Cyanate, ammonium

The preparation of ammonium cyanate has been dealt with previously in this series. The method is, however, somewhat hazardous and time-consuming. Furthermore, ammonium cyanate is not particularly stable, rearranging to urea upon standing. The method described below allows for the preparation of ammonium cyanate with a minimum amount of effort, thus avoiding the need to prepare large quantities at any one time. If necessary, the method can be scaled up to prepare whatever quantity is desired. 

In a dry-box, 31.2 g (0.41 mole) of anhydrous ammonium thiocyanate dissolved in 500 ml of anhydrous acetonitrile is combined with a solution of 70.5 g (0.41 mole) of tetraethylammonium cyanate in 200 ml of acetonitrile. The white precipitate which immediately forms is collected on a fine-fritted sin-tered-glass crucible by suction filtration and washed several times with acetonitrile. The product is dried for hr under a dynamic vacuum at ambient temperature. The yield, based on tetraethylammonium cyanate, is 19.7 g (80%). Anal Calcd. for CH4N2O C, 20.00 H, 6.71 N, 46.65 O, 26.64. Found C, 20.2 H, 6.5 N, 46.5 O, 26.8. 

Ammonium cyanate is a white solid, which rearranges to urea upon prolonged storage or heating. It is extremely soluble in water, slightly soluble in acetonitrile, ethanol, and chloroform, and insoluble in benzene and diethyl ether. The infrared spectrum and x-ray diffraction powder pattern are most useful for determining the absence of urea in the final product. Nujol mulls of pure ammonium cyanate exhibit absorptions at 3160 (s), 2190 (s), 1334 (m), 1243 (m), and 640 (m) cm-i and are free of any infrared-active bands in the regions characteristic of urea, that is, 3456 and 1683 cm-i. 

Ellestad, P. Klaeboe, E. Tucker, and J. Songstad, Acta Chem. Scand., 26,1721 (1972). 

Inorganic Syntheses, Volume XVI Edited by Fred Basolo Copyright 1976 by McGraw-Hill, Inc. 

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Urea (the diamide of carbonic acid) can be prepared by the historic method of Wohler. When an aqueous solution of ammonium cyanate is allowed to stand, the cyanate undergoes molecular rearrangement to urea, and an equilibrium mixture containing about 93% of urea is thus formed. Urea is... 

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. 

These substances, having the formula CjHjNHCONH, and OC(NHCjH6)j respectively, are both formed when an aqueous solution of urea and aniline hydrochloride is heated. Their subsequent separation is based on the fact that diphenylurca is insoluble in boiling water, whereas monophenylurea is readily soluble. The formation of these compounds can be explained as follows. When urea is dissolved in water, a small proportion of it undergoes molecular rearrangement back to ammonium cyanate, an equilibrium thus being formed. 

The ammonium cyanate then reacts with the aniline hydrochloride giving aniline cyanate which, as in the previous preparation, gives in turn monophenylurea. 

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 ... 

Thiourea (II) may be obtained from ammonium thiocyanate (I) by an isomeric change analogous to ammonium cyanate, but the equilibrium relationship is very different (compare Section 111,133) ... 

The mechanism of the reaction involves the intermediate formation of an amine cyanate (see previous Section) in aqueous solution urea behaves as an equifi-brium mixture with ammonium cyanate ... 

What particularly seemed to excite Wohler and his mentor Berzelius about this experiment had very little to do with vitalism Berzelius was interested m cases m which two clearly different materials had the same elemental composition and he invented the term isomerism to define it The fact that an inorganic compound (ammonium cyanate) of molecular formula CH4N2O could be transformed into an organic compound (urea) of the same molecular formula had an important bearing on the concept of isomerism... 

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... 

In the introduction we noted that both Berzelius and Wohler were fascinated by the fact that two different compounds with different properties ammonium cyanate and urea pos sessed exactly the same molecular formula CH4N2O Berzelius had studied examples of similar phenomena earlier and invented the word isomer to describe different compounds that have the same molecular formula... 

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) ... 

Little more than a decade later, the vitalistic theory suffered still further when Friedrich Wohler discovered in 1828 that it was possible to convert the "inorganic" salt ammonium cyanate into the "organic" substance urea, which had previously been found in human urine. 

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

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

Ammonium cyanate, NTUNCO, in water rearranges to produce urea, a common fertilizer, (NH2)2CO ... 

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 . 

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