Draw the structures of the organic products in each reaction of the following two-step synthesis. (Hint: The nucleophilic amine attacks the electrophilic carbonyl carbon, and the resulting intermediate undergoes a proton shift and dehydration. Recall what is eliminated in a dehydration process. The second step is a reduction reaction; the reducing agent is NaBH3CN (or H2, metal catalyst). The aromatic ring is unaffected by these reagents. Look at the product of the first reaction and consider what can be easily reduced.)
Concepts and reason
Major types of organic reactions are addition, substitution, elimination, condensation, rearrangement, oxidation and reduction reactions.
A condensation reaction is a type of organic reaction where an electron-deficient carbon atom reacts with an electron-rich reactant (nucleophile) to form a large molecule and remove a small molecule. In organic chemistry, a reduction reaction is a type of chemical reaction where a carbon atom gains bonds with less electronegative elements (hydrogen).
The condensation reaction of carbonyl compounds and amines is where an electron-deficient carbon atom easily reacts with an electron-rich nucleophile to form a double bond. The carbon atom carries a partial positive charge and the oxygen atom carries a partial negative charge. These electronegative properties make the carbon atom an electrophilic center. The general reaction mechanism is given below.
A nucleophile attacks the electron-deficient carbonyl carbon and is followed by dehydration to form a Schiff base form product. The carbon-nitrogen double bond undergoes a reduction reaction in the presence of a reducing agent. The reaction is as follows:
Acid catalyst protonates the oxygen atom in the aldehyde then produces an electron-deficient carbon atom. The lone pair of amine (base) nucleophiles attack on electron-deficient carbon atom followed by dehydration to form a Schiff base.
The reduction of the Schiff base is given below:
The Schiff base is reduced by using sodium cyanoborohydride and forming a secondary amine product (n-propyl aniline). This reducing agent precisely reduces the C=N double bond and does not reduce the benzene ring double bonds. So the final product formed in this reaction is n-propylaniline.