Color fading

This nitropropene should be used within a week, or stored in the cold, as the color fades to a slight orange over a couple of weeks in room temperature, which is a sign of decomposition. 

Violet Orange at pH 7.2, beautiful violet at 7.4, color fades on standing... 

Organic acids yield lemon-yellow zones on a blue background [1]. Halide ions migrate as ammonium salts in ammoniacal mobile phases and are also colored yellow. The colors fade rapidly in the air. This can be delayed for some days by covering the chromatogram with a glass plate. 

The crude bromide (10 g) is dissolved in 120 ml of acetone and 12.3 g of anhydrous potassium acetate, 3.8 ml of glacial acetic acid and 5.88 g of sodium iodide are added in that order. The mixture is refluxed with agitation for 4 hr the initial yellow iodine color fades completely during this time. Water (200 ml) is added and the acetone removed by distillation at reduced pressure, whereupon the product separates as bulky fibers. After chilling, the product is collected, washed with water and dried to give 9.4 g (98 %) of 5a,6) -dichloro-3i ,17a,21-trihydroxypregnan-20-one 21-acetate mp 192-195° (dec). 

When equimolar quantities of 80a and its dication 110 are combined in acetonitrile, single electron transfer occurs and the coproportionation product was obtained (95TL2741).Tliis deeply red-colored, air-sensitive radical cation 111 showed a strong ESR signal (g = 2.0034). On the other hand, the excellent electron donor 80a could be prepared by electrolytic reduction starting from 110. It was necessary to carry out the reduction with scrupulous exclusion of oxygen. Tlius, the electrolysis of 110 at -1.10 V initially gave rise to an intense red color, which was presumably due to the formation of 111. Upon further reduction, the red color faded and the tetraaza-fulvalene 80a was isolated at a 62% yield (Scheme 45). 

Narceine (h/ f 1-5) yielded red-brown, morphine (h/ f 5-10), codeine (h/Jf 15-20) and thebaine (h/ j 35-40) brown-violet, papaverine (h/ f 60-65) light brown and narcotine red chromatogram zones on a colorless background. Since the colors fade in the air it is recommended that the chromatogram be covered with a glass plate. 

Immediately after dipping perphenazine (h/ f 28-33) appeared as pink-colored, fluphenazine (hRj 30-35), dixyrazine (hRj 33-38) and verophene (= promazine, hRf 38-43) as skin-colored and periciazine (h/ f 35-40) as orange, promethazine (h/ f 43-48) as bright pink, alimemazine (h/ f 60-65) as skin-colored and dibutil (etho-propazine, hRf 75-80) as pink-colored chromatogram zones on a colorless background (Fig. 2). The colors faded after some time. 

Zinc metal displaces copper ions from aqueous solution. The blue color signals the presence of copper ions. The color fades and copper metal appears as the reaction proceeds. 

Most published data deals with model solutions to assess the major factors influencing betalain stability, among which pH and temperature are most frequently addressed. Until recently, total color loss was assessed by spectrophotometric monitoring of the decline at the wavelength of maximum absorption. To predict color fading over time, kinetic data were derived therefrom, most often obeying first-order decay principles. 

The equation fully complies with all observations made. The copper ion precipitates as red copper on the zinc strip, and the color of the solution fades on account of this. Zinc metal dissolves and enters the solution as zinc ions hence, the surface of the zinc metal shows pitting. Because a zinc ion solution is colorless, the increase in zinc ion concentration is physically observed as color fading. Energy is liberated, as indicated by the temperature of the solution rising by several degrees. With electrons positioned in their correct places, one can write, for the two processes, separate equations as shown below ... 

Choose peroxygen bleaches over hypochlorite to minimize color fading or fabric damage. 

An intense purple-blue species forms within a few seconds when Cr +, in excess, is added to 4,4 -bipyridinium ion, bpyH. The color fades slowly over many minutes. The formation and disappearance of the intermediate, kf and respectively, are assigned to k2 and Atj respectively from considerations of the assessed spectrum of the intermediate. The reactions involved are... 

To a solution of 9.25 g (0.06 mol) of titanium trichloride in 57 ml of boiled water is added 66 g of concentrated hydrochloric acid and the solution is diluted to 1 liter with boiled water. The mixture is heated to boiling, a current of carbon dioxide is passed through it, and a hot solution of 1.96 g (0.01 mol) of 2,4-dinitrobenzaldehyde in ethanol is added. The dark blue color fades... 

The solution becomes a pale yellow color the color fades after 6 hr. 

To 1,2-dimcthyl-3-vinylindole (0.5 g, 2.9 mmol) in dry benzene (30 ml) was added TCNE (0.37 g, 2.9 mmol). The initial dark green color faded after 5 min. The solution was concentrated to 10 mL and crystals of the product separated upon standing yield 0.68 g (79%). 

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