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The general procedure for the synthesis of ethyl 2,3-dihydroxybenzoate from 2,3-dihydroxybenzoic acid is as follows: 1. 2,3-dihydroxybenzoic acid (994 g), ethanol (3.8 L) and concentrated sulfuric acid (320 g) were added in a reactor, and the mixture was heated to reflux and kept reacting for 44 hours. 2. Upon completion of the reaction, some of the solvent was removed by distillation, after which the reaction solution was cooled to room temperature and stirred overnight. 3. the reaction solution was further cooled to 0-5°C (ice/water bath conditions) and water (5.6 L) was slowly added to promote crystallization. 4. The mixture was left to age and when the crystals were completely precipitated, filtration was carried out and the crystals were washed with water to remove residual acid and solvent. 5. The resulting wet crystals were dried under suitable conditions to give ethyl 2,3-dihydroxybenzoate (1002 g, 85% yield) with a melting point of 66.0-67.2°C. The mixture was then dried over a period of time to obtain ethyl 2,3-dihydroxybenzoate.

[1] Patent: US6172062, 2001, B2
[2] Journal fuer Praktische Chemie (Leipzig), 1891, vol. 44, p. 1,2
[3] Journal of the American Chemical Society, 2017, vol. 139, # 46, p. 16959 - 16966