Cyanates, formation

N-bridging cyanate in low yields (17-23% after heating for 24 h Scheme 11). Conversion was found to proceed at comparable rates in ethanol or acetonitrile, and it was thus concluded that hydrolytic processes by traces of water do not play a role. Cyanate formation also was observed with Af-methylurea or 7/,7/-dimethylurea, but not with Af,A -dimethylurea or tetramethylurea, which shows that at least one NH2 group is essential for the elimination reaction to occur. A possible interpretation is that bridging of urea over the binuclear core through its O atom and one amino N atom is a key step for the conversion (58). This finding is in line with the discovery of urea-to-cyanate transformation for several pyrazolate-based dinickel complexes with urea bound in the N,0-bridging mode (see below). 

Oxidation of cyanide by hydrogen peroxide was the subject of an early kinetic study which is remarkable for completeness and baffiing character. Unpublished studies by the present author show that the main reaction at high pH (greater than 12) involves quantitative cyanate formation, viz. 

Martin et al report investigations on the kinetics and the mechanism of aryl cyanate formation frx>m cyanogen bromide and phenols in the presence of different tertiary aliphatic amines. According to Vo-winkel," the use of diethyl ether as the solvent at -10 C raises the yields and various patents describe how the amines can be replaced by sodium hydroxide. There are even reports on work in aqueous solution under phase transfer conditions. With all synthetic variants it is crucial to avoid a surplus of the phenolate as only under these conditions can the often quite fast formation of imino carbonates be prevented (equation 28). 

Similar to Note 2, there is a danger of cyanate formation in this buffer. It is thus preferable to add the acetic acid at the same time as the urea. The lower pH will slow down the breakdown process. 

Hagel, R, Gerding, J. J. T., Fieggen, W., and Bloemendal, H. (1971) Cyanate formation in solutions of urea, Biochim. Biophys. Acta, 243, 366-379. 

The amides used were either reagent or spectrograde chemicals. Reagent grade urea was recrystallized and solutions were made just prior to use to reduce cyanate formation. Substituted ureas were either recrystallized or distilled. Butyrolactam and caprolactam were respectively distilled and recrystallized. All compounds were checked to assure their dryness. Water for use in solution preparation was deionized prior to distillation from a glass still. The solutions used for a typical experiment were a series of four to six equal volume dilutions wherein weight was recorded in addition to volume so that molalities could be calculated. Dilution studies were made in duplicate or triplicate except for the substituted ureas for which twenty to thirty runs were made. The measured heats, q, ranged from 3 jucal s" to 2.0x 10 jucal s" and each determination required about 3 ml of sample. The reproducibility of the measured heats was +20% at 3 cal s S +10% at 10 jucal s" 2% at 50 /ical s and 1% above 50 jucal s . ... 

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 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 ... 

Cyanide destmction by alkaline chlorination is a widely used process. With alkaline chlorination, cyanide is first converted to cyanate with hypochlorite [7681-52-9] at a pH greater than 10. A high pH is required to prevent the formation of cyanogen chloride [506-77-4] which is toxic and may evolve in gaseous form at a lower pH. With additional hypochlorite, cyanate is then oxidized to bicarbonate, nitrogen gas, and chloride. The pH for this second stage is 7—9.5 (6). 

Ethyl carbamate, C2HyN02, is developed naturally during the fermentation of alcohoHc beverages. It also appears in foods such as bread and yogurt. Since ethyl carbamate is not easily distilled, its formation most likely involves a distillable precursor. The mechanism of ethyl carbamate formation probably involves cyanate produced from the oxidation of cyanide or from urea-based compounds in the beer. Cyanate reacts with alcohol to form ethyl carbamate as follows ... 

Cyanate can be further oxidized by HOCl to nitrogen and bicarbonate along with small amounts of N2O and NCl. Hypochlorous acid reacts with peroxide with evolution of oxygen by the postulated intermediate formation of peroxyhypochlorous acid (99). 

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]... 

It has been shown52 that under similar conditions reduction of the nitrile groups in cellulose ethyl cyanate and of those in the copolymer of vinylidene cyanide with vinyl acetate, proceed simultaneously in two directions with the formation of aldehyde and amine groups. g+ g ... 

In 2004, Alterman et al. apphed their cyanation protocol to the synthesis of N-(t-butyl)-3-(4-cyanobenzyl)-5-isobutylthiophene-2-sulfonamide [61]. Deprotection of the sulfonamide followed by carbamate formation via reaction with butyl chloroformate finally gave the target compoimd for biological evaluation as a selective angiotensin 11 AT2 receptor agonist (Scheme 65). The cyano derivative, however, showed only a low affinity for the AT2 receptor (Ki value >10 p,M). 

When the reagent is the thiocyanate ion, S-alkylation is an important side reaction (10-43), but the cyanate ion practically always gives exclusive N-alkylation. ° Primary alkyl halides have been converted to isocyanates by treatment with sodium nitrocyanamide (NaNCNN02) and m-chloroperoxybenzoic acid, followed by heating of the initially produced RN(N02)CN. ° When alkyl halides are treated with NCO in the presence of ethanol, carbamates can be prepared directly (see 16-7). ° Acyl halides give the corresponding acyl isocyanates and isothiocyanates. For the formation of isocyanides, see 10-111. 

Aqueous cyanide effluent containing a little methanol in a 2 m3 open tank was being treated to destroy cyanide by oxidation to cyanate with hydrogen peroxide in the presence of copper sulfate as catalyst. The tank was located in a booth with doors. Addition of copper sulfate (1 g/1) was followed by the peroxide solution (27 1 of 35 wt%), and after the addition was complete an explosion blew off the doors of the booth. This was attributed to formation of a methanol vapour-oxygen mixture above the liquid surface, followed by spontaneous ignition. It seems remotely possible that unstable methyl hydroperoxide may have been involved in the ignition process. 

Reports of the synthesis of cytosine from cyanoacetylene (or its hydrolysis product cyanoacetaldehyde) with cyanate, cyanogens or urea show that these substances react faster with nucleophilic compounds to give side products than to give the required main product. In addition, the formation of cytosine requires concentrations which are unrealistic in prebiotic environments. 

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