Methyl Toluene Research Articles

Mechanism Study of Photocatalytic Degradation of Gaseous Toluene on TiO2 with Weak-Bond Adsorption Analysis Using In Situ Far Infrared Spectroscopy

The development of far infrared spectroscopy offers a powerful method for comprehensive study in adsorption structure and photocatalytic degradation mechanism of photocatalysis. This study presented an improved in situ diffuse reflectance infrared Fourier transform spectroscopy technique in far infrared region for investigation of weak-bond adsorption and photocatalytic degradation of gaseous toluene on the surface of TiO2. It was found that toluene tends to be adsorbed on the hydroxyl group via three possible sites, the ortho-, meta-, and para-adsorption site, instead of ipso-structure. The methyl group of toluene is consumed first during the process of toluene photocatalytic degradation. Based on these, a reaction route for the photocatalytic degradation of gaseous toluene on TiO2 surface was proposed.

Alkylation of benzene with carbon monoxide over Zn/H-ZSM-5 zeolite studied using in situ solid-state NMR spectroscopy.

Using in situ solid-state NMR spectroscopy we show that CO can act as an alkylating reagent and react with benzene to produce toluene over a Zn/H-ZSM-5 zeolite. In the alkylation reaction, CO provides the methyl group of toluene via a methoxy intermediate.

Synthesis of macrolactam analogues of radicicol and their binding to heat shock protein Hsp90

A series of macrolactam analogues of the naturally occurring resorcylic acid lactone radicicol have been synthesised from methyl orsellinate in 7 steps, involving chlorination, protection of the two phenolic groups, and hydrolysis to the benzoic acid. Formation of the dianion and quenching with a Weinreb amide results in acylation of the toluene methyl group that is followed by amide formation and ring closing metathesis to form the macrocyclic lactam. Final deprotection of the phenolic groups gives the desired macrolactams whose binding to the N-terminal domain of yeast Hsp90 was studied by isothermal titration calorimetry and protein X-ray crystallography.

Evidence for Benzylsuccinate Synthase Subtypes Obtained by Using Stable Isotope Tools

We studied the benzylsuccinate synthase (Bss) reaction mechanism with respect to the hydrogen-carbon bond cleavage at the methyl group of toluene by using different stable isotope tools. Λ values (slopes of linear regression curves for carbon and hydrogen discrimination) for two-dimensional compound-specific stable isotope analysis (2D-CSIA) of toluene activation by Bss-containing cell extracts (in vitro studies) were found to be similar to previously reported data from analogous experiments with whole cells (in vivo studies), proving that Λ values generated by whole cells are caused by Bss catalysis. The Bss enzymes of facultative anaerobic bacteria produced smaller Λ values than those of obligate anaerobes. In addition, a partial exchange of a single deuterium atom in benzylsuccinate with hydrogen was observed in experiments with deuterium-labeled toluene. In this study, the Bss enzymes of the tested facultative anaerobes showed 3- to 8-fold higher exchange probabilities than those for the enzymes of the tested obligate anaerobic bacteria. The phylogeny of the Bss variants, determined by sequence analyses of BssA, the gene product corresponding to the α subunit of Bss, correlated with the observed differences in Λ values and hydrogen exchange probabilities. In conclusion, our results suggest subtle differences in the reaction mechanisms of Bss isoenzymes of facultative and obligate anaerobes and show that the putative isoenzymes can be differentiated by 2D-CSIA.

Oxidative functionalization of benzylic C–H bonds by DDQ

C–H activation of the methyl group of toluene and related ArCH3 derivatives by 2,3-dichloro-4,5-dicyano-1,4-benzoquinone (DDQ) gives insertion products, ArCH2O[C6Cl2(CN)2]OH via a rate-determining hydride abstraction by DDQ. The resulting benzylic ether can undergo reactions with phosphines to give benzylic phosphonium salts (Wittig reagents) and with phosphites to give phosphonate esters (Horner–Wadsworth–Emmons reagents).

