Protocatechualdehyde From Pyrocatechol

This is a nifty little way to turn catechol or guaiacol into protocate-chualdehyde or vanillin using what is called the Riemer-Tiemann reaction [137 p824, 138], It is a really ancient reaction and only works on benzene molecules that have an OH group. One needs to use KOH instead of NaOH because it is better at promoting para substitutions (don't ask). And if one is going to make vanillin from guaiacol then there needs to be a little ethanol in the reaction as well.

Pyrocatechol Protocatechualdehyde

Pyrocatechol Protocatechualdehyde

To proceed one can merely throw all the ingredients into a reaction flask and reflux for 5 hours or one can do the more prudent way as follows. Using the same apparatus in fig. 15 one places 400g KOH and 400mL dH20 and heats it slightly with stirring to dissolve the salt. Next, 110g of catechol or 125g guaiacol is added and slightly heated to dissolve. The condenser and addition are attached and the temperature of the reaction flask is brought to 70°C in an oil bath. 240g (160mL) chloroform is slowly dripped from the separatory funnel into the reaction mix over a period of 3 hours during which time the solution will blacken and a thick brown sludge will form. After addition, the stuff is poured into 500mL hot water, cooled and carefully acidified with concentrated H2S04 or HCI. The whole mix is vacuum filtered from the tarry resin, extracted with ether, the ether washed with water, dried and vacuum distilled to give protocatechualdehyde or vanillin (yield=70%).

When making vanillin from guaiacol the chemist can smell success because the product will have an intense vanilla odor. One can even flavor cookies with the stuff (true!). This Riemer-Tiemann method is also an excellent way to get salicylal-dehyde from phenol in yields of up to 50%. The chemist does everything the same except uses NaOH instead of KOH.

Continue reading here: Allylbenzene From Benzene

Was this article helpful?

0 0