METHOD #1: —122g salicylaldehyde is stirred into 1L of 1N NaOH solution at room temperature then 1420g of 3% hydrogen peroxide solution (H202, the exact % solution one finds at the grocery store) is added. The solution darkens and the temperature rises to 45-50°C. An ice bath is applied if the temperature starts to rise above 50°C. The mixture then stands for 15-20 hours, neutralized to pH 7 with acetic acid and the solution vacuum distilled of all its water so that all of the stuff that remains in the flask is completely dry. 500mL toluene is poured into the flask and slowly heated to near boiling, all the while being stirred to break up the crystalline mass. The pyrocatechol will dissolve into the hot toluene but all of the crap and salts will not. The hot mix is vacuum filtered and the stuff in the filter cup can be washed with a little fresh hot toluene which is combined with the original filtrate. The toluene/pyrocatechol is allowed to cool causing the pyrocatechol to crystallize out; which can then be separated by filtration. The remaining toluene can be reduced in volume by distillation and allowed to cool again in order to afford a second crop of pyrocatechol. If desired the catechol crystals can be placed in fresh hot toluene and processed as before to give even cleaner product (yield=70%)
METHOD #2: -Sodium bicarbonate and dH20 are stirred in a 3-neck flask with two addition funnels attached. One funnel has salicylaldehyde and the other has concentrated H202 (at least 30%). Both salicylaldehyde and the H202 are dripped in simultaneously causing a vigorous reaction to occur and who's temperature needs to be kept at 48-55°C with external cooling for 30 minutes. After addition the solution stirs for 1 hour at 20°C to give a yield of catechol at 95%. Looks pretty good don't it?
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