Organic Qualitative Analysis

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, 3nd ed, 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 CC
• Alkynes CC
• Aromatics CC
• 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 CC C?C
• KMnO4 (Baeyer Test) Unsaturated CC C?C
• Ignition Aromaticity CC
• 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)
• Test Page 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
• Test Compound
  Class Ref
• 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 CC C?C p.
  465
• KMnO4 (Baeyer Test) Unsaturated CC 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

Compound Observation (Rm Temp) Observation 50oC Observation 100oC Positive() / Negative (-)
Unknown Leave Blank
Known 1
Known 2
Known 3
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 lt5 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 (CC)
• Alkynes (CC)
• 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 (Cont)
• Procedure Water H2SO4 (Cont)
• 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 gt Tertiary (3o) gt Secondary (2o)gt
  Primary (1o) gt Methyl gt Vinyl gt 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 gt Methyl gt Primary (1o) gt Secondary (2o) gt
  Tertiary (3o) gt 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 (Cr6) 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) (Cont)
• 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