Triethylamine cation radical

FDMR has also been used to detect the transient radical cations formed from secondary amines by pulse radiolysis. As mentioned earlier this technique has been used to study a variety of systems such as the radical cation of triethylamine. The radical cations of diethylamine, n-propyl amine and f-butylamine, have also been studied25. The results have shown that the FDMR signal is enhanced with increasing alkyl substitution of the amine as in the pyrrolidines (18) and the piperidines (19)25. 

The anion-radical of 2,4-dinitrochlorobenzene and cation-radical of triethylamine pass into the solvent volume. In this case, both acceptors (p-BQ, tetracyanoethylene, and tetracyanoquinodime-thide) and donors of an electron (potassium iodide, ferrous sulfate, and A/,N-tetramethyl-p-phenyl-enediamine) inhibit substitution (Shein 1983). 

Deprotonation is essential in some cation radical reactions the corresponding examples will be described in Chapter 6. Scheme 1-43 depicts a photoreaction between phenan-threne and triethylamine. This reaction includes photoinduced sequential electron-transfer, proton-transfer, and radical-recombination processes (Lawson et al. 1999). 

It is quite evident that both anion and cation radicals cannot always leave the solvent cage and exist together in the bulk solution for a long time. One such rare example is the nucleophilic substitution of chlorine in 2,4-dinitrochlorobenzene (substrate) by the diethy-lamino group from triethylamine (reactant) (Scheme 4-16). 

Little is to be found in the literature on the reaction of cation radicals with alkylamines. Shang and Blount (1974) found that DPA + reacts with triethylamine in an ECE sequence to give the... 

The radical cation and neutral radical derived from triethylamine are shown below. 

Bobrowski and Das33 studied the transient absorption phenomena observed in pulse radiolysis of several retinyl polyenes at submillimolar concentrations in acetone, n -hexane and 1,2-dichloroethane under conditions favourable for radical cation formation. The polyene radical cations are unreactive toward oxygen and are characterized by intense absorption with maxima at 575-635 nm. The peak of the absorption band was found to be almost independent of the functional group (aldehyde, alcohol, Schiff base ester, carboxylic acid). In acetone, the cations decay predominantly by first-order kinetics with half life times of 4-11 ps. The bimolecular rate constant for quenching of the radical cations by water, triethylamine and bromide ion in acetone are in the ranges (0.8-2) x 105, (0.3-2) x 108 and (3 — 5) x 1010 M 1 s 1, respectively. 

Photolysis of DMDAF in benzene containing methyl alcohol gives the ether expected from the reaction of the singlet carbene. Monitoring this reaction by laser spectroscopy reveals that the detected transient reacts with the alcohol with a bimolecular rate constant very near the diffusion limits. In contrast, the transient reacts with triethylamine at least 100 times more slowly than it does with alcohol (Table 7). This behavior is inconsistent with identification of the transient as the cation or radical and points to its assignment as the singlet carbene. 

Triethylamine can also be converted into the corresponding radical cation by /-irradiation at low temperature in trichlorofluoromethane4 5 or by oxidation with the... 

The 1,4-photoaddition of aliphatic amines with benzene via photoinduced electron transfer was first reported by Bryce-Smith more than 30 years ago [375-378], In the photoreaction of triethylamine with benzene, the proton transfer from the radical cation of triethylamine to the radical anion of benzene is proposed as a probable pathway (Scheme 113). In the case of tertiary amines, the photoaddition is accelerated by the addition of methanol or acetic acid as a proton source. Similar photoaddition of diethyl ether to benzene takes place assisted by trifluoroacetic acid, where methanol is not affective [379], In these photoreactions, a-hydrogen next to the heteroatom moves to the radical anion of benzene as a proton, followed by radical ccoupling to give 1,4-addition products. Similar photoaddition of amines to the benzene ring has been reported by Ohashi et al. [380,381],... 

An unusually easy conversion of A-alkylazinium cations into the uncharged azines occurs when the iodides (73) are treated with triethylamine at room temperature. The reaction pathway seems to involve a free radical intermediate (Scheme 27) [95MC104]. 

Various other [3 + 2] cycloadditions, affording chiral, anellated C6o derivatives with stereogenic centers in the addends are reported in literature. The products were generally obtained as racemates and resulted from reaction of buckminsterfullerene with species like 2,3-disubstituted 2//-azirincs (via nitrile ylides [under direct irradiation] or via 2-azaallenyl radical cations [sensitization by photoinduced electron transfer]),365 1-substituted 5-diazopentane-1,4-diones (via cyclic carbonyl ylides),366 7-alkylidene-2,3-diazabicyclo[2.2.1] hept-2-ene (via a diradicaloid trimethylenemethane derivative),367 1-benzylpy-razolidine-3-ones in the presence of aldehydes (via pyrazolidinium ylides),368 2-trifluoromethyl-2,5-dihydro-l,3-oxazol-5-ones (via nitrile ylides),369 nitro-alkanes in the presence of triethylamine and trimethylsilyl chloride (via N-silyloxynitrones),370 or dv-HOCH2 CH=C H C H 2 OCO 2 H( in the presence of... 

Extensive studies of the sensitizer dependence and the solvent dependence of the polarization patterns led to the identihcation of two parallel pathways of that deprotonation. One is a proton transfer within the spin-correlated radical pairs, with the radical anion A acting as the base. The other is a deprotonation of free radicals, in which case the proton is taken up by surplus starting amine DH. Furthermore, evidence was obtained from these experiments that even in those situations where the polarization pattern suggests a direct hydrogen abstraction according to Equation 9.6 these reactions proceed as two-step processes, electron transfer (Eq. 9.7) followed by deprotonation of the radical cation by either of the described two routes. The whole mechanism is summarized by Chart 9.3 for triethylamine as the substrate. Best suited for an analysis is the product V. 

As mentioned above, triplet Cgo is readily photoreduced by amines and other donors to Cgo radical anion and the donor radical cations [64], We expected this reaction to lead to adducts with covalent bonds. Such adducts are formed with some amines in ground state chemistry [33, 60, 83], but the photochemical process should be more selective and easily controlled, since only one-electron reduction is possible in the photochemical process. C o in the Si state has been suggested to produce an exciplex with triethylamine which seems to react with ground-state Cgo to give a stable product [117]. The reduction potential of the triplet is high enough that electron-transfer from many donors such as electron-rich aromatics and alkenes should be possible. 

The amine radical cation of triethylamine formed in these reactions can exist in an acid-base equilibrium, as shown in Scheme 6. 

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