95-93-2

We have found that the hydrogen abstraction reactions of 2,4,5-trimethylbenzaldehyde and 2,4-dimethylbenzaldehyde, each isolated in durene single crystals, do not occur via either of the lowest two triplet states but take place primarily through excited states above the singlet origins.The reactions can be directed to give different products by changing the wavelength of the photolyzing light.

Durene (1,2,4,5-tetramethylbenzene) dissolved in n-hexane was photoionized by 35-ps light pulses at 266 nm.Transient absorption at 1064 nm arising chiefly from geminate electrons was detected and used to monitor the recombination of the electron-cation pairs produced by two-photon ionization.An excellent fit to the recombination kinetics at 208 K was obtained by assuming that the distribution of initial electron-cation separations was of the form r2EXP=r2/(2L3)exp(-r/L) with a mean radius 3L = 5.7 nm.

Abstract: This research is devoted to a catalytic process using the H-ZSM5 catalyst for the conversion of methyl and ethyl acetate to hydrocarbon aromatics. These reactions are carried out in a fixed bed reactor under atmospheric pressure at 370°C. The distribution of products was measured by GC-Mass spectrometer. The variation of weight hourly space velocity (WHSV) on the conversion of these esters to aromatic hydrocarbons showed a significant effect on carbon distribution. The deactivation catalyst by time was monitored using product selectivity and conversion. The production of alkyl and poly alkyl aromatic compounds was formed under controlled conditions. The advantages of these methods are the formation of a higher concentration of octane number booster poly alkyl aromatic compounds (mono-aromatics) from esters as starting materials. Moreover, the catalyst lifetime on stream was investigated and exhibited longer catalyst lifetime for ethyl acetate conversion than methyl acetate.

The conversion of methanol into aromatics over unmodified H-ZSM-5 zeolite is generally not high because the hydrogen transfer reaction results in alkane formation. Now circa 80 % aromatics selectivity for the coupling reaction of methanol and carbon monoxide over H-ZSM-5 is reported. Carbonyl compounds and methyl-2-cyclopenten-1-ones (MCPOs), which were detected in the products and catalysts, respectively, are considered as intermediates. The latter species can be synthesized from the former species and olefins. 13C isotope tracing and 13C liquid-state NMR results confirmed that the carbon atoms of CO molecules were incorporated into MCPOs and aromatic rings. A new aromatization mechanism that involves the formation of the above intermediates and co-occurs with a dramatically decreased hydrogen transfer reaction is proposed. A portion of the carbons in CO molecules are incorporated into aromatic, which is of great significance for industrial applications.

The invention relates to methods for preparing durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from pinacol. Durene, 1,2,3-trimethylbenzene and o-xylene are prepared through three steps of reaction, and pyromellitic acid and trimellitic acid are prepared through four steps of reaction. A catalytic system used in the invention is green and environment-friendly, andcan be recycled. The raw materials of method, i.e., pinacol, crotonaldehyde, acrolein and crotonate can all be derived from biomass, and are cheap and easily available. All the reaction processes aresimple and are high in activity and selectivity in the dehydration of pinacol and the dehydrogenation, decarbonylation and oxidation of D-A products. The invention provides novel methods for preparingfine chemicals including durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from lignocellulose-based platform chemicals.

Tungsten carbide was employed as the catalyst in an atom-economic and renewable synthesis of para-xylene with excellent selectivity and yield from 4-methyl-3-cyclohexene-1-carbonylaldehyde (4-MCHCA). This intermediate is the product of the Diels–Alder reaction between the two readily available bio-based building blocks acrolein and isoprene. Our results suggest that 4-MCHCA undergoes a novel dehydroaromatization–hydrodeoxygenation cascade process by intramolecular hydrogen transfer that does not involve an external hydrogen source, and that the hydrodeoxygenation occurs through the direct dissociation of the C=O bond on the W2C surface. Notably, this process is readily applicable to the synthesis of various (multi)methylated arenes from bio-based building blocks, thus potentially providing a petroleum-independent solution to valuable aromatic compounds.

