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The vanadium-doped phosphomolybdic acid (H4PMo11VO40) was the most active and selective heteropoly catalyst in one-pot oxidative esterification of benzaldehyde with hydrogen peroxide.

In this work, we report for the first time, the tungstic acid-catalyzed oxidation of terpene alcohols with hydrogen peroxide. This simple, solid, and commercially available catalyst efficiently promoted the conversion of borneol, geraniol and nerol to camphor and epoxide products, respectively. Effects of main reaction parameters, such as catalyst load, the molar ratio of oxidant to the substrate, time, and reaction temperature were investigate. Conversions and selectivity greater than 90% were achieved using 1.0 mol % of H2WO4 after 2 h of reaction at 90°C. The activation energy was equal to 66 kJmol-1. We propose a reaction mechanism based on the experimental results. This solid catalyst was easily recovered and reused without loss of activity. As far as we know, it is the first time that tungstic acid was used as the catalyst in the oxidation reactions of terpene alcohols.

A green route to oxidize terpenic alcohols (nerol and geraniol) with H2O2 over a solid catalyst was developed. The Dy-doped ZnWO4 catalyst was synthesized by coprecipitation and microwave-assisted hydrothermal heating, containing different dysprosium loads. All the catalysts were characterized through infrared spectroscopy, powder X-ray diffraction, surface area and porosimetry, transmission electronic microscopy image, and n-butylamine potentiometric titration analyses. The influence of main reaction parameters such as temperature, the stoichiometry of reactants, loads, and catalyst nature was assessed. ZnWO4 2.0 mol% Dy was the most active catalyst achieving the highest conversion (98%) and epoxide selectivity (78%) in nerol oxidation. The reaction scope was extended to other terpenic alcohols (i.e., geraniol, borneol, and α-terpineol). The highest activity of ZnWO4 2.0 mol% Dy was assigned to the lower crystallite size, higher surface area and pore volume, higher acidity strength and the greatest dysprosium load.

The activity of metal nitrate catalysts was investigated in the oxidative esterification reactions of benzaldehyde with hydrogen peroxide. Several types of metal nitrates (alkaline, alkaline earth, and transition metals) were evaluated as catalysts. Among the assessed salts, Fe(NO3)3 was the most efficient catalyst toward the formation of the target product (i.e., benzoic alkyl ester). In methyl alcohol, benzaldehyde was selectively oxidized to benzoic acid and then esterified to methyl benzoate. The efficiency of the catalyst was correlated with its higher Lewis acidity character, which was established through the pH measurements of methanolic solutions of the soluble metal nitrate salts. The influence of main variables of the reaction, such as catalyst load, temperature, and reactant stoichiometry, was investigated. The size of the carbon chain and steric hindrance played an essential role in the reaction selectivity. While methyl and ethyl alcohols selectively provided ester as the main product (ca. 70–75%) and acetal as the subproduct, the other alcohols gave ester, hemiacetal, and benzoic acid, which was formed in the least amount. The use of an inexpensive catalyst, a green oxidant, mild conditions, and short reaction times were the positive aspects of this one-pot process. The high TON (ca. 900) is evidence of the high catalytic activity of Fe(NO3)3. It is noteworthy that this methodology does not rely upon ligands and other additives.

The activity of the sodium salts of vanadium-doped phosphomolybdic acid was assessed in the oxidative esterification reaction of benzaldehyde with hydrogen peroxide in alkyl alcohol solutions. The effect of main reaction parameters, such as temperature, catalyst load, vanadium doping level, and reactant stoichiometry, on the conversion and reaction selectivity was investigated. Among the tested heteropoly salts, Na4PMo11VO40 was the most active and selective catalyst, achieving almost complete conversion of benzaldehyde and high ester selectivity regardless of the alcohol investigated. The efficiency of the catalyst was correlated with its vanadium content. The size of the carbon chain of alcohol and the steric hindrance on the hydroxyl group played a key role in the reaction selectivity. While methyl and ethyl alcohols selectively provided the ester as the main product (ca. 90–95%) and benzoic acid as a subproduct, the other alcohols also afforded acetal, a condensation product, and benzaldehyde peroxide, an oxidation reaction intermediate, as secondary products. The use of an inexpensive, environmentally benign, and atom-efficient oxidant, mild conditions, and short reaction times were the positive aspects of this one-pot process.

