Semisolids form

The extract when dried failed to crystallize when cooled allowed to stand. It was then refluxed with.a mixt of acetic acid acetic anhydride for 12 hrs. The anhydride acid were distilled and the oily residue poured into water. A semisolid formed which was recrystd from ale. Yield 28%. Its expl props were not detd... 

Figure 7.10 Comparison of (a) dendritic conventionally cast and (b) nondendritic semisolid formed microstructure of aluminum alloy 357 (Al-7.0 Si-0.5 Mg). The photos are at the same magnification. (From M. Kenney, in ASM Handbook, Vol. 15, Casting, D. M. Stefanescu, Ed., 1988, p. 327. Reprinted with permission of ASM International. All rights reserved, www.asmintemational.org.)...

Because the initial rotary evaporation is faster with the organic solvent, we have usually prepared DHA in 95% ethanol. In methanol the reaction gives up to 10-20% of a methanol complex of DHA that is only partly reconverted to free DHA on repeated evaporations from water. Extensive rotary evaporation with repeated additions of diethyl ether, followed by lyophilization, yields a more manageable, semisolid product. DHA in the syrup or semisolid form is stable for many weeks when stored at —10° to —20°C. Analysis of the products prepared as described above was done by NMR, one of the few analytical techniques that gives unambiguous results on the purity and identity of this compound. 

Methylene chloride, vinyl chloride, and toluene will be present in liquid form in the trench. All would also be expected to be present in the vapor state, with vinyl chloride being the most volatile due to its high Henry s law constant. The principal dangers to site remediation workers, therefore, would be from inhalation of vapors and skin absorption of contacted liquids. Pentachlorophenol and PCBs will be present in solid and semisolid forms. Minimal vapors of these compounds would be expected. The principal dangers would be from inhalation of dusts and fumes, ingestion of solids, and skin absorption due to solids contact. In the absence of engineering controls and work practices, the necessary worker PPE would include, at a minimum, respirators and chemical protective clothing. 

Solid Form Selection A drug can exist in multiple forms in the solid state. If the two forms have the same molecular structure but different crystal packing, then they are polymorphs. Pseudopolymorphs (or solvatomorphs) differ in the level of hydration/solvation between forms. Polymorphs and pseudopolymorphs in principle will have a different solubility, melting point, dissolution rate, etc. While less thermodynamically stable, polymorphs have higher solubilities they also have the potential to convert to the more thermodynamically stable form. This form conversion can lead to reduced solubility for the formulated product. One example is ritonavir, a protease inhibitor compound used to treat acquired immune deficiency syndrome (AIDS). Marketed by Abbott Labs as Norvir, this compound began production in a semisolid form and an oral liquid form. In July 1998, dissolution tests of several new batches of the product failed. The problem was traced to the appearance of a previously unknown polymorph (Form II) of the compound. This form is thermodynamically more stable than Form I and therefore is less soluble. In this case, the solubility is at least a factor of 2 below that of Form I.12 The discovery of this new polymorph ultimately led to a temporary withdrawal of the solid form of Norvir from the market and a search for a new formulation. 

The manufacturing factors that may be affected by the choice of a particular polymorphic form include granulation, milling and compression, stability (particularly for semisolid forms), amount of dose delivered in metered inhalers, crystallization from different solvents at different speeds and temperature, precipitation, concentration or evaporation, crystallization from the melt, grinding and compression, lyophilization, and spray drying. In the manufacturing processing, crystallization is a major problem and it can be avoided by a careful study of polymorphic transition, particularly in supercritical fluids. 

Many biosurfactants and their productive processes were patented, but only some of them were commercialized. Nowadays, some products based in biosurfactants can be found at the international market, like PD5, produeed by Pendragon Holdings, sold as an addietive for fuels based on a mixture of rhanmolipid biosurfactants and enzymes, EC-601, produced by EcoChem Organics, sold as a dispersive agent of water-insoluble hydrocarbons (rhanmolipids) and the products JBR, of Jeneil Biosurfactant, rhamnolipids in aqueous solutions with different purity degrees or in a semisolid form. 

Buccal mucoadhesive tablets are mostly intended for systemic use, but adhesive tablets and semisolid forms can also be used to obtain a local effect. 

In this section focus lies on the design of the formulation of nasal preparations, first for liquids and then for semisolid forms. 

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