This work presents some modifications in the post-synthetic processing for a classical arsenic reagent: AsI3. In comparison with the widely used analog, the trichloride, arsenic triiodide presents several advantages such as low toxicity, air stability, and low volatility. It was used as a synthetic precursor in the preparation of a variety of arsenic(III) derivatives like arsines, arsenites, and thioarsenites. Besides that, AsI3 was submitted to a diversity-oriented Grignard reaction in the preparation of a homologous series of trialkyl arsines ranging from AsC3H9 to AsC12H27. The series was analyzed by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry to provide a trialkyl arsines library that can be used for the direct analysis of natural samples.

Carbon is an extremely versatile element and can generate a plethora of structures with distinct properties. Proposing new possible metastable allotropic structures for carbon has been the subject of increasing interest over the past few years. In this contribution, we present a new carbon allotrope, named ABF-Carbon, based on the connection of spiropentadiene molecular motif and sp3 carbon atoms. This new structure is a metastable carbon allotrope formed by 6 carbon atoms, being 2 sp2 and 4 sp3, in a body-centered tetragonal with space group (space group 119) and point group . By first-principles calculations using the density functional theory (DFT), we predict that this new structure is mechanically and structurally stable and presents thermal stability up to 900 K. The calculations also show that ABF-Carbon presents a direct bandgap of 2.39 eV and higher cohesive energy than other carbon allotropes, such as T-Carbon and Y-Carbon/1-diamondyne.

Arylation reactions are an important class of reactions and allow the synthesis of natural and synthetic products. Despite the efficient, but high cost and toxic methodologies involving transition metals, radical arylations have gained importance after the advent of photoredox catalysis. Arylation of enol acetates is an important tool for obtaining aryl ketones but the scope of the reaction is limited to the pattern of substitution at phenyl radical and α-carbon of the enol. Theoretical calculations ((U)BHandHLYP/6-311G**) show that the polar effect is the key factor in this reaction. A good correlation of calculated rate constants with field effect explained why phenyl radicals with electron-withdrawing groups react faster toward enol acetate. The presence of alkyl groups at α carbon at the enol showed some influence of enthalpic effect but strong influence of steric effect, evidenced by great correlations with Taft and Charton parameters. Finally, substitution at β carbon showed no significant effect at reaction rates.

An automated method based on open-source hardware was created for the separation of porphyrins fractions from crude oil, an essential step for the quantification of V and Ni as metalloporphyrins. Preparative liquid chromatography was implemented with a reverse phase gradient from MeOH to toluene. The system allows three solvents and fractions changes by using quaternary valves connected to an Arduino microcontroller, programmed on the basis of the absorbance signal measured and its first derivative. Additionally, the method was applied to crude oils (Venezuelan National Institute of Standards and Technology (NIST) 8505 and from a marine reservoir). V and Ni were determined by inductively coupled plasma mass spectrometry (ICP-MS) and the V-porphyrin profile was determined by high performance liquid chromatography (HPLC)-ICP-MS. The concentrations of the metals grow in the last eluting toluene fractions, associated with asphaltenes. On the other hand, V-porphyrins in the first eluting MeOH fractions showed profiles of labile compounds, with a higher percentage in the Brazilian crude oil (4.9 mg L-1, corresponding to 18% of total V), in comparison to the one from the biodegraded NIST 8505 (59 mg L-1, corresponding to 7% of total V). The overall methodology has a good reproducibility and provides information on elements concentrations associated with porphyrin class compounds.

A reação de Heck entre enoatos de configuração Z e E e o iodobenzeno foi estudada na presença de Pd(OAc)2. A estereoquímica nos adutos formados foi dependente da geometria do enoato (reação estereoespecífica). Os melhores rendimentos foram obtidos a partir de enoatos Z, em acetona, utilizando Ag2CO3 como base. Os principais intermediários catiônicos de paládio possivelmente envolvidos no ciclo catalítico puderam ser interceptados e caracterizados por espectrometria de massas com ionização electrospray (ESI-MS). A estereosseletividade observada pôde ser racionalizada através do mecanismo clássico da reação de Heck.

