196,450 research outputs found
Methylphosphonium methylcarbonate, ylide precursor for halyde- and base-free Wittig reactions
No full textThe phosphonium salt triphenylmethylphosphonium methylcarbonate [PΦ,Φ,Φ,1][OCOOCH3] was obtained by methylation of triphenylphosphine (Ph3P) with dimethylcarbonate, adopting a green and sustainable procedure1.
The [PΦ,Φ,Φ,1][OCOOCH3] phosphonium salt was observed to possess significant P-CH3 proton acidity, and deuterium exchange experiments showed the formation of the analogous PhP3-CD3 phosphonium salt. Spontaneous deprotonation of the methyl group lead therefore to formation of the corresponding phosphorus ylide, Ph3P=CH2.
This Ph3P=CH2 ylide was tested for the Wittig reaction with benzaldehyde PhCHO, generating the desired PhC=CH2 olefination product. It was noteworthy that this Wittig reaction protocol did not require an alkyl halide or a strong base for the formation of the ylide, and could be conducted in air, making it a greener procedure.
The scope of the olefination reaction was extended to a number of carbonyl substrates, both aldehydes and ketones, with high conversions and selectivity. It was performed under mild conditions (34 – 80 °C), using a ratio ylide:carbonyl between 1.0 -3.0, in 2-methyl tetrahydrofuran (2-Me-THF) as solvent.
The study was also extended to other alkylphosphonium methylcarbonate ionic liquids ([P8,8,8,1][OCOOCH3] and [P4,4,4,1][OCOOCH3]). It was demonstrated that, depending on the reaction conditions, it was possible to achieve not only the transfer of a =CH2 fragment, but also the selective transfer of the bulkier alkyl group e.g. =CH(CH2)nCH3, giving access to a variety of olefins. Cis-trans selectivity was in the range 20-80
Halide- and base-free Wittig reaction: phosphonium methylcarbonate salts as ylide precursors
No full textCarbonate based ionic liquids and beyond
No full textIonic liquids appear almost like a different state of matter. Just like mercury, that I enjoyed playing with as a child after bursting thermometers. A liquid metal, and a liquid salt at room temperature are awe-inspiring, as their physical state is counterintuitive. We struggle to accept that a metal may not be hard, and that a salt may be non-crystalline, let alone liquid.
Thus, for sheer curiosity, we started synthesising ammonium and phosphonium ionic liquids. The first hurdle was to make them efficiently, colourless and pure. And this was achieved by using dimethylcarbonate (non-toxic) instead of alkyl halides as quaternarisation reagent. These syntheses were, efficient (100% atom economic), tuneable, halide-free, and produced only CO2 and methanol as by-products.1
But, ionic liquids are not just pretty. So what can we do with them?
Use them as green solvents? Sometimes yes, but often too costly, and not always an elegant or green application.
Unless we can design multiphase solvent systems with other advantages.2-3
It’s might also interesting to take advantage of the chemical properties of their ions,4 or to use them as catalysts,5-6 including for the upgrade of biogenic chemicals.7
The next question might be on how these materials work, e.g. as catalysts,8 and how can these properties be monitored.9 Or whether they can be used to make new devices, e.g. based on their luminescence.10
And why not try to make old compounds, e.g. choline, by these methods?
We will discuss this “genealogy” of applications and of examples, applied to a family of carbonate based ionic liquids.
