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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 TestCompound 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 • Infrared Spectra

  6. Organic Qualitative Analysis • Elements of the Experiment – Week Two TestCompound ClassRef • 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

  7. Organic Qualitative Analysis • Known Compounds • Halides • 1-Chlorobutane • 2-Chlorobutane • T-ButylChloride • Chlorobenzene • Hydrocarbons • Cyclohexane • Toluene • Cyclohexene • Alcohols • 1-Butanol • 2-Propanol • T-Amyl Alcohol Note: Each “known” compound is to be run against just those tests for which it is applicable Ex. 1. 2-Chlorobutane is to be run against NaI & AgNO3 2. Toluene is to be run against Methylene Chloride & KMnO4 3. 2-Propanol is to be run against Acetyl Chloride and Chromic Acid

  8. 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 • Set up water baths (50oC & 100oC) using 250 mL beakers on each bench for the Halide tests (Silver Nitrate & Sodium Iodide)

  9. 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

  10. 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 and all the known compounds against only those tests for which the compounds are applicable, e.g., Sodium Iodide & Silver Nitrate for Halides; KMnO4 & Bromine in Methylene Chloride for Hydrocarbons, Acetyl Chloride & Chromic Acid for alcohols Note: See table on page 69 of Slayden Lab Manual • For each test, set up a sufficient number of test tubes to accommodate the unknown and the applicable number of knowns for that test • Add test reagent • Add compound to be tested; shake mixture • Heat reaction mixture if specified in test directions

  11. 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

  12. Organic Qualitative Analysis • Suggested table for recording Qualitative Organic test results. You can paste this table into your report Note: The positive/negative column should be left blank for the unknown Indicate positive or negative for just the known compounds, since you know the class of the compound

  13. Organic Qualitative Analysis Sample Purification / Boiling Point • Organic Lab – Unknowns, Purification, Boiling Point • Several experiments in Chem 315/318 (Org Lab I & II) involve the identification of an unknown compound • Liquid samples that students receive in Lab may contain some impurities in addition to the unknown compound that could produce ambiguous results when determining the chemical or physical properties of the compound • Simple Distillation is used to purify the sample by separating the pure compound that comes over in a narrow temperature range – corresponding to its boiling point – from impurities that have boiling points either lower than or higher than the compound

  14. Organic Qualitative Analysis • Simple Distillation – Background • Boiling Point The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the temperature at which the vapor pressure of the liquid is equal to 1 atmosphere (atm), the atmospheric pressure at sea level At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid. The standard boiling point is now (as of 1982) defined by IUPAC as the temperature at which boiling occurs under a pressure of 1 bar 1 bar = 105 Pascals = 0.98692 atmospheres = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury) = 750.06 mm

  15. Organic Qualitative Analysis • Simple Distillation – Background Note: The temperature range you obtain for your boiling point may be inaccurate for three (3) reasons 1. The atmospheric pressure in the lab may not be: 1 bar (0.98692 atm) 2. The thermometers used in the lab may not reflect the actual temperature 3. The thermal inefficiency of the glassware used for the boiling point determination may result in a lower than expected measured value by as much as 2 – 5oC You should take this potential temperature differential into account when you compare your measured results with the list of possible unknowns in lab manual tables

  16. Organic Qualitative Analysis Typical Distillation Setup

  17. Organic Qualitative Analysis Simple Distillation – Procedure • Set up Simple Distillation apparatus (previous slide) • Use 25 mL or 50 mL Distillation flask • Place a Corundum or Teflon boiling chip in the flask • Start gentle water flow through condenser • Put a waste receiving container (small beaker) into an ice water bath – especially for low boiling liquids. • Begin heating sample Note: The sample may appear to be boiling, but the actual boiling point is not reached until the temperature of the boiling liquid and the vapor surrounding the thermometer bulb reach equilibrium. At this point the vapor will start to condense in the condenser

  18. Organic Qualitative Analysis • Simple Distillation - Procedure • Note the temperature when the distillate begins to drip into the waste receiving container • Continue to collect distillate in the waste container until the temperature begins to level off • Remove the waster container and begin collecting the distillate in a small clean Erlenmeyer flask • Note the temperature when you start to collect the purified sample • Continue to collect the sample until the temperature begins to rise again (it may not change before the all of the sample has come over) • Note the temperature just before the temperature begins to change • The first and last temperatures recorded in the narrow boiling range represent the boiling point range of your sample

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. Organic Qualitative Analysis Silver Nitrate in Ethanol Test (Sn1 for Halides) • Sn1 (unimolecular nucleophilic substitution) reactions depend on: • Weak electron rich Nucleophile (NO3) • Polar Solvent (Ethanol) • Compounds equipped with good leaving groups (H2O, CL, Br, I) • The test does not distinguish between Chloride, Bromine, or Iodine • The Halide (leaving group) is replaced with the Nitrate nucleophile forming an insoluble white Halide 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)

  26. 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 concentrated Ethanoic solution of a solid sample) 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

  27. Organic Qualitative Analysis Sodium Iodide in Acetone (Sn2 for Alkyl Halides) • Sn2 – Bimolecular Nucleophilic Substitution • 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. Organic Qualitative Analysis • The Reaction

  41. 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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