- Molecular baskets in supercritical CO2
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Calixarenes are synthetic macrocyclic compounds, described as "molecular baskets" as they possess high ionophoric selectivity and form inclusion complexes with many important ionic guests. In our initial work, hexameric and tetrameric tert-butylcalixarenes, unfunctionalized at the lower rim, are shown to be separable on a diol column using supercritical fluid chromatography with methanol/chloroform-modified CO2 as mobile phase. The variation in capacity factors for these calixarenes was studied as a function of modifier composition. However, the solubility of these molecular baskets in unmodified supercritical CO2 is enhanced by fluorination at the upper rim. For example, when p-allylcalix[4]arene is derivatized by a thiol-ene addition reaction with heptadecafluorodecanethiol, CF3(CF2)7(CH2)2SH, a solubility of >0.12 mol L-1 in supercritical CO2 is measured for the p-heptadecafluorodecylthio-n-propylcalix[4]arene at 60 °C and 200 atm. However, subsequent lower rim functionalization to form the tetrahydroxamate derivative, while reducing the solubility, allows supercritical fluid extraction of Fe(III) by the fluorinated calix[4]arene ligands to be studied as a function of temperature and pressure and monitored using UV/visible and atomic absorption spectrometry. In particular, the visible absorption spectra obtained for the extracted Fe(III)-calix[4]arene tetrahydroxamate complex, collected in dimethyl sulfoxide, are indicative of octahedral Fe(III) complexation in a manner similar to that displayed by water-soluble siderophores. Studies on the efficiency and selectivity of Fe(III) extraction are also reported.
- Glennon, Jeremy D.
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Read Online
- Exploiting Sm(ii) and Sm(iii) in SmI2-initiated reaction cascades: Application in a tag removal-cyclisation approach to spirooxindole scaffolds
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A tag removal-cyclisation sequence is described that is initiated by reduction using a Sm(ii) species and completed by a Sm(iii) Lewis acid that is formed in an earlier stage. Therefore, the reaction cascade utilises both oxidation states of a samarium reagent in discrete steps and allows access to privileged, pyrrolidinyl-spirooxindole scaffolds and analogues inspired by the anti-cancer natural product spirotryprostatin A. The Royal Society of Chemistry 2011.
- Coote, Susannah C.,Quenum, Seidjolo,Procter, David J.
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supporting information; experimental part
p. 5104 - 5108
(2011/08/07)
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- S-perfluoroalkyl substituted hydroxybenzylthioethers and derivatives as surface modifiers
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The invention describes a process for reducing the surface energy of organic materials such as for example increasing the oil and water repellency and stain release of organic materials, which comprises treating the organic material with at least a compound of the formula I wherein the general symbols are as defined in claim 1; especially wherein at least one of the radicals R2, R3 or R4 is —CH(R11)—S(O)p—R12; R11 is hydrogen, C1-C8alkyl, unsubstituted or with C1-C4alkyl substituted phenyl; R12 is a monovalent perfluorinated alkyl or alkenyl, linear or branched organic radical having four to twenty fully fluorinated carbon atoms, and p is 0, 1 or 2.
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- Synthesis of terminally perfluorinated long-chain alkanethiols, sulfides and disulfides from the corresponding halides
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Semifluorinated n-alkanethiols, symmetrical sulfides and disulfides bearing the chain(s) F(CF2)n(CH2)m with n=4, 6, 8, 10, and m=2, 11 have been prepared by various synthetic methods, starting from the corresponding iodides or bromides. Methods based on sodium hydrogen sulfide, commonly used to accomplish this conversion, treatment of the Bunte salt obtained from sodium thiosulfate, the basic hydrolysis of isothiouronium salts, the hydrolysis under mild conditions of thiophosphorates formed from sodium thiophosphate and the basic hydrolysis of thiol acetic acid derivatives, have been investigated and compared relatively to the selective synthesis of the title compounds. The thiolacetic route yields essentially the thiols with some amounts of disulfides. Results from thiourea appears similar. Sodium thiophosphate constitutes an excellent route for the synthesis of thioethers, particularly when starting from the bromides. The two classical methods based on sodium hydrogen sulfide and sodium thiosulfate exhibit poor selectivity. It has been possible to obtain all the sulfur compounds reported in the pure state.
