Solvents for crystallization

There is a very important point to stress about the above procedure. Strike listed ether, DCM and ethanol as crystallization solvents. But the one chemists should use is DCM. That s right...DCM Strike is telling all of you right now that DCM is an absolutely superior solvent for crystallization. In fact it is so good that one need not purify the freebases acquired from the ends of half of the recipes in this book. 

The checkers found that a mixture of diehloromethane and ether was a more suitable solvent for crystallization of the product. The pure sample obtained from this solvent system melts at 108-109°. 

Compoimd R Molecular formula Yield (%) M.P.(C) Solvent for crystallization... 

In some mixture design problems (such as formulations), it may not be necessary to consider processing issues and hence we would not have the process model constraints. In this case the problem becomes a simple mixing problem, which would already have been addressed by the miscibility criteria in sub-problem 4M. Hence, for these problems, we will not need sub-problem 5M. Also in some cases we might have to identify a mixture whose constituents perform different functions such as solvents and anti solvents for crystallization. In such cases we would have to formulate and solve more than one single compound design problems to identify the constituents and then solve the final two sub-problems to identify the optimal mixture. In certain cases we may not have process model constraints, however, we may still have to solve an optimization problem with other constraints, in sub-problem 4 and sub-problem 5m respectively. 

McCrone (1957) has described techniques for carrying out crystallization on a microscope slide. Another useful technique, also due to McCrone (1984), can be used to screen a variety of potential solvents for crystallizing on a very small (i.e. one crystal) sample. It is shown and described in Fig. 4.8. 

Fig. 4.8 Arrangement for surveying a variety of potential solvents for crystallization. A single small crystal is placed on a microscope cover slip. (It may be helpful to mark the location of the crystal by circling it with a felt tipped pen.) The cover slip is then inverted on a short ( 4-6 mm) piece of Tygon tubing mounted on a microscope slide. A few drops of a trial solvent are placed on the side around the periphery of the tubing. They will seep into the space inside the tubing and evaporate, filling it with vapours that may or may not dissolve the crystal. Recrystallization of the sample may be followed on the microscope, and the same sample may be reused many times without loss of material, a Cover slip with crystal in a marked circle, b Microscope slide with a slice of tubing and the coverslip with the crystal (whose size has been exaggerated for clarity).

The rearrangement products derived from aromatic and non-aromatic heterocyclic amines crystallize readily from the lower alcohols. Unlike those of many of the A-substituted glycosylamines, the crystals are not solvated. On the other hand, the ketose derivatives of aralkyl- and alkyl-amines, such as 2-phenylethylamine, ethanolamine, diethanolamine, glycine ethyl ester, and phenylalanine (see Table II), are hydrated or alcoholated, or both, and are difficult to isolate in pure crystalline form. The crystals which have been isolated were hygroscopic. Alcohols, aqueous alcohols, and water are the most commonly used solvents for crystallization. Acetone, ether, or benzene have been added to the alcoholic media in order to increase the yield of crystalline compound. The use of solvents that contain peroxides promotes decomposition of the crystals during storage. ... 

Picking a Solvent. To pick a solvent for crystallization, put a few crystals of the impure solute in a small test tube or centrifuge tube and add a very small drop of the solvent. Allow it to flow down the side of the tube and onto the crystals. If the crystals dissolve instantly at room temperature, that solvent cannot be used for crystallization because too much of the solute will remain in solution at low temperatures. If the crystals do not dissolve at room temperature, warm the tube on the hot sand bath and observe the crystals. If they do not go into solution, add a drop more solvent. If the crystals go into solution at the boiling point of the solvent and then crystallize when the tube is cooled, you have found a good crystallization solvent. If not, remove the solvent by evaporation and try another solvent. In this trial-and-error process it is easiest to try low-boiling solvents first, because they can be removed most easily. Occasionally no single satisfactory solvent can be found, so mixed solvents, or solvent pairs, are used. 

Dimethyl sulfoxide (DMSO) Methyl sulfoxide (CH3SOCH3) 189 Also not a commonly used solvent for crystallization, but used for reactions. 

C,is5.7 g. This material is satisfactory for use in Chapter 35 (1.5 g required). A good solvent for crystallization of the remainder of the product is methylcyclohexane (bp lOrC, 10 mL per g use more if the solution requires filtration). Pure , -l,4-diphenyl-l,3-butadiene melts at 153°C. 

Table 3. Examples of High Temperature Solvents for Crystal Growth of Ceramic Materials ...

Use Solvent for plastics, resins, gums and electrolytes intermediate catalyst paint remover high purity solvent for crystallization and purification. 

