Iodoform

Iodine as such finds few uses but a solution in alcohol and water, also containing potassium iodide ( tincture of iodine was commonly used as an antiseptic for cuts and wounds, but had rather an irritant action. Iodoform (triiodomethane), CHI3, is also an antiseptic, but newer compounds of iodine are now in use. Silver iodide, like silver bromide, is extensively used in the photographic industry. 

Note cautiously the characteristic odour of acetaldehyde which this solution possesses. Then with the solution carry out the following general tests for aldehydes described on p. 341 Test No. I (SchiflF s reagent). No. 3 (Action of sodium hydroxide). No. 4 (Reduction of ammoniacal silver nitrate). Finally perform the two special tests for acetaldehyde given on p. 344 (Nitroprusside test and the Iodoform reaction). 

For other types of compounds which give the iodoform reaction, see H. Booth and B. C. Saunders, Chem, and Industry 1950. 824. 

If acetone is used there is no initial oxidation tri odo-acetone is first formed and is then converted by the sodium hydroxide to iodoform and... 

IODOFORM FROM ACETONE. (Semi-micro Scale.) Required Acetone, 0 5 ml. 10% potassium iodide solution, 20 ml. 10% sodium hydroxide solution, 8 ml. zM sodium hypochlorite solution, 20 ml. 

Place 0 5 ml. of acetone, 20 ml. of 10% aqueous potassium iodide solution and 8 ml. of 10% aqueous sodium hydroxide solution in a 50 ml. conical flask, and then add 20 ml. of a freshly prepared molar solution of sodium hypochlorite. Well mix the contents of the flask, when the yellow iodoform will begin to separate almost immediately allow the mixture to stand at room temperature for 10 minutes, and then filter at the pump, wash with cold w ater, and drain thoroughly. Yield of Crude material, 1 4 g. Recrystallise the crude iodoform from methylated spirit. For this purpose, place the crude material in a 50 ml. round-bottomed flask fitted with a reflux water-condenser, add a small quantity of methylated spirit, and heat to boiling on a water-bath then add more methylated spirit cautiously down the condenser until all the iodoform has dissolved. Filter the hot solution through a fluted filter-paper directly into a small beaker or conical flask, and then cool in ice-water. The iodoform rapidly crystallises. Filter at the pump, drain thoroughly and dry. 

Iodoform forms yellow crystals, of m.p. 120 , and has a characteristic odour. 

Hydrolysis of Acetoxime. Place about i g. of the recrystallised oxime in a small distilling-flask (50 ml.), add 10 ml. of dilute HjSO, and heat gently until about half the solution has distilled over. Test [a] the aqueous distillate for acetone by the iodoform reaction (p.346), b) the residual solution in the distilling-flask for hydroxylamine by... 

Place 5 mi. of ethyl acetate in a 100 ml. round-bottomed flask, and add about 50 ml. of 10% sodium hydroxide solution, together with some fragments of ungiazed porcelain. Fit the flask with a reflux water-condenser, and boil the mixture gently over a wire gauze for 30 minutes. Now disconnect the condenser, and fit it by means of a bent delivery-tube (or knee-tube ) to the flask for direct distillation (Fig. 59, or Fig. 23(0), p. 45). Reheat the liquid, and collect the first 10 ml. of distillate, which will consist of a dilute aqueous solution of ethanol. Confirm the presence of ethanol by the iodoform test Test 3, p. 336). 

Methyl iodide, ethyl bromide and iodide, higher alpihatic halides chloroform, iodoform, carbon tetrachloride chlorobenzene, bromobenzene, iodobenzene benzyl chloride. 

Aniline.—Burns with a very smoky flame, clouds of soot being produced. Typical of many aromatic substances. i,2 Dibromoethane.—Does not burn until vapour becomes hot and then burns with a slightly smoky flame. Typical of substances rich in halogens such as cldoroform, chloral hydrate, and carbon, tetrachloride. (Note, however, that iodoform evolves copious fumes of iodine when heated in this way.)... 

Alcohols containing the CH3CH(OH) group give the iodoform... 

Iodoform Reaction. To 0 5 ml. of ethanol add 3 ml. of 10% KI solution and 10 ml. of NaOCl solution. Warm gently fine yellow crystals of CHI3 separate. Isopropanol gives CHIj in the cold. Pure methanol and the other alcohols in this section go not give the reaction. 

Gives some of the tests for acetaldehyde, but more feebly e.g., it restores the colour to SchifF s reagent, gives a yellow resin with NaOH, and responds to the nitroprusside test. With ammoniacal AgN03, it gives a silver minor only after 2 -3 minutes warming. It does not give the iodoform reaction. 

Ketones containing the CH3CO— group give the iodoform reaction. (For other compounds which give this test, see p- 91.)... 

Physical Properties. All heavier than, and insoluble in water. All liquids, except iodoform, CHI3, which is a yellow crystalline solid with a characteristic odour. The remainder are colourless liquids when pure ethyl iodide, CjHjI, and iodobenzene, CjHgl, are, however, usually yellow or even brown in colour. Methyl iodide, CH3I, ethyl bromide, CgH Br, ethyl iodide, chloroform, CHCI3, and carbon tetrachloride, CCI4, have sweetish odours, that of chloroform being particularly characteristic. 

Chlorofonn, carbon tetrachloride, iodoform and the halogeno-benzenes do not give precipitates with cold aqueous silver nitrate solution. 

Similar results are obtained with methyl iodide, ethyl bromide, ethyl iodide, iodoform, carbon tetrachloride, and benzyl chloride. 

Chloroform and iodoform give also sodium formate in this reaction CHCI3 -h 4NaOH = HCOONa -h 3NaCl -f zH O. A portion of the solution, before the addition of the HNO3, should therefore be tested for formic acid (Tests, p. 350) ensure however that the solution is neutralised where necessary during these tests. 

Liberation of iodine on heating. On heating in a dry tube, iodoform gives off copious violet vapours of iodine. This will have been observed during the Preliminary Tests, p. 319. 

Isocyanide reaction. Repeat Test i for chloroform (above) using 0 5 g. of iodoform instead of i ml. of chloroform the foul odour of isocyanide is produced as before. 

Yellow. Quinones, m- and p-nitroaniline, o-nitrophenol, and many other nitrO"Compounds. [Note that some nitro-compounds often appear yellow (e.g. m-dinitrobenzene and 3, 5 -dinitro-benzoic acid), but are colourless when absolutely pure.] Iodoform. 

Aldehydes (including chloral hydrate) formates and lactates some esters chloroform and iodoform reducing sugars some phenols. 

Special Tests (i) Nitro-prusside + NaOH (red). (ii) Iodoform Nitroprusside + NaOH (red) (1) NaHSOs, immediate ppt. (i) FeCls (violet) (ii) NaHSOj, ppt. on standing. 

Special reactions — — — Fluores- cein Iodoform (KI + NaClO) FeSO, + H.O, + NaOH violet — — — (a) Fluores- cein W Phthalein —... 

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