Octyl Radicals Research Articles

Interaction of Higher Primary and Secondary Amines with Formaldehyde in Aqueous Media

Using NMR spectroscopy, the competition between different pathways of the interaction of formaldehyde with n-butylamine, n-octylamine, di-n-butylamine, and di-n-octylamine in aqueous media was studied. The effect of the ratio of secondary amines and formaldehyde on the formation of (N,N-dialkylamino)methanols and N,N,N',N'-tetraalkylmethanediamines has been determined. It has been shown that (N-alkylamino)methanols are formed in high yields when a primary amine is used. The replacement of the butyl radical in the starting amine with the octyl radical has a slight effect on the course of the reaction.

Comprehensive experimental and kinetic study of 2,4,4-trimethyl-1-pentene oxidation

A comprehensive experimental and kinetic study of 2,4,4-trimethyl-1-pentene oxidation was conducted in this work. Oxidation in JSR was investigated at the temperature range of 675–1200 K and equivalence ratios of 0.5, 1.0, 2.0 under atmospheric pressure. The high-level quantum calculation was conducted on DLPNO-CCSD(T)/cc-pVTZ//M06-2X/6-311G(d,p) level to get some rate coefficients of high accuracy and choose important pathway. Temperature and pressure-dependent rate coefficients were obtained by solving master equation and RRKM theory. A detailed chemical kinetic model for 2,4,4-trimethyl-1-pentene was developed based on the high-level quantum calculation and validated against the mole fraction data measured in JSR in this work. Available experimental data including ignition delay times and laminar flame speeds in our previous work were also used for the validation of this model. Reaction pathway analysis and sensitivity analysis were performed using the Modified model. The results demonstrate the significance of H abstraction reactions in a wide range of temperature, while fuel unimolecular decomposition reaction are only dominant at high temperature. In addition, at low temperature, O2 addition to octyl radical reactions are more important than radical decomposition and isomerization reactions. Furthermore, sensitivity analysis indicates that H abstraction reactions of fuel and isobutene have a strong inhibiting effect on low temperature reactivity.

Stabilization of long-chain intermediates in solution. Octyl radicals and cations

The rearrangements of 1-octyl, 1-decyl and 1-tridecyl intermediates obtained from thermal lead(IV) acetate (LTA) decarboxylation of nonanoic, undecanoic and tetradecanoic acid were investigated experimentally through analysis and distribution of the products. The relationships between 1,5-, 1,6- and possibly existing 1,7-homolytic hydrogen transfer in 1-octyl-radical, as well as successive 1,2-hydride shift in corresponding cation have been computed via Monte-Carlo method. Taking into account that ratios of 1,5-/1,6-homolytic rearrangements in 1-octyl- and 1-tridecyl radical are approximately the same, the simulation shows very low involvement of 1,7-hydrogen rearrangement (1,5-/1,6-/1,7-hydrogen rearrangement=85:31:1) in 1-octyl radical.

ChemInform Abstract: Dependence on Conformation of the Site of Proton Transfer from Alkane Radical Cations. Nature of the Octyl Radicals Formed by Proton Transfer from Octane Radical Cations to Octane Molecules in CCl3F Matrices at 77 K

A study has been made by EPR spectrometry of octane radical cations and octyl radicals formed by γ-irradiation of octane at various concentrations in CCl3F. The EPR spectrum at very low concentration (⩽0.5 mol%) is essentially due to octane radical cations, which are largely in the gauche-at-C-2 conformation with large unpaired-electron density on one in-plane chain-end hydrogen and one in-plane hydrogen attached to C-2. Superimposed on the radical cation spectrum, a low intensity spectrum due to octyl radicals appears above 0.5 mol%. The signal intensity and relative contribution to the paramagnetic absorption of this spectrum increase very strongly with increasing concentration of octane. It is observed that at low octane concentration both primary and secondary octyl radicals are present in irradiated CCl3F–octane systems, and this is true from the very first appearance of octyl radicals in such systems. At higher concentration, secondary octyl radicals become very much the dominant neutral radical species. The results indicate that: (i) primary and secondary octyl radicals are formed by proton transfer from octane radical cations (in the gauche-at-C-2 conformation) to octane molecules; (ii) with increasing concentration of octane in CCl3F, the size of octane aggregates increases gradually from two-molecule to higher-order clusters, resulting in intermolecular radical site transfer with transformation of primary into secondary octyl radicals. The results confirm that the nature of the alkyl radicals formed by proton transfer from alkane radical cations to alkane molecules is related to the structure of the semi-occupied molecular orbital of the parent cation.

