Reaction of a primary or secondary amine with diethyl carbonate under controlled conditions gives a carbamic ester. Propose a mechanism for this reaction.

A primary or secondary amine reacts with diethyl carbonate (DEC) to form a carbamic ester. The reactants are represented as R-NH2 for a primary amine or R-NHR' for a secondary amine, and diethyl carbonate has the structure (EtO)2C=O. The final product will be a carbamic ester, which can be represented as R-NH-CO-OEt for a primary amine and R-NR'-CO-OEt for a secondary amine.

The amine, being a nucleophile, attacks the electrophilic carbonyl carbon of diethyl carbonate. This process leads to the formation of a tetrahedral intermediate with one of the ethoxide ions leaving the molecule and forming a stable ethanol molecule. Reaction: R-NH2 + (EtO)2C=O → R-NH-C(OEt)-OEt + EtOH (primary amine) or Reaction: R-NHR' + (EtO)2C=O → R-NR'-C(OEt)-OEt + EtOH (secondary amine)

In the tetrahedral intermediate, the protons from the amine portion of the molecule are transferred to the ethoxide ion that was displaced in the previous step, resulting in the formation of ethanol as a byproduct. Reaction: R-NH-C(OEt)-OEt → R-N-CO-OEt + H-OEt (primary amine) or Reaction: R-NR'-C(OEt)-OEt → R-NR'-CO-OEt+ H-OEt (secondary amine) Now, the carbamic ester is formed along with ethanol as a byproduct. In summary, the mechanism for the reaction between a primary or secondary amine with diethyl carbonate under controlled conditions to give a carbamic ester involves nucleophilic attack by the amine on the carbonyl carbon of diethyl carbonate, followed by proton transfer from the tetrahedral intermediate to the displaced ethoxide ion. This forms the desired carbamic ester product and ethanol as a byproduct.