بسم الله الرحمن الرحيم
If that chemical does not contain any impure substance then salah will be valid in those clothes. However, if the stains are in such a quantity that it is not good to go in the meeting of respected people wearing the clothes then it is makrooh to offer salah in such clothes.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.