The invention relates to a production technology of 1,2,4,5-tetramethylbenzene. The production technology comprises the following steps: separately adding the raw materials, benzene and dimethyl disulfide, in a ratio of (1:2)-(1:4) into a reaction kettle, and adding a zeolite catalyst into the reaction kettle through a charging hole while controlling the speed of a stirring device in the reaction kettle to 20-60rpm, the temperature in the reaction kettle to 295-305 DEG C and the time to 1 hour; after the reacting, transferring the mixed solution into an evaporator, and controlling the temperature of the evaporator to 200-220 DEG C so that the mixed product with low boiling point evaporates and enters a first rectifying tower; controlling the top temperature of the first rectifying tower to 190-195 DEG C and the reflux ratio to (1:3)-(1:6) so that light boiling matters flow out of the tower through a condensing device at the tower top; and conveying a crude product at the bottom of the first rectifying tower to a second rectifying tower while controlling the top temperature of the second rectifying tower to 191-200 DEG C and the reflux ratio to (1:1)-(5:1). The production technology provided by the invention has the advantages of a few steps, low production cost, convenience in operation and yield up to 88.5%.

In this study, the effect of SiO2/Al2O3 ratio on the catalytic performance of nanocrystal ZSM-5 zeolite catalyst in the methanol to gasoline conversion (MTG) was investigated. A series of zeolite samples with different SiO2/Al2O3 ratios of 23, 47, 107, 217 and 411 were synthesised. Through systematically controlling the material synthesis conditions, these nanocrystal ZSM-5 zeolite samples were produced to have very similar crystal sizes and structural properties, thus providing an ideal opportunity to study the intrinsic effect of SiO2/Al2O3 ratio on the performance of the ZSM-5 samples in MTG. The MTG experimentation was carried out in a fixed-bed reactor under a set of constant conditions of temperature 375?°C, pressure 1?MPa and WHSV 2?h?1. A steady methanol conversion was sustained with increasing the SiO2/Al2O3 ratio, and a progressive decrease in methanol conversion was found over catalysts with low SiO2/Al2O3 ratios (≤107) after 5?h on stream. Decreasing the SiO2/Al2O3 ratio promoted C1-C4 selectivity and thus decreased gasoline yield. It was also found that decreasing the SiO2/Al2O3 ratio promoted aromatisation reactions and hence higher durene selectivity and more coke formation, resulting in rapid catalyst deactivation. The sample with SiO2/Al2O3 ratio of 217 showed the highest methanol conversion, gasoline yield, and very low coke formation.

The invention relates to a process comprising reacting mevalonic acid, or a solution comprising mevalonic acid, to yield a first product or first product mixture, optionally in the presence of a solid catalyst and/or at elevated temperature and/or pressure. The invention further relates to a process comprising: (a) providing a microbial organism that expresses a biosynthetic mevalonic acid pathway; (b) growing the microbial organism in fermentation medium comprising suitable carbon substrates, whereby biobased mevalonic acid is produced; and (c) reacting said biobased mevalonic acid to yield a first product or first product mixture.

The gas-phase reaction of dimethyl disulfide with thiophene proceeds under the action of acid catalysts under atmospheric pressure at 160-350°C and a residence time of τ = 0.6-21 s to form thioalkylation and alkylation products. Dimethyl disulfide reacts with benzene to form only alkylation products. Catalysts containing both strong protic and Lewis acid sites, as well as basic sites of moderate strength, are the most active ones.

The formation and reactivity of a methylbenzenes (MBs) hydrocarbon pool in the induction period of the methanol-to-olefins (MTO) reaction over zeolite H-ZSM-5 was investigated and the mechanistic link of MBs to ethene and propene was revealed. Time evolution analysis of the formed MBs and 12C/13C methanol-switching experiments indicate that in the induction period bulkier compounds such as tetraMB and pentaMB have higher reactivity than their lighter counterparts such as p/m-diMB and triMB. By correlating the distribution of MBs trapped on H-ZSM-5 with ethene and propene, we found that tetraMB and pentaMB favor the formation of propene, while p/m-diMB and triMB mainly contribute to the formation of ethene. On the basis of this relationship, the olefin (ethene and propene) selectivity can be controlled by regulating the distribution of trapped MBs by varying the silicon-to-aluminum ratio of ZSM-5, reaction temperature, and space velocity. The reactivity of MBs and the correlation of MBs with olefins were also verified under steady-state conditions. By observation of key cyclopentenyl and pentamethylbenzenium cation intermediates using in situ solid-state NMR spectroscopy, a paring mechanism was proposed to link MBs with ethene and propene. P/M-diMB and triMB produce ethylcyclopentenyl cations followed by splitting off of ethene, while tetraMB and pentaMB generate propyl-attached intermediates, which eventually produce propene. This work provides new insight into the MBs hydrocarbon pool in MTO chemistry.

