[Hmim]TFA catalyzed multicomponent reaction: direct,mild, and efficient procedure for the synthesis of 1,2-dihydroquinazoline derivatives

4-Substituted-spiro-1,2-dihydroquinazolines and related compounds were synthesized by direct reaction of 2-aminobenzophenones, isatin, or 1,2-diketone derivatives and ammonium acetate in the presence of dual role catalyst-solvent ionic liquid, [Hmim]TFA. Excellent conversion of starting materials was achieved to the desired 1,2-dihydroquinazoline products.     

An STM study of the localized atomic reaction of 1,2- and 1,4-dibromobenzene at Si(1 1 1)-7 × 7

A comparative study is reported of the thermal reaction of 1,2- and 1,4-dibromobenzene (1,2- and 1,4-diBrPh) on Si(1 1 1)-7 × 7, investigated by STM. Some results are given for the intermediate case of 1,3-diBrPh. The STM images gave evidence of a different pattern of reaction to yield pairs of Br-Si for 1,2-, 1,3- and 1,4-diBrPh. The ratio of pairs of Br-Si to single bromination events was 1:2 for 1,2-diBrPh and 1:3 for 1,4-diBrPh. In many cases organic residue from the bromination reaction, R-Si, was evident in the STM image. The products R-Si and Br-Si were found to be bound to adjacent Si, for both 1,2- and 1,4-diBrPh. The mean Br?Br pair separation at the surface depended on the parent molecule, being 7.6 Å for 1,2-diBrPh, 10.3 Å for 1,3-diBrPh, and 11.3 Å for 1,4-diBrPh. These separations are, in each case, about 4 Å greater than the separation of the Br-atoms in the intact parent molecule, which increases systematically down the series. There was a marked decrease in the percentage of R-Si accompanying the Br-Si in going down the series, decreasing from 70% for 1,2- to 20% for 1,4-diBrPh; this was interpreted as being due to a decrease in the percentage of `benzene-mediated' reaction dynamics, in which the benzene ring was bound to the surface. At moderately increased surface temperature (45 °C) the reaction of 1,2- and also 1,4-diBrPh no longer resulted in R-Si formation, suggesting that the dynamics had altered from benzene-mediated to `bromine-mediated'.     

Effect of chlorine atoms in chlorinated ethylene on the rate and mechanism of its reaction with ozone

The UQCISD, UB3LYP, UMP2, and MRMP2 methods in conjunction with the 6-31+G**/6-311+G** and aug-cc-PVDZ basis sets are used to study the primary reaction of ozone with chlorinated ethylene derivatives: tetrachloroethylene, trichloroethylene, 1,2-trans-dichloroethylene, 1,2-cis-dichloroethylene, 1,1-dichloroethylene, and chloroethylene. The reaction is studied for both concerted and nonconcerted ozone addition. The UB3LYP DFT method in conjunction with the 6-31+G** basis set is used to examine various modes of addition of ozone to these chlorinated ethylenes by the Criegee and DeMore mechanisms. The geometry and energy of the transition states, the enthalpy and entropy, and the rate constants and ratios thereof for all the reactions are calculated. The UB3LYP method generally satisfactorily describes the two reaction pathways and, largely correctly predicts the rate constants, in agreement with the available experimental data. At the same time, this method appears to be inapplicable to modeling the interaction of ozone with 1,1-dichloroethylene. In this case, the single-determinant approximation turns out to be unsuitable, and, therefore, MCSCF methods should be used. The MRMP2 method yields reasonable values of the rate constants for the DeMore mechanism, whereas in the case of the Criegee mechanism, the MP2 method does well. The UB3LYP/6-31+G** and UQCISD/aug-cc-PVDZ methods give similar values of the ratio between the rate constants for the two pathways, a result that demonstrates the versatility of the first one.     

Efficient library synthesis of imidazoles using a multicomponent reaction and microwave irradiation

Optimization of Radziszewski's four-component reaction employing a microwave-assisted protocol, led to a small library of 48 imidazoles with a success rate of 65% (conversion > 45%). All three diversity points of the four-component reaction were varied. Aromatic and aliphatic inputs were successfully implemented and mono-, di-, tri- and tetrasubstituted imidazoles with various substitution patterns were synthesized. Furthermore, unsymmetrical diketones could successfully be used which improved the intrinsic diversity of the method significantly. If the unsymmetrical diketone 1,2-phenylpropanedione (R¹ and R²) was used two regioisomers were formed. Depending on the type of amine (R⁴) and aldehyde (R³) applied, regioselectivity was modest to good. Based on these results, a reaction mechanism is proposed.     

