Process for preparing diisocyanates based on lysine

Process for preparing a diisocyanate of the formula (A)

• where R is selected from the group consisting of alkyl, aryl, and combinations thereof, comprising the following process steps in the indicated order:
• 1) Providing an intermediate of the formula (B) with a process using lysine and urea
• where R and each R′ are independently selected from the group consisting of alkyl, aryl, and combinations thereof;
• and
• 2) thermolytic cleavage of the intermediate of the formula (B),
• thereby affording the diisocyanate of the formula (A);
• and
• wherein the process further includes one of the following series of process steps prior to process step 1):
• either a.1) providing of lysine;
• a.2) reacting the lysine with urea to form a urea adduct of the formula (C)
• and
• a.3) reacting the urea adduct of the formula (C) with an alcohol to form the intermediate of the formula (B);
• or b.1) providing of lysine;
• b.2) reacting the lysine with a base to form a lysine salt of the formula (Z);
• where X is a counterion;
• b.3) reacting the lysine salt of the formula (Z) with urea to form a urea salt of the formula (Y);
• where X is a counterion;
• b.4) reacting the urea salt of the formula (Y) with an alcohol to form a carbamate of the formula (X)
• where each R′ is independently selected from the group consisting of alkyl, aryl, and combinations thereof, and X is a counterion;
• b.5) reacting the carbamate of the formula (X) with an acid to form the carboxylic acid of the formula (W)
• where each R′ is independently selected from the group consisting of alkyl, aryl, and combinations thereof;
• and
• b.6) reacting the carboxylic acid of the formula (W) with an alcohol to form the intermediate of the formula (B);
• or c.1) providing of lysine;
• c.2) reacting the lysine with a base to form a lysine salt of the formula (Z);
• where X is a counterion;
• c.3) reacting the lysine salt of the formula (Z) with urea to form a urea salt of the formula (Y);
• where X is a counterion;
• c.4) reacting the urea salt of the formula (Y) with an alcohol to form the intermediate of the formula (B).