Diquatemary salts

Some bipyridinium salts are remarkable herbicides. They rapidly desiccate all green plant tissue with which they come into contact, and they are inactivated by adsorption on to clay minerals in the soil. This potent herbicidal activity is found only in quaternary salts, e.g. diquat (254) and paraquat (255), with redox potentials for the first reduction step between -300 and -500 mV (equations 158 and 159) (B-80MI20504). The first reduction step, which is involved in herbicidal activity, involves a completely reversible, pH independent, one-electron transfer to yield the resonance stabilized radicals (256) and (257). The second reduction step, (256 -> 258) and (257 -> 259), is pH dependent and the p-quinoid species formed are good reducing agents that may readily be oxidized to diquatemary salts. 

It is interesting that only mono- and not di-pseudo bases are obtained, and that with 1,6-naphthyridine, pseudo base formation occurs at the quinolinoid site, the diquatemary salt (79) yielding (80) and not (81). However naphthyridinediones are formed on reaction with alkaline K3Fe(CN)6 (72CJC917, 74CJC962). 

Alkyl halides react with diazines less readily than with pyridines. All the diazines are, nevertheless, more reactive toward methyl iodide than predicted by their pKa values and the Bronsted relationship. The significant although modest rate enhancements found are considered to arise from interactions between the two lone pairs on the nitrogen atoms this interaction is largest in pyridazine. Use of oxonium ions can convert the diazines into diquatemary salts. Quinoxalines and phenazines similarly yield diquatemary salts under forcing conditions. 

Thiadiazole with Me30+BF4 gives the diquatemary salt (105) diquatemary salts are also known in the 1,2,4-triazole series. 

A diquatemary salt of 1,5-naphthyridine was prepared by refluxing the parent compound in dimethyl sulfate.150... 

Bipyridinium diquatemary salts (1.0 mmol) and acetylenedicarboxylate (1.0 mmol) were dissolved into 1 mL of acetone and adsorbed on KF-Merck Alumina 70-230 mesh. The solvent was then evaporated and the mixture was irradiated at atmospheric pressure in a focused microwave reactor Prolabo MX350 with measurement and control of power and temperature by infrared detection for the time and at power indicated in Table 1. All derivatives were characterized by IR, XH and 13C NMR spectroscopy, and elemental analyses. 

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... 

Colorless viologens composed of diquatemary salts of 4,4 bipyridine(I), 2,2 -bipyridine, and 1,10-phenanthroline turn into a violet-blue radical cation(II) by one-electron reduction,5 and are further reduced to the yellowish quinonoid(III ) via the biradical (III) (Scheme 1). 

Initially, the diquaternary ammonium macrocycle is synthesized by the quatemi-zation of a diamino compound by a diiodoether the diquatemary salt is, subsequently, demethylated with L-Selectride . Repeating this sequence of events results in the formation of a cryptand. In most cases the Air-quaternary ammonium salts were not... 

Only pyrazine among the monocyclic diazines forms well characterized JV,N -dialkylated cation-radicals Ahn and Johnson have presented detailed studies of line-shape variation in the ESR spectra of 1,4-dimethyl and 1,4-diethyl-l,4-dihydropyraziniumyl radicals.324,325 Although diquatemary salts of all three simple diazines have been prepared, it was found that only the dialky Iated pyrazine underwent spontaneous reduction to the cation-radical in alcoholic solution.326... 

Diquatemary salts of methylpyrazines have been prepared by treatment with triethyloxonium fluoroborate (621, 622). Steric hindrance has a considerable effect on the reaction as illustrated by the yield as follows pyrazine (97%), 2,5-dimethylpyrazine (95%), 2,6-dimethylpyrazine (46%), and 2,3,5,6-tetramethyl-pyrazine (5%). 

Keywords 4,4 -bipyridinium diquatemary salts, acetylenedicarboxylate, 1,3-di-polar cycloaddition, microwave irradiation, 7,7 -bis-indolizine... 

Diazoles are in principle capable of forming diquaternary salts without loss of aromaticity however, it is difficult to introduce the second alkyl group, probably because quaternization of one ring nitrogen reduces the nucleophilidty of the other. Diquatemary salts of thiadiazoles of type 373... 

Cycloaddition of 4,4 -bipyridinium ylides 218, generated in situ from 4,4 -bipyridine and substituted phenacyl bromides 216 via 4,4 -bipyridinium diquatemary salts 217, with activated alkynes has been achieved under solvent-free conditions and in the presence of basic catalyst KF on alumina within 7-10 min by MWI to give 7,7 -feir-indolizines 220 in 81-93% yields via intermediate 219 (Scheme 46). On heating in benzene (or in benzene and A-methylpyrrolidone (NMP)), the reaction times were longer (3 h) and the yields were lower (50-59%) (00SL1013). 

Coffee brew was prepared from freshly ground, roasted coffee beans (Arabica, variety Caturra) by a percolation method using hot water at 95°C. The coffee/water ratio was 50 g/L. Phenols were removed from the coffee brew by treatment with poly(vinyl pyrrolidone) as reported in the literature (14). The water used for the EPR experiments was stirred widi an ion exchange resin (Amberlite MB-1 Merck, Darmstadt, Germany) for at least 24 h prior to use, to remove adventitious metal ions. The 1,4-diethylpyrazinium diquatemary salt was synthesized as recently reported by perethylation of pyrazine with triethyloxonium tetrafluoroborate (7). 

Trialkyloxonium salts were effective in alkylation of the di-azine, furnishing mono- and diquatemary salts, which could be isolated by recrystallization (eqs 2 and 3). ... 

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... 

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