[PureMP]

Hi

By HPLC I have identified that some sulponephthalein indicator dyes are impure and these impurities effect pH measurements. Interestingly, dyes made by Kodak in the late 1980's seem to be pure enough for my purposes, but they are no longer available for purchase. My idea is to try to find a method to synthesize the dyes like Kodak did in the 1980s.

I have found two procedures. Both start with 2 phenols with appropriate R-groups and 2-sulphobenzoic anhydride. One method (from a 1916 paper) says to add concentrated H2SO4 and heat. Another method (from 2002) puts the reaction mixture in a Microwave Oven with a few drops of chlorobenzene.

I believe the impurities are structural isomers which seems obvious from the reaction methods. My question is, will there be a difference in purity using H2SO4/heat vs. Microwave/Chlorobenzene? If you think they would result in the same type of impurities, are there any tricks of the trade for reducing structural isomer formation in this simple reaction?

Thank you for your time,
MP

[orgopete]

I think if you search, you will find these dyes do effect pHs. Without knowing your situation, we won't know wether you will obtain the same impurities by doing the same reactions. Kodak may simply have purified them dyes to a greater degree.