卡尔曼波滤—分光光度法用于有机反应动力学研究

本文将卡尔曼滤波－分光光度法用于α－羰基烯顺环二硫代缩酮化合物的化学动力学研究。结果表明，用该方法能够有效地消除或减小组分间的干扰，从而进行混合体系中各组分的同时测定。该方法成功地用于１－苯基－２－（１，２－亚忆充基）亚甲基－１，３二本号间硝基苯甲醛的缩合反应动力学研究 中。     

An STM study of the localized atomic reaction of 1,2- and 1,4-dibromoxylene with Si(1 1 1)-7 × 7

Thermal reactions of 1,2- and 1,4-dibromoxylene (1,2- and 1,4-diBrXy) with Si(1 1 1)-7 × 7 were investigated by STM at room temperature under UHV conditions. Reaction led to the formation of single adsorbed Br-atoms or pairs of Br-atoms, in a ratio approx. 3:1 for both reagents. Experimental results were interpreted in terms of ‘parent-mediated’ (halogen atom accompanied by organic residue), and ‘daughter-mediated’ (no accompanying organic residue) reaction dynamics. Both mechanisms contributed to the bromination of the silicon surface in comparable amounts. For pairs of bromine atoms the Br–Br separation had a most probable value of 7.6 Å for 1,2-diBrXy, and 11.5 Å for 1,4-diBrXy. This separation was in each case greater than that in the diBrXy parent molecule by a few angstroms. For parent-mediated reaction the dynamics were revealed in detail by the STM images which gave the vectorial location of the halogen-atom products (distance and angle of the daughter atoms) relative to the prior location and alignment of the adsorbed parent molecule. Both reagents, 1,2- and 1,4-diBrXy, were found to be less reactive than the corresponding dibromobenzenes studied earlier in this laboratory [S. Dobrin et al., Surf. Sci. 561 (2004) 11], in both parent- and daughter-mediated modes.     

苯乙烯与苯酚反应的前线轨道理论分析

采用密度泛函理论的M062X方法和6-311G(d,p)基组,对苯乙烯与苯酚的反应进行了分子轨道理论计算.通过讨论反应过程中各分子的最高占据轨道(HOMO)和最低空轨道(LUMO),预测了化学反应的方向和相应的反应产物.经过前线轨道理论分析,得出苯乙烯与苯酚反应的关键步骤是形成苯乙烯基碳正离子,反应中H+起到催化作用;反应产物主要有4-(1-苯基乙基)苯酚、2-(1-苯基乙基)苯酚、2,4-双-(1-苯基乙基)苯酚、2,4,6-三-(1-苯基乙基)苯酚(SP-3)、1,3-二苯基丁烯和4-(1,2-二苯丙基)苯酚.     

苯乙烯与苯酚反应的前线轨道理论分析

采用密度泛函理论的M062X方法和6-311G(d,p)基组,对苯乙烯与苯酚的反应进行了分子轨道理论计算。通过讨论反应过程中各分子的最高占据轨道(HOMO)和最低空轨道(LUMO),预测了化学反应的方向和相应的反应产物。经过前线轨道理论分析,得出苯乙烯与苯酚反应的关键步骤是形成苯乙烯基碳正离子,反应中H+起到催化作用;反应产物主要有4-(1-苯基乙基)苯酚、2-(1-苯基乙基)苯酚、2,4-双-(1-苯基乙基)苯酚分子、2,4,6-三-(1-苯基乙基)苯酚(SP-3)、1,3-二苯基丁烯和4-(1,2-二苯丙基)苯酚。     

Photophysical properties of solutions of 6,7-dimethoxy-3,4-dihydroisoquinoline

The effect of acid-base interactions on the photophysical properties of 6,7-dimethoxy-3,4-dihydroisoquinoline in protic solvents is studied by the methods of steady-state and picosecond spectroscopy. It is found that the specific features of the spectral and luminescent properties of solutions of 6,7-dimethoxy-3,4-dihydroisoquinoline are connected with the presence of emission centers of two types—solvated initial molecules and their protonated cationic forms. Considerable long-wavelength shifts observed in the electronic absorption and fluorescence spectra of the cationic form of the molecule as compared to the spectra of its initial form are caused by the elongation of a conjugated chain present in the fragment of the molecule that separates the nitrogen atom and the oxygen atoms of the methoxy groups. The transition of the cationic form of the molecule to an excited electronic state is not accompanied by a change in its dipole moment.     

Chemo- and stereoselective reaction between alkyl isocyanides and dimethyl 1,3-acetonedicarbocxylate in the presence of acetylenic esters

The reaction of alkyl isocyanides with dimethyl 1,3-acetonedicarboxylate in the presence of dialkyl acetylenedicarboxylates in CH₂Cl₂ at ambient temperature leads to highly functionalized 2-amino-4H-pyrans and 1,2-dialkyl 4,6-dimethyl-(1E, 3E)-3 (alkylamino)-5-oxo-1,3-hexadiene-1,2,4,6-tetracarboxylates.     

