Iron(III) Chloride - Pyridine Test for Water-Insoluble Phenols

Standard
Phenol

Procedure (for water-insoluble phenols or less reactive phenols)
A more sensitive test for phenols consists of dissolving or suspending 15 mg of the unknown in 0.5 mL of methylene chloride and adding 3-5 drops of a 1% solution ferric chloride in methylene chloride. Add a drop of pyridine and stir.

Positive Test (b)
Addition of pyridine and stirring will produce a color if phenols or enols are present.

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Iron (III) Chloride Test for Water-Soluble Phenols

Standard
Phenol

Procedure (for water-soluble phenols)
The iron (III) chloride test for phenols is not completely reliable for acidic phenols, but can be administered by dissolving 15 mg of the unknown compound in 0.5 mL of water or water-alcohol mixture and add 1 to 2 drops of 1% aqueous iron (III) chloride solution.

Positive Test
A red, blue, green, or purple color is a positive test.

Cleaning up
Since the quantity of material is extremely small, the test solution can be diluted with water and flushed down the drain.

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Carboxylic Acids

Sodium Bicarbonate Test for Carboxylic Acids


Standard
5% Acetic acid solution

Procedure
A few drops or a few crystals of the unknown sample are dissolved in 1mL of methanol and slowly added to 1 mL of a saturated solution of sodium bicarbonate.

Positive Test
Evolution of a carbon dioxide gas is a positive test for the presence of the carboxylic acid and certain phenols listed in the Complications section.

Complications
Negatively substituted phenols such as nitrophenols, aldehydrophenols, and polyhalophenols are sufficiently acidic to dissolve in 5% sodium bicarbonate.
pH of an Aqueous Solution for Carboxylic Acids

Standard
5% Acetic acid solution

Procedure
See procedure for solubility tests with water.

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Ignition Test for High Degrees of Unsaturation

Standards
Benzophenone, cyclohexane, and hexanes.

Procedure
Heat a small sample on a spatula. First, hold the sample near the side of a bunsen burner to see if it melts normally and then burns. Heat it in the flame. Aromatic compounds often burn with a smoky flame.

Positive Test
A sooty yellow flame is an indication of an aromatic ring or other centers of unsaturation

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Baeyer Test for Multiple Bonds (Potassium Permanganate Solution)

Standards
Cyclohexane, Cyclohexene and Bromobenzene.

Procedure
Dissolve 1 drop or 0.02 grams of the unknown in 0.5 mL reagent grade acetone. Add a 1% aqueous solution of potassium permanganate dropwise with shaking. If more than one drop of reagent is required to give a purple color to the solution, unsaturation or an easily oxidized functional group is present. Run parallel tests on pure acetone and, as usual, the standards listed above.

Positive Test
The disappearance of the KMnO4's purple color and the appearance of a brown suspension of MnO2 is a positive test.


Complications

Water insoluble compounds should be dissolved in ethanol, methanol, or acetone.
Often, the brown precipitate fails to form and the solution turns reddish-brown.
Easily oxidized compounds give a positive test: a) Most aldehydes give a positive test. b) Formic acid and its esters give a positive test.
Alcohols with trace impurities give a positive test.
Phenols and aryl amines give a positive test.
Carbonyl compounds which decolorize bromine/methylene chloride usually give a negative test.

Cleaning up
The solution should be diluted with water and flushed down the drain. Any solutions containing organic compound should be placed in the appropriate waste container.

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Bromine (in Methylene Chloride) Test for Multiple Bonds

Standards
Cyclohexane, Cyclohexene, and Bromobenzene

Procedure
In a hood, 0.02 g or 1 drop of the unknown is added to 0.5 mL of methylene chloride. Add a dilute solution of bromine in methylene chloride dropwise, with shaking, until the bromine color persists. The bromine solution must be fresh.

Positive Test
Discharging of the bromine color without the evolution of hydrogen bromide gas is a positive test.


Complications

Should be employed in conjunction with Baeyer test (dilute KMnO4).
Electron-withdrawing groups in the vinylic position can slow down bromine addition to the point that a negative test is erroneously produced.
Tertiary amines (like pyridine) form perbromides upon treatment with bromine and lead to false positive tests.
Aliphatic and aromatic amines can discharge the bromine color without the evolution of HBr gas.

Cleaning up
The solution should be placed in the appropriate waste container.

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Beilstein Test

Standards
Any halogenated compound as a positive standard, such as, 1-Bromobutane, and any non-halogenated compound, such as 1-Butanol, as a negative standard.

Procedure
Heat the tip of a copper wire in a burner flame until there is no further coloration of the flame. Let the wire cool slightly, then dip it into the unknown (solid or liquid" and again, heat it in the flame. A green flash is indicative of chlorine, bromine, and iodine; fluorine is not detected because copper fluoride is not volatile. The Beilstein test is very sensitive, thus halogen-containing impurities may give misleading results.

