Immediate acidity

C2H4N2O3, NH2CONHCOOH. Unknown in the free state as it breaks down immediately to urea and COi- The NH4, Ba, Ca, K and Na salts are known and are prepared by treating ethyl allophanate with the appropriate hydroxide. The esters with alcohols and phenols are crystalline solids, sparingly soluble in water and alcohol. They are formed by passing cyanic acid into alcohols or a solution of an alcohol or phenol in benzene. The amide of allophanic acid is biuret. Alcohols are sometimes isolated and identified by means of their allophanates. 

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

Thalliumilll) niirate, T1(N03)3,3H20. Formed Tl plus cone. HNO,. Immediately hydrolysed by water but is soluble in dilute mineral acids, alcohols and diglyme. Used in oxythallation. ... 

Reactions in which a product remains in the him (as above) are complicated by the fact that the areas of reactant and product are not additive, that is, a nonideal mixed him is formed. Thus Gilby and Alexander [310], in some further studies of the oxidation of unsaturated acids on permanganate substrates, found that mixed hlms of unsaturated acid and dihydroxy acid (the immediate oxidation product) were indeed far from ideal. They were, however, able to ht their data for oleic and erucic acids fairly well by taking into account the separately determined departures from ideality in the mixed hlms. 

The addition of concentrated sulphuric acid to a solid dichromate mixed with a chloride produces a red vapour, chromium(VI)dioxide dichloride, Cr02Cl2 (cf. sulphur dioxide dichloride, SO2CI2). Chromium(VI) dioxide dichloride reacts with water immediately ... 

Reactions of Aspirin, (i) Distinction from Salicylic acid. Shake up with water in two clean test-tubes a few crystals of a) salicylic acid, (0) aspirin, a very dilute aqueous solution of each substance being thus obtained. Note that the addition of i drop of ferric chloride solution to (a) gives an immediate purple coloration, due to the free —OH group, whereas (b) gives no coloration if the aspirin is pure. 

Place I g. of benzamide and 15 ml. of 10% aqueous sodium hydroxide solution in a 100 ml. conical flask fitted with a reflux water-condenser, and boil the mixture gently for 30 minutes, during which period ammonia is freely evolved. Now cool the solution in ice-water, and add concentrated hydrochloric acid until the mixture is strongly acid. Benzoic acid immediately separates. Allow the mixture to stand in the ice-water for a few minutes, and then filter off the benzoic add at the pump, wash with cold water, and drain. Recrystallise from hot water. The benzoic acid is obtained as colourless crystals, m.p. 121°, almost insoluble in cold water yield, o 8 g. (almost theoretical). Confirm the identity of the benzoic acid by the tests given on p. 347. 

The crude acetonitrile contains as impurity chiefly acetic acid, arising from the action of phosphoric acid on the acetamide. Therefore add to the nitrile about half its volume of water, and then add powdered dry potassium carbonate until the well-shaken mixture is saturated. The potassium carbonate neutralises any acetic acid present, and at the same time salts out the otherwise water-soluble nitrile as a separate upper layer. Allow to stand for 20 minutes with further occasional shaking. Now decant the mixed liquids into a separating-funnel, run off the lower carbonate layer as completely as possible, and then pour off the acetonitrile into a 25 ml, distilling-flask into which about 3-4 g. of phosphorus pentoxide have been placed immediately before. Fit a thermometer and water-condenser to the flask and distil the acetonitrile slowly, collecting the fraction of b.p. 79-82°. Yield 9 5 g. (12 ml.). 

Dissolve 4 5 ml. of aniline in a mixture of 10 ml. of concentrated hydrochloric acid and 20 ml. of water cool the solution to 5°, and diazotise by the addition of 4 g. of sodium nitrite dissolved in 20 ml, of water, observing the usual precautions given on page 181. Dissolve 7 g. of 2-naphthol in 60 ml. of 10% sodium hydroxide solution contained in a 200 ml. beaker, and cool this solution to 5 by external cooling, aided by the direct addition of about 20-30 g. of crushed ice. Now add the diazotised solution very slowly to the naphthol solution, keeping the latter well stirred meanwhile the mixed solutions immediately develop a deep red colour, and the benzeneazonaphthol should... 

