SYNTHESIS OF ETHERS USING ALKALINE-EARTH METAL-SALTS

Calcium, strontium, and barium alkoxides reacted with primary alkyl ha lides such as hexyl bromide, octyl bromide, and benzyl chloride at 70- 100 degrees C in DMSO-alcohol (1/1). The substitution reaction gave th e corresponding primary alkyl ethers in 72-94% yields. The alkaline ea rth metal salts of ethylene glycol and 2-propyn-1-ol, which have two r eactive points, were heated with benzyl chloride, and gave a mono-subs tituted product exclusively, although a similar reaction of alkali met al salts is known to give both mono- and di-substituted products. On t he other hand, alkaline earth metal phenoxide and naphthyl oxide react ed with primary alkyl substrates in DMSO to afford aryl alkyl ethers i n high yields. Furthermore, secondary alkyl substrates also reacted wi th alkaline earth metal aryl oxides to give secondary alkyl aryl ether s in 56-71% yields. Isopropyl iodide, isopropyl bromide, isopropyl met hanesulfonate, 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 sal ts are much more selective than alkali metal salts in the substitution reactions. Although calcium salts are less reactive than strontium an d barium salts, calcium salts are more selective and useful for organi c synthesis from the viewpoints of safety and cost.