Ammonium cyanate, conversion

The interpretation in terms of the dehydration turns out to be useful also for the deceleration effect by polyelectrolytes observed for the ammonium cyanate-urea conversion. In this case, AW was hardly affected by polyelectrolyte addition whereas AS was decreased. For example JH and AS" were 22.9 kcal mole and — 2 e.u. in the absence of polyelectrolytes. If sodium polyacrylate (NaPAA) was added at a concentration of 0.1 equiv 1 these parameters were 20.3 kcal mole and — 12e.u. [22]. ... 

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. 

A more quantitative discussion will be given below for the ammonium cyanate-urea conversion. 

His student, Wohler (1800-1882), described (Wohler, F. Ann. Phys. Chem., 15128,88,254) the thermal conversion of the inorganic salt ammonium cyanate (NIL OCtN ) to urea (H2NCONH2), an organic substance isolated from urine. This work has been considered an important step in discrediting the then current concept of a vital force (vitalism) supposedly possessed by living systems and their components and otherwise absent. 

Carbon.— The use of isotopes in studies of the mechanisms of reactions of carbon dioxide or carbonates has been reviewed. Measurements using and give a rate constant of 1141 mol s" for the exchange reaction between carbon dioxide and carbonate ion at 25 °C the same techniques have been applied to the bovine carbonic anhydrase-catalysed exchange between carbon dioxide, its related species, and water.The decomposition rates of the alkyl monocarbonates in aqueous alkali and the effect of polyelectrolytes on the conversion of ammonium cyanate into urea have been reported. The application of calculations originally used for 5 b2 processes to the classical Sn2 halide ion-alkyl halide exchange reaction accounts quantitatively for the relative reactivities in terms of steric effects alone it is not necessary to invoke polar effects. Some further evidence for ion-pair intermediates in Sn2 substitutions has been obtained. ... 

Interest continues in the effects of micellar agents on rates of inorganic reactions. Aquation of oxalato-cobalt(m) and -chromium(iii) complexes is mentioned in a review of reversed micellar systems predicted and actual rates have been compared for a variety of reactions, including the mercury(n)-catalysed aquation of [CoX(NH3)g] + cations. Micellar effects on uncatalysed aquation of cis- and of tra j -[CoCl2(en)2]+ are small (as expected) but real. Other reactions for which the kinetic consequences of micelle or polyelectrolyte addition have been d cribed include complex formation from nickel(ii), the conversion of ammonium cyanate into urea, and the hydrolysis of pyrophosphate. ... 

Finally in this section we note a kinetic study of one of the classic reactions of chemistry, the conversion of ammonium cyanate into urea. The mechanism in DMSO is similar to that in water. A side reaction leading to NH2CONHCONH2 is thought to involve a cyanic acid dimer. 

The conversion of ammonium cyanate into urea has been... 

Faneti/ole (122) is a biological response modifier with significant immunosuppressant activity It can be synthesized by conversion of 2 phen> lethylamine (120) with ammonium thio cyanate to the corresponding thiourea analogue 121 The synthesis of faneli/ole (122) concludes by thiazole nng formation of 121 by reaction with phenacylbromide Thus its synthesis involves use of the classic Hantzsch procedure in which a bromoacetone analogue and an appropriate thio urea denvative are reacted 143]... 

Equation (1) shows the simple conversion of a quaternary ammonium anion exchange resin from the chloride form to the cyanate form. Equation (2) shows the reaction of the resin in the cyanate form with hydroxylamine hydrochloride whereby hydroxyurea is formed and the anion Cl is retained by the quaternary resin. 

The analysis of cyanate is based on its total conversion to an ammonium salt. This is achieved by heating the acidified sample. The reaction is shown below ... 

More recently, Kim et al. combined the copper-catalyzed C—H and C—B bond activation with the copper-catalyzed generation of cyanide anion in one pot to develop an efficient synthesis of aryl nitriles (Scheme 5.81) [83], which are important both in the pharmaceutical industry and in organic synthesis. In this cyanation reaction, ammonium iodide and DMF were used as the source of nitrogen and carbon atom of the cyano unit, respectively (Scheme 5.82). It is assumed that DMF is initially oxidized to its iminium species A upon the reduction of Cu(II) salts to Cu(I). Cyanide ion is envisioned to form on the reaction of A with anunonia, presumably via an amidinyl species B. The reaction is believed to proceed via a two-step process initial iodination and then cyanation. In the first step, the key intermediate iodoarene C is formed through the reaction of boronates with certain plausible iodide sources, such as NH I or the in situ-generated Cul and where copper species facilitate its conversion in the latter two cases. In the second step, cyanation of C takes place presumably upon the reaction with either cyanide anion under copper-mediated... 

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