Tert-butyl Perbenzoate Research Articles

Thermal hazard assessment of tert-butyl perbenzoate using advanced calorimetric techniques and thermokinetic methods

Tert-butyl perbenzoate (TBPB) is a common organic peroxide initiator in the polymer sector, and its thermal behavior and potential dangers are explored in this quantitative study. Advanced calorimetric techniques and thermokinetic models were used to examine the thermal stability and breakdown features of TBPB. During the first stage of the TBPB synthesis, the process safety analysis revealed a very exothermic reaction. Peak temperatures for TBPB thermal decomposition ranged from 133.37 to 156.64 °C, with heat release values of roughly 1279 ± 135 J/g, as determined by differential scanning calorimetry and thermogravimetric analysis. Apparent activation energies ranged from 78.78 to 133.92 kJ/mol in a thermokinetic analysis employing the Kissinger, Starink, ASTM E698, Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa models. Based on multiple nonlinear regression analysis, a two-step reaction mechanism was postulated, one involving an autocatalytic reaction and the other involving a reaction of the nth order. In order to evaluate the thermal dangers related with TBPB, the self-accelerating decomposition temperature (SADT) and thermal risk index (TRI) were calculated. Based on TRI calculations, TBPB was assessed as having low thermal risk, with SADT values ranging from 40 to 60 °C depending on package size. These numerical findings add to our knowledge of the thermal risks posed by TBPB and shed light on how best to handle, store, and transport the compound for use in industrial settings.

Thermal stability evaluation of tert-butyl peroxybenzoate mixed with impurities

In this article, the thermal stability of tert-butyl perbenzoate (TBPB) mixed with different concentrations of toluene and p-tert-butylcatechol (TBC) was investigated. The exothermic onset temperature (T 0), the heat of decomposition (ΔH), and the adiabatic temperature rise (ΔTad ) of the samples were obtained by differential scanning calorimetry (DSC) and Phi-TEC II adiabatic calorimetry. The apparent activation energy (Ea ) and the maximum reaction rate arrival time under adiabatic conditions were obtained by adiabatic kinetic calculations for 8 h (TD8 ) and 24 h (TD24 ). Based on Semenov’s theory, the self-accelerated decomposition temperature was calculated as a support for safe storage and transport. The results of DSC and Phi-TEC II showed that toluene was effective in reducing the thermal hazard during the decomposition of TBPB. The addition of TBC caused side reactions. The moderate addition of toluene and TBC improves the thermal stability of TBPB and can improve the safety of TBPB in industrial applications.

Synthesis of O-tert-Butyl-N,N-disubstituted Hydroxylamines by N-O Bond Formation.

The reaction of magnesium amides with tert-butyl 2,6-dimethyl perbenzoate in tetrahydrofuran at 0 °C provides a method for the synthesis O-tert-butyl-N,N-disubstituted hydroxylamines by direct N-O bond formation with a broad functional group tolerance. Less sterically hindered magnesium amides require ortho,ortho-disubstitution on the perester electrophile component, whereas sterically encumbered magnesium amides perform comparably with either tert-butyl perbenzoate or tert-butyl 2,6-dimethyl perbenzoate. A reaction mechanism is presented to account for the observed reactivity.

Approach to Trisubstituted 1H-Pyrroles from Alkynoates and Amines Mediated by tert-Butyl Perbenzoate

A simple and concise tandem cyclization of alkynoates with amines in the presence of tert-butyl perbenzoate (TBPB) leads to 1,2,4-trisubstituted 1H-pyrroles. A variety of aromatic amines and aliphatic amines can be used in this approach, and a wide range of functionalized 1,2,4-trisubstituted 1H-pyrroles are obtained in good to excellent yields. This protocol not only corresponds to the construction of a pyrrole fragment, but also provides a new way to form C–C and C–N bonds.

ChemInform Abstract: nBu4NI‐Catalyzed C3‐Formylation of Indoles with N‐Methylaniline.

AbstractRegioselective formylation of NH‐ and N‐protected indoles is smoothly achieved with N‐methylaniline in the presence of TBAI catalyst and tert‐butyl perbenzoate as oxidant.

ChemInform Abstract: Direct Amidation of Azoles with Formamides via Metal‐Free C—H Activation in the Presence of tert‐Butyl Perbenzoate.

A novel and simple method for the direct amidation of azoles with formamides has been developed. The reaction could occur smoothly in the presence of tert-butyl perbenzoate (TBPB) as an oxidant under metal- and base-free conditions. Direct dehydrogenative cross-coupling of formamides and azoles generated the corresponding products in good yields.

