Peroxy Groups Research Articles

Ions and Charged Soot Particles in Hydrocarbon Flames III. Negative Ions in Fuel‐rich Acetylene/Oxygen Flames

AbstractNegative ions up to masses > 3 · 103 u in fuel‐rich and sooting premixed low‐pressure acetylene/oxygen flames have been analyzed by means of a time‐of‐flight mass spectrometer. This work deals with the quantitative analysis of ions up to masses of 200 u, but the larger polyhedral carbon ions, which were negative charge carriers in the soot forming zone, are not considered here. Concentration profiles of ca. 50 different ions and the dependence of maximum ion concentrations on the C/O ratio are reported. ‐ Ions in the preheating zone were anions of carbonic acids and diacids which contained oxo, keto and peroxy groups. With increasing height in the flame these anions decomposed by decarboxylation and dissociative electron detachment. At higher temperature in the oxidation zone, polyynides (C2nH−), linear polycarbon ions and higher ketenides (CmHO−) prevailed. The polyynides were in chemical equilibrium with acetylene and higher neutral polyynes. Enthalpies of formation (referenced to that of C2H−, 274 kJ/mol) were determined for C4H− (414), C6H− (603), C8H− (810) and C10H− (1025 kJ/mol). Possible reaction mechanisms for the formation of the acid anions and the ketenides are discussed. Negative polycyclic aromatic hydrocarbon ions were completely missing in acetylene flames, in contrast to their occurrence in benzene flames.

ChemInform Abstract: Molecular Mechanics Study of Hindered Phenols Used as Antioxidants

The influence of 2,6-substituents on the properties and reactions of hindered phenols (1) and peroxides (2) has been studied by computer-assisted molecular modelling and molecular mechanics and the results of the calculations have been compared with our experimental observations. The minimum-energy configurations of the 2,6-disubstituted peroxides, (R2C6H3O)2(R = Me, Et, Pri, But), were evaluated in order to assess the repulsion across the peroxy group between the substituents in the phenyl rings, and hence the feasibility of the dimerisation of the corresponding phenoxy radicals.Molecular mechanics calculations were performed with the MM2 program of Allinger with a variety of forcefield parameters of the C—O—O—C linkage. In the minimised structure for bis(2,6-dimethylphenyl)peroxide there were no steric repulsions greater than 0.1 kcal mol–1 between methyl groups regardless of the values of the C(ar)—C(ar)—O—O and C(ar)—O—O—C(ar) torsion angles. However, the steric energy of the di-ethyl, -isopropyl, and -isobutyl compounds was dependent upon the values of these torsion angles with preferred C(ar)—C(ar)—O—O angles closer to 90 than 180 °. The minimum energies increased in the order Me < Et < Pri But. The steric energy of the t-butyl derivative was much the highest (47 kcal mol–1 compared with less than 12 kcal mol–1 for the other three). Owing to the steric effect of the t-butyl groups, the t-butyl peroxide is unstable and the HO group of the corresponding bis(t-butyl)phenol is protected and hence unreactive. These conclusions are consistent with experimental results which indicate the absence of hydrogen bonding and the lack of reactivity of the HO group of 2,6-di(t-butyl)phenol.

