Urea diamide is carbonic acid. Its formula is H2NCONH2. Urea has important uses as a fertilizer and food supplement, as well as a raw material for the production of plastic and medicine. It is a colorless, crystalline substance that melts at 132.7 °C (271 °F) and decomposes before boiling.
Urea is the nitrogenous end product of the metabolic breakdown of proteins in all mammals and some fish. This substance is present not only in the urine of all mammals but also in their blood, bile, milk and sweat. During the breakdown of proteins, amino groups (NH2) are removed from amino acids that make up part of proteins. These amino groups are converted to ammonia (NH3), which is toxic to the body and therefore must be converted to urea by the liver. Urea then goes to the kidneys and is finally excreted through urine.
Urea was first isolated from urine in 1773 by the French chemist Hilaire-Marin Roel. Its preparation by the German chemist Friedrich Weiler from ammonium cyanate in 1828 was the first accepted laboratory synthesis of a natural organic compound from minerals. Urea is currently commercially prepared in large quantities from liquid ammonia and liquid carbon dioxide. The two substances combine under high pressures and temperatures to form ammonium carbamate, which then decomposes at much lower pressures to produce urea and water.
Since its nitrogen content is high and easily converted into ammonia in the soil, urea is one of the most concentrated nitrogen fertilizers. It is an inexpensive compound that is used in mixed fertilizers as well as alone in the soil or sprayed on foliage. With formaldehyde, it gives methylene-urea fertilizers that release nitrogen slowly, continuously and uniformly, and a full year’s storage is consumed at one time. Although urea nitrogen is in a non-protein form, it can be used by ruminant animals (cattle, sheep) and a significant part of the protein required by these animals can be provided in this way. The use of urea to make urea-formaldehyde resin is second in importance after its use as a fertilizer. Large amounts of urea are also used for the synthesis of barbiturates.
Urea reacts with alcohols to produce urethanes and with malonic esters to produce barbituric acid. With some straight-chain aliphatic hydrocarbons and their derivatives, urea forms crystalline compounds that are useful for the purification of existing materials.
