A Suggestion for a Beginning Organic Chemistry Laboratory J. R. Sowa Union College, Schenectady, NY 12308 ysis scheduled somewhere close to the second week of the term allows the student to appreciate the introduction of functional groups received in lecture. S h e b e also learns how to take microboilingpoints (or on a larger scale if desired), to appreciate what a boiling point is and how it can help in the identification of an unknown, to learn about melting points, to appreciate solubility classifications and the acidbase nature of molecules, to run functional group reactions, and to have an appreciation for having solved a prohlem unknown. (Students seem to find project-orientated laboratories exciting. It is too bad all of our laboratories cannot he so oriented.) In addition to perfecting techniques, what the student learns in this exercise can be applied in the second term on a grander scale. Before the student arrives in the laboratory, shebe receives a write-up of the experiment, explaining the overall plan and specific steps required to identify three unknowns. The student also receives a copy of the Table 1. Clearly, the number of choices has been narrowed in hopes that the student will not he overwhelmed by what is the real world. Shebe is required to perform an ignition test, then do a m p b p determination and solubility classification. The ignition test and bp determination are run first to cut down on the fire hazard later in the laboratory period. After the solubility classification the unknown is pretty much identified. Nevertheless, a functional group test that is expected to give a positive result is run. This substantiates the conclusion. At the onset ofthe laboratory period, each student is given three vials containing unknown substances. The students are to leave these a t their station a t the end of the period so subsequent laboratory sections can use the same unknowns.
Someoneoncesaid that, if you can not use it, do not make it.This is the idea hehind beginning organic laboratories. To teach the student techniques that permit the making of usable quantities of materials that are pure enough to be useful. Many of the techniques that are emphasized in the beginning course deal with purification like recrystallization, distillation, filtration, extraction, and various chromatographic systems. These in turn require methods for physical characterization. When ~lanninna laboratorv schedule. it is desirable to coordinate the la~oratoryandiecture material with the former laaaina -- - behind hv one or two weeks. This reinforces the lecture material while lessening confusion in the laboratory brought about by the coupling of techniques and chemistry. Simply stated, if the student doesnot knowthat benzoic acid can be converted to its salt in the presence of sodium hydroxide, how can the individual appreciate the extraction process involving this material? Extraction becomes a "black box" process. There is also the question ahout which technique should be resented first and in what fashion. i.e.. as part of a or alone. In general, it seems that if r&rystallization is introduced earlv in the course, a significant number of students in two termsbf laboratory ieithir seem to understand what is happening .. .in this process nor how to make it happen better. Many organic textbooks present functional group chemistry in the beginning chapters. Although the student probably does not fully appreciate the significance of this, it is clearlv .to eive the individual an overview of what is to come and, especially, what differences should be looked at. We have found that a miniexperiment in qualitative anal-
-
Table 1. Functional Gmup Help Sheet mi. class acetamids acetic acid acetone benroic acM t-BuCI chole~terot cyclooctene cyclohexene ethyl acetate hexane meman01 methylamine. HCI l-pentanol phenol toluene
2 1 1 3 6 5 5
5 5 6 1 2 5' 1 6
mp 82 17
bp
118 56
cm3
pH (H20)
+
odw
mouse cage vinegar glue
122 musty
56 149 140 83 77 69 65 227b 43b
140 182 110
+
gas gas fruity gasoline anti~~ptic acidic ammonia antiseptic hospital glue
S o m e conclude 1. if dry. ~ c i d bom s insoi. ~g sans which do nn act like AgCi with ammonla, etc. m e you check f a HBr. 'Given time it will be Also "d +" ignition test.
+.
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Journal of Chemical Education
Br2
-d
-
+ + +-d
HOAC
-
+ -* -*
-
+ +-
NaOH heat
+-
--
+-
AgNO.
-c
-c
+ -
-+-
NH&H
-
-
+-
-
2.4-DNP
+-
-
-
F ~ C I S HND,
-
-
+
-
+
-
-
Table 2.
Unknown-Functional Group Comblnatlons
Toluene Pentand Methylamlne HCI
.
muc1 Cholesterol Hexane
-1 -3 1 I -1 -2 I
Vlll
XV
XXll
XXlX
XXXVi
IX
XVI
XXlll
XXX
Xxxvll
- 38
Phenol Cyclwctene Acetic acid
Ill - 1 -2 38
X
XVll
XXlV
XXXl
XXXVlll
MBmanol Emyl acetate Acetamide
IV
XI
XVlll
XXV
XXXll
XXXtX
Benzolc acid Acetone Cyclohexene
V-1 2 38
XI1
XIX
XXVl
XXXlll
XXXX
Xlll
XX
Xxvll
XXXlv
XXXXl
XIV
XXI
XXVIII
XXXV
XXXXll
Toluene Cholesterol Methanol & m i 0 acid Ethyl acmate Acetic acid
- 18 -2 -3
VI - l -2 - 38 VII - 1 -2 - 38
'Only tWe thtt bp of liquids labsled with a "B."
Surprisingly, there does not seem to be much comparison of results between sections, meaning the process is an individual effort. Each memher of the triad of unknowns is selected such that most can only be completely identified based on the ignition test. This would not be the case if boiling points of each liquid were taken. It is partially for this reason that the student is instructed to determine only one bp and which liquid can be used for this. The combinations are listed in Table 2. The tests confirming the unknowns are well known. Problems arise when the chromic acid solution is not cold or when 2,4-DNP precipitates from the test solution, causing the student to think the hydrazone has formed. A mp determination of the precipitate helps the student draw the correct conclusion. This paper is presented because the experiment is instructive and a good starting experience for the student. It uses small quantities of reagents consistent with scaling down experiments. It introduces techniques that are necessary for carrying out the task of identifying unknowns and are used later in the term. The experiment helps the student better appreciate the lecture material covering functional groups and gives most students a sense of accomplishment when they are expecting the worse.
Volume 66 Number 11 November 1989
939
