Red color

Reddish-brown coloration (no precipitate) Blood red coloration... 

Dissolve a small portion of the sodium derivative in a few mi. of water in a test-tube, and add one drop of ferric chloride solution. A deep red coloration is produced, but rapidly disappears as the iron is precipitated as ferric hydroxide. The sodium (derivative (A) of the nitromethane wh dissolved in water undergoes partial hydrolysis,... 

Dissolve a few drops of nitromethane in 10% sodium hydroxide solution. Add a few crystals of sodium nitrite and shake. Now add dilute sulphuric acid drop by drop. A brownish-red coloration develops, but fades again when an excess of acid is added. The sulphuric acid has thus liberated nitrous acid, which has in turn reacted with the nitromethane to give a nitrolic acid, the sodium salt of which is CH3NO2 + ONOH = CH(N02) N0H + HgO reddish-brown in colour, probably owing to mesomeric ions of the type ... 

Dissolve 2 g. of anhydrous sodium carbonate in 50 ml. of water contained in a 400 ml. beaker and add 7 g. of finely powdered crystalline sulphanilic acid (2H2O), warming the mixture gently in order to obtain a clear solution. Add a solution of 2 2 g. of sodium nitrite in 10 ml. of water and then cool the mixture in ice-water until the temperature has fallen to 5°. Now add very slowly (drop by drop) with continual stirring a solution of 8 ml. of concentrated hydrochloric acid in 15 ml. of water do not allow the temperature to rise above 10°. When all the acid has been added, allow the solution to stand in ice-water for 15 minutes to ensure complete diazotisation during this period fine crystals of the internal salt separate from the pink solution. Dissolve 4 ml. of dimethylaniline in a mixture of 4 ml. of concentrated hydrochloric acid and 10 ml. of water, cool the solution in ice-water, and add it slowly to the cold well-stirred diazo solution a pale red coloration is developed. Allow the mixture to stand for 5 minutes and then add slowly with stirring aqueous... 

To 2 ml. of a freshly prepared dilute aqueous solution of sodium nitroprusside, add 2 drops of ethyl malonate and shake then add 2-3 drops of 10% aqueous sodium hydroxide solution and shake again. A red coloration at once appears, but fades in a few minutes to pale brown,... 

Precisely similar results are obtained with ethyl acetoacetate, except that in tests 2 a) and 2 b) the deep red coloration is produced without a preliminary violet coloration. 

Deep red coloration. Boil for one minute and note the formation of a brown ppt. of basic ferric salt. Add dil. HCl the ppt. dissolves, giving a clear solution. 

On adding i drop of bromine water to catechol, a deep red coloration is produced immediately. On gradually adding bromine water to a solution of hydroquinone, a deep red coloration is produced, followed by the separation of deep green crystals which then dissolve giving a yellow solution, i- and 2-Naphthol will decolorise hromine water, but usually no precipitate of the bromo compound can be obtained. 

Nitroprusside reaction. Add 1 ml. of a freshly prepared solution of sodium nitroprusside to the aldehyde or its solution. Add dil. NaOH solution in excess a red coloration is produced. 

Sulphuric add test. Heat 0 5 g. of citric acid or a citrate with 1 ml. of H2SO4 CO and COg are evolved and the mixture turns yellow, but does not char. Acetone dicarboxylic acid, OC(CH2COOH)g, is also formed, and is tested for after heating the mixture for 1 minute cool, add a few ml. of water and make alkaline with NaOH solution. Add a few ml. of a freshly prepared solution of sodium nitroprusside and note the intense red coloration (see Test 4 a) for ketones, p. 346). 

KaOH solution in excess a bright red coloration is developed. 

Phthalcin reaction. Fuse together very gently in a dry test-tube 01 g. of phthalimide, O l g. of phenol and 2 drops of cone. HjSO, Cool, add waier and then NaOH solution in excess. A red coloration is produced which is decolorised by acids. (Note. Succinimide gives no definite coloration in these circumstances.)... 

HCl. Cool again and add a few drops of FeClg solution. A deep brown-red coloration is produced immediately. 

