Color colored solutions

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. 

Ethyl bis-(2,4-dinitrophenyl) acetate (indicator) the stock solution is prepared by saturating a solution containing equal volumes of alcohol and acetone with the indicator pH range colorless 7.4-9.1 deep blue. This compound is available commercially. The preparation of this compound is described by Fehnel and Amstutz, Ind. Eng. Chem., Anal. Ed. 16 53 (1944), and by von Richter, Ber. 21 2470 (1888), who recommended it for the titration of orange- and red-colored solutions or dark oils in which the endpoint of phenol-phthalein is not easily visible. The indicator is an orange solid which after crystallization from benzene gives pale yellow crystals melting at 150-153.5°C, uncorrected. 

After adding p-rosaniline and formaldehyde, the colored solution was diluted to 25 ml in a volumetric flask. The absorbance was measured at 569 nm in a 1-cm cell, yielding a value of 0.485. A standard sample was prepared by substituting a 1.00-mL sample of a standard solution containing the equivalent of 15.00 ppm SO2 for the air sample. The absorbance of the standard was found to be 0.181. Report the concentration of SO2 in the air in parts per million. The density of air maybe taken as 1.18 g/L. 

Colorimetric Method. A finely powdered sample treated with sulfuric acid, hydrobromic acid [10035-10-6] and bromine [7726-95-6] gives a solution that when adjusted to pH 4 may be treated with dithi one [60-10-6] ia / -hexane [110-54-3] to form mercuric dithi2onate [14783-59-6] (20). The resultant amber-colored solution has a color iatensity that can be compared against that of standard solutions to determine the mercury concentration of the sample. Concentrations below 0.02 ppm have been measured by this method. 

The reverse reaction, the photochemical ring opening of sphopyranes (22b), takes place by absorption ia the short-wave uv region of the spectmm and the merocyanine isomer (22a) is obtained. The electron transition of (22a) is ia the visible spectral region, whereas (22b) is colorless. As a result, the dye solution can change from colorless to a colored solution (87,88). These photochromic reactions can be used for technical appHcations (89). 

Color. Many water samples have a yellow to brownish-yeUow color which is caused by natural substances, eg, leaves, bark, humus, and peat material. Turbidity in a sample can make the measurement of color uncertain and is usually removed by centrifiigation prior to analysis. The color is usually measured by comparison of the sample with known concentrations of colored solutions. A platinum—cobalt solution is used as the standard, and the unit of color is that produced by 1 mg/L platinum as chloroplatinate ion. The standard is prepared from potassium chloroplatinate (K PtCl ) and cobalt chloride (C0CI26H2O). The sample may also be compared to suitably caUbrated special glass color disks. 

Bromine and bromides can be detected quaUtatively by a number of methods. In higher concentrations bromine forms colored solutions in solvents such as carbon tetrachloride [56-23-5] and carbon disulfide [75-15-0]. Bromine reacts with yeUow disodium fluorescein [518-47-8] to form red disodium tetrabromofluorescein (eosin) [548-26-5] C2QH Br4Na20. As Httle as 0.3 p.g of bromide can be detected and chlorides do not interfere (56). Bromine reacts with platinum sulfate [7446-29-9] Pt(S0 2> solution to form red to brown crystals of potassium hexabromoplatinate [16920-93-7] K PtBr ( )-... 

Chlorine dioxide is soluble in water, forming a yellow to yeUow-green color solution that is quite stable if kept cool and in the dark. Various crystalline hydrates of chlorine dioxide have been described including a hexahydrate (19), an octahydrate (20), and an orange colored decahydrate (21). The partition coefficient between water and CIO2 gas is about 21.5 at 35°C and 70.0 at 0°C (22). Data on the solubiUty of chlorine dioxide in water at various... 

A short column of alumina may also be employed for decolorization. The colored solution is placed on the column and eluted with a dry hydrocarbon solvent. If the desired product is not highly polar in nature, recovery by the technique may be excellent. 

To approximately 1.3 g of hydrogen fluoride contained in a polyethylene bottle and maintained at -60°C was added 2.3 ml of tetrahydrofuran and then a solution of 500 mg (0.0012 mol) of 6a-fluoro-9/3,11/3-epoxy-16a-methyI-17a,21 -dihydroxy-1,4-pregnadiene-3,20-dione-2T acetate in two ml of methylene chloride. The steroid solution was rinsed in with an additional 1 ml of methylene chloride. The light red colored solution was then kept at approximately -30°C for 1 hour and at -10°C for 2 hours. At the end of this period it was mixed cautiously with an excess of cold sodium bicarbonate solution and the organic materiai extracted with the aid of additional methylene chloride. 

Polycyclic aromatic hydrocarbons dissolve in chloroaluminate(III) ionic liquids to give brightly colored solutions (due to the protonated aromatic compound [31]). The... 

FIGURE 16.7 Many vanadium Loni ioundt torm vividly colored solutions in water. The are also used in pottery glazes. Tine blue colors here aie due to the vanadvl ion V t) ... 

