Carboxylic acids

• Carboxylic acids are weak acids that slightly dissociate in solution forming a H+ ion and a carboxylate ion (RCOO-).
• Carboxylic acids act as acids when reacting with carbonates to form a carboxylate salt, water and carbon dioxide.
• Short chain carboxylic acids can form hydrogen bonds with water molecules, making them soluble in water.
• Carboxylic acids can react with alcohols in the presence of a strong acid catalyst to form an ester. This is called esterification.
• In esterification, the OH is removed from the acid and the H from the alcohol to make water. The name of the resulting ester is the alcohol prefix - yl acid prefix - anoate.
• Esters are sweet smelling compounds used in flavourings and perfumes. They have low boiling points and make good solvents for other polar molecules.
• Vegetable oils and fats are esters of naturally occurring glycerol (propane-1, 2, 3-triol).
• Glycerol undergoes esterification to form triglyceride esters.
• Biodiesel is an ester produced from vegetable oils and methanol in the presence of a strong acid catalyst.
• Ester hydrolysis is the reverse reaction to esterification and happens when water is added.
• In acidic conditions, and ester undergoes hydrolysis to produce an alcohol and carboxylic acid.
• In alkaline conditions, an ester undergoes hydrolysis and the carboxylic acid produced further reacts with the base to form a carboxylate salt and an alcohol.
• The salt produced during ester hydrolysis in alkaline conditions is commonly used as soap due to hydrophilic and hydrophobic properties. This the production of this salt is called saponification.
• Carboxylic acids have derivatives where the OH group is replaced by another group. There are three main derivatives: acid anhydrides, acyl chlorides and amides.
• Acid anhydrides are formed when water is removed from two carboxylic acids and have the formula RCOOCOR.
• Acyl chlorides react violently due to being very polar. They have the formula RCOCl.
• The amide derivative formed is an N-substituted amide with the formula RCONH2.
• Carboxylic acid derivatives can react with nucleophiles in nucleophilic addition-elimination reactions.
• In nucleophilic addition elimination, the nucleophile attacks the carbon with a double bond oxygen on it and electrons move to the oxygen, breaking one of the two bonds and to the other element attached to that carbon, eliminating it. The oxygen has a negative charge and so the double bond reforms.
• Acyl chlorides can react with water to produce a carboxylic acid, an alcohol to produce an ester, ammonia to produce an amide and amines to produce an N-substituted amide.
• Aspirin is an ester produced from salicylic acid and ethanoic anhydride. Ethanoyl chloride can also be used but it is expensive and produces harmful HCL fumes.