Identification of FeS clusters in the glycyl-radical enzyme benzylsuccinate synthase via EPR and Mössbauer spectroscopy

The anaerobic degradation pathway of toluene is initiated by the addition of the methyl group of toluene to the double bond of fumarate. This reaction is catalyzed by a novel glycyl-radical enzyme, (R)-benzylsuccinate synthase (BSS). The enzyme consists of three subunits, α, β, and γ, and differs from most other glycyl-radical enzymes in having additional cofactors. We have purified a Strep-tagged nonactivated BSS from recombinant Escherichia coli and identified the additional cofactors as FeS clusters by UV/vis, EPR, and Mössbauer spectroscopy. Analysis of the metal content as well as the EPR and Mössbauer spectra indicated that BSS contains magnetically coupled low-potential [4Fe-4S] clusters. Several enzyme preparations showed differing amounts of [3Fe-4S] clusters that could be reconstituted to [4Fe-4S] clusters, indicating that they arise from partial decay of the initial [4Fe-4S] clusters. The most likely location of these FeS clusters in the enzyme are the small β and γ subunits, which are unique for the BSS subfamily of glycyl-radical enzymes and contain conserved cysteines as potential ligands.

Photoluminescence Characteristics of CdSe/ZnS Quantum Dot Doped Fibers in Different Matrices

Photoluminescence characteristics of CdSe/ZnS quantum dot (QD) doped fibers in different matrices (toluene and poly (methyl methacrylate) (PMMA) sol) are investigated in this paper. The photoluminescence (PL) spectra of the QD doped fiber with different fiber lengths and doped concentrations are measured. Effects of the doped concentration and fiber length on the spectra are also discussed. Compared with the measured PL spectra of CdSe/ZnS QD before doping in the fiber in different matrices, there are different red shifts after the QD is doped into the fiber due to re-absorption/excitation effects. The transportation loss of the fiber is related with such red shifts.

Możliwości wykorzystania mikroskopii fluorescencyjnej UV do badania rozmieszczenia impregnatów wzmacniających w nasycanym drewnie na tle metod dotychczas stosowanych

The paper describes methods of the analysis of the extent of impregnation of historic wood with strengthening consolidants. The authors propose including the method UV-fluorescence microscopy combined with the utilisation of fluorescent markers of the applied solutions to the workshop of researchers working in this field. The reader is introduced with the basics of UV-fluorescence microscopy and the chemical nature of fluorescent markers. The test were conducted on non-painted wood and wood covered with layers of priming and paint. The solutions of Paraloid B-72 in toluene, 1-metoksy-2-propanol and dipropylene glycol methyl ether. As markers an addition of fluorescent violet (or the Lumogen dyes group) and fluorescent brighteners PER and 4BCextra (Stilbene derivatives) were used. The proposed method met the requirements, allowing for determination of resin distribution in wood, the penetration paths of the impregnate as well as for estimation of the extent of saturation of polychrome layers, at the same time permitting photographic documentation of test results.

Thermal C−H Bond Activation of Benzene, Toluene, and Methane with Cationic [M(X)(bipy)]+ (M = Ni, Pd, Pt; X = CH3, Cl; bipy = 2,2′-bipyridine): A Mechanistic Study

In the thermal gas-phase ion/molecule reactions of the mass-selected cationic 2,2′-bipyridine (bipy) complexes [M(CH3)(bipy)]+ (M = Ni, Pd, Pt) with benzene and toluene, hydrogen-atom abstraction occurs that results in the loss of neutral CH4. While the Ni and Pd complexes attack exclusively the arene C−H bonds of toluene (however, without any pronounced preference for the ortho-, meta-, or para-positions), in the reaction with [Pt(CH3)(bipy)]+ 10% of the hydrogen originates from the methyl group of toluene. Further, for the Pt complex extensive hydrogen/deuterium exchange between the Pt-bound methyl group and the incoming substrates C6D6 and C6D5CH3 takes place. In addition, it is only the platinum complex that brings about a degenerate H/D exchange with CD4, as demonstrated by the eliminations of CH4−nDn (n = 1−3) from the adduct complex. The experimental findings are in keeping with DFT calculations using the BP86 functional, which is superior as compared with several other functionals for this particu...

Effect of alkali species on performance of MnO/γ-Al2O3 catalysts for the hydrogenation of methyl benzoate to benzaldehyde

Abstract The effect of alkali species on performance of MnO/γ-Al 2 O 3 catalysts for methyl benzoate hydrogenation was investigated in fixed-bed reactor. Doping alkali species on MnO/γ-Al 2 O 3 catalysts enhanced the selectivity of benzaldehyde significantly, toluene and benzyl methyl ether were greatly suppressed. The infrared spectra of adsorbed pyridine adsorption was acquired to study the surface acid properties, the results revealed that doping alkali species weakened the acid strength of MnO/γ-Al 2 O 3 catalysts, which lead to restrain from the formation of toluene and benzyl methyl ether.

