Emanuela Calcio Gaudino

A new pilot flow reactor for high-intensity ultrasound irradiation. Application to the synthesis of biodiesel.

In recent years, chemistry in flowing systems has become more prominent as a method of carrying out chemical transformations, ranging in scale from microchemistry up to kilogram-scale processes. Compared to classic batch ultrasound reactors, flow reactors stand out for their greater efficiency and flexibility as well as lower energy consumption. This paper presents a new ultrasonic flow reactor developed in our laboratory, a pilot system well suited for reaction scale up. This was applied to the transesterification of soybean oil with methanol for biodiesel production. This reaction is mass-transfer-limited initially because the two reactants are immiscible with each other, then because the glycerol phase separates together with most of the catalyst (Na or K methoxide). In our reactor a mixture of oil (1.6 L), methanol and sodium methoxide 30% in methanol (wt/wt ratio 80:19.5:0.5, respectively) was fully transesterified at about 45 degrees C in 1h (21.5 kHz, 600 W, flow rate 55 mL/min). The same result could be achieved together with a considerable reduction in energy consumption, by a two-step procedure: first a conventional heating under mechanical stirring (30 min at 45 degrees C), followed by ultrasound irradiation at the same temperature (35 min, 600 W, flow rate 55 mL/min). Our studies confirmed that high-throughput ultrasound applications definitively require flow reactors.

Efficient synthetic protocols in glycerol under heterogeneous catalysis.

The massive increase in glycerol production from the transesterification of vegetable oils has stimulated a large effort to find novel uses for this compound. Hence, the use of glycerol as a solvent for organic synthesis has drawn particular interest. Drawbacks of this green and renewable solvent are a low solubility of highly hydrophobic molecules and a high viscosity, which often requires the use of a fluidifying co-solvent. These limitations can be easily overcome by performing reactions under high-intensity ultrasound and microwaves in a stand-alone or combined manner. These non-conventional techniques facilitate and widen the use of glycerol as a solvent in organic synthesis. Glycerol allows excellent acoustic cavitation even at high temperatures (70-100 °C), which is otherwise negligible in water. Herein, we describe three different types of applications: 1) the catalytic transfer hydrogenation of benzaldehyde to benzyl alcohol in which glycerol plays the dual role of the solvent and hydrogen donor; 2) the palladium-catalyzed Suzuki cross-coupling; and (3) the Barbier reaction. In all cases glycerol proved to be a greener, less expensive, and safer alternative to the classic volatile organic solvents.

Regulation of HMGCoA Reductase Activity by Policosanol and Octacosadienol, a New Synthetic Analogue of Octacosanol

Octacosa-10,19-dien-1-ol is a newly synthesized long-chain alcohol, an unsaturated analogue of 1-octacosanol, the major component of policosanol, the purified natural mixture of different higher aliphatic alcohols obtained from sugarcane wax. Our efficient synthetic protocol (five steps with 50% overall yield) is well suited for gram scale preparations and a rapid generation of analogues with different degrees of unsaturation. Beneficial effects of policosanol in the prevention of atherosclerosis and thromboembolic disorders have been reported and related to the inhibition of sterol biosynthesis possibly by the regulation of the activity of HMGCoA reductase mediated by AMP-dependent kinase AMPK. We have compared the effect of octacosadienol and policosanol on the regulation of HMGCoA reductase in HUVEC and HepG2 human hepatoma cells. Octacosadienol was as effective as policosanol in inhibiting the upregulation of HMGCoA reductase, in inducing the phosphorylation of AMPK and in downregulating the HMGCoA reductase mRNA.

Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes

Non-conventional techniques, such as microwave (MW) and power ultrasound (US) as well as combined MW/US irradiation, have been used to promote one-pot synthesis of second-generation ionic liquids (ILs), cutting down reaction times and improving yields. However, the use of chloroalkanes in the alkylation of N-heterocycles requires more drastic conditions if results are to match those obtained with more reactive alkyl halides. The present paper describes a series of MW- or MW/US-promoted IL preparations starting from chloroalkanes and classic heterocycles (1-methylimidazole, pyridine and 1-methylpyrrolidine). When reactions were carried out under conventional heating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMR analysis and ion-exchange chromatography showed that the present solventless procedure afforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated), and short reaction times showed that a straightforward access to ILs can be also achieved with the use of alkyl chlorides, resulting in a considerable reduction of costs.

