Analysis of 3 Unknown Chemicals

by anna1987 (student)

University Degree Subjects allied to Medicine

Identification of Unknown Compounds in Organic Chemistry:

#35A, #35B, and #35C

5-11-2012

Introduction

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 ...

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Unknown #35B

Unknown #35C

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.

Results

Unknown #35A

The unknown #35A is white solid with no particular odor in the form of crystals, which has its melting point at 54°C. The solubility tests showed that it is insoluble in water, NaOH, HCL, and H2SO4.

Table 1. The results of the chemical classification tests for unknown #35A.

Figure 7. The IR spectrum for unknown #35A.

Table 2. The peaks obtained during from the IR and their corresponding functional groups for unknown #35A.

Figure 8. The mass spectra for unknown #35A.

Table 3. The molecular peaks and corresponding fragments for unknown #35A.

Figure 9. The NMR analysis of unknown #35A. (1H-NMR (300 MHz; CDCl3): δ 7.78-7.73 (m, 5H), 7.55-7.51 (m, 5H), 2.52-2.51 (m, 9H), 2.01 (s, 0H).)

Table 4. The results from the NMR spectra analysis for unknown #35A.

Unknown #35B

The unknown #35B is a colorless liquid with an ammoniacal odor, which has its boiling point at 60°C. The solubility tests showed that it is insoluble in water but soluble in both NaOH and NaHCO3.

Table 5. The results of the chemical classification tests for unknown #35B.

Figure 10. The IR spectrum for unknown #35B.

Table 6. The peaks obtained during from the IR and their corresponding functional groups for unknown #35B.

Figure 11. The mass spectra for unknown #35B.

Table 7. The molecular peaks and corresponding fragments for unknown #35B.

Figure 12. The NMR analysis of unknown #35B.(1H-NMR (300 MHz; CDCl3): δ 2.40 (dt, J = 12.6, 6.3 Hz, 1H), 1.01-0.88 (m, 3H), 0.65 (d, J = 5.2 Hz, 3H), 0.55-0.50 (m, 2H).)

Table 8. The results from the NMR spectra analysis for unknown #35B.

Unknown #35C

The unknown #35C is white solid with a sweet odor in form of crystals, which has its melting point at 63°C. The solubility tests showed that it is insoluble in water, NaOH, HCL, and H2SO4.

Table 9. The results of the chemical classification tests for unknown #35C.

Figure 13. The IR spectrum for unknown #35C.

Table 10. The peaks obtained during from the IR and their corresponding functional groups for unknown #35C.

Figure 14. The mass spectra for unknown #35C.

Table 11. The molecular peaks and corresponding fragments for unknown #35C.

Figure 15. The NMR analysis of unknown #35C. (1H-NMR (300 MHz; CDCl3): δ 7.45-7.26 (m, 10H), 5.81 (d, J = 3.5 Hz, 1H), 2.59 (t, J = 4.2 Hz, 1H), 1.74 (s, 0H).)

Table 12. The results from the NMR spectra analysis for unknown #35C.

Discussion

It was possible to determine the identity of unknown #35A due to the results from the different aspects of the experiment.

Unknown #35A

The unknown #35A has a melting point of 54°C, which is pretty close to the melting point value of 51°C in the literature (Pavia, Lampman, Kriz, & Engel, 2006). The solubility test indicated that the unknown #35A would an inert compound, which is also true as the result of the Beistein Test showed that a halogen atom being present (Table 1). The analysis of the 1H NMR data clearly shows that a benzene ring has to be present, which is para-substituted due to two multiplets with a chemical shift at around 7.531 and 7.778ppm (Table 4). The IR supports this suggestion as a peak is shown at 1597.0cm-1 for the benzene ring as well as a peak at 2907.7cm-1 for the methyl group. There is also a peak at 3322.8cm-1, which is most likely due to water in the sample (Table 2). The Tollens Test indicated the presence of a ketone, and the DNPH Test as well as Iodoform Test confirmed the presence of a methylketone in unknown #35A (Table 1). In order to determine the exact structure of unknown #35A, the mass spectra of the compound was analyzed and it seems obvious that one substituent has to be a halogen atom as the mas spectra shows an M+2 peak, which is of equal value (Table 3). Thus, it has to be a bromine atom. The mass spectrum also shows a M+1-15 peak, which represents the methyl group, which was already identified in the NMR analysis. The mass spectra also shows the presence of a carbonyl group, which is part of the methyl ketone identified previously. Thus, unknown #35A is 4-bromo-acetophenone.

Figure 16. Unknown #35A is 4-bromo-acetophenone.

