Tert-butylperoxy Radical Research Articles

Insight into the reactions of n-, iso-, sec- and tert-Butylperoxy radicals with hydroperoxyl radical in the Atmosphere: Reaction Mechanism, thermodynamic analysis and kinetics

Butylperoxy radical (C4H9O2) is recognized today as an important atmospheric intermediate which formed by the oxidation of butane (C4H10), playing a crucial role in the cycling of carbon. This work gives a theoretical investigation of the reaction mechanism, thermodynamic analysis and kinetics of the reactions between HO2 and four isomers (n-, iso-, sec- and tert-Butylperoxy radicals) of C4H9O2, which has been computed using the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311G(d,p) level of theory. As a result, the above four reactions proceed on both singlet and triplet potential energy surfaces have been demonstrated. Additionally, the formation of alkylhydroperoxides and 3O2via triplet hydrogen abstraction from the four reactions are the major reaction channels while other singlet product channels are negligibly small. Besides, rate coefficients for the title reactions were estimated using the transition state theory (TST) over the temperature range 258 – 378 K, and these results exhibit a negative temperature dependence.

EXPLORATION OF COPPER-BASED COORDINATION POLYMER AS CATALYST: HIGH YIELD OXIDATIVE COUPLING OF BENZYLAMINE TO IMINE

Benzylamine to imine conversion through oxidative coupling reaction has been achieved with almost 91% yield under very mild conditions by applying a one-dimensional coordination polymer as a catalyst and tert-butyl hydroperoxide (TBHP) as an oxidizing agent. The 1D-coordination polymer, [{Cu2(2,3-pydc)2(2,2ʹ-bpy) (H2O)2}.4H2O]n(A) has been re-synthesized by different synthetic process using the ligands 2,3- pyridinedicarboxylic acid (2,3-pydc) and 2,2Ꞌ-bipyridine (2,2Ꞌ-bpy) and it has been characterized by utilizing different physicochemical techniques such as IR-spectroscopy, UV-Vis spectroscopy, elemental analysis and TGDTA analysis including reestablishment of X-ray single crystal structure. The proposed mechanism of the reaction indicates that the catalytic reaction is facilitated by a flexible and coordinatively unsaturated Cu(II) center and through the formation of tert-butyl peroxy radical.

Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

A general catalytic methodology for the synthesis of pyrazolines from α -diazo compounds and conjugated alkenes is reported. The direct hydrogen atom transfer (HAT) process of α -diazo compounds promoted by the tert -butylperoxy radical generates electrophilic diazomethyl radicals, thereby reversing the reactivity of the carbon atom attached with the diazo group. The regiocontrolled addition of diazomethyl radicals to carbon-carbon double bonds followed by intramolecular ring closure on the terminal diazo nitrogen and tautomerization affords a diverse set of pyrazolines in good yields with excellent regioselectivity. This strategy overcomes the limitations of electron-deficient alkenes in traditional dipolar [3+2]-cycloaddition of α -diazo compounds with alkenes. Furthermore, the straightforward formation of the diazomethyl radicals provides umpolung reactivity, thus opening new opportunities for the versatile transformations of diazo compounds.

Evaluation of the Reactivity of Cyclohexanone СН Bonds in Reactions with tert-Butylperoxy Radical by Quantum Chemical Methods

Evaluation of the Reactivity of Cyclohexanone СН Bonds in Reactions with tert-Butylperoxy Radical by Quantum Chemical Methods

Tert-Butyl peroxy radical: ground and first excited state energetics and fundamental frequencies.

