Permanganate tests

Since, however, some compounds, such as aniline (p. 164), react very rapidly with bromine by substitution, the bromine test should whenever possible be confirmed by the alkaline permanganate test. 

Potassium permanganate test. Dissolve 0 -2 g. or 0 -2 ml. of the substance in 2 ml. of water or in 2 ml. of acetone (which gives a negative test with the reagent), and add 2 per cent, potassium permanganate solution dropwise. The test is negative if no more than 3 drops of the reagent are decolourised. 

Acetic acid, fp 16.635°C ((1), bp 117.87°C at 101.3 kPa (2), is a clear, colorless Hquid. Water is the chief impurity in acetic acid although other materials such as acetaldehyde, acetic anhydride, formic acid, biacetyl, methyl acetate, ethyl acetoacetate, iron, and mercury are also sometimes found. Water significantly lowers the freezing point of glacial acetic acid as do acetic anhydride and methyl acetate (3). The presence of acetaldehyde [75-07-0] or formic acid [64-18-6] is commonly revealed by permanganate tests biacetyl [431-03-8] and iron are indicated by color. Ethyl acetoacetate [141-97-9] may cause slight color in acetic acid and is often mistaken for formic acid because it reduces mercuric chloride to calomel. Traces of mercury provoke catastrophic corrosion of aluminum metal, often employed in shipping the acid. 

The permanganate test. The time taken for a mixture of 50 c.c. of the spirit with 10 c.c. of 0-02% potassium permanganate solution to become decolorised or of a pale salmon colour at a temperature of about 180 is observed. With the purest alcohol, this requires about three-quarters of an hour, whilst with impure alcohols a less time is necessary—in some cases a few seconds. 

Permanganate test The compound to be tested is treated with 10 to 15 drops of 1% KMn04 solution. A positive test is indicated by the formation of a black (Mn02) precipitate. 

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... 

Alkenes Bromine test Permanganate test Solubility in cone, sulfuric acid Positive for all alkenes Positive for all alkenes All alkenes dissolve... 

Alkynes Bromine test Permanganate test Silver nitrate Sodium metal addition Sulfuric acid Positive for all alkynes Positive for all alkynes Positive for all terminal alkynes only Positive for all terminal alkynes only Positive for all alkynes... 

C) Acid Permanganate Test. To 1-mL portions of purified ligroin, unpurified ligroin, and cyclohexene add a drop of an aqueous solution containing 1% potassium permcmganate and 10% sulfuric acid and shake. If the initial portion of reagent is decolorized, add further portions. 

Alcohols are not oxidized by cold, dilute, neutral permanganate (although primary and secondary alcohols are, of course, oxidized by permanganate under more vigorous conditions). However, as we have seen (Sec. 6.30), alcohols often contain impurities that are oxidized under these conditions, and so the permanganate test must be interpreted with caution. 

Aldehydes and similar reducing substances are tested for by the permanganate test. A solution of 1 g. potassium permanganate in a litre of water is made up and 1 c.c. of this is added to 100 c.c. of acetone. The colour should persist for at least thirty minutes at 15 5 in the dark. In Germany, a silver nitrate test is included to detect aldehydes these can also be detected by SchifTs reagent (fuchsine-bisulphite). Light oils also reduce ammoniacal silver nitrate. They may be tested for as follows. 

Alphaeucaine hydrochloride gives a yellow precipitate when 5 cc. of a 1 per cent, solution are treated with three drops of a 5 per cent, solution of chromic acid. Cocaine hydrochloride does not. Betaeucaine hydrochloride when rubbed with dry mercurous chloride and then moistened with alcohol yields no color, cocaine hydrochloride when similarly treated turns grayish black. Holocaine hydrochloride gives in aqueous solution a violet precipitate with calcium hypochlorite, cocaine hydrochloride does not. Cocaine and procaine are distinguished by the potassium permanganate test (see Procaine Hydrochloridum). 

Distillation range (°Q Acidity (ppm) max. (expressed as acetic add) Water (ppm) max. Non-volatile residue (ppm) max Permanganate test (minutes) min. Color (Pt Co) max. ... 

The unsaturated character of compounds which contain carbon atoms joined by a triple bond is shown by their behavior with bromine and with a solution of potassium permanganate. Tests for such compounds are carried out in the manner described... 

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