Toluene-/ sulplionamide is almost insolubb in cold water, but dissolves readily in sodium hydroxide solution (as the sodium derivative) aid is immediately reprecipitated on the addition of strong acids. To show the formation of the sodium derivative, dissolve about o-2 g. of metallic sodium in about 10 ml, of ethanol, cool the solution, and then add it to a solution of 1 g. of the sulphonamide in 20 ml. of cold edianol. On shaking the mixture, fine white crystals of the sodium derivative, CH,C,HjSO,NHNa, rapidly separate, and may be obtained pure by filtering at the pump, and washing firet with a few ml. of ethanol, and then with ether. 

Esters (a) and acid chlorides (6) readily react with Grignard reagents to give ketones, which immediately react with a second equivalent of the reagent as in (5) to give tertiary alcohols as before. 

Iodoform reaction. To 0 5 ml. of lactic acid add 10% NaOH solution until alkaline to litmus. Then add 5 ml. of 10% KI solution and 10 ml. of freshly prepared sodium hypochlorite solution and mix well. A yellow precipitate of iodoform separates out almost immediately in the cold. 

Oxidation, (a) Unsaturation test. Dissolve about o-i g. of cinnamic acid or of a soluble cinnamate in about 5 ml. of 10% NajCOg solution. To the cold solution add 1% aqueous KMn04 drop by drop. Immediate decolorisation denotes unsaturation. (Note. Many easily oxidisable substances, e.g.y formic acid, acetaldehyde, etc.y also rapidly decolorise alkaline permanganate. Cinnamates, however, do not reduce Fehling s solution.)... 

Hydroxamic acid formation cf. Section 9, p. 334). To a few drops of an ester, add 0 2 g. of hydroxylamine hydrochloride and about 5 ml. of 10% NaOH solution and gently boil the mixture for 1-2 minutes. Cool and acidify with dil. HCl and then add a few drops of ferric chloride solution. A violet or deep red-brown colour develops immediately. 

Sulphuric acid. Warm about 0 2 g. of the carbohydrate with 1 ml. of cone. H2SO4, using a small flame. Observe the immediate blackening. As the temperature is raised, COj, CO and SOj are evolved. 

Sorensen s reaction. First read carefully the Estimation of Glycine, p. 463. Dissolve 0 2 g. of glycine in a few ml. of water in a test-tube A, add 2 drops of phenolphthalein and then very dilute NaOH solution drop by drop until the solution just turns pink. In a second test-tube B place 2 ml. of 40% formalin solution, add 2 drops of phenolphthalein solution and then the dil. NaOH solution until the solution just turns pink. Pour the contents of B into A and note the immediate decolorisation of the phenolphthalein, the solution now being acid. Observe also that several drops of dil. NaOH solution can now be added before the pink colour is restored. 

Reduction of potassium permanganate. To a solution of uric acid in aqueous NajCO add KMnO solution drop by drop a brown precipitate of MnOj is produced immediately in the cold. 

Benzene. Pure benzene (free in particular from toluene) must be used, otherwise the freezing-point is too low, and crystallisation may not occur with ice-water cooling alone. On the other hand, this benzene should not be specially dried immediately before use, as it then becomes slightly hygroscopic and does not give a steady freezing-point until it has been exposed to the air for 2-3 hours. Many compounds (particularly the carboxylic acids) associate in benzene, and molecular weights determined in this solvent should therefore be otherwise confirmed. 

Weigh out accurately about 2 g. of glycine, transfer to a 250 ml. graduated flask, dissolve in distilled water, make up to the mark, and mix well. Transfer 25 ml. of the solution to a conical flask, add 2 drops of phenolphthalein, and then again add dilute sodium hydroxide very carefully until the solution is just faintly pink. No v add about 10 ml. (/. ., an excess) of the neutralised formaldehyde solution the pink colour of the phenolphthalein disappears immediately and the solution becomes markedly acid. Titrate with AI io sodium hydroxide solution until the pink colour is just restored. Repeat the process with at least two further quantities of 25 ml. of the glycine solution in order to obtain consistent readings. 

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