There are many reasons for identifying an unknown compounds. The reasons range from medical purposes, such as determining if the unknown could cause ailments in living things or knowing what chemical compounds are needed to make antibiotics to other purposes such as knowing the exact compound has to be used to make certain foods. The purpose of this experiment was to determine the identity of unknown #35A, #35B, and #35C by making use of their physical characteristics, solubility tests, chemical classification tests, and spectroscopy data (Pavia, Lampman, Kriz, & Engel, 2006).
First of all, a preliminary classification of the unknown compounds #35A, #35B, and #35C was done by recording the physical state, color, and odor of the unknown compounds. Following that, the melting point for unknown #35A and #35C was obtained; whereas, the boiling point for #35B was obtained due to its physical state, and solubility tests were performed as outlined the Figure 1. Figure 1. Solubility chart for compounds containing various functional groups (Pavia, Lampman, Kriz, & Engel, 2006).
After that, the IR and NMR spectra were determined for the unknown compounds in order to provide more evidence for the preliminary results and confirm the identity of the unknown compounds #35A, #35B, and #35C. The chemical classification tests chosen for this experiment were the following: DNPH Test, Beistein Test, Tollens Test, Iodoform Test, HNO2 Test, Lucas Test, and Acetyl Chloride Test. The DNPH Test is used to identify aldehydes and ketones and the Formation of a precipitate is a positive test. The mechanism is shown in Figure 2.
Figure 2. The mechanism of the DNPH Test used to detect aldehyde and ketones. The Beistein Test is used to detect halides and the appearance of a green flame is a positive test. The equation shown below represents the steps of the Beistein Test. Cu (s) + O2 (g) –> CuO (s) CuO + 2 R-X –> CuX2 + 2 R-O The Tollens Test is used to identify aldehydes and the formation of silver mirror or a black precipitate is a positive test. The mechanism is shown in Figure 5. Figure 3. The mechanism of the Tollens Test used to detect aldehydes.
The Iodoform Test is used to identify methyl ketones and the formation of solid iodoform (yellow) indicates a positive test result (Mohrig, Noring-Hammond, & Schatz, 2010). The mechanism is shown in Figure2. Figure 4. Mechanism of the Iodoform Test used to detect methyl ketones. The HNO2 Test is used to detect primary, secondary and tertiary amines and the formation of bubbles indicates a positive test results. Figure 5. The 2-step procedure of the HNO2 Test (Mohrig, Noring-Hammond, & Schatz, 2010).
The Lucas Test is used to identify alcohols and the appearance of a cloudy second layer or emulsion immediately indicates a tertiary alcohol (Mohrig, Noring-Hammond, & Schatz, 2010). Figure 5. The reaction of the Lucas test to detect an alcohol. The Acetyl Chloride Test is used to identify alcohols and the formation of a top layer indicates the presence of an alcohol (Mohrig, Noring-Hammond, & Schatz, 2010). Figure 6. The reaction of the Acetyl Chloride Test to detect an alohol. Unknown #35A The chemical tests determined the presence of a methyl ketone as well as a halide.
Further, the NMR and mass spectrum provide information about the presence of a benzene ring and the corresponding fragments of the compound. The unknown #35A was identified as 4-bromo-acetophenone (C8H7BrO). Unknown #35B The chemical tests determined the presence of a methyl ketone as well as a halide. Further, the NMR and mass spectrum provide information about the presence of a nitrogen atom and the corresponding fragments of the compound. The unknown #35B was identified as 2-aminobutane (CH3CH2CH(NH2)CH3). Unknown #35C The chemical tests determined the presence of an –OH group.
Further, the NMR and mass spectrum provide information about the presence of two benzene ring and the corresponding fragments of the compound. The unknown #35C was identified as diphenylmethanol ((C6H5)2CHOH). Procedure Unknown #35A In order to determine the identity of unknown #35A, the physical characteristics were observed and recorded, followed by melting point analysis, solubility tests, and chemical classification tests. After an elemental analysis was performed, the identity of the unknown was confirmed using IR spectroscopy, 1H NMR analysis, and mass spectra analysis.
Based on the preliminary results from the physical characteristics and solubility tests, the chemical tests chosen for unknown #35A were the DNPH Test (Pavia, p. 471), the Tollens Test (Pavia, p. 472), and the Iodoform Test (Pavia, p. 474) used to test for the compound being an aldehyde or ketone, and the Beistein Test (Pavia, p. 461), which was supposed to provide information about the presence of a halogen. For IR spectroscopy, unknown #35A, a solid sample, was first made a liquid using chloroform and then sandwiched between two plates of a salt.
The plates were transparent to the infrared light and did not introduce any lines onto the spectra. For 1H NMR analysis, the solid sample was added to the prepared solution and TMS used as an internal standard. The mass spectrum for unknown #35A was provided using by the instructor. Unknown #35B In order to determine the identity of unknown #35B, the physical characteristics were observed and recorded, followed by melting point analysis, solubility tests, and chemical classification tests. After an elemental analysis was performed, the identity of the unknown was confirmed using IR spectroscopy, 1H NMR analysis, and mass spectra analysis.
Based on the preliminary results from the physical characteristics and solubility tests, the chemical tests chosen for unknown #35C were the HNO2 Test (Pavia, p. 483), which was supposed to provide information about the presence of an amino group. For IR spectroscopy, unknown #35B, a liquid sample, was sandwiched between two plates of a salt. The plates were transparent to the infrared light and did not introduce any lines onto the spectra. For 1H NMR analysis, the liquid sample was prepared as previously described and TMS used as an internal standard.
The mass spectrum for unknown #35B was provided using by the instructor. Unknown #35C In order to determine the identity of unknown #35C, the physical characteristics were observed and recorded, followed by melting point analysis, solubility tests, and chemical classification tests. After an elemental analysis was performed, the identity of the unknown was confirmed using IR spectroscopy, 1H NMR analysis, and mass spectra analysis. Based on the preliminary results from the physical characteristics and solubility tests, the chemical tests chosen for unknown #35C were the Lucas Test (Pavia, p. 488) and the Acetly Chloride Test (Pavia, p. 4870, which was supposed to provide information about the presence of an –OH group.
For IR spectroscopy, unknown #35C, a solid sample, was first made a liquid using chloroform and then sandwiched between two plates of a salt. The plates were transparent to the infrared light and did not introduce any lines onto the spectra. For 1H NMR analysis, the solid sample was added to the prepared solution and TMS used as an internal standard. The mass spectrum for unknown #35C was provided using by the instructor.