Finding a Good Solvent

If the solubility data for your compound are not in handbooks, then 

Place 0.1 g of your solid (weighed to O.Olg) in a test tube. 

Add 3 ml of a solvent, stopper the tube, and shake the bejesus out of it. If all of the solid dissolves at room temperature, then your solid is soluble. Do not use this solvent as a recrystallization solvent. (You must make note of this in your notebook, though). 

If none (or very little) of the solid dissolved at room temperature, unstopper the tube and heat it (Careful—no flames ) and shake it and heat it and shake it. You may have to heat the solvent to a gentle boil (Careful Solvents with low boiling points often boil away). If it does not dissolve at all, then do not use this as a recrystallization solvent. 

If the sample dissolved when HOT, and did NOT dissolve at room temperature, you re on the trail of a good recrystallization solvent. One last test. 

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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. 

To find a good solvent for a polymer, the simplest thing to do is calculate the distances of a list of well-known solvents and order them by their RED (relative energy difference), which is simply the distance divided by radius, where a value of 1 means that the solvent is right on the soluble/insoluble border. Table 7.1 shows a partial list of solvents that I regularly consider. 

Because extractive solvents work by altering the relative volatihty between the components to be distilled, a good solvent causes a substantial change in relative volatihty when present at moderate compositions. As seen from equation 3, the solvent modifies the relative volatihties by affecting the ratio of the hquid-phase activity coefficients yWhereas it is possible to find solvents which increase or decrease this ratio, it is usually preferable to select a solvent which accentuates the natural difference in vapor pressures between the components to be separated that is, a solvent that increases relative to when is favored, over one that increases relative to y. In the latter case, adding small amounts of the solvent actually makes the separation... 

Bueche (16,172) proposed that the viscosity is proportional to the fourth power of the polymer concentration and a complex function of the free volume of the mixture. Kraus and Gruver (170) find that the 3.4 power fits experimental data better than does the fourth power. They used equation (58) with (r2) replaced by the mean-square radius of gyration (s2). The term r2)/(rf) indicates that poor solvents should lower the viscosity more than a good solvent. As the temperature increases, the factor increases as a function of the ratio (T - 7 (tJJ)/(7 - 7 ). The glass transition temperatures of the polymer and diluent are andT o, respectively. 

While Diehl et al. (2001) agree that the addition of DMSO to print buffer improves spot uniformity, they argue that DMSO is also toxic and a good solvent for other materials. As a result, they explored alternative chemistries to replace DMSO and also to improve upon postprint blocking conditions in an effort to find a replacement for borate-NMP (l-methyl-2-pyrrolidinone) buffer used for preparing solutions of succinic anhydride for capping of residual amine groups. 

Levulinic acid is highly reactive and moreover is capable of assuming a lacl one form (XXXII). Valeric y-lactone (XXXIII) can be obtained in very high yield by hydrogenation of levulinic acid, and this compound is a good solvent and may well find extensive uses as such. Moreover it may be hydrogenated to 1,4-pentandiol (XXXIV),which on dehydration yields 1,3-pentadiene (piperylene) (XXXV). Piperylene is... 

Water is a good solvent for many substances. You may have noticed, however, that grease-stained clothing cannot be cleaned by water alone. Grease is one substance that does not dissolve in water. Why doesn t it dissolve In this chapter, you will find out why. You will learn how solutions form. You will explore factors that affect a substance s ability to dissolve. You will find out more about the concentration of solutions, and you will have a chance to prepare your own solutions as well. 

Find a suitable solvent by carrying out small scale tests. Remember that like dissolves like. The most commonly used solvents in order of increasing polarity are petroleum ether, toluene, chloroform, acetone, ethyl acetate, ethanol, and water. Chloroform and dichloromethane are rarely useful on their own because they are good solvents for the great... 

Equations [3.4.6U64] apply for a good solvent. It is not difficult to find analogous expressions for a theta solvent. The difference lies in the osmotic contribution in a theta solvent the linear term (1 - 2 in the excluded volume vemishes, and the quadratic term in the expansion of ln(l - 0) is now dominant. Hence, the osmotic contribution is much smaller and, consequently, the brush is expected to be denser than in a good solvent. We now write F /kT N°N9, or, with e = Na ct/H,... 

The procedure for finding the surface pressure is fully analogous to that described for a good solvent AFis found by substitution of [3.4.66] into ]3.4.60] or ]3.4.65], and x follows from 3(AF) / 9A at constant N°. The result is... 

Unaware of these old findings, the present writer rediscovered the formation of complexes of chloral hydrate with amylose, and established its optimal conditions (Table II gives the critical region of concentration of chloral hydrate). Then, knowing the properties of chloral hydrate as a good solvent for starch, the development of a laboratory fractionation process became obvious. As, to date, no information regarding this work has been published, the details will be given here. 

Sikorski and Romiszowski455 study confined branched star polymers by on-lattice MC simulation. Attractive forces are excluded and only excluded volume accounted for, thus making the simulations relevant for chains in a good solvent. Contrary to expectation, they find that the diffusion constant is very similar for either moderate or highly confined chains and scales approximately as A 1, though a more accurate representation is suggested by... 

In certain circumstances, solution calorimetry may be more appropriate than vapor sorption approaches as a tool to assess powder crystallinity for example, if there was any serious fear that the amorphous material may not be accessed by the vapors or that there are no suitable vapors to induce the crystallization response. The potential disadvantage of the solution calorimetry approach is that the responses for both the amorphous and crystalline material are measured, and therefore there is a need for a substantially different heat of solution between the two if small amounts of amorphous material are to be detected. A further difficulty with solution calorimetry is that it may not be easy to find a suitable solvent system that will achieve complete solution in a rapidly enough. Thus, solution calorimetry works as a bulk technique, and measures the response for the entire sample, whereas vapor sorption works by detecting the crystallization response for the amorphous material, with little or no interfering response from the crystalline component. This fundamental difference in approach may mean that on some occasions solution calorimetry will be the preferred option, whereas on others it would be not as good as the vapor sorption approaches. 

This finding is evidenced by Fig. 43. The anisotropic filler-loaded mPDMS sample was put into cyclohexane, which is a good solvent for PDMS. The... 

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