Reaction of olefins using cerium(IV) sulfate tetrahydrate in carbonyl compounds–H2O

The reaction of olefins with cerium(IV) sulfate tetrahydrate [Ce(SO₄)₂·4H₂O, CS] in acetone–H₂O under reflux for 5 h gave 2‐oxo‐ and 2‐oxo‐5‐hydroxy derivatives. In this reaction, the yields of 2‐oxo‐5‐hydroxy derivatives were dependent on the quantity of H₂O. Moreover, the reaction of α, β‐unsaturated ketones with CS in acetone–H₂O yielded 2,7‐dioxo‐3‐hydroxy or 3,8‐dioxo‐4‐hydroxy derivatives. The reaction mechanism is also discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Nucleophilic Substitution Reactions of Meta‐ and Para‐Substituted Benzylamines with Benzyl Bromide in Methanol Medium

The rates of reactions of para‐ and meta‐substituted benzylamines with benzyl bromide were measured using conductivity technique in methanol medium. The reaction followed a total second‐order path. The end product of the reaction is identified as dibenzylamine (X‐C₆H₄CH₂NHCH₂C₆H₅) (where X = 4‐OCH₃, 4‐CH₃, H, 4‐Cl, 4‐CF₃, 3‐CF₃, 4‐NO₂). Electron‐withdrawing groups such as chloro, trifluoromethyl, and nitro in the benzylamine moiety decrease the rate of the reaction, whereas the electron‐donating groups, such as methoxy and methyl, increase the rate compared to the unsubstituted compound. A mechanism involving formation of an S_N2‐type transition state between the amine nucleophiles and the benzyl bromide and its subsequent decomposition is proposed. Hammett's reaction constant ρ of the reaction decreases with an increase in temperature. Activation parameters were calculated and discussed.     

Solventless and Metal‐Free Synthesis of High‐Molecular‐Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines

The solventless reaction of diisopropylaminoborane with n‐butylamine, at room temperature, leads to a mixture of B_(sp2)H‐, B_(sp3)H₂‐, and B_(sp3)H₃‐containing species. At low temperature, the reaction outcome is completely modified, thus leading selectively to the formation of high‐mass polybutylaminoborane. When extended to a variety of primary amines, under solventless conditions and at low temperature, this reaction provides a new, efficient, and direct metal‐free access to high‐molecular‐mass polyaminoboranes in good to high yields under mild reaction conditions.     

Theoretical investigation of ion pair SN2 reactions of alkali isothiocyanates with alkyl halides. Part 1. Reaction of lithium isothiocyanate and methyl fluoride with inversion mechanism

The gas‐phase ionic S_N2 reactions NCS^‐ + CH₃F and ion pair S_N2 reaction LiNCS + CH₃F with inversion mechanism were investigated at the level of MP2(full)/6‐311+G**//HF/6‐311+G**. Both of them involve the reactants complex, inversion transition state, and products complex. There are two possible reaction pathways in the ionic S_N2 reaction but four reaction pathways in the ion pair S_N2 reaction. Our results indicate that the introduction of lithium significantly lower the reaction barrier and make the ion pair displacement reaction more facile. For both ionic and ion pair reaction, methyl thiocyanate is predicted to be the major product, but the latter is more selective. More‐stable methyl isothiocyanate can be prepared by thermal rearrangement of methyl thiocyanate. The theoretical predictions are consistent with the known experimental results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Efficient Access to Substituted Silafluorenes by Nickel‐Catalyzed Reactions of Biphenylenes with Et2SiH2

