Remarkable Solvent Effect Research Articles

Indium(III) chloride – catalyzed Michael addition of thiols to chalcones : A remarkable solvent effect

Indium(III) chloride in methanol efficiently catalyzes Michael addition of aromatic and aliphatic thiols to chalcones and related compounds. This reaction is remarkably solvent selective and it does not proceed in conventional solvents such as tetrahydrofuran, methylene chloride and water.

Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids. Evidence of a remarkable solvent effect in the reaction of ICl2-.

The kinetic constants and activation parameters for the reactions of Br(3)(-) and ICl(2)(-) with some alkenes and alkynes have been determined in the ionic liquids [bmim][PF(6)], [emim][Tf(2)N], [bmim][Tf(2)N], [hmim][TF(2)N], [bm(2)im][Tf(2)N], and [bpy][TF(2)N] (where emim = 1-ethyl-3-methylimidazolium, bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bpy = butylpyridinium, PF(6) = hexafluorophosphate, and Tf(2)N = bis(trifluoromethylsulfonyl)imide) and in 1,2-dichloroethane. The rates of both reactions increase on going from 1,2-dichloroethane to ILs. Evidence suggests that, while the hydrogen bonding ability of the imidazolium cation is probably the main factor able to increase the rate of the addition of ICl(2)(-) to double and triple bonds, this property has no effect on the electrophilic addition of Br(3)(-) to alkenes and alkynes. Furthermore, in the case of the ICl(2)(-) reaction, the hydrogen bonding ability of ILs can be exploited to suppress the unwanted nucleophilic substitution reaction on the products by the Cl(-) anion.

A Remarkable Solvent Effect Toward the Pd/Catalyzed Cleavage of Silyl Ethers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Wilkinson′s Catalyst Catalyzed Selective Hydrogenation of Olefin in the Presence of an Aromatic Nitro Function: A Remarkable Solvent Effect.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Remarkable solvent effect on the yield and specificity of oxidation of naphthalene catalyzed by iron(III)porphyrins

Oxidation of naphthalene was performed with tetrakis(pentaflourophenyl)porphyrin iron(III)chloride (F 20TPPFe IIICl), or tetrakis(2,6-dichlorophenyl)porphyrin iron(III)chloride (TDCPPFe IIICl), or tetramesitylporphyrin iron(III)chloride (TMPFe IIICl) as catalyst and metachloroperbenzoic acid or pentafluoroiodosylbenzene or tert-butylhydroperoxide as oxidant in different media in the presence of imidazole as cocatalyst. In aprotic solvent (CH 3CN:CH 2Cl 2, 1:1) and in the presence of F 20TPPFe IIICl, 1-naphthol, 2-naphthol and 1,4-naphthoquinone yields based on metachloroperbenzoic acid oxidant were 77.7, 2.1 and 5.6%, respectively. The best yield for 1,4-naphthoquinone in methanol with F 20TPPFe IIICl was 52.8%. The effect of bases on the yield and specificity of the naphthalene oxidation were studied. When imidazole changed to pyridine in F 20TPPFe IIICl, the yield of 1-naphthol decreased from 77.7 to 55.3%, whereas for TDCPPFe IIICl catalyst, the yield changed from 61.1 to 18.3%.

Wilkinson's catalyst catalyzed selective hydrogenation of olefin in the presence of an aromatic nitro function: a remarkable solvent effect.

Optimal conditions for chlorotris(triphenylphosphine)rhodium(I) (Wilkinson's catalyst) catalyzed selective saturation of a double bond in the presence of a nitro function are developed. Aryl iodide and benzyl ether are also tolerated under these hydrogenation conditions.

Hydrocarbon Productions in Hexane Solutions of Fatty Acid Methyl Esters Irradiated with Gamma Rays.