Multichannel decomposition and isomerization of octyl radicals

The thermal cracking patterns from the decomposition and isomerization of octyl-1 radicals have been determined from the pyrolysis of n-octyl iodide in single pulse shock tube experiments at temperatures in the 850–1000K range and pressures near 2bar. Rate constants for the six beta bond scission and five of the six isomerization processes have been derived over all combustion conditions [0.1–100bar, 700–1900K]. Comparisons are made with previous studies on the decomposition of other primary radicals. Results are consistent with similar types of reactions having equal rate constants. The larger size of the octyl radicals makes contributions from secondary to secondary radical isomerization increasingly important. The results confirm that the 1–3 H-transfer process (involving a seven member cyclic transition state) have rate constants that are within a factor of 2 of those for the 1–4 process (six member cyclic transition state) It appears that rate constants for 1–2 H-transfer isomerization, involving an eight member cyclic transition state is unimportant in comparison to contributions from other isomerization processes. The strain energy does not appear to play an important role for these larger transition states. The implications of these results to larger fuel radicals will be discussed.

Catalytic reduction of 1- and 2-bromooctanes by a dinickel(I) Schiff base complex containing two salen units electrogenerated at carbon cathodes in dimethylformamide

A dinickel Schiff base complex (Ni 2(II)L) containing two salen units has been synthesized and characterized by NMR and mass spectrometry. The complex was used for the catalytic reduction of 1- and 2-bromooctanes and its electrochemical behavior, which is similar to that of nickel salen, was studied by cyclic voltammetry and controlled-potential electrolysis. Due to the proximity of the two nickel centers, the yield of octyl dimers is slightly higher for the electrochemical reduction of 2-bromooctane catalyzed by the dinickel complex than that by nickel salen. However, the yield of hexadecane does not increase for the catalytic reduction of 1-bromooctane, which can give more reactive primary radicals. In addition to the formation of various products, octylation of the dinickel complex takes place to a further extent for the reduction of 2-bromooctane than 1-bromooctane. Compared with nickel salen-catalyzed reduction, the electrochemical data also indicate that more octyl groups may incorporate into the dinickel complex. Mechanistically, the catalytic reduction of the bromooctanes involves the intermediacy of primary or secondary octyl radicals.

Catalytic reduction of 1-iodooctane by nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide: Effects of added proton donors and a mechanism involving both metal- and ligand-centered one-electron reduction of nickel(II) salen

In dimethylformamide containing tetramethylammonium tetrafluoroborate, 1-iodooctane is reduced catalytically by nickel(I) salen electrogenerated at a glassy carbon cathode. Cyclic voltammograms for the nickel(II) salen–1-iodooctane system recorded in the absence as well as in the presence of a proton or deuteron donor (1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), phenol, or D2O) exhibit enhanced cathodic peaks and diminished anodic peaks for the nickel(II) salen–nickel(I) salen couple, along with a new cathodic peak attributed to reduction of a nickel(II) salen species for which an imino bond of the ligand is octylated. Without a proton donor, controlled-potential catalytic reduction of 1-iodooctane by nickel(I) salen affords hexadecane, octane, and 1-octene. For electrolyses performed in the presence of either HFIP or phenol, the yields of hexadecane and octane are decreased and increased, respectively, whereas that of 1-octene remains unchanged. Bulk electrolyses done in the presence of D2O give a product distribution similar to that obtained when no proton donor is added; none of the octane is deuterated, indicating that octyl radicals (not octyl carbanions) are precursors for the formation of octane. Theoretical calculations involving density functional theory have been employed to establish that nickel(II) salen can undergo either a metal- or ligand-centered one-electron reduction. A mechanistic scheme is proposed that invokes both metal- and ligand-centered reduction of nickel(II) salen to explain the effects of proton donors on the catalytic reduction of alkyl halides as well as the pathway for alkylation of the imino bonds of the ligand.

