Aldehydes and Ketones Individual Laboratory Report

LBYCH63, EA2, Group # 5

Experiment #8: Aldehydes and Ketones Razote, Bernard Jomari B. Instructor: Sir Glenn Tan Date Performed: November 11, 2014 Date Submitted: November 25, 2014 Abstract  A qualitative analysis of aldehydes and ketones was conducted in the experiment. Four test samples, namely acetone, formaldehyde, benzaldehyde, and cyclohexanone, were used in the experiment. Various parameters regarding the physical properties of aldehydes and ketones were determined using tests such as the oxidation with potassium permanganate, 2,4-dinitrophenylhydrazine 2,4-dinitrophenylhydrazine test, Schiff’s test, Schiff’s test, Tollens’ test, Fehling’s test, iodoform test, reactions with sodium bisulfite, and the chromic acid test. The objectives of the experiment were met since the physical properties of the aldehydes and ketones were observed using the tests. However, some experimental results deviated from the theoretical one, such as the non-oxidation of formaldehyde with potassium permanganate, and the negative results for the reactions of formaldehyde and acetone with sodium bisulfite. These unforeseen errors and deviations in the result of the experiment can be attributed to the impurities that may have altered the original result. The experiment would be very helpful in establishing the identity of a certain unknown compound; however, additional tests such as Benedict’s test and ceric nitrate n itrate test are recommended to better establish the certainty of the unknown compound.

I.

Potassium permanganate is a strong oxidizing agent used to test the presence of an aldehyde or a ketone.

Introduction

Ketones and aldehydes are somewhat similar in their structure, due to the presence of the carbonyl group (C=O) in both of the compounds. However, the two behave differently, due to the difference of the attached groups in the carbonyl group. (1) The main objective of the experiment is to analyze qualitatively aldehydes and ketones through the use of various tests. These tests include using potassium permanganate to observe the oxidations of aldehydes, using 2,4-dinitrophenylhydrazine to determine the presence of an aldehyde or a ketone, determining the presence of an aldehyde using Schiff’s , Tollen’s, and chromic chromic acid test, using Fehling’s test to distinguish aromatic aldehydes from aliphatic aldehydes, determining the presence of methyl ketones through the appearance of iodoform, and using sodium bisulfite in determining the presence of an aldehyde or an aliphatic methyl ketone. The significance of the experiment is to establish the identity of a certain compound, and to determine whether it is an aldehyde or a ketone. The experiment is also significant in determining the identity of an unknown compound, which can be unfolded using the various tests in the experiment.  A. Oxidation of Permanganate

Aldehydes

Aldehydes and Ketones

with

If the compound present is an aldehyde, it will be readily oxidized by the potassium permanganate into a carboxylic acid due to the presence of the hydrogen atom bonded to the carbonyl group. Since 7+ the reaction is a redox reaction, Mn  will be reduced 4+ 4+ to Mn . Mn   is present in the solution as manganese dioxide, which gives the solution a brown color. The presence of the brown color is regarded as the positive result for the experiment. (2)

+ MnO2

Figure 1.1 Reaction of Aldehydes with KMnO 4 (Oxidation of aldehydes and ketones, n.d.)

If the compound present is a ketone, it is generally not oxidized by potassium permanganate, unless in extreme conditions such as the presence of heat. If KMnO4  is able to oxidize the ketone, a cleavage mixture of two carboxylic acids would be present in the solution. (3)

Potassium

Page 1 of 12

LBYCH63, EA2, Group # 5

Figure 1.2 Reaction of Ketones with KMnO 4 Oxidation of aldehydes and ketones, n.d.)

However, ketones with benzylic carbonyl groups can be easily oxidized by KMnO 4. (4) This is because the permanganate adds itself to the double bond in the enol form of the ketone. The end product of the reaction would be a dicarboxylic acid. (5)

The appearance of a magenta color in the solution is regarded as the positive result for the Schiff’s Test. This positive result is expected for aldehydes. (9)

B. 2,4-Dinitrophenylhydrazine Test with Aldehydes and Ketones The 2,4-dinitrophenylhydrazine is a compound with a hydrazine (H 2N-NH2) attached to the first carbon of a benzene ring, and two nitro groups (NO2) attached to the second and fourth carbon, respectively. Due to its sensitivity to shock and heat, it is usually dissolved in water to avoid any violent explosion. (6) The test of 2,4-dinitrophenylhydrazine is a tool used to verify if a certain compound is an aldehyde or a ketone. The appearance of a yellow to orange precipitate indicates a positive result. When an aldehyde is dropped into the solution containing 2,4-dinitrophenylhydrazine, it forms aldehyde 2,4-dinitrophenylhydrazone, which precipitates out in the solution as a yellow to orange solid. (7)

Figure 1.5 Reaction of Aldehydes with Bisulfite Ion (Identification of an Unknown – Unknown  – Alcohols,  Alcohols, Aldehydes, and Ketones, n.d).

