Isophorone diisocyanate

Isophorone diisocyanate (IPDI) is an organic compound in the class known as isocyanates. More specifically, it is an aliphatic diisocyanate. It is produced in relatively small quantities, accounting for (with hexamethylene diisocyanate) only 3.4 % of the global diisocyanate market in the year 2000. Aliphatic diisocyanates are used, not in the production of polyurethane foam, but in special applications, such as enamel coatings which are resistant to abrasion and degradation from ultraviolet light. These properties are particularly desirable in, for instance, the exterior paint applied to aircraft.

Synthesis
There are five steps to the synthesis of pure IPDI:
 * Condensation: Conversion of acetone with a catalyst to produce isophorone
 * Hydrocyanation: Reaction of the isophorone with hydrogen cyanide to form isophorone nitrile
 * Reductive amination: Reaction of the isophorone nitrile with ammonia, hydrogen and a catalyst, to form a mixture of isophorone diamine conformers (25/75 cis/trans)
 * Phosgenation: Reaction of the isophorone diamine with phosgene to form a crude mixture containing IPDI conformers (25/75 cis/trans)
 * Purification: Distillation of the crude IPDI to extract pure IPDI

Chemistry
IPDI exists in two conformers, cis and trans. Their reactivities are similar. Each conformer is an asymmetrical molecule, and thus has isocyanate groups with different reactivities. The secondary isocyanate group is more reactive than the primary isocyanate group.