The reaction of biphenylene ( 1 ) with Et₂SiH₂ in the presence of [Ni(PPhMe₂)₄] results in the formation of a mixture of 2‐diethylhydrosilylbiphenyl [ 2 (Et₂HSi)] and 9,9,‐diethyl‐9‐silafluorene ( 3 ). Silafluorene 3 was isolated in 37.5 % and 2 (Et₂HSi) in 36.9 % yield. The underlying reaction mechanism was elucidated by DFT calculations. 4‐Methyl‐9,9‐diethyl‐9‐silafluorene ( 7 ) was obtained selectively from the [Ni(PPhMe₂)₄]‐catalyzed reaction of Et₂SiH₂ and 1‐methylbiphenylene. By contrast, no selectivity could be found in the Ni‐catalyzed reaction between Et₂SiH₂ and the biphenylene derivative that bears tBu substituents in the 2‐ and 7‐positions. Therefore, two pairs of isomers of tBu‐substituted silafluorenes and of the related diethylhydrosilylbiphenyls were formed in this reaction. However, a subsequent dehydrogenation of the diethylhydrosilylbiphenyls with Wilkinson’s catalyst yielded a mixture of 2,7‐di‐tert‐butyl‐9,9‐diethyl‐9‐silafluorene ( 8 ) and 3,6‐di‐tert‐butyl‐9,9‐diethyl‐9‐silafluorene ( 9 ). Silafluorenes 8 and 9 were separated by column chromatography.     

Synthesis of Newly Substituted Pyrazoles and Substituted Pyrazolo[3,4‐b]Pyridines Based on 5‐Amino‐3‐Methyl‐1‐Phenylpyrazole

The reaction of the aminopyrazole 1 with benzenesulfonyl chloride, arenediazonium salt, chloroacetyl chloride, ethoxy methyleneamlononitrile and with ethyl 2‐cyano‐3‐ethoxyacrylate gave the substituted 3‐methyl‐1‐phenylpyrazole 2–5a,b . Compound 5b was cyclized to 6 and to 7 by treating it with AlCl₃ and with POCl₃, respectively. Compound 6 converted to 7 by boiling it in POCl₃/PCl₅. Compound 10b was produced through reaction of 9 with acetophenone. Reaction of 1 with benzylidinemalononitrile afforded 11 . New methods for preparation of 15 and 16 are described. The reaction of 8 with malononitrile, thiosemicarbazide, phenyl hydrazine and acetophenone afforded compounds 18–21 . The reaction of 21 with malononitrile gave 22 . Compounds 23–26 were produced upon reaction of 10a with malononitrile, phenyl hydrazine, thiosemicarbazide, semicarbazide and with benzaldehyde, respectively.     

Synthesis,Characterization and Polymerization of a Novel Glycidyl Phosphinate

With the aim to obtain flame‐retardant epoxy resins, a new glycidyl phosphinate, 9‐(9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide)‐2,3‐epoxypropyl (DOPO‐Gly) was synthesized via a two‐step synthesis. The subsequent reaction of DOPO‐Gly with BF₃·Et₂O resulted in a polyether with a pendant bulky phosphorylated group. Likewise, the reaction with phthalic acid anhydride gave the expected dihydroxy ester. However, the reaction with tertiary or primary amines led to isomerization and no polymer was obtained.     

Lanthanide Amide-catalyzed Aza-Henry Reaction of N-Tosyl Imines with Nitroalkanes

In the presence of 10 mol% lanthanide amide [(Me₃Si)₂N]₃Ln(µ‐Cl)Li(THF)₃, the aza‐Henry reaction of N‐tosyl imines with nitroalkanes (1:5 molar ratio) could be performed in good yields. The lanthanide amide‐catalyzed aza‐Henry reaction has the features of mild reaction conditions, tolerance of a variety of aromatic aldehyde‐derived imines and nitroalkanes, short time and good chemical yields. A catalytic mechanism for the reaction was also proposed.     

N‐heterocyclic carbene–palladium(II) complex supported on magnetic mesoporous silica for Heck cross‐coupling reaction