Molecular mechanics study of hindered phenols used as antioxidants

The influence of 2,6-substituents on the properties and reactions of hindered phenols (1) and peroxides (2) has been studied by computer-assisted molecular modelling and molecular mechanics and the results of the calculations have been compared with our experimental observations. The minimum-energy configurations of the 2,6-disubstituted peroxides, (R2C6H3O)2(R = Me, Et, Pri, But), were evaluated in order to assess the repulsion across the peroxy group between the substituents in the phenyl rings, and hence the feasibility of the dimerisation of the corresponding phenoxy radicals.Molecular mechanics calculations were performed with the MM2 program of Allinger with a variety of forcefield parameters of the C—O—O—C linkage. In the minimised structure for bis(2,6-dimethylphenyl)peroxide there were no steric repulsions greater than 0.1 kcal mol–1 between methyl groups regardless of the values of the C(ar)—C(ar)—O—O and C(ar)—O—O—C(ar) torsion angles. However, the steric energy of the di-ethyl, -isopropyl, and -isobutyl compounds was dependent upon the values of these torsion angles with preferred C(ar)—C(ar)—O—O angles closer to 90 than 180 °. The minimum energies increased in the order Me < Et < Pri But. The steric energy of the t-butyl derivative was much the highest (47 kcal mol–1 compared with less than 12 kcal mol–1 for the other three). Owing to the steric effect of the t-butyl groups, the t-butyl peroxide is unstable and the HO group of the corresponding bis(t-butyl)phenol is protected and hence unreactive. These conclusions are consistent with experimental results which indicate the absence of hydrogen bonding and the lack of reactivity of the HO group of 2,6-di(t-butyl)phenol.

In situ infrared study of the surface oxidation of activated carbon dispersed in potassium bromide

Diffuse reflectance FTIR spectroscopy has been used to study heat treatment of activated carbon dispersed in KBr in situ in oxygen at 298–853 K. Cyclic acid anhydride species were formed at moderate temperature but were decomposed at high temperatures for which the dominant products of surface oxidation were epoxides, bridging ether groups, heterocyclic rings containing COCOC groupings, C—P–K+ groups and possibly peroxy groups. The high-temperature breakdown of epoxides either by C—O cleavage to give C—O–K+ groups or by C—C cleavage to give bridging or cyclic ethers was partially reversed on cooling.

Preparation of ABCBA‐type block copolymers by use of macro‐initiators containing peroxy and azo groups

Preparation of ABCBA‐type block copolymers by use of macro‐initiators containing peroxy and azo groups

Preparation of ABCBA‐type block copolymers by use of macro‐initiators containing peroxy and azo groups

AbstractSome new macroinitiators (5) containing azo and peroxy groups were synthesized by transformation of esters of poly(ethylene glycol) (1) (PEG) of different molecular weight with hydroxyl end groups and an azo group in the middle into the corresponding polymers with tert‐butylperoxycarbonyl end groups by reaction with terephthaloyl chloride and subsequently with tert‐butyl hydroporoxide. Decomposition in the presence of styrene at 60°C or with 3,6,9‐triazaun‐decane‐1,11‐diamine in presence of methyl methacrylate gave the corresponding ABA block copolymer 6 and the ABBA block copolymer 7, respectively. Both block copolymers were used as polymeric initiators. The ABCBA block copolymer 8 was synthesized from 6 and methyl methacrylate or from 7 and styrene by thermally induced polymerization at 80°C. The resulting block copolymers were separated from the homopolymers by selective solvent extraction and characterized by spectroscopic and fractional precipitation methods.

Reactivity-structure correlations in oxidation with metalloporphyrins

Metalloporphyrins of the first transition series have been studied as catalysts in the oxidation of propene by dioxygen in ethyl acetate in the presence of propionaldehyde. With Mn IIITTP and Fe IIITTP of low redox potential, the reaction starts with generation of acyl radicals by transfer of electrons to metal orbitals, followed by formation of peroxy acid. In the case of Co IITTP, acyl radicals are generated through abstraction of hydrogen by the readily formed Co IITTP-O 2 complex. Co-porphyrin binds peroxy acid in two types of complexes: through oxygen of the carbonyl group with the peroxy oxygen atoms sticking out, or through peroxy oxygen with double-bonded oxygen of the carbonyl group exposed. Quantum chemical calculations revealed that only the terminal oxygen of the exposed peroxy group in the first type of complexes acquires electrophilic properties and can perform the addition of oxygen atom to the olefinic double bond. Such a complex of Mn III-porphyrin is unstable and decomposes to form manganese oxo species which are responsible for epoxidation. Mn III-porphyrin also shows high activity in the homolytic decomposition of peroxy acid with evolution of CO 2. In the case of Cr(III), Ni(II), Cu(II) and Zn(II) porphyrins, the reduction potential is too high to allow electron transfer from aldehyde to the metal centre, rendering the first step of the reaction difficult.

Structure defects and thermal stability of poly(vinyl chloride)

AbstractThe presence of polyene and peroxide structures in PVC and their contribution to the rate of thermal decomposition were determined using a large number of commercial suspension PVC samples. Two types of PVC having conjugated ‐C=C‐bonds with different reactivity towards dienophiles were found. Polymer samples of the first type react with chlorine, organic phosphites and maleic anhydride under mild conditions whereas the second type PVC under the same conditions reacts only with chlorine. The obtained data show that polyene structures in these two types of PVC are of cis and trans configuration, respectively. It was also demonstrated that the contribution of diene and peroxy groups to the rate of PVC thermal decomposition is greater than the contribution of any other anomalous structures.

Photochemistry of ketone polymers. 19. Temperature and solvent effects in the quenching of ketone n-.pi.* states by hydroperoxy and peroxy groups

Photolyse des copolymeres du styrene avec la phenyl vinyl cetone ou la methylisopropenylcetone en presence d'hydroperoxyde de t-butyle

Structure and thermal decomposition of potassium bis-μ-peroxo hexacarbonatodicerate(IV) dodecahydrate

The crystal structure reveals the novel anion (CO 3) 3Ce(O 2) 2Ce(CO 3) 3 8− in which the peroxy groups are edge-on, bridging and doubly-bidentate. CeO = 2.331–2.373 Å. Each CO 3 2− group is symmetrically bidentate. CeO = 2.39–2.46 ) Å. On heating, water is lost in two stages between 40 and 200 °C followed by decomposition into CeO 2 and K 2CO 3 by 450 °C. K 4Ce(CO 3) 3O 2·6H 2O, triclinic P 1 , a = 8.8871(10), b = 10.3923(13), c = 10.9582(11) Å, α = 66.85(1), β = 68.42(1), γ = 74.37(1)°. R = 0.031 for 277 parameters and 2817 reflexions.

Comment on “studies of the role of peroxy and hydroperoxy groups in polymer photodegradation”

Comment on “studies of the role of peroxy and hydroperoxy groups in polymer photodegradation”

Interaction of cytochrome P-450 with a hydroperoxide derived from butylated hydroxytoluene. Mechanism of isomerization.

Attack of O2 on the phenoxy radical derived from butylated hydroxytoluene resulted in the formation of 2,6-di-t-butyl-4-hydroperoxy-4-methyl-2,5-cyclohexadienone (BOOH). This hydroperoxide was rapidly consumed when incubated with rat liver microsomes in the absence of NADPH. The destruction of BOOH was accompanied by formation of the corresponding alcohol (BOH) and a derivative of the alcohol (B(OH)2) in which a t-butyl methyl group was hydroxylated. This diol was produced also when BOH was incubated with microsomes and NADPH, but at a slower rate. Mass spectral analyses of B(OH)2 formed from substrates labeled with either 2H or 18O, showed that oxygen was transferred from the peroxy group to a t-butyl group (via the heme iron of P-450) without migration of the intermediate alcohol from the enzyme active site. The results support a mechanism involving heterolytic O-O bond cleavage during isomerization of the hydroperoxide to B(OH)2. The chiral diol was produced from BOOH nonstereoselectively, but the NADPH/O2-supported hydroxylation of BOH resulted in the formation of a 20% excess of one enantiomer of B(OH)2. Analyses of products formed from the interaction of cumene hydroperoxide with cytochrome P-450 showed that this substrate undergoes rearrangement also; 2-phenyl-1,2-propanediol was produced, together with cumyl alcohol and acetophenone. These results indicate that isomerization competes with other pathways of hydroperoxide destruction by cytochrome P-450.

