications of Haloalkanes:**
1. **Alcohol synthesis via SN2**: Primary haloalkanes + NaOH (aqueous) → primary alcohols with Walden inversion. Example: $CH_{3}CH_{2}Br$ + NaOH (DMSO) → $CH_{3}CH_{2}OH$.
2. **Nitrile synthesis (chain extension)**: R-X + NaCN (DMSO) → R-CN (nitrile, adds one carbon). Hydrolysis → carboxylic acid. Key for increasing chain length.
3. **Ether synthesis (Williamson synthesis)**: R-X + R'$O^{-}$$Na^{+}$ → R-O-R' + NaX. SN2 mechanism; must use 1° alkyl halide to avoid E2 from the alkoxide base.
4. **Grignard reagents from haloalkanes**: R-X + Mg (dry ether) → R-MgX. Used to form C-C bonds with aldehydes (→ 2° alcohol), ketones (→ 3° alcohol), $CO_{2}$ (→ carboxylic acid), formaldehyde (→ 1° alcohol). Chain extension reactions are fundamental in synthesis planning.
5. **Alkene synthesis via elimination**: R-X + KOH/ethanol (hot) → alkene. E2 with Saytzeff selectivity. Anti-Markovnikov addition of HBr (peroxide) to alkene, then E2, allows isomerization of halide position.
6. **Halogen exchange (interconversion of haloalkanes)**:
- Finkelstein: RCl → RI (NaI/acetone). When you need iodoalkane from chloroalkane.
- Swarts: RBr → RF (AgF). When you need fluoroalkane (cannot make by direct fluorination).
- RI is most reactive and preferred for SN2 reactions due to $I^{-}$ being the best leaving group.
**Industrial Applications:**
7. **Phenol production (Dow process)**: Chlorobenzene + NaOH (623 K, 300 atm) → phenol. Phenol is a major industrial chemical for making phenolic resins, bisphenol-A (plastics), aspirin precursors. The Dow process was the first industrial route to phenol.
8. **Refrigerants (CFCs → HFCs)**: Freon-12 ($CCl_{2}F_{2}$) was used as a refrigerant but depletes ozone. Replaced by HFCs (hydrofluorocarbons, no Cl) after Montreal Protocol 1987. C-F bonds in HFCs are stable to UV and do not release ozone-depleting Cl• radicals.
9. **Solvents**: Chlorinated solvents ($CH_{2}Cl_{2}$, $CHCl_{3}$, $CCl_{4}$) are used in industry as non-flammable, polar solvents. However, they are potential environmental contaminants and health hazards ($CCl_{4}$ is hepatotoxic; $CHCl_{3}$ → phosgene on oxidation).
10. **Pharmaceutical applications**: C-F bonds are introduced into drug molecules to improve metabolic stability (C-F bond resists oxidation by cytochrome P450 enzymes), increase lipophilicity for membrane permeation, and tune pharmacological activity. Approximately 20% of pharmaceuticals contain at least one C-F bond.$
Part of OC-04 — Haloalkanes & Haloarenes
Haloalkanes & Haloarenes: Applications in Synthesis and Industry
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