Identification of Unknown Ketone Rough Draft PDF

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Identification of Unknown Ketone Rough Draft...

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Identification of Unknown

Aldehydes and Ketones

Lead author: Bradley Wurth Reviewer: Elijah Marsh Editor: Hannah Strickland Date: 2/23/2017

Section: G5

Introduction:

A variety of methods can be used in the process of identifying aldehydes and ketones. The obvious methods that can be used in the identification process are NMR and IR spectroscopy. Other processes used to identify certain compounds are chemical test. These specific tests can single out one product from another such as aldehydes and ketones. They are performed, and can also single out functional groups within these compounds by the indication of a positive or negative test result. These tests can be more accurate in testing or the identification process. They can also be more effective at identifying an unknown compound. There are two specific types of tests used in the identification of aldehydes and ketones: Tollen’s or silver mirror test, and the Iodoform or Haloform test. These specific tests directly test for functional groups within certain compounds. When determining certain compounds of aldehydes and ketones, both of these have the same carbonyl functional group. The difference in both of the compounds is that with ketones they have two carbons attached to the carbonyl carbonyl. However, aldehydes, have one or more hydrogens attached. When determining an aldehyde, a Tollen’s test is performed. (figure 2) A positive test for aldehydes would be indicated by the presence of a silver precipitate.1 To indicate whether a compound is an aldehyde or ketone, we look for the presence of oxidation. The Tollen’s solution oxidizes aldehydes because it contains a weak oxidizing agent. This is a major factor in determining the identity of wither compound.2 The balanced equation for the Tollen’s test is shown in figure 1 2[Ag (NH3)2]+ + RCHO + H2O ! 2Ag(s) + 4NH3 +RCHO2H + 2H+ The mechanism for the Tollen’s test is shown in figure 2.

Figure 2 shows the mechanism for the Tollen’s test

To distinguish between a Ketone, a Iodoform test is performed. The Iodoform test is used to detect methyl aldehdydes and ketones. The only compound of an aldehydes which would indicate a positive result would be acetaldehyde.2 However, when performed on ketones, there are many ketones which would be indicated by a positive result. If the test is positive it indicates the presence of a methyl group on one side of the carbon–oxygen double bond. A positive result would be indicated by the presence of a bright, yellow, precipitate solid.

Figure 2. shows the mechanism for the iodoform test

Further testing can be performed on certain compounds to distinguish aldehydes from ketones. A solid derivative is a compound that is derived from a similar compound. These derivatives can be compared with a specific melting point for a certain aldehyde or ketone and the known melting point of the unknown. In the preparation of derivivates of 2-4 dinitrophenylhydrazone, and semicarbazone. An orange yellow product is produced in the 2-4 dinitrophenylhyrazone indicates a positive test, and a light yellow product indicates a positive test for the semicarbazone.1 The mechanism for the derivatives of 2,4 dnp and semi carbazone are shown in figures 4 and 5

Figure 4 shows the mechanism for 2,4 dnp

Table 1. Table of Reagents1 Compound

Molecular weight G/ mol

Density g/cm3

AgNo3

169.87

4.35

380

308

NH4OH

35.04

.091

37.7

-57.5

Iodine

126.9

4.93

184.3

113.7

Semicarbazin e hydrochlorid e

95.08

115.3

235

175-177

Sodium acetate

84.99

1.53

881.4

198-202

2,4 dinitrophenyl hydrazine

198.138

1.79

378.6

198-202

NaOH

39.997

2.13

1388

604.4

Boiling point Melting point Celsius Celsius

Experimental: or the Tollen’s test 1-mL of 3M agNO3 was added to 0.5-mL of NaOH. Then 2M of NH4OH was added slowly dropwise to the solution until the brown silver oxide had completely dissolved . A drop of the unknown # 350 was added to the solution. A stopper was placed on the test tube, and the tube was shaken. The test tube was left standing for ten minutes at room temperature. Then a check was performed to see if there was a presence of precipitate. If no precipitate occurred, the test tube was heated in a hot bath for five minutes. The test tube was then rechecked to indicate the presence of a precipitate. For the Iodoform test, one drop of the unknown was placed in test tube with 0.5 mL of H2O. The next step was to add 0.53M NaOH, then 0.75-mL of I2 was added to the solution slowly dropwise. A solution of I2 was made using 0.5 I2 +1g of KI +4 mL of H2O. The test tube was then