For ketones, no color change is expected to happen. A possible color change, although not the same as magenta, is also possible to happen D. Tollens’ Test for Aldehydes The Tollens’ Test is another useful tool in distinguishing aldehydes from ketones. It is prepared by mixing silver nitrate and sodium hydroxide, and adding ammonium hydroxide to remove the red precipitate and make the solution colorless. However, it is not usually done in the laboratory due to its explosive character, and health risks due to the production of silver upon the completion of the experiment. (9) For the Tollens’ Test, the formation of a solid silver precipitate is regarded as a positive result.

Figure 1.3 Reaction of Aldehydes with 2,4-Dinitrophenylhydrazine (Addition-elimination reactions of aldehydes and ketones, 2004)

Likewise, when a ketone is dropped into a solution containing 2,4-dinitrophenylhydrazine, it forms ketone 2,4-dinitrophenylhydrazone, which precipitates out in the solution also as a yellow to orange solid. (7)

Figure 1.4 Reaction of Ketones with 2,4-Dinitrophenylhydrazine (Addition-elimination reactions of aldehydes and ketones, 2004)

C. Schiff’s Test for Aldehydes Schiff’s Test is done in order to distinguish an aldehyde from a ketone. The solution to be used, the Schiff’s reagent, is produced by the reaction of a dye such as pararosaniline with sodium bisulfite. (8)

Aldehydes and Ketones

When an aldehyde is placed into a test tube containing Tollens’ reagent, a “silver mirror” is produced. (9)

Figure 1.6 Reaction of Aldehydes with Tollens’ Reagent (Reactions of aldehydes, ketones and phenols, 2011).

However, when a ketone is placed into the test tube containing Tollens’ reagent, no precipitate would form, since no reaction will happen. (9) E. Fehling’s Test for Distinguishing  Aldehydes from Aliphatic Aldehydes

Aromatic

Page 2 of 12

LBYCH63, EA2, Group # 5

Fehling’s Test is done to distinguish distinguish aliphatic aldehydes from aromatic aldehydes. Fehling’s Solution “A” is prepared by adding a few drops of concentrated sulfuric acid to an aqueous solution of copper sulfate pentahydrate. On the other hand, Fehling’s Solution “B” is prepared by mixing  mixing   sodium hydroxide with potassium sodium tartrate. (10)  A positive result for the Fehling’s Test is the appearance of a red precipitate, cuprous oxide, which happens when there is a presence of an aliphatic aldehyde. (11)

Figure 1.8 Reaction of Methyl Ketones to NaOH-I 2-KI Solution in Iodoform Test (Triiodomethane reacted with methyl ketones, 2004)

The iodoform test is also applicable to alcohols having RCH3CHOH. If an alcohol has such structure, the yellow precipitate, iodoform, can also be formed. The same reaction mechanism happens for alcohols having the said structure with methyl ketones. (12) G. Reaction with Sodium Bisulfite for Aldehydes and Aliphatic Methyl Ketones Sodium Bisulfite Test is used to determine if an unknown compound is an aldehyde or an aliphatic methyl ketone. If the unknown substance is either of the two aforementioned, a white precipitate is formed.

Figure 1.7 Reaction of Aldehydes with Fehling’s Reagent (Reactions of aldehydes, ketones and phenols, 2011).

Due to the nucleophilic nature of the bisulfite ion, it attacks the aldehyde or methyl ketone by breaking the π bond of the carbon-oxygen carbon-oxygen double bond. The bisulfite ion then attaches itself to the original carbonyl carbon to form the bisulfite addition compound. (13)

On the other hand, aromatic aldehydes and ketones give a negative result to Fehling’s test, since no red precipitate would appear after being added to the Fehling’s solution. F. Iodoform Test for Methyl Ketones The iodoform test is used to distinguish a methyl ketone from other ketones and aldehydes. The presence of iodoform, a yellow precipitate, is the indication that the substance is a methyl ketone. (12) In basic conditions, the alpha proton, which is next to the carbon, is removed. The removal of the alpha proton causes the α-carbon α -carbon to be nucleophilic, which enables it to attack an iodine molecule. The presence of the iodine in the α-carbon α -carbon makes the two other hydrogens more acidic, therefore the two hydrogens get attacked by the nucleophilic base until all of them are replaced by the iodine. After that, the bond between carbonyl carbon and the carbon containing the iodine molecules will break, forming an acid salt and iodoform, a yellow precipitate. (9)

Figure 1.9 Reaction of Sodium Bisulfite with Aldehydes (Reactions of aldehydes, ketones and phenols, 2011).

The presence of larger groups in a ketone sterically hinders the bisulfite ion in attaching itself to the carbonyl carbon. Hence, for ketones with large bulky groups would not form the bisulfite addition compound; only methyl ketones have the capability of being attached by the bisulfite ion since the presence of the methyl group would not affect that much in the attachment of the bisulfite ion to the carbonyl carbon. (13)

Figure 1.10 Reaction of Propanone, a Ketone, with Sodium Bisulfite (Simple addition to aldehydes and ketones, 2004).

