638 research outputs found
Bio-derived Chemicals and Fuels: a scientific partnership between Venice and Sydney
No full textThe PhD cotutelle scheme between Venice and Sydney has allowed to couple research on green transformations of bio-based chemicals (including conversion mechanisms from platforms to their derivatives), with catalysts and processes for the improvement of bio-fuels (e.g. derived from algal feedstocks and by new technologies from lignocelluloses).
Bio-based chemicals in Venice. In Venice, the reactivity of bio-based platform chemicals such as levulinic acid and C4-C5 lactones with organic carbonates has been studied. This was done with a view of obtaining higher value added chemical compounds by new greener broad-based chemical technologies.
Bio-fuels in Sydney. In Sydney, on-water catalysis was applied to reduce the cloud point of biodiesel (the temperature at which crystals start to form in the fuel). This green innovative methodology was employed to carry out cycloadditions between fatty acids, constituents of biodiesel, and opportune bioderived dienes or dienophiles
Green transformations of bio-based chemicals
Get PDFThis thesis work was focused on the development of green chemical technologies for the upgrading of platform molecules obtainable from renewable feedstocks through a biorefinery scheme. The feedstocks were chosen among those considered as the most promising for the development a new, sustainable, chemical industry.
Levulinic acid (LA) can be converted into new derivatives with a higher degree of oxigenation (methyl levulinate and its 4,4-dimethyl ketal, dimethyl succinate and dimethyl 3-methylsuccinate), without actually using oxidizing agents. This result was achieved by using dimehtyl carbonate (DMC), a green reagent and solvent, in conditions of basic catalysis (K2CO3).
Bio-derived lactones such as gamma-valerolactone, gamma-butyrolactone, delta-valerolactone and epsilon-caprolactone were reacted with three dialkylcarbonates (DMC, diethyl- and dibenzylcarbonate). The five-membered ring lactones yielded the corresponding alpha-alkylated derivatives with high selectivity and yields. The six- and seven-membered ringed lactones afforded highly oxygenated acyclic monomeric derivatives otherwise hardly accessible by previous chemistry.
Gamma-valerolactone was chosen as a model to study acid catalyzed ring-opening reactions. A novel reactivity of the molecule was discovered in the presence of DMC. The 4-methoxy pentanoyl moiety was thus accessible by a green route. A reaction mechanism, supported by experimental and computational data, was proposed. The reaction was then extended to a continuous flow process, with solid acid catalysts. In such conditions, the selectivity towards methyl 4-methoxy pentanoate or methyl pentenoate, monomer for the production of polymers, can be tuned by optimising the operating parameters:
Bio-derived diols were efficiently upgraded using organic carbonates in tandem with ionic liquids as organocatalysts. The study investigated the parameters that control the selectivity towards cyclic- or linear di-carbonates.
The derivatisation of fatty acids methyl ester in conditions of on-water catalysis was investigated whilst at the University of Sydney, with the aim of developing a green strategy to reduce the cloud point of biodiesels. A new branched additive was synthesised, the thermal characteristics of which were analysed, both pure and blended with biodiesel.
The study of on-water catalysis continued by investigating the mechanism and the effect of reagent structure on on-water catalysis. It was demonstrated, by using the model reactions between cyclopentadiene (cp) and alkyl vinyl ketones, that little changes of the alkyl chain of a reactant have a dramatic influence on the catalytic effect. In particular, the reaction between ethyl vinyl ketone and cp was demonstrated to be on-water catalysed. When vinyl ketones bearing a longer or bulkier alkyl chain were tested, the catalytic effect was not observed, and the reactions were as fast as in neat conditions
Upgrading of Levulinic Acid with Dimethylcarbonate as Solvent/Reagent
No full textThe reactivity of the biobased chemical levulinic acid with dimethylcarbonate as a solvent/reagent under basic conditions is here described. The reaction yields methyl levulinate and dimethyl succinate, along with products that derive from methylation of the aliphatic chain and the dimethylketal of methyl levulinate. A degree of control over selectivity can be achieved by tuning the reaction conditions
Carbonate Phosphonium Salts as Catalysts for the Transesterification of Dialkyl Carbonates with Diols. The Competition between Cyclic Carbonates and Linear Dicarbonate Products
No full textAt 90–120 °C, in the presence of methylcarbonate and bicarbonate methyltrioctylphosphonium salts as
catalysts ([P8881][A]; [A] = MeOCO2 and HOCO2), the transesterification of non-toxic dimethyl- and
diethyl-carbonate (DMC and DEC, respectively) with 1,X-diols (2 ≤ X ≤ 6) proceeds towards the formation
of cyclic and linear products. In particular, 1,2-propanediol and ethylene glycol afford propylene- and
ethylene-carbonate with selectivity and yields up to 95 and 90%, respectively; while, the reaction of
DMC with higher diols such 1,3-butanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, 2,2-dimethyl,
1,3-propanediol, 1,4-butanediol and 1,6-hexanediol produce linear C8–C10 dicarbonates of general
Q3 formula MeOC(O)O---OC(O)OMe as the almost exclusive products. Of note, these dicarbonate derivatives
