[sargelavoie]

Recently, i have prepared a solution containing 10% NaOH in a mixture of THF/MeOH/H2O 2:1:1. This solution was prepared for hydrolysis of benzoyl protecting group. After starting my reaction, i went home without trashing the excess solution. The next morning, the solution had turned yellow. The color disappeared after neutralisation with HCl 10%. Do someone know what the cause of that color?

Thank you in advance

[nj_bartel]

THF forms an peroxide (explosive) when exposed to air.  I'm not sure what color it is, but that's the only thing I can think of that it could be.

[Fleaker]

I have a similar solution of Et2O, NaOEt, and EtOH that has a yellowish tinge to it. Most of my stock MeONa solutions all develop a yellow colouration on long standing.

I don't think it is the peroxide (although you can easily test with iodide and a drop of very dilute sulfuric).