In this work, the catalytic activity of the transition metal-substituted potassium silicotungstate salts (i.e. K8-nSiMn+W11O39 (Mn+ = Cu2+, Co2+, Ni2+, Zn2+ and Fe3+) was investigated on the oxidation reactions of the terpene alcohols with H2O2 aqueous solution. The metal-substituted silicotungstate salts were easily synthesized in one-pot reactions of the precursor metal solutions (i.e. Na2WO4, Na2SiO3 and MCln) with KCl added in stoichiometric amount; after this precipitation step, the solid heteropoly salts were filtered and dried in an oven. This procedure of synthesis avoids multi-step processes that starts from the pristine heteropolyacid. The substituted metal heteropoly salts were characterized by infrared spectroscopy, measurements of the specific surface area (BET) and porosimetry by isotherms of adsorption/desorption of N2, X-rays diffraction, thermal analyses, dispersive X-rays spectroscopy, scanning electronic microscopy. The acidity strength was estimated by potentiometric titration with n-butylamine. All the salts were evaluated as catalysts in terpenic alcohols oxidation reactions with H2O2. The K5SiFeW11O39 was the most active and selective catalyst toward oxidation products. The impacts of the main reaction variables such as catalyst concentration, temperature, oxidant load, and nature of the terpene substrate were assessed. The highest activity of the K5SiFeW11O39 catalyst was assigned to the highest Lewis acidity.

The activity of the palladium salt catalysts was investigated on the benzaldehyde reactions with H2O2. The PdCl2 salt was the most efficient catalyst for the formation of the goal products. In CH3OH, benzaldehyde was selectively oxidized to benzoic acid and posteriorly esterified to methyl benzoate. In this process, the reaction of the PdCl2 catalyst with aqueous H2O2 provided H+ ions, which also promoted the esterification and acetalization reactions. The oxidant load played a key role in the selectivity controlling; while a large excess (9:1) gave benzoic acid (90%), with a lower ratio (3:1), acid and ester were formed with selectivity of 58 and 35%, respectively. With H2O2 at an equimolar ratio, the Pd(0) reduced the benzaldehyde to benzyl alcohol (30%). In absence of the oxidant, PdCl2 (2.5 mol %) condensated benzaldehyde and alcohol to acetal (90%). Therefore, PdCl2 directly catalyzed the oxidation and reduction reactions, and participated in acid-catalyzed reactions (i.e., condensation and esterification), generating H+ ions, demonstrating to be a highly versatile catalyst. An adequate adjusting of reaction conditions allowed to control the reaction selectivity toward the desired products (i.e., benzoic acid or ester benzyl, acetal, or benzyl alcohol).

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.

In this work, efficient solid acid catalysts were obtained from the stoichiometric reactions of Keggin heteropolyacids with SnSO4 and evaluated in the etherification reactions of glycerol with tert...

In this work, we describe a new one-pot synthesis route of valuable linalool oxidation derivatives (i.e., 2-(5-methyl-5-vinyltetrahydrofuran-2-yl propan-2-ol) (1a)), 2,2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol (1b) and diepoxide (1c), using a green oxidant (i.e., hydrogen peroxide) under mild conditions (i.e., room temperature). Lacunar Keggin heteropolyacid salts were the catalysts investigated in this reaction. Among them, Na7PW11O39 was the most active and selective toward oxidation products. All the catalysts were characterized by FT-IR, TG/DSC, BET, XRD analyses and potentiometric titration. The main reaction parameters were assessed. Special attention was dedicated to correlating the composition and properties of the catalysts and their activity.

