Reaction with cyanic acid

D-Triazoles have been isolated from the reaction of several activated nitriles, such as cyanogen, cyanogen halides, methyl cyanoformate, and cyanic acid esters, with diazoalkanes. The reaction can formally be regarded as a 1,3-dipolar cycloaddition. The v-triazoles may be... 

The yields from the reactions, carried out at room temperature and a pressure of 2-4 at, increase with increasing electronegativity of the substituent X. The yield with phenyl isocyanate is 13%, with p-chlorophenyl isocyanate 55% and with p-nitrophenyl isocyanate it is 100%. Primary and secondary carba-moylphosphines cannot be isolated even when equi-molar quantities of phosphine and isocyanate are used. Their intermediate formation is probable but apparently they are more reactive towards isocyanates than phosphine itself. Similarly, phosphine does not react with free cyanic acid whereas primary and secondary phosphines react with cyanic acid, as with isocyanates, to form the corresponding carbamoylphosphines Attempts to make phosphine react with phenyl isothiocyanate did not succeed... 

Fig. 11.5 (A) Eigen-type plot for the general base-catalysed reactions of 4-chlorobenzaldehyde with a substituted hydrazine [8] the line is calculated from log kg = —0.341 log(1 + 106 09 pffa). (B) Eigen-type plot for general acid catalysis in the reaction of cyanic acid (HNCO) with aniline, and an alternative interpretation [9] the dashed line has a Bronsted slope of —0.19 and the break at p/fa near 10 in the solid line is consistent with proton transfer to an addition intermediate (PhNH2+CONH ).

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 ... 

The reaction of diacetylene with cyanic acid (HCNO) proceeds at room temperature in the presence of sulfuric acid in aqueous methanol to give 3-formyl-5,5 -diisoxazol-3 -aldoxime (85) and 3,3 -diformyl-5,5 -diisoxazoldioxime (86), whose oxidation with potassium permanganate followed by esterification results in 3,3 -dicarbomethoxy-5,5 -diisoxazoles (87) (59G598). 

Ethonam (99), an imidazole derivative with a very different substitution pattern, is also reported to possess antifungal activity. To prepare it, alkylation of aminotetralin 94 with methylchloro-acetate gives the glycine derivative 95. Heating with formic acid then affords the amide 96 this compound is then reacted with ethyl formate to yield hydroxymethylene ester 97. Reaction with isothio-cyanic acid gives the imidazole-2-thiol 98. (The... 

As for the acetyl phosphate monoanion, a metaphosphate mechanism has also been proposed 78) for the carbamoyl phosphate monoanion 119. Once again, an intramolecular proton transfer to the carbonyl group is feasible. The dianion likewise decomposes in a unimolecular reaction but not with spontaneous formation of POf as does the acetyl phosphate dianion, but to HPOj and cyanic acid. Support for this mechanism comes from isotopic labeling proof of C—O bond cleavage and from the formation of carbamoyl azide in the presence of azide ions. 

Wohler s synthesis of urea by which a product of the living cell was first prepared artificially more than a century ago is the prototype of many addition reactions which take place with the reactive molecules of cyanic acid and its esters, as well as with the series of analogous thio-compounds. In these reactions NH3 is added to the C = N double bond ... 

The esters of carbamic acid, the urethanes, which are formed by combination of alcohols with compounds of the cyanic acid series, are stable substances. The reaction by which they are formed is, likewise, capable of undergoing many variations. It may be recalled that a second method of synthesising them consists in acting on the esters of chloroformic acid with ammonia and amines. 

The reaction of primary alcohols with urea gives carbamates when the reaction is carried out at 115°-l 50°C [7-10] (Eqs. 2, 3). Since 150°C is the temperature for the optimum dissociation of urea to cyanic acid and ammonia, lower-boiling alcohols (methyl, ethyl, and propyl) must be heated under pressure. Refluxing urea and n-butanol at 115°-120°C requires a 40-hr reaction time to... 

Reaction of semicarbazides with aryl esters of cyanic acid to give semi-carbamid-carbamic acid esters [80]. 

The reaction is reversible since nitramine in aqueous solution combines with cyanic acid to reform nitrourea. Nitrourea is decomposed by gaseous ammonia, a reaction which, according to Watt and Makosky [63] proceeds as follows ... 

Reaction with liquid ammonia at —33°C probably proceeds in a manner similar to that described by Davis and Blanchard it is believed that nitramine (decomposing into N20 and water) and urea (apparently from cyanic acid and ammonia) are formed. 

A benzo derivative of l,2-dihydro-2,4,l-diazaborine (131) is known. Thus reaction of 2-aminobenzeneboronic acid with cyanic acid gave compound (146). Some non-hydroxyl-ated compounds were prepared from (V,(V -diphenylamidines and trialkylboranes or the n-butyl ester of diphenylborinic acid (Scheme 28) (79IZV174). 

Although the reaction of o- aminopyridinecarboxylic acid derivatives with cyanic acid, isocyanates and isothiocyanates to give 2-oxo- or 2-thioxo-pyridopyrimidines (e.g. 114 115) could be regarded as a [4+2] reaction, it occurs via a well-defined ureido... 

The reaction is reversible, for nitroamide in aqueous solution combines with cyanic acid to form nitrourea. 

In water and in. hydrophilic solvents nitrourea dearranges rapidly into cyanic acid and nitroamide. Alkalis promote the reaction. If an aqueous solution of nitrourea is warmed, bubbles of nitrous oxide begin to come off at about 60°. If it is allowed to stand over night at room temperature, the nitrourea disappears completely and the liquid is found to be a solution of cyanic acid. Indeed, nitrourea is equivalent to cyanic acid for purposes of synthesis. It reacts with alcohols to form carbamic esters (urethanes) and with primary and second amines to form mono-and unsym-di-substituted ureas. 

They also described the reaction of diketene with N,N-dimethylurea in acetic acid, yielding 50 (see also Ahmed et a/.177). Gunar et a/.178 used diketene in the reaction with cyanic acid (see also Ozaki179), thiocyanic acid, ethyl urethane, and N,N -disubstituted ureas in acetic acid medium to obtain 50. When a 2-thiono derivative was obtained from thiocyanic acid, as in Eq. (37), they desulfurized it with mercuric acetate. 

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