Radical Intermediates In Chloramine and N-Chloroimide Reactions

Abstract

Nitrogen-centered radicals produced by the action of Ag(0) or Ag(1)-amine systems on N-chloroazacyclononane, N-chloropiperidine, and N-chlorosuccinimide have been trapped using 2-methyl-2-nitrosopropane. The resulting nitroxides exhibited e.p.r. spectra consistent with structures 1, 2, and 3. Hydrogen gas evolved during reaction of the chioranlines with Ag(0) was shown to arise completely from the arnine derivatives.Excess Ag(0) reduced the succinamidyl radical to give the silver salt of succinimide.Les radicaux centres sur I'azote et obtenus par action des systemes Ag(0) ou Ag(1)-amine sur le N-chloroazacyclononane, I?-chloropiperidine, et N-chlorosuccinirnide ont Cte piegCs en utilisant du methyl-2 nitroso-2 propane. Les nitroxydes qui en resultent, montrent des spectres r.p.e. compatibles avec les structures 8 , 2, et 3. Le digagen~ent gazeux obtenu dans la reactior, des chloramines sur Ag (0) In connection with our studies of chloramine decomposition by silver ions or metallic silver (1) it seemed desirable to have independent evidence for the post~rlated nitrogen-centered radicals. The produces from reaction of hypochlorites (2), hypobromites, and aliphatic chloramines (1) with finely divided silver were consistent with reduction to give the oxygen and nitrogen-centered radicals respectively. However the reaction of aliphatic chloramines with silver salts was more controversial. While considerable evidence has been provided by Gassman for heterolytic fission of the W-C1 bonds in a number of cases (3), our studies showed that this did not take place at room temperat~are with N-chloropiperidine or medium ring chloramines. The need for amine to initiate reaction, the formation of parent secondary anline: and the sensitivity of the reactions to oxygen led us to conclude that traces of metallic silver were initiating these reactions a!so. This conclusion is now supported by radical trapping evidence.N o radicals were detected when a degassed soliltion of N-chlorsaaacyclononane, indolizidine, and silver perchlorate in 90% aqueous acetonitrile was examined In the e.p.r. speclrorneter. However if 2-methy"l-i-nitrosopropa11e (4) was present during the reaction, a nitroxide with hyperfine splitting consisteent with striictcre 1 was observed. Tile same i~itroxicle was formed when the chlorarnine was treated in cactio with --lNRGG No. 12946. metallic silver in the presence of the nitroso compound. In a similar manner the radical 2 was identified in reaction of N-chloropiperidine with silver.We conclude that silver induces homolytic fission of the chloramines as in eq. 1. A comparable reaction of N-chlorosuccinimide and N-bromosuccinimide takes place and the succinirnidyl radical was trapped in the N-chloro case as nitroxide 3. However preparative runs ill RzNCl + Ag(0) + R z N f AgCl with N-bromosuccinimide showed that the succinarnidyl radical was rapidly reduced further to the anion (eq. 2). This provides a convenient high yield route to the silver salt of succinimide. The stability of the aslion must contribute mar...

The free radical chemistry of the azoxy group

“…58 This intermediate nitroxyl radical was not detected by ESR in this experiment nor when generated independently at room temperature by trapping the aziridinyl radical from 37 59,60 with nitroso-t-butane. 61 Instead, the observed ESR signals were consistent with structure 38, suggesting that 35 is quite labile even at 25 °C .…”

“…Although the major product was the carboxylic acid precursor of 70, the presence of 74 was proven unambiguously, suggesting that 71 cyclizes to 72, which then reopens to 73. 73 Six-membered analogs of 72 were shown to be persistent by ESR at room temperature 59 but in our case, the gem dimethyl group, five-membered ring strain, and high temperature would all contribute to rapid opening of 72.…”

Recent controversy on imidyl radical chemistry

“…Imidyl radicals eluded efforts to detect them by direct ESR spectroscopic techniques [22,23] and by kinetic analysis [9] for almost two decades, although spin trapping with 2-nitroso-2-methylpropane during NBS decomposition gave the corresponding succinimidyl nitroxide [24,25]. These negative results serve to illustrate the complex side reactions involved in the attempted generation of imidyl radicals by the Nbromoimide decomposition route, which still remains the most popular one.…”

Aminyl Free Radicals

“…Steric shielding of the aminyl nitrogen is an important factor contributing to the stability of aminyl free radicals. The monomeric radicals (20) and (22) The lifetime of aminyls is also significantly influenced by mesomeric stabilization of the radical. An example for an extensive delocalization of the unpaired electron is the deep red 10-ethyl-5-phenazinyl (23) ["].…”

“…(19) (20) (21) Iminyl radicals (21) are readily accessible by photolysis of a~i n e s [~~] or solutions of ketimines in di-terf-butyl peroxide[331. They are also observed during the thermal rearrangement of compounds such as 0-phenylmethyleneamino-N,Ndirnethylthi~carbamate[~~~, and appear frequently, when amines are subjected to high-energy irradiation[3s-38!…”