Sublimation heat lamp

In our group we have developped an alternative method by using an infrared heat lamp which gives very efficient heat transfer and speeds up sublimation dramatically. For instance the rather involatile Group compounds Cp MC (M = Nb, Ta), which sublime at ca. 

A solution of dimethyl 3-acetyl-3-azatetracyclo[3.2.0.02-7.04 6]heptane-l,5-dicarboxylate (2, R1 = Ac R = H), formed by the photolysis (14 h 125-W Hg lamp under N2) of dimethyl 7-acetyl-7-azabicyclo-[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (1 R1 = Ac, R2 = H 1 g, 4mmol) in Et20 (400 mL) at — 40 C, was evaporated to dryness under reduced pressure. The residue (0.7 g, 2.8 mmol) was dissolved in CHC1, and the solution heated under reflux for 1 h. Evaporation of the solvent yielded the crude product which was purified by column chromatography (silica gel, C,H2C12). The yellow fractions were collected and, after removal of the solvent, the residual oil was distilled in a sublimation apparatus to give 3 (R1 = Ac R2 = H) as a yellow oil yield 0.8 g (80%) bp 50 60 C/5 x 10 4 Torr. 

Pcntacarbonyl[(methoxy)(methyl)carbene]chromium(0) (16, R1 = R2 = Me 475 mg, 1.9 mmol) and the chiral ene carbamate (see above equation) (718 mg, 3.8 mmol) in CH2Ci2 (20 mL) were placed in a Fischer Porter pressure tube and saturated with CO (3 eycles to 6.33 atm of CO) and then irradiated (450-W Conrad-Hanovia 7825 medium-pressure lamp, Pyrex well) under 6.33 atm CO overnight. The yellow-green solution was filtered through a pad of Cclitc, and the solvent evaporated. The crude mixture was placed in a sublimation apparatus and heated at 30-50°C (1 Torr) until no further Cr(CO)6 could be obtained. The residue was preabsorbed on silica gel and flash chromatographed yield 319 mg (61 %) mp 133-134"C. 

The magnesium cyclopentadienide will rapidly accumulate on the wall of the furnace tube below the furnace, and to prevent complete clogging of the tube this must be removed. We have used for this purpose a magnetically operated scraper, but the product can be sublimed or melted down with heating tape, infrared lamp, or cautiously with a flame. 

When MejGeH is irradiated by a mercury lamp with Rh(CO)2Cp- ) (5 1 ratio in benzene in a sealed evacuated tube) about 50% (MejGe)2Rh(CO)Cp- / is recovered after 5d. Workup is by chromatography on alumina and sublimation. In contrast, heating the same system at 80°C for 5d gives only about 10% yield. Here, while the thermal reaction alone might be interpreted as an oxidative addition followed by CO loss [compare Eq. (e) in 5.8.4.2.2], the photolysis probably proceeds by initially forming Rh(CO)Cp- , and this intermediate may also be formed in the thermal reaction. 

The 2 1 XeF, -AsF, complex was prepared as previo usly described. " Crystals of the compound (which is rapidly decomposed by water) were grown by sublimation under nitrogen (at —1 atm) in sealed, dry quartz X-ray capillaries, using the focused beam of a microscope lamp to heat the source material. The l.T XeF.-AsFs complex was prepared and single crystals were grown as described by Bartlett and Wechsberg. ... 

The chelates can be purified, and mixtures of the complexes can be separated by fractional sublimation and distillation. In the gas phase, in solution, and in the solid state, Tb(thd)3 emits a brilliant green fluorescence when irradiated at 3660 A. with an ultraviolet lamp. Fluorescence is also exhibited by Eu(thd)3, Dy(thd)3, and Sm(thd)3. The praseodymium complex is thermally stable in the gas phase when heated for prolonged periods of time. Vapor pressure measurements on this complex showed no increase in pressure when the sample was heated at 250° for 6 hours. Thermogravimetric analyses and discussions of trends in volatility of the rare-earth-thd chelates have been published. 

The method is based on the extraction of the fullerenes contained by the soot obtained by resistive heating (in an arc lamp) of pure graphite in an inert atmosphere. The soot containing a few per cent of C o molecules is dispersed in benzene. The fullerene dissolves giving rise to wine-red to brown colored solutions. After separation from the soot, solvent evaporation, and mild drying, dark brown to black crystalline material is obtained. Alternatively, soot with a higher content of fullerene may be obtained by sublimation. According to analysis by mass spectroscopy as well as absorption spectra (vide infra), the product contains primarily buckmisterfullerene. 

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