Five fatty acid methyl esters in hexane were irradiated in order to obtain basic data regarding the detection of irradiation of fatty foods. Fifteen hydrocarbons which were formed by radiolysis of fatty acid methyl esters were detected using capillary gas chromatography accompanied by mass spectrometry. Dose response was observed at the range of 0.74 kGy to 10 kGy. The yields of the hydrocarbons increased as the dose increased. Clear dose rate effects were not observed at the range of 10 kGy/hr to 500 Gy/hr. Temperature effects on the formation of the hydrocarbons were observed at the range of -40 to 20 degrees Celsius. Their yields were increased as the temperature rose. The effects of oxygen level in the container were examined. The yields in the containers that contained oxygen absorbers were 5-41% of those under normal pressure. Eminent reduction of hydrocarbon yields were observed in the containers that contained oxygen absorbers. Remarkable solvent effects on the formation of the hydrocarbons were observed. The yields of hydrocarbons in benzene solution were reduced to 60-95% of those in hexane. Thus, radiolytic degradation of fatty acid methyl ethers were affected mainly by absorbed dose, irradiation temperature, oxygen pressure, and fatty acid components.

Ruthenium Complex-Catalyzed Formation and Cleavage of Carbon-Carbon σ-Bonds. On the Requirement of Highly Qualified Tuning of the Reaction Conditions

Characteristic aspects of ruthenium complex-catalyzed carbon-carbon bond forming reactions and carbon-carbon σ-bond cleavage reactions are discussed. It is pointed out that these ruthenium complex-catalyzed reactions require highly qualified tuning of reaction conditions with substrates to attain high yields and selectivities of the products. In the [2 + 2] cycloaddition of alkynes and norbornenes catalyzed by RuH2(CO)(PPh3)3, Ru(cod)(cot)/PBu3 [cod: 1,5-cyclooctadiene, cot: 1,3,5-cyclooctatriene] and Cp*RuCl(cod) [Cp*: pentamethylcyclopentadienyl] giving cyclobutenes, matching of the alkyne derivative with the catalyst is essential. In the Ru3(CO)12-catalyzed intramolecular carbonylative cyclization of 1,6-enynes giving bicyclic cyclopentenones, remarkable solvent effects are observed. Linear codimerization of diphenylacetylene and methyl acrylate by Ru(cod)(cot)/pyridine; however, for the reaction of diphenylacetylene with N,N-dimethylacrylamide, pyridine is not required. N,N-Dimethylacrylamide works as a ligand as well as the substrate. Ru(cod)(cot)/dimethyl fumarate catalyzed novel dimerization of 2,5-norbornadiene in THF to give pentacyclo[6.6.0.02,6.03,13.O10,14]tetradeca-4,11-diene (PCTD) via carbon-carbon bond cleavage. In DMSO, the major product is heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14]tetradecane (HCTD) in place of PCTD, and no cleavage of the carbon-carbon bond occurs. The first catalytic deallylation of tert-homoallyl alcohols is achieved. The presence of an excess of allyl acetate is essential. The reaction can be applied to a ring-opening reaction of cyclic homoallyl alcohols. The reasons for the requirement of highly qualified tuning of the reaction conditions for the ruthenium catalysts are discussed comparing with the catalytic activities of palladium complexes.

Bis-porphyrinic clamp for photo- and electro-active guests: a spectroscopic and photophysical study

The spectroscopic and photophysical characterization of a V-shaped Zn(II) bis-porphyrinic structure, ZnH, its free-base analogue FBH and the model porphyrin components ZnB and FBB is presented. With respect to the unsubstituted zinc porphyrin Zn, asymmetric substitution with tetraazaanthracene is responsible for the increase of dipole moment in the excited state of Zn(II) derivatives. The charge transfer character of the transition causes a remarkable solvent effect on the luminescence properties. Axial complexation of the zinc ion in ZnB and ZnH by pyridine induces a strong perturbation of the photophysical properties. In the free base derivatives FBB and FBH the substituent displaces the equilibrium population with respect to unsubstituted FB, on both the ground and excited states of the two tautomers, allowing for the presence of two independent populations (ca. 90% and 10%) of distinct species detected by UV-Vis spectroscopy. The data are supported by semiempirical calculations.