Magnetic mesoporous silica was prepared via embedding magnetite nanoparticles between channels of mesoporous silica (SBA‐15). The prepared composite (Fe₃O₄@SiO₂‐SBA) was then reacted with 3‐chloropropyltriethoxysilane, sodium imidazolide and 2‐bromopyridine to give 3‐(pyridin‐2‐yl)‐1H‐imidazol‐3‐iumpropyl‐functionalized Fe₃O₄@SiO₂‐SBA as a supported pincer ligand for Pd(II). The functionalized magnetic mesoporous silica was further reacted with [PdCl₂(SMe₂)₂] to produce a supported N‐heterocyclic carbene–Pd(II) complex. The obtained catalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, vibrating sample magnetometry, Brunauer–Emmett–Teller surface area measurement and X‐ray diffraction. The amount of the loaded complex was 80.3 mg g^?1, as calculated through thermogravimetric analysis. The formation of the ordered mesoporous structure of SBA‐15 was confirmed using low‐angle X‐ray diffraction and transmission electron microscopy. Also, X‐ray photoelectron spectroscopy confirmed the presence of the Pd(II) complex on the magnetic support. The prepared magnetic catalyst was then effectively used in the coupling reaction of olefins with aryl halides, i.e. the Heck reaction, in the presence of a base. The reaction parameters, such as solvent, base, temperature, amount of catalyst and reactant ratio, were optimized by choosing the coupling reaction of 1‐bromonaphthalene and styrene as a model Heck reaction. N‐Methylpyrrolidone as solvent, 0.25 mol% catalyst, K₂CO₃ as base, reaction temperature of 120°C and ultrasonication of the catalyst for 10 min before use provided the best conditions for the Heck cross‐coupling reaction. The best results were observed for aryl bromides and iodides while aryl chlorides were found to be less reactive. The catalyst exhibited noticeable stability and reusability.     

Large‐Scale Synthesis of High‐Quality Metal Sulfide Semiconductor Quantum Dots with Tunable Surface‐Plasmon Resonance Frequencies

High‐quality CdS and Cu₇S₄ quantum dots (QDs) were synthesized with N,N‐dibutylthiourea (DBTU) as an organic sulfur source. In this method, nucleation and growth reactions were controlled simply by the heating rate of the reaction. The mild oxidation conditions gave monodisperse CdS QDs exhibiting pure band‐edge emission with relatively high photoluminescence quantum yield. During the synthesis of Cu₇S₄ QDs, the addition of dodecanethiol to the reaction system controlled the reaction rate to give monodisperse spherical or disk‐shaped QDs. A hundred‐gram scale of copper precursor could be used to generate the high‐quality Cu₇S₄ QDs, indicating that an industrial‐scale reaction is achievable with our method. As observed in anisotropic noble‐metal nanocrystals, larger disk‐shaped Cu₇S₄ QDs showed lower localized‐surface‐plasmon resonance energy in the near‐infrared region. The disk‐shaped Cu₇S₄ QDs could be used effectively as templates to form cation‐exchanged monodisperse disk‐shaped CdS QDs.     

Rapid Synthesis of 2‐Alkanol‐substituted Pyrrolo[2,3‐b]quinoxalines from Propargylic Alcohols via Copper‐free Sonogashira Coupling Reaction at Room Temperature

A practical and efficient procedure is established for the synthesis of 2‐alkanol‐substituted pyrrolo[2,3‐b]quinoxalines by the reaction of N‐alkyl‐3‐chloroquinoxaline‐2‐amines with propargylic alcohols. The reaction is carried out in the absence of any copper salt but in the presence of a catalytic amount of Pd(PPh₃)₂Cl₂ at room temperature. The Sonogashira coupling reaction step in this procedure is fast, producing clean products with high yields without contamination by unwanted homocoupling Glaser reaction products. The synthesized pyrroloquinoxaline derivatives are also screened against the three bacterial strains Micrococcus luteus, pseudomonas aeruginosa, and Bacillus subtilis.     

Unexpected regioselectivity in the palladium‐catalyzed reaction of silacyclobutanes with aryl iodides

The reaction of aryl iodides with 1,1‐diphenyl‐silacyclobutane in the presence of a catalytic amount of Pd(PPh₃)₄ affords unexpected ring‐opening adducts, 1‐ and 2‐propenyl(triaryl)‐silanes, in good yields. On the other hand, the PdCl₂(PhCN)₂‐catalyzed reaction of 1,1‐diphenylsilacyclobutanes with aryl halides gives ­unexpected products, triarylsilanols, after ­hydrolysis in moderate yields. The catalysis involves the reaction of aryl–palladium intermediates with silacyclobutanes along with ­regioselective aryl–silicon bond formation. Copyright © 2001 John Wiley & Sons, Ltd.     

