Quinones from aromatic amines

On the other hand, there is at least one case of an aromatic amine without a hydroxy group in the 2-position, namely 1-aminophenazine (25) which, after the initial diazotiza-tion, is oxidized within minutes by air or additional nitrous acid to the quinone diazide 26 (equation 9)46. In the corresponding diazotization of 2-aminophenazine the proportion of the quinone diazide (isomer of 26) amounted to only 16%, but 30% unsubstituted phenazine was also found. The phenazine may have resulted from the overall redox reaction. 

Tryptophan tryptophanylquinone (TTQ). This recently discovered quinone cofactor is similar to the lysyl tyrosylquinone but is formed from two trypto-phanyl side chains.466 It has been found in methyl-amine dehydrogenase from methylotrophic gramnegative bacteria467-469 and also in a bacterial aromatic amine dehydrogenase.470... 

Polymerization inhibitors stop or slow down polymerization by reacting with the initiator or growing-chain radicals. A wide variety of substances can behave as inhibitors quinones, hydroquinones, aromatic nitro compounds, aromatic amines, and so on. In cases where the inhibitor is a hydrogen donor (symbolized here by InH), then for inhibition to occur, the radical resulting from hydrogen transfer (In-) must be too stable to add to monomer. If it does add to monomer and starts a new chain, chain transfer occurs instead of inhibition. For perfect inhibition, the In- radicals must combine with themselves (or initiator radicals) to give inert products ... 

Figure 3.55. Plot of cf)es versus AG for the ECL systems involving Ru(phen)3+ (a), Ru(bipy)3+ (b), and Ru(baph)3+ (c) ions in 0.1 M (C2H5)4NPF6 acetonitrile solutions. Data for the ECL systems with nitrocompounds ( ), quinones (o), iV-methylpyridinium cations ( ), and aromatic amines or 2,3,7,8-tetramethoxythianthrene ( ). (From Ref. 193.)...

The spin status of the ion pair is another crucial variable affecting the overall efficiency of the process. The forward electron transfer from (or to) a diamagnetic molecule is not affected by the spin status of the excited component. The back electron transfer, however, is forbidden within the triplet ion pairs (it would violate Pauli s exclusion principle). In situations like that the intersystem crossing will very often determine the efficiency of BET. In practice, the triplet state acceptors or donors lead to overall efficiencies that are higher than those observed with singlet state acceptors or donors [38,78,102,103,116]. An additional bonus is the fact that triplet states have longer lifetimes [2] and are efficiently ET-quenched with lower concentrations of the ground state component. Quinones and ketones are the most common triplet acceptors, while aromatic amines often serve as triplet donors. 

Barium manganate, BaMn04, is commercially available. The dark-blue crystals are obtained from aqueous solutions of barium chloride and potassium permanganate [552, 555]. It oxidizes alcohols, especially benzylic alcohols, to carbonyl compounds [552, 555] hydroquinone to quinone [555] benzylamines to benzaldehydes [555] aromatic amines to azo compounds [555] and phosphines to phosphine oxides [555],... 

The liquid phase NMR spectra comprise the first direct spectroscopic evidence differentiating phenoloxidase- and metal-catalyzed reactions from noncatalyzed nucleophilic addition reactions of aniline with humic substances. The solid state NMR spectra provide the first direct evidence for nucleophilic addition of aniline to quinone and other carbonyl groups in the organic matter of whole soil and peat. The NMR approach has potential for further investigation of the effects of reaction conditions on the incorporation of aromatic amines into naturally occurring organic matter, and for studies on how aromatic amines covalently bound to organic matter may ultimately be re-released or remineralized, either chemically or microbially. 