ChemInform Abstract: 2-Siloxy-4-furanyl Anion: Remarkable Solvent Effect on Its Nucleophilicity.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Powerful Solvent Effect of Water in Radical Reaction: Triethylborane-Induced Atom-Transfer Radical Cyclization in Water

Triethylborane-induced atom-transfer radical cyclization of iodo acetals and iodoacetates in water is described. Radical cyclization of iodo acetal proceeded smoothly both in aqueous methanol and in water. Atom-transfer radical cyclization of allyl iodoacetate (3a) is much more efficient in water than in benzene or hexane. For instance, treatment of 3a with triethylborane in benzene or hexane at room temperature did not yield the desired lactone. In contrast, 3a cyclized much more smoothly in water and yielded the corresponding γ-lactone in high yield. The remarkable solvent effect of water was observed in this reaction, although the medium effect is believed to be small in radical reactions. Powerful solvent effects also operate in the preparation of medium- and large-ring lactones. Water as a reaction solvent strikingly promoted the cyclization reaction of large-membered rings. Stirring a solution of 3,6-dioxa-8-nonenyl iodoacetate in water in the presence of triethylborane at 25 °C for 10 h provided a 12-membered ring product, 4-iodo-6,9-dioxa-11-undecanolide, in 84% yield. On the other hand, reaction in benzene afforded the lactone in only 22% yield. Ab initio calculations were conducted to reveal the origin of the solvent effect of water in the cyclization of allyl iodoacetate. Calculations with the SCRF/CPCM option indicate that the large dielectric constant of water lowers the barrier not only to rotation from the Z-rotamer to the E-rotamer that can cyclize but also to cyclization constructing the γ-lactone framework. Moreover, the high cohesive energy density of water also effects acceleration of the cyclization because water forces a decrease in the volume of the reactant.

2-Siloxy-4-furanyl Anion: Remarkable Solvent Effect on Its Nucleophilicity

A significant solvent effect was observed for 2-triisopropylsiloxyl-4-furanyllithium complex (II) in nucleophilic addition of ketones. THF was found to be the best solvent in terms of yields and diastereoselectivity.

Nanosecond Laser Flash Photolysis and Steady-State Photolysis Studies of Benzyltrimethylsilane and Trimethylsilyldiphenylmethane

Photophysical and photochemical processes of benzyltrimethylsilane and trimethylsilyldiphenylmethane have been studied by fluorescence measurements and by steady-state and nanosecond laser flash photolyses. A remarkable solvent effect was observed for the laser flash photolysis of benzyltrimethylsilane; in methanol, absorption bands due to benzyl-type radicals and the triplet were observed, while in cyclohexane, only T−T absorption was observed. On the other hand, no solvent effect was observed for the laser flash photolysis of trimethylsilyldiphenylmethane; a transient absorption attributable to the 1,3-trimethylsilyl-shifted intermediate was observed with a lifetime of ca. 27 ms in both solvents, and no absorption band ascribable to diphenylmethyl radicals or the triplet was observed. GC-MS spectra of photoproducts resulting from trimethylsilyldiphenylmethane were consistent with the assignment of the transient absorption. These results were explained in terms of the calculated molecular structure for the excited singlet states of these molecules by the PM3 method.

ChemInform Abstract: Remarkable Solvent Effect on the Enantioface Selectivity in the Diels—Alder Reaction Catalyzed by an Aluminum Complex of a Newly Prepared Chiral Menthol Derivative.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Remarkable solvent effect on the enantioface selectivity in the Diels-Alder reaction catalyzed by an Aluminum complex of a newly prepared chiral menthol derivative

Reversal of enantioface selectivity was observed by merely switching the solvent from CH 2Cl 2 (enantiomer ratio of the adduct = 91:9) to THF (14:86) in the asymmetric Diels-Alder reaction catalyzed by the aluminum complex of a newly prepared chiral methol derivative. Negative nonlinear effect on the relationship between enantiomeric excesses of the reaction product and optical purities of the ligand was observed for the reaction in CH 2Cl 2 whilst linear relationship for that in THF.

