Crystalline precipitates

Pure pyridine may be prepared from technical coal-tar pyridine in the following manner. The technical pyridine is first dried over solid sodium hydroxide, distilled through an efficient fractionating column, and the fraction, b.p. 114 116° collected. Four hundred ml. of the redistilled p)rridine are added to a reagent prepared by dissolving 340 g. of anhydrous zinc chloride in a mixture of 210 ml. of concentrated hydrochloric acid and 1 litre of absolute ethyl alcohol. A crystalline precipitate of an addition compound (probable composition 2C5H5N,ZnCl2,HCl ) separates and some heat is evolved. When cold, this is collected by suction filtration and washed with a little absolute ethyl alcohol. The yield is about 680 g. It is recrystaUised from absolute ethyl alcohol to a constant m.p. (151-8°). The base is liberated by the addition of excess of concentrated... 

Prepare 10 ml. of saturated sodium bisulphite solution and add 4 ml. of the aldehyde shake thoroughly and observe the rise in temperature. Filter the crystalline precipitate at the pump, wash it with a little alcohol, followed by ether, and allow it to dry. 

Heat a mixture of 15 g. of p-nitroacetanilide and 75 ml. of 70 per cent, sulphuric acid (1) under a reflux water condenser for 20-30 minutes or until a test sample remains clear upon dilution with 2-3 times its volume of water. The p-nitroaniline is now present in the hquid as the sulphate. Pour the clear hot solution into 500 ml. of cold water and precipitate the p-nitroanihne by adding excess of 10 per cent, sodium hydroxide solution or of concentrated ammonia solution. When cold (cool the mixture in ice water, if necessary), filter the yellow crystalline precipitate at the pump, wash it well with water, and drain thoroughly. Recrystallise it from a mixture of equal volumes of rectified (or methylated) spirit and water or from hot water. Filter, wash and dry. The yield of p-nitroanihne, m.p, 148°, is 11 g. 

Dissolve 36 g. of p-toluidine in 85 ml. of concentrated hydrochloric acid and 85 ml. of water contained in a 750 ml. conical flask or beaker. Cool the mixture to 0° in an ice-salt bath with vigorous stirring or shaking and the addition of a httle crushed ice. The salt, p-toluidine hydrochloride, will separate as a finely-divided crystalline precipitate. Add during 10-15 minutes a solution of 24 g. of sodium nitrite in 50 ml. of water (1) shake or stir the solution well during the diazotisation, and keep the mixture at a temperature of 0-5° by the addition of a httle crushed ice from time to time. The hydrochloride wUl dissolve as the very soluble diazonium salt is formed when ah the nitrite solution has been introduced, the solution should contain a trace of free nitrous acid. Test with potassium iodide - starch paper (see Section IV,60). 

Reduction of methyl orange to />-aminodimethylaniline. Method 1. Dissolve 2 0 g. of methyl orange in the minimum volume of hot water and to the hot solution add a solution of 8 g. of stannous chloride in 20 ml. of concentrated hydrochloric acid until decolourisation takes place gentle boiling may be necessary. Cool the resulting solution in ice a crystalline precipitate consisting of sulphanilic acid and some p-aminodimethylaniline hydrochloride separates out. In order to separate the free base, add 10 per cent, sodium hydroxide solution until the precipitate of tin hydroxide redisaolves. Extract the cold solution with three or four 20 ml. portions of ether, dry the extract... 

The next day comes and the hung-over chemist wakens to see a dark red solution stirring away. In some cases where the chemist had made an enormous batch of this stuff, there may be seen a small mass of crystalline precipitate at the bottom of the flask. This is no big deal and will go away in the next step. If the chemist had made this in a flat-bottomed flask (which she really should have for convenience) then the ice tray is removed, the flask returned to the stir plate, a distillation setup attached, and the acetone is vacuum distilled from the flask. After all the acetone has come over the chemist can proceed in two different ways. One way is to just keep on distilling the solution until all of the formic acid has been removed. The chemist knows that just about all the formic has been removed when there is about 300mL of thick black liquid remaining in the reaction flask and hardly any clear formic acid is dripping over into the collection flask. If one were to swirl the reaction flask, the liquid will appear syrupy and kind of coat the sides of the flask. This is more evident when the flask cools. A quick sniff of the flask may indicate that some formic is still in there, but it should be too minimal to be of any concern. 

