Asymmetric Epoxidation of Dihydronaphthalene with a Synthesized Jacobsen's
Catalyst
Abstract. 1,2 diaminocyclohexane was reacted with L-(+)-tartaric acid to yield
(R,R)-1,2-diaminocyclohexane mono-(+)-tartrate salt. The tartrate salt was then
reacted with potassium carbonate and 3,5-di-tert-butylsalicylaldehyde to yield
(R,R)-N,N'-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, which was
then reacted with Mn(OAc)2*4H2O and LiCl to form Jacobsen's catalyst. The
synthesized Jacobsen's catalyst was used to catalyze the epoxidation of
dihydronaphthalene. The products of this reaction were isolated, and it was
found that the product yielded 1,2-epoxydihydronaphthalene as well as
naphthalene.
Introduction
In 1990, professor E.N. Jacobsen reported that chiral manganese
complexes had the ability to catalyze the asymmetric epoxidation of
unfunctionalized alkenes, providing enantiomeric excesses that regularly
reaching 90% and sometimes exceeding 98% . The chiral manganese complex
Jacobsen utilized was [(R,R)-N,N'-Bis(3,5-di-tert-butylsalicylidene)-1,2-
cyclohexanediaminato-(2-)]-manganese (III) chloride (Jacobsen's Catalyst).
(R,R) Jacobsen's Catalyst Jacobsen's catalyst opens up short pathways to
enantiomerically pure pharmacological and industrial products via the
synthetically versatile epoxy function .
In this paper, a synthesis of Jacobsen's catalyst is performed (Scheme
1). The synthesized catalyst is then reacted with an unfunctional alkene
(dihydronaphthalene) to form an epoxide that is highly enantiomerically enriched,
as well as an oxidized byproduct.
Jacobsen's work is important because it presents both a reagent and a
method to selectively guide an enantiomeric catalytic reaction of industrial
and pharmacological importance. Very few reagents, let alone methods, are
known to be able to perform such a function, which indicates the truly
groundbreaking importance of Jacobsen's work.
Experimental Section
General Protocol. 99% L-(+)- Tartaric Acid, ethanol,
dihydronaphthalene and glacial acetic acid were obtained from the Aldrich
Chemical Company. 1,2 diaminocyclohexane (98% mix of cis/trans isomers) and
heptane were obtained from the Acros Chemical Company. Dichloromethane and
potassium carbonate were obtained from the EM Science division of EM Industries,
Inc. Manganese acetate was obtained from the Matheson, Coleman and Bell
Manufacturing Chemists. Lithium chloride was obtained form the JT Baker
Chemical Co. Refluxes were carried out using a 100 V heating mantle (Glas-Col
Apparatus Co. 100 mL, 90 V) and 130 V Variac (General Radio Company). Vacuum
filtrations were performed using a Cole Parmer Instrument Co. Model 7049-00
aspirator pump with a Büchner funnel. For Thin Layer Chromatography (TLC)
analysis, precoated Kodak chromatogram sheets (silica gel 13181 with
fluorescent indicator) were used in an ethyl acetate/hexane (1:4) eluent.
TLC's were visualized using a UVP Inc. Model UVG-11 Mineralight Lamp (Short-wave
UV-254 nm, 15 V, 60 Hz, 0.16 A). Masses were taken on a Mettler AE 100. Rotary
evaporations were performed on a Büchi Rotovapor-R. Melting points were
determined using a Mel-Temp (Laboratory Devices, USA) equipped with a Fluke 51
digital thermometer (John Fluke Manufacturing Company, Inc.). Optical rotations
([a]D) were measured on a Dr. Steeg and Renter 6mbH, Engel/VTG 10 polarimeter.
The experiment test-bed is composed of a DC motor, an engine, a chain drive, a shaft and other accessorial components. The DC motor is used to drive the engine shaft and its speed can be up to 1450 r/min.
Seventh ed. Vol. 2. New York, NY: W.W. Norton &, 2008. 985-93. Print. 1866 to the Present.
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Through an oxidation-reduction reaction sequence, Borneol is converted to isoborneol. First, borneol is oxidized through a reaction with sodium hypochlorite at 400C to form camphor. When the camphor is then reduced by sodium borohydride, isoborneol is formed. The percent yeild of isoborneol collected was 56.4%, and the melting point range was found to be between 174.2-179.90C. Through analysis of the product through 1H NMR spectroscopy the percent purity is found to be 77.2% pure isoborneol.
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