Pyrazine cation radical derivatives

The results of analyses of the ESR spectra of various reaction systems are summarised in Table II. It was shown that all spectra have in common the splittings arising from two equivalent nitrogens (about 8.2 G) and four equivalent protons (about 3.0 G), and additionally from an even number of equivalent protons with different splitting constants. These assignments let to the reasonable assumption that the radical products are N,N -disubstituted pyrazine cation radical derivatives, as shown in Fig. 4. This assumption was strongly supported by the fact that the hyperfine structure as well as the g-value of the ESR... 

As described above, the free radical products are considered as N,N -disubstituted pyrazine cation radical products. However, formation of such pyrazine derivatives in the Maillard reaction is unknown, and little work has been done on the synthesis of N.N -diethylpyrazinium salt (8), the one—electron oxidation product of the N, N -diethylpyrazine cation radical. The... 

Formation of novel free radical products at an early stage of the Maillard reaction was demonstrated by use of ESR spectrometry. Analyses of the hyperfine structures for various sugar-amino compound systems led to the conclusion that the radical products are N,N -disubstituted pyrazine cation radicals. These new pyrazine derivatives are assumed to be formed by bimolecular condensation of a two-carbon enaminol compound involving the amino reactant residue. The presence of such a two-carbon product in an early stage reaction mixture of sugar with amine was demonstrated by isolation and identification of glyoxal dialkylimine by use of TLC, GLC, NMR, MS and IR. 

Fenner and co-workers have described radicals in which an NH from the pyrazine ring of lumazine or isoalloxazine derived radicals is replaced by S (e.g., 273-275) (cf. Part I Section III,C,5). Cation-radicals were generated by solution of the parent heterocycles in concentrated sulfuric acid or by oxidation by dibenzoyl peroxide in trifluoracetic acid-containing... 

Electron-spin resonance (e.s.r.) spectra with characteristic hyperfine structure have been recorded during the initial stages of the Maillard reaction between various sugar and amino compounds. The products responsible for the spectra appear to be IV, Af -disubstituted pyrazine radical cations. The pyrazine derivatives are assumed to be formed by the bimolecular condensation of two- and three-carbon enaminol compo-... 

Pyrazine diquatemary salts of types 16lB1 and 17152 are known and also 6,7-dihydro derivatives of 16.152a The diquaternary salt (17) was originally formulated as the monohydrate of 18, but attempts to dehydrate 17 to 18 have not been successful.152 Dipyrido[l,2-a 2, l -c]pyrazinium dibromide (16) has herbicidal properties it is reduced in aqueous solution to a stable radical cation.183 The related pyrido[l,2-a]pyrazinium salts of type 19 have also been prepared.153,1B4a... 

Substituted thieno[3,4-i>]pyrazines are generally synthesized by condensation of 3,4-diaminothiophene with substituted 1,2-diones (Scheme 1.33) [328, 329], By this synthetic approach, various alkyl-substituted thieno[3,4-fc]pyrazines 3.20 were synthesized and chemically polymerized with FeCls. The resulting polymers were highly soluble in organic solvents due to the alkyl side-chains and had low bandgaps of 0.8-1.1 eV [308, 328, 329]. There has been no report on successful electrochemical polymerization of thieno[3,4-l>]pyrazine derivatives and a popular hypothesis holds that the failure is due to the quenching of the created radical cations by the pyrazine ring [330]. 

A recipe for the synthesis of radical ions isoelectronic with that of l,4-bis(tri-methylsilyl)benzene is reported for the elements B, C, N and Al, Si, P. All the ions, both cations and anions, persist at room temperature and e.s.r. parameters reflect the structural differences. The two pyrazine derivatives have larger ring-proton and smaller methyl-proton coupling constants, and higher g factors than the three benzene derivatives. ... 

---