Reagent guide
Reducing
| Reagent | Formula | What it does | Use it for | Watch out |
|---|---|---|---|---|
| Sodium Borohydride | NaBH₄ | Mild reduction of aldehydes and ketones to alcohols | Aldehyde → Primary alcohol, Ketone → Secondary alcohol | Does NOT reduce esters, amides, carboxylic acids, or C=C bonds. Works in protic solvents (MeOH, EtOH). |
| Lithium Aluminum Hydride | LiAlH₄ | Strong reduction of most carbonyl compounds | Aldehyde → Primary alcohol, Ketone → Secondary alcohol, Ester → Two alcohols, Carboxylic acid → Primary alcohol, Amide → Amine, Nitrile → Primary amine | Very reactive! Violently reacts with water. Use anhydrous ether or THF. Quench carefully with water. |
| DIBAL-H | (i-Bu)₂AlH | Partial reduction of esters to aldehydes | Ester → Aldehyde (at -78°C), Nitrile → Aldehyde (via imine) | Temperature critical! At -78°C stops at aldehyde. Warmer or excess gives alcohol. |
| H₂/Pd (Catalytic Hydrogenation) | H₂ + Pd/C | Reduction of C=C, C≡C, and some functional groups | Alkene → Alkane, Alkyne → Alkane, Nitro → Amine (ArNO₂ → ArNH₂), Benzyl groups removed (hydrogenolysis) | Syn addition. Also works with Pt or Ni catalysts. Does NOT reduce isolated C=O. |
| Lindlar Catalyst | Pd/CaCO₃/Pb | Partial reduction of alkynes to cis-alkenes | Alkyne → cis-Alkene (stops at alkene) | Poisoned catalyst - lead prevents over-reduction. Syn addition gives cis product. |
| Dissolving Metal (Na/NH₃) | Na + NH₃(l) | Reduction of alkynes to trans-alkenes | Alkyne → trans-Alkene | Birch reduction conditions. Liquid ammonia at -33°C. Radical mechanism gives trans product. |
| Clemmensen Reduction | Zn(Hg) + HCl | Complete reduction of C=O to CH₂ | Ketone/Aldehyde → Alkane | Acidic conditions. For acid-sensitive compounds, use Wolff-Kishner instead. |
| L-Selectride | Li[sec-Bu₃BH] | Stereoselective reduction of ketones | Ketone → Alcohol (stereoselective), Reduction from less hindered face | Bulky hydride source. Gives equatorial alcohol from cyclohexanones. K-Selectride is analogous. |
Built from the reagents collection. Function, uses and cautions are the source records' own text, not paraphrased.