However, the preparation of an appropriate crystal can prove to be more difficult than the spectroscopy itself. Naturally, sugars are typically a highly crystalline family. But in order to purify them, contemporary chemists would sooner rely on the more systematic and powerful chromatographic methods than on the uncertain search for the ideal solvent for crystallization. There is also a more fundamental problem in that a conformation in the crystal may not be the... 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of NOx NFPA Health 2, Flammability 2, Reactivity 0 Uses Solvent for plastics (vinyl, acrylic, cellulose, polyimide processing), resins, gums, fibers, coatings, adhesives, electrolytes, pharmaceuticals selective solvent for butadiene extraction reagent intermediate catalyst paint remover high-purity solvent for crystallization and purification reaction medium for prod, of pharmaceuticals, plasticizers... 

In Experiments 3A and 3B, and in most of the experiments in this textbook, you are told what solvent to use for the crystallization procedure. Some of the factors involved in selecting a crystallization solvent for sulfanilamide are discussed in Technique 11, Section 11.5. The most important consideration is the shape of the solubility curve for the solubility vs. temperature data. As can be seen in Technique 11, Figure 11.2, the solubility curve for sulfanilamide in 95% ethyl alcohol indicates that ethyl alcohol is an ideal solvent for crystallizing sulfanilamide. 

In Experiment 3C you will be given an impure sample of the organic compound fluorene (see structure that follows). You will use an experimental procedure for determining which one of three possible solvents is the most appropriate. The three solvents will illustrate three very different solubility behaviors One of the solvents will be an appropriate solvent for crystallizing fluorene. In a second solvent, fluorene will be highly soluble, even at room temperature. Fluorene will be relatively insoluble in the third solvent, even at the boiling point of the solvent. Your task will be to find the appropriate solvent for crystallization and then perform a crystallization on this sample. 

In this experiment you will be given an impure sample of fluorene. Your goal will be to find a good solvent for crystallizing the sample. You should try water, methyl alcohol, and toluene. After you have determined which is the best solvent, crystallize the remaining material. Finally, determine the melting point of the purified compound and of the impure sample. 

Consider the three solvents ether, water, and toluene. (Look up their structures if you are unsure. Remember that ether is also called diethyl ether.) Based on your knowledge of polarity and solubility behavior, make your predictions. It should be clear that naphthalene is insoluble in water because naphthalene is a hydrocarbon that is nonpolar and water is very polar. Both toluene and ether are relatively nonpolar, so naphthalene is most likely soluble in both of them. One would expect naphthalene to be more soluble in toluene because both naphthalene and toluene are hydrocarbons. In addition, they both contain benzene rings, which means that their structures are very similar. Therefore, according to the solubility rule "Like dissolves like," one would predict that naphthalene is very soluble in toluene. Perhaps it is too soluble in toluene to be a good crystallizing solvent. If so, then ether would be the best solvent for crystallizing naphthalene. 

Purify Compound 1 by crystallization. See "Testing Solvents for Crystallization," Technique 11, Section 11.6, for instructions on how to determine an appropriate solvent. You should try 95% ethanol and xylene. After determining the best solvent, crystallize the compound using a hot water bath at about 70°C for heating to avoid melting the solid. Identify Compound 1 using some or all of the techniques given next in the section "Identification of Compounds."... 

In most cases, however, the handbooks will state only whether a compound is soluble or not in a given solvent, usually at room temperature. Determining a good solvent for crystallization from this information can be somewhat difficult. The solvent in which the compound is soluble may or may not be an appropriate solvent for crystallization. Sometimes, the compound may be too soluble in the solvent at all temperatures, and you would recover little of your product if this solvent were used for crystallization. It is possible that an appropriate solvent would be the one in which the compound is nearly insoluble at room temperature because the solu-bility-vs.- temperature curve is steep. Although the solubility information may give you some ideas about what solvents to try, you will most likely need to determine a good crystallizing solvent by experimentation as described in Section 11.6. 

Surface layer-MALDI-MS has been developed specifically to identify proteins adsorbed onto biomaterial surfaces. Although the experimental approach for this technique is analogous to traditional MALDI-ToF MS, surface layer-MALDI-MS does not require protein isolation from the biomaterial surface, because the protein-adsorbed surface is submerged directly in a matrix solvent for crystallization (Griesser et al., 2004). For example, surface-MALDI-MS can be used to identify which proteins from blood plasma adsorb onto a biomaterial surface directly off the original material surface, such as polyurethane, as shown in Fig. 5.14 (Oleschuk et al., 2000). The acquired spectra show clear peaks, indicating different proteins with a distinct mass. Each of these proteins can be identified by comparing the experimentally determined masses with those in the literature. 

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