Dihydrogen trioxide clusters, (HOOOH)n (n = 2-4), and the hydrogen-bonded complexes of HOOOH with acetone and dimethyl ether: implications for the decomposition of HOOOH

Hydrogen-bonded gas-phase molecular clusters of dihydrogen trioxide (HOOOH) have been investigated using DFT (B3LYP/6-311++G(3df,3pd)) and MP2/6-311++G(3df,3pd) methods. The binding energies, vibrational frequencies, and dipole moments for the various dimer, trimer, and tetramer structures, in which HOOOH acts as a proton donor as well as an acceptor, are reported. The stronger binding interaction in the HOOOH dimer, as compared to that in the analogous cyclic structure of the HOOH dimer, indicates that dihydrogen trioxide is a stronger acid than hydrogen peroxide. A new decomposition pathway for HOOOH was explored. Decomposition occurs via an eight-membered ring transition state for the intermolecular (slightly asynchronous) transfer of two protons between the HOOOH molecules, which form a cyclic dimer, to produce water and singlet oxygen (Delta (1)O 2). This autocatalytic decomposition appears to explain a relatively fast decomposition (Delta H a(298K) = 19.9 kcal/mol, B3LYP/6-311+G(d,p)) of HOOOH in nonpolar (inert) solvents, which might even compete with the water-assisted decomposition of this simplest of polyoxides (Delta H a(298K) = 18.8 kcal/mol for (H 2O) 2-assisted decomposition) in more polar solvents. The formation of relatively strongly hydrogen-bonded complexes between HOOOH and organic oxygen bases, HOOOH-B (B = acetone and dimethyl ether), strongly retards the decomposition in these bases as solvents, most likely by preventing such a proton transfer.     

A Simple and Efficient Preparation of High‐Purity Hydrogen Trioxide (HOOOH)

A simple and efficient method allows the synthesis of solutions of high‐purity hydrogen trioxide (HOOOH), released in the low‐temperature methytrioxorhenium(VII) (MTO)‐catalyzed transformation of the ozonized polystyrene‐supported dimethylphenylsilane. High‐purity hydrogen trioxide solutions in diethyl ether, separated from the polymer and free of any reactants and by‐products, can be stored at ?20 °C for weeks. By removing the solvent in vacuo, HOOOH could be isolated in highly pure form or transferred to other solvents, thus significantly extending the research perspectives of HOOOH for novel applications.     

In search of the next Holy Grail of polyoxide chemistry: explicitly correlated ab initio full quartic force fields for HOOH, HOOOH, HOOOOH, and their isotopologues

Explicitly correlated ab initio methods have been used to compute full quartic force fields for the three chain minima for HOOOOH, which are found to lie within 1 kcal mol(-1). The CCSD(T)-F12 method with the cc-pVTZ-F12 basis set was used to compute equilibrium structures, anharmonic vibrational frequencies, and rotational constants for HOOH, HOOOH, and three chain isomers of HOOOOH, with the two former force fields being used as benchmarks for the latter three. The full quartic force fields were computed in such a way as to yield fundamental frequencies for all isotopologues at once. The present research confirms the recent experimental identification of HOOOH and provides reliable force fields in support of future experimental work on the enigmatic bonding paradigms involved in the HOOOOH chain.     

Evidence for HOOO radicals in the formation of alkyl hydrotrioxides (ROOOH) and hydrogen trioxide (HOOOH) in the ozonation of C-H bonds in hydrocarbons.

