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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

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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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Organic Qualitative Analysis

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


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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


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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


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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


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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


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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


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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


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    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)


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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


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    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



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    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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