Highly stereoselective coordination polymerization of β‐myrcene from a lanthanide‐based catalyst: Access to bio‐sourced elastomers

Polymerization of β‐myrcene with neodymium borohydride‐based coordination catalysts is very efficient, affording poly‐β‐myrcene (polymyrcene, PMy) with high selectivity. With stoichiometric amounts of n‐butylethyl magnesium (BEM) as co‐catalyst, good control over macromolecular data along with cis‐stereoselectivity up to 98.5%, are obtained. In the presence of excess BEM, high level of transfer reactions efficiency between neodymium and magnesium is clearly evidenced whereas the selectivity switches to 3,4‐rich. Combining the neodymium pre‐catalyst with triisobutyl aluminum in the presence of a boron activator affords PMy in good yield, but the polymer material displays low solubility, likely due to the occurrence of crosslinking. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Extraction of essential oils from Algerian myrtle leaves using instant controlled pressure drop technology

In the present work, the new extraction process of Détente Instantanée Contrôlée DIC (French, for instant controlled pressure drop) was studied, developed, quantitatively and qualitatively compared to the conventional hydrodistillation method for the extraction of essential oils from Algerian myrtle leaves. DIC was used as a thermomechanical treatment, DIC subjecting the product to a high-pressure saturated steam. The DIC cycle ends with an abrupt pressure drop towards vacuum, and this instantly leads to an autovaporization of myrtle volatile compounds. An immediate condensation in the vacuum tank produced a micro-emulsion of water and essential oils. Thus, an ultra-rapid cooling of residual leaves occurred, precluding any thermal degradation. An experimental protocol was designed with 3 independent variables: saturated steam pressure between 0.1 and 0.6 MPa, resulting in a temperature between 100 and 160 °C, a total thermal processing time between 19 and 221 s, and between 2 and 6 DIC cycles. The essential oils yield was defined as the main dependent variable. This direct extraction gave high yields and high quality essential oil, as revealed by composition and antioxidant activity (results not shown). After this treatment, the myrtle leaves were recovered and hydrodistilled in order to quantify the essential oil content in residual DIC-treated samples. Scanning electron microscope (SEM) showed some modification of the structure with a slight destruction of cell walls after DIC treatment.     

Synthesis of Cyclic Phosphates in Hot,Concentrated Phosphoric Acid

The synthesis of transition metal phosphates in hot, concentrated phosphoric acid medium leads to highly crystalline materials and to increased condensation of the phosphate at higher temperatures. Aluminum extraction from the porcelain crucible is also observed in some circumstances. Two new compounds were produced: (Al_3.28Cr_0.72)(P₄O₁₂)₃ a = 13.512(8) Å, cubic, I-43d, V = 2470(3) ų, Z = 6, density = 2.887 mg/m³, R = 0.055, GOF = 1.29 for 254 data points, was prepared at 748 K whereas (Al_1.97Cr_1.03)P₉O₂₇ a = b = 11.170(6), c = 9.412(9) Å, trigonal P – 3c1, V = 1017(1) ų, Z = 2, density = 2.669 mg/m³, R = 0.0581, GOF = 0.87 for 676 data points, was produced at 798 K from the heating of Cr₂O₃ in H₃PO₄ in a porcelain crucible. Crystal structures of both materials show mixed metal sites containing Al and Cr.     

Solventless lactam synthesis by intramolecular cyclizations of alpha-iminoester derivatives under microwave irradiation

We have previously reported a new synthesis of amides from esters and amines under microwave irradiation, offering much higher yields than those achieved with conventional heating [1]. We have now extended these studies to the ring closure of neat iminoesters I2, I3 and I4-I6 to give five- and six-membered ring lactams L5, L6 and larger lactams L7-L9 (where I means imine and L means lactam), respectively, under both classical heating conditions and microwave irradiation.     

1,3‐Dipolar Cycloadditions of Aldehydes or Imines with Carbonyl Ylides Generated from Epoxides: Classical Heating and Microwave Irradiation

Abstract

Cycloadditions of aldehydes with carbonyl ylides to give dioxolanes have been carried out without solvent under microwave irradiation. The reactions proceeded in similar yields and stereoselectivities, but in shorter reaction times, than those obtained in toluene at reflux using an oil bath. Cycloadditions conducted between imines and carbonyl ylides using the same protocol were less efficient because the oxazolidines formed proved unstable under the reaction conditions.     

Semi-empirical correlation of solid solute solubility in supercritical carbon dioxide: Comparative study and proposition of a novel density-based model

A comprehensive data set on experimental solubility of 210 solid solutes in supercritical CO₂ counting 5550 data points has been used for comparison of the correlation performance of 21 empirical models. On the basis of the comparison results a new eight-parameter density-based model has been proposed. The comparison shows that the three-parameter models are the least accurate. The results also show that models that relate the logarithm of the solubility to the logarithm of solvent density and temperature are more accurate than models that include the pressure. When comparing the overall correlating performance in terms of average absolute relative deviation the proposed model is by far the best with an average absolute relative deviation lying in the range 0.17–81.99% and an average value of 8.88%.     

Diméthyl 3-benzyl-2-(4-méthyl-2,5-dioxoimidazolidin-1-yl)butanedioate

There are two symmetry-independent formula units of the title compound, dimethyl 3-benzyl-2-(4-methyl-2,5-di­oxo­imid­azol­idin-1-yl)­butane­dioate, C₁₇H₂₀N₂O₆, per cell. The two symmetry-independent molecules differ in their configuration and are diastereomers. This structural study confirms a new side reaction during the synthesis of seven-membered cyclopeptides. The stereochemistry of both diastereomers has been established.     

Lanthanides benzimidinates: initiators or real catalysts for the ε‐caprolactone polymerization

Lanthanides (samarium and ytterbium) tris and monobenzimidinates are efficient for the polymerization of ε‐caprolactone, the systems remaining active after consumption of the monomer. Nevertheless it is not a living polymerization because the benzimidinates are recovered. Evidence for support of the proposed catalytic cycle was obtained by NMR studies.