Singlet oxygen photooxygenation of furans : Isolation and reactions of (4+2)-cycloaddition products (unsaturated sec.-ozonides)

Tetraphenylporphin-photosensitized oxygenations of furan ( 19), 2-methylfuran ( 26), 2-ethylfuran ( 39), furfurylalcohol ( 24), 2-acetylfuran ( 40), 2-methoxyfuran ( 42), 2,5-dimethylfuran ( 30), furfural ( 25) and 5-methylfurfural ( 41) in non-polar aprotic solvents yield the corresponding monomeric unsaturated secondary ozonides due to a (4+2)-cycloaddition of singlet oxygen to these furans. With the exception of the ozonide derived from 25, the ozonides were isolated and characterized ( 1H- and 13C- NMR spectra, etc.). In non-polar aprotic solvents, the ozonides derived from 19, 26 and 39 undergo thermal rearrangements to the corresponding cis-diepoxides and epoxylactones. Ozonide 31, derived from 30, however, dimerizes, only above about 60° is a cis-diepoxide formed from either 31 or its dimer. Rose bengal-photosensitized oxygenations of the furans in alcohols (MeOH, EtOH, i-PrOH) also produce the corresponding ozonides as the primary products of (4+2)-cycloadditions of singlet oxygen to these furans. However, reactions of the alcohols with the ozonides are too fast to allow the ozonides to be isolated. Instead, the same products are obtained as are isolated from reactions carried out by dissolving the ozonides in the alcohols. Depending on the structure of the ozonide, three pathways are available to ozonide/alcohol (ROH) interactions:(1) addition of ROH to yield alkoxy hydroperoxides; one out of several possible isomers is formed in a completely stereoselective and regiospecific reaction; (2) elimination of a bridgehead proton by ROH as a base, as observed with the ozonide derived from 19 to give hydroxy butenolide ( 78) in yields between 20 and 60%, and (3) ROH-attack on a carbonyl side-chain under elimination of the corresponding alkyl ester, as observed with furfural photooxygenation which yielded hydroxy butenolide ( 78) in high yields (95%). Interaction of ozonide 31 with tert.-butyl alcohol (t-BuOH) yields quantitatively cis-3-oxo-1-butenylacetate ( 81) by a Baeyer-Villiger-type rearrangement with vinyl group migration Hydrogenbonding between the alcohol and the peroxy group of the ozonides assist the heterolysis of the C—O bonds in the ozonides; the most stabilized cation develops. Front-attack of ROH on this cation explains the stereoselectivity as well as the regiospecificity of the alkoxy hydroperoxide formation; with a bulky alcohol like t-BuOH, ROH-attack on the cation is sterically hindered thus allowing a rearrangement to occur. 1,3-Dipolar cycloaddition of p-nitrophenyl azide to ozonide 31 proceeds stereoselectively to one of the isomers 87a/ 87b. Finally, kinetic results of furan photooxygenation in methanol show the following order of furan-reactivity towards singlet oxygen: 30 > 42 > 26 > 19 > 41 > 25, with absolute rate constants ranging from 1.8 × 10 8 (with 30) to 8.4 × 1O 4 M -1P -1 (with 25).

VO(O2)2Cl]2--[V(O2)3Cl]2- pair in peroxyvanadium(V) chemistry: synthesis of the first chloroperoxyvanadate(V) compounds and evidence for diperoxyvanadate(V)-triperoxyvanadate(V) interconversion

Alkali-metal and ammonium salts of yellow oxydiperoxychlorovanadates(V), A 2 [V0(0 2 ) 2 C1], and blue triperoxychlorovanadates( V), A 2 [V(0 2 ) 3 CI] (A = Na, K, or NH 4 ), have been synthesized, for the first time, by reacting V 2 0 5 with alkali chloride, AC1, and hydrogen peroxide in varying concentrations of alkaline media. The three salts of the anion [VO(0 2 ) 2 C1] 2- are comparatively more stable than those of the complex anion [V(0 2 ) 3 Cl] 2- . Characterization of the compounds has been made from the results of elemental analyses, magnetic susceptibility measurements, and IR spectroscopic studies. The IR spectra suggest that the peroxy groups are bonded to vanadium(V) in a triangular bidentate manner and that the 0-0 bond order of peroxy ligands decreases with the increase in the number of peroxy ligands coordinated to the metal center. The conversion of [VO(0 2 ) 2 Cl] 2- to [V(0 2 ) 3 Cl] 2- and the reverse provide good evidence for the facile diperoxyvanadate( V)-triperoxyvanadate(V) interconversion.

