Alcohol iodoform test

Alcohol and acetone may be detected by their low boiling-point and by the iodoform test. Oils containing alcohol form milky mixtures with water. It may be extracted by washing with water, when the refractive index of the washed oil is found to be distinctly higher than that of the original oil. 

The condensation is carried out in the usual manner in chloroform solution. The product separates from alcohol with 1 5 molecules of solvent of crystallisation, which can be removed at 110° C. It gives the iodoform test with iodine in aqueous sodium hydroxide. At 260° to 265° C. it decomposes. It is insoluble in w ater, but dissolves in hot alcohol or aqueous sodium hydroxide. Alcoholic ferric chloride gives a faint olive-green tint concentrated sulphuric acid gives no coloration in the cold, but on warming an olive-green tint appears, changing to deep red. The chloride may be converted to the oodde in the usual manner. 

Alcohols Ceric ammonium nitrate Dichromate test Iodoform test Lucas test Positive for all alcohols Positive for 1° and 2° alcohols negative for 3° alcohols Positive for all alcohols of the general formula CH3CH(OH)R Immediate reaction for 3°, allylic or benzylic alcohols slower reaction (2-5 min) for 2° no reaction for 1° alcohols... 

Iodoform test. This test is more specific than the previous two tests. Only ethanol (ethyl alcohol) and alcohols with the part structure CH3CH(OH) react. These alcohols react with iodine in aqueous sodium hydroxide to give the yellow precipitate iodoform. 

Iodine is an oxidizing agent, and an alcohol can give a positive iodoform test if it oxidizes to a methyl ketone. The iodoform reaction can convert such an alcohol to a carboxylic acid with one less carbon atom. 

Which compounds will give positive iodoform tests (a) 1-phenylethanol (b) pentan-2-one (d) pentan-3-one (e) acetone (c) pentan-2-ol (f) isopropyl alcohol... 

A negative iodoform test would occur for the primary four-carbon alcohol, n-butyl alcohol ... 

The preparation of dimethylaniline is carried out in an iron autoclave withstanding 60 atmospheres of pressure, provided with a cast iron lin- ing, a manometer and an oil bath. The methyl alcohol used for the alkylation must be free from all traces of acetone and ethyl alcohol, because these compounds, as impurities, cause a very great increase in the pressure. The purity of the methyl alcohol should be established by an iodoform test. 

Iodoform Test for Alcohol.—It is made, in practice, by adding iodine to an alkaline (KOH or K2CO3), alcohol and water solution. The compound has a characteristic, very penetrating odor which may be detected even though an exceedingly small amount is present. On this account the reaction above may be used as a test for alcohol by simply adding a crystal of iodine and a little alkali to a solution con-... 

Whether or not an alcohol contains one particular structural unit is shown by the iodoform test. The alcohol is treated with iodine and sodium hydroxide (sodium hypoiodite, NaOI) an alcohol of the structure... 

Refer to the isomeric pentyl alcohols of Problem 1(a), p. 515. (a) Indicate which (if any) will give a positive iodoform test, (b) Describe how each will respond to the Lucas reagent, (c) Describe how each will respond to chromic anhydride, (d) Outline all steps in a possible synthesis of each, starting from alcohols of four carbons or less, and using any necessary inorganic reagents. 

Methyl ketones, and alcohols which are oxidized to methyl ketones, will give a positive iodoform test. All of the compounds in this problem except pentan-3-one (part (d)) will give a positive iodoform test. 

The reaction of methyl ketones with sodium iodate(l) gives iodoform (tri-iodomethane), which is a yellow soUd with a characteristic smeU. This reaction is used in the Iodoform test to identify methyl ketones. It also gives a positive result with a secondary alcohol of the formula RCH(OH)CH3 (which is first oxidized to a methylketone) or... 

Iodoform Test Alcohols with the hydroxyl group at the 2-position of the chain give a positive io-... 

The Iodoform Test. This test is positive for compounds that on oxidation generate methyl ketones (or acetaldehyde) under the reaction conditions. For example, methyl carbinols (secondary alcohols having at least one methyl group attached to the carbon atom to which the OH is attached), acetaldehyde, and ethanol give positive results. 

A hydrocarbon, compound A (CgHio), burned with a yellow, almost nonsmoky flame. On catalytic hydrogenation over platinum catalyst it absorbed 1 mol of hydrogen to form compound B. It also decolorized a Br2- H2Cl2 solution to yield a dibromo derivative, compound C. Ozonolysis of the hydrocarbon gave only one compoimd, D. Compoimd D gave a positive iodoform test when treated with iodine-sodium hydroxide solution. On treatment of compoimd D with an alcoholic solution of silver ammonium hydroxide, a silver mirror was formed within a few minutes. 

Iodoform test. To 1 ml of the carbonyl compound or its solution in water or dioxan, add 5 ml of sodium hydroxide solution followed by iodine/potassium iodide solution imtil the iodine colour remains on shaking. If no yellow precipitate of iodoform appears after 3 minutes, warm to 60°, adding iodine solution if the colour fades. Add drops of 2N sodium hydroxide solution to remove the excess of iodine, add water to dilute the solution, and allow to stand for 15 minutes. Yellow crystals of iodoform (m.p. 120°) separate. (Dioxan may contain alcoholic impurities perform a blank test.)... 

The iodoform test is also positive for compounds of some other classes, e.g. certain alcohols containing the grouping R.CH(0H).CH3 which in the early stages of the reaction are oxidized to the methyl ketone. 

Iodoform Test.— Addition of 1-5 ml. of I per cent, aqueous iodine and 1-2 ml. 20 per cent. NaOH to 10 ml. of a urine containing acetone produces iodoform, CHI3, which is recognisable by its smell, and its separation as a pale yellow precipitate with a characteristic microscopic appearance (hexagonal plates and stars). Pyruvic and lactic acid, which are minor constituents of normal urine, give a similar reaction, as also does alcohol, so the test is not reliable for detecting traces of acetone. 

Ethyl Alcohol.— The detection of ethyl alcohol in urine may be important in the diagnosis of intoxications. Distil carefully 50-100 ml. of the urine, and apply the iodoform test and the nitro chromic test (p. 109) to 5 ml. samples of the distillate. Alcohol gives a positive reaction with both tests. Acetone, if present, will also come over in the distillate, and give a positive iodoform reaction, but does not give a blue colour with the nitro chromic reagent. 

If the compound to be tested is insoluble in water, it should be brought into solution by the addition of a little dioxan. Alcohols and some methyl ketones frequently react slowly in such cases it is advisable to employ a large excess (4-5 fold) of the relatively unstable reagent (3NaOI -> NaI03 -f- 2NaI). Quinones and hydroquinones also give the iodoform reaction. 

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