Systemic Approach To Practical Organic Chemistry

1. Systemic Approach To Practical Organic Chemistry SATL-POC 2009 By Prof. Dr. A. Farouk Fahmy Prof. Dr. Ahmed I. Hashem Chem. Dept. Faculty of Science Ain Shams University Director of Science Edu. Center Chem. Dept. Faculty of Science Ain Shams University Prof. Dr. Nadia G. Kandil Chem. Dept. Faculty of Girls Ain Shams University

2. SYSTEMIC FUNCTIONAL GROUP TRANSFORMATION I- In Benzene-Nitrobenzene-Aniline- and Benzenediazonium salt Cycle Chemical and Spectroscopic Identification

3. Chemicals and Hazards

4. Chemical Identification a) Benzene to Nitrobenzene • Add benzene (1 ml) to a mixture of conc. HNO3 (5 ml) and conc. H2SO4 (5 ml), and shake for 2 min. • Pour into cold water whereby nitrobenzene separates as a yellow oil.

5. Spot test for the NO2 group • One drop of benzene solution of the sample, and one drop of (5%) diphenylamine in benzene are introduced into a small tube. The tube is dipped in boiling water-bath, the solvent is then evaporated. • Observation:A melt remains in the tube which is more or less • yellow in color.

6. b) Nitrobenzene to Aniline • To the nitrobenzene obtained from step (a), (5 ml) of conc. Hydrochloric acid and small pieces of granulated tin are added. • The solution is heated just to start the reaction, and then allowed to stand for some time. When the reaction ceases, filter the product and test for the amino group in the filtrate.

7. Spot test for the amino group (NH2) • This test depends on the condensation of the primary amino group with the colorless 2,4-dinitrochlorobenzene to yield yellow condensation product. • Amines containing –SO3H or –COOH groups do not react. • Procedure: A drop of the ether test solution is treated on a spot plate with a drop of (1%) ether solution of 2,4-dinitrochlorobenzene. Then ether has been evaporated. • Observation: A residual yellow or brown color or ring appears.

8. c) Aniline to Benzenediazonium chloride • Aniline oil obtained from step (b) is dissolved in conc. HCl, diluted with small amount of water (1 ml). • The solution is cooled well and then adds few drops of sodium nitrite solution.

9. Test for the diazonium salt • A small part of the diazonium salt solution is added to a cold solution of β-naphthol in sodium hydroxide. Observation:Scarlet red dye indicates the presence of the diazonium salt. Scarlet red

10. d) Conversion of Benzenediazonium Chloride to Benzene (Recycling) • Add the diazonium salt obtained from step (c) to a solution of sodium stannite (prepared from stannous chloride by adding sodium hydroxide drop wise till a white ppt is formed and then redissolves in alkali). • Heat the contents of the test tube gently; detect the odor of benzene (Starting material).

11. Spectroscopic Characterization • IR-Spectra 1- Nitro Group: (NO2): • The vibrational behaviour of the nitro group also supports the structure. The presence of nitro group in a compound is characterized by the presence of two strong bands in its infrared spectrum which arise from the symmetrical and asymmetrical modes which occur in the region: • (i) 1620-1535 cm-1 (ii) 1375-1275 cm-1 • Aromatic compounds show two bands: • (i) 1570-1500 cm-1 (ii) 1370-1300 cm-1 e.g. Nitrobenzene:

12. 2- Primary amino group: (NH2) • Primary amines show two sharp bands; these can be recognized by absorption due to N-H str. in the region 3500-3300 cm-1. The position of absorption depends upon the degree of hydrogen bonding. • The dilute solution of primary amines in an inert solvent gives two sharp bands due to symmetric and asymmetric stretching vibrations between 3500-3300 cm-1. e.g. p-Toluidine

13. ASSESSMENT QI:Analyze the following systemic diagram to chemical equations: QII:How can you differentiate between the following pairs of compounds: (Via spot tests) • Benzene and nitrobenzene. • Benzene and aniline.

14. QIII:How can you differentiate between the following compounds by I.R. spectra: Nitrobenzene and Aniline QIV: What are the main objectives for using the systemic cycle (In QI) for chemical investigation of (benzene, aniline, nitrobenzene and diazonium salt).

15. II) In Benzonitrile-Benzamide- and Benzoic Acid Cycle 1) Chemical and Spectroscopic Identification

16. Chemicals and Hazards

17. Chemical Identification a) Benzonitrile to Benzamide In a small test tube, place (0.2 ml) of the nitrile, (1 ml) of ethanol and (1 ml) of (1N) sodium hydroxide. To this mixture add dropwise (1 ml) of (12%) hydrogen peroxide. Maintain the solution at (50-60ºC) in a water-bath for 30 min. Dilute the reaction mixture with cold water and collect the solid amide. Identification of benzamide: Effect of sodium hydroxide: A small amount of the solid is heated in a test tube with sodium hydroxide solution. Observation:Evolution of ammonia which is detected by its odor indicates the presence of amide group.

18. b) Benzamide to Benzoic acid Mix (1g) of the amide from step (a) with (10 ml; 10%) sodium hydroxide. Boil the mixture for 10 minutes, cool well and then adds conc. hydrochloric acid whereby benzoic acid is separated. Wash with little water and determine its m.p.

