Insolubility hydrocarbon unit

I ipids are a broad class of biomolecules. Although strucnirally diverse, all J-F lipids are insoluble in water because each lipid molecule contains a large number of nonpolar hydrocarbon units. In this section we discuss two important types of lipids fatS9.nA steroids. 

CeUulose triacetate is insoluble in acetone, and other solvent systems are used for dry extmsion, such as chlorinated hydrocarbons (eg, methylene chloride), methyl acetate, acetic acid, dimethylformamide, and dimethyl sulfoxide. Methylene chloride containing 5—15% methanol or ethanol is most often employed. Concerns with the oral toxicity of methylene chloride have led to the recent termination of the only triacetate fiber preparation faciHty in the United States, although manufacture stiH exists elsewhere in the world (49). 

Dimethylpolysiloxane occurs as a clear, colorless, viscous liquid. It is a mixture of fully methylated linear siloxane polymers containing repeating units of the formula (CH3)2SiO that are terminated with trimethylsiloxy end-blocking units of the formula (CH3)3SiO—. It is soluble in most aliphatic and aromatic hydrocarbon solvents, but it is insoluble in water. Note Dimethylpolysiloxane is frequently used in commerce as such, or as a liquid containing silica (usually 4% to 5%), which must be removed by high-speed... 

Natural rubber is a terpene composed of repeating isoprene units, in which all the double bonds have the Z configuration. Because natural rubber is a hydrocarbon, it is water insoluble, and thus useful for waterproofing. The Z double bonds cause bends and kinks in the polymer chain, making it a soft material. 

Figure 1. Relation between molecular rotation in a hydrocarbon solvent (referred to the monomeric unit) of the unfractionated methanol-insoluble 4 (I), 2 (II), and 3 (III) samples and the optical purity of the monomers used for polymerization. (Reprinted with permission from ref 47. Copyright 1967 Wiley.)...

Ideally this system would consist of three phases only. Two of these phases would be liquid, water and cooled hydrocarbons, and the third would be the cracked gas stream. Unfortunately, solids may accumulate in this vessel. Coke fines and small particles from the furnace may be entrained into this unit, and activated olefins such as butadiene or styrene may polymerize to form insoluble particles. All of this behavior promotes foaming. In this aqueous system, foam formation may be controlled by addition of a polyglycol. 

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