羧酸盐的酯化反应

有机合成2018-05-15 19:06:39

羧酸盐与卤代烃(或芳侧链的卤代烃)作用生成酯。

M代表金属,X代表卤素,或硫酸根、亚硫酸根、磺酸根。羧酸盐常用的为银盐或铅盐,碱金属盐、碱土金属盐也可以用。X中最活泼的是碘代物,其次溴代物,氯化物一般不常用。硫酸酯等则与酸酸钾、钠反应比较适宜。

反应可以在溶剂中进行,常用溶剂如:苯、甲苯、乙酸、乙醇;也可以不用溶剂,在氧化亚铜、汞盐、乙酸铅或其它催化剂存在下加热(无水条件下)即可酯化。这种方法一般用来酯化比较贵重、较小量的酸,以及芳族和脂族位阻酸。


反应实例


To a solution of (4-bromo-2-cyclohexyloxyphenyl)acetic acid (1.33 g) inN,N-dimethylformamide (13 mL) were added K2CO3 (0.88 g)and iodomethane (1.33 g) at room temperature under nitrogen, and the mixturewas stirred at the same temperature for 2.5 d. The resulting mixture was pouredinto water and the aqueous layer was extracted with a mixture of hexane andethyl acetate (1:1). The organic layer was washed successively with water(twice) and brine, dried over anhydrous magnesium sulfate and evaporated underreduced pressure. The residue was purified by column chromatography on silicagel (hexane/toluene=1:1 to 1:2) to give ethyl(4-bromo-2-cyclohexyloxyphenyl)acetate (1.24 g)。


2-Hydroxy-1-naphthoic acid (470.5 mg, 2.5 mmol) in dry THF (2.5 mL)was treated with LiOH.H2O (104.9 g, 2.5 mol) at room temperature for30 min followed with Me2SO4 (0.24 mL, 2.5 mol), and themixture was heated for 3 h. Solvent was distilled off, and the mixture wasdiluted with saturated aqueous NaHCO3 and the extracted with Et2Oto afford the ester (485.16 mg, 96%) as a white solid .



Trethyl orthoacetate (16.0 mL, 87 mmol) was added dropwise to a solutionof 1-naphthoic acid (5.0 g, 29 mmol) in toluene (35 mL). The reaction mixturewas heated at reflux for 24 h. After the mixture has cooled, 2 N HCl (30 mL)was added. The organic extract was washed with saturated NaHCO3 (30mL) and brine (30 mL) and dried with MgSO4. The solvent was removedin cacuo to give a brown oil. Kugelrohr distillation of the product at 100 (0.45 Torr) gives the ethyl ester (5.15 g, 89%)


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