Dimethyl disulfide reacts with benzene at 250-350°C over a period of 1-20 s in the presence of catalysts containing strong Br?nsted and Lewis acid centers to give a mixture of methylbenzenes, viz. toluene, isomeric xylenes, mesitylene, and durene.

A method for producing a hydrocarbon blendstock, the method comprising contacting at least one saturated acyclic alcohol having at least three and up to ten carbon atoms with a metal-loaded zeolite catalyst at a temperature of at least 100°C and up to 550°C, wherein the metal is a positively-charged metal ion, and the metal-loaded zeolite catalyst is catalytically active for converting the alcohol to the hydrocarbon blendstock, wherein the method directly produces a hydrocarbon blendstock having less than 1 vol% ethylene and at least 35 vol% of hydrocarbon compounds containing at least eight carbon atoms.

The catalyst systems Mo/Co/K/ZSM-5 and Mo/Ni/K/ZSM-5, alone and with the added copper-based water gas shift catalyst, were used for the conversion of two CO/H2 ratios in a batch reactor. GC analysis of the gas phase was used to determine CO conversion while GCMS and NMR studies were used to characterize the liquid products formed and liquid product selectivities. The liquids were hydrocarbons consisting mainly of alkyl substituted benzenes. Methyl substitution in the alkyl benzenes in the product liquid ranged from an average of 1.3 to 4.5 methyls per ring depending on reaction conditions and reactant gas mole ratios. The additional presence of the WGS catalyst significantly increased CO conversion in the reactions taking place at 280 °C from ～25% to ～90% while increasing selectivity toward higher average methyl substitution. Similar conversions and selectivities were observed with both a bio-syngas and a 50/50 mixture of H2 and CO.

Hagemann's esters can be converted into highly functionalized phenols or arenes. The systematic functionalization of Hagemann's ester derivatives permits the preparation of tri-and tetraalkyl-substituted phenols or tetra-, penta-, and hexaalkyl-substituted benzenes. Kotnis's aromatization procedure was found to be solvent dependent, and Suzuki couplings were found to be sensitive to steric hindrance. Wittig olefination and ortho-Claisen reactions were reliable means to introduce alkyl substituents at C-4 and/or C-5 positions, respectively. The acid-promoted dehydration of tertiary alcohol 46 to produce enone 47, followed by its selective alkylation (cf. 48) is new. ARKAT USA, Inc.

(Graph Presented) Nanosecond transient absorption methods were used to determine accurate oxidation potentials (Eox) in acetonitrile for benzene and a number of its alkyl-substituted derivatives. Eox values were obtained from a combination of equilibrium electron-transfer measurements and electron-transfer kinetics of radical cations produced from pairs of benzene and biphenyl derivatives, with one member of the pair acting as a reference. Using a redox-ladder approach, thermodynamic oxidation potentials were determined for 21 benzene and biphenyl derivatives. Of particular interest, Eox values of 2.48 ± 0.03 and 2.26 ± 0.02 V vs SCE were obtained for benzene and toluene, respectively. Because of a significant increase in solvent stabilization of the radical cations with decreasing alkyl substitution, the difference between ionization and oxidation potentials of benzene is ～0.5 eV larger than that of hexamethylbenzene. Oxidation potentials of the biphenyl derivatives show an excellent correlation with substituent σ+ values, which allows Eox predictions for other biphenyl derivatives. Significant dimer radical cation formation was observed in several cases and equilibrium constants for dimerization were determined. Methodologies are described for determining accurate electrontransfer equilibrium constants even when dimer radical cations are formed. Additional equilibrium measurements in trifluoroacetic acid, methylene chloride, and ethyl acetate demonstrated that solvation differences can substantially alter and even reverse relative Eox values.

A process for the production of a hydrocarbon which comprises contacting, in a reactor, methanol and/or dimethyl ether with a catalyst comprising a metal halide, such as a zinc halide, in which the methanol and/or dimethyl ether is contacted with the catalyst in the presence of at least one phosphorus compound having at least one P-H bond.

A process for producing pyromellitic acid which comprises step A for oxidizing durene, thereby obtaining a reaction mixture comprising trimethyl benzoic acid, trimethyl benzyl alcohol and trimethyl benzaldehyde, step B for separating trimethyl benzoic acid, trimethyl benzaldehyde and trimethyl benzyl alcohol from the reaction mixture obtained in step A, and step C for oxidizing trimethyl benzoic acid and/or trimethyl benzaldehyde separated in step B, thereby obtaining pyromellitic acid.

