Interaction of chlorine dioxide with nitroxyl radicals

The formation of charge transfer complexes between chlorine dioxide and nitroxyl radicals (2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-acetylamido-2,2,6,6-tetramethylpiperidin-1-oxyl, 2,2,5,5-tetramethyl-4-phenyl-3-imidazolin-1-oxyl, and bis(4-methoxyphenyl) nitroxide) in acetone, acetonitrile, n-heptane, diethyl ether, carbon tetrachloride, toluene, and dichloromethane was found by spectrophotometry at –60—+20 °C. The thermodynamic parameters of complex formation were determined. The radical structure affects its complex formation ability. The charge transfer complex is transformed into the corresponding oxoammonium salt.     

Experimental and Quantum Chemical Studies of 2-Phosphinylphenol Derivatives

Carbon-oxygen bonds ortho to a phosphoryl group in triarylphosphine oxides undergo cleavage when the oxides are either fused with potassium hydroxide or treated with potassium tert-butoxide in refluxing toluene, presumably through a nucleophilic addition-elimination mechanism. Thus, bis(2-hydroxyphenyl)phenylphosphine oxide is produced along with the expected 2-phenoxyphenyl(phenyl)phosphinic acid from 10-phenyl-10H-phenoxaphosphine 10-oxide. The latter starting material is also produced, together with bis(2-hydroxyphenyl)phenylphosphine oxide, when bis(2-methoxyphenyl)phenylphosphine oxide is fused with potassium hydroxide. Fusion of bis(2-methoxyphenyl)phenylphosphine oxide with sodium hydroxide, however, yields 2-hydroxyphenyl(phenyl)phosphinic acid. Ab initio quantum chemical studies confirm that the downfield ³¹P chemical shift that is observed in 2-phosphinylphenols is due to hydrogen bonding to the phosphoryl group.     

Reductive chlorination of bis(4-tert-butylphenyl)amine-N-oxyl nitroxyl radical

Unlike cyclic aliphatic nitroxyls, whose oxidation with halogens gives oxoammonium salts, bis(4-tert-butylphenyl)amine-N-oxyl (1) treated with chlorine undergoes reductive chlorination to the corresponding di- and trichlorodiphenylamines. Chlorine partially dealkylates the compounds obtained. Plausible mechanisms for these reactions were suggested.     

Acid catalyzed multiple chain termination by quinone monoanilide in oxidizing hydrocarbons

A novel ternary system that causes multiple chain termination in oxidizing hydrocarbons is suggested. The system involvesN-phenylquinone imine, hydrogen peroxide, and citric acid. The inhibiting effect of the system is studied for the initiated oxidation of methyl oleate and ethylbenzene. The rate of the inhibiting oxidation of the hydrocarbon is proportional to the initiation rate and inversely proportional to the product of the concentrations of quinone imine, hydrogen peroxide, and the acid. The mechanism proposed involves the protonation of quinone imine, the abstraction of an H atom from quinone imine by the peroxyl radical, the reduction of the resulting radical cation by hydrogen peroxide to form the semiquinone radical, and the reaction of the latter with RO₂.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 79–82, January, 1995.     

Cascade synthesis of 2-amino-5-(4-methoxyphenyl)-4-phenyl-1,3-thiazole by reaction of 4-chloro-<Emphasis Type="Italic">N</Emphasis>-[2,2-dichloro-1-(4-methoxyphenyl)-2-phenylethyl]benzenesulfonamide with thiourea

4-Chloro-N-[2,2-dichloro-1-(4-methoxyphenyl)-2-phenylethyl]benzenesulfonamide reacted with thiourea on heating in DMF in the presence of sodium carbonate to give 5-(4-methoxyphenyl)-4-phenyl-1,3-thiazole-2-amine. A probable reaction scheme includes cyclization of the initial N-dichloroethyl amide to N-sulfonyl-2,3-diaryl-2-chloroaziridine which undergoes isomerization with opening of the three-membered ring to 1-arylsulfonylamino-2-chloro-2-(4-methoxyphenyl)-1-phenylethene. The subsequent heterocyclization in the reaction with thiourea is accompanied by aromatization via elimination of the arenesulfonamide fragment.     