shaken, and a check was performed to indicate the presence of a brown color or yellow precipitate. In the preparation of derivatives, a test tube was obtained and 0.2 g semicarbazone hydrochloride was placed in the test tube along with 0.3 sodium acetate and 3 mL of H2O. 0.5-mL of unknown #350 was added to the solution, and 95 % ethanol was added slowly dropwise. A stopper was placed on the test tube, and the tube was shaken for one minute. The stopper was removed, and the test tube was heated in boiling water for five minutes. The test tube was allowed to cool in an ice bath for five to ten minutes. The tube was scratched with a glass stir rod to check for crystallization. The crystals was then filtered, and the solid was rinsed with 5-mL office water. The final compound was allowed to dry in the oven for five minutes, and a melting point was taken For the 2-4 dinitrophenylhydrazone, a test tube was obtained and 4-5 drops of the unknown #350 were added to 2-mL of 95% ethanol. This solution was then added with 2mL of dnp-zine with a glass pipet. The next step was to check for the presence of a precipitate. If no precipitate was present, the test tube was stoppered and allowed to sit. After the precipitate formed a vacuum filtration was used along with 2 filter papers without the white filter. The solution was washed with ethanol. The solid was allowed to sit in in the oven on a watch glass for five minutes, and a melting point was taken. Results For the Tollen’s test, the test indicated a negative result. When the NaOh was added the solution turned from clear to brown, and after the NH4 was added the solution became light brown, then clear with a brown solid. The final product liquid solution turned black. There was also no presence of a silver precipitate. The negative result indicate there was no presence of an aldehyde. For the Iodoform test, the test indicated a positive result. When the NaOH was added the product turned into a bright yellow liquid with white solid precipitate. The positive test indicates the presence of a methyl ketone. The results of the

semicarbazone derivative had a melting point of 138-142 Celsius. The derivative contained a light white solid powdered was indicated. As for the results of the 2,4 dnp, the final melting point was 152-154 Celsius. The final product formed a light orange solid. Through experimentation we detrmined our unknown product #350 was 3- pentanone.

Test

result

Color

Melting Point 0 Celsius

Tollen’s

Negative

Black liquid No precipitate

Iodoform

Positive

Yellow white solid precipitate

Semicarbazone

Positive

White solid derivative

138-142

2,4 dnp

Positive

Light orange solid derivative

152-154

Table 2: List of test results and final melting points

Discussion. Due to the fact that aldehydes are easily oxidized, the Tollen’s test is an extremely accurate test that can be performed to distinguish between aldehydes and ketones. The results of the Tollen’s test were pretty straightforward. The test indicated a negative result. There was no presence of the silver precipitate. This shows that the product was not an aldehyde. As for the results of the Iodoform test, the presence of a white - yellow solid indicates a positive result. This simply means an iodoform was formed. The positive result indicates the presence of a ketone. We can determine this by looking at the positive result. A positive result indicates the presence of a methyl ketone. The Ag used in the test acted as the oxidizing agent. In the Iodoform test, ketones are not easily oxidized. The I2 was the product acting as an oxidizing agent in the compound works as the oxidizing agent. 3

Through experimentation, we determined our uknown #350 was 3pentanone.Our determination of 3- pentanone was based off the unknown not oxidizing. Therefore, we reached the conclusion, our product was a ketone. We were also able to reach this conclusion based on the melting point. When the functional groups of a compound have been verified, solid derivatives were prepared. A fact that must be taken into account is that the probability of two verified compounds and their derivatives having exactly the same melting point range is small. From this fact alone, we can verify the identity of unknown compounds possible. In the experiment, the 2, 4 dnp had a melting point of 152-154 Celsius. The melting point of semicarbazone had a melting point of 138-142. In the table of melting points of derivatives, the melting points for 2,4 dnp for 3- penatanone was 156 Celsius. The melting point for semicarbazone was 138 degrees Celsius. Based on the information from the table, our unknown product had to be 3-pentanone. When performing the semicarbazone procedure, the final product was a white solid. The derivatives formed solid products that were used to compare melting points of 2,4 dnp and semicarbazone. Due to nucleophilic addition, aldehydes and ketones give products with nitrogen carbon double bonds.1

Conclusion: During experimentation, miscalculations and error can occur during procedures. These errors can have an impact on the final results listed above. During experimentation, impurities can cause slight deviations in melting point temperatures. These slight deviations can throw off melting point temperature, leading to errors in final product identity. The only way to correct such errors is to make the experiment as precise as possible. Also during experimentation, Our final product for 2,4 dnp was charred due to overheating of the final product. In every experiment, caution must be taken to prevent such errors from occurring.

These tests and affirmations of derivations are a precise was of identifying a compound and the functional group contained within the compound. IR and NMR spectroscopy are a more accurate way of identifying compounds. However, these tests can be used as a backup or proof method of identity.

References: 1. Identification of an Unknown – Alcohols, Aldehydes, and Ketones http://www.chem.umass.edu/~samal/269/aak.pdf (accessed Feb 25, 2017). 2. Reactions of Aldehydes, Ketones and Phenols http:// 1chemistry.blogspot.com/2011/09/reactions-of-aldehydes-ketonesand.html (accessed Feb 28, 2017). 3. Hill, R.; Barbaro, J.!Experiments in Organic Chemistry, 3rd ed.; Contemporary Publishing Company of Raleigh: Raleigh, NC, 2005...