50727-06-5

Step 1. Synthesis of 5-hydroxyisoindoline-1,3-dione To a concentrated hydrochloric acid mixture of ammonium carbonate (5.28 g, 54.9 mmol), 4-hydroxyphthalic acid (5.0 g, 27.45 mmol) dissolved in acetic acid (25 mL) was slowly added. The reaction mixture was heated at 120 °C for 45 min, then warmed up to 160 °C for further heating for 2 hours. Upon completion of the reaction, the mixture was concentrated to about 15 mL at 160 °C and then cooled to room temperature. The pH was adjusted to 10 with 1N NaOH solution and subsequently the mixture was cooled to 0 °C and slowly acidified to pH 5 with 1N HCl solution.The resulting precipitate was collected by filtration and dried under reduced pressure to afford 5-hydroxyisoindoline-1,3-dione as a pale yellow powder (3.24 g, 72% yield). The product was characterized by 1H NMR (DMSO-d6): δ 7.00-7.03 (m, 2H), 7.56 (d, J = 9.3 Hz, 1H).

[1] Patent: US2003/144278, 2003, A1
[2] Patent: US2003/181442, 2003, A1
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