Gas phase thermolysis of allyl cyanomethyl amine,diallyl cyanomethyl amine,diethyl cyanomethyl amine,and diethyl propargyl amine

The title amines were pyrolyzed in a stirred-flow reactor at 380–510°C, pressures of 8–15 torr and residence times of 0.3–2.4 s, using toluene as carrier gas. The substrates with an allyl group yielded propene and iminonitriles as reaction products. HCN is formed by decomposition of the iminonitriles. The first-order rate coefficients for propene formation fit the Arrhenius equations

• Allyl cyanomethyl amine:
• Diallyl cyanomethyl amine:

Diethyl cyanomethyl amine gave a 20:1 gas mixture of ehylene and ethane, plus HCN. The liquid product fraction contained mainly N-ethyl methanaldimine. The first-order rate coefficients for ethylene formation followed the Arrhenius equation Diethyl propargyl amine decomposed cleanly into allene and N-ethyl ethanaldimine. The first-order rate coefficients for allene formation fit the Arrhenius equation The results suggest that the above allyl and propargyl amines decompose unimolecularly by mechanisms involving six-center cyclic transition states. For diethyl cyanomethyl amine, a nonchain free radical mechanism is proposed. © 1995 John Wiley & Sons, Inc.     

Representation of the molecular topology of cyclical structures by means of cycle graphs. 3. Hierarchical model of screening of chemical databases

The increase in the size and complexity of chemical databases necessitates the proposal and development of efficient methods of classification and recovery of information, which supposes proposal of a model of classification of database records and the use of a compatible model of screening for inspection of clusters and recovery of the molecules that satisfy the search criterion. The cycle graphs model based on consideration of all the cycles and chains (and equivalent cycles and chains) present in the molecular structure has been proven appropriate for classification of chemical databases, giving rise to a generation of different classification levels depending on the structural elements (cycles and chains) that are considered. In this paper we propose a screening model, compatible with the cycle graphs model, based on a hierarchy of levels of abstraction. The set of molecules that satisfies a screening model (or selection criterion) diminishes as we advance in the hierarchy of levels of the model, which allows filtering of records and, therefore, an increase in the efficiency of the screening process. In the following work of this series we describe and validate the screening tool developed.     

Annulative π-extension of BODIPYs made easy via gold(i)-catalyzed cycloisomerization

Here we report gold(i)-catalyzed cycloisomerization as a new powerful synthetic tool for the preparation of π-extended BODIPY derivatives. The catalytic system PPh^F₃AuCl/AgSbF₆ enables the synthesis of [b]-[2,1]naphtho-fused-BODIPYs (2a–2c) under mild conditions, in excellent yields and short reaction times. The reaction is totally regioselective to the 6-endo-dig product and for the α-position of the BODIPY, which is both the kinetically and thermodynamically favored pathway, as supported by the free energy profile calculated by means of Density Functional Theory (DFT). Moreover, this methodology also allows the synthesis of two new families of [b]-aryl-fused-BODIPYs, namely, [3,4]phenanthro- (2e and 2f) and [1,2]naphtho-fused (2g) BODIPYs. Their molecular and electronic structures were established by NMR and UV-vis spectroscopies as well as single-crystal X-ray diffraction analysis. As can be noted from the X-ray structures, 2a, 2e and 2g present interesting structural differences at both the molecular and packing level. Interestingly, despite being isomers, the UV/vis spectra of 2a and 2g revealed significant differences in their electronic structures. The origin of this finding was studied by Time-Dependent DFT calculations. Calculated DFT Nuclear Independent Chemical Shift (NICS(0)) values also supported the different electronic structures of 2a and 2g.

Here we report gold(i)-catalyzed cycloisomerization as a new powerful synthetic tool for the preparation of π-extended BODIPY derivatives.     

Alkylation of nitroaromatics with tetraalkylborate ion via electrochemical oxidation

Aromatic nucleophilic substitution reaction (S(N)Ar) is one of the most thoroughly studied reactions. Alkylation of nitroaromatics with Grignard reagents via chemical oxidation of the sigma(H)-complexes is the most general method to introduce an alkyl group into a nitroaromatic compound. This approach has considerable drawbacks, especially when more than one nitro group are present in the aromatic ring. In this article, we present an electrochemical approach, which offers a new very selective methodology for obtaining alkyl polynitroaromatic compounds. Different strategies based on the use of tetralkylborate anion as nucleophiles are used so as to increase efficiency and to reduce the drawbacks associated with this reaction. A wide list of dinitro- and trinitro-aromatic compounds are studied, the range of yields obtained being from fair (40%) to excellent (85%). The key to improvement in the process is the use of electrochemical techniques for the oxidation of the mixture sigma(H)-complexes/tetrabutylborate ion. The electroactive character of the nucleophile, which can be oxidized to an alkyl radical, means that the S(N)Ar of the hydrogen polar mechanism is not the only mechanism operating during the electroxidation process, since the hydrogen radical S(N)Ar mechanism is running at the same time. Electrochemical mechanistic studies allow the participation of each mechanism in the global product yield obtained to be quantified.     