Cycloadditions of anionic N-heterocyclic carbenes of sydnone imines

Sydnone imines were deprotonated with lithium bis(trimethylsilyl)amide at the C4 position to give the corresponding sydnone imine anions as lithium adducts. These can be represented as lithium stabilized anionic N-heterocyclic carbenes. Treatment with diisopropyl azodicarboxylate (DIAD) gave the corresponding C4 adducts, i.e. 4-hydrazinyl-sydnone imines, which form tautomers in solution. Reductive 1,3-dipolar cycloadditions of the sydnone imine anions with tetracyanoethylene (TCNE) resulted in the formation of pyrazoles, the mechanism of formation of which differs from known reactions. Reaction of the anion derived from the 2-methoxyphenyl sydnone imine with N,N-diisopropylcarbodiimide gave a ring-cleaved bisiminonitrile. Structure elucidations were accomplished by NMR spectroscopy and by four single crystal X-ray analyses.     

Access to Nitriles from Aldehydes Mediated by an Oxoammonium Salt

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4‐acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl‐imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.     

Spontaneous hydrolysis reactions of cis- and trans-beta-methyl-4-methoxystyrene oxides (Anethole oxides): buildup of trans-anethole oxide as an intermediate in the spontaneous reaction of cis-anethole oxide

Rates and products of the reactions of trans- and cis-beta-methyl-4-methoxystyrene oxides (1 and 2) (anethole oxides) and beta,beta-dimethyl-4-methoxystyrene oxide (3) in water solutions in the pH range 4-12 have been determined. In the pH range ca. 8-12, each of these epoxides reacts by a spontaneous reaction. The spontaneous reaction of trans-anethole oxide (1) yields ca. 40% of (4-methoxyphenyl)acetone and 60% of 1-(4-methoxyphenyl)-1, 2-propanediols (erythro:threo ratio ca. 3:1). The spontaneous reaction of cis-anethole oxide is more complicated. The yields of diol and ketone products vary with pH in the pH range 8-11, even though there is not a corresponding change in rate. These results are interpreted by a mechanism in which 2 undergoes isomerization in part to the more reactive trans-anethole oxide (1), which subsequently reacts by acid-catalyzed and/or spontaneous reactions, depending on the pH, to yield diol and ketone products. The buildup of the intermediate trans-anethole oxide in the spontaneous reaction of cis-anethole oxide was detected by (1)H NMR analysis of the reaction mixture. Other primary products of the spontaneous reaction of 2 are (4-methoxyphenyl)acetone (73%) and threo-1-(4-methoxyphenyl)-1,2-propanediol (ca. 3%). The rates and products of the spontaneous reaction of 2 and its beta-deuterium-labeled derivative were determined, and the lack of significant kinetic and partitioning deuterium isotope effects indicates that the isomerization of 2 to ketone and to trans-anethole oxide must occur primarily by nonintersecting reaction pathways.     

Spectroscopic and calorimetric studies on the mechanism of methylenecyclopropane rearrangements triggered by photoinduced electron transfer

2-(dideuteriomethylene)-1,1-bis(4-methoxyphenyl)cyclopropane (d(2)-1) undergoes degenerate rearrangement in both singlet- and triplet-sensitized electron-transfer photoreactions. Nanosecond time-resolved absorption spectroscopy on laser flash photolysis of the unlabeled 1 with 9,10-dicyanoanthracene, 1,2,4,5-tetracyanobenzene, or N-methylquinolinium tetrafluoroborate as an electron-accepting photosensitizer gives rise to two transients with lambda(max) at 500 and 350 nm assigned to the dianisyl-substituted largely twisted trimethylenemethane cation radical (6.+) and the corresponding diradical (6..), respectively. These intermediates are also detected, respectively, by steady state and nanosecond time-resolved EPR with chloranil or anthraquinone as a sensitizer. The degenerate rearrangement of d(2)-1 thus proceeds via these two different types of intermediates in a cation radical cleavage-diradical cyclization mechanism. Energetics based on nanosecond time-resolved photoacoustic calorimetry support this mechanism. A comparison of the reactivities and the spectroscopic results of 1, 1,1-bis(4-methoxyphenyl)-2-methylenespiro[2.2]pentane (2), and 1-cyclopropylidene-2,2-bis(4-methoxyphenyl)cyclopropane (3) suggest that the reversible methylenecyclopropane rearrangement between 2 and 3 proceeds via a similar mechanism.     