Rapid purification/oxidation of multi-walled carbon nanotubes under 300 kHz-ultrasound and microwave irradiation

The use of ultrasound (US) and microwaves (MW) in the oxidation and purification of multi-walled carbon nanotubes (MWCNTs) was investigated. These techniques, in particular US at a frequency of 300 kHz, strongly accelerate the process and avoid the heavy structural damage, observed at the 20–35 kHz classic range, even at low power. Due to the residual metal catalyst on the head of MWCNTs, MW heating is strongly absorbed, causing the rupture of the tip and the loss of the metal. All our chemico-physical treatment types were performed by suspending the CNTs in a 3 ∶ 1 H2SO4/HNO3 mixture. The resulting samples were investigated by TEM microscopy, TGA analyses and Raman spectroscopy, while the degree of oxidation was estimated by colourimetric analyses.

Reticulated Pd(II)/Cu(I) cyclodextrin complexes as recyclable green catalyst for Sonogashira alkynylation

A Pd/Cu loaded polymeric cyclodextrin catalyst was easily prepared via in situ reticulation with diisocyanates under sonochemical conditions. Excellent yields were observed for Sonogashira reactions carried out in water and glycerol and the catalyst could easily be recovered and reused three times without a significant loss in catalytic activity.

Solvent-free chemoselective oxidation of thioethers and thiophenes by mechanical milling

Organosulphur compounds can be easily and selectively oxidized to sulfones using a small excess of Oxone(®) (1.6 eq.) under solventless mechanical milling conditions. This green procedure has been efficiently applied to a series of model compounds and to the desulphurization of medium/high sulphur content paraffins (up to 3000 mg kg(-1)).

Microwave-Assisted γ-Valerolactone Production for Biomass Lignin Extraction: A Cascade Protocol

The general need to slow the depletion of fossil resources and reduce carbon footprints has led to tremendous effort being invested in creating “greener” industrial processes and developing alternative means to produce fuels and synthesize platform chemicals. This work aims to design a microwave-assisted cascade process for a full biomass valorisation cycle. GVL (γ-valerolactone), a renewable green solvent, has been used in aqueous acidic solution to achieve complete biomass lignin extraction. After lignin precipitation, the levulinic acid (LA)-rich organic fraction was hydrogenated, which regenerated the starting solvent for further biomass delignification. This process does not requires a purification step because GVL plays the dual role of solvent and product, while the reagent (LA) is a product of biomass delignification. In summary, this bio-refinery approach to lignin extraction is a cascade protocol in which the solvent loss is integrated into the conversion cycle, leading to simplified methods for biomass valorisation.

A new class of cationic cyclodextrins: synthesis and chemico-physical properties

A new class of positively charged triazole-bridged β-cyclodextrin (β-CD) derivatives have been synthesized in excellent yields (over 70%) through a copper-catalyzed azide-alkyne cycloaddition (CuAAC), starting from 6I-azido-6I-deoxy-β-CD or its permethylated derivative and a series of 1-butyl-3-alkynylimidazolium salts. The regioselective azide/alkyne [3 + 2] cycloaddition was efficiently carried out using metallic copper as the catalyst, affording very clean products. Easy access to such hybrid molecules that combine the properties of CDs and ionic liquids, may pave the way to a number of new applications in analytical chemistry and catalysis.

Synthesis of 1-octacosanol and GC-C-IRMS discrimination of samples from different origin

Lately, long-chain primary alcohols have been investigated in depth on account of their biological activities. In particular, 1-octacosanol (C28H57OH), the main component of policosanol, the hypolipidaemic fatty alcohol mixture obtained from sugar cane wax, has been the subject of a multitude of pharmacological studies. The aim of this work was to search a convenient synthetic protocol for the preparation of 1-octacosanol in a gram scale. The key step was a Wittig reaction between the octadecyltriphenylphosphonium ylide and the methyl 10-oxodecanoate. Some steps were further improved by power ultrasound and microwave irradiation, either alone or in combination. Our methodology is suitable for a rapid generation of homologues by varying the chain length in the alkyl halide. Due to the high commercial value, a series of 1-octacosanol samples, either isolated from natural sources or from synthesis (different origin and suppliers), were analysed by gas chromatography-combustion-isotopic ratio mass spectrometry (GC-C-IRMS) and according to the carbon isotopic content, classified on the basis of their origin.