4443-51-0Relevant academic research and scientific papers
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.]
Exploring the Keggin-Type Heteropolyacid-Catalyzed Reaction Pathways of the Β-Pinene with Alkyl Alcohols
Polo, Henrique Priori,Lopes, Neide Paloma Goncalves,da Silva, Márcio José
, p. 2844 - 2853 (2019/05/28)
Abstract: In this work, we investigated the activity of Keggin heteropolyacid catalysts (i.e., H3PW12O40, H3PMo12O40 and H4SiW12O40) in β-pinene reactions with alkyl alcohols (i.e. methyl, ethyl, propyl, sec-propyl, butyl and sec-butyl alcohols), and exploring the different aspects that drive the selectivity of this process. We have found that carbon skeletal rearrangements and isomerization providing intermediate carbocations that controlling the reaction selectivity. β-pinene was preferentially converted to α-terpinyl ion which undergoes a nucleophilic attack of alcohol providing alkyl alcohol. Bornyl ion was converted to bornyl and fenchyl ethers. The other secondary products were β-pinene isomers obtained from bornyl and α-terpinyl carbocations. Phosphotungstic acid (i.e., H3PW12O40) was the most active catalyst and selective toward the main product (α-terpinyl alkyl ether); the highest conversion (ca. 96%) and ether selectivity (ca. 61%) was achieved in the reactions with β-pinene. Although having also been alkoxylate, α-pinene was less reactive (ca. 40%), while camphene and limonene remained unreactive under reaction conditions studied. An increase of temperature resulted in an improvement on conversion of β-pinene and selectivity toward α-terpinyl methyl ether. Similarly, the H3PW12O40 concentration played a crucial role on reaction selectivity. This work presents positive features such as a short reaction time, high atom economy, mild reaction conditions (i.e., low temperature and room pressure). Even though soluble the catalyst was easily recovered by liquid -liquid extraction and efficiently reused. Graphical Abstract: [Figure not available: see fulltext.].
Synthesis of phenolic antioxidants with isobornyl and tert-butyl fragments
Fedorova,Chukicheva,Shumova,Kutchin
, p. 1103 - 1110 (2013/08/23)
Hybrid antioxidants, phenols with a terpene and tert-butyl substituents, were synthesized by the alkylation of 2-tert-butyl-4-methylphenol with camphene and 2-isobornylphenol with tert-butyl chloride in the presence of acidic heterogeneous catalysts, montmorillonite KSF and FIBAN K-1. Antioxidant activity of the synthesized terpenophenols was evaluated using spectrophotometry.
Methoxylation of α-pinene over heteropolyacids immobilized in silica
Pito,Matos,Fonseca,Ramos,Vital,Castanheiro
body text, p. 140 - 146 (2010/10/01)
The methoxylation of α-pinene was studied using heteropolyacids immobilized on silica as catalysts, at 60 °C, being the α-terpinyl methyl ether the main product. Tungstophosphoric acid (PW), molybdophosphoric acid (PMo), tungstosilicic acid (SiW) and molybdosilicic acid (SiMo) were immobilized on silica by sol-gel method. It was observed that the catalytic activity of the silica-supported heteropolyacids decreases in the series: PW2_S > SiW_S > PMo_S > SiMo_S. A series of PW immobilized on silica with different PW loading were prepared. It was observed that the catalytic activity increases with the amount of PW immobilized on silica. However, at high amount of PW on silica, a decrease of the catalytic activity was observed. Good values of selectivity to α-terpinyl methyl ether (about 60% near complete conversion) were obtained with all catalysts. Catalytic stability of the PW2_S was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the initial activity. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. It was observed that the kinetic model fits the experimental concentration data quite well.
Trimethylsilyldiazomethane - A mild and efficient reagent for the methylation of carboxylic acids and alcohols in natural products
Presser, Armin,Huefner, Antje
, p. 1015 - 1022 (2007/10/03)
Esterification of various naturally occurring carboxylic acids with trimethylsilyldiazo-methane proceeds nearly quantitatively under very mild conditions. Furthermore, highly sterically hindered alcohols can be converted directly to the corresponding methyl ethers. Improved methods for the preparation and quantification of this reagent are described. Springer-Verlag 2004.
Acid-catalyzed alkoxylation and hydration of camphene
Radbil',Kulikov,Sokolova,Kartashov,Zolin,Radbil'
, p. 1618 - 1622 (2007/10/03)
Camphene alkoxylation in the presence of various acid catalysts was studied. With heteropolyacids H4SiW12O40 and H3PW12O40 as catalyst the reaction afforded in high yield alkyl isobornyl ethers The mechanism of camphene hydration in water - alcohol mixtures catalyzed with acids was discussed.
Alkoxylation and hydration of camphene in the presence of acid catalysts
Radbil',Kulikov,Sokolova,Kartashov,Zolin,Radbil'
, p. 524 - 528 (2007/10/03)
The alkoxylation of camphene in the presence of various acid catalysts is studied. Alkylisobornyl ethers are obtained in high yields if the heteropolyacids H4SiW12O40 and H3PW12O40 are used
Reaction of alcohols with camphene over β-zeolite
Fomenko,Korchagina,Yarovaya,Gatilov,Salakhutdinov,Ione,Barkhash
, p. 1006 - 1017 (2007/10/03)
Alkylation of fatty-aromatic alcohols with camphene over β-zeolite takes two pathways: O-alkylation which is preceded by isomerization of protonated camphene and addition at the camphene double bond of a carbocation formed by protonation and subsequent dehydration of the alcohol. As a result, products of aralkylation or cyclization are obtained, depending on the alcohol structure.
