The Effect of Polarity on Solubility

As was emphasized in Chapter 20, whether a molecule is polar or nonpolar is one of the most important properties of a molecule. You have probably heard the saying Oil and water don t mix. That is because oil is nonpolar and water is polar. Chemists have a saying that like dissolves Uke. That is, polar substances tend to be soluble in other polar 

Like dissolves like. Polar substances tend to be soluble in other polar substances nonpolar substances tend to be soluble in other nonpolar substances. Polar and nonpolar substances, however, tend not to mix. 

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Different kinds of paint also demonstrate the effect of polarity on solubility. Oil-based (enamel) paints are nonpolar. You would not want to try to clean your paint brush afterward with soap and water. It would make a mess. Paint stores sell paint thinner, which is a mixture of nonpolar organic solvents that do dissolve oil-based paints. Other nonpolar solvents that may be used are acetone or turpentine. Latex paints, on the other hand, are water based and therefore polar, so they easily clean up with soap and water. Historically all paints were oil based. In Mark Twain s story of Tom Sawyer and the white washed fence, the white paint would have been oil based. Latex paints were developed to make cleanup easier. 

Effect of Polarity on Solubility Rank the following in order of increasing solubility in water a triacylglycerol, a diacylglycerol, and a monoacylglycerol, all containing only palmitic acid. 

In this study an extensive set of experiments was conducted to determine solubility and diffiisivity of several vapours in PTMSP. Five diff ent penetrant species were considered, three alkanes of different molecular weight and two polar components. The effect of temperature on solubility and diffiisivity was also considered by performing several sorption experiments in the range between 285 and 330 K. 

The effect of salts on the CP may be explained in terms of the polarity of the solute and the solvent. Ions prefer a water environment, and thus they increase the polarity of the solvent, which decreases the solubility of L64. CNSmd I- ions have a slight preference to associate with the L64 molecule and increase its polarity, and thus they increase the solubility, resulting in an increase in the CP. 

Effect of pH on Solubility The strongly polar hydrogen-bonding properties of water make it an... 

The solubilization techniques for injectable formulations are similar to those in oral formulations and include pH adjustment, mixed aqueous/organic cosolvents, organic solvent mixtures, cyclodextrin com-plexation, emulsions, liposomes, polymeric gels, and combinations of techniques. " Molecules that are non-ionizable, lipophilic, and non-polar are challenging to formulate owing to their low water solubility and no effect of pH on solubility. Examples include paclitaxel, docetaxel, cyclosporin A, etoposide, loraze-pam, tacrolimus, testosterone enanthate, and halo-peridol decanoate, and they are all solubilized in non-aqueous solutions composed entirely of organic solvent(s), which are usually but not always diluted prior to administration. 

SCF carbon dioxide is a lipophilic solvent since the solubility parameter and the dielectric constant are small compared with a number of polar hydrocarbon solvents. Co-solvents(also called entrainers, moditiers, moderators) such as ethanol have been added to fluids such as carbon dioxide to raise the solvent strength while maintaining it s adjustability. Most liquid cosolvents have solubility parameters which are larger than that of carbon dioxide, so that they may be used to increase yields, or to decrease pressure and solvent requirements. A summary of the large increases in solubility that may be obtained with a simple cosolvent is given at the top of Table I. Cosolvents, unlike carbon dioxide, can form electron donor-acceptor complexes (for example hydrogen bonds) with certain polar solutes to influence solubilities and selectivities beyond what would be expected based on volatilities alone. Several thermodynamic models have been developed to correlate and in some cases predict effects of cosolvent on solubilities( ,2). They are used extensively in SCF research and development... 

Since the PIT of a hydrocarbon-water emulsion stabilized with a POE nonionic surfactant is, as might be expected, related to the cloud point of an aqueous solution of the nonionic saturated with that hydrocarbon (Chapter 4), these effects on the PIT of emulsions stabilized by POE nonionics are readily understood. As mentioned in the discussion (Chapter 4, Section IIIB) of the effect of solubilizate on the cloud points of POE nonionics, long-chain aliphatic hydrocarbons that are solubilized in the inner core of the micelle increase the cloud point, whereas short-chain aromatic hydrocarbons and polar materials that are solubilized between the POE chains decrease it. They have the same effect on the PIT long-chain aliphatic hydrocarbons increase the PIT and therefore tend to form stable O/W emulsions, whereas short-chain aromatics and polar additives decrease it and tend to form stable W/O emulsions (Shinoda, 1964). An increase in the length of the POE chain increases the cloud point and the PIT and consequently increases the tendency to form O/Wemulsions, consistent with the generalization that the more water-soluble the emulsifier, the greater its tendency to form O/W emulsions. 

The effect of additives on the asphaltene from the Catalytic Incorporated (Cat. Inc.) coal liquid product was studied. Asphaltene is defined as the pentane insoluble but benzene soluble part of the coal liquid. The fractionation procedure has been described in detail elsewhere(l) and is shown schematically in Figure 1. Some work was also done with A240 petroleum pitch. Elemental analysis for the Wyoming sub-bituminous coal. Cat. Inc. coal liquid product, and Cat. Inc. asphaltene and A240 petroleum pitch are shown in Table I. Measured amounts of the additive compounds to be studied were added to the Cat. Inc. asphaltene and petroleum pitch. The samples were pyrolyzed and the pyrolysis residues examined by cross polarized light microscopy. Elemental analyses of the residues were done. 

Alternatively, if polymer particles are not quite soluble in aliphatic hydrocarbons, then they will tend to dissolve on the addition of aromatic hydrocarbons, or the more polar esters, ketones, ether-alcohols and alcohols. All of these solvents will increase either the solubility parameter of the paint solvent mixture, or its hydrogen bonding capacity, or both. If the particles dissolve, then thickening can only be carried out by polymer molecules. The effect of polar solvents on these has been described above. 

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