An Efficient Catalyst System at Mild Reaction Conditions Containing Rare Earth Metal Complexes

An efficient rare earth metal complex‐catalyzed cycloaddition reaction of CO₂ with propylene oxide using Hdpza (di(2‐pyrazyl)amine) as a N‐donor ligand has been accomplished in good to excellent yields with high selectivity. The effects of different rare earth metal salts, ligands and reaction conditions were examined. Catalytic reaction tests demonstrated that the incorporation of ErCl₃ and Hdpza can significantly enhance the catalytic reactivity of the TBAB (nBu₄NBr, tetra‐n‐butyl ammonium bromide) towards cycloaddition reaction of CO₂ and propylene oxide that produce cyclic carbonates under mild conditions without any co‐solvent.     

A kinetic study of the high temperature rearrangement of 4‐ethyl‐3,5‐diphenyl‐4H‐1,2,4‐triazole

The kinetics of the thermal rearrangement 4‐ethyl‐3,5‐diphenyl‐4H‐1,2,4‐triazoles, 1 , to the corresponding 1‐ethyl‐3,5‐diphenyl‐1‐alkyl‐1H‐1,2,4‐triazoles, 2 , was studied in 15‐Crown‐5 and octadecane at 330 °C. The reaction was very slow in octadecane but proceed well in 15‐Crown‐5. The reaction order for the reaction was not constant but changed from an initial second order rate law towards a first order rate law as the reaction progressed. This was confirmed by the concentration dependent reaction order, n_c, which was larger than the time dependent rate law, n_t. The rationale for the observation was, that at high substrate concentrations the reaction order was second order while at lower concentrations a competing solvent assisted reaction plays an increasing important role. The data were in agreement with a mechanism in which the neutral 4‐alkyl‐triazoles in an intermolecular nucleophilic displacement reaction form a triazolium triazolate, which in a subsequent nucleophilic reaction gives the observed product.     

The hydroxyl radical reaction rate constant and products of 3,5‐dimethyl‐1‐hexyn‐3‐ol

A bimolecular rate constant,k_DHO, of (29 ± 9) × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5‐dimethyl‐1‐hexyn‐3‐ol (DHO, HC?CC(OH)(CH₃)CH₂CH(CH₃)₂) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH₃)₂C?O), 3‐butyne‐2‐one (3B2O, HC?CC(?O)(CH₃)), 2‐methyl‐propanal (2MP, H(O?)CCH(CH₃)₂), 4‐methyl‐2‐pentanone (MIBK, CH₃C(?O)CH₂CH(CH₃)₂), ethanedial (GLY, HC(?O)C(?O)H), 2‐oxopropanal (MGLY, CH₃C(?O)C(?O)H), and 2,3‐butanedione (23BD, CH₃C(?O)C(?O)CH₃). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O‐(2,3,4,5,6‐pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas‐phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534–544, 2004     

Influences of product gases on the kinetics of thermal decomposition of synthetic malachite evaluated by controlled rate evolved gas analysis coupled with thermogravimetry

An instrument of controlled rate evolved gas analysis (CREGA) coupled with TG‐DTA was constructed for analyzing the influences of product gases on the kinetics and mechanism of the thermal decomposition of solids that produce more than one gaseous products at the same stage of reaction. The thermal decomposition of synthetic malachite, Cu₂(OH)₂CO₃, was subjected to the measurements of CREGA‐TG under controlled concentrations of H₂O and CO₂ in the reaction atmosphere with taking account of self‐generated H₂O and CO₂ during the course of reaction. By a series of CREGA‐TG measurements carried out under various atmospheric conditions, it was reconfirmed that the reaction is accelerated and decelerated by the effects of atmospheric H₂O and CO₂, respectively. From the kinetic analysis of the CREGA‐TG curves and results of high temperature X‐ray diffraction measurements under various reaction atmospheres, it was revealed that the anomalous effects of atmospheric H₂O on the reactivity and on the reaction rate of the thermal decomposition of synthetic malachite appear at the early stage of the reaction. Usefulness of the CREGA‐TG technique for measuring the kinetic rate data for the thermal decomposition of solids was demonstrated in the present study, by emphasizing the importance of quantitative control of self‐generated reaction atmosphere. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 346–354, 2005     

