[biohacker2020]

Hello.

I am trying to figure out a way to synthesise 2,4-dihydroxybenzoic acid from resorcinol using Kolbe-Schmitt carboxylation. I stumbled upon a paper that used methy magnesium carbonate but I figured it can be done with Kolbe-Schmitt so I started researching and found this two papers:

http://dx.doi.org/10.1002/ceat.201200633

http://dx.doi.org/10.1016/j.ultsonch.2015.05.019

Basically in both experiments CO2 is bubbled through a solution of Resorcinol in water/ethanol and either KOH or KHCO3 is added to the solution under specific temperature. I was thinking perhaps it would be possible to use Sodium Hydroxide instead of KOH and then HCL as this method work very well to produce hydroxybenzoic acid.

Any thoughts? I am looking to form specifically 2,4-dihydroxybenzoic acid and the production of any other isomers is undesirable.

mod edit tidy links

[pgk]

The Vogel’s Textbook of Practical Organic Chemistry (3rd Edition, p. 775) describes the Kolbe-Schmitt synthesis of 2,4-dihydroxybenzoic acid with KHCO3 and good yield, 4-hydroxybenzoic acid with K2CO3 and salicylic acid with C2H5ONa; which can be translated to that “a strong base promotes the formation of the meta- hydroxy-benzoic acid”.
In other words, the use of a strong base, such as NaOH risks to promote the formation of 2,6-dihydroxybenzoic acid from resorcinol.
Hint: Do not be confused by the use of KOH for the Kolbe-Schmitt synthesis of 2,4-dihydroxybenzoic acid from resorcinol “under ultrasonication”, which has a lower energy offer than heat.
http://dx.doi.org/10.1016/j.ultsonch.2015.05.019

[biohacker2020]

Thanks for the reply. Much appreciated.

[biohacker2020]

I am thinking will the reaction with KHCO3 selectively target the benzoid ring if have a an aromatic alkane?

I am trying to carboxylate the resorcinol attached to the alkane chain, without affecting the alkane chain.

[zarhym]

Kolbe-Schmitt carboxylation should work.
But this reaction may be difficult to control since there are many transitional states.
You may need a good base to achieve good selectivity.

[pgk]

Don’t worry about that.
Regardless acidic (Friedel-Crafts) or basic catalysis (Kolbe-Schmitt), alkyl group drives the aromatic substitution to its ortho-, para- position that if being synergistic with the phenol groups, there is no problem, except a slight decrease of the yield, due to the steric hindrance. But even if being at a competitive position with the phenol groups, the 2,4-dihydroxy-alkylbenzoic acid will be formed in preference (but with a slightly lower yield) because the phenoxy- group is a stronger electron donor group than the alkyl one.