Exp t 125. Oxidation of Borneol to Camphor. Reduction. Camphor. Borneol. Isoborneol

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1 Exp t 125 Oxidation of Borneol to Camphor Adapted by and R. Minard (Penn State Univ.) from Introduction to Organic Laboratory Techniques: A Microscale Approach, Pavia, Lampman, Kriz & Engel, Revised by John Landis, Rev. 3/21/01 Introduction: This experiment involves the oxidation of a secondary alcohol (borneol) to a ketone (camphor) as illustrated in the first step of the two-step oxidation/reduction sequence shown below. The use of a polymer supported chromic acid used for the oxidation makes isolation of the product very simple. It is simply removed from the resin by pipet filtration. Reduction Borneol H OH O Camphor Isoborneol H OH The spectra of borneol, camphor, and isoborneol are compared to detect structural differences and to determine the extent to which the final step produces a pure alcohol isomeric with the starting material. Prelaboratory Exercises: 1. Give the systematic IUPAC names for the three compounds shown above. 2. What do the terms exo and endo mean? Give an example of each. Cautions: The reaction should be carried out in a hood. The resin-supported chromic acid oxidizing agent is toxic. Avoid contact with skin and dispose of as a heavy metal. The starting material and product sublime readily and should be stored in tightly closed containers such as "shorty" vials. Synthesis: To a 5-mL long-neck round-bottom flask, add g of [(1s)-endo]-(-)-borneol, 2.0 ml of toluene, and 0.50 g of chromic acid on a polymer support resin. Clamp the flask on the surface of a hot sand bath and heat so that the toluene just boils gently (bp 110 C). Follow the progress of the oxidation by TLC. At intervals of 5 min, insert a long finelydrawn capillary into the reaction to draw liquid into the capillary and spot on a silica gel TLC plate (available from the stockroom). Put a spot of a 2% solution of the starting material, borneol, on the plate as a reference. Develop the TLC plate in 50% hexane/50% ethyl acetate and visualize using an iodine development chamber. The reaction should be complete in approx. 30 min. Isolation and Purification: Allow the mixture to cool to room temperature and draw off the toluene by pipet filtration and place it in a tared 20-mL vial. Add a boiling stick and evaporate the solvent in the hood by heating the vial on a warm sand bath. If possible, use a gentle stream of nitrogen gas to aid the evaporation. Watch the progress of the evaporation carefully and, as soon as a solid appears, remove the vial from the heat source; otherwise, the product may sublime and be lost. Lay the warm vial on its side on the bench top and roll around to allow the heavy toluene vapors to escape.

2 Weigh the vial and oily solid to determine the weight of your product and calculate the percentage yield. Cap the vial since the product sublimes readily. Determine its melting point in a capillary tube sealed with parafilm to prevent sublimation. The melting point of pure racemic camphor is 174 C 1. However, the observed m.p. of camphor is often low. A small amount of impurity drastically reduces the melting point and increases the mp range. Cleaning Up: The used chromic acid resin should be placed in the heavy metals waste container. Final Report: In your final lab report include all thin layer chromatography plates (taped into your notebook) and spectral data on your product. If you obtained an NMR spectrum of your product, compare your spectrum to the NMR included in this writeup. If you obtained an IR spectrum of your product, compare your spectrum with the IR included in this report. Evaluate these carefully with respect to detecting unreacted starting material still present in the product. Questions to be answered at the end of the Final Report: 1. A sample of isoborneol prepared by reduction of camphor was analyzed by infrared spectroscopy and showed a band at 1760 cm -1. This result was unexpected. Why? 2. The observed melting point of camphor is often low. The molal freezing-pointdepression constant, K f, for camphor is 40 Km -1. Calculate the expected depression of the melting point of camphor that contains 0.15 molal impurity. Assuming the impurity is isoborneol, what is the % (weight/weight) impurity of isoborneol in a 0.5m solution of isoborneol in camphor. 3. Would you expect to get the same product by oxidizing isoborneol instead of borneol? Explain. References: Markgraf, J.H. "Stereochemical Correlations in the Camphor Series." Journal of Chemical Education, 44 (1967): 36. Mohrig, J.R., Neinhuis, C.F., Van Zoeren, C., Fox, B.G., and Mahaffy, P.G. "The Design of Laboratory Experiments in the 1980's." Journal of Chemical Education, 62 (1985): 519. Exp't 125

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4 Synthetic Experiment PreLab Grading Sheet Name(s): TA: Date: PreLab For Exp't #:125 Title: Oxidation of Borneol to Camphor Date, Name, Desk #, Experiment # & Title(abbreviated after 1 st pg), Section & TA Name Possible 4 Missed Summary 8 Goals 8 Reactions, structures, conditions, diagrams 14 Completeness of Chemical Data Table(s) 14 Chromatographic Behavior Comparison 16 Spectral Features Comparison 12 Work-up - Explanation of the product isolation and purification process 12 PreLab Exercise 12 TOTAL FOR PRELAB 100 Date Handed in: General Comments: Total :

5 Synthetic Experiment Final Report Grading Sheet Name: TA: Date: Final Report For Exp't #: 125 Title: Oxidation of Borneol to Camphor Name, Date, Experiment Title (abbreviated after 1st page) and every page numbered 4 Possible Missed OBSERVATION and DATA - Overall organization, readability, completeness 8 Data: Weighing data, molecular weights, moles, density, volumes, R f 's, graphs, analysis conditions. (Examples: IR - KBr weight; NMR solvent; GC analysis conditions sheet) Yield: Show % yield calculations with limiting reagent clearly stated. Purity: Give melting point or boiling point, color, or other indicators of purity RESULTS AND DISCUSSION - Overall organization, readability, completeness 8 Results; Achievement of goals 16 Product Analysis Data: Quality and Interpretation Structure(s) drawn on each Spectrum or Chromatogram Assignment and discussion of all IR and NMR peaks. See Lab Guide Chapter 3, Section 3.4 for guidelines in annotating spectra and Ch 11 for help with interpretation. 24 POSTLAB QUESTIONS 16 TOTAL POINTS 100 Date Handed in: General Comments: Total :