Reaction of 4‐benzylidene‐2‐methyl‐5‐oxazolone with amines,Part 2: Influence of substituents in para‐position in the phenyl ring and a substituent on amine nitrogen atom on the reaction kinetics

An influence of a structure of the amine (benzylamine, N‐methyl‐benzylamine, N‐isopropyl‐benzylamine, N‐methyl‐butylamine, N‐ethyl‐butylamine, sec‐butylamine, and tert‐butylamine) on a rate constant of the ring‐opening reaction of 4‐benzylidene‐2‐methyl‐5‐oxazolone (Ox) was studied. The good correlation between logarithm of the rate constants and Charton's steric substituent constant ν as well as good correlation with a form of the simple branching equation indicate that there is a steric effect because of substitution at C1 carbon atom of nucleophile which decreases the reaction rate. Additionally, an influence of a structure of the benzylidene moiety of Ox on a rate of the oxazolone ring‐opening reaction was studied. The substituents (? OH, ? OCH₃, ? N(CH₃)₂, ? Cl, ? NO₂) in para‐position of the phenyl ring of Ox substantially modified the rate of the reaction with benzylamine in acetonitrile. The rate of the Ox ring‐opening reaction decreased with increase of the electron‐donating properties of the substituent. A good correlation between the rate constants of the reaction of 4‐(4′‐substituted‐benzylidene)‐2‐methyl‐5‐oxazolones with benzylamine and the electron density at the reaction center (carbon C5 of the oxazolone ring), calculated using ab initio method, and the Hammett substituent constants, and CR equation were established. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 148–155, 2002; DOI 10.1002/kin.10039     

Lanthanides Mediated Oxidative Cross Coupling of Benzylalcohol and Various Amines to Form Corresponding Imines

Herein, a new and efficient approach towards the oxidative cross‐coupling of benzylalcohol and various aromatic amines to form corresponding imines with high degree conversion (>80 %) and chemo‐selectivity using lanthanide salts as pre‐catalysts is presented. The catalyzed oxidative cross‐coupling reaction using La(NO₃)₃ · 6H₂O as pre‐catalyst displayed a broad substrate scope. The reaction afforded various substituted imines from the reaction of benzylalcohol with ample variety of amines in good yields.     

The Reactivity of CF3C6F4OC6F4Li towards Halogens and Cyanogen Halides

The reaction of 4‐(4′‐trifluoromethyl‐tetrafluorophenoxy)‐tetrafluorophenyllithium (R_FLi, 1 ) with halogens, dicyanogen, cyanogen halides, and xenon difluoride was examined. The corresponding halogenated aromatics R_FCl ( 2 ), R_FBr ( 3 ) and R_FI ( 4 ) were formed upon reaction with chlorine, bromine, and iodine. Essentially the same products were isolated in the reaction of 1 with cyanogen chloride, bromide, and iodide, respectively. The nitrile R_FCN ( 5 ) was obtained from the reaction of 1 with dicyanogen only as a minor product. The reaction of 1 with XeF₂ resulted in the isolation of R_FCH(CH₃)CH₂CH₃ ( 6 ). All products were identified and characterized by analytical and spectroscopic methods. In addition the molecular structures of 2 , 3 , and 4 have been determined by X‐ray crystallography. The reaction enthalpies for the gas phase reactions of pentafluorophenyllithium, C₆F₅Li, as a model for 1 , with XCN (X = F, Cl, Br, I) were calculated.     

Reaction of Some Indoles with 1,4‐Naphthoquinones in the Presence of Pd(OAc)2

The reaction available for the introduction of an indole unit into the 1,4‐naphthoquinone skeleton is described. The reaction of the indoles with 1,4‐naphthoquinones in CH₃CN in the presence of Pd(OAc)₂ gave the corresponding 2‐(3‐indolyl)‐1,4‐naphthoquinones in moderate yield.