1/17/2015 1 Physical Properties, Chemical tests and Infrared Spectroscopy to Identify: Unknown...

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

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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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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


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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


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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


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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)


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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)


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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


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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.


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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)


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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


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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


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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


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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


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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


CompoundObservation

(Rm Temp)

Observation

50oC

Observation

100oC

Positive(+) /

Negative (-)

Unknown Leave Blank

Known #1

Known #2

Known #3

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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


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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


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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


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Organic Qualitative AnalysisTypical Distillation Setup

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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


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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


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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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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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Water & Conc H2SO4 Solubility Not soluble

Alkanes Aromatic Hydrocarbons Alkyl Halides Aromatic Halides


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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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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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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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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)


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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


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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


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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


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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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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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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


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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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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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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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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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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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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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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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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 The Reaction

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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


1/17/2015 1 Physical Properties, Chemical tests and Infrared Spectroscopy to Identify: Unknown...

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