Thermal and Photochemical Decomposition of Dihydrooxadiazinones

3,6-Dihydro-1,3,4-oxadiazin-2-ones may be prepared from either α-ketols or from α-diketones and carbethoxyhydrazine. These substances undergo thermal or photolytic (253.7 nm) decomposition to give N₂, CO₂ and olefins. Oxadiazinones derived from medium ring α-ketols give bicyclic hydrocarbons in addition to olefins. These are shown to be formed by decomposition of the intermediate vinyldiazene to vinyl radicals, followed by transannular hydrogen abstraction and alkyl radical addition to the olefin. A series of 5,6-dihydro-1,3,4-oxadiazin-2-ones have also been prepared and their thermal and photolytic behavior studied.     

Effect of co-adsorbed dopants on initial diamond growth steps: H abstraction from an adsorbed CH3

The effect induced by a neighbouring co-adsorbed dopant on H abstraction from an adsorbed CH₃ species on diamond has been investigated by using an ultra-soft pseudo-potential density functional theory (DFT) method under periodic boundary conditions. Both the (100) and (111) diamond surface orientations were considered with various types of dopants in two different hydrogenated forms; AH_x (A = N, B, S, or P; X = 0 or 1 for S; X = 1 or 2 for N, B and P, and X = 2 or 3 for C). The H abstraction by gaseous radical H was found to be energetically favoured by the presence of the dopants in all of their different hydrogenated forms. For NH₂, SH, or PH₂, this effect is induced by a destabilisation of the diamond surface by sterical repulsions between the adsorbed growth species CH₃ and the co-adsorbed dopant. For BH₂ and the dopants in their radical form, the abstraction reaction is favoured due to the formation of a new covalent bond between the dopant and the co-adsorbed CH₂ (product of the abstraction reaction), which strongly stabilises the surface after the abstraction process.     

Thermisch initiierte Addition von Alkanen an Alkene. V. Addition von Cyclohexan an Oct-1-en in einer freien Radikalkettenreaktion unter überkritischen Bedingungen

Thermal Addition of Alkanes to Alkenes. V. Addition of Cyclohexane to 1-Octene in a Free Radical Chain Reaction at Supercritical Fluid Conditions Alkanes can be added to alkenes in a thermally initiated free radical chain reaction (“ane reaction”). Kinetic and mechanistic studies on the addition of cyclohexane ( 1 ) to 1-octene ( 2 ) (molar ratio = 100:1) at 330−450°C and pressures of up to 300 bar have been performed in a high pressure - high temperature flow apparatus (“HP-HT” apparatus). The free radical chain is initiated by comproportionation of 1 and 2 to give alkyl radicals 6 and 7 . Addition of cyclohexyl radical 6 to alkene 2 and competing abstraction of an allylic hydrogen atom from 2 give radicals 7a and 8 , respectively. Subsequent stabilization of the radicals 7a and 8 by hydrogen abstraction from 1 yields the addition product cyclohexyloctane ( 3 ) and isomerized octenes ( 4 ), respectively. The relative rate of addition and isomerization can be controlled by pressure and temperature. The regioselectivity of the addition reaction was also measured.     

ESR study of the effect of ferric chloride on the photodegradation of model compound for polypropylene

In our previous article on the photodegradation of polypropyle (PP), the effect of ferric chloride (FeCl₃) accelerating the formation of peroxy radical and depressing the formation of alkyl radical were reported. In the present article, the influence of FeCl₃ on model compounds of PP was examined using electron spin resonance (ESR) spectrometry. The following compounds were employed as models of PP, including its irregular structures: 2-methylpentane (2-MP), 2,4-dimethylpentane (2,4-DMP), 2-methyl-4-pentanone (2-M4P), 2,6-dimethyl-4-heptanone (2,6-DM4H), 2-methyl-1-pentene (2-M1P), and tert-butylhydroperoxide (t-BuO₂H). FeCl₃ accelerated the formation of alkyl radicals for 2-MP and 2,4-DMP, alkyl and acyl radicals for 2-M4P and 2,6-DM4H, and alkyl radicals for 2-M1P. As no definite effect of FeCl₃ was observed for n-pentane and 2-octanone, FeCl₃ was assumed to attack saturated hydrocarbons, ketones at a tertiary carbon-hydrogen bond, and hydrocabons at an allylic hydroge, leading to easier photodegradations. FeCl₃ was also effective for the photodegradation of t-BuO₂H using λ >300 nm, so that FeCl₃ is believed to contribute also to the photodegradation of PP under the same irradation conditions. The catalytic effect of FeCl₃ in photodegradation seems to origirate in a redox reaction.     