A process is described for the contemporaneous preparation of mesitylene and durene, characterized in that mesitylene and durene are obtained exclusively starting from pseudo-cumene without the use of any further chemical compound, operating in continuous, at a temperature ranging from 210 to 400°C, at a pressure ranging from 1 to 50 bar, with a weight space velocity ranging from 0.1 to 20 hours-1 and in the presence of a catalyst based on crystalline metal-silicates in acid form. After the recovery of mesitylene and durene from the reaction raw product, some of the remaining components of the raw product itself are recycled and fed to the reactor together with the pseudo-cumene.

A process is described for the contemporaneous preparation of mesitylene and durene, characterized in that mesitylene and durene are obtained exclusively starting from pseudo-cumene without the use of any further chemical compound, operating in continuous, at a temperature ranging from 210 to 400° C., at a pressure ranging from 1 to 50 bar, with a weight space velocity ranging from 0.1 to 20 hours?1 and in the presence of a catalyst based on crystalline metal-silicates in acid form. After the recovery of mesitylene and durene from the reaction raw product, some of the remaining components of the raw product itself are recycled and fed to the reactor together with the pseudo-cumene.

Radical cations of methylated benzenes and benzyl alcohols were generated by photoionization and by reaction SO4·- in aqueous solution. The photoionization requires two 248 nm photons. The lifetimes with the oxidant SO4 and absorption spectra of the radical cations produced were determined by time-resolved conductance and optical detection, and the reaction products were measured by GC. As expected, the radical cation lifetimes increase strongly with increasing number of additional methyl groups, and so does the ratio of deprotonation from a methyl or hydroxymethyl group vs. addition (of water) to a ring position. In the case of toluene the radical cation appears to have a chemical lifetime τ of 10-100 ps ≤ τ ≤ 20 ns, i.e., longer than it takes for an ion pair to separate into the free (solvated) ions, and it reacts predominantly by addition of water to the ring rather than by deprotonation from the methyl group. A further observation is that, as compared to methoxylated analogues, the methylated benzyl alcohol radical cations are much more reactive, such that OH-induction of side-chain fragmentation, as often required with methoxylated benzyl alcohol-type radical cations, is not necessary.

A process for selectively converting a feed comprising oxygenate to normally liquid boiling range C5+ hydrocarbons in a single step is provided which comprises a) contacting the feed under oxygenate conversion conditions with a catalyst comprising a unidimensional 10-ring zeolite, e.g., one selected from the group consisting of ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-57, and ferrierite, at temperatures below 350° C. and oxygenate pressures above 40 psia (276 kPa); and b) recovering a normally liquid boiling range C5+ hydrocarbons-rich product stream, e.g, gasoline and distillate boiling range hydrocarbons or C4to C12olefins.

A process produces an organic compound by catalysis of an imide compound of Formula (1): wherein R1 and R2 are each an alkyl group, aryl group, cycloalkyl group, etc., where R1 and R2 may be combined to form a double bond, or an aromatic or non-aromatic ring; and X is an oxygen atom or a hydroxyl group. In this process, the imide compound catalyst is added in installments to the reaction system to perform a reaction. Such reactions include, for example, oxidation reactions, carboxylation reactions, nitration reactions, sulfonation reactions, and carbon-carbon bond formation reactions. This process can produce a target compound with a higher conversion or selectivity in the production of the organic compound by catalysis of the imide compound catalyst such as N-hydroxyphthalimide.

Treatment of 1,2,4,5-tetramethyl-1,4-cyclohexadiene (1) on polyethylene and in pentane with excess ozone afforded mixtures of the oxydehydrogenation product 2 and of the oxidative cleavage product 4 in ratios of 0.5:1 and 19:1, respectively. Epoxidation o

Photoexcited quinones (Q*) are efficiently quenched by polymethylbenzenes (ArH) via electron transfer (ET). However, the second-order rate constants (k2) exhibit Rehm-Weller (outer-sphere) dependence on the free energy (ΔGET), despite our new findings that the quenching occurs via a series of rather strong encounter complexes [Q*, ArH] with substantial (charge-transfer) bonding. The relatively high formation constants (KEC) of the encounter complexes indicate that any mechanistic interpretation of the driving-force dependence of the observed rate constants is highly ambiguous since k2 must be a composite of KEC and the intrinsic rate constant (kET) for electron transfer within the intermediate (inner-sphere) complex. As such, the reorganization energies extracted from Rehm-Weller plots lack thermodynamic significance. On the other hand, the unambiguous driving-force dependence of kET represents a unique example for the "normal" Marcus behavior of the endergonic electron transfer between the donor/acceptor pair in van der Waals contact as extant in the encounter complex.

