Esters, in organic chemistry, are compounds formed (along with water), by the reaction of acids and alcohols. Because this process is analogous to the neutralization of an acid by a base in salt formation, esters were formerly called ethereal salts. This term is misleading because esters, unlike salts, are not ionized in solution (see acids and bases).
Esters can be formed from both organic and inorganic acids. For example, the simple ester ethyl nitrate may be obtained from ethyl alcohol and nitric acid (an inorganic acid), and the ester ethyl acetate may be obtained from ethyl alcohol and acetic acid (an organic acid). Another method of preparing esters is to employ not the acid itself but its chloride. For example, ethyl acetate may be prepared by the action of alcohol upon acetyl chloride, the chloride of acetic acid. Another important method of preparation is by the reaction of the silver salts of acids with an alkyl halide (usually iodine). For example, ethyl acetate may be prepared from silver acetate and ethyl iodide.
Esters are broken up by the action of water into their component acids and alcohols, a reaction greatly speeded by the presence of acids. For example, ethyl acetate is broken up into acetic acid and ethyl alcohol. The conversion of an acid into an ester is termed esterification. The reaction between an ester and a metallic base is known as saponification (see soap). When the decomposition of an ester occurs upon its reaction with water, the ester is said to be hydrolyzed.
The esters of organic acids are usually colorless, neutral liquids, pleasant-smelling and generally insoluble in water but readily soluble in organic solvents. Many esters have a fruity odor and are prepared synthetically in large quantities for commercial use as artificial fruit essences and other flavorings and as components of perfumes (see essential oils).
All natural fats and oils (other than mineral oils) and most waxes are mixtures of esters. For example, esters are the principal constituents of beef fat (tallow), hog fat (lard), fish oils (including cod-liver oil), and flaxseed oil (linseed oil). Esters of cetyl alcohol are found in the head oil of the sperm whale, and esters of myricyl alcohol in beeswax. Nitroglycerin, an important explosive, is an ester.
Esters such as amyl acetate (banana oil), ethyl acetate, and cyclohexanol acetate are the principal solvents for lacquer preparations. Other esters, such as dibutyl phthalate and tricresyl phosphate, are used as plasticizers in lacquers. Amyl acetate is employed as odor bait in grasshopper poisons, and several of the formates are good fumigants. Esters also have an important function in organic synthesis.
Esters have important medical uses. Ethyl nitrite is a diuretic and an antipyretic. Amyl nitrite is used in the treatment of asthma and epileptic convulsions as an antispasmodic. Nitroglycerin and amyl nitrite both cause blood-vessel dilation thereby lowering blood pressure. Ethyl chaulmoograte has been used in the treatment of leprosy. Dimethyl sulfate (often used in organic synthesis as a methylating agent) and diethyl sulfate are extremely dangerous in vapor form and must be handled cautiously.
Many additives are in the form of esters when added to the formulated oil, but carboxylic acid esters (and the sub-classes di-esters and polyol esters) are contained in fully formulated synthetic oils. Most Group III oils and PAO based oils need a small amount of ester for seal swell, increased detergency, better oxidative stability, greater VI, and increased additive solubility.
The two most common polyol esters for automotive applications are TMP (trimethylpropane) and DPE (DiPentaerythritol) PE (Pentaerythritol) or similar. Some di-esters are used in non-detergent compressor fluids, and NEO-Oil uses these as bases exclusively.
There are over 175 di-esters and over 250 polyol esters of last count.
A good overall description of esters for ester lubricating fluids can be found at:http://www.hatcocorporation.com/pages/about_esters.html
Added: Carboxylic Acid Esters
Esters are created by a process called, "esterification," the reaction of alcohols or phenols with acids. For example, react tricresyl phosphate acid with an alcohol called n-butyl alcohol and the result is an ester product called "Neutra," a fuel system and crankcase cleaner.
A carboxylic acid is a general term for a number of acids with a specific molecular arrangement. A carboxylic ester can be made with one of over 120 carboxylic acids. Carboxylic acids may be used to form dibasic esters (as in NEO base oils)and polyol esters such as TMP and PE, which are used in Amsoil and Redline oils, respectively.
Hydroxyalkyl Carboxylic ester is actually a "lactone," a cyclic ester made from the salt of a hydroxy acid.
This ester is used in many motor oil formulations that contain PAO(s) and is used to increase the VI, cause a slight seal swell, adds miscibility (mixibility) for additives, increases oxidative stability, and acts as a Friction Modifier. [ January 04, 2003, 12:37 AM: Message edited by: MolaKule ]