Esters are organic compounds that are derived from carboxylic acids. The carboxyl group –COOH is contained in a carboxylic acid. The hydrogen in this group is being replaced by a hydrocarbon group in esters. These hydrocarbon groups could be a methyl, ethyl, or phenyl group. Esters have a characteristic pleasant, fruity odor and are common in organic and biological materials. They are used mostly in the flavor and fragrance industry.
Esters are formed from the reaction of two reactants which are alcohols and acids in an esterification reaction. Fischer esterification is the classic synthesis of producing esters. This involves the treatment of carboxylic acid with an alcohol and a dehydrating agent. Sulfuric acid serves as catalyst to hasten this esterification process.
Acyl chlorides and acid anhydrides alcoholysis is another way to produce esters. Acyl chlorides and acid anhydrides react with alcohols to produce esters. Anydrous conditions are recommended since both acyl chlorides and acid anhydrides react with water.
Carbon, aluminum, and stainless steel tanks are suitable in storing of esters. A storage tank lined with a baked phenolic resin should be used if there is critical product quality and if it is detrimental to produce end-use with trace iron pickup. Esters are characterized with high volatility and high flammability. Both low boiling point and high boiling point esters should be stored under dry nitrogen to exclude air and moisture from the storage tank.
It is adequate to have transfer lines of carbon steel. It is recommended that esters use an explosion-proof motor driven centrifugal pump. Heating of outside tanks and lines is not necessary since esters have low freezing points and low viscosities.
Most common elastomers however are not compatible with esters.
Production of perfumes, essential oils, and pheromones use a wide variety of esters. A few number of esters have been useful in severe applications on the environment when it comes to synthetic lubrication.
Esters low temperature flowability and clean high temperature operation has brought their exclusive use in jet engine lubricants. Esters also play a role as synthetic refrigeration lubricants in CFC replacement refrigerants. Low and high temperature performance is improved with the miscibility of esters with HFC because of their characteristic branching and polarity.
Esters are widely used in automotive applications. Due to higher lubrication properties, esters usually are combined with Polyalphaolefins (PAOs) in full synthetic motor oils to solubilize additives, balance the effect on seals, reduce volatility, and improve efficiency of energy.