Molecular sieves degassing

Phosgene [75-44-5] M 98.9, b 8.2 /756mm. Dried with Linde 4A molecular sieves, degassed and distilled under vacuum. This should be done in a closed system such as a vacuum line. HIGHLY TOXIC, should not be inhaled. If it is inhaled operator should lie still and made to breath ammonia vapour which reacts with phosgene to give urea. 

Phosgene [75-44-5] M 98.9, b 8.2 /756mm. Dried with Linde 4A molecular sieves, degassed and distilled under vacuum. HIGHLY TOXIC, should not be inhaled. 

Bromo-2-methylpropane [507-19-7] M 137.0, b 71-73 , d 1.218, n 1.429. Neutralised with K2CO3, distd, and dehydrated using molecular sieves (5A), then vacuum distd and degassed by ireeze-pump-thaw technique. Sealed under vacuum. 

Hematoporphyrin dimethyl ester (15, 1.52 g, 2.43 mmol) (diastereomeric mixture) and Af.At-dimethyl-acetamide dimethyl acetal (8 mL) were suspended in o-xylcnc (100 mL), degassed and then heated with exclusion of light in a flask equipped with a reflux condenser and a Soxhlet apparatus containing 3 A molecular sieves. The temperature was raised during 15 min from rt to 115 C and kept at this temperature for 30 min. Then the temperature was raised to 155 C and the mixture kept at this temperature for 3 h. The mixture was evaporated in a bulb tube and the residue subjected to column chromatography [silica gel (ICN), CH2Cl2/MeOAc/MeOH 10 5 0.5] with exclusion of light yield of pure 16A 305 mg (17 %) yield of pure 16B, 375 mg (20%) and 187 mg (10%) of a mixture of 16 A and B. 

Anhydrous ethyl ether purchased from Fisher Scientific Company or Mallinckrodt Chemical Works was dried over Linde type 3A molecular sieves. The checkers degassed the solvent immediately before use by evacuating and filling the container with nitrogen three times. 

Methyl 3-oxobutanoate, available from Nakaral Chemicals (the checkers used ester purchased from Aldrich Chemical Company, Inc.), Is distilled over molecular sieves 4A under argon and stored in a 200-mL Schlenk tube. It is degassed by three treeze-thaw cycles before use. 

Guaranteed grade DMF, available from NACALAI TESQUE, INC., is distilled over 4 A molecular sieves under argon before use and stored in a 100-mL Schlenk tube. It is degassed by three freeze-thaw cycles. 

The raw materials used in this study are presented in Table 1. The polyether polyol and short chain diols were degassed at 80-90°C under vacuum overnight to remove any moisture. MEK was treated with molecular sieves 4A overnight to remove any moisture prior to use. The other materials were used as received. 

Tetrakis(dimethylamine)ethylene [996-70-3] M 300.2, b 60 /lmm, d 0.861, n 1.4817. Impurities include tetramethylurea, dimethylamine, tetramethylethanediamine and tetramethyloxamide. It was washed with water while being flushed with nitrogen to remove dimethylamine, dried over molecular sieves, then passed through a silica gel column (previously activated at 400°) under nitrogen. Degassed on a vacuum line by distn from a trap at 50° to one at -70°. Finally, it was stirred over sodium-potassium alloy for several days. [Holroyd et al. JPC 89 4244 1985],... 

B. Saturated Hydrocarbons. Purging and freeze-pump-thaw methods are effective in degassing paraffins. Distillation with the elimination of the first fractions produces dry solvent. Molecular sieves may also be used to remove water. Distillation from sodium-benzophenone ketyl is highly effective in obtaining very low levels of water and oxygen. Commercial grades of hydrocarbons are often contaminated with olefins, which can be eliminated by several washings... 

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