Catalytic Reduction of 1-Bromooctane and α , α ′ -Dibromoxylenes by Electrogenerated Cobalt(I) Salen: Formation of Aldehydes

In dimethylformamide containing tetramethylammonium tetrafluoroborate and deliberately added water, stoichiometric quantities of 1-bromooctane and electrogenerated cobalt(I) salen react to give octylcobalt(III) salen. When a solution of octylcobalt(III) salen is irradiated with ultraviolet-visible light, the cobalt-carbon bond is broken to form an octyl radical and cobalt(II) salen within a solvent cage. Introduction of dioxygen causes an insertion reaction that leads to an octylperoxocobalt(III) salen intermediate, which subsequently decomposes to produce 1-octanal in up to 47% yield. Under similar experimental conditions, a two-to-one molar ratio of electrogenerated cobalt(I) salen and -dibromo--xylene gives rise to μ-(1,3-xylenyl)-bis[(salen)cobalt(III)] which can photodecompose, followed by insertion of dioxygen, to afford μ-(1,3-xylenyl)-bis[dioxo(salen)cobalt(III)]. Then the latter intermediate undergoes decomposition to form -phthaldialdehyde in up to 61% yield. In contrast, the ortho and para isomers of -dibromoxylene react with electrogenerated cobalt(I) salen, eventually to give a dialdehyde in small quantities (3–10%).

Extraction Properties of Trioxides of Pentasubstituted Diethylenetriphosphines in Nitric Acid Solutions

Extraction of HNO3 and microamounts of U(VI), Th(IV), Sc(III), and REEs(III) from HNO3 solutions with solutions of trioxides of symmetrical dioctyltriphenyldiethylenetriphosphine and pentaphenyl-diethylenetriphosphine in dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the effective extraction constants of HNO3 and REEs were calculated. As the number of phosphoryl groups in the extractant molecule increases, the extraction of metal ions from nitric acid solutions is enhanced. Replacement of the octyl radicals at the terminal phosphorus atoms by the phenyl radicals is accom-panied by an increase in extraction of metal ions from solutions with the HNO3 concentration exceeding 3 M.

Extraction of Rare‐Earth Elements from Nitric Acid Solutions by Selected Bifunctional Acidic Organophosphorus Compounds

The extraction of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from HNO3 solutions by bifunctional acidic organophosphorus compounds R2P(O)CH2P(O)Ph(OH), R=Ph (I), R=Oct (II), R=p‐Tol (III), R=p‐CH3OC6H4 (IV), and Ph2P(O)CH2P(O)(OBu)(OH) (V) in organic diluents has been studied. The effect of HNO3 concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes has been determined. The replacement of phenyl radicals in the Ph2P(O)CH2 fragment of (diphenylphosphinylmethyl)phenylphosphinic acid (I) by p‐tolyl ones has been found to increase rare‐earth ion extraction. The introduction of p‐methoxy‐phenyl or octyl substituents instead of phenyl ones at the same part of molecule I, facilitates the extraction of Eu–Lu and Y or Tb–Lu and Y, respectively. However, the extraction of other lanthanides from 3 M HNO3 solutions decreases when p‐methoxy‐phenyl or octyl‐substituted compounds in toluene are used as extractants. The replacement of phenyl radical in the P(O)OH fragment of compound I by a butoxy‐group brings about a decrease in rare‐earth elements (REE) extraction. The effect of octyl radicals substitution by phenyl ones in compound II on the extraction of lanthanide ions decreases as the atomic number of REE increases. The extraction efficiency of octyl‐substituted compound II has been observed to be higher than that of phenyl‐substituted compound I when HNO3 concentration in the aqueous phase decreased or when diluents with a small Schmidt's diluent parameter (DP) were used.

