reduction of 9-fluorenone

2 ways to do reduction reactions

1. catalytic hydrogenation

2. reducing agent

catalytic hydrogenation

take a catalyst (typically metal, Ni, H2), preferred method

why is catalytic hydrogenation the preferred method for reduction?

financial incentive for green chemistry, metal catalysts can be isolated and reused multiple times + not a lot of waste produced

- incentive: compound can be sold at cheaper amount + helps green side of chemistry

reducing agent

hydride reducing agents (common reducing agent classes)

- LiAlH4

- NaBH4

hydride reducing agents produce?

hydride ion (H-)

if dealing with hydride ion, need to worry about?

proton sources (H+)

- must be careful of solvent, no water/acid

why are we using methanol as solvent then?

bc NaBH4 is a weak RA that allows acidic solvents to be used

reducing agent strength

has to do with electronegativity difference between metal and hydrogen

hydrgen electronegativity

2.1

where does extra H- electron come from

from metal

- thats why we use difference in electronegativity

which electrons are being taken?

valence shell electrons

smaller atoms?

have electrons closer to protons, meaning electrons are harder to give up

atoms that give up electrons easier have lower/higher electronegativity

lower

LiH and CaH2

very very powerful reducing agents, can create fires

LiAlH4

can't use acidic protons sources, have to use aprotic solvents

NaBH4

weaker RA

- safer to work with

- can use acidic solvents

- give us more flexibility w/solvent choices

what can NaBH4 not reduce

cannot reduce esters

what can NaBH4 reduce

can reduce ketones

reaction mechanism

ratio NaBH4 to 9-fluorenone

1:4

general reaction

MP

152-158

good % yield

65%

most % yield

30-40%

- done at microscale levels, small mistake leads to big loss

how to tell reduction works?

bright canary yellow --> white yellow

IR

- disappearance of carbonyl ketone (1725-1705)

- small narrow OH peak bc its solid (3400-3300)

IR image

intermediate of reaction?

secondary alkoxide