A reusable enantioselective catalytic system for the Kharasch–Sosnovsky allylic oxidation of alkenes based on a ditopic azabis(oxazoline) ligand

An easily recoverable and reusable enantioselective catalytic system based on the self-assembly of a coordination polymer through the use of a chiral ditopic ligand, is described for the allylic oxidation of cycloalkenes with tert-butyl perbenzoate. Upon addition of the substrates and a coordinating solvent (acetone or acetonitrile) the coordination polymer disassembles, allowing the catalysis to take place in homogeneous phase. After completion of the reaction, the catalyst reassembles as a coordination polymer upon solvent evaporation and addition of hexane, and is recovered as an insoluble solid. This way, good enantioselectivities and yields are obtained in seven consecutive operation cycles.

Alternative to Benzoquinone for Room-Temperature Fujiwara–Moritani Reactions

tert-Butyl perbenzoate is a substitute for benzoquinone for mild (room-temperature) Fujiwara-Moritani reactions between acetanilides and butyl acrylate under homogeneous conditions. The system was enhanced further by including Cu(OAc)(2) as a cocatalyst. Methyl methacrylate can be activated toward coupling under these conditions.

Direct amidation of azoles with formamides via metal-free C–H activation in the presence of tert-butyl perbenzoate

A novel and simple method for the direct amidation of azoles with formamides has been developed. The reaction could occur smoothly in the presence of tert-butyl perbenzoate (TBPB) as an oxidant under metal- and base-free conditions. Direct dehydrogenative cross-coupling of formamides and azoles generated the corresponding products in good yields.

The synthesis and spectral properties of amber phthalocyanines

Novel antimony(V)-phthalocyanine complexes, [Sb(tObpc)(OH) 2] +, [Sb(tppc)(OH) 2] +, and [Sb(tppc)Cl 2] + (where tObpc and tppc denote tetra( n-butoxy)phthalocyaninate, C 48H 48N 8O 4 2−, and tetrakis(2′,6′-dimethylphenoxy)phthalocyaninate, C 64H 48N 8O 4 2−, respectively) were synthesized by oxidizing the corresponding antimony(III) derivatives either with tert-butyl perbenzoate or sulfuryl chloride. The compounds are dissimilar to conventional phthalocyanines in that they are of amber color in solution. Optical properties were studied by absorption and magnetic circular dichroism spectroscopy. The amber color was attributed to a combination of an intense absorption band (Q-band; log( ɛ/M −1 cm −1) = ca. 5) at ∼735–760 nm, which was red-shifted by ∼1000–1200 cm −1 compared to conventional phthalocyanines and a less intense (log( ɛ) = ca. 4) but broad band at ∼400–500 nm, which is not observed for conventional phthalocyanines. The additional band at ∼400–500 nm was considered to be a red-shifted Soret band.

ChemInform Abstract: Asymmetric Kharasch Reaction: Catalytic Enantioselective Allylic Oxidation of Olefins Using Chiral Pyridine Bis(diphenyloxazoline)-Copper Complexes and tert-Butyl Perbenzoate.

Copper complexes of chiral pyridine bis(diphenyloxazoline)-type ligands have been studied as catalysts for the enantioselective allylic oxidation of olefins. Using 2.5−5 mol % of these chiral catalysts and tert-butyl perbenzoate as oxidant, optically active allylic benzoates were obtained in up to 86% ee. A variety of copper salts was studied under different conditions and in different solvents. Acetone was found to be a superior solvent for the reaction. Use of phenylhydrazine in conjunction with the chiral copper complex played a crucial role in increasing the rate of the reaction. Use of 4 A molecular sieves increased the optical yield of product in almost every case.

Synthesis and spectral properties of a dihydroxo(phthalocyaninato)antimony(V) complex

The title complex cation, [ Sb ( pc )( OH )2]+, (pc = phthalocyaninate, C 32 H 16 N 82-) has been prepared by oxidizing [ Sb ( pc )] I 3 with tert-butyl perbenzoate and isolated as hexafluorophosphate and triflate salts. These salts are relatively well-soluble in polar solvents (e.g. CH 2 Cl 2, acetonitrile, acetone) without detectable aggregation. In particular, they dissolve relatively well in ethanol and methanol in which [ Sb ( pc ) Br 2]+ or [ Sb ( pc ) Cl 2]+ salts are poorly soluble whereas they have extremely low solubility in 1-chloronaphthalene and CHCl 3, unlike the bromo or chloro analogs. The spectral properties of [ Sb ( pc )( OH )2]+ have been investigated by optical absorption and magnetic circular dichroism spectroscopy. Although its Q band tends to appear at a longer wavelength in a solvent with a larger refractive index, as is the case for its Br and Cl analogs, the Q band positions in donor solvents deviate considerably from linear correlation between Onsager's solvent polarity function. In the Soret band region, spectra of [ Sb ( pc )( OH )2]+ are different in CH 2 Cl 2 and acetonitrile, particularly around the B1/B2 bands, unlike the bromo and chloro analogs. The solvent dependence of absorption spectra and the difference in solubility suggests that the presence of the axial hydroxyl groups endows the phthalocyanine macrocycle with considerable hydrophilicity. It also suggests that there are some specific chemical interactions between the axial hydroxyl groups and the surrounding donor solvent molecules.

