[Seks]

how do i synthesize that?

If I stick CH3 onto benzene first, it won't work since CH3 is p- and o- directing.

Same with sticking Br onto benzene first, p- and o- directing.

[macman104]

Gatterman-Koch formylation, the aldehyde is electron withdrawing, then bromination, followed by clemmensen reduction.

[Seks]

Gatterman-Koch formylation, the aldehyde is electron withdrawing, then bromination, followed by clemmensen reduction.

gatterman isn't an option since we're not learning that.

[macman104]

K, well what benzene chemistry do you know?  Gatterman-Koch is just a variation of Friedel-Crafts acylation, do you know FC acylation?

[Seks]

K, well what benzene chemistry do you know?  Gatterman-Koch is just a variation of Friedel-Crafts acylation, do you know FC acylation?

halogenation
FC acylation
FC alkylation
Clemmensen
and a few other minor ones (NO2, SO3H, etc)

[macman104]

K, well basically, you want to use H-C(=O)-Cl, but unfortunately, this is not stable, which is where the Gatterman-Koch comes in.  It just creates the species in solution.

But anyway, let's go about it another way.  The strategy is to create the aldehyde and then add the bromide because the carbonyl is meta-directing.  Then once we have the bromide in place, we can reduce the carbonyl to the methyl group.  Somehow we have to make that carbonyl species.  So let's do it this way:

Benzene + FeBr₃, Br₂ ------> bromobenzene
bromobenzene + Mg in ether ------->  phenylmagnesium bromide
phenylmagnesium bromide + CO₂  ------->   benzoic acid (Grignard)
benzoic acid + LiAlH₄ -------->  benzyl alcohol (Reduction)
benzyl alcohol + PCC (pyridinium chlorochromate) ------> benzaldehyde (Oxidation)
benzaldehyde + FeBr₃, Br₂ -----> m-bromobenzaldehyde
m-bromobenzaldehyde + Zn(Hg), HCl --------->  m-bromotoluene (Clemmensen)

[sjb]

gatterman isn't an option since we're not learning that.

Seems a strange way to reject something

Anyway, perhaps shorter (though again, it may be off the minimum syllabus, so not good) could be

Benzene -> nitrobenzene -> 3-methylnitrobenzene -> 3-aminotoluene -> 3-methylphenyldiazonium chloride (you may not need to actually isolate this) -> 3-bromotoluene

S

[macman104]

I was thinking of the diazonium, but I too thought it was likely not in the reactions they had covered yet.

[Seks]

K, well basically, you want to use H-C(=O)-Cl, but unfortunately, this is not stable, which is where the Gatterman-Koch comes in.  It just creates the species in solution.

But anyway, let's go about it another way.  The strategy is to create the aldehyde and then add the bromide because the carbonyl is meta-directing.  Then once we have the bromide in place, we can reduce the carbonyl to the methyl group.  Somehow we have to make that carbonyl species.  So let's do it this way:

Benzene + FeBr₃, Br₂ ------> bromobenzene
bromobenzene + Mg in ether ------->  phenylmagnesium bromide
phenylmagnesium bromide + CO₂  ------->   benzoic acid (Grignard)
benzoic acid + LiAlH₄ -------->  benzyl alcohol (Reduction)
benzyl alcohol + PCC (pyridinium chlorochromate) ------> benzaldehyde (Oxidation)
benzaldehyde + FeBr₃, Br₂ -----> m-bromobenzaldehyde
m-bromobenzaldehyde + Zn(Hg), HCl --------->  m-bromotoluene (Clemmensen)

Yours do make sense.  My instructor came up with this answer:

1.   F.C acylation    (to direct the halogen to the o,p position)
2.   halogenation
3.   clemenson reduction using Zn(Hg) /HCl


I don't know if I should agree with her because I didn't think you can FCA a chloromethanal because the "R" bonded to the carbonyl C has to be an alkyl, not an H.

[macman104]

Well, in "theory" it might work, but the reality is the chloromethanal is not a stable species that you can just "use" as a reagent.  Which is why alternatives like the Gatterman-Koch and other formylation options exist.