In this work, we have assessed the activity of various Keggin heteropolyacid (HPA) salts in a new one-pot synthesis route of valuable products, which were obtained from the oxidation of terpenic alcohols (i.e., aldehyde, epoxide, and diepoxide), using a green oxidant (i.e., hydrogen peroxide) at mild conditions (i.e., room temperature). Lacunar Keggin HPA sodium salts were the goal catalysts investigated in this reaction. Starting from the HPAs (H3PW12O40, H3PMo12O40, and H4SiW12O40), we synthesized lacunar sodium salts (Na7PW11O39, Na7PW11O39 and Na8SiW11O39) and a saturated salt (Na3PW12O40). All of them were investigated in oxidation reactions in a homogeneous phase with nerol as a model molecule. Na7PW11O39 was the most active and selective towards the oxidation products. All the catalysts were characterized by FT-IR, TG/DSC, BET, XRD, and SEM-EDS analyses and potentiometric titration. The main reaction parameters were assessed. Geraniol, α-terpineol, β-citronellol and borneol were also successfully oxidized. Special attention was dedicated to correlating the composition and properties of the catalysts with their activity.

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.

Bio-oil can be converted to carbon nanostructures such as graphene, graphite-like structures, nanotubes and closed shell nanoparticles upon reaction with H2SO4 under mild conditions, i.e. 120 °C. The formation of these carbon nanostructures is discussed in terms of dehydration, condensation and aromatization processes of the complex bio-oil molecules to form nanographene precursors which in the liquid reaction medium can diffuse and further combine to produce different nanostructures.

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, we have explored the catalytic activity of Keggin-type heteropolyanions PMo12−nVnO40(3+n)− (n = 0, 1, 2, or 3) in the form of sodium salts in green oxidation routes of terpene alcohols with hydrogen peroxide. Nerol was the model molecule selected to assess the impacts of the main reaction parameters, such as temperature, catalyst load, and stoichiometry of reactants. The impacts of the presence of vanadium at different proportions (i.e., V1, V2, and V3 loads/per anion) in the structure of phosphomolybdate catalysts were assessed. All the catalysts were characterized by various techniques such as powder X-ray diffraction, attenuated diffuse reflectance infrared spectroscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, isotherms of adsorption–desorption of N2 measurements of surface area, scanning electronic microscopy, energy-dispersive X-ray spectroscopy, and n-butylamine potentiometric titration. Among the catalysts assessed, Na4PMo11VO40 was the most active and selective toward epoxides. The efficiency of this catalyst in the epoxidation of different terpene alcohols was investigated. Special attention was dedicated to correlating the composition and properties of the vanadium-doped phosphomolybdic catalysts with their catalytic activity.

In this work, bio-oil (an organic matrix rich in oxygen functionalities) was used to efficiently dissolve and disperse Fe3+ which upon thermal treatment produced a carbon containing dispersed and encapsulated Fe oxide magnetic nanoparticles. These materials were prepared by dissolution of 8, 16 and 24 wt.% Fe3+ salt in bio-oil followed by treatment at 400, 450, 500 or 600 oC in N2 atmosphere. X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopies (TEM), elemental analysis, thermogravimetric-mass spectrometry (TG-MS), potentiometric titration, Raman and Mossbauer spectroscopies showed that Fe3+ species in bio-oil is reduced to produce magnetic nanoparticles phases: magnetite Fe3O4 and maghemite γ-Fe2O3. At low temperatures, the iron phases were less protected, and the carbon matrix was more reactive, while in temperatures above 500 oC, the iron phases were more stable, however, the carbon matrix was less reactive. Reaction of these magnetic carbon materials with concentrated H2SO4 produced surface sulfonic acidic sites (ca. 1 mmol g-1), especially for the materials obtained at 400 and 450 oC. The materials were used as catalysts on esterification reaction of oleic acid with methanol at 100 oC and conversions of 90% were reached, however, after 2 consecutive uses, the conversion decreased to 30%, being required more studies to improve the material stability.