Low-temperature ozonation of cumene (1a) in acetone, methyl acetate, and tert-butyl methyl ether at -70 degrees C produced the corresponding hydrotrioxide, C(6)H(5)C(CH(3))(2)OOOH (2a), along with hydrogen trioxide, HOOOH. Ozonation of triphenylmethane (1b), however, produced only triphenylmethyl hydrotrioxide, (C(6)H(5))(3)COOOH (2b). These observations, together with the previously reported experimental evidence, seem to support the "radical" mechanism for the first step of the ozonation of the C-H bonds in hydrocarbons, i.e., the formation of the caged radical pair (R(**)OOOH), which allows both (a) collapse of the radical pair to ROOOH and (b) the abstraction of the hydrogen atom from alkyl radical R(*) by HOOO(*) to form HOOOH. The B3LYP/6-311++G(d,p) (ZPE) calculations revealed that HOOO radicals are considerably stabilized by forming intermolecularly hydrogen-bonded complexes with acetone (BE = 8.55 kcal/mol) and dimethyl ether (7.04 kcal/mol). This type of interaction appears to be crucial for the relatively fast reactions (and the formation of the polyoxides in relatively high yields) in these solvents, as compared to the ozonations run in nonbasic solvents. However, HOOO radicals appear to be not stable enough to abstract hydrogen atoms outside the solvent cage, as indicated by the absence of HOOOH among the products in the ozonolysis of triphenylmethane. The decomposition of alkyl hydrotrioxides 2a and 2b involves a homolytic cleavage of the RO-OOH bond with subsequent "in cage" reactions of the corresponding radicals, while the decomposition of HOOOH is most likely predominantly a "pericyclic" process involving one or more molecules of water acting as a bifunctional catalyst to produce water and singlet oxygen (Delta(1)O(2)).     

17O NMR spectroscopic characterization and the mechanism of formation of alkyl hydrotrioxides (ROOOH) and hydrogen trioxide (HOOOH) in the low-temperature ozonation of isopropyl alcohol and isopropyl methyl ether: water-assisted decomposition

Low-temperature ozonation of isopropyl alcohol (1a) and isopropyl methyl ether (1b) in [D6]acetone, methyl acetate, and tert-butyl methyl ether at -78 degrees C produced the corresponding hydrotrioxides, Me2C(OH)(OOOH) (2a) and Me2C(OMe)(OOOH) (2b), along with hydrogen trioxide (HOOOH). All the polyoxides investigated were characterized for the first time by 17O NMR spectroscopy of highly 17O-enriched species. The assignment was confirmed by GIAO/MP2/6-31++G* calculations of 17O NMR chemical shifts, which were in excellent agreement with the experimental values. Ab initio density functional (DFT) calculations at the B3LYP/ 6-31G*+ZPE level have clarified the transition structure (TS1, deltaE = 7.4 and 10.6 kcalmol(-1), relative to isolated reactants and the complex 1a-ozone, respectively) for the ozonation of 1a: this, together with the formation of HOOOH and some other products, indicates the involvement of radical intermediates (R*, *OOOH) in the reaction. The activation parameters for the decomposition of the hydrotrioxides 2a and 2b (Ea, = 23.5+/-1.5 kcalmol(-1), logA = 16+/-1.8) were typical for a homolytic process in which cleavage of the ROOOH molecule occurs to yield a radical pair [RO* *OOH] and represents the lowest available energy pathway. Significantly the lower activation parameters for the decomposition of HOOOH (Ea = 16.5+/-2.2 kcalmol(-1), logA = 9.5+/-2.0) relative to those expected for the homolytic scission of the HO-OOH bond [bond dissociation energy (BDE) = 29.8 kcalmol(-1), CCSD(T)/6-311++G**] are in accord with the proposal that water behaves as a bifunctional catalyst and therefore participates in a "polar" (non-radical) decomposition process of this polyoxide. A relatively large acceleration of the decomposition of the hydrotrioxide 2a in [D6]acetone, accompanied by a significant lowering of the activation energies, was observed in the presence of a large excess of water. Thus intramolecular 1,3-proton transfer probably also involves the participation of water and is similar to the mechanism proposed for the decomposition of HOOOH. This hypothesis was further substantiated by the B3LYP/6-31++ G*+ZPE calculations for the participation of water in the decomposition of CH3OOOH, which revealed two stationary points on the potential energy surface corresponding to a CH3OOOH-HOH complex and a six-membered cyclic transition state TS2. The energy barriers were comparable with those calculated for HOOOH, that is, deltaE = 15.0 and 21.5 kcalmol(-1) relative to isolated reactants and the CH3OOOH-HOH complex, respectively.     

