Inorganic acid ester is obtained through the reaction between alcohol and oxygen-containing organic acids or inorganic acid to generate esters (inorganic acid ester or organic acid esters) and water reaction. For example, sulfuric acid and ethanol, nitric acid and glycerol or pentaerythritol esters can have esterification reaction to generate important inorganic acids ester. The compound obtained through the dehydration reaction between acid (inorganic and organic acids) and the alcohol is ester. It can be divided into inorganic acid esters (e.g., dimethyl sulfate, methyl hydrogen sulfate, glyceryltrinitrate, tributyl phosphate, etc.), and organic acid esters (e.g., ethyl acetate, vinyl acetate, and [alpha] methyl methacrylate ester, etc.) two categories. But the latter one is more important. In accordance with the intramolecular or intermolecular esterification of hydroxy acid (alcohol acid), it can also be divided into two kinds, lactone and lactide. Ester is generally neutral substance and can be subject to hydrolysis. Carboxylic acid ester can participate in a series of reactions including transesterification (alcoholysis), ammonolysis, reduction (hydrogenolysis) and the Grignard reaction.

Usually refers to a carboxylic acid ester with the general formula being RCOOR ', being the product with the hydrogen in the carboxyl group of carboxylic acid being replaced by hydrocarbon. The names of the esters are based on the names of corresponding carboxylic acid and alcohol or phenol such as "a certain acid ester." The cyclic ester is called lactone.
The chemical properties of ester are similar to acyl halide and acid anhydride. It is prone to have hydrolysis, alcoholysis and aminolysis reaction. The lower esters are aromatic volatile colorless liquid with the high-grade ester being solid. Esters are important solvents and synthetic chemicals with some kinds of ester itself being medicines. Depending on the type of acid, esters can be divided into inorganic and organic esters, such as hydrogen methyl sulfate (CH3OSO3H) for the former one and ethyl acetate CH3COOCH2CH3 for the later one; depending on the type of hydrocarbon, the ester can also be divided into fatty esters and aromatic esters and ring esters; ethyl acetate belongs to fatty esters; the phenyl acetate belongs to aromatic esters; while methyl furoate belongs to cyclic ester.

From the broad definition, the reaction between alcohols and acids for generating ester should be called as esterification. But usually it only refers to acid esterification and the esterification of alcohol is called as acylation. Esterification is reversible with the ester having hydrolysis with water to generate the original alcohol (or phenol) and acid. In general, the esterfication should be conducted in the presence of catalyst (hydrogen ion) and heating conditions, in order to shorten the time required for reaching equilibrium.