Cyanate radical

Like phosphorus, nitrogen has an uneven number of electrons. Under the reducing conditions of the flame cyanide and cyanate radicals are formed, which can undergo the alkali reaction (Table 2.35). For this, the input of hydrogen and air are reduced. Instead of the flame the hydrogen burns in the form of cold plasma around the electrically heated alkali beads. 

In order to form the required cyanide and cyanate radicals, the C-N structure must already be present in the molecule. Nitro compounds are detected, but not nitrate esters, ammonia or nitrogen oxides. By taking part in the alkali reaction the cyanide radical receives an electron. Cyanide ions are formed, which react with other radicals to give neutral species. The electron released provides the detector signal. 

The results show that the dediazoniations afforded dihydrofuran derivatives which were functionalized exclusively at the site of the cyclized radical (10.58, Z = 0, n = 1) in very good yields for bromination and iodination, and moderate yields for chlorination, phenylthionation, and cyanation. All cyclizations take place in the exo mode, i.e., at the -CH= (second-last) carbon and not at the CH2 group (endo mode for nomenclature see Beckwith et al., 1980). 

The pyrene molecule is transferred by irradiation to its cation radical [29]. This reacts at the oil/water interface by nucleophilic attack from the cyanide ion. Typically, the cyanated product remains in the organic phase. 

The acridanyl radical is also obtained from N-methylacridinium chloride 83 and potassium cyanide in air-saturated DMF, DMSO, or DMSO/water mixtures. It is a remarkably stable radical 137> when 83 is treated with excess cyanide and oxygen N-methylacridone and cyanate are produced with light emission ... 

The radical 85 yields the peroxide anion 86 the decomposition of which gives rise to excited N-methylacridone and cyanate. In addition to previous suggestions put forward in respect of this exergonic decomposition 3.139) (see also p. 97), a recombination of the radical 85 and the peroxy radical 87 (from 86 and O2) according to... 

Cyanates contain the OCN group. Inorganic cyanates that are formed industrially by the oxidation of cyanide salts hydrolyze in water to form ammonia and bicarbonate ion. Alkyl cyanates are insoluble in water and form cyanurates. Alkyl isocyanates contain the OCN radical, are formed from cyanates, and, like cyanates, are readily hydrolyzed. Thiocyanates (SCN group) are formed from cyanides and sulfur-containing materials and are relatively stable. 

As described, other nucleophilic reactions in the anthraquinone series also involve the production of anion-radicals. These reactions are as follows Hydroxylation of 9,10-anthraquinone-2-sulfonic acid (Fomin and Gurdzhiyan 1978) hydroxylation, alkoxylation, and cyanation in the homoaromatic ring of 9,10-anthraquinone condensed with 2,1,5-oxadiazole ring at positions 1 and 2 (Gorelik and Puchkova 1969). These studies suggest that one-electron reduction of quinone proceeds in parallel to the main nucleophilic reaction. The concentration of anthraquinone-2-sulfonate anion-radicals, for example, becomes independent of the duration time of the reaction with an alkali hydroxide, and the total yield of the anion-radicals does not exceed 10%. Inhibitors (oxygen, potassium ferricyanide) prevent formation of anion-radicals, and the yield of 2-hydroxyanthraquinone even increases somewhat. In this case, the anion-radical pathway is not the main one. The same conclusion is made in the case of oxadiazoloanthraquinone. 

Formation of low molecular weight products from oxidation of N-methylpyrroIe is most successfully achieved with methanol and sodium cyanide as electrolyte. Tire radical-cation is captured by cyanide ion and 2-cyanopyrroles are formed in good yields when a 2-position in the substrate is vacant. In this reaction, a carbon-carbon bond is formed at the site of highest charge density. When both 2- and 5-positions are blocked by a methyl group, the intermediate radical-cation loses a proton to give the benzylic-type radical. Further reaction leads to cyanation on the 2-methyl group as in 61 [200]. 

Saczewski and Debowski reported the l,4-diaza-3-oxa-Cope rearrangement of N-cyanate anilides (equation 52). Prototropic rearomatization of 176 and internal nucleophilic addition afford the corresponding benzimidazolinone 177, usually in moderate yields (32-78%). A concerted [3,3]-sigmatropic rearrangement is proposed based on the absence of para rearrangement product that usually results from homolysis or heterolysis of the N—O bond followed by recombination of the two radicals or ions. 

C,H4S4)14 (NCSe), (2,2 -bi-l, 3-di-thiolylidene radical cation seleno-cyanate (14 8)), 19 31 (C4H4S4),4I43 2,2 -bi-l, 3-dithio-lylidene radical cation iodide (24 63)), 19 31... 

The most common strategy for laboratory scale hydrocarbon functionalization is hydrogen atom abstraction followed by free radical recombination. Although the conversions are often low, the simplicity of the approach can in some cases make this the method of choice for preparing a particular target molecule. A representative procedure is the cyanation of 2,3-dimethylbutane to give a 77% yield of 2,2,3-trimethylbutanenitrile1. 

The evidence for transient radical-cations from N-substituted indoles has been furnished by the observation of regiocontrolled anodic cyanation of the indole ring.193,194 Substitution in the 2-position dominates, although some 3-substitution takes place. When the 1,2,3-positions of indole were blocked, no cyanation occurred, but the products of anodic oxidation have not been isolated.194... 

The electrochemical oxidation of 2,5-dimethylthiophene in various electrolytes has been investigated (71JOC3673). In non-halide electrolytes such as ammonium nitrate or sodium acetate, the primary anodic process is the oxidation of the thiophene to the cation-radical (159). Loss of a proton, followed by another oxidation and reaction with solvent methanol, leads to the product (160) (Scheme 31). When the electrolyte is methanolic NaCN, however, nuclear cyanation is observed in addition to side-chain methoxylation. Attack by cyanide ion on the cation-radical (159) can take place at either the 2- or the 3-position, leading to the products (161)-(163) (Scheme 32). 

Cyanates are salts of Cyanic Acid contg the monovalent radical -CNO. See under Cyanic Acid... 

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