Iodoform test

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). 

The iodoform test. Dissolve 0 -1 g. or 5 drops of the compound in 2 ml. of water if it is insoluble in water, add sufficient dioxan to produce a homogeneous solution. Add 2 ml. of 5 per cent, sodium hydroxide solution and then introduce a potassium iodide - iodine reagent dropwise with shaking until a definite dark colour of iodine persists. Allow to... 

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. 

Jodo-. iodoxy- (IO2) iodo-. -benzoesaure,/. iodoxybenzoic acid, -benzol, n, iodoxyben-zene (C6H6IO2). -form, n. iodoform, -form-gaze, /. iodoform gauze, -formprobe, /. iodoform test,... 

Since it does not reduce Tokens or Fehltng reagent, (A) must be a ketone. (A) responds to iodoform test. Therefore, it should be a methyl ketone. The molecular formula of (A) Indicates high degree of unsaturation, yet it does not decolourise bromine water or Baeyer s reagent. This indicates the presence of unsaturation due to an aromatic ring. 

Aldehydes are easy to oxidize, but ketones are more challenging. The two important oxidation reactions of ketones are the oxidation with a strong oxidant and the iodoform test. 

For years the iodoform test was a laboratory method for the identification of a methyl ketone (a ketone where one of the R groups is a methyl group). A positive test produced the compound iodoform. Iodoform, CHI3, is a yellow precipitate with a characteristic odor. The oxidation utilizes sodium hypoiodite, which is generated in situ by the reaction of iodine with sodium hydroxide. Figure 10-35 shows an example of the iodoform test. 

In Chapter 10, you see the iodoform test as a means of identifying methyl ketones. Here we reexamine this reaction in light of enols and enolates. 

Problem 13.49 A compound, C Hj O, is oxidized under vigorous conditions to benzoic acid. It reacts with CrOj and gives a positive iodoform test (Problem 13.48). Is this compound chiral ... 

Only II has the —CH(OH)CHj needed for a positive iodoform test. II is chiral. 

Problem 15.54 Compound (A), C5H10O, forms a phenylhydrazone, gives negative Tollens and iodoform tests and is reduced to pentane. What is the compound -4... 

Phenylhydrazone formation indicates a carbonyl compound. Since the negative Tollens test rules out an aldehyde, (A) must be a ketone. A negative iodoform test rules out the CH,C=0 group, and the reduction product, pentane, establishes the C s to be in a continuous chain. The compound is CHjCHjCOCHjCH,. 

H will oxidize to the corresponding carbonyl compound and give a positive iodoform test. 

Detection of Acetone. The presence of acetone may be detected by the iodoform test, which depends on the fact that when acet is treated with iodine and Na hydroxide, iodoform and Na acetate are formed ... 

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. 

Because iodoform is a pale yellow solid, this reaction is often run as a test for methyl ketones and is called the iodoform test. 

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... 

Aldehydes Alkanes Benedict s test Dichromate test 2,4-Dinitrophenylhydrazine (2,4-DNP) Fehling test Iodoform test Oxime Permanganate test Semicarbazone Tollen s test No test Positive for all aldehydes Positive for all aldehydes Positive for all aldehydes (and ketones) Positive for all aldehydes Positive only for acetaldehyde Positive for all aldehydes (and ketones) Positive for all aldehydes Positive for all aldehydes (and ketones) Positive for all aldehydes... 

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. 

Iodoform test. Place into separate clean, dry test tubes (150 X 18 mm), labeled... 

Iodoform test. Methyl ketones give the yellow precipitate iodoform when reacted with iodine in aqueous sodium hydroxide. 

Iodoform test. Place 5 drops of each sample into separate clean, dry test tubes (150 X 18 mm). Add to each test tube 2mL of water. If the compound is not soluble, add dioxane (dropwise) until the solution is homogeneous. Add to each test tube (dropwise) 2mL of 6 M NaOH tap the test tube with your finger to mix. The mixture is warmed in a 60°C water bath, and the prepared solution of I2-KI test reagent is added dropwise (with shaking) until the solution becomes brown (approximately 25 drops). 

A8 -tetrahydrocannabinol were quantitatively separated with respective retention volumes of 6.37 and 6.62 ml (the dead volume between the UV detector and the collection point was 0.46 ml as determined by the iodoform test). Cannabidiol in the same system had a retention volume of 6.06 ml. 

When the halogen is iodine, the haloform product (iodoform) is a solid that separates out as a yellow precipitate. This iodoform test identifies methyl ketones, which halo-genate three times, then lose CI3 to give 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... 

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