The mechanism of polarity-reversal catalysis as involved in the radical-chain reduction of alkyl halides using the silane–thiol couple

The mechanism by which thiols promote the radical-chain reduction of alkyl halides by a variety of simple silanes, such as Et3SiH and Ph3SiH, has been investigated in detail. Kinetic studies of the thiol-catalysed reduction of 1-bromooctane and of 1-chlorooctane by Et3SiH in cyclohexane at 60 °C are consistent with a mechanism that involves reversible abstraction of hydrogen by the thiyl radical from the silane, followed by abstraction of halogen from the octyl halide by the resulting triethylsilyl radical and quenching of the derived octyl radical by the thiol to give octane. On the basis of this mechanism, rate constants for abstraction of hydrogen from Et3SiH by the adamantane-1-thiyl radical (kXSH) and for transfer of hydrogen in the reverse direction (kSiH) were determined as 3.2 × 104 M−1 s−1 and 5.2 × 107 M−1 s−1, respectively, at 60 °C. The equilibrium constant kXSH/kSiH is thus 6.2 × 10−4 at 60 °C and corresponds to ΔrH ≈ ΔrG = +20.4 kJ mol−1 for abstraction of hydrogen from Et3SiH by 1-AdS˙, implying that the Si–H bond in the silane is stronger by ca. 20 kJ mol−1 than the S-H bond in the alkanethiol. The silanethiol (ButO)3SiSH was found to be a more effective catalyst than 1-AdSH, because kXSH is greater (1.3 × 105 M−1 s−1) while kSiH is very similar (5.1 × 107 M−1 s−1). The value of kXSH/kSiH is now 2.6 × 10−3 at 60 °C and thus the S–H bond in this silanethiol is stronger by ca. 4 kJ mol−1 than that in 1-AdSH. The proposed mechanism for alkyl halide reduction is strongly supported by kinetic studies of the thiol-catalysed H/D-exchange between R3SiH/D and XSH/D and the thiol-catalysed racemisation of (S)-ButMePhSiH, radical-chain processes that provide independent confirmation of the values of kXSH derived from octyl bromide reduction. The value of ΔrH determined in this work indicates that abstraction of hydrogen from Et3SiH by an alkanethiyl radical in cyclohexane solvent is ca. 11 kJ mol−1 less endothermic than implied by the difference in the currently-favoured experimental gas-phase dissociation enthalpies for the Et3Si–H and MeS–H bonds.

Structure-reactivity relationships in reactions of alkane radical cations: Study of the proton transfer from alkane radical cations to alkane molecules in γ-irradiated disordered CCl 3F/alkane systems by ESR spectroscopy at cryogenic temperatures

A summary is presented of ESR results obtained in γ-irradiated disordered CCl 3F/alkane systems at cryogenic temperatures, with respect to proton-donor site selectivity in the proton transfer from alkane radical cations to alkane molecules. The nature of the alkyl radicals formed by proton transfer is indicative for the site of proton donation and is derived unambiguously from ESR results by comparison with powder spectra of authentic isomeric alkyl radicals, obtained by γ-irradiation of various chloro and bromoalkanes in perdeuterated cis-decalin. The experiments can be divided into two main classes. (i) Experiments on n-alkane radical cations in the extended all- trans conformation, i.e. ESR results on the system CCl 3F/heptane. The ESR spectrum of γ-irradiated CCl 3F/heptane consists of a triplet due to heptane radical cations in the extended all- trans conformation. In this conformation, the unpaired electron is delocalized over the carbon-carbon σ-bonds as well as the two chain-end carbon-hydrogen bonds that are in the plane of the CC skeleton. Superimposed on the ESR triplet is a low-intensity spectrum due to heptyl radicals, which increases drastically with increasing heptane concentration. The formation of these heptyl radicals can be attributed unambiguously to proton transfer from heptane radical cations to heptane molecules, taking place in small heptane clusters to which positive-hole transfer still occurs efficiently. At the onset of proton transfer with increasing heptane concentration only primary heptyl radicals are present, clearly showing that the proton transfer takes place selectively from a chain-end position, in accordance with the electronic structure of the reacting radical cations. At higher heptane concentration secondary heptyl radicals also appear as a result of intermolecular radical-site transfer, i.e. the nature of the heptyl radicals becomes governed by their thermodynamic stability. (ii) Experiments on n-alkane radical cations in the gauche-at-C 2 conformation, i.e. ESR results on the system CCl 3F/octane. The ESR spectrum of γ-irradiated CCl 3F/octane indicates that octane radical cations are largely in the gauche-at-C 2 conformation in this matrix, with large unpaired-electron (and positive-hole) density on one planar chain-end CH bond and one planar penultimate CH bond at the other side of the radical cation. Careful investigation of ESR spectra with increasing octane concentration clearly reveals that in this case secondary octyl radicals are present from the very onset of proton transfer, in accordance with the electronic structure of the reacting radical cations. The results clearly point to proton-donor site selectivity in the proton transfer from alkane radical cations to alkane molecules and to a strict dependence of the site of proton donation on the electronic structure and conformation of the reacting radical cations.