H. Chromic Acid Acid Test for Aldehydes Chromic Test is done to distinguish an aldehyde from a ketone. Since chromic acid is a strong oxidizer, it can easily oxidize an aldehyde into a carboxylic acid. This oxidation reaction results to the

Aldehydes and Ketones

Page 3 of 12

LBYCH63, EA2, Group # 5

6+

3+

3+

reduction of Cr   ions into Cr  . The presence of Cr  is seen in chromous sulftate, Cr 2(SO4)3, which is responsible for the green color. The green color symbolizes that the aldehyde is oxidized. (14) 3RCHO + 2CrO3 + H2SO4  3RCOOH + Cr 2(SO4)3 + 4 H2O On the other hand, due to stability, ketones tend to resist any reactions with oxidizing agents such as chromic acid. Hence, no discoloration of the reagent would happen in the presence of a ketone. II. Experimental Procedure  A. Oxidation of Aldehydes with Permanganate

Potassium

One milliliter of distilled water was placed into four test tubes. 5 drops of KMnO4  was added to each test tube, and 4 drops of acetone, benzaldehyde, formaldehyde and cyclohexanone st nd rd th were placed into the 1 , 2 , 3 , and 4   test tube, respectively. For acetone, the purple solution turned faint red upon addition. For benzaldehyde, the purple solution turned light brown upon addition. For formaldehyde, the purple solution turned red upon addition. For cyclohexanone, the purple solution turned red upon addition. B. 2,4-Dinitrophenylhydrazine Test with Aldehydes and Ketones One milliliter of 2,4-dinitrophenylhydrazine was placed into each of the four test tubes. Two drops of benzaldehyde, cyclohexanone, formaldehyde and st nd rd th acetone were placed into the 1 , 2 , 3 , and 4  test tubes, respectively. All test tubes containing 2,4dinitrophenylhydrazine had an initial transparent color. For benzaldehyde, an appearance of an orange precipitate was observed immediately after it was dropped on the test tube. For cyclohexanone, an appearance of a yellow precipitate was observed immediately after it was dropped on the test tube. For formaldehyde, an appearance also of a yellow precipitate was observed in the test tube immediately after it was dropped. Like formaldehyde and cyclohexanone, acetone also yielded a yellow precipitate after it was dropped on the test tube. The 2,4-dinitrophenylhydrazine test was repeated with ethanol and acetic acid. No appearance of yellow to orange precipitate was observed in both test tubes after they were dropped into the 2,4-dinitrophenylhydrazine solution.

Aldehydes and Ketones

C. Schiff’s Test for Aldehydes One milliliter of Schiff’s reagent was placed into each of the four test tubes. Four drops of acetone, benzaldehyde, formaldehyde and cyclohexanone st nd rd th were placed into the 1 , 2 , 3 , and 4   test tube, respectively. The test tubes were then swirled and observed for appearance of a pink to purple coloration. For the first test tube, the original colorless solution turned into red-orange upon addition of acetone to the Schiff’s reagent. For the second test tube, the original colorless solution turned into violet after addition of benzaldehyde to the Schiff’s reagent. For the third test tube, the original colorless solution turned into dark violet upon addition of formaldehyde to the Schiff’s reagent. For the fourth test tube, the original colorless solution turned into red-violet upon addition of cyclohexanone to the Schiff’s reagent. D. Tollens’ Test for Aldehydes The Tollens’ Test for Aldehydes was not conducted in the laboratory due to the difficulty of preparing the solution, since the solution should be freshly prepared in order to avoid any explosion. In addition, health concerns regarding the production of the silver precipitate were taken into consideration to avoid any hazardous effects. However, the theoretical results of the experiment would be explained in the Results and Discussion section. E. Fehling’s Test for Distinguishing  Aldehydes from Aliphatic Aldehydes

Aromatic

One mL of Fehling’s Solution “A” was mixed with 1 mL of Fehling’s Solution “B”. Four mixtures of Fehling’s “A” and Fehling’s “B” were then placed into the four test tubes. Consequently, 4 drops of formaldehyde, cyclohexanone, benzaldehyde and st nd rd th acetone were placed into the 1 , 2 , 3 , and 4  test tubes, respectively. Upon the addition of the test samples, the test tubes were then submerged into a hot water and were observed for the appearance of a red precipitate. The original color of the solution before the samples were placed is blue.

Page 4 of 12

LBYCH63, EA2, Group # 5

For the test tube containing formaldehyde, a blood red precipitate was observed after being submerged into the hot water bath. For cyclohexanone, no red precipitate was formed after being submerged in the hot water bath for about 5 minutes. For the test tube containing benzaldehyde, no red precipitate was formed also after being dipped in hot water bath. Instead, a thin yellow-colored immiscible layer was formed on top of the solution. For acetone, no red precipitate also was formed after being dipped in the hot water bath. Instead, an immiscible layer was formed, with white layer on top and blue layer at the bottom of the test tube. The Fehling’s Test was repeated using glucose as the test sample. For the test tube containing glucose, a red precipitate was formed after the test tube was heated.