A Study on Determination of Some Trace Nonmetals by Microwave Induced Plasma Atomic Emission Spectrometry

In general, atomic emission spectrometry (AES) is an excellent technique for determination of metal elements. However, its capability of determining nonmetals has not been developed well. The major reasons are the resonance lines of most nonmetals lie in the vacuum ultraviolet spectral region and the ionic lines of these elements are difficult to be used because the ionization potentials of the elements are very high. And furthermore only He plasma can efficiently excit those ionic resonance lines. The practical application of HeICP-AES to determining the nonmetals is also difficult because its operating and perchace costs are very high. In contrast to HeICPAES, the costs of He microwave induced plasma (MIP)-AES are relatively low, HeMIP has a high excitation capability which can excite ionic lines of various nonmetals and the nonmetals can be determined by HeMIP-AES with a high sensitivity.     

The ozonation of silanes and germanes: an experimental and theoretical investigation

Ozonation of various silanes and germanes produced the corresponding hydrotrioxides, R3SiOOOH and R3GeOOOH, which were characterized by 1H, 13C, 17O, and 29Si NMR, and by infrared spectroscopy in a two-pronged approach based on measured and calculated data. Ozone reacts with the E-H (E = Si, Ge) bond via a concerted 1,3-dipolar insertion mechanism, where, depending on the substituents and the environment (e.g., acetone-d6 solution), the H atom transfer precedes more and more E-O bond formation. The hydrotrioxides decompose in various solvents into the corresponding silanols/germanols, disiloxanes/digermoxanes, singlet oxygen (O2(1delta(g))), and dihydrogen trioxide (HOOOH), where catalytic amounts of water play an important role as is indicated by quantum chemical calculations. The formation of HOOOH as a decomposition product of organometallic hydrotrioxides in acetone-d6 represents a new and convenient method for the preparation of this simple, biochemically important polyoxide. By solvent variation, singlet oxygen (O2(1delta(g))) can be generated in high yield.     

Stark effect measurement on Ca79Br X2Σ+

Using a molecular beam laser—microwave double resonance experiment, high-precision Stark effect measurements were performed on the electronic and vibrational ground state of Ca⁷⁹Br. The dipole moment was determined to be μo = 4.364(20)D. Furthermore the use of labeling techniques has been demonstrated in which a ground-state rotational transition is induced to label a specific hyperfine component of an optical emission line.     

Mechanism of formation of hydrogen trioxide (HOOOH) in the ozonation of 1,2-diphenylhydrazine and 1,2-dimethylhydrazine: an experimental and theoretical investigation

Low-temperature (-78 degrees C) ozonation of 1,2-diphenylhydrazine in various oxygen bases as solvents (acetone-d(6), methyl acetate, tert-butyl methyl ether) produced hydrogen trioxide (HOOOH), 1,2-diphenyldiazene, 1,2-diphenyldiazene-N-oxide, and hydrogen peroxide. Ozonation of 1,2-dimethylhydrazine produced besides HOOOH, 1,2-dimethyldiazene, 1,2-dimethyldiazene-N-oxide and hydrogen peroxide, also formic acid and nitromethane. Kinetic and activation parameters for the decomposition of the HOOOH produced in this way, and identified by (1)H, (2)H, and (17)O NMR spectroscopy, are in agreement with our previous proposal that water participates in this reaction as a bifunctional catalyst in a polar decomposition process to produce water and singlet oxygen (O(2), (1)delta(g)). The possibility that hydrogen peroxide is, besides water, also involved in the decomposition of hydrogen trioxide is also considered. The half-life of HOOOH at room temperature (20 degrees C) is 16 +/- 1 min in all solvents investigated. Using a variety of DFT methods (restricted, broken-symmetry unrestricted, self-interaction corrected) in connection with the B3LYP functional, a stepwise mechanism involving the hydrotrioxyl (HOOO(*)) radical is proposed for the ozonation of hydrazines (RNHNHR, R = H, Ph, Me) that involves the abstraction of the N-hydrogen atom by ozone to form a radical pair, RNNHR(*) (*)OOOH. The hydrotrioxyl radical can then either abstract the remaining N(H) hydrogen atom from the RNNHR(*) radical to form the corresponding diazene (RN=NR), or recombines with RNNHR(*) in a solvent cage to form the hydrotrioxide, RN(OOOH)NHR. The decomposition of these very labile hydrotrioxides involves the homolytic scission of the RO-OOH bond with subsequent "in cage" formation of the diazene-N-oxide and hydrogen peroxide. Although 1,2-diphenyldiazene is unreactive toward ozone under conditions investigated, 1,2-dimethyldiazene reacts with relative ease to yield 1,2-dimethyldiazene-N-oxide and singlet oxygen (O(2), (1)delta(g)). The subsequent reaction sequence between these two components to yield nitromethane as the final product is discussed. The formation of formic acid and nitromethane in the ozonolysis of 1,2-dimethylhydrazine is explained as being due to the abstraction of a methyl H atom of the CH(3)NNHCH(3)(*) radical by HOOO(*) in the solvent cage. The possible mechanism of the reaction of the initially formed formaldehyde methylhydrazone (and HOOOH) with ozone/oxygen mixtures to produce formic acid and nitromethane is also discussed.     