The various aromatic hydrocarbons (Chart 2) constitute a sharply graded series of sterically encumbered (unhindered, partially hindered, and heavily hindered) donors in electron transfer (ET) to quinones (Chart 1). As such, steric effects provide the quantitative basis to modulate (and differentiate) outer-sphere and inner-sphere pathways provided by matched pairs of hindered and unhindered donors with otherwise identical electron-transfer properties. Thus the hindered donors are characterized by (a) bimolecular rate constants (k2) that are temperature dependent and well correlated by Marcus theory, (b) no evidence for the formation of (discrete) encounter complexes, (c) high dependency on solvent polarity, and (d) enhanced sensitivity to kinetic salt effects - all diagnostic of outer-sphere electron-transfer mechanisms. Contrastingly, the analogous unhindered donors are characterized by (a) temperature-independent rate constants (k2) that are 102 times faster and rather poorly correlated by Marcus theory, (b) weak dependency on solvent polarity, and (c) low sensitivity to kinetic salt effects - all symptomatic of inner-sphere ET mechanisms arising from the preequilibrium formation of encounter complexes with charge-transfer (inner-sphere) character. Steric encumbrances which inhibit strong electronic (charge-transfer) coupling between the benzenoid and quinonoid π systems are critical for the mechanistic changeover. Thus, the classical outer-sphere/inner-sphere distinction (historically based on coordination complexes) is retained in a modified form to provide a common terminology for inorganic as well as organic (and biochemical) redox systems.

Fast hydrogen atom transfers from various methylbenzenes (ArH) to photoactivated quinones Q* show primary kinetic isotope effects k(H)/k(D) of 2.4-5.6. The quantitative effects of added inert salt on the kinetics and on the yields of the intermediate cation radical ArH(+*) demonstrate that hydrogen transfer proceeds via a two-step sequence involving an initial electron transfer to form the ion-radical pair [ArH(+*), Q(-*)] which subsequently undergoes proton transfer according to the electron-transfer mechanism in Scheme 1.

The energy of activation (E(a)) of the dehalogenation reaction induced by Bu3Sn. was measured for some aryl, alkyl and benzyl halides. BDE values of the C-X bond undergoing homolysis were obtained from thermochemical cycles, and correlated with the E(a) values. No major effect due to the polarity of the C-X bond was found. Durene derivatives showed a buttressing effect. A comparison of the homolytic BDE of the C-X bond of organic halides with the BDE of the C-X bond in the radical anion of the same precursors is reported.

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The encounter complex between photoexcited quirtones Q* and various aromatic donors (ArH) is observed directly by time-resolved ps spectroscopy immediately before it undergoes electron transfer to the ion-radical pair [Q(°-) ArH(°+)]. The encounter complex (EC) is spectrally characterized by distinctive (near IR) absorption bands, and its temporal evolution is established by quantitative kinetics analysis. The structural characterization of the 1:1 encounter complex [Q*, ArH] identifies the cofacial juxtaposition of the donor and acceptor moieties for optimal overlap of their π-orbitals. Further comparisons of the (excited-state) encounter complex with the corresponding (ground-state) EDA complex of aromatic donors and quinones establish its charge-transfer character, which directly relates to electron transfer within the encounter complex. The mechanistic significance of the encounter complex to bimolecular electron transfer is discussed (Scheme 1).

Disproportionation of 1,2,4-trimethylbenzene was carried out at 200 deg C to investigate the effect of hydrogen spillover on the stabilization of the catalytic activities of ultrastable Y (USY) zeolite and pillared montmorillonite.The catalytic activity of pillared montmorillonite, the acidity of which is mainly due to Lewis acid sites, became stable against deactivation in the presence of spiltover hydrogen.There was a less pronounced effect of spiltover hydrogen on the deactivation of USY catalyst treated at 400 deg C.When the surface acidity of USY was converted from Broensted to Lewis acidity by treatment at temperatures as high as 750 deg C, however, the deactivation was effectively suppressed by spiltover hydrogen.We concluded from these results that the stabilization of activity by spiltover hydrogen is linked to Lewis acidity, irrespective of the type of catalyst.