The Reaction of Triplet State Benzophenone with Acetylacetone

Irradiation of benzophenone in acetic acid containing acetylacetone resulted in regiospecific addition to form cis-2,2-dihpenyl-3-hydroxy-3-methyl-4-acetyloxetane and the rearrangement products therefrom. In the co-presence of copper ions, the regiospecificity is scrambled to give these products and a small amount of 1,1-diphenyl-1-buten-3-one, the secondary decomposition product of the other oxetane arising from the alternative orientation of the addition.     

A convenient enantioselective synthesis of (S)-alpha-trifluoromethylisoserine

[reaction: see text] This report describes two straightforward synthetic methodologies to obtain alpha-CF3-isoserine, a new alpha,alpha-disubstituted beta-amino acid, from alpha-(trifluoromethyl)acrylic acid. The routes involve the synthesis of five-membered cyclic sulfates (using sulfuryl chloride) or sulfamidates (using the Burgess reagent) from the corresponding chiral diols, which are obtained by a catalytic asymmetric dihydroxylation (AD) reaction.     

Spectroscopic investigation of the adsorption and oxidation of thiourea on polycrystalline Au and Au(111) in acidic media

In the present paper, a systematic electrochemical investigation on thiourea (TU) electrooxidation was developed on polycrystalline and (111) single-crystal gold electrodes in 0.1 M perchloric acid. The combination of cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry techniques have allowed the nature of the species formed during the electroadsorption and electrooxidation of TU to be established. FTIRS experiments were performed in D2O to clean up the region of the H2O bending around 1600 cm(-1). It was concluded that TU adsorbs tilted on the surface in the 0.05-0.40 VRHE potential range. A dual-path reaction mechanism was evidenced in the oxidation process. The first pathway takes place from adsorbed TU at E > 0.40 VRHE and implies the formation of [Au(I)-(TU)2]+, which is oxidized to NH2CN and S0 at E > 0.80 VRHE. In a following oxidation step at E > 1.20 V, N2, CO2, and HSO4-/SO4(2-) were produced. The second parallel reaction occurs from TU in solution at E > 0.50 VRHE to form (TU)2(2+). All these species were characterized from the spectroscopic experiments. Similar results were obtained for both surfaces.     

Sorption of proton and heavy metal ions on a macroporous chelating resin with an iminodiacetate active group as a function of temperature

A macroporous resin containing iminodiacetic groups (Lewatit) was investigated for its sorption properties towards proton and nickel(II) and cadmium(II). Different compositions of the aqueous phase, and different temperatures were examined. The stoichiometry, the exchange coefficients and the intrinsic constants of the sorption equilibria were obtained from the experimental data by using the Gibbs-Donnan model for the ion exchange resin. The intrinsic constants were found to be independent of the composition of the solution, so that they were used for characterizing the sorption equilibria. While the first intrinsic protonation constant of the active groups in the resin was found to depend on the temperature, the second one was independent. The sorption equilibrium of nickel in the resin was different from that of cadmium, being ascribable respectively to the formation of the complexes NiL and Cd(HL)(2). inside the resin. Their intrinsic complexation constants were found to be 10(-1.84) and 10(-3.64) at 25 degrees C. Compared to those of another resin with the same active groups, but not macroporous, they are higher. The dependence of the intrinsic constant on the temperature was also different for the two metals, allowing to evaluate a DeltaH degrees of +30.9 and of +13.7 kJ mol(-1) respectively. When a comparison is possible, these values are near to those in aqueous solution for the complexation with ligands of similar structure. These results can be used to achieve metal ion separation based on temperature variations.     

Simultaneous determination of yohimbine and boldine by first-derivative synchronous spectrofluorimetry

A method for the simultaneous determination of yohimbine and boldine in mixtures by first-derivative synchronous spectrofluorimetry has been developed. The method is based on their native fluorescence in 0.1N sulphuric acid medium. The constant wavelength difference chosen to optimize the determination was =_em -_em=82 nm. Yohimbine was measured at _ex//_em= 285/367 nm, and boldine at _ex/_em=272/354 nm. The range of application is 10–500 g/l for yohimbine and 1–50 g/l for boldine. The method was applied to the determination of yohimbine and boldine in synthetic mixtures and pharmaceuticals, with errors generally 2%. Relative standard deviations were about 2%.Dedicated to Professor Fermin Capitán on his 72th birthday