The adsorption and reaction of ethylene glycol and 1,2-propanediol on Pd(111): A TPD and HREELS study

The reactions of ethylene glycol and 1,2-propanediol have been studied on Pd(111) using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). Both molecules initially decompose through O–H activation, forming ethylenedioxy (–OCH₂CH₂O–) and 1,2-propanedioxy (–OCH₂CH(CH₃)O–) surface intermediates. For ethylene glycol, increases in thermal energy lead to dehydrogenation and formation of carbonyl species at both oxygen atoms. The resulting glyoxal (O═CHCH═O) either desorbs molecularly or reacts through one of two competing pathways. The favored pathway proceeds via C–C bond scission, dehydrogenation, and decarbonylation to form carbon monoxide and hydrogen. In a minor pathway, small amounts of glyoxal undergo C–O bond scission and recombination with surface hydrogen to form ethylene and water. The same reaction mechanism occurs for 1,2-propanediol after methyl elimination and formation of glyoxal. However, this is accompanied by a minor pathway involving a methylglyoxal (O=CHC(CH₃)=O) intermediate. The prevalence of the dehydrogenation/decarbonylation pathway in the current work is consistent with the high selectivity for C–C scission in the aqueous phase reforming of polyols on supported Pd catalysts.     

Non yrast spectroscopy with the (α, n) reaction at the coulomb barrier

About 50 states with spins ≦8? in¹²⁸Xe have been populated by means of the¹²⁵Te (α, n) reaction at projectile energies near the Coulomb barrier. In particular eight 2⁺ or (1,2⁺) states have been observed. The (α, n) reaction at particle energies near the Coulomb barrier seems to be a powerful tool to by-pass the strong selectivity for the yrast states in normal (HI, xn) reactions.     

Dicopper peroxo complexes: low temperature stopped-flow reaction kinetics of [(BQPA)CuI]+ and [(Me2-TMPA)CuI]+

In the last 20 years, the reaction of many different CuI complexes and with dioxygen has been described. There is quite a big variety in their coordination geometry and most of them have been characterized by X-ray crystallography. Beyond structural information, stopped-flow kinetics experiments have provided additional mechanistic insights. In the particular systems [(BQPA)CuI]+ and [(Me2-TMPA)CuI]+ a new equilibrium between the two species trans-mu-1,2-peroxo and bis-mu-oxo is demonstrated. In the case of [(BQPA)CuI]+ the two species are in an equilibrium, presumably via the transient superoxo species. The reaction of [(Me2-TMPA)CuI]+ with dioxygen leads to the parallel formation of both species. The kinetically preferred trans-mu-peroxo species is then isomerised to the thermodynamically more stable bis-mu-oxo species.     

Ultrasound and microwave assisted synthesis of isoindolo-1,2-diazine: a comparative study

A comparative study, ultrasound (US) versus microwave (MW) versus conventional thermal heating (TH), for synthesis of isoindolo-1,2-diazine is described. The reaction pathway is fast, efficient and straight applicable, involving a Huisgen [3+2] dipolar cycloaddition of cycloimmonium ylides to 1,4-naphthoquinone. A feasible reaction mechanism for the obtaining of the fully aromatized tetra- and penta- cyclic isoindolo-1,2-diazine is presented. Under US irradiation the yields are much higher (sometimes substantially, by almost double), the reaction time decreases substantially, the reaction conditions are milder. The use of a generator with a higher nominal power induces higher yields and short reaction times. Overall the use of US it proved to be more efficient than MW or TH. A feasible explication for US efficiency is presented.     

Exploring the reaction channels between arsine and the hydroxyl radical

The aim of this study was to present the reaction mechanism channels between arsine (AsH₃) and hydroxyl (OH) which was evaluated at CCSD(T)/CBS//CCSD/cc-pVTZ level. One potential channel is the hydrogen abstraction pathway (R1), leading to AsH₂ and H₂O products, which occurs due to the formation of an entrance complex (AsH₃OH) followed by a 1,2-hydrogen shift pathway (involving the proton transfer from the arsine group to hydroxyls, with one leading to the products). Additional channels are accessed via H-elimination pathways of the entrance complexes, forming arsinous acid (AsH₂OH; R2) and arsine oxide (AsH₃O; R3). In this respect, R2 is the only exoergic route of the three exit channels, representing the major branching ratio at 200–1000 K and, after 2000 K, R1 increases gradually becoming the major route of this reaction. In contrast, even at 4000 K, R3 is a highly unfeasible pathway. Therefore, the information predicted here provides new insights into the neutral–neutral chemical reaction dynamics regarding the Group V hydrides. On the other side, the R2 pathway may have some potential to solve the arsine oxidation puzzle as a possible primary pathway to the arsenic-oxygen species formation.     