Medium 10-15 Filtration of crystalline precipitates. Removal of floaters from distilled water. 

Dimenhydrinate. Dimenhydrinate [523-87-5] (Dramamine) (18) is a white crystalline, odorless powder that melts between 102 and 107°C. It is sparingly soluble in water, freely soluble in ethanol and chloroform, and sparingly soluble in diethyl ether. Dimenhydrinate is prepared by combining dimethylaminoethyl ben2hydryl ester with 8-ch1orotheophy11ine and refluxing in an isopropyl alcohol solution. The crystalline precipitate of dimenhydrinate that forms on cooling is collected by filtration, washed with cold ethyl acetate, and dried. 

Sodium niobate(7 6) [12201 -59-17, 7Na20 6Nb20 3IH2O or Naj4Nbj2 037-31H2 0, forms a crystalline precipitate when a hot solution of a soluble niobium compound is added to a hot concentrated sodium hydroxide solution. It is insoluble in the presence of excess sodium hydroxide but is sparingly soluble in pure water. It also can be formed by addition of sodium hydroxide or chloride to a solution of the 4 3 potassium niobate. 

Ammodendrine, C jH oONj, HjO (No. 1, table, p. 116). The base has m.p. 73 °, becomes anhydrous at 70-80°, and then melts at 50-60°, Wd i 0°. The salts are amorphous and deliquescent except the hydriodide B. HI, which forms a crystalline precipitate, m.p. 218-20°, from alcohol, and the perchlorate, m.p. 199-200°. An amorphous A-benzoyl derivative was obtained. With methyl iodide ammodendrine behaves as a secondary base, yielding first A-methylammodendrine hydriodide (a crystalline precipitate, m.p. 183-5°, from a mixture of alcohol and acetone), and at the second stage iV-methylammodendrine methiodide, m.p. 163-5°. On hydrogenation ammodendrine furnishes a dihydro-base, which is hydrolysed into acetic acid and 2 3 -dipiperidyl, C oHjoNj, and must be dZ-A-acetyl-3-a-piperidylpiperidine. Ammodendrine should therefore be acetyltetrahydroanabasine and is of biological interest as the first recorded occurrence of this type of alkaloid in the Leguminoss. ... 

Koppeschaar), is a crystalline precipitate, sparingly soluble in water (1 in 1,265 at 10°), almost insoluble in sodium potassium tartrate solution, and is the form in which the alkaloid is usually estimated. 

Aconitine produces an intense tingling sensation when a drop of a solution, 1 in 10,000, is applied to the tip of the tongue. It also gives a characteristic unstable, crystalline precipitate when a few drops of potassium permanganate solution are added to a solution of the alkaloid in dilute acetic acid. The formation of acetic acid when the alkaloid is heated dry, or of benzoic acid when it is hydrolysed by alkali, have also been suggested as identification tests. For the recognition of minute quantities a biological test is probably the best procedure. ... 

Cyano-3 -hydroxy-5a-pregnan-20-one A suspension of 5a-pregnane-3, 20-dione (2 g) in ethanol (90 ml) is treated with acetone cyanohydrin (4 ml) and three drops of triethylamine and stirred at room temperature until complete dissolution. After 3 hr, the solution is diluted with 200 ml of water, acidified with acetic acid and the crystalline precipitate is thoroughly washed with water and dried under vacuum to give 2.1 g (97%) of product mp 172-178° (dec). A sample recrystallized from ethyl acetate melts at 176-179° (dec) [a]p 86° (ethyl acetate). 

