in for example ep a 0 289 840 and typical examples of suitable aliphatic triamines are mentioned in for example ep a 749 958 these diamines are suitable for preparing the corresponding diisocyanates or triisocyanates by the process of the invention typical examples of suitable aromatic diamines are the pure isomers or the isomer mixtures of diaminobenzene diaminotoluene diaminodimethylbenzene diaminonaphthalene and diaminodiphenylmethane preference is given to 2 4 2 6 toluenediamine mixtures having isomer ratios of 80 20 and 65 35 or the pure 2 4 toluenediamine isomer as triamine preference is given to using 1 8 diamino 4 aminomethyl octane also known as triaminononane the starting amines of the formula ii are fed into the reactor in gaseous form and are if appropriate vaporized and preferably heated to from 200 u00b0 c to 600 u00b0 c particularly preferably from 250 u00b0 c to 450 u00b0 c before carrying out the process of the invention and are fed if appropriate after dilution with an inert gas such as n 2 ne he ar or with the vapour of an inert solvent into the reactor the phosgene is fed into the tube reactor in a stoichiometric excess and at from 200 u00b0 c to 600 u00b0 c when using aliphatic diamines the molar excess of phosgene based on one amino group is preferably from 25 to 250 and when using aliphatic triamines is preferably from 50 to 350 when aromatic diamines are used the molar excess of phosgene based on an amino group is preferably from 150 to 300 in the following the invention is illustrated by way of example with the aid of fig1 the feed stream a diamine and or triamine flows via the inlet 1 and the central nozzle 5 into the tube reactor 6 the.