前文说到甲基芳基醚去甲基化反应常用试剂之一酸性试剂，除了浓HI，HBr，HCl还有一些其他酸性试剂。

2、48% HBr 加入相转移催化剂

     在 48%HBr 中加入相转移催化剂是对仅使用强质子酸如48%HBr 的改进。加入相转移催化剂后，能提高去甲基化的效率，大大缩短反应的时间。此反应是在一个多相体系（水和有机）中进行，可使用的相转移催化剂有四丁基溴化铵，十六碳烷基三丁基溴化磷,四辛基溴化铵，三辛基甲基溴化铵等。对于甲基芳基醚，一般使用5 mol 量的HBr，对于甲基烃基醚，一般使用10 mol 量的HBr；值得注意的是，反应的收率和时间不是依赖于使用那一种相转移催化剂，而是依赖于相转移催化剂的浓度和其在有机相的溶解度。

范例：

Table 1. Cleavage of Ethers with 47% HBr in Presence of Hexadecyltributylphosphonium Bromide

a) Yield of isolated product

Typical Pocedure.Cleavage of Di-n-octyl Ether. Di-n-octyl ether (12.1 g, 0.05 mol), 47% aqueous hydrobromic acid (56mL, 0.5 mol), and hexadecyltributylphosphonium bromide (2.5g, 0.005 mol) are mixed in a flask equipped with a magnetic stirrer and reflux condenser, and heated at 115°C (inner temperature) with stirring for 5 hrs. After this time GLC analysis (SE 30, 3% over chromosorb sulfate, and distilled to give pure 1-bromooctane. The organic layer is separated, dried with sodium sulfate, and distilled to give pure 1-bromooctane; yield: 17.5 g

(91%), bp 88°/torr. By treating the distillation residue with hexane, 2.3 g (92%) of pure phosphonium bromide are recovered, mp 54-56°C. In the case of aryl alkyl ethers, aqueous alkaline extraction of the organic phase affords the corresponding phenol.

3、BBr3, BI3, BCl3

    BBr3 是一种温和、优良的去甲基化试剂，并且不影响分子中的酯基和双键，在许多天然产物的全合成中常使用它。一般使用CH2Cl2, benzene, pentane 作为溶剂，在-78 ℃到 室温下进行。有一点需注意，当底物分子中杂原子数多时，应增加BBr3 量。使用BBr3 有一个最大的缺点是BBr3 对空气敏感，使用时会冒出大量气雾；并在加水后处理时常 出现大量的络合物，此时最好使用其它的方法，否则后处理艰难并导致收率下降。BI3,BCl3 的使用如同BBr3。

范例：

Table 2. Cleavage of Ethers by Boron Tribromide

General Procedure for Cleavage of Ether with BBr3.  A weighed quantity of the ether (usually 15 to 20 g) is introduced into the reaction flask and cooled in an ice-bath. The calculated quantity of boron tribromide is slowly introduced through a dropping funnel. In all cases boron tribromide and ether are allowed to react in the ratio of 1 mol of boron tribromide to 3 mol of ether. After addition of boron tribromide, the reaction mixture is heated on a water bath for 40 min. The alkyl bromide is distilled directly from the reaction mixture. After

removal of the alkyl bromide by distillation, the residure remaining in the flask is hydrolyzed with a minimum amount of 10% sodium hydroxide solution. The resulting solution is acidified with hydrochloric acid and extracted with ether.