Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Esters, in organic chemistry, 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; Organic Chemistry).

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.

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. See also Fats and Oils.