Chapter 9

Carboxylic Acids | Organic Chemistry 2

The carboxylic acids are studied in this chapter: the naming and properties of carboxylic acids, their synthesis, their reactivity: reduction and addition-elimination reactions, the preparation of carboxylic acid derivatives: acyl halides, carboxylic anhydrides, esters, amides.

Naming the Carboxylic Acids

Order of Precedence of Functional Groups:

The -ane ending of the corresponding alkane is replace by -oic acid.
Same rules as alcohols (except that the position of carboxylic acid is always 1 ⇒ do not specified it).
When -COOH attached to a ring = cycloalkane-carboxylic acid (and carbon bearing the -COOH is C1).
The aromatic counterperts are the benzoic acids.

Properties of Carboxylic Acids

C=O bond: short, strong and very polar; C-O bond: polar
Hybridization: sp² ⇒ trigonal planar
-COOH forms hydrogen bonds (with other -COOH or polarized molecules).

NMR: ¹H δ ~ 10-13 ppm (O-H); ¹³C δ ~ 180 ppm.
IR: O-H stretching ⇒ broad band ~ 2500-3300 cm^-1; C=O stretching ⇒ intense band ~ 1710 cm^-1

Reactivities:

Synthesis of Carboxylic Acids

Oxidation of Alcohols and Aldehydes (see Chapter 8 - Organic Chemistry 1):

Carbonation of Organometallic Reagents:

Hydrolysis of Nitriles:

Reduction of Carboxylic Acids

The Addition-Elimination Mechanism

Substitution at the carboxy carbon occurs by addition-elimination:

with Nu = Nucleophile and L = Leaving group

For -COOH, the process is complicated by the poor leaving group (HO^-)
⇒ Convert -COOH to carboxylic acid derivatives (e.g. Acyl Halides).
Nucleophilic Attack on C=O of carboxylic acid derivatives is a key step of the Addition-Elimination process.
It can be catalyzed by both base and acid.