Microscale
`
`and Miniscale
`
`Organic Chemistry
`
`Laboratory Experiments
`
`Second Edition
`
`Allen M. Schoffstall
`
`The University of Colorado
`
`at Colorado Springs
`
`and
`
`Barbara A. Gaddis
`
`The University of Colorado
`
`at Colorado Springs
`
`with
`
`Melvin L. Druelinger
`
`Colorado State University-Pueblo
`
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`

`

`MICROSCALE AND MINISCALE ORGANIC CHEMISTRY LAB EXPERIMENTS
`SECOND EDITION
`
`Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York,
`NY 10020. Copyright © 2004, 2000 by The McGraw-Hill Companies, Inc. All rights reserved. No part of this publication
`may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior
`written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic stor-
`age or transmission, or broadcast for distance learning.
`
`Some ancillaries, including electronic and print components, may not be available to customers outside the United States.
`
`This book is printed on acid-free paper.
`
`1 2 3 4 5 6 7 8 9 0 VNH/VNH 0 9 8 7 6 5 4 3
`
`ISBN 0–07–242456–7
`
`Publisher: Kent A. Peterson
`Sponsoring editor: Thomas D. Timp
`Senior developmental editor: Shirley R. Oberbroeckling
`Senior marketing manager: Tamara L. Good-Hodge
`Project manager: Joyce Watters
`Lead production supervisor: Sandy Ludovissy
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`Senior media technology producer: Jeffry Schmitt
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`
`"Permission for the publication herein of Sadtler Standard Spectrar has been granted, and all rights are reserved, by BIO-
`RAD Laboratories, Sadtler Division."
`
`"Permission for the publication of Aldrich/ACD Library of FT NMR Spectra has been granted and all rights are reserved by
`Aldrich Chemical."
`
`All experiments contained in this laboratory manual have been performed safely by students in college laboratories under the
`supervision of the authors. However, unanticipated and potentially dangerous reactions are possible due to failure to follow
`proper procedures, incorrect measurement of chemicals, inappropriate use of laboratory equipment, and other reasons. The
`authors and the publisher hereby disclaim any liability for personal injury or property damage claimed to have resulted from
`the use of this laboratory manual.
`
`Library of Congress Cataloging-in-Publication Data
`
`Schoffstall, Allen M.
`Microscale and miniscale organic chemistry laboratory experiments / Allen M.
`Schoffstall, Barbara A. Gaddis, Melvin L. Druelinger.—2nd ed.
`p.
`cm.
`Includes bibliographical references and index.
`ISBN 0–07–242456–7 (acid-free paper)
`1. Chemistry, Organic—Laboratory manuals.
`Melvin L.
`III. Title.
`
`I. Gaddis, Barbara A.
`
`II. Druelinger,
`
`QD261 .S34 2004
`547.0078—dc21
`
`www.mhhe.com
`
`2003008663
`CIP
`
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`

`

`Dedication
`To Carole, Larry, and Judy for their patience, help, and encouragement.
`
`To organic students who develop a passion for doing and learning from organic laboratory experiments
`and to the instructors who make laboratory learning meaningful.
