Dear Sara Dokh

I would say that one of the four spots will be phenyl isocyanate (probably) and the other spots will be impurities. Phenylisocyanate is known to decompose upon iradiaton. Also, isocyanates in general are very reactive species.

See: https://pubs.acs.org/doi/pdf/10.1021/ja00354a064

J. Am. Chem. Soc., Vol. 105, No. 16, 1983, page 5500

Best,

Tereza

Dear Sarah,

please note that phenylisocyanate (Ph-N=C=O) is quite reactive. It easily reacts with water to form aniline and CO2, while reactions with alcohols lead to formation of carbamates. The presence of isomers (e.g. phenyl cyanate, Ph-O-CN) is less likely. The isomer Ph-O-NC is unstable. I think that TLC is not a good method to check the purity of phenyl isocyanate because hydrolytic decomposition is not easily ruled out. If you need to purify a sample of phenyl isocyanate, vacuum distillation would be a better choice.

Good luck with your work!

Dear Sara

Suitable gradient elution (mobile phase) is difficult to find for the TLC. I will suggest you to use latest technology, like HPLC.