Alkylperoxy radicals (RO2˙) are key intermediates in combustion and atmospheric oxidation processes. As such, reliable detection and monitoring of these radicals can provide a wealth of information about the underlying chemistry. The tert-butyl peroxy radical is the archetypal tertiary peroxy radical, yet its vibrational spectroscopy is largely unexplored. To aid in future experimental investigations, we have performed high-level theoretical studies of the fundamental vibrational frequencies of the ground- and first excited states. A conformer search on both electronic surfaces reveals single minimum-energy structures. We predict an Ã2A' ← X[combining tilde]2A'' adiabatic excitation energy of 7738 cm-1via focal point analysis, approximating the CCSDT(Q)/CBS level of theory. This excitation energy agrees to within 17 cm-1 of the most accurate experimental measurement. We compute CCSD(T) fundamental vibrational frequencies via second-order vibrational perturbation theory (VPT2), using a hybrid force field in which the quadratic (cubic/quartic) force constants are evaluated with the ANO1 (ANO0) basis set. Anharmonic resonance polyads are treated with the VPT2 + K effective Hamiltonian approach. Among the predicted fundamental frequencies, the ground state O-O stretch, excited state O-O stretch, and excited state C-O-O bend fundamentals are predicted at 1138, 959, and 490 cm-1, respectively. Basis set sensitivity is found to be particularly great for the O-O stretches, similar to what has already been noted in smaller, unbranched peroxy radicals. Exempting these O-O stretches, agreement with the available experimental fundamentals is generally good (±10 cm-1).

Investigation of the two- and three-fragment photodissociation of the tert-butyl peroxy radical at 248 nm.

The photodissociation dynamics of the tert-butyl peroxy (t-BuOO) radical are studied by fast-radical-beam coincidence translational spectroscopy. The neutral t-BuOO radical is formed by photodetachment of the corresponding t-BuOO- anion at 700 nm (1.77 eV), followed by dissociation at 248 nm (5.00 eV). Photofragment mass and translational energy distributions are obtained. The major channel is found to be three-body fragmentation to form O, CH3, and acetone (83%), with minor two-body fragmentation channels leading to the formation of O2 + tert-butyl radical (10%) and HO2 + isobutene (7%). Experimental results show that the translational energy distribution for two-body dissociation peaks is close to zero translational energy, with an isotropic angular distribution of fragments. These results indicate that two-body fragmentation proceeds via internal conversion to the ground electronic state followed by statistical dissociation. For three-body dissociation, the translational energy distribution peaks closer to the maximal allowed translational energy and shows an anisotropic distribution of the plane of the dissociating fragments, implying rapid dissociation on an excited-state surface. A small shoulder in the three-body translational energy distribution suggests that some three-fragment dissociation events proceed by a different mechanism, involving internal conversion to the ground electronic state followed by sequential dissociation.

The fate of the tert-butyl radical in low-temperature autoignition reactions.

Alkyl combustion models depend on kinetic parameters derived from reliable experimental or theoretical energetics that are often unavailable for larger species. To this end, we have performed a comprehensive investigation of the tert-butyl radical (R• in this paper) autoignition pathways. CCSD(T)/ANO0 geometries and harmonic vibrational frequencies were obtained for key stationary points for the R• + O2 and QOOH + O2 mechanisms. Relative energies were computed to chemical accuracy (±1 kcal mol-1) via extrapolation of RCCSD(T) energies to the complete basis-set limit, or usage of RCCSD(T)-F12 methods. At 0 K, the minimum energy R• + O2 pathway involves direct elimination of HO2∙ (30.3 kcal mol-1 barrier) from the tert-butyl peroxy radical (ROO•) to give isobutene. This pathway lies well below the competing QOOH-forming intramolecular hydrogen abstraction pathway (36.2 kcal mol-1 barrier) and ROO• dissociation (35.9 kcal mol-1 barrier). The most favorable decomposition channel for QOOH radicals leads to isobutene oxide (12.0 kcal mol-1 barrier) over isobutene (18.6 kcal mol-1 barrier). For the QOOH + O2 pathways, we studied the transition states and initial products along three pathways: (1) α-hydrogen abstraction (42.0 kcal mol-1 barrier), (2) γ-hydrogen abstraction (27.0 kcal mol-1 barrier), and (3) hydrogen transfer to the peroxy moiety (24.4 kcal mol-1 barrier). The barrier is an extensive modification to the previous 18.7 kcal mol-1 value and warrants further study. However, it is still likely that the lowest energy QOOH + O2 pathway corresponds to pathway (3). We found significant spin contamination and/or multireference character in multiple stationary points, especially for transition states stemming from QOOH. Lastly, we provide evidence for an A∼-X∼ surface crossing at a Cs-symmetric, intramolecular hydrogen abstraction structure.

