When tianeptine sodium (C21H24ClN2NaO4S) is reacted with DMSO (dimethyl sulfoxide; C2H6OS) the resulting solution is a bright yellow color. Can anybody explain why this is? I apologize for not being able to figure this out for myself, but I’ve only taken one undergraduate lab course in chemistry. All I know are the rudimentary basics.
Why is tartrazine yellow ?
The azo chromophore?
@ Washoe: do you know for a fact that they react (like, form a covalent bond)? Under what conditions does this reaction take place?
No, sorry—I was being stupid. They don’t react; they form a solution. This is evidenced by the fact that tianeptine, which is a psychoactive drug, retains its psychoactive properties when dissolved in DMSO.
No, you’re the smart one. It’s just the organic chemist in me who insists that a “reaction” between two compounds must involve the formation of a covalent bond.
Actually, I know that there’s plenty of substances whose color in solution depends on the qualities of the solvent. Take, for example, iodine: it is brownish-yellow in polar solvents (alcohol, acetone, ether) but purple in apolar (dichloromethane, pentane, cyclohexane).
I bet it’s something like that going on with your tianeptine. DMSO is, indeed, polar like water, but unlike water it is aprotic. This might account for the change in color!
But as for why, I’m at a loss. As you said, this is a *hard *chemistry question!
For what it’s worth, dissolution is often a chemical change, not just a physical one. Yes, I know that most textbooks say otherwise. They’re wrong.