vanillin > protocatechualdehyde (aq.HBr/HOAc)

[3base]

berichte der deutschen chemischen gesellschaft, 1908 41 I, 321-324
"ueber eine bequeme entalkylierungsmethode für phenolaether"
r stoermer

hydrobromic acid (specific gravity 1.49)

anisic acid ... 5g in 50mL glacial acetic acid refluxed with
10mL hydrobromic acid gave after 2h 48% of the phenolic acid,
that could be separated from the methylether via fractional
crystallization from water.

vanillin, treated in the same manner, gave after 2h 38% yield
of protocatechualdehyde mp 149°C, that can be separated from
vanillin by toluene.

it is stated explicitly, that with HBr gas saturated glacial
acetic acid in no way takes effect that advantageous like the
named mixture. it has been found in several cases, that such
a solution does not or that it demethylates in much lower level.

"Whatever there is to learn has to be learned the hard way."
Castaneda's teacher Don Juan Matus

[3base]

"protocatechualdehyde ... can be made via different routs; known are e.g.
the method by REIMER-TIEMANN (from pyrocatechol [10]) ...
also the demethylation of vanillin [13] resp. veratrumaldehyd [3]
leads to 3,4-dihydroxybenzaldehyde. by the method of LANGE (1962, [5])
vanillin can be demethylated with high yield (87%) to crystalline
protocatechualdehyd of good purity ..."

 [3] DREYFUS, ger. pat.

Patent DE193958

[Frdl. 9, 161 (1908-10)]

 [5] LANGE R.G., Monsanto Chem. Co. (1962),
     cited in FIESER/FIESER, p 1010-... (see lit. [3])

[10] REIMER und TIEMANN, Ber. 9, 1268 (1876);
     TIEMANN und KOPPE, Ber. 14, 2015 (1881)

[13] TIEMANN und HAARMANN, Ber. 7, 620 (1874)