Calculated energies of adsorption of non-hydrocarbon species on diamond H/C(1 1 1) surface and the abstraction energies of these species abstracted by hydrogen atoms using ab initio calculation

The energetics of adsorption of non-hydrocarbon radical species on H/C(1 1 1) diamond surface and the abstraction energies of these species abstracted by hydrogen atoms, which are in excess in gas phase in the diamond thin film growth using the chemical vapor deposition (CVD) method, were examined using ab initio calculation method. Based on the calculated results for the examined species, which include H, F, OH, NH₂, Cl, CH_mX_n (X=F or Cl) radicals, the tendency of incorporation of F, O, N, H and Cl atoms in the diamond thin film is discussed. The high adsorption energy and the high abstraction energy abstracted by excess gas-phase H atoms for F radicals suggest that F atom has the highest tendency to stay in the diamond thin film among the examined non-carbon atoms. In contrast, the comparable adsorption energy of Cl atom with other examined radicals except F radical, and its low abstraction energy, indicate that Cl atom possesses the least tendency to be incorporated in the diamond thin film. For O, N and H atoms, their calculated abstraction energy values suggest that the overall order of tendency of incorporation in diamond thin film is F>O>N>H>Cl. In addition, the energetically comparable adsorption energy for the CH₂Cl radical, compared with the other examined CH_mX_n species, and the low abstraction energy of Cl atom support that CH₂Cl is a good growth species in diamond CVD thin film growth.     

Study of the coupling reactions between electrochemically generated aromatic radical anions and methyl, alkyl and benzyl radicals

Alkyl radicals produced in the indirect reduction of alkyl halides or alkyldimethylsulfonium salts by electrochemically generated aromatic radical anions couple fast with the latter and alkylated or dialkylated dihydro compounds are formed. Rate constants measured for the coupling reaction between on one hand methyl, primary, secondary and tertiary alkyl radicals as well as benzyl and cumyl radicals and on the other hand a wide spectrum of electrochemically generated aromatic radical anions are found to be about 1×10⁹ M⁻¹ s⁻¹. Previous measurements of coupling rate constants for primary alkyl radicals have been re-evaluated since they were affected by the presence of an S_N2 reaction occurring between the alkyl halides used as radical precursors and the aromatic radical anions. New experiments are also included using alkyldimethylsulfonium salts as precursors in order to prevent such S_N2 artefacts. It is concluded that sterical hindrance does not play a significant role for the radical-radical anion coupling reactions. In general the rate constants for the coupling reactions are all close to 10⁹ M⁻¹ s⁻¹.     

MECHANISMS OF THE GAS-PHASE REACTIONS OF AROMATIC HYDROCARBONS AND PAHS WITH OH AND NO 3 RADICALS

Chemical removal for the simple monocyclic aromatic hydrocarbons (benzene and the C ₁ -C ₃ alkylbenzenes) and naphthalene and the C ₁ -C ₂ alkylnaphthalenes in the atmosphere is by reaction with hydroxyl (OH) radicals. Naphthalene and the C ₁ -C ₂ alkylnaphthalenes may also be removed, but to a much lesser extent, by reaction with nitrate (NO ₃ ) radicals. While rate constants for the gas-phase reactions of OH radicals and NO ₃ radicals with many of the simple monocyclic aromatic hydrocarbons and with naphthalene and the C ₁ -C ₂ alkylnaphthalenes have been measured, the detailed mechanisms of these OH radical-and NO ₃ radical-initiated reactions in the atmosphere are less well understood, especially for naphthalene and the alkylnaphthalenes. Here we present the available data on the reaction mechanisms occurring under laboratory conditions and attempt to reconcile these data with ambient atmospheric measurements. The OH radical reactions with benzene and alkylbenzenes and the OH radical and NO ₃ radical reactions with naphthalene and alkylnaphthalenes proceed mainly by initial addition of the OH or NO ₃ radical to the aromatic ring(s) at room temperature and below. The NO ₃ radical reactions with alkylbenzenes proceed by H-atom abstraction from the C-H bonds of the alkyl substituent group(s), while the NO ₃ radical reactions of naphthalene and the alkylnaphthalenes proceed by addition and with rates proportional to the NO ₂ concentration. The OH-monocyclic aromatic adducts react with O ₂ under atmospheric conditions, while the OH-naphthalene/alkylnaphthalene and NO ₃ -naphthalene/alkylnaphthalene adducts appear to undergo significant reaction with NO ₂ under urban atmospheric conditions.     

Oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran with molecular oxygen in the presence of N-hydroxyphthalimide

Catalytic system Cu(NO₃)₂/NHPI can be successfully used for the mild oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran with molecular oxygen. The oxidation reaction takes place at 50 °C and 1 atm O₂ and selectively converts the primary hydroxymethyl group of HMF to the aldehyde one. The selective formation of aromatic aldehyde is observed because of the higher rate of hydrogen abstraction from primary alcohols by the phthalimide-N-oxyl radical, as compared to the rate of the hydrogen abstraction from the aldehydes.     

Aziridines. 69. Reactions of N-Acylaziridines with Sodium Metal and Sodium Naphthalenide. Elimination of olefines

Reactions of N-acylaziridines 1a – g (N-benzoyl except 1d ) with sodium or naphthalenide N ^.− in THF provide a variety of products that usually arise via the aziridino ketyls 2 . Homolytic ring opening of 2 generates the amidatoalkyl radicals 3 . Only with a very short reaction time were small amounts of benzil or benzoylnaphthalenes obtained indicating a reversible trapping of 2 by dimerization or coupling with N^.−. Homolysis of 2 produced always the more stable 3 apart from reactions of monomethylaziridines 1c , d where the primary radical i-3c , d is kinetically favoured. The amides R¹CONHCHR⁴CHR²R³ ( 9 , isopropylamides i - 9c , d from 1c , d ) were usually the main products. 9 arise from 3 either by H atom abstraction from THF (probably in sodium metal runs) or by reduction of 3 to carbanions 5 that abstract a proton from THF ( N^.− runs). Addition of 5a (R²⁻⁴ = H) to 1a gives finally the ketone 8a . Self reaction of primary radical 3a is dimerization. Self reaction of tertiary or secondary radicals is disproportionation when an allylamide arises. This isomerizes to an enamide unless it is conjugated. R²R³CCHR⁴ and R¹CONH₂ arise (probably) always. The mechanism, possibly a cyclic process of anion 6 , is not clear.     

Effect of substitutional N on the diamond CVD growth process: A theoretical approach

For both (111) and (100) diamond surface orientations, one C atom within the first or second surface carbon layer has substitutionally been replaced by an N atom. The effects of this impurity on CH₃ adsorption and H abstraction from a newly adsorbed CH₃ have been carefully investigated by using ultra-soft pseudo-potential density functional theory (DFT) under periodic boundary conditions. The effects of N at various positions within the two atomic layers were especially studied. It was generally found that nitrogen in the first atomic layer will never affect the initial growth reactions. An exception exist for the dopant in one of the three studied positions within the (100) surface, where a β-scission rearrangement is observed. When N is positioned within the second carbon layer for both surface orientations with all surface carbons H-terminated (i.e. no surface radicals), nitrogen is moving off-site and one of the N–C bonds is thereby broken. On the other hand, when a radical is present on the surface (formed by the abstraction of one surface H), N move back on-site and one electron is transferred from N to the surface C radical with a resulting electron lone pair formation. When CH₂ is bonded to the surface as a result of gaseous H abstraction from the adsorbed CH₃ species and with N directly bonded to the surface carbon onto which CH₃ is initially adsorbed, a β-scission rearrangement is also observed.     