The reinterpretation of the zero-field double resonance spectra of the lowest excited 3T1u state of the F center in CaO in terms of random internal strain of Eg symmetry

The zero-field double resonance spectra of the relaxed excited ³T_1u state of the F center in CaO were determined and interpreted previously. In the present paper the phosphorescence microwave double resonance (PDMR) spectra are reinterpreted in terms of random internal strain of E_g symmetry. The strain variables of the subensemble of F centers responding to a particular microwave-induced transition are exclusively determined by the microwave and the phosphorescence frequency. Consequently, the level structure in this subensemble can be calculated. To each PMDR spectrum, two graphical representations describing the possible spread in the phosphorescence frequency and the vibronic level structures of the F centers contributing to the PMDR signal are related. From these graphical representations, the occurring radiationless transitions can be traced. It is shown that, at the low energy side, the bounds of the PMDR lines are determined by the random strain distribution whereas the upper bounds are determined by fast radiationless transitions or by the lack of a population difference between the spin levels involved in the microwave-induced transition.     

聚丙烯酰胺存在下微波高压合成银纳米粒子及其光谱特性

以聚丙烯酰胺为还原剂和稳定剂 ,采用微波高压液相合成法制备了黄色银纳米粒子。用吸收光谱和共振散射光谱研究了其制备条件的影响。在 4 2 1.6nm处产生最大吸收峰 ,在 4 70nm处产生一个最强共振散射峰。实验表明 :该法制备的银纳米粒子粒径均匀 ,平均粒径为 6 6nm ,其稳定性和分散性较好 ,合成方法简便、快捷。     

An efficient methyltrioxorhenium(VII)-catalyzed transformation of hydrotrioxides (ROOOH) into dihydrogen trioxide (HOOOH)

Dihydrogen trioxide (HOOOH) is formed nearly quantitatively in the low-temperature (-70 degrees C) methyltrioxorhenium(VII) (MTO)-catalyzed transformation of silyl hydrotrioxides (R3SiOOOH), and some acetal hydrotrioxides, in various solvents, as confirmed by 1H, and 17O NMR spectroscopy. The calculated energetics (B3LYP) for the catalytic cycle, using H3SiOOOH as a model system, is consistent with the experimentally observed activation energy (9.5 +/- 2.0 kcal/mol) and a small kinetic solvent isotope effect (kH2O/kD2O = 1.1 +/- 0.1), indicating an initial concerted reaction between the silyl hydrotrioxide and MTO in the rate-determining step. With the addition of water in the next step, the intermediate undergoes a sigma-bond metathesis reaction to break the Re-OOOH bond and form HOOOH, together with the second dihydroxy intermediate. The final step in the catalytic cycle involves a second, catalytic water that lowers the barrier to form H3SiOH and MTO.     

Multifrequency time-resolved electron paramagnetic resonance investigations after photolysis of phosphine oxide photoinitiators. Dependence of triplet mechanism chemically induced dynamic electron polarization on microwave frequency

