Color appearance

Dissolve ca. 0 2 g. of product (I) in cold ethanol, and add with shaking 1-2 drops of dilute sulphuric acid. A deep purple coloration appears at once. This shows that salt formation has occurred on the quinoline nitrogen atom to form the cation (Ha), which will form a resonance hybrid with the quinonoid form tils). [Note that the forms (IIa) and (11b) differ only in electron position, and they are not therefore tautomeric.] If, hoAvever, salt formation had occurred on the dimethylaniino group to give the cation (III), thrs charge separiition could not occur, and the deep colour would be absent. 

Recovery of the wopropyl alcohol. It is not usually economical to recover the isopropyl alcohol because of its lo v cost. However, if the alcohol is to be recovered, great care must be exercised particularly if it has been allowed to stand for several days peroxides are readily formed in the impure acetone - isopropyl alcohol mixtures. Test first for peroxides by adding 0-6 ml. of the isopropyl alcohol to 1 ml. of 10 per cent, potassium iodide solution acidified with 0-6 ml. of dilute (1 5) hydrochloric acid and mixed with a few drops of starch solution if a blue (or blue-black) coloration appears in one minute, the test is positive. One convenient method of removing the peroxides is to reflux each one litre of recovered isopropyl alcohol with 10-15 g. of solid stannous chloride for half an hour. Test for peroxides with a portion of the cooled solution if iodine is liberated, add further 5 g. portions of stannous chloride followed by refluxing for half-hour periods until the test is negative. Then add about 200 g. of quicklime, reflux for 4 hours, and distil (Fig. II, 47, 2) discard the first portion of the distillate until the test for acetone is negative (Crotyl Alcohol, Note 1). Peroxides generally redevelop in tliis purified isopropyl alcohol in several days. 

Interesting note, using CuCk for the first time.. NO OLIVE GREEN color appeared. Stayed slightly yellow -dark brown... All the way through the rxn. Never came close to Green (light, dark or olive). When rxn finished solution was very dark reddish-brown, even when acid washed it stayed dark reddish brown. 

Anhydrous iron(II) fluoride [7789-28-8] white soHd. The off-white to buff-colored appearance of the material is attributed to the partial... 

Quantitative. Classically, silver concentration ia solution has been determined by titration with a standard solution of thiocyanate. Ferric ion is the iadicator. The deep red ferric thiocyanate color appears only when the silver is completely titrated. GravimetricaHy, silver is determined by precipitation with chloride, sulfide, or 1,2,3-benzotriazole. Silver can be precipitated as the metal by electro deposition or chemical reduciag agents. A colored silver diethjldithiocarbamate complex, extractable by organic solvents, is used for the spectrophotometric determination of silver complexes. 

Identification. When a solution of ferric chloride is added to a cold, saturated vanillin solution, a blue color appears that changes to brown upon warming to 20°C for a few minutes. On cooling, a white to off-white precipitate (dehydrodivanillin) of silky needles is formed. Vanillin can also be identified by the white to slightly yellow precipitate formed by the addition of lead acetate to a cold aqueous solution of vanillin. 

An excellent reagent for detection and quantitative estimation of the mustards is j -nitrobenzylpyridine (11). On treatment of the reaction product with alkah a blue color appears, which detects as Httie as 0.1 p.g of mustard. 

Sample until color appears probably 10 ml of air 94-99 Reacts with absorbing solution Ozone in fivefold excess peroxyacyl nitrate... 

Initially the reaction may take on various colors, red, purple, etc., but after a short time a dull gray-brown color appears, which is gradually replaced by a yellow-brown or olive-drab color. 

The reduction is carried out much as described in Procedure 2. Ammonia (950 ml) is distilled into a 5-liter reaction flask and 950 ml of /-amyl alcohol and a solution of the ketal in 950 ml of methylcyclohexane are added with good stirring. Sodium (57 g, 2.5 g-atoms) is added in portions. The reaction mixture becomes blue within 30-45 min after the sodium is added and the metal is consumed within about 3 hr after the blue color appears. After the mixture becomes colorless, 200 ml of ethanol is added and the ammonia is allowed to boil off through a mercury trap. Then 500 ml of water and 500 ml 0% potassium bicarbonate solution are added and the organic layer is separated. The organic layer is washed once with 10 % potassium bicarbonate... 

Anstrich, m. paint, painting, coat varnish dye tint, color appearance, -blndemittel, n. (Painting) binder, -farbe,/, painting color, pigment priming,... 

The direct synthetic process is described in U.S. Patent 2,772,280. A solution of 73.3 g (0.332 mol) of (3-aminoxyalanine ethyl ester dihydrochloride in 100 ml of water was stirred in a 500 ml 3-necked round-bottomed flask cooled in an ice-bath. To the above solution was added over a 30-minute period 65.6 g (1.17 mols) of potassium hydroxide dissolved in 100 ml of water. While the pH of the reaction mixture was 7 to 10.5, a red color appeared which disappeared when the pH reached 11 to 11.5. The light yellow solution was allowed to stand at room temperature for 14 hour and then added to 1,800 ml of 1 1 ethanol-isopropanol. The reaction flask was washed twice with 10 ml portions of water and the washings added to the alcohol solution. The precipitated salts were filtered out of the alcohol solution and the filtrate cooled to 5°C in a 5 liter 3-necked round-bottomed flask. To the cold, well-stirred solution was added dropwise over a 35-minute period sufficient glacial acetic acid to bring the pH of the alcohol solution to 6.0. When the pH of the solution had reached 7 to 7.5, the solution was seeded and no further acetic acid added until Crystallization of the oil already precipitated had definitely begun. The crystalline precipitate was collected on a filter, washed twice with 1 1 ethanol-isopropanol and twice with ether. The yield of 4-amino-3-isoxazolidone was 22.7 g. 