The Effect of Temperature on Competing Photochemical Hydrogen Abstraction Reactions in the Solid State

Irradiation of 4aα,5,8,8aα-tetrahydronaphthoquin-1-on-4β-o1 (1a) and its 6,7-dimethyl derivative 1b in the solid state leads to two products. The first is formed via intramolecular hydrogen abstraction by carbonyl oxygen followed by radical coupling, and the second is produced through initial hydrogen abstraction by enone carbon and subsequent radical coupling. X-ray crystallography reveals that both processes are topochemically allowed, and the geometric parameters for the hydrogen transfers and the radical coupling reactions are tabulated. In the case of 1b, the photoproduct ratio was found to be temperature dependent with hydrogen atom abstraction by carbon predominating at lower temperatures. From the slope of the linear plot of the natural logarithm of the photoproduct ratio versus the reciprocal of the temperature, an activation energy difference of approximately 4 kcal/mole is calculated. The results are interpreted as being due to competing reactions from (n,π*)³ and (π*)³ excited states, the latter (hydrogen abstraction by carbon) having a lower activation energy than the former (hydrogen abstraction by oxygen).     

Electroreduction of organic compounds. 31. Electroreduction of 2- and 3-Chlorodibenzofuran in Deuterated Methanol

The cathodic reduction of dibenzofuran ( 2 ), 2-chlorodibenzofuran ( 4 ), and 3-chlorodibenzofuran ( 1 ) in deuterated methanol is investigated. The Birch-type reduction product 1,4-dibenzofuran ( 3 ) is formed from 1 via 2 , whereas 2-chloro-1,4-dihydrodibenzofuran ( 5 ) is obtained as by-product besides 3 from 4 as starting compound. Deuterium is only incorporated into the reduction products if CH₃OD or CD₃OD but not if CD₃OH are used. This observation is strongly indicative of a polar mechanism involving protonation rather than a radical mechanism with hydrogen atom abstraction to be operative.     

Synthese und Reaktionen von 1,3-Azaphosphorinan-2-thionen

Synthesis and Reactions of 1,3-Azaphosphorinane-2-thiones Aminopropylphosphines, R P(H) (CH₂)₃ NH₂, react with carbon disulfide to give 1,3-azaphosphorinane-2-thiones. In presence of strong bases the title compounds are converted by alkyl halides into 2-alkylthio-3, 4, 5, 6-tetrahydro-1, 3-azaphosphorines whereas in absence of bases quaternization at the phosphorus atom occurs to give 2-thiono -1,3-azaphosphorinanium salts. The structures of the compounds prepared are elucidated by IR. ¹H-n.m.r. and mass spectra.     

Radiation Chemistry of Ethylene Glycol,Meso-Erythritol, 2-Deoxy-D-Ribose and Alkyl Phosphates as DNA Model Compounds

The γ-radiolysis of ethylene glycol, meso-erythritol, 2-deoxy-ribose, and alkyl phosphates has been studied in diluted (10^?2 M), N₂ O-saturated, deoxygenated aqueous solutions. Products and their G values have been determined. Reaction schemes were derived from complete material balances. In the polyols the primary attack of the radiolytically formed OH radicals and H atoms leads to α, β-dihydroxyalkyl radicals (A) which eliminate water to give substituted α-carbonyl-methyl radicals: (B) Disproportionation reactions of the radicals A and B yield products having the structural units ? CO? CHOH? and ? CO? CH₂ —. In ethylene glycol a chain reaction is induced, radical B abstracts a hydrogen from ethylene glycol to give acetaldehyde and radical A. In 2-deoxy-ribose the major attack is at C-1. Products from this radical are 2-deoxy-ribonic acid and 2,5-dideoxy-ribonic acid. In the formation of the latter a rearrangement is involved. With trimethyl phosphate, the reaction of the solvated electron is only small (2 × 10^s 1/mole sec), as shown by pulse radiolysis. Dimethyl and methyl phosphates do not react with the solvated electron to a measurable extent. The attack of the OH radical apparently leads to a cleavage of the alkyl phosphate linkage.     