`
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`

`

`Brief Contents
`
`Preface
`
`xxi
`
`Introduction 1
`
`Chapter One Techniques in the Organic Chemistry Laboratory 9
`
`Chapter Two Spectroscopic Methods and Molecular
`Modeling 109
`
`Chapter Three Applications Using Laboratory Resources and
`Techniques 183
`
`Chapter Four Alcohols and Alkyl Halides 221
`
`Chapter Five Synthesis of Alkenes 229
`
`Chapter Six Alkene Addition Reactions 237
`
`Chapter Seven Stereochemistry 255
`
`Chapter Eight
`
`Introduction to Nucleophilic Substitution
`Reactions 261
`
`Chapter Nine Dienes and Conjugation 271
`
`Chapter Ten Qualitative Organic Analysis I
`
`281
`
`Chapter Eleven Reactions of Aromatic Side Chains 290
`
`Chapter Twelve Electrophilic Aromatic Substitution 298
`
`Chapter Thirteen Combined Spectroscopy and Advanced
`Spectroscopy 323
`
`Chapter Fourteen Organometallics 351
`
`Chapter Fifteen Alcohols and Diols 364
`
`Chapter Sixteen Ethers 376
`
`Chapter Seventeen Aldehydes and Ketones 385
`
`Chapter Eighteen Enols, Enolates, and Enones 404
`
`iv
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`Brief Contents
`
`v
`
`Chapter Nineteen Carboxylic Acids 419
`
`Chapter Twenty Carboxylic Acid Esters 430
`
`Chapter Twenty-One Dicarbonyl Compounds 441
`
`Chapter Twenty-Two Amines 450
`
`Chapter Twenty-Three Aryl Halides 475
`
`Chapter Twenty-Four Phenols 480
`
`Chapter Twenty-Five Carbohydrates 489
`
`Chapter Twenty-Six Lipids 507
`
`Chapter Twenty-Seven Amino Acids and Derivatives 518
`
`Chapter Twenty-Eight Qualitative Organic Analysis II
`
`529
`
`Chapter Twenty-Nine Projects 578
`
`Appendix A Tables of Derivatives for Qualitative Organic
`Analysis 627
`
`Appendix B Laboratory Skills and Calculations 632
`
`Appendix C Designing a Flow Scheme 637
`
`Appendix D Material Safety Data Sheet
`
`639
`
`Appendix E Tables of Common Organic Solvents and Inorganic
`Solutions 643
`
`Index 645
`
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`Preface to Second Edition
`
`This book is a comprehensive introductory treatment of the organic chemistry labora-
`tory. The student will be guided in doing numerous exercises to learn basic laboratory
`techniques. The student will then use many proven traditional experiments normally
`performed in the two-semester organic laboratory course.
`Several trends in organic laboratory education have emerged since publication of
`the first edition. These trends are recognition of the pedagogical value of discovery
`experiments, the increased emphasis on molecular modeling and computer simulations,
`and the development of green experiments. All of these trends are incorporated into this
`book along with the use of traditional experiments.
`
`DISCOVERY EXPERIMENTS
`
`Discovery experiments are given a special label in the Table of Contents and in each
`chapter where they appear. Discovery experiments incorporate the pedagogical advan-
`tages of inductive inquiry experiments with the ease of design found in expository
`experiments. Discovery experiments (or guided inquiry experiments) have a specific
`procedure designed to give a predetermined but unspecified result. Students use a
`deductive thought process to arrive at a desired conclusion. Students are “guided” by
`inferring a general scientific principle. Discovery experiments have been employed
`successfully in large laboratory sections, as well as in small classroom environments.
`Student interest is increased during discovery experiments because the result of the
`experiment is unknown to the student. The desired goal of discovery experiments is
`increased student learning. Discovery experiments can also provide the opportunity
`for individual reflection and class discussion and may involve students in developing
`and interpreting laboratory procedures. These features and advantages of discovery
`experiments have caused your text authors to emphasize discovery experiments in this
`edition of the text.
`
`MOLECULAR MODELING
`
`Molecular modeling by computer saw a revolution in the late 1990s with the advent of
`affordable, sufficiently fast personal computers with adequate memory. Computer mod-
`eling enhances the benefits of assembling molecular models using model kits. Use of
`these kits is still encouraged. However, gone are the days where students had to depend
`only on molecular model kits to represent molecules in three dimensions. While these
`models still have their uses, computer modeling programs now provide exciting visual-
`ization of molecules and calculation of physical properties and thermodynamic parame-
`ters. Where possible, it is desirable to incorporate computer modeling into organic
`laboratory programs. The exercises in this book can be done using relatively inexpen-
`sive commercial software from one or more providers.
`
`xxi
`
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`xxii
`
`Preface
`
`COMPUTER SIMULATION OF EXPERIMENTS
`
`Another use of computers is for simulation of laboratory procedures and experiments.
`Demonstrations of laboratory techniques are available as clips on the CD accompany-
`ing this text. Simulations of experiments are useful as prelab exercises to familiarize
`students with the experiment and to enhance learning in the laboratory. Simulations are
`also useful as illustrations of experiments that are difficult to carry out in the undergrad-
`uate laboratory environment. Experiments that require special equipment, inert gaseous
`environments, or especially noxious and toxic reagents can be experienced by students
`through virtual experiments on the computer. Examples of such experiments are avail-
`able on the CD accompanying this text.
`
`GREEN CHEMISTRY
`
`Academic and industrial organic chemists have led an initiative to replace the use of
`organic solvents with aqueous solvents. They have encouraged the recycling of chemi-
`cals in order to reduce production requirements of chemicals. They have encouraged
`use of environmentally benign reagents in place of hazardous and toxic reagents where
`possible. In this text, there have been efforts to reduce quantities of toxic reagents and
`solvents wherever possible and to develop “green” experiments. For example, new
`Experiment 14.2 is on the use of indium reagents in aqueous solvents to accomplish
`coupling reactions similar to Grignard reactions. Another objective of green chemistry
`is to prevent waste. In this book, microscale and miniscale experiments are used in
`order to help minimize waste.
`
`MICROSCALE AND MINISCALE TECHNIQUES
`
`Microscale and miniscale organic techniques were first introduced two decades ago.
`However, changing over to new, smaller glassware and equipment has been slow in
`some laboratories for a number of reasons. One reason is the initial cost, but most institu-
`tions benefit by reduced costs of chemicals and hazardous waste disposal. The decision
`of whether to use a microscale procedure or a miniscale procedure often depends on the
`methods of characterization chosen by the instructor. This governs how much product is
`required for analysis. If a distillation is desired, a miniscale procedure is often chosen
`because of difficulties associated with distilling very small quantities of liquid. If an
`analysis of liquid products is to be done only by gas chromatographic analysis, a
`microscale procedure will cut down on costs of waste disposal.
`
`NEW FEATURES IN THE SECOND EDITION
`
`Accompanying a new section on molecular modeling, significant additions to this edi-
`tion include expanded coverage of Diels-Alder chemistry, inclusion of enone chemistry
`with a chapter on enols, a new chapter on dicarbonyl compounds, and expanded cover-
`age of heterocycles in the chapter on amines. New experiments and new options within
`experiments are included in many chapters. Many are discovery experiments. Among
`these are
`
`Experiment 3.3, Relationships Between Structure and Physical Properties;
`Experiment 3.8, Purification and Analysis of a Liquid Mixture;
`Experiment 5.1B, Miniscale Synthesis of Alkenes Via Acid-catalyzed Dehydration
`of 3,3-Dimethyl-2-butanol;
`
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`Preface
`
`xxiii
`
`Experiment 9.1C, Microscale Reaction of Cyclopentadiene with Maleic Anhydride;
`Experiment 9.1E, Reaction of Anthracene with Maleic Anhydride;
`Experiment 14.2, Using Indium Intermediates: Reaction of Allyl Bromide with an
`Aldehyde;
`Experiment 15.3, Photochemical Oxidation of Benzyl Alcohol;
`Experiment 16.2, Nucleophilic Aliphatic Substitution Puzzle: Substitution Versus
`Elimination;
`Experiment 17.1C, Microscale Horner-Emmons Reaction of Diethylbenzyl
`Phosphonate and Benzaldehyde;
`Experiment 18.2A, Microscale Reduction of 2-Cyclohexenone;
`Experiment 18.2B, Microscale Reduction of trans-4-Phenyl-3-buten-2-one;
`Experiment 18.3, Catalytic Transfer Hydrogenation Miniscale Reaction
`of Cyclohexenone;
`Experiment 21.1, Base-Catalyzed Condensations of Dicarbonyl Compounds;
`Experiment 22.2, Synthesis of Pyrazole and Pyrimidine Derivatives;
`Experiment 24.1, Exploring Structure-function Relationships of Phenols;
`Experiment 26.1, Soap from a Spice: Isolation, Identification and Hydrolysis
`of a Triglyceride;
`Experiment 26.2, Preparation of Esters of Cholesterol and Determination of Liquid
`Crystal Behavior;
`Experiment 29.2, Multistep Synthesis of Sulfanilamide Derivatives as Growth
`Inhibitors;
`Experiment 29.3, Structural Determination of Isomers Using Decoupling and
`Special NMR Techniques.
`
`INSTRUCTOR’S MANUAL
`
`An instructor’s manual is available on the website accompanying this text. This manual
`includes directions for laboratory preparators, instructor’s notes for each experiment,
`solutions to problems, and prelab and postlab assignments. Test questions about many
`experiments are available on the web CT.
`
`COURSE WEBSITE
`
`The website http://www.mhhe.com/schoffstall2 offers supportive backup for the organic
`laboratory course. It presents updated helpful hints for lab preparators and instructors,
`typical schedules, sample electronic report forms, sample quiz and exam questions,
`examples of lab lecture or material for self-paced prelab student preparation, and rele-
`vant links to other websites. Some additional experiments are available on the website.
`
`ACKNOWLEDGMENTS
`
`We wish to acknowledge several individuals who have contributed to the second edition.
`Connie Pitman, laboratory technician at the University of Colorado Springs, has made
`numerous valuable comments about the experiments. She has also coauthored the
`Instructor’s Manual and Solutions Guide. Shirley Oberbroeckling has served as the
`Developmental editor and Joyce Watters as the Project Manager for this edition of the
`text. The following faculty and students have contributed to the second edition by testing
`experiments and suggesting improvements:
`Robert A. Banaszak, Anna J. Espe, Sam T. Seal, Shannon J. Coleman, Shannon R.
`Gilkes, Molly M. Simbric, Daniela Dumitru, Patricia D. Gromko, Amy M. Scott,
`
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`

`xxiv
`
`Preface
`
`Tomasz Dziedzic, Paul J. Lunghofer, Rafael A. Vega, Justin A. Russok, Darush Fathi,
`and Michael Slogic.
`We are grateful to the following individuals who served as reviewers for this edi-
`tion. They are:
`
`Monica Ali, Oxford College
`Steven W. Anderson, University of Wisconsin - Whitewater
`Satinder Bains, Arkansas State University - Beebe
`David Baker, Delta College
`John Barbaro, University of Alabama - Birmingham
`George Bennett, Milikin University
`Cliff Berkman, San Francisco State University
`Lea Blau, Stern College for Women
`Lynn M. Bradley, The College of New Jersey
`Bruce S. Burnham, Rider College
`Patrick E. Canary, West Virginia Northern Community College
`G. Lynn Carlson, University of Wisconsin - Kenosha
`Jeff Charonnat, California State University - Northridge
`Wheeler Conover, Southeast Community College
`Wayne Counts, Georgia Southwestern State University
`Tammy A. Davidson, East Tennessee State University
`David Forbes, University of South Alabama - Mobile
`Eric Fossum, Wright State University - Dayton
`Nell Freeman, St. Johns River Community College
`Edwin Geels, Dordt College
`Jack Goldsmith, University of South Carolina - Aiken
`Ernest E. Grisdale, Lord Fairfax Community College
`Tracy Halmi, Pennsylvania State Behrend - Erie
`C. E. Heltzel, Transylvania University
`Gary D. Holmes, Butler County Community College
`Harvey Hopps, Amarillo College
`William C. Hoyt, St. Joseph’s College
`Chui Kwong Hwang, Evergreen Valley College
`George F. Jackson, University of Tampa
`Tony Kiessling, Wilkes University
`Maria Kuhn, Madonna University
`Andrew Langrehr, Jefferson College
`Elizabeth M. Larson, Grand Canyon University
`John Lowbridge, Madisonville Community College
`William L. Mancini, Paradise Valley Community College
`John Masnovi, Cleveland State University
`Anthony Masulaitis, New Jersey City University
`Ray Miller, York College
`Tracy Moore, Louisiana State University - Eunice
`Michael D. Mosher, University of Nebraska - Kearney
`Michael J. Panigot, Arkansas State University
`Neil H. Potter, Susquehanna University
`Walda J. Powell, Meredith College
`John C. Powers, Pace University
`Steve P. Samuel, SUNY - Old Westbury
`Greg Spyridis, Seattle University
`
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`Preface
`
`xxv
`
`Paris Svoronos, Queensboro Community College
`Eric L. Trump, Emporia State University
`Patibha Varma Nelson, St. Xavier University
`Chad Wallace, Asbury College
`David Wiendenfeld, University of North Texas
`Linfeng Xie, University of Wisconsin - Oshkosh
`
`We hope you find your laboratory experience profitable and stimulating.
`
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`22
`
`Chapter One
`
`Techniques in the Organic Chemistry Laboratory
`
`Table 1B-1 Densities of Selected
`Organic Liquids
`
`Organic Compound
`
`Density20/4(g/mL)
`
`Hexane
`3-Methylpentane
`Heptane
`Cyclohexane
`1-Propanol
`3-Pentanone
`p-Xylene
`Toluene
`Tetrahydrofuran
`Ethyl acetate
`
`0.6603
`0.6645
`0.6837
`0.7785
`0.8035
`0.8138
`0.8611
`0.8669
`0.8892
`0.9003
`
`Technique C: Melting Points
`
`Introduction
`Most organic compounds are molecular substances that have melting points below
`300°C. The melting point of a solid compound is a physical property that can be mea-
`sured as a method of identification. Melting points of pure compounds are recorded in
`handbooks of physical data, such as the Handbook of Chemistry and Physics (CRC).
`The reported melting point is that temperature at which solid and liquid phases exist in
`equilibrium. A melting point of a solid is actually a melting range, which starts from the
`temperature at which the first drop of liquid appears and ends at the temperature at
`which the entire sample is liquid. Students should report melting points as melting
`ranges. Sometimes only a single temperature is reported in the tables of physical prop-
`erties; in this case, the value represents the upper temperature of the melting range.
`The measured melting range gives a rough indication of the purity of the com-
`pound: the purer the compound, the higher its melting point and the narrower its melt-
`ing range. Melting a solid requires energy to overcome the crystal lattice energy.
`Impurities disrupt the crystal lattice, so less energy is required to break intermolecular
`attractions; impurities thus generally lower and broaden the melting point. Since the
`decrease in melting point of a solid is generally proportional to the amount of impurity
`present, the difference between the expected melting point of the pure compound and
`the experimentally measured melting point gives a rough approximation of purity.
`Figure 1C-1 is a phase diagram of a mixture of phenol and diphenylamine. The
`phase diagram is a graph of temperature versus composition. The top convex line repre-
`sents the temperature at which the entire solid is melted, and the bottom concave line
`represents the temperature at which the solid just begins to melt. The distance between
`these two lines represents the melting point range. Pure phenol (at 0 mol percent
`diphenylamine) exhibits a sharp melting point at 41°C; that is, both the liquid and the
`solid line converge at 41°C. A sample of phenol containing 5 mol percent of diphenyl-
`amine begins to melt at 35°C and the solid is all melted by 40°C, giving a melting point
`range of 35–40°C. A sample of phenol containing 10 mol percent of diphenylamine has
`a melting point range of 30–37°C. As the amount of impurities increases, the melting
`point range becomes proportionally lower and broader.
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`Technique C Melting Points
`
`23
`
`Figure 1C-1
`
`Temperature vs. compo-
`sition diagram of a
`phenol/diphenylamine
`binary mixture
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`E
`
`Eutectic
`composition
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`Temperature (°C)
`
`0
`
`10
`
`20
`
`30
`
`40
`
`50
`
`60
`
`70
`
`80
`
`90
`
`100
`
`Pure phenol
`
`Mole % diphenylamine
`
`Pure diphenylamine
`
`It would be tempting to say that addition of impurities always lowers the melting
`point and broadens the melting point range. However, this is not the case. The lowest melt-
`ing point on the phase diagram occurs at 32 mol percent diphenylamine. A sample of phe-
`nol containing this amount of diphenylamine melts sharply at 19°C. For a binary
`(two-phase system), the minimum melting point temperature is called the eutectic point,
`and the composition at this temperature is called the eutectic mixture. For the
`phenol/diphenylamine system, the eutectic point occurs at 32 mol percent diphenylamine.
`A mixture of 68 mol percent phenol and 32 mol percent diphenylamine (the eutectic com-
`position) behaves like a pure compound, exhibiting a sharp melting point. Addition of
`more diphenylamine beyond the eutectic composition actually increases the melting point:
`a sample of phenol containing 40 mol percent diphenylamine begins to melt around 21°C.
`Not all two-phase mixtures exhibit eutectic behavior; a sharp melting point is usu-
`ally indicative of purity. However, a sharp melting point may also be obtained if the
`compound and impurity form a eutectic mixture. For nearly pure compounds, the pres-
`ence of small amounts of impurities generally lowers the melting point. Purification
`generally affords crystals having a higher and sharper melting point than the impure
`solid. In rare cases, the melting point may rise when a certain additive is present.
`
`Mixed Melting Behavior
`Because impurities change (usually lower) the melting point, a mixed melting point can
`be used to determine whether two compounds are identical or different. Suppose that
`there are two beakers of a white solid sitting on the bench top. The melting point of each
`solid is found to be 133°C. Are the two solids the same or are they different? In a mixed
`melting point, samples of the two compounds are thoroughly mixed and a new melting
`point is measured. If the two compounds are not identical, the melting point of the mix-
`ture generally will be depressed and broadened. If the melting point is unchanged, the
`two compounds are most probably identical.
`
`Melting Behavior of Solids
`Several physical changes occur as a solid melts. In many cases, the crystals will soften
`and shrink immediately before melting. The crystals may appear to “sweat” as traces
`of solvent or air bubbles are released. These are normal occurrences, but shouldn’t be
`
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`24
`
`Chapter One
`
`Techniques in the Organic Chemistry Laboratory
`
`considered as “melting.” The melting point is measured beginning at the time the first
`free liquid is seen. Sometimes compounds decompose rather than melt. Decomposition
`usually involves changes such as darkening or gas evolution. Decomposition may occur
`at or even below the melting point for compounds that are thermally labile. In general,
`decomposition occurs over a fairly broad temperature range. For this reason, a sample
`should not be used in two consecutive melting point determinations. The sample may
`decompose, causing the second measured melting point to be lower than the first.
`Some compounds having fairly high vapor pressures can change directly from a
`solid to a gas without passing through the liquid phase. This is called sublimation. In
`order to measure a melting point (more accurately, a sublimation point) for such com-
`pounds, a sealed, evacuated melting point capillary tube must be used.
`
`Calibration of the Thermometer
`Frequently, thermometers are not equally accurate at all temperatures and must be cali-
`brated to obtain accurate melting points. To calibrate a thermometer, the melting points of
`pure solid samples are measured and a graph is made of the measured (observed) melting
`point temperatures versus the difference between the observed and the expected melting
`points. When reporting experimental melting points, corrections should be made by adding
`the appropriate value from the graph to the observed melting point. A sample thermometer
`calibration curve is shown in Figure 1C-2. An observed melting point of 190°C would be
`reported as 188°C (observed temperature + correction factor = 190°C + [–2°C] = 188°C).
`
`Apparatus for Measuring Melting Points
`Several commercial devices that measure melting points are available. These include
`the Mel-Temp apparatus and the Fisher-Johns Block, which are heated metal block
`devices. The Mel-Temp uses a closed-end capillary tube. The Fisher-Johns uses two
`glass plates horizontally placed to sandwich the substance between them. The Thomas-
`Hoover device is a mechanically stirred oil bath that also uses capillary tubes. These
`devices are shown in Figure 1C-3.
`
`How to Determine a Melting Point
`Preparing the sample. Use 1–2 mg of dry solid. For a mixed melting point determination,
`thoroughly mix approximately equal amounts of the two samples using a mortar and pestle.
`
`50
`
`100
`150
`200
`Observed melting point (°C)
`
`250
`
`+3
`
`+2
`
`+1
`
`0
`
`–1
`
`–2
`
`–3
`
`Temperature correction (°C)
`
`Figure 1C-2
`
`Temperature
`calibration curve
`
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`Technique C Melting Points
`
`25
`
`Figure 1C-3
`
`Devices for measuring
`melting points
`
`Thermometer
`
`Slot for
`sample
`
`Magnifying
`lens
`
`Variable
`transformer
`
`Thomas Hoover
`CAPILLARY QUALITIES POWER APPARATUS
`
`2
`
`1
`
`POWER
`ON
`
`OFF
`
`54
`
`3
`
`6
`
`7
`
`8
`9
`10
`
`STABLE
`
`VIBRATOR
`
`ON
`
`MUDD
`
`OFF
`
`Slot for
`sample
`
`Magnifying
`lens
`
`Variable
`transformer
`
`M
`
`E LT-T E
`
`5 0
`4 0
`3 0
`
`M
`
`P
`
`8 0
`
`O
`
`N
`
`9 0
`
`1 0 0
`
`O F F
`
`2 0
`
`1 0
`
`0
`
`Light
`
`Mel-Temp apparatus
`
`Thomas-Hoover apparatus
`
`Light
`
`Magnifying
`glass
`
`Hot stage
`
`20 30
`
`10
`
`0
`
`100
`
`40
`
`50
`
`60
`70
`80
`90
`
`Variable
`transformer
`
`Thermometer
`
`Fisher-Johns block
`
`Loading the capillary. Do not load the capillary tube with too much sample: this
`causes the melting point to be wide and slightly high because the temperature will con-
`tinue to rise while the compound continues to melt. Place 1–2 mg of the sample on a
`watch glass or a piece of weighing paper. Push the open end of the capillary down onto
`the sample and tap on the solid sample. Then invert the tube. Gently tap the bottom of
`the tube on the bench or drop the tube through a short 2-ft piece of glass tubing; this
`causes the sample to pack more tightly and give a more accurate melting point. This
`process is illustrated in Figure 1C-4.
`Setting the heating rate. If the melting point is unknown, heat the sample rapidly to
`establish an approximate melting point. Turn off the apparatus as soon as the compound
`melts and note the temperature. Let the temperature drop until it is approximately 10°C
`below the observed melting point and repeat the melting point determination with a
`new sample. Heat the sample rapidly to within 10°C of the known melting point. Then
`slow to 1–2°C per minute. Heating too rapidly results in inaccurate, usually wider,
`melting point measurements. An appropriate heating rate can also be determined by
`referring to the heating-rate curve that often accompanies the melting point apparatus.
`Observe the sample through the magnifying eyepiece as the sample melts. Record the
`melting point as the temperature from the start of melting until all solid is converted to liq-
`uid. Remember that shrinking, sagging, color change, texture changes, and sweating are
`not melting. When the sample has melted, turn off the melting point apparatus and remove
`the capillary tube. Discard the capillary after use into the glass disposal container.
`
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`

`

`26
`
`Chapter One
`
`Techniques in the Organic Chemistry Laboratory
`
`Figure 1C-4
`
`Loading a sample into a
`melting point capillary
`tube
`
`Open end
`
`Solid
`
`Capillary tube
`
`Glass tube
`(2-ft length)
`
`Bench top
`
`Exercise C.1: Calibration of a Thermometer
`
`Safety First!
`
`Always wear eye
`protection in the
`laboratory.
`
`Determine the melting points of a series of pure solids. Suggested compounds are
`diphenylamine (53°C), m-dinitrobenzene (90°C), benzoic acid (122°C), salicyclic acid
`(159°C), succinic acid (189°C), and 3,5-dinitrobenzoic acid (205°C). Calculate the dif-
`ference between the known melting point and the measured melting point for each com-
`pound. The differences will be positive or negative. Plot the measured melting point on
`the x axis and the correction factor on the y axis as in Figure 1C-2.
`
`Exercise C.2: Melting Point of an Unknown Solid
`
`Safety First!
`
`Always wear eye
`protection in the
`laboratory.
`
`Melting points should be
`recorded as corrected or
`uncorrected.
`
`Calibrate the thermometer, if directed to do so by the instructor (Exercise C.1). Obtain a
`sample of an unknown solid and record the number of the unknown in your lab note-
`book. Load a capillary tube with a small amount of the solid. Prepare another sample in
`the same manner. Place the tube in a melting point apparatus. Heat rapidly to get an esti-
`mate of the actual melting point. Turn off the apparatus immediately when the com-
`pound melts and note the temperature. Let the temperature drop until it is
`approximately 10°C below the observed melting point. Then place the second tube in
`the melting point apparatus and start heating at a rate of 1–2°C per minute. Record the
`melting point range of the sample (corrected, if necessary). The unknown sample may
`be identified by comparing the melting point with a list of unknowns in Table 1C-1.
`Report the melting point range and the identity of the unknown solid. Dispose of the
`capillary tube in a glass disposal container and return any unused solid to the instructor.
`
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`

`

`Technique C Melting Points
`
`27
`
`Table 1C-1 Melting Points of Selected
`Organic Solids
`
`Organic compound
`
`Melting point (°C)
`
`Benzophenone
`2-Naphthaldehyde
`Benzhydrol
`Vanillin
`Benzil
`o-Toluic acid
`4-Hydroxyacetophenone
`4-Hydroxybenzaldehyde
`Benzoic acid
`trans-Cinnamic acid
`3-Nitrobenzoic acid
`2-Nitrobenzoic acid
`Adipic acid
`Camphor
`p-Anisic acid
`
`48
`60
`68
`80
`95
`104
`109
`115
`122
`133
`140
`146
`153
`178
`184
`
`Exercise C.3: Mixed Melting Point
`
`Obtain two vials from the instructor: one will be a sample of cinnamic acid and the
`other will be an unknown, which will be either cinnamic acid or urea. Record the num-
`ber of the unknown in your lab notebook. Measure the melting points of cinnamic acid
`and the other sample and record the melting points in your lab notebook. Use a spatula
`to transfer 1–2 mg each of cinnamic acid and the unknown solid to a pestle. With a mor-
`tar, grind the solids together to mix thoroughly. Measure and record the melting point of
`the mixture in your lab notebook. Determine whether the unknown is cinnamic acid or
`urea. Justify your conclusions.
`
`Safety First!
`
`Always wear eye
`protection in the
`laboratory.
`
`Questions
`1. A student measures the melting point of benzoic acid and reports the melting point
`in the lab notebook as 122°C. Explain what the student did wrong.
`
`2. Two substances obtained from different sources each melt at 148–150°C. Are they
`the same? Explain.
`
`3. A substance melts sharply at 135°C. Is it a pure compound? Explain.
`
`4. Benzoic acid and 2-naphthol each melt at 122°C. A sample of unknown solid melts
`around 122°C. The solid is either benzoic acid or 2-naphthol. Describe a method to
`determine the identity of the unknown compound.
`
`5. Explain why atmospheric pressure affects boiling points of liquids, but does not
`affect melting points of solids.
`
`6. Refer to the temperature vs. composition diagram of the phenol/diphenylamine binary
`system (Figure 1C-1). Estimate the melting point range for a mixture of 85 mol
`percent phenol/15 mol percent diphenylamine.
`
`7. Do impurities always lower the melting point of an organic compound? Explain.
`
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`

`Experiment 28.2
`
`Experimental Methods of Qualitative Organic Analysis
`
`537
`
`8. Propose a mechanism for the reaction of 2-pentanone with 2,4-dinitrophenyl-
`hydrazine.
`9. List the compound(s) that reacted with silver nitrate (Tollens test). In this reaction,
`silver ion is reduced to metallic silver. What is the organic product?
`10. List the compound(s) that dissolved in NaOH, but not in water. Write a balanced
`reaction for each positive test and explain why the compound dissolved.
`11. List the compound(s) that dissolved in NaHCO3, but not in water. Write a balanced
`reaction for each positive test and explain why the compound dissolved.
`12. Draw the structures of the benzenesulfonamides that formed between benzenesul-
`fonyl chloride and m-anisidine, N-methylaniline, and N,N-diethylaniline. Draw the
`structures of the benzenesulfonam