Synthetic and Structural Insights into the Zincation of Toluene: Direct Synergic Ring Metallation versus Indirect Nonsynergic Lateral Metallation

Toluene has been directly zincated by reaction with the heteroleptic sodium zincate [(tmeda)Na(tBu)(tmp)Zn(tBu)] (1) to afford a statistical mixture of the meta and para regioisomers of [(tmeda)Na(C(6)H(4)Me)(tmp)Zn(tBu)] (2) (TMEDA = N,N,N',N'-tetramethylethylenediamine, TMP = 2,2,6,6-tetramethylpiperidide). Interestingly, the methyl group of toluene has been left untouched by the mixed-metal base. The crystal structures of both regioisomers have been elucidated by using X-ray crystallography, which revealed a common motif, in which zinc lies in the same plane as the tolyl ring and binds strongly to the carbon that has experienced the deprotonation, leading to a covalent sigma bond; whereas sodium adopts a perpendicular disposition, pi-engaging with the aromatic ring. DFT studies of the reaction of 1 with toluene showed that of the four possible regioisomers, the experimentally observed meta and para ones are the most thermodynamically preferred products due to a large extent to the combined (synergic) effect of the zinc and sodium and the different way in which each metal binds to the tolyl anion. In contrast, the more straightforward benzyl-based zincate [(tmeda)(2)Na(CH(2)Ph)Zn(tBu)(2)] (3) is obtained through an indirect route, in which toluene is first laterally metallated by monometallic butylsodium to afford benzylsodium, which then forms a mixed-metal compound by co-complexation with tBu(2)Zn. Zincate 3 has been characterised by X-ray crystallography in the solid state and by NMR spectroscopy in deuterated THF solution.

Theoretical study of the mechanism behind the para-selective nitration of toluene in zeolite H-Beta

Periodic density functional theory calculations were performed to investigate the origin of the favourable para-selective nitration of toluene exhibited by zeolite H-beta with acetyl nitrate nitration agent. Energy calculations were performed for each of the 32 crystallographically unique Brønsted acid sites of a beta polymorph B zeolite unit cell with multiple Brønsted acid sites of comparable stability. However, one particular aluminum T-site with three favourable Brønsted site oxygens embedded in a straight 12-T channel wall provides multiple favourable proton transfer sites. Transition state searches around this aluminum site were performed to determine the barrier to reaction for both para and ortho nitration of toluene. A three-step process was assumed for the nitration of toluene with two organic intermediates: the π- and σ-complexes. The rate limiting step is the proton transfer from the σ-complex to a zeolite Brønsted site. The barrier for this step in ortho nitration is shown to be nearly 2.5 times that in para nitration. This discrepancy appears to be due to steric constraints imposed by the curvature of the large 12-T pore channels of beta and the toluene methyl group in the ortho approach that are not present in the para approach.

A Convenient Preparation of C-Silylated Calixarenes

Calix[4]arenes having multiple silyl groups on the upper (wide) rim were prepared from the corresponding bromocalixarenes by halogen-metal exchange with t-BuLi followed by silylation. The best results were obtained using the clear supernatant from a mixture of chlorosilane and triethylamine. With the higher molecular weight chlorosilanes, an aqueous workup was replaced by a filtration through a column of silica gel. p-(Trimethylsilyl)calixarene 17, the silicon analogue of the well-studied p-tert-butylcalixarene 1, formed a crystalline complex with toluene having a toluene molecule in the cone cavity with the toluene methyl protruding out at an angle.

Side-chain alkylation of toluene with propene over a basic catalyst: A DFT study

The toluene methyl group alkylation by propene over a basic catalyst, approximated by the Na 2 molecule, was modeled by the B3LYP/6-311++G ** method. The process starts by formation of the PhCH 2Na molecule in complex with the NaH molecule. Then, the two reaction paths are considered: Path A at which PhCH 2Na…NaH complex is dissociated, and Path B at which the whole PhCH 2Na…NaH complex enters in the next reaction step. Next, at the two paths both insertion of the propene double bond into the C–Na bond and the Na/H exchange, leading to one of the isomers of butylbenzene, are examined. At Path A, the PhCH 2Na molecule plays role of catalyst: it is re-formed in the last stage and can return to the propene insertion step. At Path B, the Na 2 molecule is a catalyst: it is re-constructed in the last stage and can return to the beginning step of formation of the PhCH 2Na molecule. The energy levels at Path A are always above those of Path B, whereas the barriers at the essential steps of Path A are always significantly lower than the appropriate ones at Path B. Path A seems to be preferred kinetically while Path B thermodynamically. At the two paths isobutylbenzene is favored over n-butylbenzene by both thermodynamic and kinetic factor. This is in good agreement with experimental findings. We interpret Path A as describing the reaction in the bulk gas phase whereas Path B as describing the reaction at the metal surface. Because, the number of molecules is usually greater in the bulk than in the surface Path A, which is practically the same as that described by Pines et al. more than fifty years ago, is the main mechanism describing the toluene side chain alkylation by propene over a basic catalyst.