1. Fabris, M.; Lucchini, V.; Noè, M.; Perosa, A.; Selva, M., Chem. Eur. J. 2009, 15 (45), 12273-12282.
2. Tundo, P.; Perosa, A., Chem. Soc. Rev. 2007, 36 (3), 532-550.
3. Gottardo`, M.`; Selva`, M.`; Perosa`, A. work in progress
4. Noè, M.; Perosa, A.; Selva, M.; Zambelli, L., Green Chem. 2010, 12 (9), 1654-1660.
5. Fabris, M.; Noe, M.; Perosa, A.; Selva, M.; Ballini, R., J. Org. Chem. 2012, 77 (4), 1805-1811.
6. Selva, M.; Noe, M.; Perosa, A.; Gottardo, M., Org. Biomol. Chem. 2012, 10 (32), 6569-6578.
7. Stanley`, J.`; Caretto`, A.`; Perosa`, A. work in progress
8. Lucchini, V.; Noè, M.; Selva, M.; Fabris, M.; Perosa, A., Chem. Commun. 2012, 48 (42), 5178-5180.
9. Lucchini, V.; Fabris, M.; Noe, M.; Perosa, A.; Selva, M., Int. J. Chem. Kinet. 2011, 43 (3), 154-160.
10. Fiorani`, G.; Selva, M.; Perosa`, A.`; Malba, C.; work in progress
Transesterificazione di carbonati organici con acetali del glicerolo in condizioni di flusso continuo
No full text
Non Catalytic Continuous-Flow Transesterification of Dialkyl Carbonates with Glycerol Acetals
No full textCD20-depleting therapy in autoimmune diseases: from basic research to the clinic
No full textPerosa F, Prete M, Racanelli V, Dammacco F (University of Bari Medical School, Bari, Italy). CD20-depleting therapy in autoimmune diseases: from basic research to the clinic (Review). J Intern Med 2010; 267: 260-277. The B lymphocyte-associated antigen CD20 is becoming an important immunotherapy target for autoimmune diseases, although its biological function has not been defined. Besides rheumatoid arthritis, growing experience with B cell-depleting therapy indicates that it may be effective in Sjögren's syndrome, dermatomyositis-polymyositis, systemic lupus erythematosus and some types of vasculitides. However, controlled clinical trials are still lacking for some of these indications. Infection has not been seen as a major limitation to this therapy, but reports of progressive multifocal leukoencephalopathy in an extremely small number of patients are of concern. Here, we review the therapeutic actions of anti-CD20 antibodies, and the recent and ongoing clinical trials with CD20-depleting therapy in autoimmune diseases. © 2010 Blackwell Publishing Ltd
Dimethyl carbonate as a green solvent for the synthesis of platform chemicals from renewable lignin feedstocks
No full textDimethyl carbonate was evaluated as a green methylating and transesterification reagent and solvent for the chemical-valorisation of renewable platform chemicals from lignin model compounds using a range of catalysts. Of the major components of lignocellulosic biomass (namely cellulose, hemicellulose, and lignin), chemical technologies for the conversion of lignin into higher value-added compounds are the least studied.[1] With a view to developing new chemical products from lignin, it is desirable to first study lignin model compounds. Thus, cinnamyl alcohol, 3-(4-hydroxypropyl)phenol, vanillyl alcohol, and syringic acid were chosen as representative of the p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol building blocks of lignin. Moreover, dimethyl carbonate was chosen because it is cheap, readily available, and has low toxicity, making it a good alternative to traditional methylating agents such as dimethyl sulfate and methyl halides.[2] In the present work, a range of catalysts, including K2CO3, CsF/αAl2O3, NaX, NaY and [P8881][CH3OCOO], are investigated for the methylation and transesterification of the model compounds. One approach is to form the methyl carbonate product in a first step, followed by the methylation reaction in a second step.
References
[1] J. Zakzeski, P. C. A. Bruijnincx, A. L. Jongerius, B. M. Weckhuysen, Chem. Rev. (Washington, DC, U. S.) 2010, 110, 3552-3599.
[2] M. Selva, A. Perosa, Green Chem. 2008, 10, 457-464
Tungstate ionic liquids as catalysts for CO2 fixation into epoxides
No full textHerein we describe the syntheses of a series of ammonium, phosphonium, imidazolium and diazabycicloundece- nium tungstate and peroxotungstate ionic liquids, their full spectroscopic characterisation (FT-IR, 1 H-, 1 3C-and 1 83W-NMR) and a comparison of their properties and possible applications in catalysis. The synthetic procedures to obtain the ionic liquids rely on anion exchange and acid-base reactions – including an innovative route for the synthesis of tungstate and peroxotungstate ionic liquids using, for the first time, a halide-free organic ionic liquid as precursor. The tungstate ionic liquids were used as catalysts for CO2 fixation in styrene oxide as well as in a series of other epoxides to yield the corresponding carbonates. Under optimized conditions, styrene carbonate is obtained in up to 67 % yield at 90 °C with just butylmethylimidazolium tungstate, and in 91 % yield by coupling tetrabutylammonium tungstate and bromide. Preliminary tests indicate that the same catalysts can also promote epoxidation reactions, paving the way for their use in the direct oxidative carboxylation of olefins
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