potassium iodide-iodine-sodium hydroxide mixture, a cloudy yellow precipitate was formed. G. Reactions with Sodium Bisulfite for Aldehydes and Aliphatic Methyl Ketones Four drops of acetone, benzaldehyde, formaldehyde, and cyclohexanone were placed into st nd rd th the 1 , 2 , 3 , and 4   test tube respectively. One milliliter of sodium bisulfite solution was then placed. Upon addition, the test tubes were shaken, and after the shaking, the solution was let stand for 1 to 2 minutes. All of the test samples were transparent before the addition of sodium bisulfite. For acetone and benzaldehyde, the solution remained transparent after addition of sodium bisulfite. On the other hand, for benzaldehyde and cyclohexanone, a colloidal precipitate was formed in both of the test tubes after addition of sodium bisulfite. H. Chromic Acid Acid Test for Aldehydes

F. Iodoform Test for Methyl Ketones Two milliliters of the reagent provided by the technician, which is a combination of sodium hydroxide and iodine-potassium iodide solution, was placed into four test tubes. Four drops of acetone, benzaldehyde, formaldehyde and cyclohexanone st nd rd th were placed into the 1 , 2 , 3 , and 4   test tube, respectively. Immediately, upon the addition of acetone to the mixture of sodium hydroxide and iodine-potassium iodide, a creamy whitish yellow precipitate was observed. When benzaldehyde was added to the mixture of sodium hydroxide and iodine-potassium iodide, a cloudy yellow bubble formation was observed. After some time, the solution turned to cloudy white. For formaldehyde, the solution stayed clear when added to the mixture of iodine-potassium iodide and sodium hydroxide. The addition of cyclohexanone to the mixture of iodine-potassium iodide and sodium hydroxide produced a cloudy with yellow bubbles solution. Similar as that of benzaldehyde, the solution turned cloudy white after some time. The iodoform test was repeated using isopropyl alcohol as the test sample. Upon addition to the

Aldehydes and Ketones

One milliliter of acetone was placed inside a test tube. 5 drops of chromic acid were then added to acetone, and was observed for any reaction. When no reaction was recorded after three minutes of observation, one milliliter of acetone was placed into four test tubes. 5 drops of chromic acid were placed into each test tube, and 2 drops of acetone, benzaldehyde, formaldehyde, and st nd rd cyclohexanone were placed into the 1 , 2 , 3 , and th 4  respectively. The test tubes were then shook and observed for color change. The original color of the solution before the test samples were dropped is yellow. For acetone, the solution remained yellow after the addition of the test sample. For both benzaldehyde and cyclohexanone, the solution turned dark yellow upon the addition of the test sample to their respective test tubes. For formaldehyde, the solution turned light blue green upon the addition of the test sample.

III.

Results and Discussion

 A. Oxidation of Permanganate

Aldehydes

with

Potassium

Page 5 of 12

LBYCH63, EA2, Group # 5

Theoretically, formaldehyde, benzaldehyde and cyclohexanone would positive results, since they would be oxidized by potassium permanganate to form brown manganese dioxide. On the other hand, acetone is not expected to produce a positive result for potassium permanganate. Upon experimentation, acetone produced the expected negative result, since a faint red color was produced instead as brown. The absence of manganese dioxide, which gives the brown color, can be attributed to the inability of potassium permanganate to completely oxidize acetone. Since acetone is stable (since it has properties of a ketone), it has a tendency to resist oxidation, that is why no manganese dioxide appeared. The red to purple color change can be attributed to another unforeseen reaction of acetone with potassium permanganate. CH3COCH3 + KMnO4 No reaction Benzaldehyde was able to produce the expected positive result in the experiment; a light brown color, which signifies the presence of manganese dioxide, appeared in the test tube. Being a strong oxidizer, potassium permanganate was able to convert benzaldehyde into benzoic acid. On the other hand, 7+ 4+ benzaldehyde reduced Mn   into Mn , which gave rise to the formation of brown manganese dioxide.

-

HCHO + MnO4  No reaction

B. 2,4-Dinitrophenylhydrazine Test with Aldehydes and Ketones For benzaldehyde, an orange precipitate was expected to be observed. Acetone, cyclohexanone and formaldehyde were expected to have the formation of a yellow precipitate upon addition to 2,4-dinitrophenylhydrazine. On the other hand, for the ethanol and acetic acid, no precipitate was expected to be observed when dropped in the solution containing 2,4-dinitrophenylhydrazine. Upon experimentation, benzaldehyde produced a positive result for the 2,4Dinitrophenylhydrazine Test, since there was a formation of an orange precipitate in the test tube. The orange precipitate, benzaldehyde 2,4dinitrophenylhydrazone, was produced from the reaction:

+

5C6H6CHO + 2KMnO4 + 6H  5C6H6COOH + 2+ + 2Mn  + 3H2O + 2K Cyclohexanone was also able to produce a positive result for the experiment, due to the sepia coloration upon addition. Since the permanganate ion was able to attach itself to the enol form of cyclohexanone, it was able to oxidize cyclohexanone into adipic acid. Hence, it resulted to 7+ 4+ the reduction of Mn  into Mn , which is the reason why a sepia coloration was formed.

Figure 3.1 Reaction of Benzaldehyde with 2,4Dinitrophenylhydrazine

Cyclohexanone also produced a positive result for the 2,4-Dinitrophenylhydrazine Test. The yellow precipitate, cyclohexanone 2,4dinitrophenylhydrazone, was formed from the reaction:

-

2C6H10O + 3MnO4  2C6H10O4 + 3MnO2 Formaldehyde, theoretically, must produce a positive result for the experiment. This is because formaldehyde will be oxidized into formic acid, which 7+ will result in the reduction on Mn . However, for the experiment, a negative result was recorded, since no brown color was seen which would indicate the presence of manganese dioxide. This non-reaction of formaldehyde can be attributed to the absence of a basic medium such as sodium hydroxide that can help in the reaction of formaldehyde with potassium permanganate.

Aldehydes and Ketones

Figure 3.2 Reaction of Cyclohexanone with 2,4Dinitrophenylhydrazine

 An appearance of a yellow precipitate, which is an indication of a positive result, was also observed in the addition of formaldehyde to the test tube containing 2,4-dinitrophenylhydrazine. The

Page 6 of 12

LBYCH63, EA2, Group # 5

precipitate, formaldehyde dinitrophenylhydrazone, was formed reaction:

from

2,4the

Figure 3.3 Reaction of Formaldehyde with 2,4Dinitrophenylhydrazine

 Acetone also produced a positive result, as indicated by the formation of a yellow precipitate. The precipitate, acetone 2,4-dinitrophenylhydrazone, was formed from the reaction:

when added to the solution containing 2,4dinitrophenylhydrazine. On the other hand, compounds that do not contain a conjugated carbonyl group produce a yellow phenylhydrazone derivative. This is the reason why a compound that contained a conjugated carbonyl group like benzaldehyde produced an orange phenylhydrazone derivative, while the compounds that did not contain a conjugated carbonyl group such as cyclohexanone, acetone and formaldehyde produced a yellow phenylhydrazone derivative. (15) For ethanol, a negative result was observed since no yellow to orange precipitate was observed. This is because no reaction took place between the two compounds. No reaction

 Also, for acetic acid, a negative result was observed since no yellow to orange precipitate was observed. This is because no reaction between the compounds took place.

No reaction

Figure 3.4 Reaction of Acetone with 2,4-Dinitrophenylhydrazine

No precipitate was observed when the two compounds were placed in 2,4dinitrophenylhydrazine because, in both of these compounds, the electrons are more delocalized. This delocalization of electrons enables them to have various resonance structures which add to the stability of the certain compound. Hence, the stability of the compound resists the reaction of the acetic acid and ethanol with 2,4-dinitrophenylhydrazine, which is the reason why no precipitate was formed for both ethanol and acetic acid. (16)

Due to the nucleophilicity of 2,4dinitrophenylhydrazine, it attacked the electrophilic aldehyde and ketone compounds by bonding the terminal nitrogen in the amino group to the carbonoxygen double bond, forming an intermediate compound. However, since the reaction of 2,4dinitrophenylhydrazine with the aldehyde and ketone is a nucleophilic addition-elimination reaction (or in general terms condensation reaction), both the oxygen in double bond with the carbon as well as the hydrogen atoms bonded to the terminal amino group were displaced, which gave rise to the formation of the yellow or orange precipitate, a phenylhydrazone derivative. (7)

Theoretically, benzaldehyde and formaldehyde should produce a positive result. On the other hand, acetone and cyclohexanone were not expected to produce the magenta color which signifies positive results.

The difference of the color phenylhydrazone derivative depended on whether the compound being tested contained a conjugate carbonyl group.  A compound containing a conjugated carbonyl group has double bond that is separated only to the carbonyl group by one single bond only, and produces an orange phenylhydrazone derivative

Upon experimentation, acetone produced a negative result for the Schiff’s Schiff’ s reagent, because the carbonyl group in acetone was sterically hindered. This is due to the bulky methyl groups that surround the carbonyl group. Hence, the bisulfite ion cannot bond firmly into the acetone, which resulted to another color change. The different color produced

Aldehydes and Ketones

C. Schiff’s Test for Aldehydes

Page 7 of 12

LBYCH63, EA2, Group # 5

is a possible indicator that some of the acetone molecules were able to bond with some of the bisulfite ions but were not enough to give a positive result. (15)

Figure 3.8 Reaction of Cyclohexanone with Bisulfite Ion

D. Tollens’ Test for Aldehydes Theoretically, benzaldehyde will produce a positive result for Tollens’ Test. It is because when benzaldehyde is placed inside the test tube containing Tollens’ reagent, a silver mirror would be produced. This formation of precipitate is due to the reaction:

Figure 3.5 Reaction of Acetone with Bisulfite Ion

Benzaldehyde and formaldehyde produced positive results for the Schiff’s reagent since the carbonyl group in both of the compounds was not sterically hindered. This is because the hydrogen atom bonded to the carbonyl group was small; it allowed the bisulfite ion to bond into the carbonyl group, which resulted to the bisulfite addition complex that produced the violet to dark violet color.

