Question

The best reagent for converting 2-phenylpropanamide into 2-phenylpropanamine is:
(A) Excess ${{H}_{2}}$ in presence of Pd/C
(B)$B{{r}_{2}}$​ in aqueous NaOH
(C) Hydrogen iodine in the presence of red phosphorus
(D)$LiAl{{H}_{4}}$​ in ether

Answer 1

Hint: Approach this question by writing down the reaction conversion and check the change in any functional group or substituents. This is because many reagents cause different functional changes in the substituents of the reactant in the reaction which can be noticed well.

Complete answer:
Let us first discuss about the reaction followed by the function of each reagent given in the question as follows:-
The reaction of converting 2-phenylpropanamide into 2-phenylpropanamine is shown below:-

As we can see that the amide group of reactant is changed into amine group or we can say that the carbonyl part of amide group is converted into amine group without any changes in the benzene ring or any other part of it. So we require a reagent that does the same when reacted with an amide functional group.
(A) Excess${{H}_{2}}$ in presence of Pd/C: When hydrogen gas reacts with an unsaturated compound, it reduces it and changes it into a saturated compound. It could be used in this reaction but this reagent also reduces the benzene ring, hence this is not the best reagent for the above conversion.
(B)$B{{r}_{2}}$​ in aqueous NaOH: This can be used to convert an amide group to amine group which is known as Hoffmann rearrangement. But it also requires heat for the decarboxylation step. Hence it is not the best reagent as well.
(C) Hydrogen iodine in the presence of red phosphorus: this combination forms $P{{I}_{3}}$ which leaves only hydrogen atoms that completely replaces alcohol group from any compound or in simple words, it reduces alcohol group. Therefore is not the best reagent for this conversion.
(D)$LiAl{{H}_{4}}$​ in ether: This reagent is especially used in the reduction of carbonyl groups without affecting the double bonds of the benzene ring. So it can easily convert the amide part of 2-phenylpropanamide to amine. Hence this is the best reagent for this conversion.

Therefore, the best reagent for converting 2-phenylpropanamide into 2-phenylpropanamine is: (D)$LiAl{{H}_{4}}$​ in ether.

Note:
-Remember to learn the function, selectivity and chemoselectivity of each and every reagent as they are very helpful in conversions of organic reactions.
-All the reagents in organic chemistry are mainly categorized as reducing, oxidizing and organometallic reagents.