Chemical. CAS 82354-19-6. Formula C31H29ClN2O6S2. MW 625.15. Synthetic. Sulforhodamine 101 sulfonyl chloride also called Texas Red sulfonyl chloride is a popular long wavelength amine-reactive rhodamine dye. Because the dye is quite unstable in water, reactions with amines in an aqueous solution must be carried out at low temperature over ice or at 4°C and usually at pH 8.5.