The particles, or molecules, of the gas nitric oxide cannot be exactly like those of nitrogen dioxide. There must be differences that account for the fact that one gas is colorless and the other reddish-brown. Yet, when nitric oxide and air are mixed, color appears, suggesting that nitrogen dioxide has been formed. Apparently molecules present in air somehow combine with the molecules of nitric oxide to form molecules of nitrogen dioxide. We would like to develop our picture of molecules so it will aid us in discussing these changes. 

Figure 9-1 shows the addition of solid iodine to a mixture of water and alcohol. At first the liquid is colorless but very quickly a reddish color appears near the solid. Stirring the liquid causes swirls of the reddish color to move out— solid iodine is dissolving to become part of the liquid. Changes are evident the liquid takes on an increasing color and the pieces of solid iodine diminish in size as time passes. Finally, however, the color stops changing (see Figure 9-1). Solid is still present but the pieces of iodine no longer diminish in size. Since we can detect no more evidence of change, we say that the system is at equilibrium. Equilibrium is characterized by constancy of macroscopic properties ...

Procedure B. Pipette 25 mL of the diluted solution into a 250 mL conical flask containing 5mL 6 M nitric acid. Add a slight excess of standard 0.1M silver nitrate (about 30 mL in all) from a burette. Then add 2-3 mL pure nitrobenzene and 1 mL of the iron(III) indicator, and shake vigorously to coagulate the precipitate. Titrate the residual silver nitrate with standard 0.1M thiocyanate until a permanent faint reddish-brown coloration appears. 

The sodium hydroxide solution should be added slowly, since the reaction with the acidic ether extract is exothermic and may cause boiling of the ether. The ether extract should be washed with aqueous sodium hydroxide until the aqueous layer remains basic to litmus. This extraction is self-indicating the ether turns from a bright yellow to a light brown and color appears in the aqueous phase. 

Storage The spray and dipping solutions should always be made up fresh. Solution III is stable for up to 3 days at 0 °C. Solutions I, II and —IV are stable over longer periods. Chromatogram zones of various colors appear on a colorless background, usually immediately but occasionally after a little time [3, 5, 11]. The colors remain stable over ... 

Saturation is the clarity of a color. It can also be understood as the intensity of hue in comparison to brightness. A saturated color looks clear and bright an unsaturated color appears pale, muddy, or dull. 

Detailed information about carotenoids found in food or extracted from food and evaluated for their potential as food colorants appeared in Sections 4.2 and 6.2. We would like to mention some new data about the utilization of pure carotenoid molecules or extracts as allowed food additives. Looking to the list of E-coded natural colorants (Table 7.2.1), we can identify standardized colorants E160a through f, E 161a, and E161b as natural or semi-synthetic derivatives of carotenoids provided from carrots, annatto, tomatoes, paprika, and marigold. In addition, the extracts (powders or oleoresins) of saffron, - paprika, and marigold are considered more economical variants in the United States and European Union. 

In order to control food color, underlying mechanisms cansing variation in color must be understood. Three types of colorants can be distinguished from the perspective of quality and safety control natural colorants, formed colorants, and color additives. Depending on the type of colorant, specific strategies are required to control dynamics of colorants and achieve constant qnality in terms of safety, desired color, appearance, and health (Section 7.1.3). The extent to which underlying food color-affecting mechanisms are understood determines how well the quality of food color can be predicted. 

Place iodine crystal in a closed tank place the plates in the tank nntil color appears Prepare a 2% aqneons solntion of resorcinol add 10 ml of this solntion to 80 ml of HCl containing 10.5 ml of 0. l-MCnS04 solntion spray the plates with the reagent and heat for few min at 110°C... 

The nitrobenzene is then removed by vacuum distillation using a 2-1. Claisen flask, and the residue in the flask is distilled under diminished pressure the fraction boiling at 180-195°/ 15 mm. is collected (Notes 8 and 9). The red-yellow oil, which solidifies on cooling, amounts to 128-176 g. (40-55%) and is sufficiently pure for some purposes (Note 10). A nearly white product can be obtained by dissolving the crude product in ether, shaking the ether solution with portions of 5% sodium hydroxide solution until no color appears in the aqueous layer, evaporating the ether, and recrystallizing the residue from a mixture of petroleum ether (b.p. 60-90°, Skellysolve B) and benzene (Note 11). The recrystallized product melts at 83-84° the recovery is 80-85%. 

Under these conditions, blue flowers can be achieved as a metal complex of anthocyanin (called a metalloanthocyanin) is stabilized through the association of a metal ion with two hydroxy groups oriented ortho to one another on the anthocyanin ring, as illustrated in Fig. 9.4.3J2 In basic solution, the structure of the anthocyanin (Fig. 9.4.4) no longer has ortho-oriented hydroxy groups. Metal complexation is no longer possible, and the flower color appears red. 

When an aqueous solution of f-BuOOH is added to a solution of la at pH 14 (0.01 M phosphate, 1M KOH), a red color appears promptly that is stable at room temperature for hours. The same species can be obtained at any pH higher than 12. A titration of la by f-BuOOH followed by UV/Vis spectroscopy revealed that ca. 0.5 equivalent of the peroxide per Fem is needed to obtain the maximum change. Similar results have been obtained with H202 under identical conditions all suggesting the formation of an FeIV species (48). 

The first tint of red color appears when Ag2Cr04 begins to precipitate when Qsp = Ksp = [Ag+]2[Cr042-]. 

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