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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
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

organic qualitative analysis2
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

organic qualitative analysis3
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
organic qualitative analysis4
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
organic qualitative analysis5
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
organic qualitative analysis6
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
organic qualitative analysis7
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
organic qualitative analysis8
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
organic qualitative analysis9
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
organic qualitative analysis10
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
organic qualitative analysis11
Organic Qualitative Analysis
  • Suggested table for recording Qualitative Organic test results (Create your own, don’t copy)
organic qualitative analysis12
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
organic qualitative analysis13
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
organic qualitative analysis14
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
organic qualitative analysis15
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
organic qualitative analysis16
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
organic qualitative analysis17
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
organic qualitative analysis18
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)

organic qualitative analysis19
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
organic qualitative analysis20
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
organic qualitative analysis21
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
organic qualitative analysis22
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
organic qualitative analysis23
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
organic qualitative analysis24
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
organic qualitative analysis25
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

organic qualitative analysis26
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
organic qualitative analysis27
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
organic qualitative analysis28
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
organic qualitative analysis29
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
organic qualitative analysis30
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
organic qualitative analysis31
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
organic qualitative analysis32
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
organic qualitative analysis34
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