Color in compounding

These manifest themselves in the appearance of a yellowish color in compounds 18b,c, e,f as crystals, whereas compound 18d with an elongated... 

Quinoid Structure of Dyes.— This is known as the quinone or quinoid structure and, according to theories regarding the relation between constitution and color in compounds possessing properties of dyestuffs, it is the presence of a group with this structure which endows the dyes of this and related classes with color. 

When atoms become ions, properties are drastically altered. For example, a collection of Brg molecules is red, but bromide ions (Br ) contribute no color to a crystal of a compound such as NaBr. A chunk of sodium atoms (Figure 5.3, left) is soft, metallic, and violently reactive with water, but Na ions are stable in water. A large collection of Clg molecules (Figure 5.3, center) constitutes a greenish-yellow poisonous gas, but chloride ions (Cl ) produce no color in compounds and are not poisonous. We have everyday evidence of this because we use NaCI (Figure 5.3, right) to season food. When atoms become ions, atoms change their nature. 

Yttrium oxide is one of the most important compounds of yttrium and accounts for the largest use. It is widely used in making YVOr europium, and Y2O3 europium phosphors to give the red color in color television tubes. Many hundreds of thousands of pounds are now used in this application. 

The most important class of redox indicators, however, are substances that do not participate in the redox titration, but whose oxidized and reduced forms differ in color. When added to a solution containing the analyte, the indicator imparts a color that depends on the solution s electrochemical potential. Since the indicator changes color in response to the electrochemical potential, and not to the presence or absence of a specific species, these compounds are called general redox indicators. 

Color can be removed effectively and economically with either alum or ferric sulfate at pH values of 5—6 and 3—4, respectively. The reaction is stoichiometric and is a specific reaction of the coagulant with the color to form an insoluble compound (17). The dosage required may be as high as 100—150 mg/L (380—570 mg/gal). Raw-water colors may be as high as 450—500 units on the APHA color scale. The secondary MCL (maximum contaminant level) for color in the finished water is 15 units, although most municipal treatment plants produce water that seldom exceeds 5 units. 

Pentaphenylbismuth is a violet-colored, crystalline compound that decomposes spontaneously after standing for several days in a dry nitrogen atmosphere. With a variety of agents, eg, hydrohahc acids, halogens, and triphenylboron, one phenyl group is cleaved to form quaternary bismuth compounds. 

Color in Organic Compounds. In organic molecules, particularly those containing conjugated chains of alternating single and double... 

The anthocyanins are pH sensitive. Their color, in part, is deterrnined by the pH of the sap. Cyanin, for example, is red at pH 3, violet at 8, and blue at 11. However, there are other factors that affect the colors of the anthocyanins metallic salts, notably iron and aluminum, react with those anthocyanins containing vicinal hydroxy groups and produce highly colored complex compounds. Other factors are the colloidal condition of the cell sap and copigmentation (91). 

Quinoxaline-2,3-dithione (2,3-dimercaptoquinoxaline) (90) forms chelates with several transition elements and is used as a colorimetric agent for the detection and quantitative estimation of nickeT and also for the quantitative estimation of palladium. " Nickel gives a pink coloration with (90) in ammoniacal solution, and palladium an orange-red color in AA-dimethylformamide solution containing a little hydrochloric acid. Spectrophotometric studies of the chelate compounds of (90) with Ni(II), Co(II), and Pd(II) in alkaline solu-... 

Organic metal salts retard the development of color in the thermal treatment of PVC, and their ability to react selectively with allylic and tertiary chlorine structures according to Eq. 23 has been demonstrated with model compounds [19,32,113,115]. 

Oxidizing agents also attack the double bond. When a reaction between an unsaturated compound and the permanganate ion occurs, the violet color of permanganate fades. This reaction, as well as reaction (29b) in which a color change also occurs, is used as a qualitative test for the presence of double bonds in compounds. 

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