Dependence on conformation of the site of proton transfer from alkane radical cations. Nature of the octyl radicals formed by proton transfer from octane radical cations to octane molecules in CCl3F matrices at 77 K

Download options Please wait... Article information DOI https://doi.org/10.1039/P29920001449 Article type Paper Download Citation J. Chem. Soc., Perkin Trans. 2, 1992, 1449-1453 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Dependence on conformation of the site of proton transfer from alkane radical cations. Nature of the octyl radicals formed by proton transfer from octane radical cations to octane molecules in CCl3F matrices at 77 K D. Stienlet and J. Ceulemans, J. Chem. Soc., Perkin Trans. 2, 1992, 1449 DOI: 10.1039/P29920001449 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Dominique Stienlet Jan Ceulemans

ChemInform Abstract: Free‐Radical Carbonylation. Efficient Trapping of Carbon Monoxide by Carbon Radicals.

The authors examined the AIBN-induced radical reaction of n-octyl bromide (1) (Scheme 1) with Bu{sub 3}SnH under CO pressure in hope of trapping of carbon monoxide by octyl radical followed by hydrogen abstraction from tin hydride. When the reaction on a 0.5-mmol scale was conducted under CO pressure, using an autoclave with an inserted glass tube (5 mol % of AIBN, benzene (10 mL), 80{degree}C, 3 h), the desired aldehyde 2 was obtained together with n-octane (3), formed via simple reduction of 1. Surprisingly, this radical/CO trapping sequence proceeds even at 15 atm of CO pressure to give 2 in 38% yield (run 2). Generally, higher pressures of CO resulted in the increase of 2. These results demonstrate that the control of the relative concentrations of CO to tin hydride is an important factor to effect the CO trapping leading to aldehyde 2.

Free radical carbonylation. Efficient trapping of carbon monoxide by carbon radicals

The authors examined the AIBN-induced radical reaction of n-octyl bromide (1) (Scheme 1) with Bu{sub 3}SnH under CO pressure in hope of trapping of carbon monoxide by octyl radical followed by hydrogen abstraction from tin hydride. When the reaction on a 0.5-mmol scale was conducted under CO pressure, using an autoclave with an inserted glass tube (5 mol % of AIBN, benzene (10 mL), 80{degree}C, 3 h), the desired aldehyde 2 was obtained together with n-octane (3), formed via simple reduction of 1. Surprisingly, this radical/CO trapping sequence proceeds even at 15 atm of CO pressure to give 2 in 38% yield (run 2). Generally, higher pressures of CO resulted in the increase of 2. These results demonstrate that the control of the relative concentrations of CO to tin hydride is an important factor to effect the CO trapping leading to aldehyde 2.

