Process for preparing carbodiimides utilizing a phosphonium salt catalyst

A process for preparing organic carbodiimides from organic isocyanates having no active hydrogen containing substituents which are reactive with the isocyanate group which comprises heating said organic isocyanates, under anhydrous conditions and at a reaction temperature of about 155.degree. to about 215.degree. C, together with about 0.1 to about 10 mole percent based on isocyanate concentration of a phosphonium salt catalyst having a boiling point above the reaction temperature utilized and having the formula:

• ##STR10## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may be the same or different and represent alkyl groups of 1 to 8 carbon atoms, cycloalkyl, aryl, aralkyl, and alkaryl and their derivatives or two of said groups together may constitute a cyclic hydrocarbon, and X represents a halogen.