Efficient synthesis of novel tricyclic fused pyranothiazolopyrimidine derivatives via isocyanide-based three-component reactions

An efficient and facile one-pot synthesis is described for the preparation of novel tricyclic fused pyranothiazolopyrimidines containing both biologically active thiazolopyrimidine and pyranopyrimidine templates via three-component reaction involving an isocyanide with a dialkylacetylenedicarboxylate (DAAD) and 2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine-5,7(6H)-dione, in high yields.     

Salting-Out of Some Alkyl Acetates in Aqueous Sodium Chloride Solutions

Summary.  Solubilities of methyl acetate (MeOAc), ethyl acetate (EtOAc), 1-propyl acetate (1-PrOAc), 1-butyl acetate (1-BuOAc), 2-methyl-1-propyl acetate (iso-BuOAc), 2-butyl acetate (sec-BuOAc), 2-methyl-2-propyl acetate (ter-BuOAc), 1-pentyl acetate (1-PeOAc) and 1-hexyl acetate (1-HeOAc) in water and in aqueous sodium chloride solutions at concentrations ranging up to 1.0 molċdm⁻³ were determined at 25.0°C by analyzing the saturated aqueous or salt solutions. Solubility ratios of alkyl acetates in pure water and in aqueous sodium chloride solution were calculated and found to be linearly dependent on the concentration of sodium chloride. The solubility ratios were also calculated by the approach of the scaled particle theory and according to the theories of McDevit and Long, Cross, Conway et al., and Aveyard. All these theories, except that of Conway, correctly predict the order of magnitude of the experimental results, but do not discriminate between isomeric butyl acetates. The theoretical values obtained from the scaled particle and Aveyard theories coincide well with the experimental values, especially for the higher alkyl acetates. The purely electrostatic theory of Conway et al. not even predicts the salting-out effect for the alkyl acetates investigated. Received July 12, 1999. Accepted September 23, 1999     

Efficient and simple method for the quantification of alkyl polyglycosides by hydrolysis and photometric determination of reducing sugars

Alkyl polyglycosides (APG) are important biodegradable surfactants for many applications. The lack of a chromophoric group and the mixture of stereoisomers and oligomers make the quantification by merely chromatic separation difficult. A simple and efficient quantification assay was developed based on the acid hydrolysis of alkyl polyglycoside and subsequent quantification of the hydrolytically cleaved glucose using the neocuproine assay. Complete hydrolysis of alkyl polyglycoside is achieved with 16 wt% sulfuric acid at 100 °C after 30  min and the separation of fatty alcohol and clouding of the reaction mixture is prevented by adding 1,2-propylene-glycol. Hydrolytically cleaved sugars reduce the Cu^(II)-neocuproine complex, leading to a color shift which permits the spectrophotometric quantification at 452 nm. A linear correlation between the absorbance of reduced Cu^(II)-neocuproine complex and glucose or alkyl polyglycoside concentration is observed up to an analyte concentration of 25 mg/L. Statistical analysis according to one-tailled T-test (S’ 95%), has shown that the lower detection limit for alkyl polyglycosides is 2.97 mg/L and the limit of quantification 8.24 mg/L, respectively. Apart from the simple execution, the assay is reliable and can be utilized both as scientific technique to quantify APG as well as for process and quality control in the industry.     

Synthesis and characterization of polyamides containing pendant pentadecyl chains

A new aromatic diacid monomer viz., 4-(4′-carboxyphenoxy)-2-pentadecylbenzoic acid was synthesized starting from cardanol and was characterized by FTIR, ¹H- and ¹³C NMR spectroscopy. A series of new aromatic polyamides containing ether linkages and pendant pentadecyl chains was prepared by phosphorylation polycondensation of 4-(4′-carboxyphenoxy)-2-pentadecylbenzoic acid with five commercially available aromatic diamines viz., 1,4-phenylenediamine, 4,4′-oxydianiline, 4,4′-methylenedianiline, 1,3-phenylenediamine, and 4,4′-(hexafluoroisopropylidene)dianiline. Inherent viscosities of the polyamides were in the range 0.45-0.66 dL/g in N,N-dimethylacetamide at 30 ± 0.1 °C. The introduction of ether linkages and pendant pentadecyl chains into polyamides led to an enhanced solubility in N,N-dimethylacetamide and 1-methyl-2-pyrrolidinone at room temperature or upon heating. The polyamides could be solution-cast into tough, flexible and transparent films from their N,N-dimethylacetamide solution. Wide angle X-ray diffraction patterns exhibited broad halo indicating that the polymers were essentially amorphous in nature. X-Ray diffractograms also displayed a diffuse to sharp reflection in the small-angle region (2θ = ∼2-5°) for the polyamides characteristics of formation of loosely to well-developed layered structure arising from packing of flexible pentadecyl chains. The glass transition temperature observed for the polyamides was in range 139-189 °C. The temperature at 10% weight loss (T₁₀), determined by TGA in nitrogen atmosphere, of the polyamides was in the range 425-453 °C indicating their good thermal stability.     