Unknown #35B

The unknown #35B had a boiling point of 60°C, which is pretty close to the boiling point value of 63°C in the literature (Pavia, Lampman, Kriz, & Engel, 2006). The solubility test indicated that the unknown #35B would be carboxylic acid. The analysis of the 1H NMR data clearly shows that two different methyl groups have to be present. A methyl group is presented by a doublet with a chemical shift at 0.65ppm and the other CH3 group is presented by a multiplet with chemical shift of 0.9465ppm (Table 8). The IR supports this suggestion as two peaks are shown at 2876.5 and 2961.4cm-1 for the methyl groups. There is also two peaks at 3385.5 and 3359.1cm-1, which indicate a secondary amine (Table 6). The HNO2 Test, however, indicated a primary amine (Table 5), and analysis of the mass spectrum supports this suggestion as the m/z is 73 (Figure 11), which is an odd number and can only explain an odd number of nitrogen atoms. In order to determine the exact structure of unknown #35B, the mass spectra of the compound was analyzed and the mass spectrum shows a M+1-15 peak, which represents the methyl group, which was already identified in the NMR analysis (Table 7). The most prominent peak is at m/z =44, which presents a fragment with the molecular formula C2H6N, and another fragment at m/z=58, which has the molecular formula C3H8N. The results from the mass spectra analysis could also suggest N-methylisopropylamine or but 2-aminobutane seems more accurate as the results from the NMR analysis shows different signals and the HNO2 Test indicates a primary amine. Thus, unknown #35B is 2-aminobutane.

Figure 17. Unknown #35B is 2-aminobutane.

Unknown #35C

The unknown #35C had a melting point of 63°C, which is pretty close to the melting point value of 67°C in the literature (Pavia, Lampman, Kriz, & Engel, 2006). The solubility test indicated that the unknown #35C would be inert compound. The analysis of the 1H NMR data clearly shows that a benzene ring has to be present as the NMR data shows a multiplet at 7.355ppm, which represents 10 hydrogen signals. The number of hydrogen signals would also explain two phenyl groups. The IR supports this suggestion as one peaks is shown at 1678.0cm-1 for the benzene ring. There is also a peak at 3335.9cm-1, which indicates an OH group (Table 10). The Acetyle Chloride Test most likely indicated an alcohol, however, this test was not considered conclusive as it took a long time to actually see the positive result. The Lucas Test was performed instead in order to get conclusive test results. As expected, the Lucas Test showed also a positive test result, which indicated a secondary alcohol (Table 9). The analysis of the mass spectrum supports this suggestion as the molecular weight is m/z =184, which would explain two phenyl groups as substituents. In order to determine the exact structure of unknown #35B, the mass spectra of the compound was analyzed and the mass spectrum shows peaks at m/z=77, 105, and 167, which represent the fragments shown in Table 11. The most prominent peak is at m/z =105, which presents a fragment with the molecular formula of C7H5O. As the NMR data only shows signals A-D as shown in Table 12, the unknown compound has to have two phenyl groups as substituents. Thus, unknown #35C is diphenylmethanol.

Figure 18. Unknown #35C is diphenylmethanol.

Conclusion

Unknown #35A

A variety of tests were performed in order to determine the identity of unknown #35A. Based on chemical classification tests as well as data from spectroscopy, it was possible to identify unknown #35A as 4-bromo-acetophenone. The data obtained in this experiment was consistent with the data in the literature.

Unknown #35B

A variety of tests were performed in order to determine the identity of unknown #35B. Based on chemical classification tests as well as data from spectroscopy, it was possible to identify unknown #35B as 2-aminobutane. The data obtained in this experiment was not conclusive to due to inconclusive chemical shifts in the NMR analysis; however, the results from the chemical tests and spectroscopic data are consistent with the data on 2-aminobutane in the literature.

Unknown #35C

A variety of tests were performed in order to determine the identity of unknown #35C. Based on chemical classification tests and data from spectroscopy, it was possible to identify unknown #35C as diphenylmethanol. The data obtained in this experiment was conclusive and consistent with the data in the literature.

References

Mohrig, J.R., Noring-Hammond, C., & Schatz, P.F. (2010). Techniques in Organic Chemistry. New York, NY: W.H.Freeman and Company.

Pavia, D.L., Lampman, G.M., Kriz, G.S., & Engel, R.G.(2006). Introduction to Organic Laboratory Techniques; A Microsale approach. Belmont, CA: Thomson Brooks/Cole.

Pavia, D.L., Lampman, G.M., Kriz, G.S., & Vyvyan, J.K. (2008). Introduction to Spectroscopy. Belmont, CA: Thomson Brooks/Cole.