The Heck reaction between E- and Z-enoates and iodobenzene was studied in the presence of Pd(OAc)2. The stereochemistry in resulting adducts was dependent on the enoate geometry (stereospecific reaction). Best yields were obtained from Z-isomers in acetone using Ag2CO3 as base. The main cationic palladium intermediates possibly involved in the catalytic cycle could be intercepted and characterized by electrospray ionization mass spectrometry (ESI-MS). The stereoselectivity observed was rationalized through the classic mechanism of the Heck reaction.

Os ácidos tribromo- e tricloro-isocianúricos reagem com ácidos cinâmicos na presença de NaOH/H2O/Et2O à temperatura ambiente para produzir regiosseletivamente (E)-2-halo-estirenos em 25-95% de rendimento. Estudo sobre o mecanismo da reação utilizando correlações Hammett e cálculos DFT (teoria do funcional da densidade) mostraram que esta reação tem como passo determinante a velocidade da adição eletrofílica de um átomo de cloro à ligação dupla.

Tribromo- and trichloroisocyanuric acids react with cinnamic acids in NaOH/H2O/Et2O at room temperature to produce (E)-2-halostyrenes regioselectively in 25-95% yield. Mechanism studies using Hammett correlations and DFT (density functional theory) calculations have shown that this reaction has as rate determining step the electrophilic addition of chlorine atom to the double bond.

Primary, secondary and tertiary alcohols can be easily distinguished due to their reactivity towards tribromoisocyanuric acid (TBCA). The test is performed by adding TBCA to the alcohol in a test tube heated in a boiling water bath. Orange color develops in the tube containing the primary alcohol, light yellow is observed in the tube containing the secondary alcohol while the tertiary alcohol results in a colorless mixture.

O ácido dicloro-iodo-isocianúrico foi preparado em 93% de rendimento através do aquecimento do ácido tricloro-isocianúrico com 1,05 equiv. mol de iodo. Esse novo reagente se mostrou bastante eficiente para a iodação regiosseletiva de arenos ativados. Os alquenos reagem com o ácido dicloro-iodo-isocianúrico na presença de solventes nucleofílicos oxigenados (água, álcoois, ácido acético) para gerar, respectivamente, iodoidrinas, β-iodoéters e β-iodoacetatos em menos de um minuto de reação e em alto grau de regiosseletividade. Enol-éteres levam à formação regiosseletiva dos iodo-dialquilacetais correspondentes. Os resultados experimentais juntamente com os cálculos por DFT mostraram que, para reações com sistemas insaturados, o ácido dicloro-iodo-isocianúrico é mais reativo do que o ácido triiodo-isocianúrico.

Dichloroiodoisocyanuric acid was prepared in 93% by heating trichloroisocyanuric acid with 1.05 mol equiv. of iodine. This new reagent is very efficient for regioselective electrophilic iodination of activated arenes. Alkenes react with dichloroiodoisocyanuric acid in the presence of oxygenated nucleophiles (water, alcohols, and acetic acid), leading to the corresponding iodohydrins, β-iodoethers and β-iodoacetates with reaction times of less than one minute and with a high degree of regioselectivity. Enol ethers resulted in the regioselective formation of the corresponding iodine-dialkylacetals. Experimental results and DFT calculations showed that dichoroiodoisocyanuric acid is more reactive with unsaturated systems than triiodoisocyanuric acid.

O polieterglicol derivado do líquido da casca da castanha do caju (CNSL) inibiu a formação de hidrato de metano. O polímero mostrou-se mais eficiente que o copolímero poli(vinilpirrolidona)-poli-(N-vinilcaprolactama)(PVP-PVCap) nas condições testadas (CH4, 1470 psi e 4 ºC), sendo esse último um dos melhores inibidores de hidratos comercialmente disponíveis.