Mercuric nitrite reaction (Millon s reaction). Dissolve a very small crystal of tyrosine in i ml. of water, add 1-2 drops of mercuric nitrate solution, and I drop of dil. HjSO, and then boil. Cool, add i drop of sodium nitrite solution and warm again a red coloration is obtained. 

Meicuric sulphate may be used instead of the nitrate mercuric chloride must not be used, however, as chlorides interfere with the formation of the red coloration. 

Formation of methyl-orange cf. p. 214). Dissolve about 0 3 g. of sul-phanilic acid in 2 ml. of 10% aqueous NajCOj solution. Cool m ice-water and add 2 to 3 drops of 20% NaNOj solution. Now add about I ml. of cold dil. HCl, shake and leave for 2-3 minutes. Meanwhile dissolve i drop of dimethylaniline in a few drops of dil. HCl, cool thoroughly in ice-water and then add to the cold diazo solution. Shake well and make alkaline with aqueous NaOH solution note the formation of a deep orange-yellow coloration or precipitate. On the addition of HCl, a bright red coloration is produced. 

Ferric chloride coloration. Add FeCl, solution to a few crystals (or to an aqueous solution) of /> nitrophenol a violet-red coloration is produced. o-Nitrophenol does not give a coloration. 

Make a concentrated solution of anthracene in hot acetone. To about 2 ml. of this solution add a cold concentrated acetone solution of picric acid drop by drop, and note the formation of a red coloration which becomes deeper on further addition of the acid. If excess of picric acid is added, however, the solution becomes paler in colour, and this is to be avoided if possible. Boil to ensure that both components are in solution and then transfer to a small porcelain basin or watch-glass ruby-red crystals of anthracene picrate separate out on cooling. The product, however, is often contaminated with an excess of either anthracene or of picric acid, which appear as yellowish crystals. 

L. Treat with hydroxylamine and ferric chloride (pp. 334, 353). Violet or red colorations given particularly by esters. Deep colorations also given by acid chlorides, acid anhydrides and by some acid amides (usually aliphatic) and by a few of the simpler anilides. 

It is essential to use an excess of sodium, otherwise if sulphur and nitrogen are both present sodium thiocyanate, NaCNS, may be produced in the test for nitrogen it may give a red coloration with ferric iron but no Prussian blue since there will be no free cyanide ions. With excess of sodium the thiocyanate, if formed, will be decomposed ... 

Yttrium oxide is one of the most important compounds of yttrium and accounts for the largest use. It is widely used in making YVOr europium, and Y2O3 europium phosphors to give the red color in color television tubes. Many hundreds of thousands of pounds are now used in this application. 

To be able to prepare and study these elusive species in stable form, acids billions of times stronger than concentrated sulfuric acid were needed (so called superacids). Some substituted carbocations, however, are remarkably stable and are even present in nature. You may be surprised to learn that the fine red wine we drank tonight contained carbocations which are responsible for the red color of this natural 12% or so alcoholic solution. I hope you enjoyed it as much as I did. 

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. 

Marquis reagent (gives a purple-red coloration, then violet, then blue with morphine, codeine, dionine, and heroine) mix 3 mL of concentrated H2SO4 with 3 drops of a 35% formaldehyde solution. 

This reaction occurs quickly and is of known stoichiometry. A titrant of SCN is easily prepared using KSCN. To indicate the titration s end point we add a small amount of Fe + to the solution containing the analyte. The formation of the red-colored Fe(SCN) + complex signals the end point. This is an example of a direct titration since the titrant reacts with the analyte. 

A few substances indicate the presence of a specific oxidized or reduced species. Starch, for example, forms a dark blue complex with 13 and can be used to signal the presence of excess 13 (color change colorless to blue), or the completion of a reaction in which 13 is consumed (color change blue to colorless). Another example of a specific indicator is thiocyanate, which forms a soluble red-colored complex, Fe(SCN) +, with Fe +. 

In the absence of Fe +, the membrane is colorless, but when immersed in a solution of Fe + and C, the membrane develops a red color as a result of the formation of a Fe +-bathophenanthroline complex. A calibration curve determined using a set of external standards with known molar concentrations of Fe + gave a standardization relationship of... 

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