Solid‐state graft polymerization of styrene in spherical polypropylene granules in the presence of TEMPO

AbstractA series of polypropylene‐graft‐polystyrene (PP‐g‐PS) were prepared by solid‐state graft polymerization of styrene (St) in the presence of tert‐butyl perbenzoate (TBPB) and 2,2,6,6‐tetramethyl‐piperidinyloxy (TEMPO) using nascent spherical isotactic polypropylene (PP) granules as matrix. Reaction conditions such as ratio of TEMPO to TBPB, amount of TBPB and St, reaction time and temperature were investigated. The grafting degree (GD) decreased slightly with the addition of TEMPO, but the introduction of TEMPO reduced gel formation and degradation of PP chain. Introduction of camphor sulfonic acid in the TEMPO‐mediated grafting polymerization system lead to evident increase in molecular weight of PP‐g‐PS and decrease of gel formation with slight changes of GD. GPC curves of the product synthesized with TEMPO addition showed obvious tailing at high molecular weight end. Complex viscosity in dependence on angular frequency of the melt of product showed obvious shear‐thinning behaviors. All the experimental results indicated existence of long‐chain branches in the product of graft polymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Theoretical Insights into Enantioselective Catalysis: The Mechanism of the Kharasch–Sosnovsky Reaction

The mechanism of the Kharasch-Sosnovsky reaction has been investigated using B3 LYP/6-31G* calculations on a chiral reaction model [cyclohexene+tert-butyl perbenzoate-->cyclohex-2-enyl benzoate+tert-butyl alcohol, catalyzed by a chiral bisoxazoline-copper(I) complex]. Although two previous reaction mechanisms have been considered, the results are consistent with a new mechanistic pathway. This path involves ligand exchange between the catalyst-cyclohexene complex with tert-butyl perbenzoate to give a catalyst-perester complex, which undergoes an (either one- or two-step) oxidative addition reaction to yield a copper(III) complex. The limiting step of the Kharasch-Sosnovsky reaction consists of an intramolecular step involving the abstraction of an allylic hydrogen from cyclohexene [which is pi-bound to the copper(III) complex]. The resulting allyl-copper(III) complex (subsequent to the loss of tert-butanol) can undergo a haptotropic rearrangement by means of an eta1-allyl/eta3-allyl equilibrium, leading to scrambling between vinylic and allylic positions when an isotopically labeled substrate is used. The allyl-copper(III) ion undergoes a stereospecific reductive elimination involving the pi-bond migration to yield a reaction product-catalyst complex, which can regenerate the alkene-copper(I) complex by ligand exchange. The proposed reaction mechanism is consistent with all known experimental results (including enantioselectivity data).

Chiral Boron‐Bridged Bisoxazoline (Borabox) Ligands: Structures and Reactivities of Pd and Cu Complexes

Anionic boron-bridged bisoxazolines (borabox ligands) have been synthesized and characterized in their protonated forms. The ligands are tuneable over a wide range, allowing either alkyl or aryl substituents at the oxazoline rings and the central bridging boron atom. The structural parameters of this new ligand type have been investigated by X-ray analyses of palladium and copper complexes. Electronic properties have been studied by (13)C NMR spectroscopy and by DFT calculations on palladium allyl complexes and compared to those of analogous bisoxazoline (box) complexes. Borabox complexes are more electron-rich at the metal center than their neutral box congeners, and as a consequence of the longer bonds between the bridging atom and the oxazoline rings, their bite angles are larger. Palladium(II) complexes bearing an unsubstituted allyl ligand and homoleptic copper(II) complexes each possess an almost flat chelate ring. NMR analysis of a (1,3-diphenylallyl)(borabox)palladium complex showed a 92:8 mixture of (syn,syn) and (anti,syn) allyl isomers, in contrast with a previously reported box analogue that existed exclusively in the (syn,syn) form. Comparison of the corresponding crystal structures revealed that the distance between the bisoxazoline and the allyl ligand in the borabox complex is shorter. In the copper-catalyzed allylic oxidation of cyclohexene and cyclopentene with tert-butyl perbenzoate, borabox ligands gave results similar-and in some cases superior-to those obtained with analogous box ligands.

