Urea, from ammonium cyanate

Ammonium cyanate, urea from, 2 Ammonium ion, acidity of, 921-922 Ammonium salt, IR spectroscopy of. 952-953... 

In the nineteenth century, experiments showed that organic compounds could be synthesized from inorganic compounds. In 1828, the German chemist Friedrich Wohler converted ammonium cyanate, made from ammonia and cyanic acid, to urea simply by heating it in the absence of oxygen. 

Thus it is necessary to pay due attention to the rate constant term, in addition to the concentration factor, if the adequate explanation of the polyelectrolyte influence on chemical reactions is sought. As has been mentioned in the present paper, the polyelectrolyte influence was accounted for in terms of the rate constant change by using the Bronsted equation. Because of the limitation of the Bronsted equation, quantitative discussion was restricted to small influence of polyelectrolyte (as seen from the deceleration effect on the ammonium cyanate-urea conversion). One of the most important future problems in this field is to extend the Bronsted equation to account for such huge polyelectrolyte influences as described above. 

Urea is a colorless, odorless solid, mp. 133 C. It is generally recognized as the first organic compound to be synthesized from inorganic raw materials Wohler synthesized it in 1828 by heating ammonium cyanate. Urea is now made in immense quantities for use as a fertilizer and cattle feed supplement. It is made by reacting carbon dioxide with ammonia under high pressure. Ammonium carbamate is first formed but releases a molecule of water to form urea ... 

Ammonium cyanate, because of its instability in solution, is usually prepared (NHJaSO, + 2KCNO 2NH4CNO + KjSO by mixing aqueous solutions of ammonium sulphate and potassium cyanate. Complete evaporation then gives a mixture of potassium sulphate and urea, from which the urea may be extracted w ith hot absolute ethanol, in which potassium sulphate is insoluble. 

Wohler s classical synthesis of urea from ammonium cyanate may be carried out by evaporating solutions of sodium cyanate and ammonium sulphate ... 

In aqueous solution at 100° the change is reversible and equilibrium is reached when 95 per cent, of the ammonium cyanate has changed into urea. Urea is less soluble in water than is ammonium sulphate, hence if the solution is evaporated, urea commences to separate, the equilibrium is disturbed, more ammonium cyanate is converted into urea to maintain the equilibrium and evfflitually the change into urea becomes almost complete. The urea is isolated from the residue by extraction with boiling methyl or ethyl alcohol. The mechanism of the reaction which is generally accepted involves the dissociation of the ammonium cyanate into ammonia and cyanic acid, and the addition of ammonia to the latter ... 

From the concept of isomerism we can trace the origins of the structural theory—the idea that a precise arrangement of atoms uniquely defines a substance Ammonium cyanate and urea are different compounds because they have different structures To some degree the structural theory was an idea whose time had come Three scientists stand out however for independently proposing the elements of the structural theory August Kekule Archibald S Couper and Alexander M Butlerov... 

Cyanuric acid can also be prepared from HNCO (100). Isocyanic acid [75-13-8] can be synthesized directiy by oxidation of HCN over a silver catalyst (101) or by reaction of H2, CO, and NO (60—75% yield) over palladium or iridium catalysts at 280—450°C (102). Ammonium cyanate and urea are by-products of the latter reaction. 

The hydroxyl derivative of X-CN is cyanic acid HO-CN it cannot be prepared pure due to rapid decomposition but it is probably present to the extent of about 3% when its tautomer, isocyanic acid (HNCO) is prepared from sodium cyanate and HCI. HNCO rapidly trimerizes to cyanuric acid (Fig. 8.25) from which it can be regenerated by pyrolysis. It is a fairly strong acid (Ka 1.2 x 10 at 0°) freezing at —86.8° and boiling at 23.5°C. Thermolysis of urea is an alternative route to HNCO and (HNCO)3 the reverse reaction, involving the isomerization of ammonium cyanate, is the clas.sic synthesis of urea by F. Wohler (1828) ... 

Unsaturation, degree of. 174 Upfield, (NMR), 445 Uracil, structure of, 1101 Urea, from ammonium cyanate, 2 Urethane, 1214 Uric acid, pKa of, 778... 

The naturally occurring compound urea, CO(NH,), was first synthesized by Friedrich Wohler in Germany in 1828 by heating ammonium cyanate. This synthesis was a significant event because it was the first time that an organic compound had been produced from an inorganic substance. Urea may also be made by the reaction of carbon dioxide and ammonia ... 

The term organic chemistry was first used by the Swedish chemist Berzelius in 1807 (Larsson, 1981). He coined the name to describe the chemistry of substances derived from living matter. Berzelius was a staunch believer in the vis vitalis theory, which held that such substances were endowed with a mystical vital force that precluded their synthesis in the laboratory from materials of mineral origin. Ironically, it was a student of Berzelius, Wohler, who heralded the demise of vitalism with his synthesis of urea from ammonium cyanate (Wohler, 1928). In a letter to Berzelius in 1828, Wohler wrote I must tell you that I can make urea without requiring kidneys, or even an animal, whether a human being or a dog . 

The rate of production of urea, (NH CO, from ammonium cyanate increases by a factor of 4 when the concentration of ammonium cyanate is doubled. Show whether this is accounted for by the following mechanism ... 

Wohler s preparation of urea from ammonium cyanate, which could in principle be derived totally from inorganic constituents, is cited as an early demonstration (1828) that living cells were not obligatorily required for the synthesis of natural products. I can prepare urea without requiring a kidney or an animal—either man or dog. Three years after the death of Pasteur the finding by Hans and Edouard Buchner (1897) that fermentation still occured in a cell-free extract from yeast and so did not require the presence of organized cells, was virtually the final nail in the coffin for vitalism and an essential preliminary to the study of intermediary metabolism (Chapter 4). 

Wohler. Synthesis of urea from ammonium cyanate. Microscopic examination of plant and animal cells by Dutrochet, Schlieden, and Schwann led to acceptance of the cellular origin of all tissues. ... 

Until the mid-eighteenth century, scientists believed organic compounds came only from live plants and animals. They reasoned that organisms possessed a vital force that enabled them to produce organic compounds. The first serious blow to this theory of vitalism, which marked the beginning of modern organic chemistry, occurred when Friedrich Wohler (1800-1882) synthesized urea from the two inorganic substances lead cyanate and ammonium hydroxide ... 

The reaction can undoubtedly be explained by the formation of an equilibrium mixture of urea and ammonium cyanate in boiling solution the ammonium cyanate reacts at the moment of its formation with aniline hydrochloride, yielding phenylurea. This latter compound also undergoes a secondary reaction, involving the intermediate formation of phenyl isocyanate, which reacts with aniline hydrochloride forming carbanilide so that in order to obtain the best yield it is necessary to interrupt the process from time to time and remove the phenylurea first formed. 

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