Acidity of Alcohols

By the Bronsted definition, an acid is a proton donor. Alcohols are only weakly acidic, comparable to water: water's Ka is about 1.8x10^-16, while alcohols' Ka values fall in the range 10^-16 to 10^-18. Alcohols react with reactive metals such as sodium or aluminium to liberate hydrogen gas and form the corresponding alkoxide -- 2 C2H5-OH + 2 Na gives 2 C2H5-ONa + H2 -- which demonstrates their (weak) acidic character; alcohols do NOT show a comparable reaction with NaOH, unlike phenols. Acid strength falls in the order PRIMARY > SECONDARY > TERTIARY alcohol: the O-H bond's polarity, and hence its tendency to donate a proton, is reduced by the electron-releasing (+I) effect of alkyl groups on the -OH-bearing carbon, and this effect strengthens as more alkyl groups are added going from primary to tertiary (ethanol Ka about 1.3x10^-16; a tertiary alcohol's Ka about 1x10^-18). By the same electro …