Cyanamides, basicity

In 1880, R. Andreasch (52) confirmed the new formula (37) by preparing thiohydantoine through condensation of thioglycolic acid with cyanamide (the reverse reaction of the basic hydrolysis of thiohydantoin). 

Hydrogen sulfide reacts with nitriles in the presence of a basic catalyst forming thioamides. A commercial example is its addition to cyanamide with the formation of thiourea [62-56-6]. ... 

The nitrogen of aHphatic and aromatic amines is alkylated rapidly by alkyl sulfates yielding the usual mixtures. Most tertiary amines and nitrogen heterocycles are converted to quaternary ammonium salts, unless the nitrogen is of very low basicity, eg, ia tn phenylamine. The position of dimethyl sulfate-produced methylation of several heterocycles with more than one heteroatom has been examined (22). Acyl cyanamides can be methylated (23). Metal cyanates are converted to methyl isocyanate or ethyl isocyanate ia high yields by heating the mixtures (24,25). 

Sinulatly, nucleophilic reagents are suitable for addition reactions only if they are not so strongly basic as to produce the cyanamide anion in large amounts. In such cases, dicyandiamide is produced or a cyanamide salt is obtained. Ai,Ai-Disubstituted cyanamides do not ionize, of course, and react easily with strongly basic nucleophiles. 

The basic chemical of the cyanamide industry is calcium cyanamide CaNCN, mp 1340°, obtained by nitrogenation of CaCi. 

It was found that 1,2,4-triazine 4-oxides 55 are active enough to react with cyanamide under basic conditions according to the deoxygenative mechanism to form 5-cyanamino-l,2,4-triazines 73 (00TZV1128). This reaction seems to be facilitated by the easy aromatization of cr -adducts by the Elcb elimination of water. 

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>. 

An interesting legal case ensued in the English High Court [87], where Ethicon (Johnson Johnson) maintained, among other things, that the formation and hydrolytic behaviour of polyglycolide fibres were already known and that it was therefore obvious to use the material as an absorbable suture. The outcome was basically favourable to American Cyanamid. 

Reaction with cyanamide in the presence of basic catalyst yields thiourea ... 

Nitroguanidine has weakly basic properties and this accounts for its ability to form salts with concentrated acids, e.g. it forms a sulphate with concentrated sulphuric acid. Nitroguanidine is hydrolysed on heating with concentrated sulphuric acid evolving nitrous oxide and carbon dioxide, the former probably derived from hydrolysis of nitramine and the latter from hydrolysis of cyanamide. The latter also yields ammonia on decomposition. 

Only a few examples of the formation of 1,2,4-triazines by this fragment combination have been published, all cases being 1,2,4-benzotriazine syntheses. 2-Nitroaniline reacts with cyanamides to give 2-nitrophenylguanidines (601) which cyclize under basic conditions to 3-amino-l,2,4-benzotriazine 1-oxides (602) <78HC(33)189, p.699). With benzoyl isothiocyanate it affords Ar-(2-nitrophenyl)-N -benzoylthiourea (603), which cyclizes to l,2,4-benzotriazine-3-thione 1-oxide (604) (80MI21900).. 

Cyclotrimerization of nitriles with heteroatomic substituents are also facile and important reactions. Melamine is formed on heating cyanamide above its melting point (equation 74) (59HC(l3)l, p. 309). Substituted cyanamides react to give either the expected 1,3,5-triazine or the isomer (142). The 1,3,5-triazine is the preferred product at high temperatures, under acid catalysis, and for cyanamides with bulky substituents, whilst the isomer is favoured by basic conditions and low temperatures (Scheme 80). The mechanism of formation of (142) has been proposed (Scheme 81) (78RCR975). 

Iminologue, cyanamide benzologue and vinylogue compounds and their hydrogen-bond basicity... 

Quite fascinating compounds are the super-basic nitriles102. The cyanamides are the most basic nitriles presently known103,104. The high basicity of such compounds is explained by a so-called push-pull mechanism, described schematically by the resonance structures. 

TABLE 16. Hydrogen-bond basicity of cyanamides and related compounds... 

Table 16 shows that the cyanamide iminologues are actually more basic on the hydrogenbonding basicity scale than many pyridines or tertiary amines are. This knowledge and the aforementioned basicity orders will make it possible to create still more basic nitriles by an appropriate selection of alkyl substituents R, R, R" in the amidine skeleton of cyanoamidines. 

The reader is already familiar with the weakly basic properties of ammonia. The commercial preparations of this base, both from the elements and from hydrolysis of calcium cyanamide, have already been noted. For preparation of small quantities of ammonia in the laboratory, an ammonium salt, either dry or in solution, may be heated with base. 

It is made by dimerizing cyanamide in basic aqueous solution, and is a colorless solid melting at 208°C. Dicyandiamide is soluble in polar solvents, but at room temperature is insoluble in bisphenol A epoxy resins. It can be made into a very fine powder and milled into epoxy resins to form stable dispersions. Because the dicy is insoluble in the epoxy, the only possible reaction sites are at the particle surfaces. Although some reaction certainly occurs over a short time, the adhesives easily can have a useful shelf life of six months. On heating to about 150°C, the dicyandiamide becomes soluble in the epoxy resin, and the adhesive polymerizes rapidly. Cure can be accelerated by incorporation of tertiary aromatic amines or substituted ureas. 

First, the role of rubber modification in high rate impact is to suppress spallation by inducing the material to yield in the presence of dynamic tensile stresses arising from impact. Second, this yield-spall transition occurs at different strain rates for different rubber contents and may be predictable using quasistatic, low temperature tests of this type. These tests can also provide information concerning the basic nature of the yield process in these materials through the activation parameters which are obtained. Third, the Bauwens-Crowet equation seems to be a good model for the rate and temperature sensitive behavior of the American Cyanamid materials and is therefore a likely candidate for a yield criterion to use in the analytical code work on these materials which we hope to perform as a continuation of this work. 

Unlike the digestion with sulfuric acid, calcium is present in a soluble form. Since calcium nitrate is very hygroscopic, it is mostly either converted or separated (and then further utilized). [In a process developed by Lonza AG the calcium nitrate remains in the mixture. The digestion mixture is dehydrated up to the point that only 2 to 3 moles of water are present per mole calcium nitrate. Then the not yet solidified mass is granulated and coated with, for example, basic slag (Thomas meal) or calcium cyanamide etc.]... 

Diarock (Nitto Chemical Ind., Japan), marketed internationally for about a decade beginning in the mid-1960s, appears (from the manufacturer s literature) to be basic urea-formaldehyde resin (not a prepolymer). Cyanaloc 62 (American Cyanamid Company, Wayne, New Jersey) is a prepolymer marketed as a concentrated liquid which is diluted with water for field use. Sodium bisulfate is the catalyst normally used, and the relationship between catalyst concentration and setting time is shown in Fig. 

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