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A carboxylic acid is an organic compound that contains at least one carboxyl group (-COOH) or (-C(=O)OH). The general formula of a carboxylic acid is R–COOH, with R being a substituent, usually organic.
Carboxylic acids can be classified under several categories:
- Monocarboxylic acids: only have one -COOH group. Most are liquid at room temperature and have strong odor. Ex: formic acid, acetic acid;
- Dicarboxylic acids: have two -COOH groups. Solid and poorly volatile at standard conditions. Ex: oxalic acid, succinic acid;
- Polycarboxylic acids: can have more than three -COOH groups. Solid and non-volatile. Ex: citric acid;
- Organic: The R substituent is an organic group. Ex: acetic acid, benzoic acid.
- Inorganic: The R substituent is an inorganic group (exception for formic acid, where R is H and is organic due to the C-H bond). Ex: carbonic acid, trifluoroacetic acid;
- Aminoacids: Organic carboxylic acids that also contain an amino (-NH2) group. Ex: glycine;
Salts and esters of carboxylic acids are called carboxylates. The carboxylate anion R–COO− is usually named with the suffix -ate (ex: formic acid - formate).
Monocarboxylic acids are liquid (except for aromatic), volatile and have a strong poignant smell. Polycarboxylic acids on the other hand are all solids and non-volatile. Carboxylic acids are polar compounds.
Carboxylic acids are Brønsted–Lowry acids because they are proton (H+) donors. Generally they are weak acids.
Citric acid can be purchased as lemon salt from most stores, while diluted acetic acid is available as vinegar.
- CH3OH + [O] → HCOOH + H2O
- CH3CH2OH + [O] → CH3COOH + H2O
Carbonation of a Grignard and organolithium reagents, followed by acidification:
- RLi + CO2 → RCO2Li
- RCO2Li + HCl → RCO2H + LiCl
Carboxylates are the side products from the haloform reaction. The following ketones/alcohols will give the following carboxylates:
- Ethanol/acetaldehyde - Formate
- Acetone/isopropanol - Acetate
- Methyl ethyl ketone/sec-Butanol - Propanoate
- Acetylacetone - Acetate
- Acetophenone - Benzoate
Concentrated carboxylic acids, such as formic or acetic acids are corrosive to skin and have a strong irritant smell. Wear proper protection when working with them.
Polycarboxylic acids are less corrosive and volatile, though conc. aqueous solutions are irritant.