Chapter 12: Alcohol Synthesis from Carbonyl Compounds – Oxidation, Reduction, and Organometallics

Posted on Aug 30, 2024 in Chemistry

Key Terms and Concepts

Carbonyl Compounds and Derivatives

Carbonyl Group (Sec 2.9, 12.1, 16.1): A functional group consisting of a carbon atom doubly bonded to an oxygen atom, >C=O.

Aldehyde (Sec 2.9, 12.1, 16.1): A molecule containing a terminal carbonyl group, >C=O, attached to one hydrogen and one carbon atom (RCHO).

Ketone (Sec 2.9, 12.1, 16.1): A molecule containing an internal carbonyl group, >C=O, attached to two carbon atoms (RCOR).

Carboxylic Acid (Sec 2.10A, 12.1, 17.2A): A molecule containing a carboxyl group, -COOH, which consists of a carbonyl group, >C=O, attached to a hydroxyl group, -OH (RCOOH).

Carboxylic Ester (Sec 2.10B, 12.1, 17.2E): A molecule containing a carbonyl group, >C=O, attached to an alkoxy group, -OR’ (RCOOR’). Formed by the reaction of a carboxylic acid and an alcohol.

Oxidation and Reduction

Nucleophilic Addition (Sec 12.1A, 16.6, 17.4, 19.1): A reaction where a nucleophile adds to a polar multiple bond (e.g., carbonyl group). In carbonyl addition, an alkoxide intermediate forms, then reacts with an electrophile like H+.

Oxidation State (Sec 12.2A, Lab 16.1): The hypothetical charge of an atom if all bonds were 100% ionic. Also called oxidation number.

Oxidation (Sec 12.2, 12.4): Loss of electrons or increase in oxidation state. In organic chemistry, often involves increasing oxygen content or decreasing hydrogen content.

Reduction (Sec 12.2, 12.3): Gain of electrons or decrease in oxidation state. In organic chemistry, often involves increasing hydrogen content or decreasing oxygen content.

Oxidizing Agent (Sec 12.2): A substance that causes oxidation (and is itself reduced).

Reducing Agent (Sec 12.2, 12.3): A substance that causes reduction (and is itself oxidized).

Dehydrogenation:

  • Removal of a hydrogen pair (H•) or a hydride ion (H–) and a proton (H+).
  • Elimination reaction forming a double bond by removing H• from adjacent atoms.

Hydrogenation (Sec 4.16, 7.3A, 7.13 – 7.15, 12.2):

  • Addition of a hydrogen pair (H•) or a hydride ion (H–) and a proton (H+).
  • Addition of hydrogen to a double or triple bond, often using a metal catalyst.

Key Reagents and Reactions

Hydride Ion (Sec 12.1B, 12.3): A hydrogen anion (H–), a strong nucleophile and base. Sources include LiAlH4 and NaBH4.

Lithium Aluminum Hydride, LiAlH4 (Sec 12.3): A strong reducing agent. Reduces carbonyls to alcohols and other functional groups to amines. Does *not* react with C=C or C≡C bonds.

Sodium Borohydride, NaBH4 (Sec 12.3): A milder reducing agent. Reduces aldehydes and ketones to alcohols. Does *not* reduce carboxylic acids or esters, or react with C=C or C≡C bonds.

Pyridinium Chlorochromate, PCC (Sec 12.4A): Oxidizes primary alcohols to aldehydes and secondary alcohols to ketones. Does *not* react with C=C or C≡C bonds.

Collins Oxidation: Similar to PCC, using CrO3 and pyridine in dichloromethane. Oxidizes primary alcohols to aldehydes and secondary alcohols to ketones.

Jones Oxidation (Sec 12.4, Lab 25.7D, 25.11A): Uses chromic acid (H2CrO4) to oxidize primary alcohols and aldehydes to carboxylic acids, and secondary alcohols to ketones.

Organometallic Compounds

Organometallic Compound (Sec 12.5): A compound containing a carbon-metal bond.

Carbanion (Sec 3.4, 3.8, 12.1A, 12.7): A carbon anion (C–), a strong base and nucleophile. Sources include organolithium and Grignard reagents.

Organolithium Compound (Sec 12.6, 12.7): Contains a carbon-lithium bond (RLi), a source of carbanions.

Grignard Reagent (Sec 12.6-12.8): An organomagnesium halide (RMgX), a source of carbanions.

Protecting Group (Sec 11.11, 12.9, 15.14A, 16.7C): A group used to temporarily protect a sensitive functional group during a reaction.