Trimeric nitrile

Although acetonitrile is one of the more stable nitriles, it undergoes typical nitrile reactions and is used to produce many types of nitrogen-containing compounds, eg, amides (15), amines (16,17) higher molecular weight mono- and dinitriles (18,19) halogenated nitriles (20) ketones (21) isocyanates (22) heterocycles, eg, pyridines (23), and imidazolines (24). It can be trimerized to. f-trimethyltriazine (25) and has been telomerized with ethylene (26) and copolymerized with a-epoxides (27). 

Triazines can be obtained either by condensation methods using the fluorinated anhydride (89IZV928) or by trimerization of nitriles, e.g., per-... 

A slightly related reaction involves nitriles, which can be trimerized with various acids, bases, or other catalysts to give triazines (see OS III, 71). HCl is most often used. Most nitriles with an a hydrogen do not give the reaction. 

Moser et al. (1968) (one of the co-authors was Clifford Matthews) reported a peptide synthesis using the HCN trimer aminomalonitrile, after pre-treatment in the form of a mild hydrolysis. IR spectra showed the typical nitrile bands (2,200 cm ) and imino-keto bands (1,650 cm ). Acid hydrolysis gave only glycine, while alkaline cleavage of the polymer afforded other amino acids, such as arginine, aspartic acid, threonine etc. The formation of the polymer could have occurred according to the scheme shown in Fig. 4.9. 

Another example of the remarkable reactivity of Mg actuated by our procedure is its reaction with nitriles. In this respect, the Mg resembles an alkali metal more than an alkaline earth. Benzonitrile reacts with Mg overnight, in refluxing DME, to give 2,4,6-triphenyl-l,3,5-triazine and 2,4,5-triphenylimidazole in 26 and 27% yield, respectively, based on magnesium. Jhe imidazole was shown to arise, at least in part, from the action of Mg on the triazine. The trimerization of aromatic nitriles to give symmetrical triazines is not unknown, but generally the reactions are... 

In the presence of Co(I)-catalysts alkynes and nitriles can be co-trimerized in organic solvents to yield substituted pyridines under rather harsh conditions. The reaction is biased by formation of large quantities of benzene derivatives and with acetylene gas as much as 30 % of all products may arise from homotrimerization. It has been found recently, that with cobalt(I) catalysts heterotrimerization of various nitriles and C2H2 could be achieved under ambient conditions using aqueous/organic biphasic systems and irradiating the reaction mixture with visible light (Scheme 7.12) [39,40]. 

In this approach the C(2)-N(3) and C(6)-N(l) components are usually the same. Formamide or nitriles are common C-N components. A classical example is the trimerization of acetonitrile to give 2,6-dimethyW-pyrimidinamine <1994HC(52)1 >, while a modern example involves a similar trimerization of a variety of alkyl and benzylic nitriles 707 under microwave conditions <2005JC0483>. 

The pyrolysis gas chromatogram of ABS at 550°C changes considerably when the pyrolysis products are passed over zeolite catalysts. The specific activity towards certain reactions, e.g., cycliza-tion, aromatization, or chain cleavage is somewhat dependent on the nature of the individual zeolite. In general, enhanced benzene, toluene, ethylbenzene at the cost of dimer, trimer formation is observed. Nitrogen containing compounds do not appear in the pyrolysis oil after catalytic conversion. However, the product gas is rich in nitriles (132). 

Trimerization of imidates is a valuable route to 1,3,5-triazines. Imidates can be considered as activated nitriles and cyclotrimerize more readily. Most symmetrical 2,4,6-trialkyl-1,3,5-triazines are easily formed, although large alkyl substituents may give rise to steric hindrance (61JOC2778). Symmetrical isocyanurates (525) are readily available from isocyanates, RNCO catalysts include tertiary amines, phosphines and sodium methoxide. Aldehydes RCHO and ammonia give hexahydro-1,3,5-triazines (526), known as aldehyde ammonias (73JOC3288). 

Probably the cyclotrimerization of nitriles is the best known route to 1,3,5-triazines. The reaction has the obvious limitation that it is of value for preparing the symmetrical derivatives only. Nevertheless, many important triazines, such as cyanuric chloride, are made in this way. There are a number of other cyclotrimerization reactions which are also useful, in particular the trimerization of imidates. An easy route to 1,3,5-triazine from ammonium acetate has been developed. 

This method has been reviewed recently (78RCR975). Alkyl cyanides are difficult to trimerize, needing both very high pressures and temperatures (Table 14). It is one of the few organic reactions which requires pressures above 1000 atm. In contrast to other nitriles, the alkyl cyanides will not trimerize in acid conditions thus in the presence of hydrogen chloride, alkyl cyanides form N-substituted amidines (73BCJ292). 

Phenylsodium is formed initially in the reaction between benzonitrile and sodium (Scheme 79) (59JOC208). Trimerizations of aryl or heterocyclic nitriles catalyzed by amines or alkoxides resemble the reactions of the perfluoronitriles described above (Schemes 77 and 78 respectively). Kurabayashi et al. (71BCJ3413) studied the trimerization of benzonitrile under pressure in methanol, and have shown that the rate determining step is the reaction of the benzimino ether with benzonitrile. Steric factors exert an important influence in the trimerizations of aryl cyanides. The cyclizations of ort/zo-substituted aryl cyanides need more severe conditions than either the corresponding meta or para derivatives (Table 14). 

The preparation of 1,3,5-triazine 1,3,5-trioxides by trimerization of a nitrile oxide was reported (09CB803) however, the structure of the product has been reassigned as a polymer (65LA(687)191>. 

In this context it is interesting to note that benzonitrile, Ph—C=N, trimerizes to a triazine on a Raney nickel surface. It was assumed that Jt-bonded nitriles were involved in the reaction mechanism.10 This reaction resembles the well-known template synthesis of phthalocyanine complexes from phthalodinitrile. Formation of linear polymers [—C(R)—N—] occurs on heating aryl or alkyl cyanides with metal halides.11... 

Acids Phosphoric acid, FFAP (carbowax-20m-terephthalic acid ester), trimer acid These modifiers will act as subtractive agents for basic components in the sample FFAP will selectively abstract aldehydes phosphoric acid may convert amides to the nitrile (of the same carbon number), desulfonate sulfur compounds, and may esterify or dehydrate alcohols... 

Baxendale and Ley [60] employed the Smith Synthesizer as well as the Emrys Optimizer from Biotage [59] for conducting neat KOf-Bu mediated trimerizations of various liquid nitriles to give aryl- and alkyl-substituted 4-... 

Hydroboration of nitriles has also been used in syntheses of N-halo-organoborazines (see II.2.4.). Furthermore, a hydrogen-transfer reaction has been described by which borazines are formed through the reaction of trimeric aminoboranes with dimethylaminoborane in high yield 26> [Eq. (5)]. The latter method, however, is primarily of theoretical interest. 

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