Figure 3.9 Reaction of Benzaldehyde with Tollens’ Reagent

Formaldehyde will also produce a positive result for Tollens’ Test, since a silver mirror would be produced if placed in the test tube containing Tollens’ Tollens’ reagent. The formation of the solid silver precipitate is governed by the reaction:

Figure 3.6 Reaction of Benzaldehyde with Bisulfite Ion

Figure 3.10 Reaction of Formaldehyde with Tollens’ Reagent

Figure 3.7 Reaction of Formaldehyde with Bisulfite Ion

Contrary to what was expected, cyclohexanone produced a positive result in the Schiff’s Test. This was possible because, even though the carbonyl group present in cyclohexanone is sterically hindered due to the presence of the phenyl group, the bisulfite ion was still able to attack cyclohexanone by forming a bond in the carbonyl group. Hence, it resulted to the formation of the bisulfite addition complex which produced the redviolet color.

On the other hand, cyclohexanone would produce theoretically a negative result, because no silver precipitate would be formed for the Tollens’ Test. This is because no reaction would happen to facilitate the formation of the silver precipitate.

No reaction

Same with cyclohexanone, acetone would also produce theoretically a negative result, because no silver precipitate would be formed for the Tollens’ Test. This is again due to the fact that no reaction

Aldehydes and Ketones

Page 8 of 12

LBYCH63, EA2, Group # 5

would happen between acetone and the aqueous diamminesilver(I) complex. 2C6H6CHO + NaOH  C6H6CH2OH + C6H6COONa No reaction

Both of the aldehydes would produce a silver mirror upon the addition to Tollens’ reagent. This is because aldehydes are easily oxidized by the Tollens’ reagent, due to the attached hydrogen to the carbonyl-containing carbon. Therefore, aldehydes can reduce easily the silver present in the + 0 Tollen’s reagent (Ag ) to the solid silver metal (Ag ) through redox reaction. This is the reason why upon addition to Tollens’ reagent, formaldehyde and benzaldehyde was able to produce a silver mirror. On the other hand, ketones would not be able to produce a silver mirror upon addition to Tollens’ reagent. It is because unlike aldehydes, ketones are not easily oxidized by the Tollens’ reagent due to the lack of hydrogen attached to the carbonyl-containing carbon. With the exception of alpha-hydroxy ketones or acyloins, no reaction would proceed from the test tubes containing ketones like cyclohexanone and acetone that is why no silver mirror would be formed. (17) E. Fehling’s Test for Distinguishing  Aldehydes from Aliphatic Aldehydes

No reaction

For acetone, a negative result was also recorded, since no red precipitate was observed. Similar to that of cyclohexanone, acetone did not react with the Fehling’s solution that is why no precipitate was formed.

No reaction

For glucose, a positive result was observed, because a red precipitate was seen in the test tube. The reaction of glucose with Fehling’s solution is represented by the reaction below.

Aromatic

For the experiment, formaldehyde and glucose were expected to produce the red cuprous oxide precipitate. On the other hand, benzaldehyde, acetone, and cyclohexanone were not expected to produce the red precipitate. Formaldehyde produced a positive result on the Fehling’s Test, due to the formation of the red precipitate. The precipitation of cuprous oxide from formaldehyde is governed by the reaction

Figure 3.11 Reaction of Formaldehyde with Fehling’s Reagent

Benzaldehyde produced a negative result for the Fehling’s test, because of the absence of the red precipitate. The reaction of benzaldehyde with Fehling’s solution is represented by the reaction below.

Aldehydes and Ketones

Cyclohexanone also produced a negative result for the Fehling’s test due to the absence of the cuprous oxide precipitate. The reason for this is that no reaction took place between cyclohexanone and that of Fehling’s solution.

Figure 3.13 Reaction of Glucose with Fehling’s Reagent (Carbohydrates, 2010)

Formaldehyde produced a positive result for the Fehling’s Test because it was oxidized by the bistartatocuprate complex(II) into a carboxylate ion. (10) This resulted to the reduction of copper(II) ions into copper(I), which caused the formation of cuprous oxide. Benzaldehyde produced a negative result for the Fehling’s Test because upon addition to the Fehling’s solution, the benzaldehyde reacted to form benzyl alcohol and sodium benzoate. This is due to the presence of an alkali, which proceeded to Cannizzaro’s Reaction instead of reducing the copper(II) ions into copper(I) ions. (18) Hence, no formation of cuprous oxide took place. The yellowish immiscible layer formed on top of the blue Fehling’s solution upon the addition is possibly due to impurities in the benzaldehyde sample.

