78 research outputs found
Obituary: Arthur Cruickshank 1932 - 2011. A native Gondwanan, who studied the former continent's fossil tetrapods
Dr Arthur Richard Ivor Cruickshank died
on 4th December 2011, aged 79, in the
Borders General Hospital, Melrose, Scotland.
Arthur Cruickshank was part of the post-war
generation of palaeontologists who laid the
foundations on which today’s researchers
build. Appropriately for someone from
an expatriate Scots family living in Kenya,
much of his work was on the extinct reptiles
of the great southern palaeocontinent of
Gondwana
Obituary: Arthur Cruickshank 1932 – 2011. A native of Gondwanaland, who studied the former continent’s fossil tetrapods
Ionic Liquids Made with Dimethylcarbonate: Solvents as well as Boosted Basic Catalysts for the Michael Reaction
Abstract: This article describes 1) a methodology for the green synthesis of a class of methylammonium and methylphosphonium ionic liquids (ILs), 2) how to tune their acid–base properties by anion exchange, 3) complete neat-phase NMR spectroscopic characterisation of these materials and 4) their application as active organocatalysts for base-promoted carbon– carbon bond-forming reactions. Methylation of tertiary amines or phosphines with dimethyl carbonate leads to the formation of the halogen-free methyl-onium methyl carbonate salts, and these can be easily anion-exchanged to yield a range of derivatives with different melting points, solubility, acid–base properties, stability and viscosity. Treatment with water, in particular, yields bicarbonate-exchanged liquid onium salts. These proved strongly basic, enough to efficiently catalyse the Michael reaction; experiments suggest that in these systems the bicarbonate basicity is boosted by two orders of magnitude with respect to inorganic bicarbonate salts. These basic ionic liquids used in catalytic amounts are better even than traditional strong organic bases. The present work also introduces neat NMR spectroscopy of the ionic liquids as a probe for solute– solvent interactions as well as a tool for characterisation. Our studies show that high catalytic efficacy of functional ionic liquids can be achieved by integrating their green synthesis, along with a fine-tuning of their structure. Demonstrating that ionic liquid solvents can be made by a truly green procedure, and that their properties and reactivity can be tailored to the point of bridging the gap between their use as solvents and as catalysts. Keywords: dimethyl carbonate · green chemistry · ionic liquids · Michael addition · NMR spectroscop
The tail of the Jurassic fish Leedsichthys problematicus (Osteichthyes: Actinopterygii) collected by Alfred Nicholson Leeds - an example of the importance of historical records in palaeontology
The specimen of the tail of <i>Leedsichthys problematicus</i>, now in The Natural History Museum, London, was one of the most spectacular fossil vertebrates from the Oxford Clay Formation of Peterborough, but as an isolated find it shares no bones in common with the holotype of the genus and species. However, a letter from Alfred Nicholson Leeds and related documents cast valuable new light on the excavation of the tail, indicating that it was discovered with cranial bones, gill-rakers, and two pectoral fins, thereby including elements that can potentially be compared with those of the holotype. The documents also clearly indicate that The Natural History Museum's specimen is not part of the same individual as any other numbered specimen of <i>Leedsichthys</i> as had been speculated on other occasions. The maximum size of the animal represented by The Natural History Museum's specimen was possibly around 9 metres, considerably less than previous estimates of up to 27.6 metres for <i>Leedsichthys</i>. Historical documentary evidence should therefore be rigorously checked both when studying historical specimens in science, and in preparing text for museum display labels
Sintesi pulite all’Università Ca’ Foscari Venezia: recenti attività di GOST (Green Organic Synthesis Team)
Methylcarbonate and Bicarbonate Phosphonium Salts as Catalysts for the Nitroaldol (Henry) Reaction
Phosphonium ionic liquids exchanged with bicarbonate and methylcarbonate anions (CILs) exhibit catalytic performances comparable to those of sterically hindered (non nucleophilic) organosuperbases such as DBU. At 25–50 °C, under solventless conditions, CILs efficiently catalyze the Henry addition of different aldehydes and ketones to nitroalkanes: not only they allow the selective formation of nitroaldols but they unlock a novel high-yielding access to dinitromethyl derivatives of ketones
Cooperative nucleophilic-electrophilic organocatalysis by ionic liquids
The anionic and the cationic partners of ionic liquids may act
cooperatively and independently as nucleophilic and electrophilic catalysts. This ambiphilic propensity was demonstrated by kinetically
discriminating the contributions of the anion (nucleophilic catalyst)
and of the cation (electrophilic catalyst) to the solvent-free Baylis–Hillman dimerization of cyclohexenone catalysed by ionic liquids
Functional Ionic Liquids Made with Dimethylcarbonate: Bicarbonate Turned into a Strong Enough Base to Catalyse Michael Reactions
Phosphonium ionic liquids (PILs) as organocatalysts for green reactions: nucleophilic electrophilic cooperative catalysis
With the aim of developing a green synthesis of phosphonium ionic liquids (PILs), we prepared a series of methyltrialkylphosphonium methyl carbonates [Pn,n,n,1]+[O(CO)OCH3]- by the alkylation of trialkylphosphines with the non toxic dimethylcarbonate. These compounds proved to be active organocatalysts for a number of base-promoted organic reactions such as Michael, Henry, and Baylis-Hillman condensations, and transesterification reactions. In addition methyl carbonate salts were a convenient starting material 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. Mechanistic studies indicated that the anionic and the cationic partners of such ionic liquids acted cooperatively and independently as nucleophilic and electrophilic catalysts. The ambiphilic propensity of these 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
Rivestimenti epossidici fotopolimerizzati derivati da oli vegetali = UV-cured epoxy coatings from vegetable oils
This study presents the characterization of innovative epoxy coatings derived from vegetable oils. They are photopolymerized materials derived from epoxidized grape seed oils or epoxidized rose hip seed oils. A complete characterization of the coatings was performed, both to study chemico-physical properties such as contact angle and glass transition temperature, and to investigate their corrosion protection effectiveness. The coatings were deposited on mild steel substrates and then characterized by means of Electrochemical Impedance Spectroscopy (EIS) in order to analyse their barrier properties. A good protection effectiveness was found, specifically for the coatings characterized by a higher crosslinking density. Thus, results show the possibility to optimize the barrier properties of these bio-based materials by means of a proper choice of the precursor oils
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