Solvent-Dependent Radiationless Transitions of Excited 1-Aminonaphthalene Derivatives

Photophysical parameters in the excited singlet states of a series of 1-aminonaphthalene derivatives in cyclohexane, 3-methylpentane, and acetonitrile have been determined by means of time-resolved and steady-state fluorometry and time-resolved thermal lensing technique with the aid of MO calculations to elucidate the mechanism of internal fluorescence quenching of 1-aminonaphthalenes observed in nonpolar media. It is revealed that (1) the radiationless processes in nonpolar solvents are mainly due to fast internal conversion (IC; Φic = 0.97, kic = 8.1 × 109 s-1 for N,N-dimethyl-1-aminonaphthalene (DMAN) in cyclohexane at 293 K), (2) the fast IC occurs predominantly in the compounds having a pretwisted and flexible amino group with respect to the naphthalene ring, and the rate remarkably depends on temperature (the activation energy for the temperature dependent IC process of DMAN in 3-methylpentane is 5.1 kcal mol-1), indicating that the IC process is linked with an internal twisting motion of the amino group in nonpolar solvents, and (3) for the pretwisted compounds the rate of the S1 → T1 intersystem crossing (ISC) is also enhanced both in nonpolar and polar solvents. On the basis of the rate parameters obtained, the IC and ISC mechanisms of 1-aminonaphthalenes are discussed together with the remarkable solvent effects on their relaxation processes.

Methylchalcogen Derivatives of 1,4,5,8‐Tetrathiatetralin

AbstractTetrakis(methylthio)‐ and tetrakis(methylseleno)‐1,4,5,8‐tetrathiatetralin 3 and 4 were prepared by the reaction of tetrathiatetralin 2 with LDA (lithium diisopropylamide) and MeS‐SMe or MeSeSeMe in diethyl ether. A remarkable solvent effect was observed in that the similar reaction in tetrahydrofuran gave tetrakis(methylthio)tetrathiafulvalene 5 through a novel rearrangement. The iodine complex of 3 was prepared to be a rare example of complex formation in the tetrathiatetralin series.

Photochemical processes of benzyltrimethylsilane at 77 K remarkable solvent effects and reaction mechanism

Photophysical and photochemical processes of benzyltrimethylsilane have been studied in 3-methylpentane and ethanol glass at 77 K. Remarkable solvent effects were observed in the UV photolysis: in ethanol glass, benzyl radicals were produced, while in 3-methylpentane glass α-trimethylsilylbenzyl radicals and benzyltrimethylsilane radical cations were produced. It was confirmed that the α-trimethylsilylbenzyl radicals and benzyltrimethylsilane radical cations were formed via the lowest triplet state and the benzyl radicals via the excited singlet state or higher triplet state. The molecular structure of the excited-state benzyl-trimethylsilane has been studied by MNDO-PM3 calculations. Based on the results, a possible mechanism involving the excited state of radical pair character has been proposed for the photochemical process of benzyltrimethylsilane.

ChemInform Abstract: Photooxidations of Sulfenic Acid Derivatives. Part 2. A Remarkable Solvent Effect on the Reactions of Singlet Oxygen with Disulfides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Photooxidations of sulfenic acid derivatives 2. A remarkable solvent effect on the reactions of singlet oxygen with disulfides

Photooxidations of a series of 9 disulfides reveal that the thiosulfinate/thiosulfonate product ratios can be dramatically influenced by the nature of the solvent. The unique ability of methanol to influence this ratio is attributed to nucleophilic addition to a thiopersulfoxide intermediate.