In this work, phosphomolybdic acid salts were synthesized exchanging their protons by the Sn(II) cations (i.e., H3-xSnx/2PMo12O40; x = 0.0, 1.0, 2.0, 3.0), and evaluated in the etherification reactions of glycerol with tert-butyl alcohol (TBA). The catalytic activity of the phosphomolybdate salts containing a variable load of Sn(II) ions was further compared to phosphotungstic and silicotungstic acid salts (i.e., H3-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 3.0 and H4-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 4.0, respectively). The integrity of the Keggin anion after the synthesis was confirmed by infrared spectroscopy analysis. Physical properties were determined through thermal analyses, powder X-Rays diffraction patterns, N2 adsorption-desorption isotherms, and scanning electron microscopy. The acidity properties were analyzed by adsorbed pyridine FT-IR spectroscopy, NH3-programmed-temperature desorption, and potentiometric titration. Among all the Sn(II) heteropoly salts tested, the Sn3PMo12O40 was the most active and selective catalyst toward glyceryl ethers. The highest activity of Sn3PMo12O40 was assigned to the greater Lewis acidity strength. Modeling, simulation, and economic analysis allowed to evaluate the viability of the process. An annual capacity of 30,000 metric tons was developed, and the process is feasible with a return on investment (ROI) of 30.7%.

Lacunar potassium undecasilicotungstate salt catalyst was highly efficient in oxidation reactions of terpenic alcohols with hydrogen peroxide. Carbonylic products were selectively obtained from alcohols such as borneol, nerol, geraniol and β-citronellol. The K8SiW11O39 catalyst was synthesized in one pot reaction starting from precursor salts (KCl, Na2WO4, and Na2SiO3). The catalyst salt was characterized by FT-IR, TG/DSC, BET, XRD analyses and potentiometric titration. The main reaction parameters were assessed. Based on experimental data, a reaction pathway was proposed. In borneol oxidation, TON of 2720 was achieved, indicating the high catalytic activity. As far we know, it is the first time where the monolacunar catalyst is used without an additional introduction of metal transition into Keggin anion. A comparison of the catalytic performance of different lacunar silicotungstic acid salts exchanged with different cations was performed. The K8SiW11O39 catalyst was used without loss activity.

Keggin heteropolyacids (i.e. H3PW12O40, H3PMo12O40 and H4SiW12O40) were converted to potassium lacunary salts and afterwards their vacancy were filled by metal cations (i.e. Cu2+, Co2+, Fe3+, Ni2+ or Al3+). These solid catalysts were assessed on oxidation of benzaldehyde to benzoic acid by hydrogen peroxide. Remarkably, among heteropoly salts investigated, the K6SiW11CoO39 was the most active catalyst. High conversion (ca. 90%) and benzoic acid selectivity (ca. 90%) were achieved. The activity of solid catalyst remained unaltered after successive cycles of reuse. Effect of catalyst nature, temperature, reactants concentration on conversion and selectivity were assessed.

Sodium tungstate was found to be an active and highly selective catalyst to oxidation of various primary or secondary origin renewable alcohols by hydrogen peroxide as green oxidant. Borneol, nerol, geraniol and β-citronellol were efficiently and selectively converted to respective carbonyl derivatives by hydrogen peroxide. ATR/FT-IR measurements confirmed that Na2W(O2)4 was the specie active catalytically. The role of the main reaction variables, including temperature, reactants and catalyst concentration, solvent, and nature of substrate were also assessed. In addition to use a green oxidant, this simple and environmentally friendly catalyst system did not require additive to control pH, molecular sieves or phase transfer catalyst.

Solid SnF2 was able to catalyze the glycerol ketalization with propanone giving solketal (i.e. 2,2-dimethyl-1,3-dioxolane-4-methanol) in reactions with high conversions and regioselectivity (ca. 97%). Tin(II) fluoride is commercially available, water tolerant and less corrosive solid Lewis acid catalyst. Herein, we have described an alternative process to the Bronsted acid-catalyzed reactions in homogeneous phase, where the product neutralization steps are avoided, and the catalyst is easily recovered and reused without loss activity. In addition to develop a catalytic system, the process engineering including the definition of basic equipment for economic evaluation was too investigated. A process flow diagram (PFD) was developed to generate the most favorable operating conditions for solketal production through SnF2-catalyzed glycerol condensation with propanone. We used the UNISim™ software to perform the material and energy balances. The plant could work with 432 t/y of glycerol and could produce 620.9 t/y of solketal. The solketal cost was 12.29 $ (USD)/kg. This analysis suggests that solketal production from glycerol deserves serious consideration by the investors.

