Valéria B. Riatto

Stereoselective addition of chiral titanium enolates to 5-substituted five-membered oxocarbenium ions

The sterochemical outcome of the addition of chiral titanium enolates to g-lactols derived from (S)-glutamic acid were examined. When 5-substituted g-lactols were treated with chiral titanium enolates of N-acetyl-, N-propionyl-, N-bromoacetyl- and N-phenylacetyl oxazolidin-2-ones, only two diastereoisomers were obtained, revealing complete facial control by the chiral titanium enolate while the oxocarbenium ion facial discrimination was dependent on the nature of the enolate R3 substituent. After desilylation with aqueous HF/CH3CN, LiBH4 reduction allowed the efficient preparation of the corresponding trans-2,5-disubstituted tetrahydrofuran diols and recovery of the chiral auxiliary.

Efficient synthesis of 1,3,5-oxygenated synthons from dimethyl 3-oxoglutarate: first use of borane-dimethyl sulfide complex as a regioselective reducing agent of 3-oxygenated glutarate derivatives

The selective reduction of dimethyl 3-oxoglutarate was accomplished in different levels. A high yielding sodium borohydride reduction of the keto group is fully described leading to dimethyl 3-hydroxyglutarate. When borane-dimethyl sulfide (BMS) complex was used, a diol or a triol compound can be obtained by selective or total reduction of 3-hydroxy- or 3-oxoglutarate, respectively, allowing an efficient and practical route to 1,3,5-oxygenated compounds.

An on-line system using ion-imprinted polymer for preconcentration and determination of bismuth in seawater employing atomic fluorescence spectrometry

This work proposes an on-line preconcentration system using ion-imprinted polymer (IIP) for determination of bismuth in seawater employing atomic fluorescence spectrometry (AFS). The polymer was synthesized using 2- (5-bromo-2-pyridylazo) -5-diethylaminophenol (Br-PADAP) for complex formation, ethylene glycol dimethacrylate (EGDMA), cross-linking reagent and methacrylic acid (AMA) reagents, used as the functional monomer, 2,2-azobisisobutyronitrile was used as the radical initiator. The polymer was characterized employing the Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The determination of bismuth was performed employing hydride generation atomic fluorescence spectrometry (HG AFS) and the experimental conditions were optimized using a Box Behnken design involving the factors sample pH, eluent concentration and sodium tetrahydroborate concentration. So, using the optimized conditions the system allows the determination of bismuth with limits of detection and quantification of 26 and 88u202fngu202fL-1, a preconcentration factor of 19.8. All these parameters were determined using a sample volume of 25u202fmL. The precision expressed as relative standard deviation (RSD%) was 3.7% for a bismuth(III) solution of concentration 0.25u202fµgu202fL-1. The system proposed was applied for the determination of bismuth in four seawater samples collected in Salvador City, Bahia State, Brazil. The concentrations obtained varied from 0.38 to 0.45u202fμgu202fL-1. The accuracy was evaluated by addition/recovery test, and the recoveries found varied from 92% to 101%.

NEW ALKYL PHENOLS AND FATTY ACID PROFILE FROM OILS OF PULPED Spondias mombin L. SEED WASTES

Larissa C. de Rezendea,c, Patricia de A. Santosa, Valéria B. Riattoa, Jorge M. Davida,* and Juceni P. Davidb Instituto de Química, Universidade Federal da Bahia, 40170-290 Salvador – BA, Brasil Faculdade de Farmácia, Universidade Federal da Bahia, 40170-290 Salvador – BA, Brasil Departamento de Ciências Exatas e Naturais, Universidade Estadual do Sudoeste da Bahia, Praça Primavera, 40, 45700-000 Itapetinga – BA, Brasil

Biotechnological Properties of Sponges from Northeast Brazil: Cliona varians as a Biocatalyst for Enantioselective Reduction of Carbonyl Compounds

To research the potential ability of whole marine sponges to act as biocatalysts, this paper describes for the first time the employment of whole Cliona varians sponge in the stereoselective reduction of prochiral α-keto esters and isatin to the corresponding chiral alcohols. The addition of D-fructose, D-glucose or sucrose remarkably increased the conversion ratios and stereoselectivities by this marine sponge. Furthermore, in the presence of D-glucose and D-maltose, the reduction of isatin by C. varians afforded the corresponding 3-hydroxyindolin-2-one with high conversions (8590%) and good enantioselectivities (60-74%). These results showed that the marine sponge presents great potential to be used as biocatalyst for stereoselective reduction of carbonyl compounds.

CRAQUEAMENTO TÉRMICO DA GLICERINA: UMA PROPOSTA DE EXPERIMENTO PARA QUÍMICA ORGÂNICA

In this work, an undergraduate organic chemistry experiment based on thermal cracking of glycerin is proposed. The reagent is obtained as a by-product from the practice of biodiesel synthesis, and allows reduction of waste produced in the lab. The main product obtained from thermal cracking was characterized by GC analysis as acrolein. This substance was also identified by chemical derivatization as 2,4-dinitrophenylhydrazone, allowing a combined experiment of identification by synthesis of the derivative.

Síntese e hidrólise de azalactonas de Erlenmeyer-Plöchl mediadas por radiação micro-ondas em aparelhos doméstico e dedicado: experimentos de química orgânica para a graduação

This work describes a green chemistry experiment for the synthesis of Erlenmeyer-Plochl azalactones mediated by microwave irradiation, employing both dedicated and domestic equipment. Hippuric acid was reacted with equimolar amounts of benzaldehyde, p-chloro-benzaldehyde or p-N,N-dimethyl-benzaldehyde in acetic anhydride as the solvent. Acid hydrolysis of obtained 4-benzylidene-2-phenyloxazol-5(4H)-one under microwave and convectional heating afforded Z-α-(benzoylamino)cinnamic acid at a 51-61.5% yield. The UV-Vis molecular spectra of 4-benzylidene-2-phenyloxazol-5(4H)-one and 4-(4-N,N-dimethylbenzylidene)-2-phenyloxazol-5(4H)-one were obtained in ethanol, CH2Cl2 and DMSO and bathochromic shift was observed for the latter azalactone.