In the Laboratory
Vial Organic™—Organic Chemistry Labs for High School and Junior College
W
Thomas J. Russo* Theta Technologies, Southgate, KY 41071 Mark Meszaros* Flinn Scientific, Batavia, IL 60510
The study of organic chemistry has been relegated, for the most part, to college laboratories. The cost of ground-glass joints and other specialized glassware makes organic chemistry too costly for high school. The need for large blocks of time for traditional organic laboratories and the use of volatile and toxic starting materials also discourages incorporating organic chemistry into most high school chemistry curricula. Advanced Placement Chemistry curriculum covers organic chemistry nomenclature (1) and a rudimentary treatment of some simple organic reactions, and the ACS ChemCom program does an admirable job of showing the importance of organic compounds in the community; but little attention is given to the laboratory or mechanistic study of this branch of chemistry. Because organic chemistry is exciting and is a foundation for biochemistry, health sciences, petroleum-based industries, textiles, and many other important disciplines and fields, high school students would benefit from learning more about it. The challenge is to develop an organic chemistry laboratory curriculum and procedures that are affordable for high schools, safe to perform in a typical high school laboratory, and fit within a traditional 40- to 50-minute class period. The following laboratory activity is an example of a new organic chemistry procedure designed especially for the high school chemistry curriculum. It is called Vial Organic because most of the activities are performed in low-cost, sealed vials. When heat is required, a simple hot-water bath is prepared from a beaker of water and an inexpensive immersion heater. Advantages of Vial Organic™ Vial Organic activities are easily preformed within one 40- to 50-minute class period. Time is used productively. The most effective approach to a Vial Organic laboratory is to have the students add the reactants to the vial and place the vial in a water bath to heat at the beginning of the class. While the reaction occurs, the instructor can continue to discuss the topics being studied. Near the end of the class period, the students remove the reaction vial from the hot-water bath, cool the reaction vial, separate out the product, and perform a simple extraction or purification step. Further purification or analysis of the product is easily performed during the next laboratory period. In some cases, simple tests can show differences between the product and the starting material, indicating that a chemical reaction has occurred. W Supplementary materials for this article are available on JCE Online at http://jchemed.chem.wisc.edu/Journal/issues/1999/ Jan/abs69.html.
*Email:
[email protected] (Russo, T.);
[email protected] (Meszaros, M.).
Safety is of paramount importance in this pedagogy. Vial Organic is extremely safe because only micro quantities of reactants are used, reactants are contained in tightly sealed vials, and only water baths are used for temperature control. Whenever possible, hazardous reactants have been replaced by less hazardous ones. The sealed vial prevents ignition of the vial contents from sparks or excessive heat. While a sealed system might seem dangerous, there is very little danger of the vial’s exploding. This most catastrophic event happened only once in all development trials. In that event, the sole hazard was the splashing of water onto the benchtop. Splash danger can be minimized by using a splash/explosion shield or inverting a 1000-mL or larger beaker over the entire setup. All organic reactions in Vial Organic take place in a sealed vial. With a sealed vial there is no need for complex glassware like reflux condensers or vapor traps. The equipment for heating or cooling the reaction is also simplified. The sealed vial can be placed in a boiling-water bath and heated without regard to careful monitoring of the reaction temperature. If there is water in the bath and it is boiling, the temperature of the reaction is 100 °C! Cooling a small reaction vial is just as easy. The small volume of liquid used in any reaction permits almost instantaneous cooling of a reaction. A sealed vial has the additional advantage that since vapors cannot escape, the pressure inside is increased; and a modest increase in pressure favors the formation of product in most organic reactions. Figure 1 shows the same reaction being run in microchemical apparatus and using the Vial Organic methodology. A brief description of two of the procedures follows. A detailed laboratory description including disposal and other safety information for each lab described below is available from the authors* or from JCE Online.W The procedures may
A
Speed
B
Heat
Figure 1. A: Microorganic setup for aldol reaction. Cost ~$221 per setup. B: Vial Organic setup for aldol reaction. Cost ~$4.17 per setup.
JChemEd.chem.wisc.edu • Vol. 76 No. 1 January 1999 • Journal of Chemical Education
69
In the Laboratory
be modified for individual laboratory needs or for educational goals set by the reader. We hope that the low cost, ease of use, and relatively short time requirement will allow more organic chemistry to be introduced at the high school level and better prepare students for their collegiate chemistry experience. Our protocols do have a limited scope and are not meant to be the inclusive organic chemistry laboratory course, especially at the collegiate level. However, Vial Organic procedures may have some application even in college organic chemistry laboratories. Preparation of Iodoform (2 )
A mixture of sodium iodide and acetone is stirred in an ice bath. Sodium hypochlorite is added and a yellow precipitate forms. Small-scale isolation techniques are used to isolate the precipitate. Cross Aldol Reaction (3 ) The aldol reaction is a common method of forming new carbon–carbon bonds. In this laboratory procedure, acetone undergoes a double aldol condensation with benzaldehyde to form dibenzalacetone. The reaction is catalyzed by sodium hydroxide. O
O
A common organic qualitative test for functional groups is the iodoform test, which gives a positive result for the presence of methyl ketones. It involves the hydrolysis and cleavage of methyl ketones to form a yellow precipitate of iodoform (CHI3). Iodoform has been used as a disinfecting agent. It has the odor associated with medical offices and some topical antiseptics. In this experiment, iodine is not directly added to the reaction, but is generated in situ by oxidation of the iodide anion by an oxidizing agent. In this reaction, potassium or sodium iodide is oxidized by household bleach (5% sodium hypochlorite) by the following reaction: O H3C
O
NaOCl, NaI
C H3
"in situ I2"
+ H3C
C H3
OH
NaOCl + 2 I ᎑ + 2 H+ → I 2 + H 2O
70
O
+ H3C
H
NaOH
CH3
acetone
benzaldehyde
dibenzalacetone
Benzaldehyde, acetone, and a solution of sodium hydroxide in ethanol are combined in a reaction vial and placed in a hot-water bath. The mixture is heated for 10–20 minutes. Then the reaction vial is cooled and the product is isolated. Literature Cited 1. Advanced Placement Chemistry; Educational Testing Service: Princeton, NJ, 1989. 2. Campbell, B.; Ali, M. Organic Chemistry Experiments; Brooks/ Cole: Pacific Grove, CA, 1994. 3. Mayo, D.; Pike, R.; Trumper, P. Microscale Organic Laboratory; Wiley: New York, 1994.
Journal of Chemical Education • Vol. 76 No. 1 January 1999 • JChemEd.chem.wisc.edu