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Phenyliodinium (I.(+1)) and diphenylsulfinium radical cations (II.(+1)) have been generated by flash photolysis (λinc = 347 nm) of diphenyliodonium ions (I(+1)) and diphenyl(4-phenylthiophenyl)sulfonium ions (II(+1)) in acetonitrile solutions at room temperature.I.(+1) and II.(+1) were found to undergo electron-transfer reactions with benzene derivatives resulting in the formation of radical cations of the aromatic compounds.A study involving 25 compounds including various methyl- and methoxy-benzenes, biphenyl, phenol and cresols revealed that electron transfer is independent of the ionizations energy Ei provided that the rates are encounter-controlled.This applies to cases where Ei does not exceed a critical value: Ei,crit ca. 820 kJ mol-1 (I.(+1)) and 780 kJ mol-1 (II.(+1)).Bimolecular rate constants decrease with increasing Ei in the case of aromatic compounds having ionization energies exceeding the critical values.A Marcus-inverted region was not detected.

A study has been made of the relative merits of range of decomplexation reagents in the demetallation of salts. 1,8-Phenanthroline have good yields of the free ligand when simple arene complexes were used but did not demetallate more sterically hindered species.The reaction was found to be light sensitive.Bipyridine gave much lower yields.Potassium tert-butoxide in pyridine or DMSO was found to be an excellent demetallating agent even with sterically crowded complexes.A one-pot arylation procedure was developed and extended to include a number of important heterocyclic derivatives.The mechanism of these decomplexation reactions is briefly adressesd.

Charge-transfer nitration of various aromatic hydrocarbons (ArH) is readily achieved by the deliberate photoactivation of their electron donor-acceptor (EDA) complexes with N-nitropyridinium (PyNO2+). Time-resolved spectroscopy unambiguously identifies (ArH?+, NO2, Py) as the reactive triad resulting directly from the charge-transfer activation of the [ArH,PyNO2+] complex; and the subsequent homolytic annihilation of the aromatic cation radical with NO2 leads to the Wheland intermediate pertinent to aromatic nitration. Charge-transfer nitration of such aromatic donors as toluene, anisole, mesitylene, and terf-butylbenzene as well as the polymethylbenzenes and substituted anisoles forms the basis for detailed comparisons with the products from electrophilic aromatic nitration, especially with regard to the unique isomer distributions, nuclear versus side-chain nitrations, and ipso adducts in nonconventional nitrations. Mechanistic implications are discussed in terms of the electron-transfer activation of electrophilic aromatic nitration.

The reaction between NO3. and polyalkylbenzenes was studied using 308-nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the alkylbenzenes in acetonitrile solution.For all benzenes, with the exception of monoalkylbenzenes and o- and m-xylene, the reaction with NO3. was found to yield the corresponding radical cations and to proceed in an apparently straightforward bimolecular manner.For monoalkylbenzenes and o- and m-xylene, radicals were seen which are derived from the parents by formal loss of H. from the side chain of the aromatic.This reaction proceeds via a complex between the aromatic and NO3. with the decomposition of the complex being rate determining at higher concentrations of aromatic (rate constants for decomposition between 6 * 105 and 4 * 107 s-1).In the complex, electron transfer from the aromatic to NO3. is suggested to be concerted with deprotonation of the incipient radical cation.Formation of a complex between NO3. and aromatics is likely even in those cases where radical cations are observed, with the assumption that in these cases the complex decomposition rate is greater than 6 * 107 s-1.

Photoinduced electron transfer in various 1:1 aromatic EDA complexes with nitrosonium by the direct laser-pulse (20-ps and 10-ns fwhm) excitation of the charge-transfer bands leads to the spontaneous generation of the redox pair Ar?+ and NO. Temporal relaxation by back electron transfer to regenerate the EDA complex [Ar,NO+] is measured by following the spectral decay of Ar?+ with the aid of time-resolved spectroscopy over the two separate time domains I and II. Picosecond kinetics (k1) are associated with the first-order collapse of the geminate ion radical [Ar?+,NO] by inner-sphere electron transfer back to the EDA complex - the relatively slow rates with k1 ～ 108 s-1 arising from driving forces that approach the isoergonic region, coupled with the rather high reorganization energy of nitric oxide. These allow effective competition from diffusive separation (ks) to form Ar?+ and NO as kinetically separate entities. Microsecond kinetics (kII) are thus associated with the second-order (back) electron transfer from the freely diffusing Ar?+ and NO. However, the comparison of the second-order rate constants calculated from Marcus theory shows that outer-sphere electron transfer is too slow to account for the experimental values of kII. The second-order process is unambiguously identified (by the use of the thermochemical cycle in Scheme IV) as the alternative, more circuitous inner-sphere pathway involving the (re)association (ka) of Ar?+ and NO to afford the cation radical pair [Ar?+,NO] followed by its collapse to the EDA complex. The general implications of inner-sphere complexes as reactive intermediates in electron transfer mechanisms in the isoergonic and endergonic regions are presented.

