酯分解制备羧酸

hydroxide solution (500 mL) was refluxed for 1 hour. The clear yellowish solution was acidified while hot with a slight excess of concentrated hydrochloric acid to precipitate 3-methylcoumarilic acid. The suspension was cooled to room temperature, and the colorless solid was filtered with suction. The filter cake was resuspended in 500 mL of cold water, stirred vigorously for several minutes, and filtered again with suction. The colorless powder The filter cake was dried in a desiccator under reduced pressure to give a colorless powder (54~57 g, 90~95%) which melts at 192~193°C.

Reference: Organic Syntheses: Coll. Vol. 4, 590

二、甲基的醛氧化

某些情形对于一些特定结构的甲基所需在溶解必要条件下来进行氧化，例如兄碘甲烷和一些 对盐酸不稳定性甲基。有些残基甲基在1 N 硫醛移出必要条件下氧化（一般移出1~2 小时才可），蒸干反应物后可直接以盐的形式来进行下面的中间体，而并不需要进一步精制，此时也可以顾虑用醛来进行氧化。兄碘甲烷一般比Boc 难脱，一般要用50-100%TFA 或4N HCl/Dioxane （请注意：在用HCl/dioxane 来脱除兄碘甲烷时，千万不会在反应物管控时中应运而生甲羟基，乙羟基或其他小位迫的羟基，否则兄碘甲烷会转变为具体来说的甲基。

2.1 、兄丁醛甲基的醛氧化

1-(4-Methoxycarbonyl-2-methylbutanoyl)-L-proline t-butyl ester (3.4 g, 10.8 mmol) was dissolved in trifluoroacetic acid (25 mL) and the resulting solution was kept at room temperature for one hour. The trifluoroacetic acid was removed in vacuo and the residue was used to the next reaction directly.

2.2 、对盐酸不稳定性甲基的醛氧化

A solution of ethyl α-chlorophenylacetate (119 g, 0.6 mol) in glacial acetic acid (238 mL) and concentrated hydrochloric acid (119 mL) was heated under reflux in a hood for 1.5 hours. At the end of the heating period the solution was concentrated by heating in an oil bath at 100°C at reduced pressure (15~20 mmHg) until no further material was distilled. The residue was allowed to cool to room temperature and poured slowly with stirring into 1 L of ice-cold saturated sodium bicarbonate solution. Solid sodium bicarbonate was added in small portions until the solution became neutral to universal indicator paper. The solution was then extracted with two 200 mL portions of ether. The aqueous phase was acidified cautiously with ice-cold 12N sulfuric acid until the mixture was acid to Congo red paper. The oily suspension was extracted with two 200 mL portions of ether. The ether extracts were washed with two 100mL portions of water and dried over 45 g of anhydrous sodium sulfate. The dried ether extract was concentrated on a steam bath until ether was no longer distilled. To the residue there was added 500 mL of warm (50~60°C) concentrated hydrochloric acid (in a hood) and the suspension was allowed to cool with occasional swirling. Crystallization was completed by chilling in ice and the product was collected on a sintered-glass funnel. After the product was dried as much as possible on the funnel it was dried to constant weight in a vacuum desiccator over solid potassium hydroxide to give the dry acid (82~84 g, 80~82%) which melts at 77.5~79.5°C.

Reference: Organic Syntheses. Coll. Vol. 4, 169

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