Foi investigado o efeito da temperatura, razão molar e quantidade de catalisador na hidrólise ácida do cetal de glicerol/acetona (solketal) e acetais de glicerol/formaldeído. A reatividade do solketal foi bem maior que a dos acetais de glicerol/formaldeído. A 80 o C, 5:1 de razão molar água/ cetal e uma quantidade de catalisador correspondendo a 3.0 mmol de sítios ácidos (amberlyst-15), a hidrólise do solketal foi praticamente quantitativa, enquanto os acetais de glicerol/formaldeído apresentaram cerca de 40% de conversão. A maior reatividade do solketal para hidrólise pode ser associada à formação de um carbocátion terciário como intermediário, enquanto no caso dos acetais de glicerol/formaldeído a hidrólise acontece via deslocamento nucleofílico direto. Cálculos teóricos no nível DFT sobre a estabilidade relativa dos acetais e cetais com anéis de cinco e seis membros explicam a distribuição experimental dos isômeros.The effect of temperature, molar ratio and catalyst loading on the acid-catalyzed hydrolysis of glycerol/acetone ketal (solketal) and glycerol/formaldehyde acetals was studied. The reactivity of the solketal was significantly higher than the glycerol/formaldehyde acetals. At 80 o C, 5:1 water/ketal molar ratio and 3.0 mmol of catalyst loading (amberlyst-15) the hydrolysis of the solketal was almost complete, whereas the glycerol/formaldehyde acetals showed around 40% conversion. The higher reactivity of solketal toward hydrolysis is associated with the formation of a tertiary carbocation intermediate, whereas in the case of glycerol/formaldehyde acetals hydrolysis takes place through direct nucleophilic displacement. DFT theoretical calculations of the relative stability of the ketal and acetal isomers, having five and six-membered rings, explain the experimental distribution. Keywords: glycerol, biodiesel, hydrolysis, solketal, acetals IntroductionBiodiesel is one of the main biofuels used worldwide. It is produced through the transesterification of vegetable oils or animal fat with methanol, under base catalysis conditions.1 In this process, glycerol or glycerin is formed as byproduct in approximately 10 wt%. The overall world production of glycerin from biodiesel processing is estimated to reach 1.2 million tons by 2012, 2 but the forecast points to a much higher value in the future, due to the widespread production of this biofuel.In Brazil, biodiesel is presently blended with the petrodiesel in 5% (v/v), yielding approximately 250 thousand tons of glycerin per year. This value is much higher than the glycerin market in Brazil, in the order of 30 thousand tons per year, and it is imperative to the economical feasibility of the biodiesel program to drain this excess of glycerin. Personal care products, soaps, pharmaceuticals and foods are the main sectors that make regular use of glycerin. However, they cannot absorb, alone, all the glycerin produced from the biodiesel industry. Thus, it is necessary to find new applications for this excess of glycerin produced by the biodiesel industry.The use ...

This review surveys six classes of heterogeneous catalysts that have been used in the conversion of epoxides and CO2 into cyclic carbonates; metal organic frameworks (MOFs); silica-based catalysts; organic polymer supports; metal oxides; zeolites and carbon-based catalysts. Many of these catalysts are extremely active in the ring-opening of terminal epoxides, require fairly mild conditions and can be made in a sustainable manner. Some catalytic systems however require toxic and hazardous chemicals in their synthesis, and many struggle to ring-open the more sterically demanding and hindered internal epoxides. This review covers the most recent heterogeneous catalysts reported in the literature, not only from a catalytic efficiency perspective but also from a green chemistry and sustainable viewpoint.

No abstract

Five metal oxides (ZnO, SnO2, Fe2O3, CeO2, La2O3) were produced by the sol–gel method and tested in the direct carbonation of glycerol with CO2. Initial tests with Fe2O3 showed that the best reaction condition was 180 °C, 150 bar, and 12 h. The other oxides were evaluated at these conditions and were all active to the formation of glycerol carbonate. Zinc oxide was the most active catalyst, with a yield of 8.1 % in the organic carbonate. The catalytic activity decreased upon washing and drying the ZnO catalyst between the runs. Nevertheless, the activity is maintained if the ZnO is washed and calcined at 450 °C between the runs. FTIR and TGA results indicated the formation of ZnCO3 as the main cause of catalyst deactivation, which may be decomposed upon calcination of the material. No appreciable leaching of Zn was observed, indicating a truly heterogeneous catalysis.

IntroduçãoAs bananas Prata (subgrupo Prata) e Nanicão (subgrupo Cavendish) pertencem ao gênero Musa sp., da família Musaceae e são as mais produzidas no Brasil. A cultivar Prata é a mais consumida no país e a Nanicão, a mais aceita no mercado mundial (IBGE, 2007). Muito apreciada no Brasil e no mundo, a banana é a quarta cultura agrícola mais importante do planeta, ficando atrás apenas do arroz, do trigo e do milho e apresentando o maior volume de produção mundial. O Brasil é o segundo maior produtor mundial de banana, com uma produção de 7,1 milhões de toneladas em 2006, em uma área de 507,7 mil hectares, cerca de 10% da produção mundial, atrás apenas da Índia (ONU, 2006).Durante o amadurecimento da banana, muitas transformações físicas, físico-químicas e químicas que ocorrem, são importantes para monitorar o processo de amadurecimentos dos frutos e caracterizar os estágios de maturação: a firmeza diminui acompanhada por uma mudança na coloração da casca devido à degradação da clorofila e à síntese de carotenóides. O teor de sólidos solúveis aumenta, atingindo valores de até 27%; a acidez normalmente aumenta até atingir um máximo, quando a casca está totalmente amarela, para depois decrescer, predominando o ácido málico. O amido é degradado rapidamente, com o acúmulo de açúcares. A adstringência, representada pela presença de taninos, decresce à medida que o fruto vai amadurecendo, podendo também variar com a época de colheita do fruto (LICHTEMBERG, 1999).O aroma característico da banana também se intensifica com o amadurecimento, sendo um importante contribuinte para a qualidade dos frutos e influencia a aceitabilidade do consumidor. Bananas produzem durante o amadurecimento substâncias voláteis importantes para o aroma, tais como: ésteres, álcoois, aldeídos, cetonas, aminas e fenóis; sendo principalmente os AbstractFresh green bananas [Nanicão (Musa sp., subgroup Cavendish) and Prata (Musa sp., subgroup Prata)] were studied during their ripening. Physical (firmness), physicochemical (pH, total titrable acidity and soluble solids) and chemical properties (sugars, phenolics and volatile compounds) were analyzed and showed significant differences (p ≤ 0.05). Prata presented higher values of phenolic compounds, soluble solids, sugars and firmness than Nanicão. A method to quantify the emission of esters was developed by cryogenic headspace and gas chromatography. Acetates, butyrates, isobutyrates and isovalerates were predominant. Prata produced a higher volatile concentration than Nanicão, except for acetates. In most cases, the amount of volatiles increased continuously until peel browning, followed by a decrease or a plateau. Keywords: bananas; ripening; volatiles; gas chromatography; quantitative evaluation. ResumoBananas verdes [Nanicão (Musa sp., subgrupo Cavendish) e Prata (Musa sp., subgrupo Prata)] foram estudadas durante o seu amadurecimento. As propriedades físicas (firmeza), físico-químicas (pH, acidez total titulável e sólidos solúveis) e químicas (açúcares, compostos fenólicos e voláteis) foram anal...