(a) Gabriel Phthalimide Synthesis for Aromatic Primary Amines:
The Gabriel Phthalimide Synthesis is a method used for the preparation of primary amines, but it is not preferred for preparing aromatic primary amines. This is primarily because aromatic primary amines tend to undergo undesirable side reactions under the harsh conditions of the Gabriel synthesis. The Gabriel synthesis involves the following steps:
Reaction of phthalimide with ethanolic potassium hydroxide (KOH): This step generates the potassium salt of phthalimide.
Alkylation of the potassium salt with an alkyl halide: This results in the formation of an N-alkyl phthalimide.
Hydrolysis of the N-alkyl phthalimide: This step converts the N-alkyl phthalimide into the primary amine.
The problem with aromatic primary amines is that they are more prone to undergoing side reactions during the alkylation step. For example, they can undergo Friedel-Crafts acylation or alkylation reactions with the aromatic ring due to the presence of a strong electron-withdrawing group (the amino group) on the aromatic ring. This can lead to the formation of unwanted byproducts and result in low yields of the desired primary amine. Therefore, alternative methods such as reduction of nitro compounds or nucleophilic substitution are often preferred for the synthesis of aromatic primary amines.
(b) Solubility of Products from the Reaction of Primary Amines with Benzene Sulphonyl Chloride:
When primary amines react with benzene sulphonyl chloride (also known as benzenesulfonyl chloride or benzenesulfonyl chloride), they undergo a reaction known as sulfonation. This reaction results in the formation of sulfonamides. The solubility of the sulfonamide products depends on the nature of the amine group.
Solubility of Sulfonamide from Primary Amine: The sulfonamide produced from a primary amine is typically soluble in alkali (aqueous sodium hydroxide, NaOH) because it can form water-soluble salts due to the presence of the amine group. This is because the amine can react with the hydroxide ions from NaOH to form a water-soluble ammonium salt.
Solubility of Sulfonamide from Secondary Amine: In the case of a secondary amine, the product sulfonamide is generally insoluble in alkali. This is because secondary amines lack an active hydrogen atom on the nitrogen atom, so they cannot readily form ammonium salts with hydroxide ions. Therefore, the sulfonamide from a secondary amine remains insoluble in aqueous alkali.
In summary, the solubility of the sulfonamide product from the reaction of primary and secondary amines with benzene sulphonyl chloride is determined by the presence or absence of an active hydrogen atom on the amine nitrogen, which affects the ability to form water-soluble ammonium salts with alkali.
