xwinorb - 15-3-2010 at 20:28
Does hydroquinone reacts directly with NaOH ? If so, what is the reaction product ?
I think it might be the sodium salt ( the two H - O - in the hydroquinone replaced with two Na - O - ) but I am not sure about it.
[Edited on 16-3-2010 by xwinorb]
xwinorb - 15-3-2010 at 20:57
I think I have found out. Looks like hydroquinone is oxidized by O2 and that happens faster under basic condition. So looks like it has nothing to do
with the sodium salt, wrong guess.
Who knows better please confirm and/or elaborate a bit more. THX.
not_important - 15-3-2010 at 22:40
The phenolic HO- groups are acidic enough to form a salt with NaOH, or more properly a mono and a di sodium salt can be formed depending on the ratio
of base to hydroquinone.
As you've found the polyhydroxyl benzenes are quite reactive towards O2 when in alkaline solution, so in a sense it has to do with the sodium salt.
Unless precautions are taken, using air-free water for making up the solutions, working under an inert gas, such solutions quickly become discoloured
with the oxidation products. Alkaline pyrogall, 1,2,3 trihydroxybenzene, was used to remove oxygen from gas mixtures in gas analysis.
The products of oxidation can be quite complex. Hydroquinone oxidises to 1,4-benzoquinone, which form a 1:1 complex with further hydroquinone giving
dark, greenish solutions and precipitates ofquinhydrone. However under alkaline conditions benzoquinone can result in various condensation reactions
forming mixtures of coloured compounds.
xwinorb - 16-3-2010 at 16:08
I think I understand it better now.
Yes, the reference I have seen ( not read as carefully as I should BTW but I will ) seems to mentions also more products of the oxidation than just
quinone and the quinhydrone complex.
EDITED BY XW ( QUINONE, NOT HYDROQUINONE ) ABOVE.
I think I have also seen some reactions of interest using NaOH and hydroquinone ( or closely related to hydroquinone ) in which inert atmosphere is
used.
Many thanks.
[Edited on 17-3-2010 by xwinorb]