Process for the manufacture of (poly-)isocyanates in the gas phase

A process for the manufacture of a diisocyanate of the formula (I)

• OCN—R—NCO (I),
• wherein
• R represents a (cyclo-)aliphatic or aromatic hydrocarbon group having up to 15 carbon atoms, provided that at least two carbon atoms are arranged between the two NCO groups,
• by phosgenation of the corresponding vaporous diamine of the formula (II)
• H2N—R′—NH2 (II),
• wherein
• R′represents a (cyclo-)aliphatic or aromatic hydrocarbon group having up to 15, provided that at least two carbon atoms are arranged between the two amino groups,
• in which the vaporous diamine, optionally rarefied with an inert gas or with the vapors of an inert solvent, and phosgene are heated separately to temperatures of from about 200° C. to about 600° C., mixed and reacted in a tube reactor having a number n≧2 of nozzles directed parallel to the axis of the tube reactor arranged in the tube reactor, the diamine-containing stream being fed into the tube reactor through the n nozzles and the phosgene stream being fed into the tube reactor through remaining free space.