Organic Chemistry Laboratory - Experiment 21. Report. Mallol

Experiment 21: Qualitative analysis of an Unknown Compound Objective: In many laboratories, oftentimes there are accidental spills or reagents left behind that were meant to be put away. The only way to properly store these reagents is through identification of the reagent and so, in this experiment, identification of an unknown compound will be explored. The objective of this experiment is to identify an unknown compound through a series of physical and chemical tests with the only possibilities of the unknown being a carboxylic acid, ketone, aldehyde, or an alcohol. Physical tests are crucial to identifying an unknown as they reveal characteristics of the compound like melting point, solubility, odor, boiling point and even physical appearance, that reveal a lot about the identity of the compound. whereas Chemical tests can yield a positive or negative result depending on the chemical test being done solely off an assumption. For example, if you assume your compound is a ketone/aldehyde, but your chemical tests to examine if it is a ketone or aldehyde is negative, or produces no reaction, then your compound is not a ketone or an aldehyde as it did not yield the expected product for that reaction. Chemical tests are done after a series of physical tests to help pinpoint the unknown compound more precisely. With that being said, in this experiment with unknown compound 11, a melting point test for the unknown and its derivative will be performed as well as, examination of the compound’s appearance, odor, solubility in water, 1M NaOH, and 5% NaHCO3 and most importantly, an IR spectroscopy, DNP test, and a preparation of the derivative of a carboxylic acid to further examine unknown 11. General Reaction for preparation of a carboxylic acid derivative: General Reaction Mechanism for preparation of a carboxylic acid derivative: General Reaction for DNP test General mechanism for the solubility tests: Reagents: Reagent Used:___________________________________Safety Info: - O- toluic acid - 1 mL 1M NaOH - 1 mL water - 1 mL 5% NaHCO3 - 2 mL Thionyl Chloride - 35 mL methylene chloride - 15 mL ammonium hydroxide - 8 drops DNP reagent - 2-5 drops 10% HCl - extremely volatile, use under hood don’t breathe fumes - caustic, avoid contact with fabrics and skin Procedure: In this experiment, the first thing to do is examine the appearance and odor of the unknown compound. Does it look familiar? Is it a liquid? Solid? Once this is established, the melting point of the unknown must be established to further identify this compound. Using the Digi melt apparatus, establish the melting point of your compound. after this, examine the solubility of the compound in various solvents using ~25 mg of the unknown and 1 mL of the solvents. Firstly, examine the solubility in water and it is insoluble. Then, we examine the solubility of the compound in 1M NaOH and it is somewhat soluble, then examine the solubility of it in NaHCO3 and it proves to be soluble. This means the unknown can be a carboxylic acid or phenol. Moving along you want to examine the compound using IR spectroscopy as this will give you further insight on the main functional groups that are present in the unknown compound. Once the IR has been done, perform a DNP test to confirm or negate the possibility of the compound being an aldehyde or ketone. To perform this, use a few crystals of the solid and add 7-8 drops of DNP reagent, a red or yellow precipitate indicates a positive result and the lack of this indicates a negative result. Once this negative was established, proceed with a derivative test for carboxylic acids. Under a hood, transfer 0.4g of the unknown to a dry conical vial containing a spin vane or boiling chips, then add 2 mL thionyl chloride and equip the conical vial with a reflux condenser and calcium chloride drying tube. Stir this for 10 minutes at room temperature and then heat the reaction with a sand bath for 15 minutes. Once it is done refluxing, cool the reaction to room temperature and transfer the contents to a 100 mL beaker. Using 1mL of methylene chloride, rinse the conical vial three times with 1 mL methylene chloride each rinse and transfer these contents to the 100 mL beaker. Cool the reaction and 15 mL OF Ammonium hydroxide in an ice bath and once cooled, slowly add 15 mL of ammonium hydroxide dropwise to the reaction mixture being careful as it does produce a large amount of smoke. Once done allow the reaction to cool to room temperature