Ketone/aldehyde qualitative identification Essay Example

creating a known positive and a known negative reaction with a Tollens reagent test solution.

The unknown was then tested and compared to the known positive and known negative solutions to determine the unknown identity. The Tollens reagent is prepared in the laboratory because it will become explosive upon standing. The first part of the preparation follows equation number 1. This creates a brown precipitate of silver oxide (AG20). This precipitate is then treated with ammonia until all of the brown AG20 has reacted and the solution is clear.

This reaction results in a silver solution that contains silver ions. These ions will oxidize as presented in equation 2 A positive on this test is either a silver mirror forming on a test tube or a heavy black precipitate. A negative indicator for this test is a clear solution. Equation 1: rhe next test performed was a Schiff test for an aldehyde. The Schiff reagent will indicate positive for an aldehyde with a purple fuchsia color.

The negative will result in a solution with a yellow hue. The unknown is then compared to the known positive and the known negative to determine if it is an aldehyde.

The chemical equations for this test are complex and are not yet understood . The next test was an Iodoform test.

This test is to determine if a molecule is a methyl ketone. This test is carried out by oxidizing a methyl ketone with 12 as seen in equation 3. Elemental iodine is produced in equation 4 by reacting hypochlorite (OCL-) with iodide to oxidize the iodide. A known positive and a known negative are prepared and the unknown is compared

to them to determine if it is a methyl ketone. A positive on this test is indicated by the formation of a cloudy light yellow precipitate n the solution.

Equation 3: Equation 4: 21-(aq) +OCL- (aq) + H20 (l) 12 + CL- (aq) + 20H- (aq) The final test performed was a semicarbazide derivative melting point analysis.

This test includes forming a derivative of the unknown with a semicarbazide to form derivative called semicarbazon. After the derivative is formed, the melting point is determined. This information was then compared to known literature 'alues of semicarbazone derivatives to determine the identity of the unknown Semicarbazone is derived by reacting an aldehyde or ketone with semicarbazide as een in equation 5.

Semicarbazide hydrochloride is then reacted with sodium acetate to obtain semicarbazone as in equation 6.

Equation 5: Equation 6: Experimental procedure To perform the Tollens test, 3 test tubes were labeled as "known positive", "known negative" and "unknown". Two ml of 5% AgN03 and 1 ml of 10% NaOH was added to each test tube. This created a brown Precipitate of Ag20. The precipitate was dissolved by adding ammonia (NH40H) dropwise until the solution was clear. This required 9 drops of ammonia. After each solution was clear, one drop of o- olualdehyde was added to the "known positive" test tube.

Next, one drop of 2- butenone was added to the test tube labeled "known negative". Finally, two drops of the unknown was added to the tube labeled "unknown". The unknown was then compared to the "known positive" and the "known negative" to determine if an aldehyde was present. A mirroring on the test tube or heavy dark precipitate

in the solution was considered a positive test, while a mostly clear solution was considered as a negative test. again, three test tubes were labeled as "known positive", "known negative" and unknown".

One ml of Schiff solution was then added to each test tube. Following this, one drop of o-tolualdehyde was added to the "known positive" test tube, one drop of 2-butenone was added to the test tube labeled "known negative", and one drop of the unknown was added to the tube labeled "unknown". The unknown solution was then compared to the "known positive" and the "known negative" to determine if an aldehyde was present. A positive for the Schiff test was a heavy purple or fuchsia solution coloring, while a negative was a yellow solution.

The Iodoform test was accomplished using with an Iodoform reagent. To perform the Iodoform test, three test tubes were labeled as in the previous two tests.

Two ml of Iodoform solution was then added to each test tube (1). After the Iodoform solution was in all three test tubes, they were all heated in an 80 0 C water bath for 30 s. One drop of 2-butenone was added to the "known positive" test tube, one drop of o-tolualdehyde was added to the test tube labeled "known negative" and two drops of the unknown was added to the tube labeled "unknown".

The unknown solution was then compared to the other two test tubes to determine if a Methyl Ketone was present. A positive result for methyl ketone was a cloudy light yellow precipitate, while a negative was a translucent yellow solution. The final test was to determine a melting point

using a semicarbazone derivative.

Three ml of 95% ethanol and Three ml of distilled water was mixed together and placed in the ice bath to create a rinsing solution (1). After this, One ml of 95% ethanol was placed into a test tube and 5 drops of the unknown solution was added to it.

Next, . 15 gof anhydrous sodium acetate and .

15 g of semicarbazide hydrochloride were placed in a test tube and 2 ml of distilled water was added. This contents of this test tube was added to the test tube containing the unknown mixture. This test tube was placed in the ice bath to cool for 10 minutes. It was shaken for 5- 10 seconds every minute that it was in the ice bath.

After precipitate formed in the reaction tube, it was poured into a Buchner funnel, vacuum filtered and rinsed with 25 ml of distilled water to obtain the initial semicarbazone precipitate.

The semicarbazone precipitate was then cooled to room temp and reheated in a 2 ml of ethanol/2 ml water mixture until the precipitate dissolved. Again the test tube containing the dissolved precipitate was placed in the ice bath, recrystallized, and filtered. These crystals were rinsed with the previously prepared ethanol water mixture. The derivative was allowed to dry and was tested for a melting point.