Solubility, Solvents, and Solution Formulations

Phenyldiazonium chloride and other similar diazonium compounds are very soluble in water, are completely insoluble in ether and other organic solvents, and are completely dissociated in aqueous solution to organic cations and inorganic anions (e.g., chloride ions) a convenient formulation is therefore, for example, CjHjNj+CP. 

For aqueous inks, the resins are water- or alkali-soluble or dispersible and the solvent is mosdy water containing sufficient alcohol (as much as 25%) to help solubilize the resin. To keep the alkah-soluble resin in solution, pH must be maintained at the correct level. Advances include the development of uv inks. These are high viscosity inks that require no drying but are photocurable by uv radiation. In these formulations, the solvent is replaced by monomers and photoinitiators that can be cross-linked by exposure to uv radiation. The advantage of this system is the complete elimination of volatile organic compounds (VOC) as components of the system and better halftone print quaUty. Aqueous and uv inks are becoming more popular as environmental pressure to reduce VOC increases. 

Practical Solubility Concepts. Solution theory can provide a convenient, effective framework for solvent selection and blend formulation (3). When a solute dissolves in a solvent, a change in free energy occurs as a result of solvent—solute interactions. The change in free energy of mixing must be negative for dissolution to occur. In equation 1,... 

The widespread applicability of di-O-methylisosorbide as a medium for chemical reactions or as a solvent for pharmaceutical formulations is well documented. In some cases, an additive synergism of the solvent and the solute was observed. Some typical examples mentioned include that it acts as a solvent for muscle-relaxant drugs, which are otherwise difficultly soluble,226 and is used for topical and other types of pharmaceutical formulations,227,228 transdermal controlled-release films229 and tapes,230 anthelmintic solutions,231 antimycotic emulsions,232 and for the treatment of skin disorders, such as eczema.233... 

It is important to characterize the physicochemical properties of the suspensions well, so that the PK data can be interpreted appropriately. Typical characterization of the drug substance includes purity, residual solvents, aqueous solubility pro Lie (pH 2, FaSSIF), crystallinity (XRPD/DSC), particle size, pl and logP. For solution formulations at various stages of discovery studies, dose analysis is essential, and for efLcacy assessment and toxicology studies, chemical stability for the... 

There are several theoretical models to estimate the solubility of a solute in a solvent. However, use of dielectric constant is one of the oldest and simplest approach and is very popular with the formulators. Fractional method to estimate the dielectric constant is the simplest approach and is not the most accurate. However, it offers a good starting point for the estimation. In addition, the solubility of a solute is dependent on the dielectric constant of a solvent mixture and not to the particular composition. Other approaches, such as solubility parameter method and UNIFAC group theory contributions are less frequently used by industry formulators. 

The choice of mobile phase is largely empirical but general rules can be formulated. A mixture of an organic solvent and water with the addition of acid, base or complexing agent to optimize the solubility of the components of a mixture can be used. For example, good separations of polar or ionic solutes can be achieved with a mixture of water and n-butanol. Addition of acetic acid to the mixture allows more water to be incorporated and increases the solubility of basic materials, whilst the addition of ammonia... 

Solutions. To deliver a spray, the formulated aerosol product should be as homogeneous as possible. That is, the active ingredients, the solvent, and the propellant should form a solution. Because the widely used kalocarbon and hydrocarbon propellants do not always have the desired solubility characteristics for all the components in the product concentrate, special formulating techniques using solvents such as alcohols (qv), acetone (qv), and glycols (qv), are employed. 

The active ingredient in water-soluble liquids or concentrates (S, WS, WSC or WSL) is soluble in water and is formulated either with water or with a solvent, such as alcohol, which mixes readily with water. When added to water in the spray tank, WSCs form a true solution and require no further agi-... 

---