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 Cs
2.5
H
0.5
PW
12
O
40
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 Cs
2.5
H
0.5
PW
12
O
40
salt was efficiently recovered and reused without loss of catalytic activity.
Graphic abstract
The application of immobilizing calixarene onto the surface of silica using a sol-gel method, as an efficient heterogeneous catalyst (CX4SO3HSi(n)) for multicomponent Povarov reaction has been ...described. Catalytic activity of the CX4SO3HSi(n) for the synthesis of julolidines under greener and environmentally benign conditions in simple and efficient method was explored. Notably, only 0.5 mol% of the catalyst is sufficient to catalyze the Povarov solvent-free reaction under microwave-assistance. Besides, this protocol allows the construction of four new C–C bonds and two C–N bonds in a single step. To the best of our knowledge, this consists the first silica support calix4arene as a heterogeneous catalyst for multicomponent synthesis of julolidines.
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Teakwood from fast-growth plantations is commercialized at increasingly younger ages for economic reasons. However, wood features are influenced by the age of the tree. This study examined how age ...affects heartwood proportion, color parameters, chemical composition, and natural teakwood durability. Trees with 5, 10, 15, and 20 years of fast-growth at commercial plantations located in Mato Grosso, Brazil were evaluated. The base diameter of the trees ranged from 13.1 (5 years) to 28.3 cm (20 years), and the heartwood percentage increased from 16.3 to 60.0%, respectively. The color parameters in the CIELab system indicated that wood became darker and more saturated, and the predominance of yellow color decreased compared with red as age advanced. The total extractive content ranged between 7.4 (5 years) and 9.6% (15 years), without a clear trend of age affecting the extractive content. The extractives from five-year-old wood were mainly composed of tectoquinone (43.3%), phthalic acid (19.1%), and 1,3-indandione (9.2%), while those from 20-year-old wood were mainly composed of tectoquinone (60.7%), lapachol (13.8%), and phthalic acid (9.7%). Teakwood can be classified as resistant (5 years) to very resistant (20 years) after being submitted to an accelerated decay test.
This work reports the novel results of p-sulfonic acid calix4arene-catalyzed esterification reactions of palmitic acid with deuterated methanol. The p-sulfonic acid calix4arene organocatalyst is ...easily obtained and handled, and is significantly less corrosive than mineral acids commonly used in esterification reactions. Although used in homogeneous conditions, p-sulfonic acid calix4arene catalyst can be recovered and reused without losing its activity and may therefore be potentially useful in biodiesel production. A comparative study by use of in situ 1H NMR spectroscopy between the kinetic and thermodynamic parameters obtained from the palmitic acid esterification reaction, showed that at 0.5mol% concentration the activation energy of the p-sulfonic acid calix4arene-catalyzed reaction is lower than that measured for sulfuric acid. However, a higher dependence in relation to sulfuric acid concentration was observed. Conversely, ΔG values obtained suggested that this reaction becomes more spontaneous with an increase in temperature than calix4arene catalyzed esterification reactions.
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► Calix4arene catalyst is highly active for fatty acids esterification. ► Kinetic data showed that the calix4arene was as active as H2SO4. ► p-sulfonic acid calix4arene is a recoverable and reusable catalyst. ► The order in relation to calix4arene and H2SO4 was 0.57 and 1.0 respectively.
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•The kinetics of H3PW12O40 or H3PMo12O40-catalyzed acetalization furfural was studied.•Ultraviolet spectroscopy was an efficient tool to monitoring the reactions.•Activation energy of ...heteropolyacid-catalyzed reactions were determined.•Among Bronsted acids assessed, Keggin heteropolyacids were the most active catalysts.•The soluble H3PW12O40 was easily recovered and reused without loss activity.
In this work, the ultraviolet spectroscopy was used as a tool to monitor the kinetics of acetalization reaction of furfural with alkyl alcohols. Among the Bronsted acids evaluated, Keggin heteropolyacids (e.g., H3PW12O40 and H3PMo12O40) were the more active and selective in the acetalization of furfural in reactions carried out at room temperature. The ultraviolet spectroscopy, a simple and inexpensive analytic technique was used to quantify the furfural and acetals during the reaction progress. The influence of main reaction parameters such as temperature, time, and catalyst load were assessed. The reaction scope was extended to the other alcohols. The activation energy of heteropolyacid-catalyzed reactions was determined.