and stir for five minutes. Once done stirring, extract the amide from the biphasic mixture with 10 mL of methylene chloride and transfer this to a separatory funnel and extract using 2 more washes with 10 mL methylene chloride. Combine the methylene chloride fractions and evaporate the solvent using a warm sand bath until it is completely dry and collect your precipitate and obtain a melting point for the crude amide derivative. Observations: In this experiment, the DNP reagent test for aldehyde and ketones did not yield any red or yellow precipitate. In fact, the reaction did not proceed and remained stagnant--which is a negative result. However, in the preparation for the derivative of a carboxylic acid test, a yellow amide was formed and was a positive result for the unknown compound being a carboxylic acid. Additionally, during the reaction for preparing the derivative of a carboxylic acid, one knew that this would yield a carboxylic acid derivative because the reaction was proceeding as expected and that includes the visibility of the biphasic mixture and the smoking of the reaction upon addition of ammonium hydroxide. Results: Identity of Unknown 11: O-Toluic acid Physical appearance: Chalky, coarse, pale white color Odor: Synthetic, honey scent Melting point of Unknown 11: 106 º C Solubility in Water: Insoluble Solubility in 1M NaOH: Soluble Solubility in 5% NaHCO3: Soluble Melting point of amide derivative: 142 º C DNP Aldehyde/Ketone chemical test: Negative Preparation of carboxylic acid derivative test: Positive Characterization: Analysis: In the IR spectrum of the unknown compound 11, it revealed plenty of the compound’s secrets. For example, at 1672.36 cm-1, one can observe the presence of a C=O carbonyl group shown by the intense and pronounced peak at 1672.36 cm-1. This indicates that the compound we have at the minimum must have a carbonyl functional group as it is present in the IR. Moving along, it is difficult to not notice the broad band that starts at ~3300 cm-1 and ends at 2000 cm-1. Upon first glance, one may not recognize it as an OH band, but it indeed is the presence of an O-H bond and OH group present in the unknown compound. in addition to that, the small peak at 2970.38 cm-1 shows an SP3 hybridized carbon found in the molecule confirming the potentiality that the unknown may be either an aldehyde, ketone, or carboxylic acid. However, the presence of various intense peaks in the 1400-1500 cm-1 region shows the presence of an aromatic ring as well as C-C stretching in the ring at ~1500cm-1. Discussion and Conclusion: In this experiment, the objective was to identify the identity of the unknown compound 11. Upon receiving the unknown compound, it was clear that this compound had a synthetic, honey odor and had a coarse, chalky, pale white appearance. Our familiarity with various carboxylic acids led us to believe this was a carboxylic acid and so we proceeded with a melting point test using a small amount of the unknown to further narrow the list of possibilities. The melting point established that our unknown compound had a melting point of 106 º C and so this led us to narrow the list of possibilities to o-toluic acid and p-toluic acid. However, the potentiality of this being an aldehyde was not ruled out yet. To further examine this and establish a firmer identity, the solubility of the unknown was examined in water, 1M NaOH, and 5% NaHCO3. Approximately ~25mg of the unknown was combined with 1 mL of each reagent to examine its solubility. In water, the unknown did not dissolve and when 1M NaOH was added, the unknown was dissolving, even further, once the 5% NaHCO3 was added, the unknown completely dissolved. The compound’s solubility in a base, tells us there is a high chance this can be a carboxylic acid. As we feel we are getting closer to uncovering the identity of the compound, we sample a small amount and perform an IR spectroscopic analysis to examine any intense and notable peaks that might give us a further clue as to what the identity of the unknown is. The In the IR spectrum of the unknown compound 11, it revealed plenty of the compound’s secrets. For example, at 1672.36 cm-1, one can observe the presence of a C=O carbonyl group shown by the intense and pronounced peak at 1672.36 cm-1. This indicates that the compound we have at the minimum must have a carbonyl functional group as it is present in the IR. Moving along, it is difficult to not notice the broad band that starts at ~3300 cm-1 and ends at 2000 cm-1. Upon first