are not otherwise accessible in good yields by other conventional base catalyzed methods. Among
1,3-diols, the only exception was 2-methyl 2,4-pentandiol that yields the corresponding cyclic carbonate,
i.e. 4,4,6-trimethyl-1,3-dioxan-2-one. In no one case, polycarbonates are observed. Such remarkable
differences of product distributions are ascribed to the structure (branching and relative position of OH
groups) of diols and to the role of cooperative (nucleophilic and electrophilic) catalysis which has been
proved for onium salts. The investigated carbonate salts are not only effective in amounts as low as
0.5 mol%, but they are highly stable and recyclable
Green catalytic upgrading of renewable bio-based lactones
Get PDFStudies on biomass transformation into chemicals have demonstrated that some of them can be efficiently produced. Lactones are among the most interesting ones, being a key step for the synthesis of fine chemicals, solvents, and polymers. In this work, the reactivity of bio-based lactones (γ-butyro-, γ-valero-, δ-valero- and ε–capro-lactone; GBL, GVL, DVL, and ECL respectively), with dialkyl carbonates (DAlCs), has been studied, aiming to obtain higher value added chemical compounds by new greener broad-based chemical technologies. Under basic catalysis, the lactones reacted with three different DAlCs (both reactants and solvents) to yield selectively either the α-alkyl derivatives from of the five-membered ring GBL and GVL or the highly oxygenated acyclic monomeric derivatives from of the six- and seven-membered rings DVL and ECL. The ring-opening derivatives of the model lactone GVL can be obtained in conditions of acidic catalysis. The novel effect of DMC in such conditions was investigated, both in batch and continuous flow conditions. The selectivity towards methyl 4-methoxy-pentanoate or methyl pentenoate can be tuned by optimising the operating parameters
Dimethylcarbonate-Assisted Ring-Opening of Biobased Valerolactones with Methanol
No full textThe methanolysis reaction of renewable gamma-valerolactone and alpha-methyl-gamma-valerolactone in the presence of dimethylcarbonate and under acid conditions can be tuned to yield selectively each of three acyclic biobased products: 4-hydroxy-methylpentanoate I, 4-methoxy-methylpentanoate 2, and methyl-pent-3-enoate 3. The reaction was studied in batch and in continuous flow, and a reaction mechanism based on experimental and computational evidence was proposed. The protocol is based on a set of greener chemical technologies and was implemented in continuous flow
Upgrade of glycerol derivatives: the selective catalytic etherification of glycerol formal and solketal with dialkyl carbonates
Get PDFPhosphonium salts as organocatalysts for green reactions
No full textWith the aim of developing a green synthesis to ammonium and phosphonium ionic liquids, we prepared a series of methyltrialkyl phosphonium methyl carbonates by the alkylation of trialkyl phosphines with the non toxic dimethylcarbonate. These salts were a convenient stepping-stone to synthesise a large array of ionic liquids where the phosphonium cation was coupled to weakly basic anions such as bicarbonate, acetate, trifluoroacetate, phenate, chloride, bromide and many more.
As well as paving the way to a versatile synthesis of ILs, these compounds proved to be very active organocatalysts for base-promoted C-C bond forming addition reactions such as the Michael, Henry, nitroaldol, and Baylis-Hillman reactions. For these types of reaction, mechanistic studies indicated that the anionic and the cationic partners of ionic liquids acted cooperatively and independently as nucleophilic and electrophilic catalysts. This ambiphilic propensity of these phosphonium salts was demonstrated by kinetically discriminating the contributions of the anion (nucleophilic catalyst) and of the cation (electrophilic catalyst) on the model solvent-free Baylis–Hillman dimerization of cyclohexenone.
Methyl carbonate, hydrogencarbonate, acetate and phenate trioctyl methyl phosphonium salts were also excellent organocatalysts for the synthesis of an array of alkylcarbonates by transesterification of dimethyl- and diethyl-carbonate with primary and secondary alcohols, including benzyl alcohol, cyclopentanol, cyclohexanol, and the hindered menthol.Conditions were optimized to operate with very low catalyst loadings up to 1 mol% and to obtain non symmetrical dialkyl carbonates (ROC(O)OR’; R= Me, Et) with selectivity up to 99% and isolated yields > 90%. Also 1,2 and 1,3 diols could be used to obtain the corresponding cyclic carbonates rapidly (less than half an hour in the case of propylenediol), with very good yields (80-100%) under mild conditions
Upgrading of Biobased Lactones with Dialkylcarbonates
No full textFour renewable lactones, γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone (GBL, GVL, DVL, ECL, respectively) were shown to react with dimethyl-, diethyl-, and dibenzyl-carbonate (DMC, DEC, DBnC, respectively) in the presence of K2CO3 as basic catalyst, to yield selectively either the α-alkyl derivatives 1c–6c in the case of the five-membered ring GBL and GVL or the highly oxygenated acyclic monomeric derivatives 7a, 8a, and 9a in the case of the six- and seven-membered rings DVL and ECL. Selectivity and reaction conditions are investigated and a reaction mechanism is proposed. The organic carbonates act both as reagent and as reaction solvents, and the catalyst can be recovered by filtration and recycled
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