該類反應屬于典型的親核取代反應，按照反應歷程分兩種類型：單分子的親核取代反應(SN1)和雙分子的親核取代反應(SN2)。
一、單分子的親核取代反應(SN1)
單分子的親核取代反應(SN1)歷程中反應速度只與反應底物鹵代物的濃度有關，與堿的濃度無關。因此，從動力學上講它是一個一級反應。例如溴代叔丁烷的水解：
此反應是分兩步進行,第一步是反應物在溶劑中首先離解成叔丁基正離子和溴負離子：
第二步則是生成的叔丁基碳正離子再與HO-作用,生成叔丁醇：
二、雙分子的親核取代反應(SN2)
另一類為雙分子的親核取代反應(SN2)，它的水解速度與鹵代烴的濃度和堿的濃度成正比，因此該類反應是一個二級反應。例如溴甲烷的水解：
反應過程中C-Br鍵的斷裂與C-O鍵的形成是同時進行的。當進攻試劑HO-從離去基團Br的背后進攻中心碳原子時(這是比較有利的進攻方式)。此時，HO- 、Br和中心碳原子幾乎處于同一直線上，形成一個“過渡態(tài)”。而中間碳上的三個H原子則處于垂直于這個直線的平面上，當HO-與中心碳原子進一步接近，最終形成一個穩(wěn)定的C-O鍵時，C-Br也徹底斷裂，生成Br-離子，同時中心碳上的三個H原子也向后翻轉，使碳原子恢復成原來的sp3雜化狀態(tài)。從立體化學上來看，在反應過程中發(fā)生了構型的轉化，使得產(chǎn)物與原來的反應物構型正好相反，這也正是在1893年發(fā)現(xiàn)的瓦爾登(Walden)轉化。另外許多反應，鹵代物直接水解并不是太好，因此一般先用AcO－取代，而后再水解得到相應的醇。
反應實例
一、鹵代烴的水解反應制備醇示例
Combined the material with 75%DMF, 1.2 equiv of NaOH were stirred for 30 min at room temperature. Andrecrystallized from MeOH to give the colourless needles (95% yield).
【J.Org.Chem.1982, 47, 4024-4029】
二、鹵代烴的水解反應制備醇示例
Water (100mL) and CaCO3(18g, 180mmol) were added into a solution of 10.5g (35mmol) of1-bromo-2-(bromomethyl)naphthalene in 100mL of p-dioxane ,and the mixture wasrefluxed for 10hrs. The solution was cooled and the dioxane removed underreduced pressure. Methylene chloride (200mL) was added followed by treatmentwith dilute HCl until all solid had dissolved .The organic phase was separated,washed with NaHCO3 solution, dried over MgSO4, and filtered. Removalof the solvent left a white solid, which was recrystallized from hexane to give7.9g of (1-bromonaphthalen-2-yl)methanol (95% yield).
【J.Org.Chem.1986, 51, 3762-3768】
三、鹵代烴的乙酰氧基取代示例
A 150 g portion of thethus obtained 1-chloro-(E,Z)-7,9-dodecadiene was admixed with 150 g ofanhydrous potassium ace-tate and 100 g of acetic acid and the mixture washeated at 160 .deg.C for 6 hours under agitation in an atmosphere of nitrogento convert the chloride into acetate.. After completion of thereaction, the reaction mixture was poured into a large volume of water and theorganic phase taken by phase separation was distilled under reduced pressure togive 80 g of 7,9-dodecadienyl acetate of which the purity of the E,Z-isomer wasat least 75percent.
【Patent; Shin-Etsu Chemical Co., Ltd.; Publ.: EP241335 A1 (1987/10/14),Appl.: EP1987-400592 (1987/03/17)】
四、酯水解得到相應的醇示例
2N sodium hydroxide (40 ml) was added to a solution of 5-(2-acetoxyethyl)-2-methyl-4-phenyloxazole (16.6 g) in methanol (40 ml) and the mixture was stirred for 30 minutes, diluted with water and extracted withethyl acetate..The ethyl acetate layer was washed with water and dried overanhydrous magnesium sulfate.
The solvent was thendistilled off and the residue wwas purified by silica gel chromatography(silica gel: 190 g, eluent: isopropyl ether) to give an oil of5-(2-hydroxyethyl)-2-methyl-4-phenyloxazole, yield 11.7 g (84.8percent).NMR(CDCl3) : 2.40 (3H, s), 3.07 (2H, t), 3.20 (1H, broad), 3.97 (2H, broad),7.23-7.80 (5H, m).
【Patent;Takeda Chemical Industries, Ltd.; Publ.: US4596816 A1 (1986/06/24), Appl.:US198】
本文非原創(chuàng)內(nèi)容，版權歸原作者所有。