Phosphinoyl radicals were produced in benzene solution by photolysis of three acylphosphine oxide photoinitiators, diphenyl-2,4,6-trimethylbenzoyl phosphine oxide (I), bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (II), and bis(2,4,6-trimethylbenzoyl) phenylphospine oxide (III). The chemically induced dynamic electron polarization (CIDEP) of the radicals was measured by time-resolved electron paramagnetic resonance spectroscopy at different microwave frequencies/magnetic fields, in S- (2.8 GHz, 0.1 T), X- (9.7 GHz, 0.34 T), Q- (34.8 GHz, 1.2 T), and W-bands (95 GHz, 3.4 T). The CIDEP was found to be due to a triplet mechanism (TM) superimposed by a radical pair mechanism comprising ST(0) as well as ST(-) mixing. Contributions of the different CIDEP mechanisms were separated, and the dependence of the TM polarization on microwave frequency was determined. It agrees well with the numerical solution of the relevant stochastic Liouville equation, which proves the TM theory quantitatively. The applicability of previous approximate analytical formulas for the TM polarization is discussed. Parameters of the excited triplet state of III were estimated from the dependence of the TM polarization on microwave frequency. They are zero-field splitting constant 0.169 cm(-1) 相似文献   

A practical method for heterogeneously-catalyzed Mizoroki–Heck reaction: Flow system with adjustment of microwave resonance as an energy source

The microwave-assisted and continuous-flow Mizoroki–Heck reaction using a heterogeneous palladium catalyst supported on the anion-exchange resin DIAION WA30 (7% Pd/WA30) is described. The microwave resonance is finely adjusted to 2.4?GHz according to the electric permittivity of the reaction medium for efficient heating. Organic solvents, such as acetonitrile, N,N-dimethylacetamide, and toluene, can be sufficiently heated even with a low intensity of microwave irradiation in a 7% Pd/WA30-packed, glass tube-shaped catalyst cartridge, which was designed based on the electric permittivity of the solvents. The catalyst cartridge can be continuously reused at least 5 runs without exchange.     

Peculiar structure of the HOOO(-) anion

The HOOO(-) anion (1) can adopt a triplet state (T-1) or a singlet state (S-1), where the former is 9.8 kcal/mol (DeltaH(298) = 10.3 kcal/mol) more stable than the latter. S-1 possesses a strong O-OOH bond with some double bond character and a weakly covalent OO-OH bond (1.80 A) according to CCSD(T)/6-311++G(3df,3pd) calculations (the longest O-O bond ever found for a peroxide). In aqueous solution, S-1 adopts a geometry closely related to that of HOOOH (OO(O), 1.388 A; (O)OO(H), 1.509 A; tau(OOOH), 78.3 degrees ), justifying that S-1 is considered the anion of HOOOH. Dissociation into HO anion and O(2)((1)Delta(g)) requires 15.4 (DeltaH(298) = 14.3; DeltaG(298) = 8.9) kcal/mol. Structure T-1 corresponds to a van der Waals complex between HO anion and O(2)((3)Sigma(g)(-)) having a binding energy of 2.7 (DeltaH(298) = 2.1) kcal/mol. Modes of generating S-1 in aqueous solution are discussed, and it is shown that S-1 represents an important intermediate in ozonation reactions.     

The determination of organochlorine pesticides based on dynamic microwave-assisted extraction coupled with on-line solid-phase extraction of high-performance liquid chromatography

A rapid technique based on dynamic microwave-assisted extraction coupled with on-line solid-phase extraction of high-performance liquid chromatography (DMAE-SPE-HPLC) has been developed. A TM₀₁₀ microwave resonance cavity built in the laboratory was applied to concentrate the microwave energy. The sample placed in the zone of microwave irradiation was extracted with 95% acetonitrile (ACN) aqueous solution which was driven by a peristaltic pump at a flow rate of 1.0 mL min⁻¹. The extraction can be completed in a recirculating system in 10 min. When a number of extraction cycles were completed, the extract (1 mL) was diluted on-line with water. Then the extract was loaded into an SPE column where the analytes were retained while the unretained matrix components were washed away. Subsequently, the analytes were automatically transferred from the SPE column to the analytical column and determined by UV detector at 238 nm. The technique was used for determination of organochlorine pesticides (OCPs) in grains, including wheat, rice, corn and bean. The limits of detection of OCPs are in the range of 19-37 ng g⁻¹. The recoveries obtained by analyzing the four spiked grain samples are in the range of 86-105%, whereas the relative standard deviation (R.S.D.) values are <8.7% ranging from 1.2 to 8.7%. Our method was demonstrated to be fast, accurate, and precise. In addition, only small quantities of solvent and sample were required.     