- Naud,Calas,Blancou,Commeyras
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p. 173 - 183
(2007/10/03)
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- Free-radical addition of 2-(perfluoroalkyl)ethanethiols to alkenes, alkadienes, cycloalkenes, alkynes and vinyl monomers
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The free-radical addition of 2-(perfluoroalkyl)ethanethiols (RFCH2CH2SH) to alkenes, cycloalkenes, alkadienes and alkynes has been studied to determine: (1) the mode of reaction, i.e. the stereochemistry, regiochemistry and any skeletal changes: (2) the relative reactivity towards unsaturates of differing structures and classes as affected by the presence of the RF group; and (3) the influence of the reaction conditions on the rate of addition or selectivity for different products.Adducts from 2-(F-hexyl)ethanethiol (1) and alkenes have been obtained in high yield,but containing small amounts of regio isomers.For example compound 1 with 1-heptene gave 1-heptane (3, 96percent yield) as well as 2-heptane (4, O.61percent) and 3-heptane (5, 2.22percent). 1,6-Hexadiene and 1,7-octadiene gave chiefly linear adducts, i.e.RFCH2CH2S(CH2)nCH=CH2 (7, n=4; or 12, n=6, respectively) and RFCH2CH2S(CH2)nSCH2CH2RF (8, n=6; or 14, n=8, respectively).A small amount (2-3percent) of cis- and trans-1-methyl-cyclohexane (13) isomers were present in 12.Compound 1 with 1,6-heptadiene gave 7--1-heptene (9), the bis adduct, 1,7-bis-heptane (11) and the cyclic adducts, cis- and trans-1-methal-2-methylcyclopentane (10).The relative amounts of cyclic isomers depended on the reactant ratio.Compound 1 added readily with free-radical initiation to vinyl monomers such as styrene and vinyl acetate, and to phenyl acetylene, propargyl acetate and ethyl propynoate.These new addition products are useful as models for further study.
- Brace, Neal O.
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p. 217 - 241
(2007/10/02)
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- Reactive collisions of C6H6?+ and C6D6?+ at Self-assembled monolayer films prepared on gold from n-alkanethiols and a fluorinated alkanethiol: The influence of chain length on the reactivity of the films and the neutralization of the projectile
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Low-energy ion-surface collisions were used to probe the reactivity, electron barrier properties, and relative degree of order of self-assembled monolayer films after transfer of the films from solution to vacuum (10-7 Torr). Mass-selected polyatomic projectiles (ionized benzene, benzene-d6, and fluorobenzene) collided with self-assembled monolayer films at collision energies in the range of 20-70 eV, and the resulting ions were mass-analyzed and detected. The surfaces were prepared by the spontaneous assembly of n-alkanethiols (CH3(CH2)nSH, n = 3, 11, 17), perdeuterioeicosanethiol (CD3(CD2)19SH), and 2-(perfluorooctyl)ethanethiol (CF3(CF2)7CH2CH2SH) on both gold foil and vapor-deposited gold. Chemical reactions between the benzene molecular ion and the monolayer films (e.g., H, CH3, D, CD3, F, and CF3 additions) are evident from deuterium labeling results. Ion-surface collision spectra for ionized benzene are sensitive to (i) the chemical composition of the monolayer, (ii) the chain length of the alkanethiol used to prepare the film, (iii) the preparation of the gold surface prior to reaction (mechanically polished gold foil vs vapor-deposited gold vs plasma-cleaned vapor-deposited gold), and (iv) the exposure time between the alkanethiol solution and the gold. For comparison with our experimental results, ab initio calculations have also been carried out to predict the energetics of the loss of H and H2 from selected ion-surface reaction adducts (H, F, and CH3 addition products). Experimental data not directly available from the tandem mass spectra (i.e., total ion signals and surface currents) are used to characterize the relative degree of neutralization of the projectiles at the films. The data suggest that the relative electron barrier properties of the films in vacuum mimic those reported for electrochemistry experiments in solution. The mass spectra and the current measurements indicate that the relative degree of order of the monolayers is retained upon transfer of the films from solution to vacuum.
- Somogyi, árpád,Kane, Thomas E.,Ding, Jian-Mei,Wysocki, Vicki H.
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p. 5275 - 5283
(2007/10/02)
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- FONTIONNALISATION DES IODURES DE F-ALKYL-2 ETHANE PAR CATALYSE PAR TRANSFERT DE PHASE: IMPORTANCE DE CETTE TECHNIQUE EN SERIE F-ALKYLEE
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F-alkyl-2 ethane iodides are very important starting materials in the field of organic chemistry.Their reactivity in homogeneous medium shows some drawbacks: reactions are uncomplete and resulting compounds are not pure.We resolved these problems using phase transfer catalysis and obtained outstanding results.F-alkyl-2 ethane iodides are strongly hydrophobic; so organic solvents are not necessary (water was used) and moreover the emulsions promoted during the reaction are not stable.
- Szonyi, F.,Cambon, A.
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