Color compounding

The high reactivity of the 5-position in 1.3-selenazoles toward electrophilic substitution was also observed on azocoupling. By reacting molar quantities of an aqueous solution of a diazonium salt with an ethanolic solution of a 2-arylamino selenazole. for example, the corresponding 2-arylamino-5 azoselenazoles are formed in a smooth reaction (100). They deposit from the deeply colored solution and form intenselv red-colored compounds after their recrystallization from a suitable solvent (Scheme 36l. 

Section 24 14 Oxidation of 1 2 and 1 4 benzenediols gives colored compounds known as qumones... 

A colored compound whose change in color signals the end point of a titration. 

The concentration of fluoride in drinking water may be determined indirectly by its ability to form a complex with zirconium. In the presence of the dye SPADNS, solutions of zirconium form a reddish colored compound, called a lake, that absorbs at 570 nm. When fluoride is added, the formation of the stable ZrFe complex causes a portion of the lake to dissociate, decreasing the absorbance. A plot of absorbance versus the concentration of fluoride, therefore, has a negative slope. 

Upon maturation of both softwoods and hardwoods, the parenchyma cells at the core die. This portion of the wood is called heartwood and often contains polyphenols, davones, and other colored compounds that do not occur in the contrasting sapwood. A clear, visual distinction usually exists between heartwood and sapwood, depending on the species. Heartwood compounds, eg, dihydro quercetin (taxifofin,... 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

Analogous reactions form sodiummethyldithiocarbamate [137-42-8] from methylamine, and disodiumethylenebis(dithiocarbamate) [142-59-6] from ethylenediamine. Iron, manganese, and 2iac salts can be prepared from the sodium salts heavy metals form characteristically colored compounds with dithio c arb amate s. 

Mineral fillers are used for light-colored compounds. Talc has a small particle size and is a semireinforcing filler. It reduces air permeabihty and has htde effect on cure systems. Calcined clay is used for halobutyl stoppers in pharmaceutical appHcations. Nonreinforcing fillers, such as calcium carbonate and titanium dioxide, have large particle sizes and are added to reduce cost and viscosity. Hydrated siUcas give dry, stiff compounds, and their acidity reduces cure rate hence, their content should be minimized. 

The success of separation of colored compounds is usually monitored visually. Such compounds absorb a particular portion of the polychromatic (white) light in the visible wavelength range. The remaining radiation (complementary radiation) is reflected and detected by the eye it determines the color of the substance zone. Table 1 correlates the wavelengths, colors and complementary colors. 

The mechanism of reaction with steroids has not been elucidated. Various nonquantitative reactions occur simultaneously. Cyclopentenyl cations have been postulated as intermediates which condense with anisaldehyde to yield colored compounds [4]. It is probable that triphenylmethane dyes are also formed with aromatic compounds. 

The action of ferric chloride and hydrogen peroxide on isopropyli-dene and benzylidene derivatives of 2-hydrazinoselenazole yields deeply colored compounds of the 2,2 -dioxo-A -biselenazol-5,5 -inylidene bis-hydrazone type. (Cf. Table VIII.)... 

Sulfur dioxide is a reducing bleach and can counter the effects of oxidizing bleaches, thus preserving color in fruits dried in the sun. The combination of fruit acids and ultraviolet light would otherwise react with the colorful compounds, making the fruit pale. 

Another class of colored compounds is the anthocyanins. Flowers, blueberries, apples, and red cabbage get their color from anthocyanins, which are part of a group of compounds known as flavenoids. 

Sometimes rather than adding color to a product, it is necessary to take color away. We bleach our clothes, our hair, and sometimes even our food. Most often chemicals react with colorful compounds to make them colorless through a process called oxidation. 

Chromium, Cr, is a bright, lustrous, corrosion-resistant metal. Its name, which comes from the Greek word for color, was inspired by its colorful compounds. The metal is obtained from the mineral chromite, FeCr204, by reduction with carbon in an electric arc furnace ... 

Normally, most of the colorless urobilinogens formed in the colon by the fecal flora are oxidized there to urobilins (colored compounds) and are excreted in the feces (Figure 32-16). Darkening of feces upon standing in air is due to the oxidation of residual urobilinogens to urobilins. 

The binary chalcogenides of antimony and bismuth are highly colored compounds that are readily prepared by direct reaction of the elements at 500-900 C. They have rather complex ribbon or layer structures and exhibit semiconductor properties. 

Comparative studies of the widely employed spectrophotometric readings at the Soret and Q bands (405 and 630 nm, respectively) and the elemental analysis of copper and nitrogen showed that the spectrophotometric assay based only on the Soret band can overestimate the purity of a preparation. Erroneous data were attributed to an increase in absorptivity at the Soret band when other colored compounds like metal-free analogs and carotenoids are present. Indeed, copper-free chlorin e6 exhibits a specific absorbance 3.6 times greater than that of its coppered counterpart. Therefore, measurements at the Q band (630 mn) and the establishment of the S Q ratio are preferred. 

Like chemical reactions, electrochemical reactions are often accompanied by a change in color. For example, colorless WO3 can be reduced either chemically or electrochemically to form intensely colored compounds known as tungsten bronzes ... 

Ru 2,2 -bipyridine complexes can form a large number of colored compounds upon successive reduction, with the formal Ru oxidation state from +2 to -4. In the case of highly reduced complexes, proper representation of the electrochromic reaction is actually the reduction of the hgand, not that of the metal center. 

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