okay so for this practice problem we have benzene we're starting with benzene
and we are going to subject this to a series of four sets of reaction
conditions so take a look at these and think about what reactions we might need
to be using and see if you can come up with a correct product.
so let's take a look at this we've got benzene we're starting with benzene and what is the
first thing we're gonna do so reaction one we've got Br2 and FeBr3
so we've got benzene we've got something aromatic and FeBr3 this iron tribromide
catalyst that should be a tip-off we know that we're doing electrophilic
aromatic substitution we know that we are going to brominate this benzene ring
so if we recall that reaction this is electrophilic aromatic substitution with
that iron tribromide catalyst we know that we're gonna get a bromine on there
put it anywhere on the ring we just throw a bromine on there so that's
reaction one. then we've got reaction two so what are we going to be using
magnesium for, probably at this stage of organic chemistry there's
really only one application and when we see magnesium we're thinking grignard. we
know that we're gonna be generating a grignard reagent and so let's go ahead
and make that grignard reagent we know that magnesium is going to insert itself
into that carbon bromine bond so we know that we're gonna get from Br we're
gonna get MgBr so magnesium remember in diethyl ether that's going to give us
our grignard reagent so that's that's where we are now how about this third
reaction let's talk about number three we know that grignard
agents will usually attack carbonyl containing compounds and so usually
that's an aldehyde or ketone sometimes we see this happening with an ester as
well but there is one special case here we see in two steps we've got CO2
followed by your typical aqueous acidic workup for a grignard. CO2 how is that
going to work? well it really behaves just like any other carbonyl containing
compound we know that this carbon is going to attack here and we're gonna pop
up we're gonna we're gonna have that pi bond go up there into the oxygen the
only difference is there is another carbonyl there and so when you do a
grignard with CO2 you actually are able to get a carboxylic acid right so this
followed by the aqueous acidic workup is going to protonate that oxyanion and we
do get benzoic acid here so that's a little bit different than your typical
grignard but that is what we're gonna get here that is the case with CO2 so we
do want to remember that that is a special case and then lastly we know
that lithium aluminum hydride right lithium aluminum hydride is a very
strong reducing agent it is capable of reducing not just aldehydes and ketones
but also carboxylic acids and esters so lithium aluminum hydride is able to take
this all the way down to the primary alcohol and so we do get this as our
answer. so once again we did electrophilic aromatic substitution we
did a bromination here pop the bromine on there, the magnesium allowed us to
make the grignard reagent then we did a grignard reaction with our grignard
reagent and CO2 to get benzoic acid and then from there we reduced with lithium
aluminum hydride to get this alcohol, and that is the product of this sequence of reactions.