CA34:26495
The oxidation of salicylates in alkaline solutions
By: Brecht, E. A.; Rogers, C. H.
The brown oxidn. product (termed temporarily "sodium salicylate-brown" or, in the acid form, "acid salicylate-brown" (I)) formed in the
discoloration of salicylate solns. is an intermediate product because it is further oxidized to colorless compds. (oxalates and carbonates); 3
methods are described for its prepn. in slightly acid, slightly alk. and strongly alk. media, resp., by oxidizing with air and with H2O2. I has the
formula C12H8O6 and contains 3 OH groups which are easily methylated and form metallic salts with alkalies. 2,5-Dihydroxyquinone yields a
dehydro compd. (C12H6O6) having the same chem. and phys. properties as I. To prep. Na2O2.8H2O add 13.5 cc. of 30% H2O2 (d. 1.11) to a cooled soln.
of 62.5 g. NaOH in 175 cc. H2O, collect the crystals formed on a filter, mix twice with portions of alc. and drain well on a filter after each
washing, and dry in a vacuum desiccator over H2SO4 for 3 h. To prep. a dihydrated form of the di-Na deriv. of 2,5-dihydroxyquinone, to a
reaction mixt. composed of 125 g. Na salicylate, 625 g. NaOH and 1875 cc. H2O add not over 15 cc. (to avoid formation of Na2C2O4) of 30% H2O2,
after redn. of the H2O2 is complete (about 3 days) add another similar portion, and continue until up to 18 portions of H2O2 have been added, collect
the orange needle crystals on a suction filter, wash twice with 25% NaOH and then 5-6 times with alc. The formula of the crystals was proved by
assay for Na content and by conversion to 2,5-dihydroxyquinone, m. 222° (cor., decompn.), obtained by acidifying the red aq. soln. of the
di-Na deriv. |