微波谐振腔微扰技术检测造纸法再造烟叶水分

研究了基于微波谐振腔微扰技术检测造纸法再造烟叶水分的方法.用最小二乘法探讨了不同微波测量参数与造纸法再造烟叶水分含量的校准模型,并将检测结果与标准烘箱法进行了比较.研究表明:该方法的测量误差小于0.4%,检测的响应速度仅为 0.1 ms.     

endo/exo isomerism in norcarane and 2-norcaranol hydrotrioxides (ROOOH)

Ozonation of norcarane (1) yielded endo and exo norcarane hydrotrioxides (2a, 2b), as characterized by (1)H and (13)C NMR spectroscopy. Further ozonation of the primary decomposition products of these hydrotrioxides, i.e., 2-norcaranols (3), produced the corresponding isomeric 2-norcaranol hydrotrioxides (4a, 4b), and hydrogen trioxide (HOOOH).     

Hemiortho esters and hydrotrioxides as the primary products in the low-temperature ozonation of cyclic acetals: an experimental and theoretical investigation

Low-temperature ozonation (-78 degrees C) of 1,3-dioxolanes 1a-1f and 1,3-dioxanes 1g and h in acetone-d6, methyl acetate, and tert-butyl methyl ether produced both the corresponding hemiortho esters (2a-h, ROH) and acetal hydrotrioxides (3a-h, ROOOH) in molar ratios ROH/ROOOH ranging from 0.5 to 23. Both types of intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy. DFT calculations suggest that ozone abstracts a hydride ion from 1 to form an ion pair, R+ -OOOH, which subsequently collapses to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH). Hemiortho esters decomposed quantitatively into the corresponding hydroxy esters. Experimentally obtained activation parameters for the decomposition of 2a (E(a) = 13.5 +/- 1.0 kcal/mol, log A = 8.3 +/- 1.0) are in accord with a highly oriented transition state involving, according to B3LYP calculations (deltaH(a)(298) = 13.2 kcal/mol), two molecules of water as a bifunctional catalyst. This mechanism is also supported by the magnitude of the solvent isotope effect for the decomposition of 2e, i.e., k(H2O)/k(D2O) = 4.6 +/- 1.2. Besides the hydroxy esters and oxygen (3O2/1O2), dihydrogen trioxide (HOOOH) was formed in the decomposition of most of the acetal hydrotrioxides (ROOOH) investigated. The activation parameters for the decomposition of the hydrotrioxides 3a-e in various solvents were E(a) = 20 +/- 2 kcal/mol, log A = 13.5 +/- 1.5. Several mechanistic possibilities for the decomposition of ROOOH were tested by experiment and theory. The formation of the hydroxy esters and oxygen could be explained by the intramolecular transfer of the proton to form the hydroxy ester. The assistance of water in the decomposition of ROOOH to form the hydroxy esters, either directly or via hemiortho esters, was also investigated. According to DFT calculations, the formation of a hydroxy ester via hemiortho ester is energetically more favorable (deltaH(a)(298) = 14.5 kcal/mol), again due to the catalytic effect of two water molecules. HOOOH generation requires the involvement of water in the decomposition of ROOOH where the direct formation out of ROOOH is energetically preferred. The energy for a reaction between two molecules of water and singlet oxygen (delta1O2) is too high to occur in solution.     

Impact of molecular conformation on barriers to internal methyl rotation: the rotational spectrum of m-methylbenzaldehyde

The ground state spectrum of m-methylbenzaldehyde (m-MBA) was measured with a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer. The methyl rotor on m-MBA introduces an internal rotation barrier, which leads to splitting of the torsional energy level degeneracy into A and E states. Ab initio calculations predict a low torsional barrier for both the O-cis and O-trans conformers, resulting in a large doublet splitting up to several gigahertz in the frequency spectrum. The rotational constants, distortion terms, and V(3) values for both species have been determined from the ground state rotational spectrum using the BELGI-C(s) fitting program. There are significant differences in the torsional potential for the O-cis and O-trans m-MBA conformers. Molecular orbitals and resonance structures for each conformer are analyzed to understand the difference in torsional barrier height as well as the irregular shape of the O-trans torsional potential.