Novel reduction of perfluoroalkyl ketones with lithium alkoxides

The reaction of tert-butyl N-(2-bromophenyl)carbamate (1) with ethyl perfluorooctanoate in the presence of tert-butyllithium did not give the desired N-(2-perfluorooctanoylphenyl)carbamate (3) but gave 1-hydroxy-1H-perfluorooctyl compound (4), which was supposed to be formed by the reduction of 3. A similar reaction of 2,2,2-trifluoroacetophenone with tert-butyllithium did not gave any reduction product. Detailed investigation showed that lithium ethoxide worked as the reducing agent of this abnormal reduction. By the reaction of lithium isopropoxide, an aldol product from 2,2,2-trifluoroacetophenone with acetone was isolated, while perfluoroheptyl or perfluoropropyl phenyl ketones were reduced by this alkoxide in a high yield without formation of the aldol adduct.     

A Convenient One-Pot Synthesis of Phosphino-Dipeptide Analogs

A general "one-pot" synthetic method is described for the preparation of phosphinodipeptides of type 1 , in 60-80% overall yield, allowing the variation of the substituents in f and/or g position to the phosphorus atom and also in f position to the nitrogen atom.     

Intramolecular and Intermolecular Schmidt Reactions of Alkyl Azides with Aldehydes

Despite recent advances in the use of alkyl azides in ring expansion reactions of ketones, there has been little work done on the corresponding chemistry of aldehydes. In the present study, the Lewis acid-promoted reactions of alkyl azides with aldehydes were studied in both intermolecular and intramolecular contexts. The intramolecular reactions of azidoalkyl aldehydes in which the azide and carbonyl groups were separated by 2-5 carbons were examined. Although the examples having the shortest tether failed (3-azidopropanals), each of the other systems gave good yields of either NH-substituted lactams (resulting from hydride migration in the initially formed azidohydrin adduct) or formamides (alkyl migration). The product formed was dependent on the chain length of the starting azido aldehyde. The intermolecular reactions were less efficient, requiring TiCl₄ promotion for even moderate yields, and in each case gave mixtures of products resulting from hydride and alkyl migration.     

Interpretation of surface dilational elasticity data based on an intrinsic two-dimensional interfacial compressibility model

The present analysis shows that the introduction of intrinsic two-dimensional compressibility of a surfactant adsorption layer allows a much better interpretation of experimental data on the limiting (high-frequency) elasticity and characteristic frequency of diffusional relaxation than models using Frumkin's or other adsorption isotherms. The proposed model describes experimental data on surface dilational elasticity, as well as on surface pressure, sufficiently well at low and high surfactant concentrations, assuming the Lucassen and van den Tempel model of surface dilational elasticity is realized.     

A High Yielding, One-Pot, Triton-B Catalyzed, Expeditious Synthesis of Carbamate Esters by Four Component Coupling Methodology

Summary. A novel process for the one-step chemoselective conversion of alkyl halides into carbamates as protected amines was developed using benzyltrimethylammonium hydroxide (Triton-B) in presence of gaseous carbon dioxide. Thus, carbamate esters of different amines were prepared in very good to excellent yields. Present address: Institute of Organic and Biomolecular Chemistry, George–August University, 37077, G?ttingen, Germany     

Theoretical investigation of anthanthrene-based dyes in dye‐sensitized solar cell applications: Effect of nature of alkyl-substitutions and number of anchoring groups

In dye-sensitized solar cells (DSSCs), the dye material plays a crucial role in determining the amount of electrical current obtained, which is the primary outcome of the cell. Therefore, it is crucial to explain the performance of a dye at a molecular level. This work investigates using density functional theory and time-dependent density (DFT and TD-DFT, respectively) four experimentally tested anthanthrene-based dyes abbreviated as D1 to D4. The four dyes differ in their alkyl-substitutions (nonane or 3-ethylheptane) and the number of anchoring groups (one/two cyanoacrylic acid/s). To study the effect of these two structural features, the work involves the calculations of the geometrical structures, electronic and optical properties of isolated forms. In addition, the adsorption behaviour of these dyes on TiO₂ clusters was explained. Properties such as the adsorption energies, and electro-optical properties were calculated and discussed.