Síntese de catalisadores Ziegler-Natta: algumas rotas e suas dificuldades

The Ziegler-Natta catalyst and the polymerization thereof are systems which require careful handling and special treatment of chemicals. In spite of the use of inert atmosphere and dry chemicals, some Ziegler-Natta systems may present low activities or even may deactivate because of unsuitable handling. Some features of the TiCl3 synthesis and its characterization when related to the presence of impurities are described. Evidences of poor handling of chemicals and/or laboratory devices while in synthesis of the catalyst are emphasized. The problems arising from butadiene polymerization and some relevant details in propylene polymerization are also presented with teaching objectives.

Estudo da Determinação dos Grupos Silanóis ( º Si-OH) em Sílica: Aplicação à Materiais de Recheio Utilizados em Cromatografia Gasosa

A simple chemical method has been developed to quantify the silanol groups (º Si-OH) in silica as well as in coated chromatographic supports for use in packed - column Gas Chromatography. After adsorption of 10 mg/mL methylene blue, centrifuging action and filtration, the absorbance of the solution was inversely proportional to the silanol quantity. The difference between the absorbance of the pure solution and that of the solid - free filtrate was related to the silica weight, yielding a quantitative analysis of these groups.

Utilização de α,α-Diclorociclobutanonas em Síntese de Produtos Naturais

The preparation and chemical potentiality of a,a-dichlorocyclobutanones as useful intermediates in the total synthesis of natural products are reviewed. Some aspects related to the recent advances reported in the literature about the mechanism of [2+2] cycloaddition reaction between dichloroketene and olefins are also presented.

Síntese e caracterização estrutural de complexos mono e bimetálicos de paládio e platina com ligantes contendo nitrogênio e enxofre

The synthesis of several mono- and bimetallic platinum and palladium complexes are reported. The monometallic complexes are of the type MCl2(PEt3)2L (L=2-aminothiazol; benzothiazol; 2-imidazolidithione; M=Pt; Pd), and the bimetallic complexes (M2Cl4(PEt3) 2L) are derived from them. Infrared spectroscopic characterization of the monometallic complexes shows that the metal centre are coordinated through the N-endocyclic (L=2-aminothiazol; benzothiazol) and through the sulphur when L=2-imidazolidithione. Coordination of a second metal fragment occurs via the sulphur atom (L=2-aminothiazol; benzothiazol) according to infrared studies. 31P{¹H} NMR spectroscopy suggest that the complexes have a cis- configuration since the ¹J Pt-P are around the value found for this type of compound.

Síntese de β-cetoésteres cíclicos: novo procedimento para ciclizações de Dieckmann empregando ALCL3 e trietilamina

In this communication we describe a new methodology to Dieckmann cyclization of diethyl adipate (1) and diethyl pimelate (3) applying "push-pull" strategy using anhydrous aluminium trichloride and triethylamine in dichloromethane at room temperature. This method is very efficient, simple, safe and reproducible, giving the corresponding cyclic β-keto ester derivatives in 84% and 71% yield, respectively.

Ação promotora do berílio em catalisadores da síntese do estireno

The catalytic dehydrogenation of ethylbenzene in presence of steam is the main commercial route to produce styrene. The industrial catalysts are potassium- and chromia-doped hematite which show low surface areas leading to bad performance and short life. In order to develop catalysts with high areas, the effect of beryllium on the textural properties and on the catalytic performance of this iron oxide was studied. The influence of the amount of the dopant, the starting material and the calcination temperature were also studied. In sample preparations, iron and beryllium salts (nitrate or sulfate) were hydrolyzed with ammonia and then calcinated. The experiments followed a factorial design with two variables in two levels (Fe/Be= 3 and 7; calcination temperature= 500 and 700ºC). Solids without any dopant were also prepared. Samples were characterized by elemental analysis, infrared spectroscopy, surface area and porosity measurements, X-ray diffraction, DSC and TG. The catalysts were tested in a microreactor at 524ºC and 1 atm, by using a mole ratio of steam/ ethylbenzene=10. The selectivity was measured by monitoring styrene, benzene and toluene formation. It was found that the effect of beryllium on the characteristics of hematite and on its catalytic performance depends on the starting material and on the amount of dopant. Surface areas increased due to the dopant as well as the nature of the precursor; samples produced by beryllium sulfate showed higher areas. Beryllium-doped solids showed a higher catalytic activity when compared to pure hematite, but no significant influence of the anion of starting material was noted. It can be concluded that beryllium acts as both textural and structural promoter. Samples with Fe/Be= 3, heated at 500ºC, lead to the highest conversion and were the most selective. However, catalysts prepared from beryllium sulfate are the most promising to ethylbenzene dehydrogenation due to their high surface area which could lead to a longer life.

Projeto e construção de um bioreator para síntese orgânica assimétrica catalisada por saccharomyces cerevisiae (fermento biológico de padaria)

A model for the construction of a simple and cheap apparatus to be used as bioreactor for reactions catalyzed by baker's yeast (Saccharomyces cerevisiae) is described. The bioconversion and separation of cells from products and residual substrates are obtained at the same time. The reactions carried out in this type of reactor are faster than those catalyzed by immobilized cells. Yeast cells can be cultivated in this bioreactor operating with cell recycling at appropriated conditions using glucose and other nutrients.

