羧酸鹽的酯化反應

羧酸鹽與滷代烴（或芳側鏈的滷代烴）作用生成酯。

M代表金屬，X代表滷素，或硫酸根、亞硫酸根、磺酸根。羧酸鹽常用的為銀鹽或鉛鹽，鹼金屬鹽、鹼土金屬鹽也可以用。X中最活潑的是碘代物，其次溴代物，氯化物一般不常用。硫酸酯等則與酸酸鉀、鈉反應比較適宜。

反應可以在溶劑中進行，常用溶劑如：苯、甲苯、乙酸、乙醇；也可以不用溶劑，在氧化亞銅、汞鹽、乙酸鉛或其它催化劑存在下加熱（無水條件下）即可酯化。這種方法一般用來酯化比較貴重、較小量的酸，以及芳族和脂族位阻酸。

反應實例

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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