Upload
buck-anthony
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
1/17/2015 1
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
Organic Qualitative Analysis
1/17/2015 2
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 Analysis
1/17/2015 3
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
CC KMnO4 (Baeyer Test) Unsaturated C=C
CC Ignition Aromaticity C=C Acetyl Chloride Alcohols Lucas Test Alcohols Chromic Acid Alcohols
Organic Qualitative Analysis
1/17/2015 4
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
Organic Qualitative Analysis
1/17/2015 5
Elements of the Experiment Two week experiment Pre-lab must cover both weeks Week I
Purification & Boiling Point via Simple Distillation Physical Characteristics of the purified sample Solubility in Water (H2O) & Conc Sulfuric Acid
(H2SO4)
Density relative to Water Refractive Index Beilstein Test for Halides Ignition Test for Aromaticity IR Spectrum
Organic Qualitative Analysis
1/17/2015 6
Elements of the Experiment (Con’t)
Week I (Con’t)
Chemical Tests for known compounds
Tests
Bromine in Methylene Chloride (Unsaturation)
Baeyer (KMnO4) Test (Unsaturation)
Acetyl Chloride (Alcohols)
Lucas Test (Primary, Secondary, Tertiary, Benzylic Alcohols)
Chromic Acid Test (Primary, Secondary, Tertiary Alcohols)
Organic Qualitative Analysis
1/17/2015 7
Known Compounds Halides
1-Chlorobutane 2-Chlorobutane T-Butyl Chloride (2-Chloro-2-Methyl Propane) Chlorobenzene
Hydrocarbons Cyclohexane Toluene Cyclohexene
Alcohols 1-Butanol 2-Propanol T-Amyl Alcohol (2-Methyl-Butanol)
Organic Qualitative Analysis
1/17/2015 8
Elements of the Experiment (Con’t) Week I (Con’t)
Chemical Tests for known compounds (Con’t) Approach
Each “known” compound is to be run against just those tests for which it is applicable
Ex.2-Chlorobutane is to be run against AgNO3 in
Ethanol and NaI in Acetone (week 2)
Cylcohexene is to be run just against Bromine in Methylene Chloride & KMnO4
Toluene is to be run just against Bromine in Methylene Chloride & KMnO4
2-Propanol is to be run just against Acetyl Chloride, Lucas Reagent and Chromic Acid
Organic Qualitative Analysis
1/17/2015 9
Elements of the Experiment (Con’t) Week II
Continuation of known compounds Tests
Silver Nitrate/Ethanol Alkyl & Aryl HalidesSodium Iodide/Acetone Alkyl & Aryl Halides
Unknown Compound Based on the results of the refractive index,
Beilstein test, Ignition Test and IR Spectroscopy, the student will select the test(s) for which his/her unknown is applicable. Ex:
If IR indicates alcohol, unknown will be run against Acetyl Chloride, Lucas Reagent & Chromic Acid.
Organic Qualitative Analysis
1/17/2015 10
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)
Organic Qualitative Analysis
1/17/2015 11
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 pre-lab template (see slide 15)
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 Analysis
1/17/2015 12
Testing Sequence for Knowns & Unknown
The Boiling Point, Solubility, Refractive Index, Flame tests, 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
Organic Qualitative Analysis
1/17/2015 13
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
Organic Qualitative Analysis
1/17/2015 14
The Report Each “Test” is a Procedure and must be set up with:
A TitleMaterials & Equipment, including reagents, known
and unknown compounds, test tubesProcedure Description in bullet formatTest 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 Analysis
1/17/2015 15
Suggested table for recording Qualitative Organic test results. You can paste this table into your report
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
Note: For tests not involving temperature differentials, leave the 50oC & 100oC blocks blank or just remove the columns
Organic Qualitative Analysis
CompoundObservation
(Rm Temp)
Observation
50oC
Observation
100oC
Positive(+) /
Negative (-)
Unknown Leave Blank
Known #1
Known #2
Known #3
1/17/2015 16
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
Organic Qualitative Analysis
1/17/2015 17
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 levelAt 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 bar1 bar = 105 Pascals = 0.98692 atmospheres = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury) = 750.06 mm
Organic Qualitative Analysis
1/17/2015 18
Simple Distillation – BackgroundNote: 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 – 5oCYou should take this potential temperature differential into account when you compare your measured results with the list of possible unknowns in lab manual tables
Organic Qualitative Analysis
1/17/2015 19
Organic Qualitative AnalysisTypical Distillation Setup
1/17/2015 20
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
Organic Qualitative Analysis
1/17/2015 21
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
Organic Qualitative Analysis
1/17/2015 22
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 Analysis
1/17/2015 23
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 Analysis
1/17/2015 24
Solubility Test(Water (H2O) and Conc Sulfuric Acid (H2SO4)
Water & Conc H2SO4 Solubility Not soluble
Alkanes Aromatic Hydrocarbons Alkyl Halides Aromatic Halides
Organic Qualitative Analysis
1/17/2015 25
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 Analysis
1/17/2015 26
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 Analysis
1/17/2015 27
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 Analysis
1/17/2015 28
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 reactionBenzyl Allyl > Tertiary (3o) > Secondary (2o)> Primary (1o) > Methyl > Vinyl > Aryl (Aromatic)
Organic Qualitative Analysis
1/17/2015 29
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
Organic Qualitative Analysis
1/17/2015 30
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
Organic Qualitative Analysis
1/17/2015 31
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 Allyl, Benzyl, and Aryl Halides, like Chlorobenzene, will
not give a precipitate, even after heating
Organic Qualitative Analysis
1/17/2015 32
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 Analysis
1/17/2015 33
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 Analysis
1/17/2015 34
Bromine in Methylene Chloride The Test
Dissolve 50 mg of unknown solid or 4 drops of unknown liquid sample to 1 mL Methylene Chloride (dichloromethane) or in 1,2-dimethoxy ethane .in a 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 Analysis
1/17/2015 35
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 Analysis
1/17/2015 36
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 Analysis
1/17/2015 37
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 Analysis
1/17/2015 38
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 Analysis
1/17/2015 39
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 Analysis
1/17/2015 40
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 Analysis
1/17/2015 41
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 Analysis
1/17/2015 42
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 Analysis
1/17/2015 43
Organic Qualitative Analysis The Reaction
1/17/2015 44
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
Organic Qualitative Analysis