ORGANIC CHEMISTRY Chapter 16 HCi(g) OH OEt Etoh CH3 CH=O + EtOH- CH3CH CH2CH H,o OEt HCl(g) OEt Hemiacetal(半缩醛 Acetal(缩醛) Catalyst: HCl(g), TsOH/C6H6, HCl/EtO o Most open-chain hemiacetals are not sufficiently stable to allow their isolation g Cyclic hemiacetals with five- or Six-membered rings however, are usually much more stable OH HOCHCHCHCH=O Department of Chemistry, Xiamen UniversityORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 16 CH3CH O + EtOH CH3CH OH OEt HCl (g) Hemiacetal (半缩醛) HCl (g) CH3CH OEt OEt + H2O Acetal (缩醛) EtOH Catalyst: HCl (g) , TsOH / C6H6 , HCl / Et2O Most open-chain hemiacetals are not sufficiently stable to allow their isolation. Cyclic hemiacetals with five- or six-membered rings, however, are usually much more stable: HOCH2CH2CH2CH O O OH