The polyether glycol derived from cashew nutshell liquid (CNSL) inhibited the formation of methane hydrate. The polymer proved to be more efficient than the polyvinyl pyrrolidone-poly(N-vinyl) caprolactam (PVP-PVCap) co-polymer under tested conditions (CH4, 1470 psi and 4 ºC), being the latter one of the best commercially available hydrate inhibitors.

Carbocátions atuam de formas diferentes quando interagem com anéis aromáticos. É interessante como na biosíntese de terpenos, os intermediários carbocatiônicos não alquilam a cadeia lateral aromática de aminoácidos presentes no sítio ativo, como seria esperado para outros carbocátions, como o cátion terc-butila. Neste trabalho, a interação entre benzeno e diferentes carbocátions alílicos é analisada, mimetizando carbocátions terpenóides, para melhor compreender como esta interação ocorreria. Cálculos em nível de teoria do funcional da densidade (DFT) mostram que para carbocátions alílicos secundários e terciários (como os encontrados na natureza), a forma não ligada da interação é mais estável energeticamente do que a alquilação do anel aromático, justificando a escolha da natureza por esses carbocátions mais estabilizados.

Carbocations act in different ways when interacting with aromatic rings. It is interesting that in terpene biosynthesis, the carbocationic intermediates do not alkylate the aromatic side chain of the amino acids present in the enzymatic active site, as would be expected by other carbocations such as the tert-butyl cation. In this study, the interaction between benzene and different allylic carbocations, mimicking terpenoid cations, is analysed in order to better understand how this interaction would occur. Density-functional-theory (DFT) calculations show that for secondary and tertiary allylic carbocations (as found in nature), the non-covalent interaction is energetically favoured with respect to alkylation of the aromatic ring.

A isatina e seus derivados são conhecidos na literatura por possuírem uma diversidade de propriedades biológicas. O método de Sandmeyer é o mais utilizado para síntese de diferentes isatinas substituídas, geralmente com altos rendimentos. Apesar de eficiente, este método apresenta algumas limitações, tais como a formação de uma mistura de regioisômeros e baixos rendimentos dependendo do tipo e posição do substituinte presente no material de partida, a anilina. Para superar estas limitações, é preferível que alguns derivados de isatina sejam obtidos por métodos alternativos. Este artigo descreve a cloração de derivados da isatina empregando ácido tricloroisocianúrico [1,3,5-tricloro-1,3,5-triazina-2,4,6-(1H,3H,5H)-triona ou TCCA) em diferentes condições reacionais.

Isatin and its derivatives have been extensively reported in the literature as having range of potential pharmacological compounds. The Sandmeyer method is the most widely used for isatin synthesis and furnishes different substituted isatins, usually with high yields. Although efficient, the Sandmeyer route has certain limitations, such as the formation of a mixture of regiosiomers and low yields depending on the type and position of the substituent. Thus, overcome these limitations, it is preferable that some derivative isatins be obtained by alternative methods. This article has investigated the chlorination of isatin derivatives using trichloroisocyanuric acid [1,3,5-trichloro 1,3,5-triazine-2,4,6-(1H,3H,5H)-trione or TCCA] at different reaction conditions.

A ferramenta de Gassman-Fentiman da demanda crescente de elétrons foi usada para identificar íons carbênios e íons carbônios. Contudo, devido ao seu entendimento ambíguo, ela foi pivô de uma disputa histórica. Nós aplicamos a metodologia da Teoria Quântica de Átomos em Moléculas - QTAIM - para caracterizar íons carbênios e íons carbônios de uma forma mais eficaz e mais fácil. Essa metodologia pode ser usada para avaliar se um carbocátion é clássico ou não. Além disso, é possível classificar um conjunto de íon carbônio na ordem de magnitude da deslocalização σ, ou π. Há poucas diferenças entre os resultados de nosso modelo baseado na QTAIM e da ferramenta de Gassman-Fentiman. Contudo, diferentemente da ferramenta de Gassman-Fentiman, os cátions 7-anisol-7-norbornenila e 2-anisol-2-norbornila são não-clássicos, embora sejam os menos íons não-clássicos em seus conjuntos correspondentes de cátions estudados.