19. Identification of the acid: 1- Acidity test:To a small amount of the acid add sodium bicarbonate solution. Observation:Effervescence and evolution of CO2 indicates the presence of the acid. 2- FeCl3 test:To a suspension of the acid in water, add ammonium hydroxide solution till just alkaline. Boil the solution till the excess of ammonia has been expelled i.e. no odor of ammonia is detected, add FeCl3 solution. Observation:A buff precipitate indicates benzoic acid.

20. c) Benzonitrile to Benzoic acid • Boil (1 ml) of benzonitrile with (10 ml) of 10% sodium hydroxide till all the oil drops disappear. Cool well and then adds conc. hydrochloric acid whereby benzoic acid is separated. • Confirm the formation of benzoic acid as described above.

21. 1) Spectroscopic Characterization • IR-Spectra Nitrile group: • The infrared absorption occurs in the triple bond region between (2280-2200 cm-1). The shift in νC≡N stretching absorption depends upon the electronic effects of atoms or groups attached to the C≡N group. • In aliphatic nitriles, the intensity of νC≡N stretching band is low. • CH3-C≡N 2280 cm-1 • CH3-CH2-C≡N 2257 cm-1

22. In aromatic nitriles, the νC≡N stretching decreases by about 20 cm-1 but band intensity increases as compared to the saturated compounds. • e.g. I.R. spectrum of benzonitrile

23. Amide group: • The νC=O absorption in amides takes place at lower wave number. In addition to the νC=O absorption, amides can be recognized by N-H stretching and N-H def. bands. • Primary amides in dilute solutions show two bands (N-H str.) near 3400 cm-1 and 3500 cm-1. These two bands arise due to symmetrical and asymmetrical N-H stretching. e.g. I.R. spectrum of benzamide

24. Signals and their absorption peaks:

25. Carboxylic Group: • Carboxylic group (-COOH) is the easiest functional group to detect by infrared spectroscopy since this group can be considered as being formed from C=O and O-H units. The absorption of O-H stretching appears as a broad band near 3000 cm-1. The νC=O stretching absorption in aliphatic acids occurs at 1725-1700 cm-1. • Some of the acids viz., acetic acid, benzoic acid, exist as dimmers due to hydrogen bonding. Formation of bridge lowers the force constants and thus, νC=O and νO-H absorption occur at lower wave numbers. As the hydrogen bonded structure is stabilized by resonance, the O-H stretching occurs as a broad band in the region 3300-2500 cm-1.

26. 1H-NMR- Spectra: The following chart represents the 1H-NMR- Spectrum of a-chloro propionic acid as a representative of this class of compounds.

27. 2) Quantitative Determination of Carboxylic Acids • This method is generally applied for water soluble acids. e.g. succinic acid, acetic acid, ……………., • This method is based on the fact that a normal alkali neutralizes one equivalent weight of the acid (N. NaOH ≡ eq.wt of the acid) • N.B. Use succinic acid for this determination. Procedure: • Dissolve a small amount (2.5-3 g) of the exactly weighed carboxylic acid in a 100 ml measuring flask. • Titrate (10 ml) of this solution against 0.5 N sodium hydroxide solution using phenolphthalein as an indicator. The appearance of faint but permanent pink color is the end point. • Take at least three concordant readings. Calculations: (10 ml) of the acid = V ml x 0.5 N NaOH (100 ml) of the acid = 10 x V ml x 0.5 N NaOH (100 ml) of the acid = 5 x V ml x N NaOH Or 5 x V ml x N NaOH = X g of the acid

28. 3- Synthesis (i) Synthesis of Benzamide from Benzonitrile • Equation: • Procedure: Add (2g; 2 ml) of benzonitrile to (20 ml) of 90% sulfuric acid in a conical flask, a clear solution is rapidly obtained. Heat the solution in an oil-bath at 120-130ºC for 20 minutes, and then cool the solution and pour it onto (50g) of crushed ice. Filter the precipitated benzamide at the pump, wash it with water, and recrystallize it once or (twice) from water. Determine its melting point. M.p. 128-130ºC.

29. (ii) Synthesis of Benzoic Acid from Benzamide Procedure: Place (1g) of benzamide from step (i) and (15 ml) of (10%) sodium hydroxide solution in a 100 ml round-bottomed flask fitted with a reflux condenser, and boil the mixture gently for (30) minutes, during which ammonia is freely evolved. Transfer the contents of the flask to a beaker, cool the solution in ice-water and add conc. Hydrochloric acid until the mixture is strongly acidic. Benzoic acid immediately precipitates. Allow the reaction mixture to stand in the ice-water for few minutes, and then filter off the benzoic acid at the pump, wash with cold water, and dry. Recrystallize from hot water. Determine its melting point. M.p. (121ºC).

30. (iii) Synthesis of Benzoic Acid from Benzonitrile Procedure: Boil (5 ml; 5.1g) of benzonitrile and (75 ml) of (10%) aqueous sodium hydroxide in a 200 ml round bottom flask under reflux until no more oily drops of unchanged nitrile run down from the condenser (usually about 40 minutes). Then remove the condenser and boil the solution for a few minutes to remove free ammonia. Cool the liquid, and add conc. hydrochloric acid cautiously until precipitation of benzoic acid is complete. Cool the mixture again thoroughly, filter off the benzoic acid at the pump, and wash with cold water and finally recrystallize from hot water. Determine its melting point. M.p. (121ºC).

31. ASSESSMENT QI: Analyze the following systemic diagram to chemical equations:

32. QII: Arrange the following nitriles in the following systemic diagram according to their νC≡N CH3C≡N, CH3CH2C≡N, CH2=CH-CN QIII: Write mechanisms of the following reactions: