Heteroaromatic compounds quatemization

The simultaneous ionic and covalent character of quaternary ammonium compounds (197a) is central to most of their applications. TV-Quatemized heteroaromatic compounds possess many of the properties of 197a, and will be mentioned occasionaly in this chapter. In Table 4 are listed some quaternary ammonium compounds that have found industrial application. Many analytical methods make use of this class of compounds both as essential reagents or as accessories however, in the present chapter quaternary ammonium compounds will appear only as analytes. 

Addition can also occur to the formal ring double bonds of a nitrogen heteroaromatic compound. The usual preference is for addition adjacent to the nitrogen (equation 41), but this may be modified by substitution, cryptand complexation, quatemization, or copper salt catalysis. Pyridine N-oxides may yield deoxygenated product. 

Quatemization of Heteroaromatic Compounds Quantitative Aspects John A. Zoltewicz and Leslie W. Deady Part I. Discussion... 

While diaza-heteroaromatic compounds (e.g. pyrimidines, diazoles) can, in principle, form diquatemary salts without loss of aromaticity, the introduction of the second alkyl group is difficult, undoubtedly because of the reduction in nucleophilicity of the second ring-nitrogen resulting from the quatemization of the first. Diquatemary salts of thiadiazoles of type... 

Amino-1,2,4-triazoles (50) or their derivatives are usually starting material for the synthesis. They are readily available and already contain the exocyclic N-N bond required for heteroaromatic A-imines. 4-Amino-1,2,4-triazoles can be quaternized by alkyl halides or tosylates at the N-l atom to give the salt 52.79-82 (Scheme 5) The orientation of quatemization is proved by the reactions in Scheme 6 for the example of the quaternary acylamino salts 52. Quaternary salts of the type 52 can also be prepared by reaction of 1,3,4-oxadiazolium salts (51)83 with aryl hydrazines84 and from aryl hydrazine hydrohalides and orthoesters.86 With alkali, the 1-alkyl-s-triazole-4-imines8(7-82 86 can be obtained in the normal manner from these salts (Scheme 5). The free A-imines are all stable except the A-unsubstituted compound itself.87 Recently, other structures were tentatively reported 88 for the deprotonation products of analogous quaternary salts (52) with hydrazine. 

Among the known classes of heteroaromatic carbenes, the benzimidazole derivatives have received the least attention thus far. They [89] present new results in terms of the synthesis and properties of stable heteroaromatic monocarbenes and biscarbenes of the benzimidazole series. One of the major aims in this area was the attachment of sterically bulky groups to the benzimidazole nucleus. The introduction of the 1-adamantyl substituent into the benzimidazole system was achieved by direct adamantylation of benzimidazole using 1-bromoadamantane in the presence of sodium acetate in acetic acid. However, in this case the reaction was incomplete and yields of only 33% of pure salt 134 were realized. In o-dichlorobenzene in the presence of potassium carbonate, a 54% yield of l-(l-adamantyl)benzimidazole (86) can be achieved and this compound can be further quatemized by treatment with 1 -bromoadamantane in o-dichlorobenzene to afford a high yield of salt 134 (90%).As is well known, in the... 

---