Co-distillation

Consider co-distillation (replace one liquid with another in portionwise distillation) or azeotropic distillation... 

Co-distillation leads to long period of time under heat resulting in exceeding the isothermal aging characteristics for a thermally unstable material which leads to thermal decomposition and overpressure of the vessel. 

Consider using the same solvent in the next step (i.e. eliminate the co-distillation)... 

Has been purified by co-distillation with ethylene glycol (boils at 197.5°), from which it can be recovered by additn of water, followed by crysm from 95% EtOH, benzene, toluene, a mixture of benzene/xylene (4 1), or EtjO. It has also been chromatographed on alumina with pet ether in a dark room (to avoid photo-oxidation of adsorbed anthracene to anthraquinone). Other purification methods include sublimation in a N2 atmosphere (in some cases after refluxing with sodium), and recrystd from toluene [Gorman et al. J Am Chem Soc 107 4404 1985]. 

Dialkyltetralins (DATs) and dialkylindanes are formed as byproducts during the alkylation process and these byproducts co-distill with LAB [9]. Examples of the unsulfonated and sulfonated dialkyltetralin are shown in Fig. 4. The level of DAT in LAB will vary depending on the type of alkylation process [10,11]. Table 3 lists the composition of several types of LABs and their DAT content as determined by gas chromatography-mass spectrometry (GCMS). It is important to note that a high level of DAT is not the result of alkylation with A1C13 catalyst. As seen in Table 3, AlCl3-catalyzed LAB can have a very low DAT content. 

Si02 -I- 2 C -I- 2 CI2 > S1CI4 -F 2 CO Distillation yields SiClq of very high purity, which is then reduced with magnesium SiClq + 2 Mg Si -F 2 MgCl2... 

Methylcydopent-2-enone typically is prepared by an intramolecular Claisen-Schmidt condensation from 2,5-hexanedione. The product is usually required free from traces of starting material but these substances co-distil. Accordingly, literature methods have employed strong aqueous base in 2-3% concentration at reflux and have been continued until all of the starting material has been consumed. Under those circumstances, the product also has undergone aldol and Claisen-Schmidt condensations severely lowering the yield. 

An early CO distillation pilot plant described by Johns (in London (1961), reading list), used a two section vacuum insulated column packed with wire gauze rings. The upper section was 5.2 m long with a diameter of 3.2cm, the lower 4.6 m x 1.9 cm. The column contained about 600 plates. An intermediate boiler re-evaporated part of the downward flowing liquid at the junction. This plant accumulates product in the liquid and enriches toward the bottom. Enriched CO (0.4 g day-1 of 65% 13C and 0.05 g day-1 of 5% lsO) was withdrawn from the bottom... 

Owing to the volatility of technetium heptoxide, Tc (VII) may be co-distilled with strong acids (Fig. 3). 

However, a more detailed study of the co-distillation with sulfuric acid has revealed that technetium can be distilled quantitatively with HjS04 provided the acid and the distillation apparatus are free from contaminations. Reducing agents only inhibit distillation but display no effect on the complete separation of technetium. If, for example, bromide ions are present, distillation begins at 155 °C instead of 110 °C thus resulting in a rapid and quantitative distillation of technetium. 

Since the hydroxylamine product is readily oxidized by air to the blue nitroso compound, these manipulations should be performed rapidly to minimize exposure of the product to atmospheric oxygen. Any nitroso compound formed at this stage will co-distil with the ether and is difficult to recover. 

The color of the distillate Is pale yellow because of co-distillation of trlmethylsilyldiazomethane. Therefore, the rate of concentration is very important. If the rate of concentration Is more rapid, the yield of trlmethylsilyldiazomethane will decrease. 

Hydroxy-1-nonene was prepared by the following procedure 0.219 mol (25.0 g) of heptaldehyde (Eastman Kodak Co.), distilled prior to use, was stirred in 450 mL of anhydrous ether (Note 2) under a nitrogen atmosphere. The solution was cooled to 0 C with an ice bath and 0.260 mol (260.4 mL) of vinylmagnesium bromide (1.0 M solution in tetrahydrofuran, Aldrich Chemical Company, Inc., 1.2 equiv) was then added dropwise over a 0.5-hr period. The... 

A water bath should be used as a heat source to avoid overheating, which leads to lowered yields. This distillation should be carried out carefully to prevent loss of product by co-distillation with the ethanol. 

Tissue pulverization and extraction with acetone. Concentration and purification by sweep co-distillation and Florisil/anhydrous sodium sulfate column chromatography. Elution with 20% ether in hexane followed by hexane. Addition of internal standard. 

Kirkbride (1987) described the estimation of diazinon in human omental tissue (fatty tissue) after a fatal poisoning. In this method, the tissue was pulverized and extracted with acetone. After extract concentration and purification by sweep co-distillation and Florisil fractionation, diazinon was measured by gas chromatography (GC) with nitrogen-phosphorus detection (NPD). After another fatal diazinon poisoning, diazinon was quantified by GC/electron capture detection (ECD) and GC/flame ionization detection (FID) by Poklis et al. (1980). The diazinon in human adipose, bile, blood, brain, stomach contents, kidney, and liver was recovered by macerating the sample with acetonitrile followed by the addition of aqueous sodium sulfate and extraction into hexane. Following an adsorption chromatography clean-up, the sample was analyzed. 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

Cognate preparation. 1-Phenylethanol. Use 10.4g (11.5ml, 0.1 mol) of styrene, and carry out the oxymercuration and reduction as described above. The yield of recovered mercury is 17.5 g (87%), and traces continue to separate during the work-up procedure. Distil the final crude product under reduced pressure and collect the 1-phenylethanol at 110-115 °C/25mmHg. Towards the end of the distillation the decomposition of residual organo-mercurial compounds ensues, and co-distillation of mercury contaminates the product collect the contaminated fraction separately. The first fraction, yield 6.2 g (51%), is 92 per cent pure by g.l.c. (retention time 5.33 minutes) the impurity is mainly styrene (tR 2.16 minutes). The mercury-contaminated fraction (3.0 g, 25%) is 85 per cent pure by g.l.c. 

While HPLC grade water is commercially available, I have found it to be expensive and to have limited shelf life. The best technique for purifying water seems to be to pass it through a bed of either reverse-phase packing material or of activated charcoal, as in a Milli-Q system. Even triple distillation tends to co-distill volatile impurities unless done using a fractionation apparatus. 

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