Approach toward the total synthesis of griseoviridin: formation of thioethynyl and thiovinyl ether-containing nine-membered lactones through a thioalkynylation-macrolactonization-hydrostannylation sequence

Synthesis of the lactone core 17 of 8-epi-griseoviridin is reported. Thioethynyl derivative 11 was easily prepared via an anionic coupling reaction between acetylenic compound 9 and sulfone 10. After desilylation of 11, saponification of the resulting hydroxy ester 12 followed by a Mitsunobu macrolactonization furnished the unusual triple-bond-containing nine-membered lactone 13 in 50% yield for the last two steps (39% after recrystallization). Stannylation under Magriotis conditions led to the pure regio- and stereocontrolled vinyltin 14 (80% yield). After a Sn/I exchange, palladium-catalyzed carbonylation delivered either the ester lactone 16 in 67% yield or the propargyl amide 17 in 65% yield. Synthesis of propargyl amide 17 of the lactone core of 8-epi-griseoviridin was achieved in 11.9% overall yield from commercial L-cystin dimethyl ester (nine steps).     

Materials analysis using confocal Raman microscopy

The recent development of Raman microscopes with high optical throughput and very sensitive CCD cameras has led to Raman spectroscopy again competing effectively with FTIR methods for materials analysis. Modern Raman instruments, designed to operate confocally without serious alignment or energy trade-off problems, allow depth profiling of optically transparent polymers and polymer matrices to be routinely obtained with a spatial resolution of 1–2 μm. The use of such an instrument is illustrated by describing recent work on polymeric material problems including, 1 The distribution and redistribution of small molecules in polymeric matrices. 2 The monitoring of adhesion primer diffusion at a polymer/silica interface. 3 The determination of the extent of interdiffusion and interaction at a polymer/polymer interface. 4 A comparison of confocal and micotoming approaches to polymer laminate analysis. The range of possible applications is increasing rapidly. It is clear that Raman microscopy will become a very important tool for future materials analysis, both in the polymer area and many other areas.     

Microstructures and structural properties of sol-gel silica foams

Silica xerogels were synthesized and annealed at 1000 degrees C for different durations to yield stable silica materials. The samples were prepared through base-catalyzed hydrolysis and condensation of tetramethyl orthosilicate in methanol. After aging and drying steps, clear and solid xerogels exhibiting a narrow pore size distribution were achieved. The annealing treatment of these xerogels was performed at 1000 degrees C and proved in the present study to lead to a monolithic glass when a progressive heat-treatment procedure was employed to attain 1000 degrees C. In addition to the expected glass, silica foams and ordered phases were observed when the samples were instantaneously heat-treated at 1000 degrees C. Raman spectra of the foamed materials exhibit the classical features of amorphous silica, whereas transmission electronic microscopy pictures reveal the presence of crystallized domains within the vitreous matrix. These crystallites are prone to nucleation and growth processes, which jeopardize the believed stability of the silica foam. The assessment of the hydroxyl content by IR spectroscopy reveals the role played by the latter polycondensation of silanols. The occurrence of foaming process was thus found to result from two competitive phenomena occurring at 1000 degrees C: evacuation of water-related species and viscous sintering.     

Ultrasonic sludge pretreatment under pressure

The objective of this work was to optimize the ultrasound (US) pretreatment of sludge. Three types of sewage sludge were examined: mixed, secondary and secondary after partial methanisation (“digested” sludge). Thereby, several main process parameters were varied separately or simultaneously: stirrer speed, total solid content of sludge (TS), thermal operating conditions (adiabatic vs. isothermal), ultrasonic power input (P_US), specific energy input (ES), and for the first time external pressure. This parametric study was mainly performed for the mixed sludge. Five different TS concentrations of sludge (12–36 g/L) were tested for different values of ES (7000–75,000 kJ/kg_TS) and 28 g/L was found as the optimum value according to the solubilized chemical oxygen demand in the liquid phase (SCOD). P_US of 75–150 W was investigated under controlled temperature and the “high power input – short duration” procedure was the most effective at a given ES. The temperature increase in adiabatic US application significantly improved SCOD compared to isothermal conditions. With P_US of 150 W, the effect of external pressure was investigated in the range of 1–16 bar under isothermal and adiabatic conditions for two types of sludge: an optimum pressure of about 2 bar was found regardless of temperature conditions and ES values. Under isothermal conditions, the resulting improvement of sludge disintegration efficacy as compared to atmospheric pressure was by 22–67% and 26–37% for mixed and secondary sludge, respectively. Besides, mean particle diameter (D[4,3]) of the three sludge types decreased respectively from 408, 117, and 110 μm to about 94–97, 37–42, and 36–40 μm regardless of sonication conditions, and the size reduction process was much faster than COD extraction.