92379-42-5

Preparation by reaction of 2,3,4-trihydroxybenzoic acid with resorcinol,
? in the presence of zinc chloride and phosphorous oxychloride at 70–80° for 1.5 h (65%) ;
? in the presence of zinc chloride and a mixture of polyphosphoric acid/85% phosphoric acid (60:40) at 27°. Then, during 2h, phosphorous trichloride was added between 27° and 37° and the mixture heated at 60° for 16h.