Q32E - Organic Chemistry (Mcmurry)

Question

Melmac, a thermosetting resin often used to make plastic dishes, is prepared by heating melamine with formaldehyde. Look at the structure of Bakelite shown in Section 31-6, and then propose a structure for Melmac.

Step-by-Step Solution

Answer

The proposed structure of thermosetting resin Melmac is shown below:

Step 1: Thermosetting resins

Thermosetting resins refers to a petrochemical material that is irreversibly cures, because they retain their form and stay solid under heat once they are cured. Thermosetting resin becomes highly cross-linked and solidify into a hard, insoluble mass when heated.

For example, Bakelite, a thermosetting resin first produced in 1907, has been in commercial use longer than any other synthetic polymer. It is widely used for molded parts, adhesives, coatings, and even high-temperature applications such as missile nose cones. 

Chemically, Bakelite is a phenolic resin, produced by reaction of phenol and formaldehyde.

Step 2: Propose a structure

As the mentioned structure of polymer is highly crossed link like a Bakelite, so it is also a thermosetting resin, produced by reaction of 1,3,5-triazine-2,4,6-triamine and formaldehyde. 

On heating, water is eliminated, many cross-links form, and the polymer sets into a rocklike mass. The cross-linking in this thermosetting resins is three-dimensional and is so extensive that we can’t really speak of polymer “chains like Bakelite

Step 3: Result

The proposed structure of thermosetting resin Melmac is shown below: