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Organic Qualitative Analysis

Organic Qualitative Analysis. Physical Properties, Chemical tests and Infrared Spectroscopy to Identify: Unknown Halide (primary, secondary, tertiary) Hydrocarbon (alkane, alkene, aromatic) Alcohol (primary, secondary, tertiary) References:

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Organic Qualitative Analysis

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  1. Organic Qualitative Analysis Physical Properties, Chemical tests and Infrared Spectroscopy to Identify: Unknown Halide (primary, secondary, tertiary) Hydrocarbon (alkane, alkene, aromatic) Alcohol (primary, secondary, tertiary) References: Slayden, S., Stalick, W.; 2010, Catalyst - Organic Chemistry Laboratory Manual, GMU Print Services Pavia, D., Lampman, G., Kriz, G, Engel, R, 2010, A Small Scale Approach to Organic Laboratory Techniques, 3nded, Cengage Learning

  2. Organic Qualitative Analysis • Purpose: Become familiar with a combination of physical and chemical tests for characterizing classes of organic compounds. To use these tests plus Refractive Index and IR to identify an unknown. • Classes: Compounds without a Carbonyl group or Nitrogen group • Alkanes C-C • Alkenes C=C • Alkynes C≡C • Aromatics C=C • Alkyl (1o, 2o, 3o) & Aryl Halides R-X • Alcohols (1o, 2o, 3o) R-OH Note: Tests for carbonyl based compounds (Aldehydes & Ketones) will be presented next semester

  3. Organic Qualitative Analysis • The Tests – Compound Classes • Test Compound Class • Solubility Relative to H2O & H2SO4 All • Density Relative to H2O All • Beilstein (Flame) Halides • Silver Nitrate/Ethanol Alkyl & Aryl Halides • Sodium Iodide/Acetone Alkyl & Aryl Halides • Bromine/Methylene Chloride Unsaturated C=C CC • KMnO4 (Baeyer Test) Unsaturated C=C CC • Ignition Aromaticity C=C • Acetyl Chloride Alcohols • Lucas Test Alcohols • Chromic Acid Alcohols

  4. Organic Qualitative Analysis • The Tests – Test References (Pavia (3rd ed) – GMU Version or Pavia Main text as indicated) • TestPage No. • Solubility Relative to H2O & H2SO4 p. 453-458 • Density Relative H2O p. 717-719 Beilstein (Flame) p. 459-460 • Silver Nitrate/Ethanol P. 460-461 • Sodium Iodide/Acetone p. 158 Pavia Main Text • Bromine/Methylene Chloride p. 464-466 • KMnO4 (Baeyer Test) p. 466-467 • Ignition p. 467-468 • Acetyl Chloride p. 585 • Lucas Test p. 585 • Chromic Acid p. 586-487

  5. Organic Qualitative Analysis • Elements of the Experiment • Week One • Boiling Point & Purification (Simple Distillation) • Physical Characteristics of Unknown • Solubility Relative to Water & Conc H2SO4 (Just the unknown) – Page 453 • Density relative to Water (Just the unknown) • Refractive Index (unknown only) • Temperature Correction for Refractive Index • Beilstein Test (Halides) – Page 459 • Ignition Test (Aromaticity) – Page 467

  6. Organic Qualitative Analysis • Elements of the Experiment • Week Two • Silver Nitrate/Ethanol Alkyl & Aryl Halides p. 460 • Sodium Iodide/Acetone Alkyl & Aryl Halides Note: This experiment is not in the GMU Pavia text, but is in the regular hard cover Pavia Text p. 158 • Bromine/Methylene Chloride Unsaturated C=C CC p. 465 • KMnO4 (Baeyer Test) Unsaturated C=C CC p. 466 • Acetyl Chloride Alcohols p. 485 • Lucas Test Alcohols p. 485 • Chromic Acid Alcohols p. 486 • IR Spectra p. 851

  7. Organic Qualitative Analysis • General Notes • Dangerous Chemicals – Acetyl Chloride, Conc H2SO4 Use Gloves, Goggles, and Lab Coat (Buttoned) • Use a test tube rack from cabinet • Use medicine droppers from equipment set Pasteur pipettes are not available • Make sure to wash and dry the medicine dropper and test tubes for each test

  8. Organic Qualitative Analysis General Notes • The Beilstein (flame) Test for Halides and the Ignition test for Aromaticity with be done in the hood with the assistance of the instructor • Record the results of the chemical tests in a 5-column table created in the prelab template (see slide 11) • Use simple, direct language to describe your test.It is very important to describe an observation completely Ex. The Unknown was soluble in water • Be sure to obtain a good positive result for each test; repeat the test until a good positive result is obtained

  9. Organic Qualitative Analysis • Testing Sequence for Knowns & Unknown • The boiling point, solubility, refractive Index, flame test, and IR should indicate the general class of the unknown compound – Halogen, Hydrocarbon, Alcohol • Test your unknown against all the reagents • Test each of the known samples against only those tests that are applicable to the class of compounds to which the known belongs Note: See table on page 57 of Slayden Lab Manual • For each test, set up a sufficient number of test tubes to accommodate the unknown and as many knowns specified in the table on page 57 • Add test reagent • Add compound to be tested; shake mixture • Heat reaction mixture as specified in test directions

  10. Organic Qualitative Analysis • The Report • Each “Test” is a Procedure and must be set up with: • A Title • Materials & Equipment, including reagents, known and unknown compounds, test tubes • Procedure Description in bullet format • Test Results – include a 5-column table (see next slide) containing the name of the compound, your observations, and an indication of whether a result for a givent compound was positive or negative relative to the compound tested and the test applied • Summary – All results summarized in a paragraph • Analysis & Conclusions • Arguments showing how your results support your identification of the unknown

  11. Organic Qualitative Analysis • Suggested table for recording Qualitative Organic test results (Create your own, don’t copy)

  12. Organic Qualitative Analysis Solubility Test (Water (H2O) and Conc Sulfuric Acid (H2SO4) • Only the unknown is to be tested for solubility in Water and Concentrated Sulfuric Acid • Water • Compounds with <5 Carbons containing O, N, S are soluble • Compounds with 5-6 Carbons containing O, N, S are borderline (slightly soluble) • Branching Alkyl chains result in lower melting/boiling points and increased solubility • Increase N, O, S to Carbon ratio increases solubility

  13. Organic Qualitative Analysis Solubility Test (Water (H2O) and Conc Sulfuric Acid (H2SO4) • Conc H2SO4 Solubility • Compounds containing N, O, S can be protonated in Conc H2SO4 and thus are considered soluble. • Alkenes (C=C) • Alkynes (C≡C) • Ethers (C-O-C) • Nitroaromatics (Nitrobenzene) • Amides • Alcohols (R-OH) • Ketones • Aldehydes • Esters

  14. Organic Qualitative Analysis Solubility Test (Water (H2O) and Conc Sulfuric Acid (H2SO4) • Water & Conc H2SO4 Solubility • Not soluble • Alkanes • Aromatic Hydrocarbons • Alkyl Halides • Aromatic Halides

  15. Organic Qualitative Analysis Relative Solubility & Density • Procedure – Water & H2SO4 Note: Solubility & Density test is performed only on the Unknown • Place about 2 mL of Distilled Water or Conc H2SO4 in a test tube • Add 3-5 drops of the compound to be tested • Shake vigorously • Solubility is indicated by a “single” clear liquid, i.e. no bubble or additional layers • Production of a gas, a change in color, and/or a change in temperature indicates a chemical reaction; thus, solubility

  16. Organic Qualitative Analysis Relative Solubility & Density (Con’t) • Procedure Water & H2SO4(Con’t) • Density relative to water of an insoluble compound is indicated by where the insoluble compound settles: top (less dense) suspended (similar density) bottom (more dense) • Solubility of a hydrocarbon in water indicates 4 or less carbons

  17. Organic Qualitative Analysis Beilstein Test (General for Halides) • Procedure • Bend small loop in the end of piece of copper wire. • Heat loop in Bunsen Burner • After cooling • Liquid sample: dip wire in sample. • Solid sample: dip wire in water then sample. • Heat wire • Compound first burns with yellow flame. • After burning for a few seconds, a green flame is produced if a halogen is present • Does not differentiate between Chlorine, Bromine, or Iodine • Weak color could indicate present of impurities in a non-halide sample

  18. Organic Qualitative Analysis Silver Nitrate in Ethanol Test (Sn1 for Halides) • Does not distinguish between Chloride, Bromine, or Iodine • Sn1 (nucleophilic substitution) reactions depend on: • Weak Nucleophile (NO3) • Polar Solvent (Ethanol) • Compounds equipped with good leaving groups (H2O, CL, Br, I) • The Halide (leaving group) is replaced with the nitrate nucleophile forming an insoluble white precipitate • The degree of precipitate formation is dependent on the relative stability of the compound and the resulting Carbocation that forms in the reaction Benzyl Allyl > Tertiary (3o) > Secondary (2o)> Primary (1o) > Methyl > Vinyl > Aryl (Aromatic)

  19. Organic Qualitative Analysis Silver Nitrate in Ethanol Test (Sn1 for Halides) • The Test • Add 1 to 2 drops of liquid sample (or 5 drops of solid sample dissolved in Ethanol) to 2 mL of 2% Ethanoic Silver Nitrate • Positive test – cloudy to heavy white precipitate depending on relative stability of Carbocation • Allyl, Benzyl, Tertiary Halides give white precipitate at room temperature • Primary & Secondary Alkyl Halides test positive (usually cloudy ppt) when heated (100oC) • Aromatic and many Vinyl Substituted Halides do not give positive tests

  20. Organic Qualitative Analysis Sodium Iodide in Acetone (Sn2 for Alkyl Halides) • Sodium Iodide is soluble in Acetone, but Sodium Chloride and Sodium Bromide are not soluble • The Iodide ion is an excellent Nucleophile – A Lewis Base with a pair of unshared electrons that seeks a positive part of an atom • Acetone is a non-polar solvent • Alkyl Chlorides and Bromides would react with the Sodium Iodide in an Sn2 reaction in which the Chloride & Bromide ions are replaced with the Iodine atoms • The reaction equilibrium is continuously forced to the right as the NaCl & NaBr precipitate in acetone • As the reactivity of the Halide becomes less reactive (Benzyl and Aromatic) precipitation ceases

  21. Organic Qualitative Analysis Sodium Iodide in Acetone (Sn2 for Alkyl Halides) • Relative Halide reactivity for an Sn2 reaction is the opposite of an Sn1 reaction, that is: Vinyl > Methyl > Primary (1o) > Secondary (2o) > Tertiary (3o) > Allyl Benzyl  Aryl (Aromatic) Note: Aryl (Aromatic) Halides are unreactive for both Sodium Iodide (Sn2) and Silver Nitrate (Sn1) tests • Primary Alkyl Halides will give an immediate precipitate at room temperature • Secondary Alkyl Halides will give a cloudy precipitate when heated to 50oC and then cooled • Tertiary Alkyl Halides will also give a precipitate when heated to 50oC and then cooled • Aryl Halides, like Chlorobenzene, will not give a precipitate, even after heating

  22. Organic Qualitative Analysis Sodium Iodide in Acetone (Sn2 for Alkyl Halides) • The Test • Add 6-8 drops of sample to 2mL of the 15% Sodium Iodide (NaI) in Acetone solution and shake gently • Positive Test is a white or cloudy white precipitate • If a precipitate forms but disappears with mild shaking, the instructor may suggest adding additional sample • Record the observed results at room temperature • If no precipitate forms, heat solution in a water bath (maximum 50oC) for 1 minute and cool solution to room temperature • Observe results • Record results for both room temperature and at 50oC

  23. Organic Qualitative Analysis Bromine in Methylene Chloride (Simple Multiple Bonds) • Addition reaction of Bromine (Br2), a red liquid, to a compound containing a double or triple bond produces a colorless Dibromide • The double (or triple bond) must be sufficiently electron-rich to initiate the reaction. Therefore, minimal electron withdrawing groups (Deactivators), such as Carboxyl Groups attached to molecule, would hinder the reaction • Unsubstituted Aromatic compounds do not react with the Bromine reagent • Even if the ring has substituted activating groups (donate electrons to the ring) the reaction would be a substitution and not an addition

  24. Organic Qualitative Analysis Bromine in Methylene Chloride • The Test • If sample is a solid, add 50 mg of a solid sample to1 mL Methylene Chloride in a test tube • If sample is a liquid, add 2 mL of liquid sample directly to test tube • Add 2% Bromine solution (Br2 & Methylene Chloride) dropwise to the test tube and shake solution • The test is positive for presence of double or triple bonds if 5 drops of Bromine decolorize the solution • If HBr is evolved, the test is negative indicating a substitution reaction, instead of an addition reaction, i.e., there are no double or triple bonds present

  25. Organic Qualitative Analysis Potassium Permanganate (Baeyer) Test(double or triple bonds) • Potassium Permanganate (KMnO4) is an oxidizing agent. • It has a Purple color • Following the oxidation of an unsaturated compound, the Permanganate ion is reduced to Manganese Dioxide (MnO2), a brown precipitate Note: Other easily oxidized compounds – Aldehydes, some Alcohols, Phenols, and Aromatic Amines – should be accounted for in your analysis

  26. Organic Qualitative Analysis Potassium Permanganate (Baeyer) Test(double or triple bonds) • The Test • Dissolve 25 mg a solid sample or two drops of a liquid sample in 1-2 mL of one of the following solvents: • Water (if soluble, skip Ethanol & Dimethoxymethane) • 95% Ethanol (if soluble, skip Dimethoxymethane) • 1,2-Dimethoxymethane • Slowly add 1% aqueous solution Potassium Permanganate, drop by drop, while shaking (usually just one drop works) • If the purple MnO4-1 ion is reduced to Manganese Dioxide (MnO2), a brown precipitate, the test is positive for double or triple bonds, but not Aromatic rings

  27. Organic Qualitative Analysis Ignition (Aromaticity) (=C-H bonds in Aromatic rings) • The Test • In a hood, place a small amount of the compound on a spatula and place it in the flame of a Bunsen burner • Positive test is a sooty yellow flame Note: The Sooty flame usually comes off fairly quickly. Look for it moving quickly away and upward from the yellow/blue flame area • Positive test is indicative of a high degree of Unsaturation and is probably Aromatic

  28. Organic Qualitative Analysis Acetyl Chloride (Alcohols) • Acid Chlorides react with Alcohols to form esters • Acetyl Chloride forms Acetate esters • This test does not work well with solid alcohols • Phenols also react with Acetyl Chloride and should be eliminated prior to testing for Alcohols • Amines also react with Acetyl Chloride to produce heat and also should be eliminated prior to testing

  29. Organic Qualitative Analysis Acetyl Chloride (Alcohols) • The Test • Cautiously add 10-15 drops of Acetyl Chloride, drop by drop, to about 0.5 mL of liquid sample • Positive test is evolution of Heat and Hydrogen Chloride (HCl) gas • Addition of water will sometimes precipitate the ester, further confirming the test

  30. Organic Qualitative Analysis Lucas Test (Alcohols) • Primary Alcohols dissolve in reagent giving clear solution • Secondary Alcohols produce cloudiness after about 3-5 minutes. May need to heat slightly • Tertiary, Benzylic, and Allylic alcohols produce immediate cloudiness; eventually, an immiscible Alkyl Halide separates into a separate layer

  31. Organic Qualitative Analysis Lucas Test (Alcohols) • The Test • Reagent – Conc HCL + Anhydrous Zinc Chloride • Lucas test does not work well with solid alcohols • Place 2 mL Lucas Reagent in small test tube. • Add 3-4 drops of liquid sample; shake vigorously

  32. Organic Qualitative Analysis Chromic Acid (Alcohols) • Chromic Acid (Cr+6) oxidizes Primary and Secondary Alcohols to Carboxylic Acids and Ketones, respectively • Chromium (+6) is reduced to Chromium (+3) The color change is from orange to green • Tertiary Alcohols do not react with Chromic Acid • Distinguish Primary & Secondary Alcohols from Tertiary Alcohols

  33. Organic Qualitative Analysis • The Reaction

  34. Organic Qualitative Analysis Chromic Acid (Alcohols) (Con’t) • The Test • Dissolve one drop of liquid sample or 10 mg of solid sample in 1 mL pure Acetone • Add 1 drop of Chromic Acid reagent • Blue green color appears in less than 2 seconds for Primary and Secondary Alcohols • Tertiary Alcohols do not produce blue-green color within 2 seconds and solution remains orange

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