Many of the d-block elements form characteristically colored solutions in water. For example, although solid copper(II) chloride is brown and copper(II) bromide is black, their aqueous solutions are both light blue. The blue color is due to the hydrated copper(II) ions, [Cu(H20)fJ2+, that form when the solids dissolve. As the formula suggests, these hydrated ions have a specific composition they also have definite shapes and properties. They can be regarded as the outcome of a reaction in which the water molecules act as Lewis bases (electron pair donors, Section 10.2) and the Cu2+ ion acts as a Lewis acid (an electron pair acceptor). This type of Lewis acid-base reaction is characteristic of many cations of d-block elements. 

The complexes [Co(NH,)6l24, [Co(H20)6]2+, and [CoCI4]2 form colored solutions. One is pink, one yellow, and the third blue. Use the spectrochemical series and the relative magnitudes of A() and Ar to match each color to a complex. Explain your reasoning. 

Ionic polysulfides dissolve in DMF, DMSO, and HMPA to give air-sensitive colored solutions. Chivers and Drummond [88] were the first to identify the blue 83 radical anion as the species responsible for the characteristic absorption at 620 nm of solutions of alkali polysulfides in HMPA and similar systems while numerous previous authors had proposed other anions or even neutral sulfur molecules (for a survey of these publications, see [88]). The blue radical anion is evidently formed by reactions according to Eqs. (5)-(8) since the composition of the dissolved sodium polysulfide could be varied between Na2S3 and NaaS with little impact on the visible absorption spectrum. On cooling the color of these solutions changes via green to yellow due to dimerization of the radicals which have been detected by magnetic measurements, ESR, UV-Vis, infrared and resonance Raman spectra [84, 86, 88, 89] see later. 

Depending on the means of extraction, decreasing the ratio of extraction solvent to plant material may avoid the need for a concentration step. However, quantitative extractions usually require an adequate rate of solvent to material and two or more re-extractions until a clear or faintly colored solution is obtained. ... 

As an example, five different synthetic colorants (Tartrazine, Sunset Yellow, Ponceau 4R, Amaranth, and Brilliant Blue FCF) from drinks and candies were separated on a polyamide adsorbent at pH 4, eluted with an alkaline-ammonia solution. By another method, 13 synthetic food colorants were isolated from various foods using specific adsorption on wool. After elution with 10% ammonia solution and gentle warming, an absorption spectrum of the resulting colorant solution was recorded, compared to the reference spectra of pure colorants, and identified by linear regression analysis. ... 

The diastase activity was traditionally determined according to the Schade method in the earlier years (Schade et al., 1958). One unit of diastase activity (or more specifically, a-amylase), DN, is defined as that amoimt of enz)nne that converts 0.01 g of starch to the prescribed endpoint in 1 h at 37 °C under the experimental conditions. In this assay, a standard solution of starch, which reacts with iodine to produce a color solution, is used as a substrate for honey enzymes under the standard conditions (Rendleman, 2003). A recently developed procedure uses an insoluble, dyed starch substrate (Persano Oddo and Pulcini, 1999). As this substrate is hydrolyzed by ot-amylase, soluble dyed starch fragments are released into solution. After reaction termination and insoluble substrate removal by centrifugation, absorbance of the supernatant solution (at 620 nm) is measured. The absorbance is proportional to the diastase activity. This procedure has been widely adopted in the honey industry due to the convenience of a commercially available substrate and the simple assay format. 

Attention is finally focused on the advantages of conductometric titrations, which include (i) colored solutions where no indicator is found to function satisfactorily can be successfully titrated by this method (ii) the method is useful for titrating weak acids against weak bases, which does not produce a sharp change in color with indications in ordinary volumetric analysis and (iii) more accurate results are obtained because of the graphical determination of the end-point. 

Removal of Proteinaceous Clouds. With the unchanged method of Averell and Norris (1) the final colored solution of 50.0 ml. may contain as much as 20% ethyl alcohol. Many plant materials, particularly apple pulp, yield proteinaceous substances to the benzene during extraction if the aliquot of extract represents more than 40 to 50 grams of sample, these substances will be present in this final solution as a cloud of solid particles. These substances, whatever their nature, appear to be completely soluble in 60% ethyl alcohol. Thus, the authors recommend the addition of 50 ml. more of ethyl alcohol at this stage, the addition of more hydrochloric acid to maintain pH, and final dilution to 100.0 ml. with water. The resulting solution will be optically clear except for oily or waxy substances, which are removed in the next step. 

A stock solution of the triazole in hexane was made up and diluted to various strengths, and 1.0-ml. aliquots of the diluted solutions were carried through the procedure described below. The transmittance of the colored solutions obtained from 10 to 50 micrograms of the 118-phenyldihydrotriazole was plotted against concentration to make a standard curve. In subsequent analyses, the amount of Compound 118 is readily calculated from the amount of dihydrotriazole formed. 

Absorption curves of the colored solutions were run on a Beckman spectrophotometer using 1.00-cm. quartz cells. A typical curve, shown in Figure 1, has an absorption maximum at about 515 millimicrons. The Coleman Junior spectrophotometer was used for routine determinations of Compound 118 throughout this study. 

The crude material to be used for desulfonamidation should be tested for absence of syw.-tribromoaniline by ascertaining its solubility in 1 N alkali. A clear, though colored, solution should result. If the solution is cloudy, purification of the impure material by dissolving it in alkali, filtering the solution, and reprecipitating the amide is essential. 

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