Blue Colors

The most important ingredient for blue colors is cobalt (Co) or vanadium (V). A typical formula for cobalt blue stains is one part of cobalt oxide (CoO), three parts of zinc oxide (ZnO), and nine parts of alumina (Al Oj). This formula will give matte blue. If we use silicate such as feldspar (see Chap. 14) and silica (SiO ) instead of alumina, we get royal blue and Mazarine blue.  

Vanadium-zirconia is another blue stain used often. A mixture consists of zirconia ZrO, silica SiO, and vanadium pentoxide (vanadium in + oxidation state, which is colorless). The blue color is due to the formation of in the calcination process. The V atom in is in the -hIV oxidation that has a characteristic blue color. The formation of scans to be facilitated by the addition of 

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Addition of dilute potassium dichromate(VI) solution, K2Cr207, to a solution of hydrogen peroxide produces chromium peroxide, CrOj, as an unstable blue coloration on adding a little ether and shaking this compound transfers to the organic layer in which it is rather more stable. 

Ltebermann Reaction To 1 minute crystal of sodium nitrite in a clean dry test-tube add 0 5 g. of phenol and heat very gently for about 20 seconds allow to cool and add twice the volume of cone. H2S04. On rotating the tube slowly in order to mix the contents, a deep green or deep blue coloration develops (some times only after i 2 minutes). Dilute cautiously with water the solution turns red. Now add an excess of NaOH solution the green or blue coloration reappears. 

Hydrolysis by acids. Place 15 ml. of starch solution in a boiling-tube, add I ml. of cone. HCl, mix well and place in a boiling water-bath for 20 minutes. Cool and add 2 drops of iodine solution to i ml. of the solution no blue coloration is produced. On the remainder, perform tests for glucose in particular show that glucosazone can be formed. Neutralise the excess of acid before carrying out these tests. (Note that a more concentrated acid is required to hydrolyse starch than to hydrolyse the disaccharides, such as sucrose.)... 

Coloured oxidation products, a) Dissolve a few small crystals of diphenylamine in 1 ml. of cone. H2SO4. Add 2 drops of cone. HNO3 to about 10 ml. of water, shake, and add i drop of this diluted HNO3 to the diphenylamine solution an intense purple-blue coloration is produced. Monomethylaniline merely turns a dirty brown when treated in this way. 

The gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale blue color and are strongly paramagnetic. 

Scandium is apparently much more abundant (the 23rd most) in the sun and certain stars than on earth (the 50th most abundant). It is widely distributed on earth, occurring in very minute quantities in over 800 mineral species. The blue color of beryl (aquamarine variety) is said to be due to scandium. It occurs as a principal component in the rare mineral thortveihte, found in Scandinavia and Malagasy. It is also found in the residues remaining after the extrachon of tungsten from Zinnwald wolframite, and in wiikite and bazzite. 

The salts have been used for centuries to produce brilliant and permanent blue colors in porcelain, glass, pottery, tiles, and enamels. It is the principal ingredient in Sevre s and Thenard s blue. A solution of the chloride is used as a sympathetic ink. Cobalt carefully used in the form of the chloride, sulfate, acetate, or nitrate has been found effective in correcting a certain mineral deficiency disease in animals. 

Iodine compounds are important in organic chemistry and very useful in medicine. Iodides, and thyroxine which contains iodine, are used internally in medicine, and as a solution of KI and iodine in alcohol is used for external wounds. Potassium iodide finds use in photography. The deep blue color with starch solution is characteristic of the free element. 

The electrophilic site of an acyl cation is its acyl carbon An electrostatic poten tial map of the acyl cation from propanoyl chloride (Figure 12 8) illustrates nicely the concentration of positive charge at the acyl carbon as shown by the blue color The mechanism of the reaction between this cation and benzene is analogous to that of other electrophilic reagents (Figure 12 9)... 

Examine the electro r static potential map of butanoic acid on t Learning By Modeling and notice how much more in tense the blue color (positive charge) is on the OH hydro gen than on the hydrogens bonded to carbon... 

Titrate liberated iodine with thiosulfate Ee/1 = 55.847 Ee203/2 = 79.845 I2 + 2 820 = 2 D + 8401 [titrate solution (pH ° 7.0) with thiosulfate until color is pale yellow. Add K1 and starch and continue titration to disappearance of blue color. I2/2 =... 

In a recent paper, Lozano-Calero and colleagues describe a new method for the quantitative analysis of phosphorus in cola beverages. The method is based on the formation of an intensely blue-colored phosphomolybdate complex,... 

In the presence of a reducing agent, such as ascorbic acid, the yellow-colored complex is reduced to a blue-colored complex of Mo(V). 

The reduction of the yellow-colored Mo(VI) complex to the blue-colored Mo(V) complex is a slow reaction. In the standard spectrophotometric method, it is difficult to reprodudbly control the amount of time that reagents are allowed to react before measuring the absorbance. To achieve good precision, therefore, the reaction is allowed sufficient time to proceed to completion before measuring the absorbance. In the FIA method, the flow rate and the dimensions of the reaction coil determine the elapsed time between sample introduction and the measurement of absorbance (about 30 s in this configuration). Since this time is precisely controlled, the reaction time is the same for all standards and samples. 

Some treatments are practiced so widely that untreated material is essentially unknown ia the jewelry trade. The heating of pale Fe-containing chalcedony to produce red-brown carnelian is one of these. Another example iavolves turquoise where the treated material is far superior ia color stabiUty. Such treatments have traditionally not been disclosed. Almost all blue sapphire on the market has been heat treated, but it is not possible to distinguish whether it was near-colorless comndum containing Fe and Ti before treatment, or whether it had already been blue and was only treated ia an attempt at marginal improvement. The irradiation of colorless topa2 to produce a blue color more iatense than any occurring naturally is, however, self-evident, and treatments used on diamond are always disclosed. 

The intense blue color of Pmssian Blue is attributed to electron transfer between the [Fe(CN)3] and Fe(Ill) ions. A related pigment called Berlin Green is obtained by oxidation of Pmssian Blue. It is thought that the intense color of this other compound results only if oxidation of the [Fe(CN)3] units is incomplete and some remain as hexakiscyanoferrate(4—). The compound in which only h on(Ill) is present, Fe[Fe(CN)3] [14433-93-3], is brown and is subject to autoreduction processes. 

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). 

A number of reaction products have been isolated from the (Tj -C H )2TiCl —N2—reductant system, where n = 1, 2, all of which assume an intense blue color in solution. Spectroscopic absorption occurs at a maximum, of ca 600 nm. The relationship among these products is unclear (185,186), but the labihty of the ring maybe an important complicating factor. When (Tj -C R 2TiCl2 [11136-36-0] R = CH3, is used, two distinct interconvertible... 

Secondary nitroparaffins give alkali-insoluble nitroso derivatives known as pseudonitroles. As monomers in the hquid state, pseudonitroles have a characteristic blue color as sohds they exist as white crystalline dimers. Tertiary nitroparaffins do not react with nitrous acid and no color develops. 

Qualitative Analysis. Several quaUtative analyses can be employed. For example, in the oxamide method (59), oxaUc acid is first heated at approximately 200°C with concentrated aqueous ammonia in a sealed tube. When thiobarbituric acid is added and heated to 140°C, a condensed compound of red color forms. The analysis limit is 1.6 pg. In the diphenylamine blue method (59,60), oxaUc acid is heated with diphenylamine to form a blue color, aniline blue. The analysis limit is 5 pg. 

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