Ultrasound promoted synthesis of 5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones in water

A convenient method for the preparation of 5-hydroxy-5-trihalo-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones, from the reaction of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones with hydroxylamine and anilines, respectively, using water as solvent and under ultrasound irradiation is reported.     

One-pot synthesis of N-Cbz-l-BMAA and derivatives from N-Cbz-l-serine

We report herein an asymmetric synthesis of the modified amino acid N-Cbz-l-BMAA and seven of its alkyl derivatives (2a-h) from N-Cbz-l-serine via ring-opening of the β-lactone (formed under modified Mitsunobu conditions) by different amines. This procedure is simple, one-pot and can generate various derivatives that can be investigated for their toxicological effects. In addition, it can be employed to produce analytical standards for water monitoring as well as labeled compounds for biotransformation studies. This toxin has been the focus of serious ecological and public concern since its implication in degenerative disease such as Alzheimer and Parkinsonism dementia.     

A low-cost non instrumental method for semiquantitative determination of mercury in fish

A non instrumental method for the semiquantitative determination of mercury in fish is described. The sample is acid digested and the mercury vapor released after chemical reduction with SnCl₂. The mercury vapor is then collected on a detecting paper covered with an emulsion of Cu₂I₂, 3% carboxymethylcellulose and MgCl₂ as moistener agent. The colored Cu₂[HgI₄] complex is formed and the color intensity is proportional to the mercury concentration in the original sample. Parameters such as sample mass/digestion solution volume ratio, emulsion composition, paper covering technique, carrier gas flow were investigated. Comparative studies using CVAAS and digital color analysis after scanning the papers confirmed the applicability of the method to real samples. Received: 3 July 1999 / Revised: 29 September 1999 / Accepted: 21 October 1999     

A flow injection procedure based on solenoid micro-pumps for spectrophotometric determination of free glycerol in biodiesel

A flow system designed with solenoid micro-pumps is proposed for fast and greener spectrophotometric determination of free glycerol in biodiesel. Glycerol was extracted from samples without using organic solvents. The determination involves glycerol oxidation by periodate, yielding formaldehyde followed by formation of the colored (3,5-diacetil-1,4-dihidrolutidine) product upon reaction with acetylacetone. The coefficient of variation, sampling rate and detection limit were estimated as 1.5% (20.0 mg L⁻¹ glycerol, n = 10), 34 h⁻¹, and 1.0 mg L⁻¹ (99.7% confidence level), respectively. A linear response was observed from 5 to 50 mg L⁻¹, with reagent consumption estimated as 345 μg of KIO₄ and 15 mg of acetylacetone per determination. The procedure was successfully applied to the analysis of biodiesel samples and the results agreed with the batch reference method at the 95% confidence level.     

Ultrasound-Promoted Environmentally Friendly Synthesis of 5-(3,3,3-Trifluoro-2-oxopropylidene)pyrrolidin-2-ones

A facile, one-pot, ultrasound-promoted synthesis of N-substituted 5-(3,3,3-trifluoro-2-oxopropylidene)pyrrolidin-2-ones from methyl 7,7,7-trifluoro-4-methoxy-6-oxohept-4-enoate and a wide range of primary alkyl(aryl)amines using ethanol as a green solvent and employing triethylamine as a base is described.     

Exploiting Mn(III)/EDTA complex in a flow system with solenoid micro-pumps coupled to long pathlength spectrophotometry for fast manganese determination

The formation of the Mn(III)/EDTA complex in a flow system with solenoid micro-pumps was exploited for fast manganese determination in freshwater. Manganese(II) was oxidized in a solid-phase reactor containing lead dioxide immobilized on polyester. Long pathlength spectrophotometry was exploited to increase sensitivity, aiming to reach the threshold limit established by environmental legislation. A linear response was observed from 25 to 1500 μg L^− 1, with a detection limit of 6 μg L^− 1 (99.7% confidence level). Sample throughput and coefficient of variation were 36 samples/h and 2.6% (n = 10), respectively. EDTA consumption and waste generation were estimated as 500 μg and 3 mL per determination, respectively. The amount of Pb in the residue corresponds to 250 μg per determination and a solid-phase reactor could be used for up to 1600 determinations. Adsorption in active charcoal avoided interferences caused by organic matter and the developed procedure was successfully applied for determination of manganese in freshwater samples. Results were in agreement with those attained by GFAAS at the 95% confidence level.     

