110g hydroquinone (1mol)
150g KOH (2.7 mol)
412g NaBr (4mol)
250ml CH3OH (5mol)
230ml 93% H2SO4 (4mol)
In a 1L RBF flask equipped with a dropping funnel and set up for distillation, methanol and sulfuric acid were slowly mixed together with cooling, and dropped onto a boiling (saturated) solution of sodium bromide over the course of two hours. The water/methanol/HBr (very little formed) vapors were condensed into a sealed flask, and the methyl bromide was collected with a plastic tube connected to the vacuum adapter, which led directly into a solution of hydroquinone in methanol. The methyl bromide was first slowly released to displace the oxygen in the flask, and potassium hydroxide (flake) then quickly added with *good* stirring while cooling the flask on ice bath. Methyl bromide was then generated (controlled by rate of MeOH/H2SO4 addition) more rapidly and driven through the solution until the supply was exhausted (2 hours), with vigorous stirring.
The solution first turns brownish (oxidation of hydroquinone) with a yellow tint (phenoxide of 4-methoxyphenol) and eventually a large mass of whitish crystals form (potassium bromide).
The potassium bromide was filtered (the solution is completely neutral at the end), washed with methanol and dried. 250g was recovered (79% recovery).
About half the methanol was then evaporated (~200ml) and the remains were quenched with 1.5L water and cooled to 5°C. The precipitated clear/white crystals were then filtered, washed a few times with warm water, vacuum filtered and dried.
Yield: 114g (83% yield)
The obtained DMB melts at 54-56*C.