Synthesis of trans-1,3-diaryl-2-(5-methylisoxazol-3-yl)-2,3-dihydro-1H-naphtho[1,2-e][1,3]oxazines via bismuth(III)-catalyzed one-pot pseudo-four component reaction

An expeditious, straightforward and efficient synthesis of diversely naphtho[1,2-e][1,3]oxazines via one-pot condensation reaction of ??- naphthol, 3-amino-5-methylisoxazole and arylaldehydes catalyzed by bismuth(III) trifluoromethanesulfonate is described. The reaction preferentially afforded 1,3-trans oxazines.     

Ultrafast reaction dynamics of the complete photo cycle of an indolylfulgimide studied by absorption, fluorescence and vibrational spectroscopy

The reaction dynamics of the complete photo cycle, ring-opening (C → E) and ring-closure (E → C), of N-methyl-(6-bromo-1,2-dimethyl-3-indolyl)fulgimide dissolved in acetonitrile are analysed via steady-state and ultrafast spectroscopy using transient absorption in the UV/VIS and mid-IR complemented by ultrafast fluorescence broad-band spectroscopy with a Kerr-gate setup. For the C → E ring-opening reaction induced by light at ~ 550 nm, a time constant of ~ 3 ps was found for the S₁ decay and the S₀ repopulation. Non-exponential signatures, which occur in the 10 ps time domain, were observed and are assigned to the cooling of hot molecules in the electronic ground state. The E → C reaction dynamics induced by UV-light pulses at 360 nm and 387 nm occur within less than 1 ps and are followed by vibrational cooling on the 10 ps time domain. Thus, both ring-opening and ring-closure reactions are completed within a few picoseconds. From transient IR studies and fluorescence measurements it is concluded that these pericyclic reactions occur from different geometries on the excited state potential energy surface.     

氮氧化物与几种氯代烷烃化学反应的激光磁共振研究

以激光磁共振方法研究氮氧化物与二氯甲烷，三氯甲烷，四氯甲烷，１，２－二氯乙烷在紫外光照射和火花放电条件下的化学反应。实验结果表明氯代烷烃与ＮＯ／ＮＯ２在火花放电，紫外光照射条件下发生快速化学反应。所获得的信息对了解大气化学反应及光化学烟雾有着重要的意义。     

负载Cu的镁铝复合金属氧化物催化合成碳酸丙烯酯

通过浸渍法制备了负载Cu的镁铝水滑石类化合物Cu/HT,经过450℃焙烧得到负载Cu的镁铝复合金属氧化物Cu/LDO,利用X射线衍射(XRD)、红外光谱(FTIR)分析等技术对催化剂的结构进行了表征。研究了其对尿素与1,2-丙二醇合成碳酸丙烯酯的催化性能。考察了反应温度、反应时间、催化剂用量等工艺条件对反应性能的影响。结果表明,以水滑石为前躯体的负载Cu的镁铝复合金属氧化物cu/LDO对尿素与1,2-丙二醇合成碳酸丙烯酯具有比较好的催化活性。当反应温度为170℃、1,2-丙二醇与尿素的摩尔比为4:1、催化剂用量为原料总质量的1.0%、反应时间为3h时,碳酸丙烯酯的收率达到95.2%。     

An experimental and computational investigation of the reaction between pent-1-en-3-yl radicals and oxygen molecules under autoignition conditions

We have measured the kinetics of the reaction between pent-1-en-3-yl (

) radicals and oxygen molecules using laser-photolysis/photoionization mass spectrometry at temperatures relevant for autoignition (600–710 K). The rate coefficient of the title reaction was found to be relatively large for an allylic radical in the studied temperature range (1.27–1.79×10⁻¹⁵cm³ s⁻¹). With such a large rate coefficient the studied reaction is expected to be an important sink of pent-1-en-3-yl radicals under autoignition conditions. Quantum chemical calculations and master equation simulations were performed to complement the experimental work. Experimental data was used to fix the values of key parameters in the master equation model. The model was then used to investigate the title reaction over a wide range of conditions (200–1500 K and 10⁻⁵ – 10² bar). The simulations predict that the title reaction mainly forms (E/Z)-pent-1,3-diene and hydroperoxyl at elevated temperatures (T > 500 K), but non-negligible amounts of (2R/S)-1,2-epoxypent-3-ene and hydroxyl are also formed. We found experimental evidence for both product channels, but it was not conclusive. Arrhenius representations are given for the product channels to facilitate the use of our results in combustion modelling.