The catalytic activity of p-sulfonic acid calix[4]arene was studied in the transesterification reactions of Passiflora seed oil with methanol or ethanol. Calix[n]arenes are highly versatile organocatalysts and conversion rates >98 % were obtained for the transformation of Passiflora seed oil to its methyl or ethyl esters after 5 h of reaction in the presence of p-sulfonic acid calix[4]arene (3.52 mol % in ethanol; 5.28 mol % in methanol). Moreover, the organocatalyst was recovered and reused in two subsequent cycles without a significant decrease in the activity or selectivity. The use of a non-corrosive and reusable organocatalyst is the positive aspect of this process.

Herein, an efficient and environmentally benign tin-based process who is a simple and available commercially catalyst, was used in the glycerol ketalization with different ketones at room temperature and solvent-free reactions. Although being a molecule highly functionalized, glycerol was selectively converted to ketal in all the SnCl2-catalyzed reactions. A high regioselectivity (ca. 78–99 % for 1,3-dioxolane derivatives) was achieved for ketones with straight or cyclic chain having up to six carbon atoms. Conversely, glycerol ketalization with branched carbon chain ketones containing six carbon atoms (i.e. 4-methyl-2-pentanone) resulted in the equimolar formation of two isomers products (i.e. cis and trans-1,3-dioxolane isomers glycerol derivatives). The main reaction parameters such as the ketone nature, reactants stoichiometry and catalyst concentration were assessed. The SnCl2 catalyst operate at mild and solvent-free reaction conditions and was successively recovered and reused without activity loss. Tin-catalyzed glycerol ketal synthesis

Simple Fe(NO3)2·9H2O was demonstrated to be able to catalyze the oxidation of monoterpenes by hydrogen peroxide in methyl alcohol solution. Compared with the previous iron-catalyzed methods, the present procedure avoids the use of stabilizing ligands, additives, and corrosive peroxide organic oxidants. A novel, simple and highly efficient catalyst system was developed for oxidizing monoterpenes into a valuable derivates using hydrogen peroxide, an environmentally friendly oxidant. Possible steps involved in the Fe(III)-catalyzed oxidation of β-pinene by hydrogen peroxide into myrtenol methyl ether in methyl alcohol

The Fe(III)-catalyzed aerobic oxidation of monoterpenes in CH3OH has been developed, in which simple Fe(III) salts are used as catalysts in the absence of stabilizing ligands. Remarkably, Fe(NO3)3 catalyst efficiently promotes the oxidation of monoterpenes under air or dioxygen. The highest TON and TOF reached 476 and 162 h− 1, respectively. In general, reactions with 1.0–9.0 mol% of catalyst reached high conversions (ca. 90–99%) and high oxidation products selectivity (ca. 80%). Notably, α-pinene and β-pinene were selectively oxidized into only allylic product, myrtenol methyl ether. The significant breakthroughs of this simple oxidative process are the use of inexpensive Fe(III) salts as catalysts and environmentally-friendly oxidants (air or dioxygen).

The selective transformation of glycerol into value-added products remains a challenging task due to its polyfunctional nature. Conversion of glycerol into 2,2-dimethyl-1,3-dioxolane-4-methanol (i.e., solketal) was efficiently catalyzed by SnCl2 at room temperature and in solvent-free conditions. Solketal is an useful additive for the formulation of gasoline, diesel, and biodiesel. Tin chloride, an inexpensive, water-tolerant, and minimally corrosive Lewis acid catalyst, has demonstrated excellent catalytic behavior in the acetalisation of glycerol with acetone to yield solketal with a higher efficiency than traditional Bronsted acids (i.e., p-toluenesulfonic acid or sulfuric acid). The effects of various parameters, such as catalyst loading, acetone/glycerol molar ratio, and temperature on the selectivity and conversion of glycerol was investigated in detail. Although used in the homogeneous phase, the SnCl2 catalyst was easily recovered and reused without any reactivation treatment up to six times, keep...