Theoretical and experimental investigation on the near-infrared and UV–vis spectral regions of a newly synthesized triarylamine electrochromic system

A new triarylamine derivative, N,N′-Bis(4-heptanoylamidophenyl)-N,N′-di(4-methoxyphenyl)-1,4-phenylenediamine, with stable electrochromism in near-infrared and visible light regions, has been synthesized and characterized at theoretical and experimental level. The detected and simulated spectra, with and without the presence of an external potential at different values, clearly show that this mixed-valence system undergoes ionization at a low value of the applied potential, and the formed radical cation absorbs in the near-infrared region with an intense peak located at 1,040 nm. Density functional computations give the geometrical structure and absorption properties in very good agreement with experiment, allowing assigning the electronic transition and contributing to an understanding of the electron-transfer process between the two redox centers.     

Functionalized β-lactams based on (<Emphasis Type="Italic">E</Emphasis>)-1-(furan-2-yl)-<Emphasis Type="Italic">N</Emphasis>-[(4-methoxyphenyl)methyl]methanimine and its imine–imine rearrangement initiated by potassium hydride

Functionalized β-lactams were synthesized by reaction of (E)-1-(furan-2-yl)-N-[(4-methoxyphenyl)-methyl]methanimine with ketenes generated in situ from chloro- and dichloroacetic acids and 3-(methoxyimino) butanoic acid. (E)-1-(Furan-2-yl)-N-[(4-methoxyphenyl)methyl]methanimine underwent imine–imine rearrangement by the action of potassium hydride to give thermodynamically more stable (E)-N-[(furan-2-yl)-methyl]-1-(4-methoxyphenyl)methanimine.     

Synthesis of mannich bases of bioactive benzylphenols

2,4-Bis(1,1-dimethyl)-6-[(4-methoxyphenyl)methoxymethyl]phenol ( 4 ), prepared by oxidation of 2,4-bis(1,1-dimethylethyl)-6-[(4-methoxyphenyl)methyl]phenol ( 1 ) with silver oxide in methanol, reacts with secondary amines in boiling toluene to give Mannich bases ( 6 ) related to the biologically active o-benzylphenol. Mannich basis of the isomeric p-benzylphenol ( 7 ) were prepared by reaction of amines with the p-quinone methide formed by oxidation of 7 .     

Trimethylsilyl triflate as an initiator for cationic polymerization: Improved initiation through the use of promoters

Trimethylsilyl triflate (TMSOTf) can be used as an initiator for the cationic polymerization of alkenes and heterocycles. However, TMSOTf without additives and promoters acts inefficiently. Initiation in the cationic polymerization of tetrahydrofuran is slow because of unfavorable charge distribution in the trimethylsilyltetrahydrofuranium cation—a product of the reaction of monomer with TMSOTf. Acetone, 1,3-dioxolane, and 1,2-propylene oxide have been used as promoters to react with TMSOTf to create more reactive initiating species and to improve efficiency of initiation. Of these promoters, 1,2-propylene oxide has been the most successful. When TMSOTf has been used to initiate the polymerization of 2-methyl-2-oxazoline, unfavorable charge distribution in the N-trimethylsilyl-2-methyl-2-oxiranium cation has produced an unreactive imine dimeric cation which extends the time required for polymerization to several weeks. 1,2-Propylene oxide has been utilized to prevent formation of the imine dimeric cation by producing a more reactive initiating species. In the polymerization of isobutyl vinyl ether initiated by TMSOTf, 1,2-propylene oxide has been shown to be ineffective as a promoter, but acetone can be used successfully. © 1995 John Wiley & Sons, Inc.     

Reaction of some N-substituted 1,4-benzoquinone imines with sodium arenesulfinates

N-Arylsulfonyl, N-aroyl, and N-[arylsulfonylimino(phenyl)methyl] derivatives of 1,4-benzoquinone imine reacted with sodium arenesulfinates to give 1,4-, 1,6-, and 6,1-addition products which were formed according to two concurrent paths: direct nucleophilic addition of arenesulfinate anion to neutral quinone imine molecule and radical ion addition of arenesulfinate radical to radical anion derived from quinone imine.     

Pinacol-Pinacolone Rearrangement of 1, 2-Di-(p-methoxyphenyl)-ethane-1, 2-diol and Bis-(4-methoxyphenyl)-acetaldehyde in Acid Media

1, 2-Di-(p-methoxyphenyl)-ethane-1, 2-diol gave in acid media bis-(4-methoxy-phenyl)-acetaldehyde, 4-4′-dimethoxy-deoxybenzoin, and 1, 2-di-(p-methoxyphenyl)-ethylene oxide; their respective yields being influenced by at least 3 factors: (i) the acid, (ii) its concentration, and (iii) the reaction period. Bis-(4-methoxyphenyl)-acetaldehyde rearranged to the deoxybenzoin in boiling sulfuric (50%) or phosphoric (75%) acids (w/w), and to two isomeric 1, 2-diacetoxy-1, 2-di-(p-methoxyphenyl) ethanes when it was heated with acetic anhydride. The mechanisms of these reactions are discussed.     