Kinetic isotope H/D effect in the oxidation of ethers of linoleic acid in solutions

It is shown that the initiated oxidation of deuterated esters of linoleic acid proceeds as a radical chain process. The value of the kinetic isotope effect for hydrogen atom abstraction from the bisallyl group of linoleic acid esters is determined: 3.0 for tert-butyl peroxy and cumylperoxy radicals.

Slow photoelectron velocity-map imaging of cold tert-butyl peroxide.

Photoelectron spectra of cryogenically cooled X∼1A' tert-butyl peroxide anions are obtained using slow electron velocity-map imaging. The spectra show highly structured bands corresponding to detachment to the X∼2A″ and A∼2A' electronic states of the neutral radical and represent a notable improvement in resolution over previous photoelectron spectra. We report an electron affinity of 1.1962(20) eV and a term energy T0(A∼2A') of 0.9602(24) eV for the tert-butyl peroxy radical. New vibrational structure is resolved, providing several frequencies for both neutral states. Additionally, the threshold behavior of the photodetachment cross section is investigated within the context of Dyson orbital calculations.

ChemInform Abstract: Difunctionalization of Styrenes with Perfluoroalkyl and tert‐Butylperoxy Radicals: Room Temperature Synthesis of (1‐(tert‐Butylperoxy)‐2‐perfluoroalkyl)‐ethylbenzene.

A novel strategy for the difunctionalization of styrenes was developed. This synthesis includes the use of electrophilic perfluoroalkyl and tert-butylperoxy radicals and produces (1-(tert-butylperoxy)-2-perfluoroalkyl)ethylbenzene at room temperature, which has been traditionally difficult to synthesize. With at least four radical species included in the transformation, its high chemoselectivity was extraordinary; the results were further elucidated using computational studies. The methodology also holds a good potential for application as a result of its mild reaction conditions, ease of further modification, and insensitivity to moisture and air.

Difunctionalization of Styrenes with Perfluoroalkyl and tert-Butylperoxy Radicals: Room Temperature Synthesis of (1-(tert-Butylperoxy)-2-perfluoroalkyl)-ethylbenzene.

A novel strategy for the difunctionalization of styrenes was developed. This synthesis includes the use of electrophilic perfluoroalkyl and tert-butylperoxy radicals and produces (1-(tert-butylperoxy)-2-perfluoroalkyl)ethylbenzene at room temperature, which has been traditionally difficult to synthesize. With at least four radical species included in the transformation, its high chemoselectivity was extraordinary; the results were further elucidated using computational studies. The methodology also holds a good potential for application as a result of its mild reaction conditions, ease of further modification, and insensitivity to moisture and air.

Interaction of 9-substituted anthracenes with oxidation systems tert-butylhydroperoxide-metal tert-butoxide

9-R-Anthracenes (R = Me, Ph) are effective acceptors of peroxyl and metalalkoxyl radicals in the systems tert-butylhydroperoxide-metal tert-butoxide (M = Al, V, Cr; C6H6, 20°C). Isolation of 9-R-9,10-dihydro-9,10-di-tert-butylperoxyanthracenes, 10-R-10-tert-butylperoxy-9-anthrones as major products reliably confirms the formation of tert-butylperoxy radicals and can be used for quantitative assessment of their content.

Oxidation of alkylarene C-H Bonds by tert-butyl hydroperoxide in the presence of cobalt, chromium, and vanadium acetylacetonates

Cobalt, chromium, and vanadium acetylacetonates catalyze efficient hydroperoxide oxidation of alkylarenes under mild conditions (20°C). The process takes place with either conservation, or destruction of carbon backbone of the hydrocarbon. Oxidizing agents are oxygen generated in the system, as well as tert-butylperoxy radicals. In the formation of end products alkylperoxy radicals originating in the substrates, tert-butylperoxy radicals, as well as metal-containing peroxides are involved. For the oxidative degradation processes a recombination reaction of the alkylperoxy radicals is suggested with the intermediate formation of 1,2-dioxetanes.