Positive Test
A green flash is indicative of chlorine, bromine, and iodine, but NOT fluorine.

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Sodium Iodide in Acetone Test

Standards
Reference tests done in Classification Tests for Halides Lab

Procedure
In a test tube place 0.25 mL or 0.2 g of your unknown. Add 2 mL of a 15% solution of sodium iodide in acetone, noting the time of addition. After the addition, shake the test tube well to ensure adequate mixing of the unknown and the solution. Record the time needed for any precipitate to form. After about 5 minutes, if no precipitate forms, place the test tube in a 50oC water bath. Be careful not to allow the temperature of the water bath to go above this temperature since the acetone will evaporate, giving a false positive result. After 6 minutes more in the bath, if no precipitates are visible, remove the test tube and let it cool to room temperature. Note any change that might indicate that a reaction has occurred. Continue slow reactions for up to 45 minutes at room temperature.

Positive Test
The formation of a white precipitate indicates the presence of halides.

Complications
When the sodium iodide solution is added to the unknown, a precipitate of sodium iodide might occur leading to a false positive test. Upon mixing, the precipitate of sodium iodide should dissolve.

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Silver Nitrate in Ethanol Test

Standards, as done in the Classification Tests for Halides lab


1-chlorobutane 1-bromobutane 1-iodobutane
2-chlorobutane 2-bromobutane 2-iodobutane
2-chloro-2-methylpropane 2-bromo-2-methylpropane
benzyl chloride bromobenzene


Procedure
Place approximately 0.25 mL of each compound into a test tube. Add 2 mL of a 1% ethanolic silver nitrate solution to the material in each test tube, noting the time of addition. After the addition, shake the test tube well to ensure adequate mixing of the compound and the solution. Record the time required for any precipitates to form. If no precipitates are seen after 5 minutes, heat the solution on the steam bath for approximately 5 minutes. Note whether a precipitate forms in the test tube. Continue slow reactions for up to 45 minutes at room temperature.

Complications
Carboxylic acids have been known to react in this test, giving false positives.

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Lucas Test for Secondary and Tertiary Alcohols

Standards
1-Butanol, 2-Butanol, t-Butyl alcohol.

Procedures
To 0.2 mL or 0.2 g of the unknown in a test tube add 2 mL of the Lucas reagent at room temperature. Stopper the tube and shake vigorously, then allow the mixture to stand. Note the time required for the formation of the alkyl chloride, which appears as an insoluble layer or emulsion.
The Lucas reagent is already prepared for you.

Positive test
Appearance of a cloudy second layer or emulsion

3o alcohols: immediate to 2-3 minutes
2o alcohols: 5 -10 minutes
1o alcohols: no reaction

Complications
The test applies only to those alcohols soluble in the reagent (monofunctional alcohols lower than hexyl and some polyfunctional alcohols.) This often means that alcohols with more than six carbon atoms cannot be tested.

Cleaning Up
Place all solutions in the appropriate waste container.

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Jones Oxidation for Primary and Secondary Alcohols

Standards
1-Butanol, 2-Butanol, t-Butyl alcohol

Procedure
Dissolve 10 mg or 2 drops of the unknown in 1 mL of pure acetone in a test tube and add to the solution 1 small drop of Jones reagent (chronic acid in sulfuric acid). A positive test is marked by the formation of a green color within 15 seconds upon addition of the orange-yellow reagent to a primary or secondary alcohol. Aldehydes also give a positive test, but tertiary alcohols do not.
The Jones reagent will already be prepared for you.

Positive Test
A positive test for aldehydes and primary or secondary alcohols consists in the production of an opaque suspension with a green to blue color. Tertiary alcohols give no visible reaction within 2 seconds, the solution remaining orange in color. Disregard any changes after 15 seconds.

Complications

Enols may give a positive test.
Phenols give a dark colored solution which is not blue-green like a positive test.
Cleaning up
Place all solutions in the appropriate waste container

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Iodoform Test for Methyl Ketones

Standard
Acetone

Procedure
If the substance to be tested is water soluble, dissolve 4 drops of a liquid or an estimated 50 mg of a solid in 2 mL of water in a large test tube. Add 2 mL of 3 M sodium hydroxide and then slowly add 3 mL of the iodine solution. Stopper the test tube and shake vigorously. A positive test will result in the brown color of the reagent disappearing and the yellow iodoform solid precipitating out of solution. If the substance to be tested is insoluble in water, dissolve it in 2 mL of 1,2-dimethoxyethane, proceed as above, and at the end dilute with 10 mL of water.

Positive Test
Formation of solid iodoform (yellow) is a positive test. (Iodoform can be recognized by its odor and yellow color and, more securely, from the melting point 119o-123oC).

Complications
Test will not be positive if the R group is a di-ortho substituted aryl group

Cleaning Up
Place solutions in the appropriate waste container.

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