Typical Drying Agents

Anhydrous calcium chloride tends to form alcohols of crystallization, so you really can t use it to dry alcohols. 

Anhydrous magnesium sulfate. In my opinion, anh. MgS04 is about the best all-around drying agent. It has a drawback, though. Since it is a fine powder, lots of your product can become trapped on the surface. This is not the same as water of crystallization. The product is only on the surface, not inside the crystal structure, and you may wash your product off. 

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The feed preparation differs from that for sulfuric acid by the inclusion of a hydrocarbon feed dryer. Due to the very corrosive nature of hydrofluoric acid-water mixtures, a feed dryer is necessary to prevent water from entering the system. Activated alumina is a typical drying agent used in this service. 

Typical Drying Agents Using a Drying Agent... 

After drying or decomposing a sample, it should be cooled to room temperature in a desiccator to avoid the readsorption of moisture. A desiccator (Figure 2.9) is a closed container that isolates the sample from the atmosphere. A drying agent, called a desiccant, is placed in the bottom of the container. Typical desiccants include calcium chloride and silica gel. A perforated plate sits above the desiccant, providing a shelf for storing samples. Some desiccators are equipped with stopcocks that allow them to be evacuated. 

An appropriate number, type, and size of hand-held fire extinguishers should be provided throughout the building to handle ordinary combustibles and electrical fires in the control room and related areas. Typically, clean agent or carbon dioxide fire extinguishers should be provided for electrical and electronic equipment. Dry chemical extinguishers should be avoided because of equipment contamination with powder. For use on ordinary combustible fires in the associated areas water or multipurpose dry chemical fire extinguishers should be provided. 

The gas stream containing sulfur dioxide is either dried before passing to the catalytic oxidation step, or is oxidized in the presence of water vapor with subsequent acid condensation and removal. When acid is produced from elemental sulfur, the air used for sulfur burning is predried. In all cases, typical plant designs use sulfuric acid from the process as a drying agent. Wet catalytic oxidation is relatively uncommon. Some applications of Haldor Topsme s WSA-2 wet gas catalysis process are described in the literature (97). 

Collect the organic phase and add a drying agent, typically magnesium or sodium sulfate. 

Table 6.2 lists the ultraviolet cutoff for a variety of solvents commonly used in UV-VIS spectroscopy. The solvent chosen must dissolve the sample, yet be relatively transparent in the spectral region of interest. Typically, very low concentrations of sample will be present in the solvent. It is therefore important to avoid solvents that have even weak absorptions near the solute s bands of interest. Methanol and ethanol are two of the most commonly used solvents. Care must be exercised when using the latter that no benzene (an azeotropic drying agent) is present as this will alter the solvent s transparency. Normally, this will not be a problem in spectral grade solvents. 

In most cases purification of a solvent simply involves drying and distilling it, so the next sections are devoted to drying agents and methods used for drying common solvents, and the final section contains descriptions of typical continuous stills. Apart from water the only other commonly encountered contaminant is peroxidic material formed by aerial oxidation of ethereal solvents. Methods for dealing with these dangerous impurities are described in the section on the purification of diethyl ether. 

Water can get into your reaction by condensation from the atmosphere or by condensation of the steam produced in a water bath. To exclude water, you should fit a guard tube containing a solid drying agent such as anhydrous calcium chloride or calcium sulphate to the top of the condenser, A typical guard tube is shown in Fig. 16.4 use a coarse-sized drying agent rather than a fine powder, which would cake very quickly as it absorbs moisture. 

Figure 2-8 (a) Components of a typical desiccator. The base contains a chemical drying agent, which... 

BTF has unique properties that encourage its consideration as a solvent for synthetic chemistry. BTF (bp 102°C) forms an azeotrope (bp 80 °C, 90% BTF) with water which can be used to drive dehydration reactions [30]. Since BTF is heavier than water, a reverse Dean-Stark trap must be used. Commercial BTF (distilled) contains less than 50 ppm water, and this low water content suggests that commercial BTF could be used directly for many applications. The use of phosphorus pentoxide as drying agent is also recommended [31], but we found that over time, decomposition of BTF took place, resulting in black precipitation. We instead typically dried BTF over anhydrous potassium carbonate followed by distillation however, we have not measured the water content of the BTF before and after drying so the effectiveness of this procedure is not known. 

The protective effect of the surfactant can be compromised by lyophilization [48], It has been found that, to prevent an increase in particle size, the lipid content of the SLN dispersion should not exceed 5%. Direct contact of lipid particles is decreased in diluted samples. Furthermore, diluted SLN dispersions will also have higher sublimation velocities and a higher specific surface area [49], The addition of cryoprotectors will be necessary to decrease SLN aggregation and to obtain a better redispersion of the dry product. Typical cryoprotective agents are sorbitol, mannose, trehalose, glucose, and polyvinylpyrrolidone. 

Formation of N,A -dialkylhydrazones from ketones and aldehydes is generally a facile reaction. In the case of most aldehydes, all that is required is stirring of the unsymmetrical A/,fV-dialkylhydrazine with the aldehyde in the presence of a drying agent. In some cases, these reactions can be carried out at room temperature. Ketones react similarly but can require more vigorous conditions. In the case of less-reactive carbonyl substrates, acid catalysts like p-toluenesulfonic acid or azeotropic distillation are commonly used to promote hydrazone formation. Formation of the aldehyde and ketone dimethylhydrazones and of the chiral hydrazone in equations (l)- 4) are examples of typical procedures. Monosubstituted hydrazones such as (6) are prepared in a similar manner (equation 5). These reactions often proceed in near-quantitative yield. 

Typical solvents in Soxhlet extraction of PBBs, PBDEs, PBDFs, and PBDDs from soil, sediment, and sewage sludge samples have been hexane, toluene, and hexane acetone mixtures. 17,68,69 rpjjg extraction time has varied from 4 to 24 h. Before the extraction, the sample usually is mixed with anhydrous sodium sulphate or other drying agent. 

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