14576-08-0Relevant articles and documents
Selective methoxylation of limonene over ion-exchanged and acid-activated clays
Catrinescu,Fernandes,Castilho,Breen,Carrott, M.M.L. Ribeiro,Cansado
, p. 38 - 46 (2013)
In this study, we report the use of clay-based catalysts in the methoxylation of limonene, for the selective synthesis of α-terpinyl methyl ether. Na-SAz-1, Ca-SWy-2 and Sap-Ca source clays and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal were modified by (i) ion-exchange with Al, Fe, Ni and Na and (ii) acid activation, to produce catalysts with markedly different acidic and textural properties. The lack of activity of Ni2+-SAz-1 (with Lewis acidity maximized), provided evidence that the process occurs preferentially on Bro?nsted acid sites. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150°C, afforded the highest number of Br?nsted acid sites located in the clay gallery and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize limonene conversion and selectivity, was studied over Al-SAz-1. When the reaction was performed for 20 h at 40°C, the conversion reached 71% with 91% selectivity to the mono-ether. Mild acid activation (1 M HCl, 30 min, reflux) of the raw SAz-1 clay leads to a material with a good catalytic behaviour (slightly inferior to Al-SAz-1), while any increase in the severity of the acid-treatment (6 M HCl, 30 min, reflux), caused a marked decrease in catalytic activity.
Monoterpenes etherification reactions with alkyl alcohols over cesium partially exchanged Keggin heteropoly salts: effects of catalyst composition
da Silva, Márcio José,Lopes, Neide Paloma Goncalves,Ferreira, Sukarno Olavo,da Silva, Rene Chagas,Natalino, Ricardo,Chaves, Diego Morais,Texeira, Milena Galdino
, p. 153 - 168 (2020/07/21)
In this work, cesium partially exchanged Keggin heteropolyacid (HPA) salts were prepared, characterized, and evaluated as solid catalysts in monoterpenes etherification reactions with alkyl alcohols. A comparison of the activity of soluble HPAs and their insoluble cesium salts showed that among three different Keggin anions the phosphotungstate was the most efficient catalyst. Assessments on the effects of the level of the protons exchange by cesium cations demonstrated that Cs2.5H0.5PW12O40 solid salt was the most active and selective phosphotungstate catalyst, converting β-pinene to α-terpinyl methyl ether. The influences of the main reaction parameters such as reaction temperature, time, catalyst load, substrate nature (i.e., alcohols and monoterpenes) were investigated. We have demonstrated that the simultaneous presence of the cesium ions and protons in the catalyst plays an essential role, being the 2.5–0.5 the optimum molar ratio. The Cs2.5H0.5PW12O40 salt was efficiently recovered and reused without loss of catalytic activity. Graphic abstract: [Figure not available: see fulltext.]
Oxidation of imidazole- and pyrazole-derived aldehydes by plant aldehyde dehydrogenases from the family 2 and 10
Fr?mmel, Jan,Kon?itíková, Radka,Kope?ny, David,Soural, Miroslav,?ebela, Marek
, p. 194 - 201 (2019/03/06)
Plant cytosolic aldehyde dehydrogenases from family 2 (ALDH2s, EC 1.2.1.3) are non-specific enzymes and participate for example in the metabolism of acetaldehyde or biosynthesis of phenylpropanoids. Plant aminoaldehyde dehydrogenases (AMADHs, ALDH10 family, EC 1.2.1.19) are broadly specific and play an important role in polyamine degradation or production of osmoprotectants. We have tested imidazole and pyrazole carbaldehydes and their alkyl-, allyl-, benzyl-, phenyl-, pyrimidinyl- or thienyl-derivatives as possible substrates of plant ALDH2 and ALDH10 enzymes. Imidazole represents a building block of histidine, histamine as well as certain alkaloids. It also appears in synthetic pharmaceuticals such as imidazole antifungals. Biological compounds containing pyrazole are rare (e.g. pyrazole-1-alanine and pyrazofurin antibiotics) but the ring is often found as a constituent of many synthetic drugs and pesticides. The aim was to evaluate whether aldehyde compounds based on azole heterocycles are oxidized by the enzymes, which would further support their expected role as detoxifying aldehyde scavengers. The analyzed imidazole and pyrazole carbaldehydes were only slowly converted by ALDH10s but well oxidized by cytosolic maize ALDH2 isoforms (particularly by ALDH2C1). In the latter case, the respective Km values were in the range of 10–2000 μmol l?1; the kcat values appeared mostly between 0.1 and 1.0 s?1. The carbaldehyde group at the position 4 of imidazole was oxidized faster than that at the position 2. Such a difference was not observed for pyrazole carbaldehydes. Aldehydes with an aromatic substituent on their heterocyclic ring were oxidized faster than those with an aliphatic substituent. The most efficient of the tested substrates were comparable to benzaldehyde and p-anisaldehyde known as the best aromatic aldehyde substrates of plant cytosolic ALDH2s in vitro.
Fe(III)-catalyzed α-terpinyl derivatives synthesis from β-pinene via reactions with hydrogen peroxide in alcoholic solutions
Da Silva,Carari,Manoel Da Silva, Adalberto
, p. 10529 - 10536 (2015/01/30)
In this study, a novel and environmentally benign Fe(iii)-catalyzed terpinyl derivatives synthesis using hydrogen peroxide in alcohol solutions (i.e. methyl, ethyl, propyl, isopropyl and butyl alcohols) was investigated. The use of Bronsted acid catalysts was avoided and β-pinene was used as the starting reactant. High conversions (ca. 90%) and combined selectivities for the α-terpineol and terpinyl alkyl ethers (ca. 70-73%) were obtained when Fe(NO3)3 was used as the catalyst. The role of each component catalyst system was studied with special focus on the solvent. The use of a biodegradable and renewable origin solvent (ethyl alcohol), which was added to an inexpensive and mildly toxic catalyst and a green oxidant are the main positive features of this process.