Homogeneous Catalytic Cleavage of Saturated Carbon-Nitrogen Bonds

An evaluation of the catalytic reactivity of [CPD (CO)₂RuH]₂ (1) and (CPD)(CO)₃Ru (2) (where CPD = tetraphenylcyclopentadienone) with amines suggests that these complexes catalyze C-N bond cleavage by activating C-H bonds alpha to the nitrogen atom of tertiary, secondary and primary amines at ca. 140° C. When two different amines are used, transalkylation takes place. With secondary and primary amines, ammonia and tertiary amines are formed. A series of amine complexes (CPD)(CO)₂Ru.NR₃ (R = alkyl/H) was isolated from stoichiometric reactions of 1 or 2 with primary and secondary amines. It was found that tertiary amines do not generate complexes of the above type but rather unexpectedly give secondary amine complexes by cleavage of an alkyl group. The only isolatable tertiary amine complex is the moderately stable (CPD)(CO)₂RuNMe₃. All amine complexes were characterized by spectral and elemental analyses. Catalytic aspects of C-N bond cleavage were studied. Complexes (1) and (2) were found to react with primary, secondary and tertiary amines to generate imminium or eneamine species which subsequently undergo hydrolysis with water. This is in contrast to the Ru carbene mechanism previously proposed for cluster catalyzed C-N bond activation and cleavage. The two reactions are compared with respect to D for H exchange (with D₂O), water requirement and production of trace products during catalysis. A primary alcohol was found to substitute alkyl groups of a tertiary amine under the catalytic action of 1. A catalytic reaction cycle is proposed.     

Cold remote nitrogen plasma polymerization from 1.1.3.3-tetramethyldisiloxane–oxygen mixture

Cold remote nitrogen plasma (CRNP) selectively reacts with silane-terminated organosiloxane compounds such as 1.1.3.3-tetramethyldisiloxane to give polymeric layers. Deposition rate measurements, FT-IR and Raman spectroscopy were performed. The chemical composition of the deposited film is closely dependent on the reactive gas composition and its flowing conditions. An original effect of dioxygen addition in the nonionic reactive media is pointed out: dioxygen addition leads to a fast and highly hydrocarbonated polymer formation with a nitrogen fixation in a silazane structure. Polymerization is described by a model where ?Si? O^· type of radicals are the critical reactant. A global mechanism is proposed involving active species of the CRNP in initiation step of hydrogen abstraction and the nitrogen triplet state molecule N₂(A³Σ) in methyl abstraction on ?Si^· type of free radical. Dioxygen adjunction appears to limit the methyl abstraction steps. The efficient direct oxygen reaction on free radicals leads to an increase of the ?Si? O^· radical density and, consequently of the average length of the growing polymeric fragments. Nitrogen fixation, involving oxygenated species, is discussed. Under defined conditions, a highly hydrophobic polymeric film is obtained with a volumic mass of 1.34g/cm³ and a deposition rate of about 12 mg/cm² h corresponding to a growth rate of 200 Å/s. © 1994 John Wiley & Sons, Inc.     

Photochemistry and photoinitiation activity of radical polymerization of 2-substituted anthraquinone derivatives. III. Nanosecond laser flash photolysis study

A nanosecond laser flash photolysis study was undertaken on a selected range of 2-substituted anthraquinone derivatives and the data are discussed in relation to the photoactivities in industrial photopolymerization. All the compounds give rise to a triplet-triplet absorption that is quenched by ground-state molecular oxygen. The transient half-lives range from 0.64 to 11.3 μs of which the 2-(1,1 -dibromomethyl) anthraquinone exhibits the longest life-time. In a reductive solvent, 2-propanol, hydrogen atom abstraction takes place with the compounds haveing the lowest-lying triplet ³nπ^* state, whereas those with a low-lying triplet³ππ^* state show mixed kinetics. In the latter case, a disproportionation reaction involving the semianthraquinone radical may be taking place, competing with the direct hydrogen atom abstraction reaction. In addition, investigation of the halogenated derivatives has indicated the possibility of the corresponding halo radicals being formed. In the presence of a tertiary amine, triethylamine, all anthraquinone derivatives show the formation of stable species related to either the exciplex or the radical ion pair. The extent of exciplex formation is more effective with compounds possessing a lowest-lying triplet ³ππ^* excited state than those with a triplet ³nπ^* excited state. The results from the nanosecond laser flash photolysis study show the differences in behavior toward hydrogen atom abstraction and electron transfer processes that is dependent on the nature of the low-lying triplet state and the type of substituent present, i.e., electron-donating or electron-withdrawing. © 1996 John Wiley & Sons, Inc.     