Exploring the chemical profile of designer drugs by ESI(+) and PSI(+) mass spectrometry—An approach on the fragmentation mechanisms and chemometric analysis

The consumption of design drugs, frequently known as new psychoactive substances (NPS), has increased considerably worldwide, becoming a severe issue for the responsible governmental agencies. These illicit substances can be defined as synthetic compounds produced in clandestine laboratories in order to act as analogs of schedule drugs mimetizing its chemical structure and improving its pharmacological effects while hampering the control and making regulation more complicated. In this way, the development of new methodologies for chemical analysis of NPS drugs is indispensable to determine a novel class of drugs arising from the underground market. Therefore, this work shows the use of high‐resolution mass spectrometry Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) applying different ionization sources such as paper spray ionization (PSI) and electrospray ionization (ESI) in the evaluation of miscellaneous of seized drugs samples as blotter paper (n = 79) and tablet (n = 100). Also, an elucidative analysis was performed by ESI(+)MS/MS experiments, and fragmentation mechanisms were proposed to confirm the chemical structure of compounds identified. Besides, the results of ESI(+) and PSI(+)‐FT‐ICR MS were compared with those of GC–MS, revealing that ESI(+)MS showed greater detection efficiency among the methodologies employed in this study. Moreover, this study stands out as a guide for the chemical analysis of NPS drugs, highlighting the differences between the techniques of ESI(+)‐FT‐ICR MS, PSI(+)‐FT‐ICR MS, and GC–MS.     

Microwave assisted regiospecific synthesis of 5‐trifluoromethyl‐4,5‐dihydropyrazoles and—pyrazoles

The regiospecific synthesis of a series of twelve 5‐trifluoromethyl‐4,5‐dihydropyrazoles and ‐pyrazoles from the cyclocondesation reaction of 4‐alkoxy‐1,1,1‐trifluoro‐3‐alken‐2‐ones [F₃CC(O)CH=C(R¹)OR, where R¹ = Me, Et, Pr, iso‐Pr, Bu, iso‐Bu, Ph, H; and R = Me, Et] with phenylhydrazine in toluene by environmentally benign microwave induced techniques is reported. It is shown that under appropriated conditions, the variation of microwave irradiation power leads to 4,5‐dihydropyrazole or pyrazole derivatives. This paper also includes the use of montmorillonite K‐10 as a solid support for the synthesis of pyrazoles under solvent free conditions.     

Cyclocondensation between fatty acid hydrazides and 1,1,1-trifluoro-4-alkoxy-3-alken-2-ones: Introducing a trifluoromethylated head onto fatty acid moieties

This paper reports the regioselective synthesis of new trifluoromethylated lipid derivatives, namely, 1-(5-hydroxy-5-trifluoromethyl-3-alkyl-4,5-dihydro-1H-pyrazol-1-yl)alkan-1-ones, through cyclocondensation reactions between a series of fatty hydrazides (palmitoyl, stearoyl, and oleoyl hydrazides) obtained from fatty acids from renewable resources (1,1,1-trifluoro-4-alkoxy-3-alken-2-ones [F₃CC(O)CH?C(R¹)OR, where R¹?=?H and R?Et; R¹?=?–(CH₂)₆CH₃, –(CH₂)₆CH₃, –(CH₂)₈CH₃, –(CH₂)₉CH₃, –(CH₂)₁₀CH₃, –(CH₂)₁₂CH₃, –(CH₂)₂Ph], and R?Me). Experimental observations showed that the lipophilic characteristic of 5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-pyrazoles (5–7) prevent the acid catalyzed dehydration to aromatization of 1H-pyrazole ring, although in some cyclocondensations a proportion of the aromatic derivative 1-(5-trifluoromethyl-3-alkyl-1H-pyrazol-1-yl)alkan-1-one was obtained. All products were characterized using multinuclear (¹H, ¹³C, ¹⁹F) NMR spectroscopy.