Substituent Effects in Formally Quintuple-Bonded ArCrCrAr Compounds (Ar = Terphenyl) and Related Species

The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C6H2-2,6-(C6H3-2,6-iPr2)2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures display similar trans-bent C(ipso)CrCrC(ipso) cores with short Cr-Cr distances that range from 1.8077(7) to 1.8351(4) A. There also weaker Cr-C interactions [2.294(1)-2.322(2) A] involving an C(ipso) of one of the flanking aryl rings. The data show that the changes induced in the Cr-Cr bond length by the different substituents X in the para positions of the central aryl ring of the terphenyl ligand are probably a result of packing rather than electronic effects. This is in agreement with density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-independent paramagnetism in 1-4. UV-visible and NMR spectroscopic data indicated that the metal-metal-bonded solid-state structures of 1-4 are retained in solution. Reduction of (4-F3CAr')CrCl (4-F3CAr' = C6H2-2,6-(C6H3-2,6-iPr2)2-4-CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr')Cr(mu-F)(THF)}2 (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-iPr2Ar*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5-iPr2Ar* = C6H1-2,6-(C6H-2,4,6-iPr3)2-3,5-iPr2) were obtained with use of the larger 3,5-Pri2-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated CrI atoms, with high-spin 3d5 configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-iPr2Ar*)Cr(eta3:eta6-CH2Ph)Cr(Ar*-1-H-3,5-iPr2)] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.

Alkylation of the toluene methyl group: A DFT study

Abstract Alkylation of the methyl group of toluene was modeled at the B3LYP/6-311++G∗∗ level. In the presence of Na2; the model basic catalyst, the methyl group is more active for the Na/H exchange than the H atoms at the aromatic ring. The PhCH2Na molecule formed is next alkylated by ethene to produce PhC3H6Na. This needs a 30 kcal/mol barrier to be overcome. Finally, the Na/H exchange between PhC3H6Na and (unreacted) toluene molecules proceeds through a 18 kcal/mol barrier and ca. 10 kcal/mol is released. The study has confirmed the basic alkylation scheme proposed by Pines, Vesely, and Ipatieff more than 50 years ago.

Deuterium Isotope Effects in the Unusual Addition of Toluene to Fumarate Catalyzed by Benzylsuccinate Synthase

The first step in the anaerobic metabolism of toluene is a highly unusual reaction: the addition of toluene across the double bond of fumarate to produce (R)-benzylsuccinate, which is catalyzed by benzylsuccinate synthase. Benzylsuccinate synthase is a member of the glycyl radical-containing family of enzymes, and the reaction is initiated by abstraction of a hydrogen atom from the methyl group of toluene. To gain insight into the free energy profile of this reaction, we have measured the kinetic isotope effects on Vmax and Vmax/Km when deuterated toluene is the substrate. At 30 degrees C the isotope effects are 1.7 +/- 0.2 and 2.9 +/- 0.1 on Vmax and Vmax/Km, respectively; at 4 degrees C they increase slightly to 2.2 +/- 0.2 and 3.1 +/- 0.1, respectively. We compare these results with the theoretical isotope effects on Vmax and Vmax/Km that are predicted from the free energy profile for the uncatalyzed reaction, which has previously been computed using density functional theory [Himo, F. (2002) J. Phys. Chem. B 106, 7688-7692]. The comparison allows us to draw some conclusions on how the enzyme may catalyze this unusual reaction.

