[GinaTageldin]

Is it easy to add isocyanates or isothiocyanate derivatives on the amino group of 2-amino-4,6-dichloropyrimdine or it is difficult since tautomerism can be occurred to imino form?? any conditions for this rx?

[pgk]

Aromatic conjugation decreases the nucleophilicity of amines and thus, the condensation with isocyanates will possibly be slower.  But for safety reasons, work in adequate dilution at room temperature and avoid heating.

[GinaTageldin]

Aromatic conjugation decreases the nucleophilicity of amines and thus, the condensation with isocyanates will possibly be slower.  But for safety reasons, work in adequate dilution at room temperature and avoid heating.

Sir, what did you mean by safety reasons? i didn't use isocyanates before and what about work in adequate dilution at room temperature and avoid heating? Thank you so much

[wildfyr]

Isocyanates react quite vigorously it is an exothermic reaction, which can cause thermal runaway leading to explosions, damaged materials, or a ruined reaction.

Dilutions and cooling can help avoid this issue.

[GinaTageldin]

Isocyanates react quite vigorously it is an exothermic reaction, which can cause thermal runaway leading to explosions, damaged materials, or a ruined reaction.

Dilutions and cooling can help avoid this issue.

Ahh, i got it now. Thank you Sir

[rolnor]

I dont understand, they are not more reactive than for example acid chlorides?

[pgk]

The reaction of aliphatic isocyanates with amines is instant; in contrast to aromatic isocyanates that delay their condensation with amines for a few minutes, due to the aromatic resonance, the electron attractor character of any o-,p-substituents and the steric hindrance of any o-substituents.

[rolnor]

The reaction between acid chlorides and amines are also instant? There is something wrong talking about these reactions as they are more dangerous than normal chemical reactions, there is nothing special about isocyanates or isothiocyanates, I have done dozens of this type of reactions, there is no problem at all.

[pgk]

Isothiocyanates are quite less reactive than isocyanates with amines.

[rolnor]

I have worked with both isocyanates and isothiocyanates and condensate them with both aliphatic and aromatic amines, there is nothing special at all.

[pgk]

Yes, if you work in adequate dilution and by gradual addition of the reagents.

[rolnor]

There seems to be a problem here, have you yourself worked with these type of reactions pgk? Do you yourself dilute this reactions more then you do otherwise?

[pgk]

Yes, because I have worked with these type of reactions in polymers and thus, in high "dilution" due to the high molecular weight. Nevertheless, I had got serious exothermic problems with short polymer chains and polyamines.

[rolnor]

Maybe you are working on a much larger scale then I have done, I do not have any problems of this sort.

[hypervalent_iodine]

Maybe you are working on a much larger scale then I have done, I do not have any problems of this sort.

Neither have I, though I work with amines similar to the OP and they tend not to be very reactive. That being said, others in my group working on separate projects have worked with aliphatic amines and isocyanates and the procedure they normally use is reflux in toluene. Probably a difference in scale, as you say.