Amines

Step 1: Recall the effect of –NH group.
Aniline (C H NH ) contains an amino group (–NH ), which is a strong activating group. It strongly activates the benzene ring towards electrophilic substitution, especially at ortho and para positions.

Step 2: Reaction with bromine.
When aniline is treated with bromine water, it undergoes bromination very easily, even without a catalyst. Instead of monobromination, it directly gives 2,4,6-tribromoaniline.

Step 3: Identify product.
The product formed is tribromoaniline (2,4,6-tribromoaniline), which is a white precipitate.
Step 4: Final Answer.
Thus, bromination of aniline gives tribromoaniline.

Step 1: Recall the carbylamine reaction.
The carbylamine reaction is a test for primary amines (aliphatic or aromatic). In this reaction, a primary amine reacts with chloroform (CHCl ) and alcoholic KOH to form isocyanides (carbylamines), which have a very unpleasant odor.
General reaction:

Step 2: Check each option.
- (A) CH –CH –NH : This is a primary aliphatic amine. It gives the carbylamine test.
- (B) CH –NH : This is also a primary aliphatic amine, so it gives the carbylamine test.
- (C) CH –NH–CH : This is a secondary amine. Secondary (and tertiary) amines do not give the carbylamine reaction.
- (D) C H –NH : Aniline is a primary aromatic amine. It also gives the carbylamine test.
Step 3: Final Answer.
Thus, the amine which does not give the carbylamine reaction is the secondary amine, CH –NH–CH .

Step 1: Reaction with primary amine.
Primary amines react with benzenesulfonyl chloride to give sulfonamides which are soluble in alkali due to the presence of an acidic hydrogen atom. This product dissolves in alkali, forming a soluble salt.

Step 2: Reaction with secondary amine.
Secondary amines react to form sulfonamides which have no acidic hydrogen and hence remain insoluble in alkali. The product is insoluble in alkali.

Step 3: Reaction with tertiary amine.
Tertiary amines do not react with benzenesulfonyl chloride under these conditions. They remain unreacted and can be recovered unchanged. Conclusion:
- Primary amines: give soluble sulfonamide salts.
- Secondary amines: give insoluble sulfonamides.
- Tertiary amines: do not react.

Step 1: Intermolecular forces in amines.
Amines can form intermolecular hydrogen bonds because of the presence of a nitrogen atom with a lone pair. However, N–H bonds are less polar than O–H bonds, and nitrogen is less electronegative than oxygen. Thus, the hydrogen bonding in amines is weaker compared to alcohols and carboxylic acids.

Step 2: Intermolecular forces in alcohols.
Alcohols have O–H bonds, which are more polar and form stronger hydrogen bonds than N–H bonds. Hence, alcohols have higher boiling points than corresponding amines.

Step 3: Intermolecular forces in carboxylic acids.
Carboxylic acids form very strong dimeric hydrogen bonds in which two molecules are linked via two O–H…O bonds. This gives them the highest boiling points among the three classes of compounds. Conclusion:
Boiling point order for comparable molecular masses is:

Step 1: Recall the requirement.
The question asks for the preparation of primary amines from alkyl halides without changing the number of carbon atoms in the chain. This means the reaction must directly substitute the halogen with an –NH group, giving a pure primary amine.

Step 2: Analyze each option.
- This involves the conversion of amides to amines using Br and NaOH. However, it reduces the carbon chain length by one (–CO group is removed). Hence, it is not suitable here.
- In this method, phthalimide reacts with alkyl halide to form an N-alkyl phthalimide, which on hydrolysis gives a pure primary amine. This method introduces the –NH group without changing the carbon skeleton. This is the correct choice.
- This is used to prepare aryl halides from aromatic amines via diazonium salts. It is not a method to prepare primary amines.
- :} \) Direct reaction of alkyl halides with NH gives amines but also produces secondary and tertiary amines due to multiple substitutions. Hence, it is not a selective method for pure primary amines.

Step 3: Final Answer.
Thus, the best method is Gabriel's phthalimide synthesis.