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Description of experiment
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experiment.
Needed compounds: ----------------- sodium hydroxide : NaOH hydroquinone : HO C6H4 OH resorcinol : HO C6H4 OH catechol : C6H4 (OH)2
Class: ------ elem=C redox
Summary: -------- Catechol, resorcinol and hydroquinone all are dihydroxy benzenes. When an ortho-pair (1,2-pair) or a para-pair (1,4-pair) is present, then the compound is easily oxidized by air in alkaline environment. When a meta-pair (1,3-pair) is present, such a reaction does not occur.
Description: ------------ Add a solution of NaOH to a solution of catechol: On shaking, with air-contact, the liquid turns green/brown, after a while dark brown/black. On strong dilution it turns green/brown again.
Add a solution of NaOH to a solution of resorcinol: The liquid hardly changes. After a while it has become pale yellow. Shaking with intense contact to air for a long time does not result in any changes.
Add a solution of NaOH to a solution of hydroquinone: The liquid turns red/ brown when shaken. After a while it has turned dark brown, almost black.
Remark: ------- Two hydroxy-groups on a benzene ring can be oxidized together, forming a so called quinone structure (two oxygen atoms coupled to the benzene ring, occupying a double bond on the corresponding C-atoms, thereby fixing the double bonds in the benzene ring). Formation of a quinone structure can only be done for double bonded oxygen at ortho and para positions. For meta positions, the C-atom between the two oxygens only has three bonds used, no fourth is available (one from each of the adjacent C atoms and one from its hydrogen atom). This prevents the formation of a quinone-like structure for meta-dihydroxy benzene, a.k.a. resorcinol.
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