Brønsted acid-catalyzed chlorination of aromatic carboxylic acids

Abstract

The chlorination of aromatic carboxylic acids with SOCl₂ has been effectively performed by reacting with a Brønsted acid as the catalyst. Based on this discovery, an efficient catalytic method that is cheaper than traditional catalytic methods was developed. 20 substrates were chlorinated offering excellent yields in a short reaction time. And the SOCl₂/Brønsted acid system has been used in a larger scale preparative reaction. A dual activation mechanism was proposed to prove the irreplaceable system of SOCl₂/Brønsted acid.

Graphical Abstract

Keywords:

• Brønsted acid-catalyzed
• aromatic carboxylic acid
• thionyl chloride
• chlorination

Acknowledgments

We are grateful for the Zhejiang Provincial Key R&D Project (No. 2020C03006 & 2019-ZJ-JS-03 & 2018C03074) and the National Natural Science Foundation of China (No. 22078299).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Notes

1 During our pilot-scale chlorination process of the production of Dinitroamine, the catalyst DMF was accidentally omitted, leading to a rapid reaction in 3–4 h, which was distinctly different from the laboratory test. In the laboratory test, the chlorination of 1-methyl-3,5-dinitrobenzoic acid (1a) would take at least 8-10 h without catalyst. By examining the operation process, it was found that the remained unwashed H₂SO₄ in the reaction still might play the role of catalyst in the chlorination process; While in the laboratory, the residual H₂SO₄ was always sufficiently washed and removed.

2 We investigated the market prices of traditional catalysts (such as DMF, pyridine, BTAC, TBAC, FeCl₃, and FeC₆H₅O₇) and H₂SO₄, and detailed information was attached to the Supplemental Materials (see Figure S1).