Mechanistic Investigation of Oxidative Mannich Reaction with tert-Butyl Hydroperoxide. The Role of Transition Metal Salt

A general mechanism is proposed for transition metal-catalyzed oxidative Mannich reactions of N,N-dialkylanilines with tert-butyl hydroperoxide (TBHP) as the oxidant. The mechanism consists of a rate-determining single electron transfer (SET) that is uniform from 4-methoxy- to 4-cyano-N,N-dimethylanilines. The tert-butylperoxy radical is the major oxidant in the rate-determining SET step that is followed by competing backward SET and irreversible heterolytic cleavage of the carbon-hydrogen bond at the α-position to nitrogen. A second SET completes the conversion of N,N-dimethylaniline to an iminium ion that is subsequently trapped by the nucleophilic solvent or the oxidant prior to formation of the Mannich adduct. The general role of Rh(2)(cap)(4), RuCl(2)(PPh(3))(3), CuBr, FeCl(3), and Co(OAc)(2) in N,N-dialkylaniline oxidations by T-HYDRO is to initiate the conversion of TBHP to tert-butylperoxy radicals. A second pathway, involving O(2) as the oxidant, exists for copper, iron, and cobalt salts. Results from linear free-energy relationship (LFER) analyses, kinetic and product isotope effects (KIE and PIE), and radical trap experiments of N,N-dimethylaniline oxidation by T-HYDRO in the presence of transition metal catalysts are discussed. Kinetic studies of the oxidative Mannich reaction in methanol and toluene are also reported.

Reactivity of the C-H bonds of methyl hexanoate toward the tert-butylperoxy radical

The kinetics of oxygen uptake and the kinetics of accumulation of methyl hexanoate oxidation products in the presence of tert-butyl hydroperoxide have been investigated to determine the partial rate constants for the interaction of the tert-butylperoxy radical with C-H bonds of the ester at 373 K. The ester group deactivates the C-H bonds in the 2- and 3-positions and does not deactivate the same bonds in the 5-position, which are similar in reactivity to the methylenic C-H bonds of hydrocarbons. The C-H bonds of the methoxyl group of methyl hexanoate are substantially more reactive than the C-H bonds of the methyl group.

Dirhodium-Catalyzed Phenol and Aniline Oxidations with T-HYDRO. Substrate Scope and Mechanism of Oxidation

Dirhodium caprolactamate, Rh(2)(cap)(4), is a very efficient catalyst for the generation of the tert-butylperoxy radical from tert-butyl hydroperoxide, and the tert-butylperoxy radical is a highly effective oxidant for phenols and anilines. These reactions are performed with 70% aqueous tert-butyl hydroperoxide using dirhodium caprolactamate in amounts as low as 0.01 mol % to oxidize para-substituted phenols to 4-(tert-butyldioxy)cyclohexadienones. Although these transformations have normally been performed in halocarbon solvents, there is a significant rate enhancement when Rh(2)(cap)(4)-catalyzed phenol oxidations are performed in toluene or chlorobenzene. Electron-rich and electron-poor phenolic substrates undergo selective oxidation in good to excellent yields, but steric influences from bulky para substituents force oxidation onto the ortho position resulting in ortho-quinones. Comparative results with RuCl(2)(PPh(3))(3) and CuI are provided, and mechanistic comparisons are made between these catalysts that are based on diastereoselectivity (reactions with estrone), regioselectivity (reactions with p-tert-butylphenol), and chemoselectivity in the formation of 4-(tert-butyldioxy)cyclohexadienones. The data obtained are consistent with hydrogen atom abstraction by the tert-butylperoxy radical followed by radical combination between the phenoxy radical and the tert-butylperoxy radical. Under similar reaction conditions, para-substituted anilines are oxidized to nitroarenes in good yield, presumably through the corresponding nitrosoarene, and primary amines are oxidized to carbonyl compounds by TBHP in the presence of catalytic amounts of Rh(2)(cap)(4).

