Halides cyanamides

The cyanogen halides polymerize on standing to the trimers, the cyanuric halides. Cyanamide is converted into the corresponding trimer, melamine, on heating to about 150°C. Isocyanic acid, however, polymerizes far more readily. If urea is distilled, isocyanic acid is formed but polymerizes to cyanuric acid, (NCOH)3, a crystalline solid, the vapour of which, on rapid cooling, yields isocyanic acid as a liquid which, above 0 C, polymerizes explosively to cyamelide, a white porcelain-like solid. This latter material is converted into salts of cyanuric acid by boiling with alkalis. These reactions are summarized in Chart 21.1. Cyanuric derivatives... 

Alkylation with a vatiety of common alkyl halides oi sulfates gives stable dialkylcyanamides. However, the intermediate monoalkylated compounds usually cannot be isolated and cychc trimers or cotrimers with cyanamide ate obtained (13). The reaction can be carried out efficientiy in water or alcohol. Allyl chloride is an especially useful reagent, producing diallylcyanamide [538-08-9J (4). 

A convenient way of obtaining secondary amines without contamination by primary or tertiary amines involves treatment of alkyl halides with the sodium or calcium salt of cyanamide NH2—CN to give disubstituted cyanamides, which are then hydrolyzed and decarboxylated to secondary amines. Good yields are obtained when the reaction is carried out under phase-transfer conditions. The R group may be primary, secondary, allylic, or benzylic. 1, co-Dihalides give cyclic secondary amines. 

An efficient synthesis of 2-amino derivatives 256 is depicted in Scheme 70 2-halopyridines are first Ar-alkylated with various halides under microwave activation and next reacted with cyanamide under basic conditions <1999T2317>. A rapid parallel synthesis of derivatives bearing a benzoyl substituent at C-3 based on this reaction has been described <2002SL1544>. 

Biguanides are accessible by a Grignard reaction of guanidinomagnesium halide with a substituted cyanamide, and hydrolysis of the resulting complex [59—61). The method is of considerable theoretical interest but so far only of limited practical importance. 

The interaction of guanidinomagnesium halides (XLV) with disubsti-tuted cyanamides (XLVI), for example, affords substituted biguanides (XLVIII) [59). The variation in 3nelds (7 to 48%) is attributed [59) to differences in solubility in ether of the guanidinomagnesium halides and the resultant complexes, and to the electronic effects of the substituents. 

Monosubstituted cyanamides require two equivalents of guanidinomagnesium halide to allow for replacement of the acidic cyanamide hydrogen by the Mgl moeity [59). The reaction proceeds in low 3neld and fails with monoarylcyanamides. 

The active hydrogens of pseudoureas react with various reagents, such as sodium hypochlorite [72], acyl halides [73], sulfonyl halides [19], isocyanates [26], isothiocyanates [26, 74] cyanamide, [75] and esters [76], to give linear or cyclic derivatives as shown in Scheme 2. 

Conversion of Alkyl Halides to Secondary Amines with Cyanamide Imino-de-dihalo-aggre-substitution (overall transformation)... 

The preparation of diallyl cyanamide by the above method has only recently been described in the literature.1 However, other dialkyl cyanamides have been prepared by the following methods the action of chlorocyanogen or bromocyanogen on dialkyl amines 2 the reaction of dialkylchloroamines with potassium cyanide 3 the action of bromine on a mixture of dialkyl amines and potassium cyanide 4 the action of alkyl halides on disilver cyanamide5 and on disodium cyanamide.6 Dimethyl cyanamide has also been prepared by the action of dimethyl sulfate on lime nitrogen 7 and on cyanamide. 8... 

The preparation of pure symmetrical secondary amines (e.g. dibutylamine, Expt 5.199) is conveniently achieved by the hydrolysis of dialkylcyanamides with dilute sulphuric acid. The appropriate dialkyl cyanamide is prepared by treating sodium cyanamide (itself obtained from calcium cyanamide and aqueous sodium hydroxide solution) with an alkyl halide. In this case the reagent [ —C=N]20 may be regarded as a masked NH group. 

The reaction of compound 90 with imidoyl halides without added base gives the hydrochloride salts of 1,2,4-thiadiazol-5-imines 95. The corresponding free bases can be liberated from the salts 95 with weak bases such as bicarbonate, but these imines are labile and decompose readily to form the W-cyanamide 96 and sulfur. The free base can be treated in situ with a second electrophile, such as an acid chloride, imidoyl chloride, or aryldiazonium salt, affording pentalene derivatives 97-99. It should be noted that the compound 98 cannot be prepared in a one-pot procedure from compound 90 and 2 equiv of imidoyl chloride in the presence of base, in contrast to the corresponding dioxa compound 91 (Scheme 22) <1981BSB89, 1992JHC1317>. 

Cyanamides are pseudo-halide nitrogen ligands that are readily coordinated to metals. A novel compound is 2-cyanaminofluoren-9-one (HL4)24. Its thallium salt T1+(L4)-(Scheme 7) is useful as a transmetallating agent in a reaction with trimethyltin chloride to produce the corresponding tin cyanamide complex [SnMe3L4] (Scheme 8). 

The availability of different types of amino groups allows a variety of reactions typical for amines which are suitable for the derivatization of PEI. Reaction partners can be aldehydes, ketones, alkyl halides, isocyanates and thioisocyanates, epoxides, cyanamides, guanides, ureas, acids, and anhydrides. The synthesis and chemical modification reactions of PEI will be discussed in the next sections. 

Trialkyl- and alkoxysilyl halides react similarly with silver cyanamide or cyanamide and triethylamine. Also, PhsSiBr reacts with silver cyanamide to give bis(triphenylsilyl)-carbodiimide. Similarly, disilyl chlorides, MesSiSiCR, R )C13 react with silver cyanamide... 

Salts of phenylcyanamide react with RsSiCl (R = Me, Ph) to give the carbodiimide R3SiN=C=NPh." Instead of silyl halides also trimethylsilylcyanideis used. In this manner a 90 % yield of bis(timethylsilyl)carbodiimide is obtained from cyanamide and trimethylsi-lylcyanide (1 min, rt). " ... 

Several oligomeric metal carbodiimides are obtained from metal halides and salts of phenyl-cyanamide. Eor example, reaction of SbCE with KNCNPh 14 affords Sb(N=C=NPh)315, mp 271 °C (dec.) in 41 % yield. ... 

Thallium(I) forms salts with cyanide (CN ), cyanamide (NCN ), azide (Ns"), cyanate (OCN ), isocyanate (CNO"), thiocyanate (SCN"), and selenocyanate (SeCN ) however, complexes with these hgands, hke the Tl -halide complexes, are very weak. In contrast, the neutral Tl Xs species are not well known, although the Tl -pseudohahde complexes are more or less stable. 

The cyanogen halide can be fruitfully replaced by cyanamide [163], especially if the -phenylencdiamine is heated with cyanamide and... 

The von Braun reaction involves the cleavage of tertiary amines by cyanogen bromide to give an alkyl bromide and a disubstituted cyanamide, and can be applied to many tertiary amines.Usually, the R group that cleaves is the one that gives the most reactive halide (e.g., benzyl or allyl). For simple alkyl groups, the smallest... 

---