A Beginning Undergraduate Organic Laboratory Course for the Serious Student Melvin S. Newman The Ohio State University. Columbus, OH 43210 In the late 1940s I spent much of my teaching time in developing an improved (according to my criteria) organic lahoratory course for first-year graduate students. I did this hecause I found that the lahoratory know-how of most of our eraduate students was so ooor that . oroeress on a research " problem was much too slow. In this course (two quarters), I gave many lectures on various techniques, including discussion of advantages and disadvantages of alternate procedures. I then encouraged students to devise their own directions for carrying o u t a reaction rather than to hand out specific directions to he followed. In this wav each exueriment was research-oriented. I gave this course only to gaduate students until the middle 1960s. At this time I thought about giving such a course as the first organic lahoratory course an undergraduate student would take. I have been asked many times how I could expect beginning students (sophomores) to perform well with almost no experience behind them. My answer to this is that I believe the philosophical approach to lahoratory work is more important than the actual experiments done. Experience has shown that many students hecome enthused a t this approach to lahoratory work.' As the vears have oassed I have become convinced that mv philosophy is right.'ln any experiment in which a student follows a set of directions (no matter how excellent) he (or she) is being taught to be a technician. With a little thought (and often a few experiments done by the teacher) the experiments can be presented in such a way that the students have a research-oriented auuroach. In the remainder of this article I hope to convince-the reader that this approach has much merit.
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Selection of Student This course is designed only for the serious student who is interested in becoming an excellent experimental scientist (not necessarilv a chemist. because manv ore-med and eneineering studedts have elected to take tkis course). This Feouirement means that relativelv few students can he accommoduted. The studena at Ohio Staw are selected as explained below. In the Fall Quarter we eive a lecture course fin chemistry majors and others (for the past few years most of the pre-med students have taken this course rather than a less demanding one also given in the Fall Quarter). About the middle of the quarter the faculty member in charge of the coming Honors Laboratory Course (which this course is now termed) speaks to those in the lecture course and describes that each student who takes the Honors Lab will he given his or her own lahoratory space so that his equipment and experiments need not he put away at the end of any given period of time. The regular lab course consists of three 3-hour lab sessions Der week for two quarters. No extra time in lab is allowed exiept on rare occasions. The students are advised that a minimum of 15 laboratory hours uer week is expected of them and no extra academic-credit will he given! TI& insures that only really interested students will sign up for the course. Most f the work done in the earlv,vears ~-~o . of this course is described in the book A n Aovanced Organic Laooratory Co.rse" oy Melvin S. Newman. MacMillan. New York. 1972. For more dela led descriptions 01 the wor* discusseo n this anicie th s text should oe consulted. Newman,M. S., J. CHEM.Eouc.. 54, 191 (1977). ~
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The requirement that each student has his or her own lahoratory space (which can he used at any time there is a suoervisor in the lab) means that relativelv few students can he udmitted. For example in this spt.cial lalx)mtory, n.t. mly have mace tor 25 students and two lahmitorv ussistants. Preferahh the two lahoratory assistants do thei; own research in thrs laboratory so that some responsible person is always there. If the lab assistants work on Saturday andlor Sunday the undergraduates may also, and manv of them have done so. The petson whb is togive the Honors Lab sets up meetings with each student who professes interest. The last times I gave this course over 40 students professed interest. The choice of 25 is up to the person in charge and is made as a result of the interviews. In this connection it is of interest to point out that some A students did not fare too well in the lab course while some C students did A work and also improved on their grades in the lecture course. Earlv Coverage -
Equipment. Items of equipment are shown and their uses exolained. I t is stressed that in each experiment over 90% of the starting material must be accounted for-not merely the one desired component. The adequacy of equipment to meet these needs is discussed. For example the first experiment is to esterify a given weighed amount of adipic acid withethanol to produce diethyl adipate. The minimum yield accepted is 95%. The purity of the products can he checked by GLPC. Most of the students hand in 97%99% yields. When a student gets, say, 92%, I am always asked if the experiment must be reneated. Mv answer is alwavs ves! Imagine a teacher re" " garding a 92% yield as unsatisfactory! it I think it is imoortant to insist on high standards.. esueciallv when these are . easily met. For many details regarding this experiment see reference ( 1 ) . Techniques. Methods of isolating reaction products from reaction mixtures are discussed. Distillation and fractional crysraldistillation are well covered a s nrr chn~matugr;~ph?., li7atiun. and suhlimntiun. Steam and superheated stenm distillation equipment is shown and discussed. Many fine points in these techniques are brought up! Balancing Equations. The importance of balancing equations for organic reactions is stressed. Especially important is the measurement of gas evolved in anv reactions in which a gas is evolved. Specific examples are taken from WolfeKishner reactions (where the evolution of nitrogen allows one to determine an operating temperature and t h i time needed for complete reaction). Often these reactions are complete in 30 min as judged by the amount of nitrogen collected (easily, over water) whereas literature directions often call for relatively long hours of heating. Frequently, hy measuring the temperature at which nitrogen evolution begins at a fairly rapid rate, the temperature needed for the reaction turns out to he lower than that described in the literature. In another exoeriment. the svnthesis of o-acetvlhenzoicacid by heating a m i k u r e of phthalic anhydride, maionic acid, and .ovridine is imoroved to 80-90% over the literature vield of 50% by using information gained from measuring the evolution of carbon dioxide.2 Solvent. The decision as to what solvent should he used and
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Volume 59
Number 4
April 1982
387
how much is an important one. Various functions of a solvent in a reaction mixture are emphasized: (1)control of concentration of reactants often controls the rate a t which reactions ucrur; (21 contn,l c , i maximum temperature l)y the boiling point; (3, the insuring of l~om~~gcnc~ousol!lfions when desirable: ( 4 ) rhoiw of solwnr 1,) facilitate work up o111r~d11ct. Too often the running of a renctim and rhc work up arecons~demd separately, whereas both should he thought ahout a t the heginning. In particular the use of the ternary azeotrope of benzene, ethanol, and water finds much use because of the simple removal of water by this means. After the removal of the water-rich layer (Dean-Stark trap) the solvent may he made either henzene rich or alcohol rich depending on the desired isolation procedure for products. Safety Precautions. In addition to the many safety procedures that are to he found and stated, students should b e cautioned about t h e d a n g e r of absorbing chemicals through their hands by the improper handling of equipment. This is es~eciallvtrue in research where one is likelv to ahsorh small amounts bf the same material through the gands over months. The chief point is that whenever one transfers aliquid from one container to another the contents should never he allowed on the outside of a container. This can he prevented by carefully rlnslng the outside of the container being poured from with solvent from a wash hottle.'This procedure not only avoids contact of the material with the skin hut also aids in quantitative transfer from one container to the next. Another cause of serious accidents is the failure to reahze the large heat effect when scaling up a reaction. If test runs are made on small amounts (as they usually are) the heat effect often goes unnoticed. The student may then wish to scale UD the reaction without realizing the danger that can be caused by an exothermic reaction. In my observation most serious accidents arise in this way-and escaping solvent mixed with air can he set afire in several ways. Alternate Techniques for Running Reactions. 1)
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3) 4) 5) 6)
Conventional %Necked Flask. Discussion of the type of reflux condenser (Hershherg reflux-distillingcondenser best), stirrer (magneticor motor-driven),and additional funnel (or hypodermic needle) should be made with advantages and disadvantages of each mentioned. H r u < t i c win Liquld .\mmm~a.'Tnr ndwntapei of liquid ammonia tor ~urryiw