Selective crosslinking of the elastomer phase in high-impact polysterene

The mechanism of crosslinking in the elastomer phase of high impact (HIPS) polystyrene is considered and the requirements for the crosslinking initiator are formulated. For elastomers of low reactivity, particularly, the importance of selective dispersion of the initiator in the elastomer phase is indicated. It was shown experimentally that tert-butyl perbenzoate, normally used for crosslinking the diene rubber phase in HIPS, was ineffective for crosslinking HIPS containing a slightly unsaturated silicone as the elastomer phase. Oligodimethylsiloxane with terminal peroxy groups, which is not very compatible with styrene-polystyrene blends but readily compatible with the rubber, was shown to be an effective crosslinking agent. Crosslinking of the elastomer phase was shown to result in a substantial increase in the impact resistance of the material.

Studies on the role of peroxy and hydroperoxy groups in polymer photodegradation

AbstractInteractions of carbonyl singlet and triplet excited states with peroxides and hydroperoxides were examined in order to ascertain the reasons why the latter two compounds act as nearly diffusion controlled quenchers of ketone‐containing polymer photodegradation. From singlet state fluorescence quenching and laser flash photolysis measurements of triplet decays, direct interaction with the carbonyl excited states was ruled out. These processes occurred with rate constants at least one to two orders of magnitude below the diffusion controlled limit. Trapping of the 1,4‐biradical precursor to chain scission, thereby preventing its disproportionation was also tentatively eliminated. Results obtained using benzoyl peroxide suggest that quencher photodissociation into alkoxy radicals might represent the key step in the quenching of ketone‐containing polymer photodegradation.

Evidence that the peroxidase of the fatty acid cyclooxygenase acts via a fenton type of reaction

Addition of ferrous sulfate to a solution containing peroxy-methyl arachidonate resulted in cleavage of the peroxy group on the methyl arachidonate as assessed by absorption at 232nm. The results suggest that ferrous iron can be involved in the reduction of fatty acid peroxides and supports the possibility that the peroxidase component of the fatty acid cyclooxygenase occurs via a Fenton type reaction.

Peroxo complexes of phosphotungstic heteropoly acid

1. During investigation of complex formation between the phosphotungstic heteropoly acid and hydrogen peroxide by spectrophotometric and31P NMR methods complexes containing between one and four peroxy groups were identified. 2. On the basis of the PMR spectra and also the dependence of the rate of complex formation between PW12O403− and hydrogen peroxide on the pH of the solution proposals were made about the structure of the complexes.

ChemInform Abstract: SURFACE RAMAN SCATTERING FROM EFFERVESCENT MAGNETIC PEROXYBORATES

AbstractDie Oberflächen‐Raman‐Streuung an rotierenden Proben wird für festes NaBO3 · C 4 H2O und NaBO3 · H2O, für erhitzte (110‐180 °C) und mit Elektronen beschossene Peroxyborate sowie für festes Na2O2 und BaO2 untersucht.

Alkali-metal and ammonium triperoxyfluorovanadates(V), A2[V(O2)3F

Blue alkali-metal and ammonium triperoxyfluorovanadates(V), A 2 [V(O 2 ),F] (A = NH 4 , Na, and K) have been synthesized by reacting V 2 0 5 with fluorides AF and hydrogen peroxide in a highly alkaline medium. The compounds have been characterized by elemental analyses, magnetic susceptibility measurements, and IR spectroscopic studies. The compounds do not permit molar conductance measurements. The IR spectra of the compounds suggest the presence of triangularly bonded peroxy ligands. The complex species [V(O 2 ) 3 F] 2- may be a seven-coordinated monomer or it may have a polymeric structure through a weak V-F-V bridging. The basicity of peroxy ligands increases with the increase in the number of peroxy groups coordinated to the vanadium(V) center.