Azeotrope freeze drying

A total 6.5 g (1 1.55 mmol) of7-[D-a-t-butoxycarbonylamino-a-(p-hydroxyphenyl)acetamido]-3-(l,2,3-triazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid was dissolved in 175 ml (98 to 100% formic acid under anhydrous conditions. The mixture was stirred at room temperature for 2.5 hours. Part of the solution, 125 ml, was evaporated under reduced pressure to an amber oil. The oil was then azeotroped 3 times with 70 ml of toluene under reduced pressure. The residue was suspended in an 80 20 H20-CH30H solution (700 ml) and stirred for 0.5 hour until most of the solid dissolved, then filtered. The filtration was treated with 1.59 of (Darko) charcoal for about 20 minutes. The charcoal was filtered off through a Celite pad. The solution was then freeze-dried in 9 separate 100 ml round bottom flasks. The freeze-dried material weighed 2.415 g. It was recrystallized in batches of 0.200 g as described above to yield a total of 0.923 g 7-[D-a-amino-a-(p-hydroxyphenyl) acetamidol-3-(l,2,3-triazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid. NMR was consistent, indicating the presence of 0.33 mol of CH3OH. 

Before extraction, soil and sediment samples may be dried, for example, by freeze-drying — provided that volatile compounds are not to be analyzed — or by mixing with anhydrous sodium sulfate and extraction in a Soxhlet apparatus. It should, however, be noted that it has frequently been found advantageous to add low concentrations of water, and this is consistent with the finding that addition of water to dry soils inhibits sorption of PAHs (Karimi-Lotfabad et al. 1996). If wet samples are to be analyzed directly, acetonitrile, propan-2-ol, or ethanol may be employed first, and these may be valuable in promoting the chemical accessibility of substances sorbed onto components of the matrices the analyte may then be extracted into water-immiscible solvents and the water phase discarded. Alternatively, if the analyte is sufficiently soluble in, for example, benzene, the water may be removed azeotropically in a Dean Stark apparatus and the analyte then extracted with the dry solvent. Analytes may, however, be entrapped in micropores in the soil matrix so that, for example, recovery of even the volatile 1,2-dibromoethane required extraction with methanol at 75°C for 24 h (Sawhney et al. 1988). 

The types of distillation processes to be examined will be simple, fractional, steam, immiscible solvent, azeotropic, extractive, vacuum, molecular, entrainer sublimation, and freeze drying. 

I, azeotropic removal (e g., rotary evaporation), 2, freeze-drying 3, desalting proceedure (see Subheading 2.4.3.)... 

Luan et al. [14] dried BaTiOs precipitate in three different ways direct oven drying, azeotropic distillation drying, and tert-butyl alcohol-replacement freeze-drying. Their results showed that the solvent-replacement freeze-dried nanoparticle s size is approximately 30 nm, and... 

The acetal (b 82.5°) is removed during fractional distn. Traces of benzene, if present, can be removed as the benzene/MeOH azeotrope by distn in the presence of MeOH. Distn from LiAlHa removes aldehydes, peroxides and water. Dioxane can be dried using Linde type 4X molecular sieves. Other purification procedures include distn from excess C2H5MgBr, refluxing with Pb02 to remove peroxides, fractional crystn by partial freezing and the addition of KI to dioxane acidified with aq HCl. Dioxane should be stored out of contact with air, preferably under N2. 

Dried, either by azeotropic removal of water with benzene or toluene, or by stirring 20g of P2O5 with 500ml of the acid at 100° for 0.5h. Then distd under vacuum and fractionally crystd by partial freezing. Sulphuric acid, if present, can be removed by prior addition of Ba(OH)2 to a dilute soln, filtering off the BaSQ4 and concentrating under reduced pressure, and is sufficiently pure for most applications. 

Refluxing with acetic anhydride in the presence of 0.2g % of 2-naphthalenesulfonic acid as catalyst has also been used [Orton and Bradfield J Chem Soc 983 1927]. Other suitable drying agents include CUSO4 and chromium triacetate P2O5 converts some acetic acid to the anhydride. Azeotropic removal of water by distn with thiophene-free benzene or with butyl acetate has been used [Birdwhistell and Griswold 7 Am Chem Soc 77 873 7955]. An alternative purification uses fractional freezing. 

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