Carboxylic Acids and their Derivatives - SS2 Chemistry Lesson Note

Carboxylic acids are a class of organic compounds that contain the carboxyl functional group (-COOH). They are versatile compounds with diverse applications in various fields, including pharmaceuticals, food additives, and polymers. Carboxylic acids can undergo several transformations to form derivatives, such as esters, amides, and acid halides.

Nomenclature of Carboxylic Acids:

The systematic nomenclature of carboxylic acids follows the rules established by the International Union of Pure and Applied Chemistry (IUPAC). Carboxylic acids are named by replacing the "-e" in the name of the corresponding parent hydrocarbon with the suffix "-oic acid."

IUPAC Naming Rules:

●     Identify the longest continuous carbon chain that contains the carboxyl group. This chain becomes the parent hydrocarbon.

●     Number the carbon atoms in the chain, starting from the end nearest to the carboxyl group.

●     Indicate the position of the carboxyl group with the lowest possible number.

●     Add the suffix "-oic acid" to the name of the parent hydrocarbon.

Examples of IUPAC Names:

●     Methanoic Acid: The simplest carboxylic acid, also known as formic acid.

●     Ethanoic Acid: A carboxylic acid with two carbon atoms, also known as acetic acid.

Properties of Carboxylic Acids:

Carboxylic acids possess several important properties that arise from the presence of the carboxyl group.

●     Acidity: Carboxylic acids are weak acids due to the ability of the carboxyl group to donate a proton (H+). The carboxylate anion (RCOO-) is formed when the carboxylic acid loses a proton.

●     Hydrogen Bonding: Carboxylic acids can form intermolecular hydrogen bonds due to the presence of the carboxyl group, leading to higher boiling points and greater solubility in water compared to hydrocarbons of similar molecular weight.

●     Odour: Many carboxylic acids have distinct odours, ranging from the pungent smell of formic acid to the vinegar-like odour of acetic acid.

Derivatives of Carboxylic Acids:

Carboxylic acids can undergo various reactions to form derivatives with modified functional groups. Common derivatives include esters, amides, acid halides, and anhydrides.

●     Esters: Esters are formed through the reaction of a carboxylic acid with an alcohol, resulting in the elimination of water. Esters have the general structure RCOOR', where R represents the alkyl or aryl group from the carboxylic acid and R' represents the alkyl or aryl group from the alcohol.

●     Amides: Amides are formed through the reaction of a carboxylic acid with an amine, resulting in the elimination of water. Amides have the general structure COBR2, where R represents the alkyl or aryl group from the carboxylic acid and R2 represents alkyl or aryl groups from the amine.

●     Acid Halides: Acid halides are formed through the reaction of a carboxylic acid with a halogen, such as thionyl chloride (SOCl2) or phosphorus trichloride (PCl3). Acid halides have the general structure RCOX, where X represents a halogen atom.

●     Anhydrides: Anhydrides are formed through the condensation reaction of two carboxylic acid molecules, resulting in the elimination of water. Anhydrides have the general structure (RCO)2O.

Reactions of Carboxylic Acids and Their Derivatives:

Carboxylic acids and their derivatives can undergo several reactions, including:

●     Esterification: Carboxylic acids react with alcohols to form esters in the presence of an acid catalyst. This reaction is important in the production of fragrances, flavours, and plasticizers.

●     Hydrolysis: Esters and amides can undergo hydrolysis, which involves the cleavage of the ester or amide bond in the presence of water or a strong acid or base.

●     Decarboxylation: Carboxylic acids can undergo decarboxylation, a reaction that results in the removal of a carbon dioxide molecule from the carboxyl group. This reaction is often catalysed by heat or a transition metal catalyst.

●     Reduction: Carboxylic acids and their derivatives can be reduced to alcohols using reducing agents such as lithium aluminium hydride (LiAlH4) or sodium borohydride (NaBH4).

●     Nucleophilic Acyl Substitution: Carboxylic acid derivatives, such as acid halides and anhydrides, undergo nucleophilic acyl substitution reactions where a nucleophile replaces the leaving group on the carbonyl carbon.

Applications of Carboxylic Acids and Their Derivatives:

●     Pharmaceuticals: Carboxylic acids and their derivatives serve as important building blocks in the synthesis of pharmaceutical compounds, such as antibiotics and nonsteroidal anti-inflammatory drugs (NSAIDs).

●     Food Industry: Carboxylic acids and their derivatives are used as food additives, preservatives, and flavour enhancers.

●     Polymers: Carboxylic acid derivatives, such as esters, are used in the production of polymers, such as polyesters and polyamides.

Carboxylic acids are versatile compounds with important applications in various fields. They can be named systematically according to IUPAC rules, and their properties, including acidity and hydrogen bonding, contribute to their distinctive characteristics. Carboxylic acids can undergo various reactions to form derivatives such as esters, amides, acid halides, and anhydrides, which have their own unique properties and applications. Understanding the nomenclature, properties, and reactions of carboxylic acids and their derivatives enables chemists to effectively utilise these compounds in diverse areas, including pharmaceuticals, food, and polymer industries.