Organo-gel: um novo sistema para a imobilização de lipases e sua aplicação em síntese orgânica

Lipases have been immobilized in microemulsion-based organogels (MBG's) and successfully utilized for the enantioselective esterification, diesterification and transesterification reactions, in organic solvents at 25ºC. This methodology is described as a new alternative for the use of enzymes in organic solvents. High enzymic stability has been observed. We have also used this methodology for the successful resolution of chiral secondary alcohols. This is a convenient way of using this catalyst in organic solvents which employs small amounts of the enzyme (250mg/mL).

Hidróxidos duplos lamelares: síntese, estrutura, propriedades e aplicações

The layered double hydroxides, known as anionic clays and represented by the general formula [M2+1-x M3+x (OH) 2]x+ Am-x/m·nH 2O, are a group of materials which are of much interest currently. They present a variety of potential applications as adsorbents, catalysts and catalyst support, ion-exchangers, antacids and as a polymer stabilizer. It is possible to obtain a broad variety of layered double hydroxides (LDHs), depending on the identity and ratio of the cations M2+ and M3+, as well as the interlamelar anion. The aim of this review is to give out some information about this class of materials, concerning to the synthesis, characterization, properties and applications.

Abordagens em síntese assimétrica

The approaches in asymmetric synthesis as the chiron approach, chiral auxiliaries, chiral reagents and asymmetric catalysis are described in a simplified way.

Síntese e caracterização de cloro[ácido 2-(difenilfosfino)benzóico]-ouro(I) e alguns de seus derivados

In this contribution a few new gold(I)phosphine complexes, [2-(PPh2)C6H4CO 2H]AuX (where X = Cl, SCN, Br3) and a similar gold(III) derivative [{2-(PPh2)C6H4CO 2H}AuIII Cl (C6H4CH2NMe2 )]Cl have been synthesised and characterised. The phosphine, 2-(diphenylphosphino)benzoic acid, has been employed for the first time in gold chemistry. This ligand is potentially bidentate through bonding of the phosphine and carboxylate groups. The X-ray structure of the complex chloro[2-(diphenylphosphino) benzoic acid]gold(I) has been elucidated and the bond lengths encountered show great similarity to those of chloro(triphenylphosphine)gold(I). [2-(PPh2)C6H4CO 2H]AuCl crystallises in the space group P2(1)/c with a = 9.113(2) Å, b = 10.925(2) Å, c = 23.069(4) Å, beta = 99.95º(3), V = 2299 ų, Z = 4 and R = 0.091. Biological tests for anti-fungal and anti-bacterial activity demostrate that [2-(PPh2)C6H4CO 2H]AuCl exhibits broad spectrum activity against a range of organisms.

Isolamento e caracterização de acil-tiossemicarbazidas como intermediários na síntese de compostos mesoiônicos

1,3,4-thiadiazolium-2-aminides and their isomers 1,3,4-triazolium-2-thiolates have been synthesized via anhydroacylation reactions. This work presents a study by infrared monitoring of the reaction between substituted aroyl acid chlorides and 1,4-diphenylthiosemcarbazide. The intermediates and products were isolated, purified and charaterized by IR and 13C NMR spectroscopy. The increasing or decreasing in intensity of characteristic stretching bands indicated the rate dependence on the electronic nature of substituents. The results also demonstrate that 1,3,4-triazolium-2-thiolates are obtained in anhydrous conditions whereas presence of water leads to a mixture of the isomers.

Síntese e atividade antibacteriana de imidas cíclicas: 3,4-dicloromaleimidas e 3-cloro-4-substituída-maleimidas

In the present study, new N-aryl and N-alkylarylcyclic imides were synthesized and their antibacterial properties against Escherichia coli and Staphylococcus aureus were evaluated by using the diffusion method. All compounds were obtained in good yield (54 - 95%) and characterized by spectral data (¹H-NMR, MS, IR) and elemental analysis (CHN). The biological results indicated that some compounds exert significative antibacterial effects, confirming previous studies on biological activities of cyclic imides.

Rotas de síntese e a homogeneidade dos precursores de mulita e cordierita

Multicomponent ceramics are mainly synthesized by conventional solid-state reaction route and sol-gel routes. In the sol-gel route, colloidal or polymeric gel are envolved. In this work, some principles of the chemistry of theses routes are discused and it is ilustrated a variety of strategies for obtaining a homogeneous multicomponent precursors.

Síntese e caracterização dos nanocompósitos K0,1(PEO)xMoS2 (X= 0,5; 1,2)

The reaction of an aqueous solution of poly(ethylene oxide) (peo - mw 100.000) with a neutral aqueous suspension of single layers of MoS2 was studied. The single layers aqueous suspension was prepared by first intercalating lithium (using n-Butyllithium in n-hexane) and reaction of these ternary compound with water under ultrasound stirring. The suspension was washed several times with water until neutral pH. The suspension was mixed with the PEO aqueous solution in the presence of KCl. Two single phase compounds were obtained with the expansion of 4,8 and 9,0Å, attributed to the solvation of the intercalated potassium cations with mono and double layers, respectively.