Asymmetric Allylic Oxidation Catalyzed by Copper(I) Complexes of Chiral (Iminophosphoranyl)ferrocenes

The chiral (iminophosphoranyl)ferrocenes 1−3 are highly versatile ligands in Cu-catalyzed asymmetric allylic oxidation of a series of cyclic olefins with tert-butyl perbenzoate, achieving almost complete enantioselectivity (up to 99% ee) in a reasonably short period of time (36 h).

Synthesis and properties of a highly soluble dihydoxo(tetra- tert-butylphthalocyaninato)antimony(V) complex as a precursor toward water-soluble phthalocyanines

The title complex cation, [Sb(tbpc)(OH) 2] + (where tbpc denotes tetra( tert-butyl)phthalocyaninate, C 48 H 48 N 8 2 - ), has been prepared by oxidizing [Sb(tbpc)]I 3 with tert-butyl perbenzoate in CH 2Cl 2, CHCl 3, o-dichlorobenzene and also without solvent in the range of 20–80 °C. This species has been isolated as I 3 - salt and characterized by elemental analysis, ESI-MS, FT-IR, optical absorption and emission, and magnetic circular dichroism spectroscopy. This compound is quite well soluble in common polar organic solvents (e.g., CH 2Cl 2, acetonitrile, acetone) without detectable aggregation at least up to ca. 10 −4 M while much less soluble (e.g., benzene, chloronaphthalene) or insoluble (hexane) in non-polar solvents. Although this compound is insoluble in water, it makes hydrophilic colloids in acetone–water mixtures. The most intense absorption band (Q-band) in a specific solvent red-shifts with an increase in the refractive index of the solvent. However, considerable deviation of the Q-band positions in donor-solvents from linear correlation between the positions and Onsager’s solvent polarity function suggests that there are significant specific chemical interactions between the axial hydroxyl groups and the surrounding donor molecules. The low fluorescence quantum yield (ca. 0.01) for [Sb(tbpc)(OH) 2] + suggests that the singlet excited state of this species is considerably quenched by the presence of antimony ion in the chromophore.

Influence of cobalt(III) dimethyldithiocarbamate complexes on styrene polymerization initiated by tert-butyl perbenzoate

Kinetic features of radical polymerization of styrene initiated by tert-butyl perbenzoate in the presence of tris(N,N-dimethyldithiocarbamato)cobalt(III) (CoL3) and its adduct with iodine (CoL3 · 2I2) were studied. The optimal concentration ratios of the activators and tert-butyl perbenzoate, providing fast styrene polymerization at 338–368 K, were determined.

Enantioselective oxidation of olefins catalyzed by chiral copper bis(oxazolinyl)pyridine complexes: a reassessment

Copper complexes of chiral tridentate pybox ligands synthesized using a modified procedure have been studied as catalysts for the enantioselective allylic oxidation of olefins. A variety of olefins have been used in this reaction. Using 5 mol% of a Cu(II) complex of the tridentate pybox ligand, phenylhydrazine, and tert-butyl perbenzoate as oxidant in acetone, optically active allylic benzoates were obtained up to 94% ee in few hours. It was also observed that the use of molecular sieves in the reaction did not alter the enantioselectivity. Temperature was found to be very crucial in rate of the enantioselective allylic oxidation of olefins. Using EPR spectra, it has been shown that the Cu(II) species is reduced to Cu(I) by phenylhydrazine and phenylhydrazone, but the reduction with the former is faster in comparison to the latter. It was concluded that the rate enhancement was not specific to the presence of phenylhydrazine or phenylhydrazone, but both were equally responsible provided acetone was used as a solvent.

New chiral bidentate ligands containing thiazolyl and pyridyl donors for copper-catalyzed asymmetric allylic oxidation of cyclohexene

Chiral bidentate ligands 1– 3, which contain a combination of thiazolyl and pyridyl donors units, were prepared. The syntheses are facile and being based on Kröhnke condensation of a pinene derivative to form the pyridine ring. Modification at the 8-position of the tetrahydroquinoline ring can be carried out by alkylation reaction with 2a and 3a but not 1a. The structure of a copper(II) perchlorate complex of 1a was characterized with X-ray crystallography, which reveals the binding of the pyridyl–thiazole as a N– N donors at the copper center. The copper(I) thiazolyl–pyridine complexes prepared in situ are active catalysts in the enantioselective allylic oxidation of cyclohexene using tert-butyl perbenzoate as the oxidant. The isolated yields of the allylic benzoate were up to 98%, and enantioselectivity was up to 62% e.e.