Activities Color Relativity

Activity 1.17 Color Relativity Physical Properties and Physical Change... 

Activity 1.17 Color Relativity Physical Properties and Physical Change. . 71 Demonstration 1.5 Color Relativity Chemical Properties and Chemical... 

Trace amounts of polar impurities can contaminate crystallized products, and very small amounts of impurities can be responsible for producing intensely colored products. Polar impurities can be removed by stirring a solution of the product with 1—2 wt% of activated carbon relative to the solute, adsorbing these impurities to the finely divided solids. Impurities are trapped in the pores of the activated carbon by van der Waals attractive forces. There are three categories of pore sizes macroporous (1000—100,000 A), mesoporous (100—1000 A), and microporous (<100 A). Viscous solvents slow the penetration of molecules into the pores [18], and polar solvents are generally more effective than nonpolar solvents for treatment [19], A filter aid (Section II.D.) is often used to avoid slow filtrations in removing activated carbon. After filtration, the filtrate is processed to the product. 

Tocotrienols differ from tocopherols by the presence of three isolated double bonds in the branched alkyl side chain. Oxidation of tocopherol leads to ring opening and the formation of tocoquinones that show an intense red color. This species is a significant contributor to color quaUty problems in oils that have been abused. Tocopherols function as natural antioxidants (qv). An important factor in their activity is their slow reaction rate with oxygen relative to combination with other free radicals (11). 

In general, the amines are more active than the phenoHcs which are in turn more active than the phosphites. Amine antioxidants, however, often cause staining problems and are therefore used mainly in black stocks. The phenoHcs and phosphites are relatively nonstaining and are normally used ia light-colored mbbers. 

Foam Fractionation. An interesting experimental method that has been performed for wastewater treatment of disperse dyes is foam fractionation (88). This method is based on the phenomenon that surface-active solutes collect at gas—Hquid iaterfaces. The results were 86—96% color removal from a brown disperse dye solution and 75% color removal from a textile mill wastewater. Unfortunately, the necessary chemical costs make this method relatively expensive (see Foams). 

The development and reports of methods for colorless chlorophyll derivative (RCCs, FCCs, and NCCs) analysis are relatively recent and the structures of the compounds are being elucidated by deduction from their chromatographic behaviors, spectral characteristics (UV-Vis absorbance spectra), mass spectrometry, and nuclear magnetic resonance analysis. The main obstacle is that these compounds do not accumulate in appreciable quantities in situ and, moreover, there are no standards for them. The determination of the enzymatic activities of red chlorophyll catabolite reductase (RCCR) and pheophorbide a monoxygenase (PAO) also helps to monitor the appearance of colorless derivatives since they are the key enzymes responsible for the loss of green color. ... 

Polymerization screening mns using porphyrin catalysts with different linker groups between the 700 Da polyethylene tail and the porphyrin core showed little variability. The catalytic activity for the 4 x 700 PE porphyrin catalysts with ether (5), ester (7) or polyether (8) linkers was nearly identical, with only small differences in the resin colors being noted (Figures 36.3 and 36.4). These results are consistent with literature findings that porphyrin CCT catalysts are relatively insensitive to functional groups on the equatorial plane. ... 

Photochemical activation of [ESE, TNM] complexes. Colored solutions of the ESE derived from the relatively unreactive cycloalkanones and acyclic ketones in Table 2 and TNM persist for prolonged periods, and they can thus be separately subjected to filtered actinic radiation with /exc > 420 nm. (Note that under these conditions, neither TNM nor ESE alone is excited since they absorb only below 400 nm.) The photonitrations of ESE with TNM are carried out at low temperatures (—40°C) at which the thermal reactions are too slow to... 

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