Physical Properties, Chemical tests and Infrared Spectroscopy to Identify: (alkane, alkene, aromatic) (primary, secondary, tertiary)

Transcription

1 Physical Properties, Chemical tests and Infrared Spectroscopy to Identify: Unknown Halide Hydrocarbon Alcohol (primary, secondary, tertiary) (alkane, alkene, aromatic) (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, 3 nd ed, Cengage Learning 1/17/2015 1

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 Alkenes Alkynes Aromatics Alkyl (1 o, 2 o, 3 o ) & Aryl Halides Alcohols (1 o, 2 o, 3 o ) C-C C=C C C C=C R-X R-OH Note: Tests for carbonyl based compounds (Aldehydes & Ketones) will be presented next semester 1/17/2015 2

3 The Tests Compound Classes Test Solubility Relative to H 2 O & H 2 SO 4 Density Relative to H 2 O Beilstein (Flame) Silver Nitrate/Ethanol Sodium Iodide/Acetone Bromine/Methylene Chloride KMnO4 (Baeyer Test) Ignition Acetyl Chloride Lucas Test Chromic Acid Compound Class All All Halides Alkyl & Aryl Halides Alkyl & Aryl Halides Unsaturated C=C C C Unsaturated C=C C C Aromaticity C=C Alcohols Alcohols Alcohols 1/17/2015 3

4 The Tests Test References (Pavia (3 rd ed) GMU Version or Pavia Main text as indicated) Test Page No. Solubility Relative to H 2 O & H 2 SO 4 p Density Relative H 2 O p Beilstein (Flame) p Silver Nitrate/Ethanol P Sodium Iodide/Acetone p. 158 Pavia Main Text Bromine/Methylene Chloride p KMnO 4 (Baeyer Test) p Ignition p Acetyl Chloride p. 585 Lucas Test p. 585 Chromic Acid p /17/2015 4

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 (H 2 O) & Conc Sulfuric Acid (H 2 SO 4 ) Density relative to Water Refractive Index Beilstein Test for Halides Ignition Test for Aromaticity IR Spectrum 1/17/2015 5

6 Elements of the Experiment (Con t) Week I (Con t) Chemical Tests for known compounds Tests Bromine in Methylene Chloride (Unsaturation) Baeyer (KMnO 4 ) Test (Unsaturation) Acetyl Chloride (Alcohols) Lucas Test (Primary, Secondary, Tertiary, Benzylic Alcohols) Chromic Acid Test (Primary, Secondary, Tertiary Alcohols) 1/17/2015 6

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) 1/17/2015 7

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 AgNO 3 in Ethanol and NaI in Acetone (week 2) Cylcohexene is to be run just against Bromine in Methylene Chloride & KMnO 4 Toluene is to be run just against Bromine in Methylene Chloride & KMnO 4 2-Propanol is to be run just against Acetyl Chloride, Lucas Reagent and Chromic Acid 1/17/2015 8

9 Elements of the Experiment (Con t) Week II Continuation of known compounds Tests Silver Nitrate/Ethanol Sodium Iodide/Acetone Unknown Compound Alkyl & Aryl Halides Alkyl & Aryl Halides Based on the results of the refractive index, Beilstein test, Ignition Test, Mass Spectrum, 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. 1/17/2015 9

10 General Notes Dangerous Chemicals Acetyl Chloride, Conc H 2 SO 4 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 (50 o C & 100 o C) using 250 ml beakers on each bench for the Halide tests (Silver Nitrate & Sodium Iodide) 1/17/

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 1/17/

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; KMnO 4 & Bromine in Methylene Chloride for Hydrocarbons, Acetyl Chloride & Chromic Acid for alcohols Note: See table on page 69 of Slayden Lab Manual 1/17/

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 1/17/

14 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 1/17/

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 Compound Observation (Rm Temp) Observation 50 o C Observation 100 o C Positive(+) / Negative (-) Unknown Leave Blank Known #1 Known #2 Known #3 Note: For tests not involving temperature differentials, leave the 50 o C & 100 o C blocks blank or just remove the columns 1/17/

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 1/17/

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 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 = 10 5 Pascals = atmospheres = psi (pounds per square inch) = in Hg (inches of mercury) = mm 1/17/

18 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 ( 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 5 o C 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 1/17/

19 Typical Distillation Setup 1/17/

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 1/17/

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 1/17/

22 Solubility Test (Water (H 2 O) and Conc Sulfuric Acid (H 2 SO 4 ) 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 1/17/

23 Solubility Test (Water (H 2 O) and Conc Sulfuric Acid (H 2 SO 4 ) Conc H 2 SO 4 Solubility Compounds containing N, O, S can be protonated in Conc H 2 SO 4 and thus are considered soluble Alkenes (C=C) Alkynes (C C) Ethers (C-O-C) Nitroaromatics (Nitrobenzene) Amides Alcohols (R-OH) Ketones Aldehydes Esters 1/17/

24 Solubility Test (Water (H 2 O) and Conc Sulfuric Acid (H 2 SO 4 ) Water & Conc H 2 SO 4 Solubility Not soluble Alkanes Aromatic Hydrocarbons Alkyl Halides Aromatic Halides 1/17/

25 Relative Solubility & Density Procedure Water & H 2 SO 4 Note: Solubility & Density test is performed only on the Unknown Place about 2 ml of Distilled Water or Conc H 2 SO 4 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 1/17/

26 Relative Solubility & Density (Con t) Procedure Water & H 2 SO 4 (Con t) Density relative to water of an insoluble compound is indicated by where the insoluble compound settles: top suspended bottom (less dense) (similar density) (more dense) Solubility of a Hydrocarbon in water indicates 4 or less carbons 1/17/

27 Beilstein Test Procedure (General for Halides) 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 1/17/

28 Silver Nitrate in Ethanol Test (Sn1 for Halides) Sn1 (unimolecular nucleophilic substitution) reactions depend on: Weak electron rich Nucleophile (NO 3 ) Polar Solvent (Ethanol) Compounds equipped with good leaving groups (H 2 O, 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 > Tertiary (3 o ) > Secondary (2 o ) > Primary (1 o ) > Methyl > Vinyl > Aryl (Aromatic) 1/17/

29 The Test Silver Nitrate in Ethanol Test (Sn1 for Halides) 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 Note: It may be necessary to additional sample to get a reaction Allyl, Benzyl, Tertiary Halides give white precipitate at room temperature Primary & Secondary Alkyl Halides test positive (usually cloudy ppt) when heated (100 o C) Aromatic and many Vinyl Substituted Halides do not give positive tests 1/17/

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 1/17/

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 (1 o ) > Secondary (2 o ) > Tertiary (3 o ) > 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 50 o C and then cooled Tertiary Alkyl Halides will also give a precipitate when heated to 50 o C and then cooled Allyl, Benzyl, and Aryl Halides, like Chlorobenzene, will not give a precipitate, even after heating 1/17/

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 Note: It may be necessary to add additional sample if an expected reaction with a known does not occur 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 50 o C) for 1 minute and cool solution to room temperature Observe results Record results for both room temperature and at 50 o C 1/17/

33 Bromine in Methylene Chloride (Simple Multiple Bonds) Addition reaction of Bromine (Br 2 ), 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 1/17/

34 The Test Bromine in Methylene Chloride 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 (Br 2 & 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 1/17/

35 Potassium Permanganate (Baeyer) Test (double or triple bonds) Potassium Permanganate (KMnO 4 ) is an oxidizing agent It has a Purple color Following the oxidation of an unsaturated compound, the Permanganate ion is reduced to Manganese Dioxide (MnO 2 ), a brown precipitate Note: Other easily oxidized compounds Aldehydes, some Alcohols, Phenols, and Aromatic Amines should be accounted for in your analysis 1/17/

36 The Test Potassium Permanganate (Baeyer) Test (double or triple bonds) 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 MnO 4-1 ion is reduced to Manganese Dioxide (MnO 2 ), a brown precipitate, the test is positive for double or triple bonds, but not Aromatic rings 1/17/

37 The Test Ignition (Aromaticity) (=C-H bonds in Aromatic rings) 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 1/17/

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 1/17/

39 The Test Acetyl Chloride (Alcohols) Cautiously add 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 1/17/

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 1/17/

41 The Test Lucas Test (Alcohols) 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 1/17/

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 1/17/

43 The Reaction Organic Qualitative Analysis 1/17/

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 1/17/