Intermolecular Insertion of an N,N‐Heterocyclic Carbene into a Nonacidic CH Bond: Kinetics, Mechanism and Catalysis by (K‐HMDS)2 (HMDS=Hexamethyldisilazide)

The reaction of 2-[13C]-1-ethyl-3-isopropyl-3,4,5,6-tetrahydropyrimidin-1-ium hexafluorophosphate ([13C1]-1-PF6) with a slight excess (1.03 equiv) of dimeric potassium hexamethyldisilazide ("(K-HMDS)2") in toluene generates 2-[13C]-3-ethyl-1-isopropyl-3,4,5,6-tetrahydropyrimid-2-ylidene ([13C1]-2). The hindered meta-stable N,N-heterocyclic carbene [13C1]-2 thus generated undergoes a slow but quantitative reaction with toluene (the solvent) to generate the aminal 2-[13C]-2-benzyl-3-ethyl-1-isopropylhexahydropyrimidine ([13C1]-14) through formal C-H insertion of C2 (the "carbene carbon") at the toluene methyl group. Despite a significant pKa mismatch (Delta pKa 1+ and toluene estimated to be ca. 16 in DMSO) the reaction shows all the characteristics of a deprotonation mechanism, the reaction rate being strongly dependent on the toluene para substituent (rho = 4.8(+/-0.3)), and displaying substantial and rate-limiting primary (k(H)/k(D) = 4.2(+/-0.6)) and secondary (k(H)/k(D) = 1.18(+/-0.08)) kinetic isotope effects on the deuteration of the toluene methyl group. The reaction is catalysed by K-HMDS, but proceeds without cross over between toluene methyl protons and does not involve an HMDS anion acting as base to generate a benzyl anion. Detailed analysis of the reaction kinetics/kinetic isotope effects demonstrates that a pseudo-first-order decay in 2 arises from a first-order dependence on 2, a first-order dependence on toluene (in large excess) and, in the catalytic manifold, a complex noninteger dependence on the K-HMDS dimer. The rate is not satisfactorily predicted by equations based on the Brønsted salt-effect catalysis law. However, the rate can be satisfactorily predicted by a mole-fraction-weighted net rate constant: -d[2]/dt = ({x2 k(uncat)} + {(1-x2) k(cat)})[2]1[toluene]1, in which x2 is determined by a standard bimolecular complexation equilibrium term. The association constant (Ka) for rapid equilibrium-complexation of 2 with (K-HMDS)2 to form [2(K-HMDS)2] is extracted by nonlinear regression of the 13C NMR shift of C2 in [13C1]-2 versus [(K-HMDS)2] yielding: Ka = 62(+/-7) M(-1); delta(C(2)) in 2=237.0 ppm; delta(C(2)) in [2(K-HMDS)2] = 226.8 ppm. It is thus concluded that there is discrete, albeit inefficient, molecular catalysis through the 1:1 carbene/(K-HMDS)2 complex [2(K-HMDS)2], which is found to react with toluene more rapidly than free 2 by a factor of 3.4 (=k(cat)/k(uncat)). The greater reactivity of the complex [2(K-HMDS)2] over the free carbene (2) may arise from local Brønsted salt-effect catalysis by the (K-HMDS)2 liberated in the solvent cage upon reaction with toluene.

低気圧直流グロー放電中でのベンゼン，トルエンおよびキシレンの分解特性

The decomposition characteristics of hazardous substances such as benzene, toluene, xylene and their mixture in a low pressure DC glow discharge in nitrogen are investigated by mass spectrometry and infrared spectroscopy. It is found that C2H2, H2 and HCN are produced in nitrogen containing benzene, toluene or xylene, and that a trace of CH4 is also produced in nitrogen containing toluene or xylene. C2H2 and HCN are intermediate products, which are decomposed in the discharge, and only H2 remains in a gas phase. It is likely that C2H2 is chiefly produced by the destruction of the aromatic benzene ring of benzene, toluene or xylene and the methyl groups of toluene and xylene slightly contribute to C2H2 production. The damping coefficients of the aromatic benzene ring and the methyl group in the glow discharge in the nitrogen containing benzene-toluene or benzene-xylene mixtures are obtained separately.

Vapour phase reaction of toluene with ethyl acetate over Al-MCM-41 molecular sieves

Al-MCM-41 molecular sieves of Si/Al ratios 25, 50 and 150 were synthesised hydrothermally. The vapour phase reaction of toluene with ethyl acetate was studied over these catalysts at 175, 200, 225, 250, 275 °C. The products were p-xylene, ethyl benzene (EB), p-ethyl toluene ( p-ET), m-ethyl toluene ( m-ET), p-methyl acetophenone ( p-MAP), o-methyl acetophenone ( o-MAP). Transalkylation of toluene to p-xylene, ethylation of toluene to p-ET and isomerisation of the latter to m-ET were observed as the major reactions with minor acylation of toluene. The transalkylation and isomerisation were found to be strongly influenced by the feed ratio and WHSV, respectively. The study of time-on-stream indicated blocking of particularly strong acid sites by coke, which was suggested advantageous in order to reduce such site dependent transalkylation and isomerisation.