A new and mild route of furfural acetalization with various alkyl alcohols catalyzed by cheap and simple SnCl2 has been developed. This process consists of the conversion of furfural to alkyl acetals ...under benign and mild reaction conditions (i.e., room temperature, without solvent, recyclable catalyst), achieving a very good selectivity (97–100%) and almost complete conversion of furfural. Various tin(ii) salts were used as catalysts for the upgrading of furfural to alkyl acetal in an alcoholic solution at room temperature. SnCl2 was the most active and selective catalyst toward furfural diethyl acetal. Tin(ii) chloride is a commercially available and water tolerant Lewis acid and was demonstrated to be an efficient and recyclable catalyst for the synthesis of furfural alkyl acetal. The effects of the main variables of the reaction such as the catalyst load, temperature, reaction time and alcohol nature were assessed. SnCl2 was easily recovered and reused without loss of activity and selectivity.
In this work, Sn(II)-exchanged Keggin heteropoly acid salts were evaluated as solid catalysts in glycerol esterification reactions with acetic acid. All the Sn(II) heteropoly salts and their ...precursor Keggin acids were characterized by FT-IR/ATR, XRD, TG/DSC, BET, and EDS/SEM analyses. Among salts synthesized (i.e., Sn3/2PW12O40, Sn2SiW12O40, and Sn3/2PMo12O40), Sn3/2PW12O40 was the most active and selective catalyst toward glycerol esters. Effects of thermal treatment on the physical and chemical properties of Sn3/2PW12O40 were investigated. The Sn3/2PW12O40-300 K catalyst was efficiently recovered and reused without a loss in activity. The influences of main reaction parameters such as reaction temperature, the stoichiometry of reactants, load, and thermal treatment temperature of the Sn3/2PW12O40 catalyst were assessed. The simple workup of synthesis and the high activity and selectivity for glycerol esters in addition to the high efficiency during successive recycles are positive aspects of this catalyst.
A new and mild route of furfural acetalization with various alkyl alcohols catalyzed by cheap and simple SnCl 2 has been developed. This process consists of the conversion of furfural to alkyl ...acetals under benign and mild reaction conditions ( i.e. , room temperature, without solvent, recyclable catalyst), achieving a very good selectivity (97–100%) and almost complete conversion of furfural. Various tin( ii ) salts were used as catalysts for the upgrading of furfural to alkyl acetal in an alcoholic solution at room temperature. SnCl 2 was the most active and selective catalyst toward furfural diethyl acetal. Tin( ii ) chloride is a commercially available and water tolerant Lewis acid and was demonstrated to be an efficient and recyclable catalyst for the synthesis of furfural alkyl acetal. The effects of the main variables of the reaction such as the catalyst load, temperature, reaction time and alcohol nature were assessed. SnCl 2 was easily recovered and reused without loss of activity and selectivity.
A new and mild route of furfural acetalization with various alkyl alcohols catalyzed by cheap and simple SnCl
2
has been developed. This process consists of the conversion of furfural to alkyl ...acetals under benign and mild reaction conditions (
i.e.
, room temperature, without solvent, recyclable catalyst), achieving a very good selectivity (97-100%) and almost complete conversion of furfural. Various tin(
ii
) salts were used as catalysts for the upgrading of furfural to alkyl acetal in an alcoholic solution at room temperature. SnCl
2
was the most active and selective catalyst toward furfural diethyl acetal. Tin(
ii
) chloride is a commercially available and water tolerant Lewis acid and was demonstrated to be an efficient and recyclable catalyst for the synthesis of furfural alkyl acetal. The effects of the main variables of the reaction such as the catalyst load, temperature, reaction time and alcohol nature were assessed. SnCl
2
was easily recovered and reused without loss of activity and selectivity.
A new and mild route of furfural acetalization with various alkyl alcohols catalyzed by cheap and simple SnCl
2
has been developed.
Esterification yields were significantly improved using calixnarenes catalysts under simple conditions. p-Sulfonic acid calix4arene and p-sulfonic acid calix6arene were powerful organocatalysts in ...several esterification reactions, which showed activity comparable or even superior to other well-established acids catalysts, such as, sulfuric acid, p-toluenesulfonic acid, and p-hydroxybezenesulfonic acid described in the literature.
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