Generation and reactions of the ammoniumyl radical cation (NH₃^+˙): an electron spin resonance investigation

Abstract

E.s.r. spectroscopy has been employed to study the reactions of a variety of organic compounds with ammoniumyl (N H,+') generated in a flow system from the titanium( Ill)-hydroxylamine couple. Radicals resulting from hydrogenatom abstraction from certain substrates ( e . g . alkanols) have been detected and it is concluded that NH,+* is an electrophilic species with a greater degree of selectivity than hydroxyl. A pseudo steady-state analysis for radicals in the cavity is shown to be appropiiate and values have been obtained for the rate constant for the initiating reaction [k(TiIII + NH,OH) ca. 6 x 105 I mo1-I s-l at pH 21 and for the relative rates of attack of NH,+' on different substrates. YO1 5DDIT is generally accepted that the titanium(II1)-hydroxylamine redox couple is an effective source of *NH2-or, depending on the pH, NH3+*-as shown in reactions (i) and (ii) . For example, synthetic applications involving

Electron spin resonance studies. Part 61. The generation and reactions of the t-butoxyl radical in aqueous solution

“…Since the two adducts are of similar molecular weight and would be expected to have similar radical-solvent interactions it is suggested that the assumption that 2k,, = 2k,, = k,, may be made without introducing significant errors. Thus equation ( 24) reduces to (25).…”

“…Expression (25) was employed to determine k4/k,, for propan-2-01 by varying the concentration of the latter and plotting the ratio [MeT*]/[RT*] against l/[Me,CHOH] (Figure 2). The slope of this plot which, as predicted by (from ButOOH and Ti1IX) in the presence of propan-2-01 and cis-butenedioate (0.03 mol dm-3) at pH 6.3 equation ( 25), passes through the origin, leads to a value for the ratio of the rate constants for fragmentation and for abstraction from propan-2-01 of 1 : 3.7 5 0.4.…”

Electrochemical amination of unsaturated and aromatic compounds

“…The rate constants of reactions like ( 17) and ( 18) and relative reactivity of organic compounds towards the aminating reagent are usually estimated by physical methods [22,23,30,31]. The electrochemical methods are based on changes in the limiting current of the M n+ oxidation wave in time or in the M ~n+ 1)+ catalytic reduction current.…”

“…It is expedient to aminate unsaturated and aromatic organic compounds in acidic media, where the aminating reagent is presented by the most electrophilic radical cation. Moreover, in acidic solutions, problems of the mediator hydrolysis and the hydroxylamine decomposition (equations ( 7), ( 8)) disappear; the rate of reaction (3) competing with the amination process decreases; and the following reactions are completely suppressed [28,30,31,34]:…”

Gas and solution phase thermochemistry and transition energies of NH2• and NH3•+, and their aquo complexes: an ab initio study

“…~i " ' + NH20H + ~i " + NH2' + OHor in pulse radiolysis by abstraction of H atoms from NH3 with OH' (7,8) PI OH' + NH3 + H 2 0 + NH2' NH3'+ cations can be made by photolysis of NH3 complex ions (1,9), e.g., Radicals produced by those methods have been examined by polarography (10,11) and ESR (12,13), and the kinetics of some of their reactions have been investigated by fast-reaction techniques (6)(7)(8)(9)13). Extensive gas phase investigations on the species have been conducted (14)(15)(16) and theoretical calculations on their energies and structures have been made at relatively high level (17).…”