Application of lanthanide n.m.r. shift reagents for functional group studies of shale bitumen asphaltenes

Ytterbium (fod)₃ was used as a shift reagent in conjunction with solution ¹H n.m.r. studies of asphaltene isolated from Devonian shale bitumen. Upon addition of the reagent, bands attributed to protons on alkyl groups alpha to oxygen atoms were shifted and separated from that attributed to protons alpha to two aromatic systems. Similar experiments with Green River bitumen asphaltene did not show any observable shift. The presence and absence of the ether formations in shale asphaltenes can be substantiated by ¹³C n.m.r.     

CuII Pyrazolyl-Benzimidazole Dinuclear Complexes with Remarkable Antioxidant Activity

Three dinuclear coordination complexes generated from 1-n-butyl-2-((5-methyl-1H-pyrazole-3-yl)methyl)-1H-benzimidazole ( L ), have been synthesized and characterized spectroscopically and structurally by single crystal X-ray diffraction analysis. Reaction with iron(II) chloride and then copper(II) nitrate led to a co-crystal containing 78 % of [Cu(NO₃)(μ-Cl)( L’ )]₂ ( C₁ ) and 22 % of [Cu(NO₃)(μ-NO₃)( L’ )]₂ ( C₂ ), where L was oxidized to a new ligand L^’ . A mechanism is provided. Reaction with copper chloride led to the dinuclear complex [Cu(Cl)(μ-Cl)( L) ]₂ ( C₃ ). The presence of N−H⋅⋅⋅O and C−H⋅⋅⋅O intermolecular interactions in the crystal structure of C₁ and C₂ , and C−H⋅⋅⋅N and C−H⋅⋅⋅Cl hydrogen bonding in the crystal structure of C₃ led to supramolecular structures that were confirmed by Hirshfeld surface analysis. The ligands and their complexes were tested for free radical scavenging activity and ferric reducing antioxidant power. The complex C₁ / C₂ shows remarkable antioxidant activities as compared to the ligand L and reference compounds.     

Pyryliumverbindungen. 30. C-Alkylierung von 1,3,5-Triaryl-penten-1,5-dion-Enolaten: Ein einfacher Zugang zu 3-alkylsubstituierten 2,4,6-Triaryl-pyryliumsalzen

Pyrylium Compounds. 30. C-Alkylation of 1,3,5-Triaryl-pentene-1,5-dione Enolates: A Simple Approach to 3-Alkylsubstituted 2,4,6-Triarylpyrylium Salts 1,3,5-Triaryl-pentene-1,5-dione enolates ( 10 ), obtainable in crystalline form from 2,4,6-triarylpyrylium pseudobases ( 9 ) and sodium methoxide in benzene/ether, react in dipolar aprotonic solvents (e.g. DMSO, DMF) with various types of alkyl iodides to give C-alkylation products ( 11 ) which afford 3-substituted 2,4,6-triarylpyrylium salts ( 12 ) on treatment with perchloric acid. This reaction sequence proved to be a convenient synthetic route to pyrylium salts ( 12 ) having 3-oriented substituents such as normal or branched alkyl groups C_nH_2n+1 (e.g.n = 1–5), isotopically modified alkyl groups (e.g. C[²H₃], C₂[²H₅]), allyl type substituents (e.g. CH₂CHCH₂, MeCHCHCH₂, CH₂, CH₂CMeCH₂) or benzyl groups (e. g. PhCH₂, 4-Br C₆H₄CH₂). Bifunctional alkylating agents (e.g. 1,4-diiodobutane, o-xylylenediiodide) resulted in a novel type of bispyrylium salts ( 14 ) with 3,3′-linkage. The pyrylium salts obtained were characterized by their ¹H-n.m.r. and u.v. spectra as well as, in most cases, by transformation into the corresponding pyridine derivatives ( 13 ) and bispyridines ( 15 ) respectively.