The Natural and Laboratory Resistance of Gram‐negative Rods to [(Alkylthio) Methyl]Pyridinium Chlorides

AbstractThe sensitivity and resistance of chosen Gram‐negative rods to[(alkylthio)methyl] pyridinium chlorides, dodecyl‐ and hexadecylpyridinium chlorides, benzyldimethylhexadecylammonium chloride, and 1‐methyl‐3[(dodecylthio)methyl]imidazolium chloride have been investigated. The relationship between the alkyl chain lengths and resistance has been demonstrated. The rods experimented acquired high resistance to chlorides with dodecyl and hexadecyl radicals, whereas the level of resistance acquired to chlorides with hexyl and octyl radicals was low.

Rate constants for the analysis of alkyl iodide mechanistic probe studies

Rate constants for reactions of octyl radical at 22°C with ethyl, butyl and cyclohexyl iodide and with ether and THF were determined; these values and other radical rate constants from the literature can be used to analyze the results of mechanistic probe studies.

Isomerization of n‐hexyl and s‐octyl radicals by 1,5 and 1,4 intramolecular hydrogen atom transfer reactions

Abstractn‐Hexyl and s‐octyl radical isomerizations by intramolecular hydrogen atom shift have been studied in the presence of high methyl radical concentration where isomerized alkyl radicals reacted predominantly by combination and disproportionation reactions with methyl radicals.By assuming the rate coefficient of 1‐hexyl radical recombination to be equal to that of ethyl self‐combination, the rate coefficient of log(k1/s−1) = (9.5 ± 0.3) – (11.6 ± 0.3) kcal mol−1/RT ln 10 has been derived for the 6sp isomerization of n‐hexyl radicals, 1‐hexyl → 2‐hexyl (1).Investigation of s‐octyl radical isomerization was complicated by fast interconversion between 3‐octyl, 2‐octyl, and 4‐octyl radicals. Use of the methyl trapping technique and systematic variation of methyl radical concentration made possible the determination of log(k2/s−1) = (9.4 ± 0.7) − (11.2 ± 1.0) kcal mol−1/RT ln 10 for the 6ss isomerization of 3‐octyl and the estimation of log(k3/s−1) = 10.5–17 kcal mol−1/RT ln 10 for the 5ss isomerization of 2‐octyl radicals, where 3‐octyl → 2‐octyl (2), and 2‐octyl → 4‐octyl (3).

ChemInform Abstract: Fast Halogen Abstractions from Alkyl Halides by Alkyl Radicals. Quantitation of the Processes Occurring in and a Caveat for Studies Employing Alkyl Halide Mechanistic Probes.

AbstractSecond‐order rate constants for halogen atom transfer (kRX) in benzene at 50 °C are determined for reactions of octyl radical with the alkyl halides (I) using two methods.

Fast halogen abstractions from alkyl halides by alkyl radicals. Quantitation of the processes occurring in and a caveat for studies employing alkyl halide mechanistic probes

Abstract : Reactions of nucleophilic tin anionoids with alkyl halides are broadly applied for formation of tin-carbon bonds. The mechanisms of these reactions have been studied by the use of alkyl halide mechanistic probes. This report demonstrates how qualitative mechanistic probes can give misleading information about the extent of electron transfer processes in reactions of nucleophiles with alkyl halides. Second order rate constants for halogen atom transfer (k sub RX) in benzene at 50 C were determined for reactions of octyl radical with tert-butyl, iopropyl and cyclohexyl iodides and bromides and with ethyl iodide, n-butyl bromide, tert-butyl chloride, and carbon tetrachloride using two methods. In Method A, an alkyl iodide and tributylstannane were allowed to compete for octyl radical in radical chain reactions; in Method B, an alkyl halide competed with 1-(oxononoxy)-2(1H)-pyridine (1) for octyl radical. The values of k sub RX were calculated from the product distributions, the reactant ratios and the known rate constants for reaction of tributylstannane or 1 with octyl radical. The possibility that rearranged products can be formed in reactions of alkyl halide mechanistic probes with nucleophiles via a sequence involving radical chain isomerization that converts the probe halide into a rearranged halide followed by nucleophilic attack on the isomerized halide is discussed as are possible chain terminating reactions. The conclusion is reached that the percentage of rearranged substitution products formed in reactions of alkyl halide mechanistic probes with nucleophiles can give misleading information about the number of radical initiating events.