Page 9 of 12

LBYCH63, EA2, Group # 5

Cyclohexanone and acetone produced a negative result for the Fehling’s Test because of the 2+ weak oxidizing nature of Cr    complex. Ketones are not easily oxidized due to their stability, and the availability of a weak oxidizer would not facilitate in the oxidation of the ketone. Hence, no precipitation of cuprous oxide took place for both cyclohexanone and acetone. For glucose, a positive result was observed because it contains an aliphatic aldehyde group, which makes it a reducing sugar. (19) Since (19) Since aliphatic aldehydes are easier to be oxidized as compared to aromatic aldehydes and ketones, the copper(II) complex easily oxidized the aldehyde group in glucose into its carboxylate ion. The oxidation of glucose resulted to the reduction of the copper(II) ions into copper(I) ions, which resulted to the formation of the red precipitate cuprous oxide.

iodoform test, since precipitate was seen.

no

formation

of

yellow

 Although there was a carbon in one of the attached groups (both for cyclohexanone), the carbon-containing group present was a phenyl group rather than a methyl group. Since iodine is a weak oxidizing agent, it cannot oxidize phenyl groups, which is the main reason why benzaldehyde and cyclohexanone did not produce any yellow precipitate. Benzaldehyde:

+ I2 + OH

-

+ I2 + OH

-

No reaction

Cyclohexanone: F. Iodoform Test for Methyl Ketones  Acetone and isopropyl alco hol were expected to produce positive results. On the other hand, cyclohexanone, benzaldehyde and formaldehyde were not expected to produce positive results. Upon experimentation, acetone yielded a positive result for the iodoform test, due to the formation of the yellow precipitate. The presence of the methyl group in one of the groups attached to the carbonyl group is the reason why the iodoform was formed upon the addition of acetone. The expected result for acetone is a positive result.

No reaction

For isopropyl alcohol, a positive result was recorded for the iodoform test even though it is an alcohol. This is due to the presence of a methyl group that contains the α-carbon, α -carbon, which was oxidized by the iodine to form the yellow precipitate, iodoform.

+ 4I2 + OH

-

CHI3 + HCOONa + 8HI

Figure 3.13 Reaction of Acetone with KI-I 2-NaOH Solution

For formaldehyde, a negative result was recorded for the iodoform test, since no formation of yellow precipitate was observed. This result can be attributed to the absence of the methyl group that contains the αα-carbon. Due to the lack of α-carbon, α-carbon, no attachment of iodine to carbon happened, which resulted to the absence of the yellow precipitate.

+ I2 + OH

-

No reaction

In the experiment, both benzaldehyde and cyclohexanone also yielded negative results for the

Aldehydes and Ketones

G. Reaction with Sodium Bisulfite for Aldehydes and Aliphatic Methyl Ketones Theoretically, acetone and formaldehyde were expected to produce positive results, since they have small groups that would possibly hinder the attachment of the bisulfite ion to the carbonyl carbon. On the other hand, benzaldehyde and cyclohexanone were not expected to produce positive results. Upon experimentation, negative results were recorded for both acetone and formaldehyde, which is contrary to what was expected. This non-reaction of acetone and formaldehyde may be attributed to

Page 10 of 10 of 12

LBYCH63, EA2, Group # 5

some impurities present in the sodium bisulfite solution which may have interfered in the reaction. Formaldehyde: HCHO + NaHSO3  No reaction  Acetone: CH3COCH3 + NaHSO3  No reaction On the contrary, both benzaldehyde and cyclohexanone produced positive results for the experiment, since a colloidal white precipitate was formed in both test tubes. This reaction of the two compounds to sodium bisulfite is due to the fact that the bisulfite ion was able to attach itself to the carbonyl carbon even though the carbonyl carbon was hindered by the bulky carbon rings. Benzaldehyde: + C6H6CHO + NaHSO3  C6H6CHOHSO3  + Na Cyclohexanone + C6H10O + NaHSO3  C6H10OHSO3  + Na H. Chromic Test for Aldehydes Benzaldehyde and formaldehyde were expected to produce positive results for experiment, since aldehydes are easily oxidized by chromic acid to form carboxylic acids. On the other hand, cyclohexanone and acetone were not expected to produce positive results. Upon experimentation, acetone and cyclohexanone produced the expected negative result. Since both of them are ketones, they cannot be oxidized easily by chromic acid due to their stability and tendency to resist reaction.  Acetone: CH3COCH3 + 2CrO3 + 3H2SO4  No reaction Cyclohexanone: C6H10O + 2CrO3 + 3H2SO4

 No

reaction

For benzaldehyde, an unexpected negative result was recorded, since a dark yellow color was recorded instead of green. The negative result can be attributed to the difficulty of the bisulfite ion in oxidizing benzaldehyde, since the presence of the aromatic ring makes it harder for the bisulfite ion to attach itself to the carbonyl carbon (sterically hindered).

Aldehydes and Ketones

C6H6CHO + 2CrO3 + 3H2SO4  No reaction For formaldehyde, the expected positive result was recorded due to the appearance of chromous sulfate in the solution. Due to the easiness of 6+ oxidizing formaldehyde into formic acid, the Cr   was 3+ readily reduced to Cr  , which caused the formation of the light blue green color. HCHO + 2CrO3 + 3H2SO4  3HCOOH +3H2O + Cr 2(SO4)3 IV.

