Calcium hydroxide
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH). It is a colorless crystal or white powder and is obtained when calcium oxide (called "lime" or "quicklime") is mixed, or slaked with water. It has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater is the common name for a saturated solution of calcium hydroxide.
Hydroxide
The hydroxide ion may act as a base catalyst. The base abstracts a proton from a weak acid to give an intermediate that goes on to react with another reagent. Common substrates for proton abstraction are alcohols, phenols, amines, and carbon acids. The p"K" value for dissociation of a C–H bond is extremely high, but the pK alpha hydrogens of a carbonyl compound are about 3 log units lower. Typical p"K" values are 16.7 for acetaldehyde and 19 for acetone. Dissociation can occur in the presence of a suitable base.
The base should have a p"K" value not less than about 4 log units smaller or the equilibrium will lie almost completely to the left.