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EXAMPLE 4 Preparation of 5-Methylisoxazole-4-Carboxylic Acid A two-necked flask fitted with mechanical stirrer and a horizontal condenser for distillation was charged with 40.0 g of crude Ethyl-5-methylisoxazole-4-carboxylate and 44 g of 60% sulfuric acid and the mixture was heated to 85 C. with continuous distillation of ethanol from the reaction product. After four hours of heating at 85 C., TLC showed the complete disappearance of the upper spot of ester. The mixture was allowed to cool in the refrigerator and the solid acid was filtered (16.5 g) Filtrate kept at room temperature for second crop. Acid was crystallized in 60 mL 2% acetic acid-Toluene to obtain about 99.9% pure acid (9.5 g). Mother liquor of the final crystallization was kept for second crop. Crystallization was accomplished by: The crude acid was taken in 2% acetic acid-toluene mixture and heated for 30 minutes. Brown oil was separated at the bottom of the flask. The clear organic phase was neatly transferred and kept for crystallization.
60%
With sulfuric acid; In water; at 20℃; for 20.0h;Reflux;
Ethyl-5-methylisoxazole-4-carboxylate 7 g (0.045 mol) was heated under reflux in aqueous sulphuric acid (20 % v/v, 30 ml) for 16 hr followed by cooling to room temperature with stirring for 4 h. The crystallized solid product was filtered and washed using toluene followed by water and dried. The product then was crystallized from ethanol to produce 3.5 g (60 %) of 5-Methylisoxazole-4-carboxylic acid as a white solid, mp. 147-148 C (reported mp. 144-147 C).
With sulfuric acid; In water; for 16.0h;Heating / reflux;
S-MethyIisoxazole-4-carboxyiic acid:Ethyl-5-methylisoxazole-4-carboxylate 72.58 g (0.47 mol) was taken in 20% v/v aqueous sulphuric acid (193.5 ml) and refluxed for 16 hours. Toluene (73 ml) was added at 90 0C, cooled to 25 to 35 0C and stirred for 4 hours. The crystallized solid product was filtered and washed with toluene (2x36 ml) followed by water (2x72.5 ml). The product was dried under vacuum to get 27.2 g of 5-Methylisoxazole-4-carboxylic acid as an off white solid with 99.5 % HPLC purity having isomeric impurity 0.27 %
In hydrogenchloride;
(iii) 5-Methylisoxazol-4-yl carboxylic acid <strong>[51135-73-0]Ethyl 5-methylisoxazol-4-yl carboxylate</strong> (65 g) was heated under reflux in 10 M HCl (500 ml) for 3 hours. On cooling the product crystallized out. This was filtered and dried giving 42 g of a white crystalline solid, m.p. 134-136C.
In hydrogenchloride;
(iii) 5-Methylisoxazol-4-yl carboxylic acid <strong>[51135-73-0]Ethyl 5-methylisoxazol-4-yl carboxylate</strong> (65 g) was heated under reflux in 10M HCl (500 ml) for 3 hours. On cooling the product crystallized out. This was filtered and dried giving 42 g of a white crystalline solid, m.p. 134-136 C.
In hydrogenchloride;
(iii) 5-Methylisoxazol-4-yl carboxylic acid <strong>[51135-73-0]Ethyl 5-methylisoxazol-4-yl carboxylate</strong> (65 g) was heated under reflux in 10 M HCl (500 ml) for 3 hours. On cooling the product crystallized out. This was filtered and dried giving 42 g of a white crystalline solid, m.p. 134-136 C.
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