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.
2-ethyl-1,3-hexanediol. The molecular weight of this compound is 146.2g/mol. It is converted into 2-ethyl-1-hydroxyhexan-3-one. This compounds molecular weight is 144.2g/mol. This gives a theoretical yield of .63 grams. My actual yield was .42 grams. Therefore, my percent yield was 67%. This was one of my highest yields yet. I felt that this was a good yield because part of this experiment is an equilibrium reaction. Hypochlorite must be used in excess to push the reaction to the right. Also, there were better ways to do this experiment where higher yields could have been produced. For example PCC could have been used. However, because of its toxic properties, its use is restricted. The purpose of this experiment was to determine which of the 3 compounds was formed from the starting material. The third compound was the oxidation of both alcohols. This could not have been my product because of the results of my IR. I had a broad large absorption is the range of 3200 to 3500 wavenumbers. This indicates the presence of an alcohol. If my compound had been fully oxidized then there would be no such alcohol present. Also, because of my IR, I know that my compound was one of the other 2 compounds because of the strong sharp absorption at 1705 wavenumbers. This indicates the presence of a carbonyl. Also, my 2,4-DNP test was positive. Therefore I had to prove which of the two compounds my final product was. The first was the oxidation of the primary alcohol, forming an aldehyde and a secondary alcohol. This could not have been my product because the Tollen’s test. My test was negative indicating no such aldehyde. Also, the textbook states that aldehydes show 2 characteristic absorption’s in the range of 2720-2820 wavenumbers. No such absorption’s were present in my sample. Therefore my final product was the oxidation of the secondary alcohol. My final product had a primary alcohol and a secondary ketone
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