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Bromine (in Methylene Chloride) Test for Multiple Bonds

Alkene

Alkyne

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.

Baeyer Test for Multiple Bonds (Potassium Permanganate Solution)

Alkene

Alkyne

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.

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

Bromine (in Methylene Chloride) Test for Multiple Bonds

Alkene

Alkyne

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.

Baeyer Test for Multiple Bonds (Potassium Permanganate Solution)

Alkene

Alkyne

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.

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.

شناسایی هالیدهای آلیفاتیک

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.

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 50^oC 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.

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.

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.   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. 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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