A solution of 1.1 g of the cyanohydrin in 6 ml of pyridine is treated with 0.6 ml of phosphorus oxychloride and allowed to stand at room temperature overnight. The reaction mixture is quenched with ice and water and the resulting crystalline precipitate is collected, washed with water and dried to yield 1.05 g. Recrystallization from aqueous pyridine affords 0.88 g (83%) of 20-cyano-21-hydroxy-3,3-ethylenedioxypregna-5,17(20)-dien-l l-one acetate mp 197-200°. 

Add I c.c. of a saturated alcoholic solution of cupric acetate to a few drops of the ester, a bluish-green crystalline precipitate of copper acetoacetic ester, (CoH903), Cu, is formed. See Appendix, p. 248. i . ... 

Add a few drops of concentrated ammonia. A while crystalline precipitate of oxamide rs formed, C20, (0CH3).2-1-... 

Add calcium chloride and stir with a glass rod. A crystalline precipitate of calcium tartrate, C.,H40(,Cad-4H20, is formed u hich dissolves in acetic acid and caustic alkalis. Repeat the fniegoing test, but add a few drojts of acetic acid before the calcium chloride. There is no precipitate. Calcium sulphate also gives no precipitate with tartaric acid or neutial tartrates, ( compare reactions for OKalic acid, p. 100). 

Dissolve the acetanilide in the acetic acid in a flask (-J litre), and add gradually the bromine, dissolved in. bout twice its volume of glacial acetic acid, and shake well. When tlie bromine has been added, let the mixture stand hour mid then pour into 200 c.c. water and rinse out with writer. Filter the crystalline precipitate at the pump and wash three or four times with water. Press it well down and let it cl min. Dissohe the moist substance in spirit (about 60 c.c.) incl pour into a beaker to crystallise. Filter the crystals, w ish with a little dilute spirit, and dry on filter paper. Yield 6—7 grams. 

Dissolve the substance in cold water and add it to a solution of phenol in caustic soda, drop by drop. An orange crystalline precipitate of hydvoxya/,obcn/ene is formed. Repeat, using /3 n.iphthol in place of phenol. A scarlet precipitate is obtai ned. 

Dissolve in cold water and add a fevv drops of aniline, and shake up. Diazoaminobenzene separates out as a yellow crystalline precipitate. 

Rciufion.—Dissolve a little of the substance in alcohol and add a drop or two of an alcoholic solution of silver nitrate. A red crystalline precipitate of CqHjNiN.NAg.CjjH is deposited. See Appendix., p. 285. 

Add to another portion a drop of bromine water. A white crystalline precipitate of tribromophenol is formed. 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

A crystalline precipitate of barium salt will be obtained, from which the acid can be re ily liberated and identified. 

To the filtrate obtained, there are then added about 0.2 gram of sodium hydrosulfite or sodium sulfite and 15.0 grams of anhydrous sodium acetate in about 27 grams of acetic anhydride at 40°C. The reaction mixture formed is cooled to 8° to 10°C with stirring and held at this temperature for 60 minutes. A crystalline precipitate of about 27 grams of N-acetyl-p-aminophenol is obtained melting at 169°-171°C. This is equivalent to a yield of 85%. 

At the end of the reflux period the mixture was cooled to 30°C and the heavy crystalline precipitate was collected and washed with 2 X 75 ml of ethanol. The product was dried in vacuo at30°C. Wt = 111g. Yield = 82%, MP 173°-175°C. 

A mixture consisting of 2 grams of 2-hydroxy-3-(N,N-diethylcarboxamido)-9,10-dimethoxy-1,2,3,4,6,7-hexahydro-1 Ib-H-benzopyridocoline (OH-axial) hydrochloride (prepared by treating the base with hydrogen chloride gas in absolute ether) dissolved in 7 ml of acetic anhydride containing 3 ml of pyridine was heated at 100°C for 2 hours under a nitrogen atmosphere. At the end of this period, a crystalline precipitate had formed and the resultant mixture was subsequently diluted with an equal volume of diethyl ether and filtered. 

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