The major difference between primary, secondary, and tertiary amines lies in the number of carbon atoms directly bonded to the nitrogen atom. In primary amines, the nitrogen atom is bonded to one carbon atom and two hydrogen atoms. In secondary amines, the nitrogen atom is bonded to two carbon atoms and one hydrogen atom. In tertiary amines, the nitrogen atom is bonded to three carbon atoms and no hydrogen atoms.Primary amine: R-NH2Secondary amine: R-NH-R'Tertiary amine: R-N-R'-R''Now, let's discuss the reaction mechanism of a primary amine with a carboxylic acid to form an amide. The reaction is an example of nucleophilic acyl substitution. Here's a step-by-step explanation of the mechanism:1. Nucleophilic attack: The nitrogen atom in the primary amine R-NH2 acts as a nucleophile due to its lone pair of electrons. It attacks the electrophilic carbonyl carbon atom in the carboxylic acid R'-COOH , forming a tetrahedral intermediate.2. Proton transfer: A proton H+ is transferred from the nitrogen atom in the tetrahedral intermediate to the oxygen atom of the hydroxyl group OH in the carboxylic acid. This results in the formation of a hydroxyl group OH on the nitrogen atom and a negatively charged oxygen atom O- in the tetrahedral intermediate.3. Elimination of water: The negatively charged oxygen atom in the tetrahedral intermediate extracts a proton H+ from the nitrogen atom, forming a double bond between the nitrogen and the carbonyl carbon atom. Simultaneously, the hydroxyl group OH leaves as a water molecule H2O , resulting in the formation of an amide R-NH-C O -R' .Overall, the reaction can be summarized as follows:R-NH2 + R'-COOH R-NH-C O -R' + H2OIn this reaction, a primary amine R-NH2 reacts with a carboxylic acid R'-COOH to form an amide R-NH-C O -R' and water H2O .