Synthesis of Ethers Using Alkaline Earth Metal Salts

Abstract

Calcium, strontium, and barium alkoxides reacted with primary alkyl halides such as hexyl bromide, octyl bromide, and benzyl chloride at 70-100° C in DMSOalcohol (1/1). The substitution reaction gave the corresponding primary alkyl ethers in 72 94% yields. The alkaline earth metal salts of ethylene glycol and 2-pr opyn-1-ol, which have two reactive points, were heated with benzyl chloride, and gave a mono-substituted product exclusively, although a similar reaction of alkali metal salts is known to give both mono and di-substituted products. On the other hand, alkaline earth metal phenoxide and naphthyl oxide reacted with primary alkyl substrates in DMSO to afford aryl alkyl ethers in high yields. Furthermore, secondary alkyl substrates also reacted with alkaline earth metal aryl oxides to give secondary alkyl aryl ethers in 5671% yields. Isopropyl iodide, isopropyl bromide, isopropyl methanesulfonate, s-butyl iodide, and s-butyl methanesulfonate were used as the secondary alkyl substrate. According to the previous study, the reaction of secondary alkyl substrates with sodium alkoxides and aryl oxides gave only 20 30% of ethers. Therefore alkaline earth metal salts are much more selective than alkali metal salts in the substitution reactions. Although calcium salts are less reactive than strontium and barium salts, calcium salts are more selective and useful for organic synthesis from the viewpoints of safety and cost.