The Gassman-Fentiman tool of increasing electron demand was used to identify carbonium and carbenium ions. Nonetheless, due to its ambiguous understanding, it was pivot of a historical dispute. We applied the Quantum Theory of Atoms in Molecules (QTAIM) metodology to characterize the carbonium and carbenium ions on an easier and more effective way. By comparing selected topological information of reference carbenium ions the QTAIM metodology can be used to evaluate whether a carbocation is classical or not. In addition, it is possible to rank a set of carbonium ions in order of their corresponding σ or π delocalization. There are few differences between our QTAIM-based model and Gassman-Fentiman tool. Unlike Gassman-Fentiman tool results, 7-anisyl-7-norbornenyl and 2-anisyl-2-norbornyl cations are non-classical, although they are the least nonclassical ions in their corresponding set of studied cations.

O ácido triiodo-isocianúrico (TICA) foi preparado em 90% de rendimento a partir do aquecimento do ácido tricloro-isocianúrico com iodo em um tubo selado. A reação do TICA com arenos ativados em acetonitrila gera regiosseletivamente os respectivos iodo-arenos em 73-93% de rendimento isolado. Anilina e fenol também são monoiodados seletivamente usando MeOH (53%) e CH2Cl2 (88%) como solventes, respectivamente.

Triiodoisocyanuric acid (TICA) was prepared in 90% yield by heating trichloroisocyanuric acid with iodine in a sealed tube. The reaction of TICA with activated arenes in acetonitrile led to an efficient and highly regioselective formation of the corresponding iodoarenes, in 73-93% isolated yield. Aniline and phenol are monoiodinated regioselectively using MeOH (53%) and CH2Cl2 (88%) as solvents, respectively.

A estabilidade relativa do dicátion 1,3-desidro-5,7-adamantanediila é atribuída a sua aromaticidade tridimensional. Contudo, sua natureza eletrônica não é bem conhecida. A fim de entendê-la melhor, os di- e monocátions do adamantanodiil e alguns de seus análogos foram estudados utilizando a teoria de átomos e moléculas (AIM). Eles foram comparados com análogos de adamantano não-aromáticos. Os resultados de AIM indicam que a densidade eletrônica no centro da estrutura em gaiola e a média de todos os índices de deslocalização, envolvendo seus átomos cabeças-de-ponte são maiores em compostos aromáticos do que em não-aromáticos. A degenerescência energética dos átomos cabeça-de-ponte, a uniformidade e magnitude da carga compartilhada entre estes, distingue os dicátions 1,3-adamantila e 1,3-desidro-5,7-adamantanediila. Contudo, ambos são aromáticos, assim como o 1,3-desidro-5,7-diboroadamantano. O cátion 1,3-desidro-7-adamantila tem uma homoaromaticidade planar característica.

The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its tridimensional aromaticity. However, its electronic nature is not well known. In order to improve its understanding, dicationic and monocationic adamantanedyil species and some key analogues were studied by atoms in molecules (AIM) theory. They were compared to non-aromatic adamantane analogues. AIM results indicate that the density in center of the cage structure and the average of all delocalization indexes involving its bridged atoms are higher in aromatic than in non-aromatic compounds. Degeneracy in energy of the bridged atoms, uniformity and magnitude of their shared charge distinguish the dications 1,3-adamantyl and the 1,3-dehydro-5,7-adamantanediyl. However, both are aromatic as well as the 1,3-dehydro-5,7-diboroadamantane. The 1,3-dehydro-7-adamantyl cation has a characteristic planar homoaromaticity.

A reação de alquenos com ácidos trialo-isocianúricos / NaX em acetona aquosa produz os dialo-alcanos vicinais em rendimentos de moderados a excelentes

The reaction of alkenes with easily handled trihaloisocyanuric acids / NaX in aqueous acetone produces the corresponding vicinal dihaloalkanes in moderate to excellent yields.