In this work, the efficiency of Lewis acid catalysts, SnX2 (X = F−, Cl−, Br−, or −OAc), was investigated on the esterification reactions of fatty acids (i.e., myristic, palmitic, stearic, oleic, linoleic, and linoleic) with different alcohols (i.e., methyl, ethyl, propyl, isopropyl, and butyl alcohol). Tin(II) bromide was the most active catalyst in all reactions studied. We investigated the effects of main reaction parameters, such as catalyst concentration, temperature, and nature of alcohol and fatty acid. The highest activity of SnBr2 catalyst was discussed in terms of its lower activation energy, higher Lewis acid strength, and higher softness of anionic ligand. Finally, the SnBr2 catalyst can be easily recovered and reused without loss of catalytic activity. Effect of the tin catalyst nature on the oleic acid esterification with ethyl alcohol.

Application of PdX2 catalysts (X=Cl−, −OAc, −OCOCF3, acac) for the oxidation of β-pinene by hydrogen peroxide in methanol is presented. The reactions performed in CH3OH were much faster and more selective than those described in the literature. Moreover, the peculiar tunability of Pd(II) selectivity dependent on the nature of the anionic ligand is highlighted. Although they present different chemoselectivity, PdCl2 and Pd(OAc)2 were the most active catalysts; high conversions of β-pinene into allylic oxidation products were obtained (ca. 80 %) when catalyzed by Pd(OAc)2 and up to ca. 99 % when catalyzed by PdCl2, both in short reaction times (ca. 2 h).

This work reports the novel results of p -sulfonic acid calix[4]arene-catalyzed esterification reactions of palmitic acid with deuterated methanol. The p- sulfonic acid calix[4]arene 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 calix[4]arene 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 1 H NMR spectroscopy between the kinetic and thermodynamic parameters obtained from the palmitic acid esterification reaction, showed that at 0.5 mol% concentration the activation energy of the p -sulfonic acid calix[4]arene-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 calix[4]arene catalyzed esterification reactions.

Molecular sieves, complex organic bases and radical oxidants are commonly used in alcohols oxidation reactions. In this work, we have evaluated the beneficial effects of addition of K2CO3 to Pd(II)-catalyzed oxidation alcohols, which resulted in a remarkable increase in the oxidation reaction rates without selectivity losses. Herein, in a metallic reoxidant-free system, terpenic alcohols (β-citronellol, nerol and geraniol) were selectively converted into respective aldehydes from Pd(II)-catalyzed oxidation reactions in presence of dioxygen. High conversions and selectivities (greater than 90%) were achieved in the presence of the Pd(OAc)2/K2CO3 catalyst and pyridine excess. The exogenous role of others auxiliary anionic and nitrogen compounds was appraised. Reaction conditions: β-citronellol (2.75 mmol); Pd(OAc)2 (0.05 mmol); pyridine (5.0 mmol); K2CO3 (2.5 mmol); toluene (10 mL); MS3A (0.5 g); O2 (0.10 MPa); 60 °C.

In this work, a novel process based on use of a SnCl2·2H2O catalyst which is less corrosive, inexpensive, and a water tolerant Lewis acid was employed for synthesis of fuel bio-additives from glycerol. High yields and selectivities were achieved for glycerol esterification with acetic acid under mild reaction conditions. The SnCl2 catalyst showed to be as active as p-toluene sulfonic and sulfuric acid, catalysts commonly used in acid-catalysed esterification reactions. However, its use has significant advantages in comparison to these Bronsted acid catalysts, including lower reactor corrosion and unnecessary neutralization at the end reaction. The SnCl2 catalyst can also be recovered and reused without loss of catalytic activity. Additionally, effects of reaction temperature, HOAc:glycerol molar ratio and catalyst concentration on both selectivity and yield of glycerol acetates were also investigated. The lower corrosiveness, facilitated handling, as well as potential for reuse without activity loss after simple recycle protocols are positive aspects of SnCl2 catalysts. SnCl2-catalyzed glycerol esterification with HOAc at the molar ratio of 3:1 at 60 °C.

