Process for producing 1, 5-pentamethylene diisocyanate from cadaverine salt

A process for producing 1,5-pentamethylene diisocyanate (PDD) from a cadaverine salt, the process comprising:

• (a) providing a phosgene source;
• (b) providing a solution comprising a cadaverine salt dissolved in an inert solvent in the presence of a tertiary amine base;
• and
• (c) subjecting the solution to a liquid-phase phosgenation reaction to convert the cadaverine to PDI, wherein the phosgenation reaction is a multistage phosgenation reaction comprising at least a first stage in which the solution is heated to a first temperature such that the cadaverine reacts with phosgene from the phosgene source to produce a dicarbamoyl chloride intermediate, and a subsequent second stage in which the solution is further heated to a second temperature higher than the first temperature to subject the dicarbamoyl chloride intermediate to dehydrochlorination, wherein the second stage comprises said step of maintaining the reaction at temperatures between 100° C. and 120° C. for a sufficient time to achieve a threshold yield of PDI, wherein the amounts of the phosgene source and/or tertiary amine base reactants employed in the multistage phosgenation reaction is lower than the amounts required to achieve the same PDI yield as a corresponding single-stage phosgenation reaction occurring only at the second temperature,
• wherein the tertiary amine base enables the phosgenation reaction to occur to completion at said temperature range.