242 Lab 1: Reduction of Camphor

What stereochemistry is produced when ketones are reduced?

ketones are flat so they generally give both stereoisomers of an alcohol

what are the possible products of camphor and NaBH4?

diastereomers of one another, new chiral center

why is sodium borohydride attractive for use?

ease of handling, does not react as violently with water so it can be used in alcohol based solvents, used in excess to avoid losing too much

mechanism of NaBH4 reduction?

delivery of a hydride at the electrophilic carbon of the ketone four times to generate a tetraalkoxycarbon compound, this can then be decomposed, at elevated temperatures

what are the different attacks a hydride can do on camphor?

endo or exo attack

what is the safety information?

NaBH4 reacts vigorously with water & releases H2 gas, avoid mixing with aqueous solns, acetone and methanol are highly flammable

procedure for reduction

dissolve camphor in methanol and stir @ room temp, add NaBH4 in 2 portions, heat until boiling, continue heating 5 min then cool to room temp

procedure for isolation of borneol and isoborneol

cool rxn in ice bath, add cold H2O, white solid appears, collect on buchner funnel, filter and allow dry for 5 min

procedure for purification and characterization

rinse product off paper w/ hexanes, fully dissolve product, dry over Na2SO4, decant, evaporate hexanes soln w/ air, and take mp

how to normalize GC spectra?

remove unwanted peaks, renormalize remaining peaks by added wanted peaks areas dividing each peak area by the total area

what analysis techniques were used?

NMR, GC-MS

borneol vs isoborneol H-C-O nmr shift

borneol: 4 ppm, isoborneol: 3.6 ppm

what was the major product according to NMR and GCMS?

NMR: isoborneol because of 3.6 peak

GCMS: largest % due to summary sheet

why did the reaction show this selectivity?

the hydride will attack the less hindered side of camphor

does the reaction favor an endo or exo attack?

endo attack

what kind of reaction is this?

irreversible reaction, under kinetic control so whichever one has the more stable TS will be the major product

why don’t we need a reflux condenser for this reaction?

the reaction is over so quickly that barely any solvent will have boiled away

what would tell us if camphor was transformed into borneol + isoborneol?

mp, IR (above 1500 cm^-1), NMR (3-5 ppm), NMR (below 3 ppm) (absence of CH next to C=O at 2.5 ppm), MS (molecular ion peak)

which of these would tell us if the major product was borneol or isoborneol?

NMR (between 3-5 ppm), MS (fragmentation pattern) if computer assistance

why were the webmo chemical shifts for the OH peak different than the literature values?

webmo doesn’t take into account intermolecular interactions, only looking at a single molecule so it doesn’t show the deshielding of the OH peak accurately, not representing the H bond strength

camphor has ___ chiral centers and borneol has ___ chiral centers.

camphor has 2 chiral centers and borneol has 3 chiral centers

borneol and camphor are ______ of each other.

not isomers

why is water not a suitable solvent?

the NaBH4 would decompose in H2O so no reaction would occur and camphor is not soluble in H2O so no reaction would occur