Ferrocene forms a series of unusual charge-transfer crystals with the isoelectronic bis(arene)iron(II) dication, in which X-ray crystallography establishes the alternate (heterosoric) stacking of sandwich structures comprising the donor-acceptor pairs. In acetonitrile, the 1:1 complex [Cp2Fe, Ar2Fe2+] shows a broad absorption band centered at λmax ～ 630 nm. Bis(arene)iron(II) acceptors also form highly colored crystals with various arene donors, in which the charge-transfer absorption (hvCT) derives from the same heterosoric stacking of donor-acceptor pairs-despite the structurally divergent nature of the arene (planar) and ferrocene (sandwich) donors. These absorptions undergo a predictable red-shift with increasing acceptor strength in the order (BZ)2Fe2+ > (MES)2Fe2+ > (DUR)2Fe2+ > (HMB)2Fe2+, as judged by the reduction potentials Eored of the benzene, mesitylene, durene, and hexamethylbenzene derivatives, respectively. Common to both classes of 1:1 bis(arene)iron(II) complexes [Ar2Fe2+, D], where D is either a ferrocene or arene donor, is the efficient photoinduced substitution of the arene ligands that occurs in solution when the charge-transfer bands are selectively irradiated with monochromatic light. Time-resolved picosecond spectroscopy identifies such a charge-transfer deligation to occur via the direct photoexcitation of the complex to the ion radical pair, i.e., [Ar2Fe2+, D] hvCT→ [Ar2Fe+, D?+], followed by the spontaneous loss of arene ligands by the acceptor moiety. Indeed, the substitution lability of the 19-electron intermediate Ar2Fe+ can be independently demonstrated by the application of transient electrochemical methods to the reduction of various bis(arene)iron(II) dications.

The invention relates to pharmaceutical compositions containing novel nitrate esters, of which it was found that they are useful for the treatment of ischemiatic heart diseases, decompensatio cordis, myocardial infarction and hypertension.

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13C-Magic angle spinning (MAS)-NMR of thermally treated samples of zeolite H-ZSM-5 with adsorbed methanol identifies the organic species present in the adsorbed phase, monitors their fate, and distinguishes between mobile and attached species.Only MeOH is present at room temperature; in samples treated at 150 deg C dimethyl ether (DME) is also found.At 250 deg C and above a new signal, due to CO intermediate, appears.A number of aliphatic and aromatic compounds form at 300 deg C and above, and the role of CO in this process is discussed.Neither 1,2,3- or 1,3,5-trimethylbenzene is found in the products, but both are present in the adsorbed phase, which is the first direct experimental demonstration of product selectivity.Tetramethylbenzenes have not been found in the products of the reaction at 300 deg C, but all three are present in the adsorbed phase in considerable concentrations.Their distribution (tetramethylbenzenes are not formed in the thermodynamic equilibrium distribution) reveals the presence of a new kind of shape selectivity.At 370 deg C the shape-selective action is still present but is different because of the increased effective channel diameters.MAS-NMR has a considerable potential for monitoring and prediction of the course of catalytic reactions directly at the active centers in molecular sieves and will assist the design of shape-selective solids.

In photoinduced electron-transfer processes the primary step is conversion of the electronic energy of an excited state into chemical energy retained in the form of a redox (geminate radical-ion) pair (A + D →hν A?-/D?+). In polar solvents, separation of the geminate pair occurs with formation of free radical ions in solution. The quantum yields of product formation, from reactions of either the free ions, or of the geminate pair, are often low, however, due to the return electron transfer reaction (A?-/D?+ → A + D), an energy-wasting step that competes with the useful reactions of the ion pair. The present study was undertaken to investigate the parameters controlling the rates of these return electron transfer reactions. Quantum yields of free radical ion formation were measured for ion pairs formed upon electron-transfer quenching of the first excited singlet states of cyanoanthracenes by simple aromatic hydrocarbon donors in aceonitrile at room temperature. The free-ion yields are determined by the competition between the rates of separation and return electron transfer. By assuming a constant rate of separation, the rates of the return electron transfer process are obtained. These highly exothermic return electron transfer reactions (-ΔG-et = 2-3 eV) were found to be strongly dependent on the reaction exothermicity. The electron-transfer rates showed a marked decrease (ca. 2 orders of magnitude in this ΔG-et range) with increasing exothermicity. This effect represents a clear example of the Marcus "inverted region". Semiquantum mechanical electron-transfer theories were used to analyze the data quantitatively. The electron-transfer rates were found also to depend upon the degree of charge delocalization within the ions of the pair, which is attributed to variations in the solvent reorganization energy and electronic coupling matrix element. Accordingly, mostly on the basis of redox potentials, one can vary the quantum yield of free-ion formation from a few percent to values approaching unity. Use of a strong donor with a strong acceptor to induce reactions based on electron transfer is likely to be inefficient because of the fast return electron transfer in the resulting low-energy ion pair. A system with the smallest possible driving force for the initial charge-separation reaction results in a high-energy, and therefore long-lived ion pair, which allows the desired processes to occur more efficiently. The use of an indirect path based on secondary electron transfer, a concept called "cosensitization", results in efficient radical-ion formation even when the direct path results in a very low quantum yield.