An indirect electrochemical method developed for nitrite determination may be of general applicability for PAA determination, as shown in equation 13. A nitrite sample is placed into a cell containing a known amount of 3-sulfanilic acid in dilute HC1 at pH 3. After 5 min the diazonium ion formation is complete an excess of catechol (109) is added and the concentration of the remaining 3-sulfanilic acid is determined at +0.12 V with a GCE vs. standard calomel electrode, by measuring the adduct (110) formed between the aromatic amine and the quinone derived from catechol in the diffusion layer of the electrode. The 3-isomer of sulfanilic acid was chosen among the three isomers, aniline and 4-nitroaniline for its highest sensitivity and its lowest LOD, 0.7 pM, with linearity from 20 to 80 pM. A spectrophotometric assay may be carried out for nitrite by measuring at 516 nm the azo dye derived from catechol and the diazonium ion after 3 h ... 

Pyrolysis of the Mannich base (109) derived from 2-naphthol leads to generation of a quinone methide which when trapped with an aromatic amine leads to benz[a]acridines (0. Bilgic and D.W. Young, J. chem. Soc. Perkin I, 1980, 1233). Thus, aniline yields the parent compound together with 7,12-dihydrobenz[a]acridine. Formation of the dihydro compound appears to be variable for whereas /7-metlylaniline and o-anisidine yield only... 

The constant potential amperometric detector determines the current generated by the oxidation or reduction of electoactive species at a constant potential in an electrochemical cell. Reactions occur at an electrode surface and proceed by electron transfer to or from the electrode surface. The majority of electroactive compounds exhibit some degree of aromaticity or conjugation with most practical applications involving oxidation reactions. Electronic resonance in aromatic compounds functions to stabilize free radical intermediate products of anodic oxidations, and as a consequence, the activation barrier for electrochemical reaction is lowered significantly. Typical applications are the detection of phenols (e.g. antioxidants, opiates, catechols, estrogens, quinones) aromatic amines (e.g. aminophenols, neuroactive alkaloids [quinine, cocaine, morphine], neurotransmitters [epinephrine, acetylcoline]), thiols and disulfides, amino acids and peptides, nitroaromatics and pharmaceutical compounds [170,171]. Detection limits are usually in the nanomolar to micromolar range or 0.25 to 25 ng / ml. 

An elegant new synthesis of polycyclic heteroaromatic compounds via quinone-methide intermediates is illustrated in Scheme 60. The required quinone-methides have also been generated from hydroxy-pyridones and -coumarins, and these have been allowed to react with a wide selection of aromatic amines. ... 

The dehydration of 3-hydroxyindolines (cf. 2 inSchane 2) was the tactic for indolization in other indole syntheses. For example, Boimet-Delpon s team prepared 3-trifluQro-methylindoles from the corresponding 3-hydroxyindoIines (SOCl, pyridine, 80%-87%), which were obtained from the reaction of aromatic amines and triflnoiomethyl epoxy ethers [13], and Swenton and cowoikers prepared 2,3-dime-thyl-5-methoxyindole by acid-catalyzed dehydration of the 3-hydroxyindoline, and they also effected loss of methanol from C-5 of quinone imine ketals to give, for example, 5,6-dimethoxyindole (73%) [14]. A more common indolization of indolines is the elimination of sulfinate from Al-substi-tuted-sulfonylindoles, and both base- and acid-catalyzed examples are known (Scheme 3, equations 1-3) [15-17]. 

The scope of the catalytic potential of the cerium(III) ion was intimated by Pratt (1962) in an investigation of the addition of aromatic amines to quinones. Use of hydrated cerous chloride in place of cupric acetate as an oxygen carrier in the oxidation of byproduct hydroquinone resulted in improved yields and easier product separation from metal complexes. 

Tyrosinase catalyzes the reactions other than those shown in eq. (28), e.g, stepwise oxidation of aromatic amines to o-aminophenols and o-quinone imines as shown in eq. (29) [244]. Products were isolated as quinone anils or phenoxazones. The reaction is different from those by other oxidizing agents, because of the regiospecific hydroxylation of the ortho position and further oxidation of the intermediate -aminophenol. The... 

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