Conclusion and Recommendation

The objectives of the experiment were met after the experiment. This is due to the fact that the physical properties of aldehydes and ketones were observed using the four test samples. However, some unexpected results were recorded, such as the non-oxidation of formaldehyde in potassium permanganate, non-oxidation of benzaldehyde in chromic acid, and the negative results of acetone and formaldehyde and positive results of benzaldehyde and cyclohexanone for sodium bisulfite. The deviations of the experimental results from the theoretical one may be attributed to the impurities present in some of the samples. These impurities present may have hindered any reaction, or produced a new reaction which may be the reason why the results deviated from the expected one. In order to avoid the confusion in determining whether the compound is an aldehyde or a ketone, it is recommended to conduct additional tests that would better establish the identity of a certain compound such as Benedict’s Test and Ceric Nitrate Test. Sources: (1) Oxidation of Aldehydes and Ketones. http://www.chemguide.co.uk/organicprops/carbonyls /oxidation.html (accessed November 23, 2014) (2) Potassium Permanganate. http://en.wikipedia .org/wiki/Potassium_permanganate (accessed November 22, 2014) (3) Oxidation of Aldehydes and Ketones. http://www.wikipremed.com/03_organicmechanisms. php?mch_code=030208_030 (accessed November 22, 2014)

Page 11 of 11 of 12

LBYCH63, EA2, Group # 5

(4) Oxidation of Organic Molecules by KMnO4. http://chemwiki.ucdavis.edu/Organic_Chemistry/Rea Reacti/Oxidation_of_Organic_Molecules_by_KMnO 4 (accessed November 22, 2014)

/docs_file.php?v=SWRlbnRpZmljYXRpb24gb2YgY W4gVW5rbm93biDigJMgQWxjb2hvbHMsIEFsZGVo eWRlcywgYW5kIEtldG9uZXMKaHR0cDovL3d3dy5j aGVtLnVtYXNzLmVkdS9+c2FtYWwvMjY5L2Fhay5 wZGYKMA== (accessed November 21, 2014).

(5)  (5)  An Oxidation Reaction: Adipic Acid from Cyclohexanone. http://academic.pgcc.edu/~rgross/ LM_204_sp11/Lab%2007%20An%20Oxidation%20 Reaction--cyclohexanone%20to%20Adipic%20Acid .doc. (accessed November 24, 2014)

(16) Smith, (16) Smith, J. Organic Chemistry , 3  ed., New York, NY; 2011.

(6)  (6)  2,4-Dinitrophenylhydrazine. http://en.wikipedia. org/wiki/2,4-Dinitrophenylhydrazine (accessed November 20, 2014) (7) Addition-Elimination (7) Addition-Elimination Reactions of Aldehydes and Ketones. http://www.chemguide.co.uk/organicprops/ carbonyls/addelim.html (accessed November 20, 2014 (8) Schiff (8) Schiff Test. http://en.wikipedia.org/wiki/Schiff_test (accessed November 21, 2014) (9)  (9)  Qualitative Test for Carbonyls; Unknown Carbonyl. http://myweb.brooklyn.liu.edu/swatson/ Site/Laboratory_Manuals_files/Exp13.pdf. (accessed November 21, 2014)

rd

(17) Tollens’ Reagent. http://en.wikipedia.org/wiki/ Tollens%27_reagent (accessed November 22, 2014) (18)  (18)  Cannizzaro Reaction. http://en.wikipedia.org/ wiki/Cannizzaro_reaction (accessed November 22, 2014) (19)  (19)  Glucose. http://en.wikipedia.org/wiki/Glucose (accessed November 22, 2014)

“I hereby certify that I have given a substantial contribution to this report and I did not copy and/or quote from any resource material unless being cited as reference. I am make known that failure to accomplish the second clause would be grounds for plagiarism and a failing grade for my final laboratory report.”

(10) Fehling’s Solution. http://en.wikipedia.org/ wiki/Fehling's_solution (accessed November 21, 2014) (11)  (11)  Identification of Aldehydes and Ketones. http://www.copharm.uobaghdad.edu.iq/uploads/activ activ%202014/lect.2year%20tagreed/Identification% 22of%20aldehyde%20and%20keton%D9%85%D8% B9%D8%AF%D9%84.pdf (accessed November 21, 2014)

 ___________________________ RAZOTE, BERNARD JOMARI B.

(12)  (12)  The Triiodomethane (Iodoform) Reacted with  Aldehydes and Ketones. http://www.chemguide. co.uk/organicprops/carbonyls/iodoform.html (accessed November 21, 2014) (13) Simple Addition to Aldehydes and Ketones. http://www.chemguide.co.uk/organicprops/carbonyls /addition.html (accessed November 22, 2014). (14)  Aldehydes , Ketones and Carboxylic Acids. http://www.laney.edu/wp/cheli-fossum/files/2012/ 01/7-Aldehydes-Ketones-C.-Acids.pdf (accessed November 23, 2014) (15)  15)  Identification of An Unknown  –   –  Alcohols,  Aldehydes, and Ketones. https://docs.askives.com

Aldehydes and Ketones

Page 12 of 12 of 12