Disulfides, imines, and metal coordination within a single system: interplay between three dynamic equilibria

We report a system in which three distinct dynamic linkages, disulfide (S-S), imine (C=N), and coordinative (N-->metal) bonds were shown to be capable of simultaneous reversible exchange. The "disulfide layer" of the system under study consists of two homo-disulfides, bis(4-aminophenyl) disulfide 1 and bis(4-methoxyphenyl) disulfide 2 that equilibrate in the presence of catalytic amount of triethylamine to favor the formation of a hetero-disulfide product, 4-aminophenyl-4'-methoxyphenyl disulfide 3. The addition of 2-formylpyridine and a metal salt strongly perturbed this 1+2<-->3 equilibrium through the formation of metal complexes incorporating disulfide 1 as a subcomponent. CuI perturbed the equilibrium by a factor of 3.3, and FeII by a factor of 179, in both cases in favor of the homo-disulfides. The disulfide equilibrium could be further modified, following metal-complex formation, by coordinative (transmetallation: substitution of FeII for CuI) or covalent (imine exchange: the substitution of one amine residue for another) exchange. Thus, although the three kinds of dynamic linkages were demonstrated to be mutually compatible, changes at one kind of linkage could be used to predictably perturb an equilibrium involving another.     

Kinetics and mechanism of one-electron oxidation of bilirubin in dichloromethane solution

Bilirubin (BR) was oxidized by tris-(4-bromophenyl)-ammonium hexachloraantimonate (1), 2,2,6,6-tetramethyl-4-acetyloxypiperidine oxoammonium hexachloroantimonate (2) and 2,2,6,6-tetramethyl-4-methoxypiperidine oxoamonium tetrafluoroborate (3) to the corresponding radical cation. The rate and activation parameters for the reaction were determined. An electron transfer mechanism is proposed based on the kinetic results.     

Polymerization of Methyl Methacrylate with Ni(II) α‐Diimine/MAO and Fe(II) and Co(II) Pyridyl Bis(imine)/MAO

Polymerizations of methyl methacrylate with (α‐diimine)nickel(II)/methylaluminoxane (MAO) and (pyridyl bis(imine))iron(II) and (pyridyl bis(imine))cobalt(II)/MAO are reported. Effects of structural variation of the ligand on the activities of catalysts and polymer microstructure are described. The catalyst systems gave syndio‐rich poly(methyl methacrylate). The α‐diimine system showed much higher activity than the pyridyl bis(imine) systems under similar polymerization conditions.

     

EPR Study on the Complex Formed by Charge‐Transfer Process between Ground‐state Acceptor 2, 3‐Dicyano‐5, 6‐dichloro‐1, 4‐benzoquinone and Some Donors and on Cation Radical of Perylene (or Pyrene)

EPR study showed that the semi‐quinone radical anion of 2,3‐dicyano‐5,6‐dichloro‐1,4‐benzoquinone (DDQ) was formed in a charge transfer process between ground‐state DDQ as acceptor and each one of following ground state donors, i.e., 4‐methyl‐4′‐tridecyl‐2, 2′‐bipyridyl; 4‐methyl‐4′‐nonyl‐2, 2′‐bipyridyl; bis (2,2′‐bipyridyl) (4‐methyl‐4′‐heptadecyl‐2, 2′‐bipyridyl)ruthenium(2+) perchlorate and perylene. EPR study also showed that there are perylene cation radical and pyrene cation radical in the following experimental conditions: (a) in 98% sulfuric add. (b) 10^?3 mol/L perylene (or pyrene) was dissolved in trifluoroacetic acid‐nitrobenzene (1: 1 V/V).     

Synthesis and oxidation of triarylamine derivatives bearing hydrogen-bonding groups

Hydrogen-bonding triarylamines, 4-(N,N-bis(4-methoxyphenyl)amino)benzoic acid (TPA1), 5-(N,N-bis(4-methoxyphenyl)amino)isophthalic acid (TPA2), and N-(4-(1H-benzimidazol-2-yl)phenyl)-N,N-bis(4-methoxyphenyl)amine (BImTPA), were synthesized as radical cation precursors. TPA1 and TPA2 are readily p-doped by AgSbF(6) to give highly persistent radical cations. Poor solid-state spin yields of the radical cation from BImTPA may be due to spin delocalization.