Sterically hindered acylarenes are deacylated to arenes in good yields on heating in boiling 1,2-dichloroethane containing a catalytic amount of triflic acid and water.Hindered arenecarboxylic acids undergo decarboxylation under the same conditions to give arenes in high yields.

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Facile transacylation between acylpentamethylbenzene and activated arenes such as anisole was found to occur in boiling trifluoroacetic acid (TFA).The mechanism for the transacylation between acetylpentamethylbenzene (AcPMB) and anisole with TFA was elucidated by means of product isolation and kinetics.The reaction proceeds via reversible protodeacetylation of AcPMB involving an ipso-protonated intermediate B to give pentamethylbenzene and acetic trifluoroacetic anhydride followed by irreversible acetylation of anisole by the mixed anhydride.The mechanism resulting in an ipso-protonated intermediate B was deduced from the reaction of acetylmesitylene with TFA as well as from the rate of deacetylation of 3,5-dideuterioacetylmesitylene with TFA.The formation of such an intermediate was also independently confirmed by 13C n.m.r. spectroscopic syudies on AcPMB in superacid solutions under stable conditions.

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Mechanism of hydrogen atom abstraction reactions by triplet state p-chloranil (3CA) from durene (DH) were studied by picosecond and nanosecond laser photolysis and transient photoconductivity measurements. 3CA was quenched by DH through diffusional encounter to form a triplet ion pair (IP) between CA and DH, p-chloranil semiquinone radical (CAH.), and 2,4,5-trimethylbenzyl radical (D.).Ionic dissociation of IP was observed in 1,2-dichloroethane (DCE) as well as in acetonitrile.However, no transient species was observed by direct excitation of a charge-transfer (CT) band of the electron donor-acceptor (EDA) complex between CA and DH.The H-atom transfer leading to production of CAH. was found to proceed through two distinct mechanisms; H-atom transfer via IP (Mechanism I) and a more rapid transfer competing with IP formation (Mechanism II).The quantum yields of CAH. produced by Mechanism I and II and the first-order rate constants for proton transfer, ionic dissociation, and intersystem crossing competing with one another in the IP state were estimated to be (0.1 and 0.2) and (2,5, and 13)X106 s-1, respectively, in DCE at room temperature.

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The fast rates of proton transfer from various methylbenzene cation radicals to a series of substitued pyridine bases are successfully measured in acetonitrile solutions.The technique utilizes the production of the cation radical as a transient intermediate during the electron-transfer oxidation of the methylbenzene with an iron(III) oxidant.Complete analysis of the complex kinetics affords reliable values of the deprotonation rate constants k2 which span a range from 3 x 102 to more than 2 x 107 M-1 s-1.The relative acidities of the cation radicals of hexamethylbenzene, pentamethylbenzene, durene, and prehnitene can be obtained from the Broensted correlation of the deprotonation rate constants with the pyridine base strengths and the standard oxidation potentials of the methylarenes.An estimate of the acidity constant for the hexamethylbenzene cation radical is based on several empirical extrapolations to that of the toluene cation radical previously evaluated by Nicholas and Arnold on thermochemical grounds.The kinetic acidities of the various methylarene cation radicals are also examined in the context of the Marcus equation, as applied to proton transfer.The mechanism of proton transfer from these labile carbon acids is discussed with regard to the electronic effects relevant to the methylarene oxidation potential and the pyridine base strength, the kinetic isotope effects with deuterated methyl groups, the salt effects in acetonitrile, and the steric effects of ortho substituents on pyridine.