An Unprecedented Method for the Generation of tert-Butylperoxy Radical Using DIB/TBHP Protocol: Solvent Effect and Application on Allylic Oxidation

tert-Butylperoxy radical was generated with PhI(OAc)(2) and tBuOOH. Ester solvent was found to be critical and the protocol was applied in the allylic oxidation of various olefinic substrates, which gave the corresponding alpha,beta-unsaturated enones in good yield and regioselectivity.

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

Dirhodium(II) caprolactamate exhibits optimal efficiency for the production of the tert-butylperoxy radical, which is a selective reagent for hydrogen atom abstraction. These oxidation reactions occur with aqueous tert-butyl hydroperoxide (TBHP) without rapid hydrolysis of the caprolactamate ligands on dirhodium. Allylic oxidations of enones yield the corresponding enedione in moderate to high yields, and applications include allylic oxidations of steroidal enones. Although methylene oxidation to a ketone is more effective, methyl oxidation to a carboxylic acid can also be achieved. The superior efficiency of dirhodium(II) caprolactamate as a catalyst for allylic oxidations by TBHP (mol % of catalyst, % conversion) is described in comparative studies with other metal catalysts that are also reported to be effective for allylic oxidations. That different catalysts produce essentially the same mixture of products with the same relative yields suggests that the catalyst is not involved in product-forming steps. Mechanistic implications arising from studies of allylic oxidation with enones provide new insights into factors that control product formation. A previously undisclosed disproportionation pathway, catalyzed by the tert-butoxy radical, of mixed peroxides for the formation of ketone products via allylic oxidation has been uncovered.

Solvent and oxidant effects on the Au/TiO 2-catalyzed aerobic epoxidation of stilbene

Molecular oxygen can be used as the main oxidant to selectively epoxidize trans-stilbene over Au/TiO 2 catalysts, in a free-radical process. However, the nature of the radical initiator has a critical influence on the reaction selectivity. tert-Butylhydroperoxide (TBHP, catalytic amount) leads to high yields of epoxide; on the other hand, hydrogen peroxide and di- tert-butylperoxide merely cause degradation of trans-stilbene. The choice of the solvent is also critical. Amongst the selected solvents, only alkyl-substituted cyclohexanes lead to high yields of epoxide, despite the poor dispersion of the catalytic powder. Other solvents, including the more polar ones and cyclohexane, are significantly less efficient, both in terms of total activity and epoxide production. The latter does not go beyond the yield expected from the potential stoichiometric reaction between TBHP and trans-stilbene (5%). On the basis of these results, an aerobic epoxidation mechanism is proposed in which molecular oxygen is activated by a substituted cyclohexyl radical produced by abstraction of a tertiary hydrogen atom from the solvent molecule by a tert-butylperoxy radical.

Rate Constants for the Reactions of a Series of Alkylperoxy Radicals with NO

The rate constants for the gas-phase reactions of isopropyl- and tert-butylperoxy radicals with nitric oxide (NO) have been studied at 298 +/- 2 K and a total pressure of 3-4 Torr (He buffer) using a laser flash photolysis technique coupled with a time-resolved negative-ionization mass spectrometry. The alkyl peroxy radicals were generated by the reaction of alkyl radicals with excess O(2), where alkyl radicals were prepared by laser photolysis of several precursor molecules. The rate constants were determined to be k(i-C(3)H(7)O(2) + NO) = (8.0 +/- 1.5) x 10(-12) and k(t-C(4)H(9)O(2) + NO) = (8.6 +/- 1.4) x 10(-12) cm(3) molecule(-1) s(-1). The results in combination with our previous studies are discussed in terms of the systematic reactivity of alkyl peroxy radicals toward NO.