The catalytic activity of Bronsted acids on fatty acid (FA) esterification at room temperature has been investigated. Noticeably, the H3PW12O40 heteropolyacid (HPW) showed a very high activity than other catalysts herein evaluated, i.e. p-toluene sulfonic acid and sulfuric acid. High yields in ethyl esters (ca. 90%) were reached after a 4 h reaction at 25 °C on a HPW catalysed reactions. Despite the fact that HPW catalyst was used in a homogeneous phase, it could be efficiently recovered and reused through out a simple recycling protocol, without any activity loss. The effects of alcohol and the FA nature on yield reaction were also investigated. Noticeably, the H3PW12O40 heteropolyacid (HPW) showed a very high activity than other catalysts herein evaluated, i.e. p-toluene sulfonic acid and sulfuric acid. High yields in ethyl esters (ca. 90%) were reached after a 4 h reaction at 25 °C on a HPW catalysed reactions.

Castor bean (Ricinus communis L.) seeds serve as raw material for the production of nonedible oil used in medicine and industry, whereas the presence of allergenic and toxic proteins in the residue left after oil extraction precludes the use of this protein-rich by-product in animal feeding. To better understand the enzymes involved in the biosynthesis and degradation of fatty acids and to identify proteins with toxic/anti-nutritional properties, extracts of developing and germinating seeds were prepared and prefractionated according to solubility properties of the proteins. An enriched plastid organelle fraction embracing mostly plastids and mitochondria was also prepared. Two-dimensional electrophoresis (2DE) reference maps of these fractions were obtained from which nearly 400 proteins were identified by matrix-assisted laser desorption ionization-time of flight-time of flight (MALDI-TOF-TOF) mass spectrometry after a search in a National Center for Biotechnology Information (NCBI) database and in an expressed sequence tag (EST) primary bank prepared from a cDNA library of developing seeds. These proteomics techniques resulted in the identification of several classes of seed reserve proteins such as 2S albumins, legumin-like and seed storage proteins, as well as other proteins of plastidial or mitochondrial functions and proteins involved in plant defense against biotic and abiotic stresses. It is expected that the collected data will facilitate the application of genetic techniques to improve the quality/profile of castor seed fatty acids, and pave the way for a rational approach to inactivate allergenic and toxic proteins, allowing the use of castor bean meal in animal feeding.

Currently, the oxidative transformations of natural olefins are complicated for competitive reactions such as isomerization, skeletal rearrangements and nucleophilic addition. These concurrent reactions are promoted by metal reoxidant, normally a Lewis acid, and by protic solvent. In this article, the oxidation of terpenes, namely camphene, β-pinene, α-pinene and 3-carene were performed in PdCl2/H2O2/CH3CN system. This metal reoxidant-free system showed highly efficient, especially on camphene and β-pinene oxidation, which resulted in the selective conversion of these substrates into epoxy-derivates and allylic oxidation products, respectively. Additionally, the effects of the principal reactional parameters such as the peroxide/catalyst and substrate/catalyst molar ratio were also investigated.

The structures of diterpene derivatives resulting from the palladium catalyzed tandem oxidative coupling-oxidation of camphene, i.e., bis(2,2-dimethyl-bicyclo[2.2.1]hept-3-ylidene)ethane and (4,4-dimethylbicyclo[3.2.1]oct-2-on-3-yl)(2,2-dimethylbicyclo[2.2.1]hept-3-ylidene)methane, were elucidated using one- and two-dimensional 1H and 13C NMR techniques. Their stereochemistry was determined unambiguously by NOESY experiments.