[madscientist]

Hi all,

Am having a bit of trouble figuring out how to transform benzene into 1,3-dichlorobenzene. My trouble is that Cl is ortho-para directing i.e:

STEP 1:
C6H6 + Cl -----> C6H5Cl

STEP 2:
C6H5Cl + Cl ----> C6H4(Cl)2 (ORTHO) + C6H4(Cl)2 (PARA)

further chlorination would not occur (i think?) because the Chlorines on the ring would compete with each other for position of further substitution.

So i thought that it could be done by starting with nitration (or another meta directing substituent) i.e:

STEP 1: NITRATION

C6H6 + NO2 ----> C6H5(NO2)

STEP 2: CHLORINATION

C6H5(NO2) + Cl ----> C6H4(NO2)(Cl)  [1-chloro-3-nitrobenzene]

STEP 3: SUBSTITUTION

This is where i get stuck cause i cant figure out what reagent would be used to replace the nitro group with a Chlorine atom,(hence giving 1,3-dichlorobenzene), or indeed if this type of reaction is even possible?

Any help or hints would be greatly appreciated,

madscientist

[wilson]

Hi, I am too stuck on when and what substituents will be replaced. See: http://www.chemicalforums.com/index.php?topic=13270.0

1. For the deactivating part:
Anyway, you mentioned that further chlorination will not occur. Do you mean it will not occur because chlorine is deactivating by withdrawing electrons from the ring? Then look at TNT, the nitro group is a strong deactivator. How now?
I think we can use catalysts and impose harsh conditions. For TNT, I heard they use oleum or a larger amount of concentrated sulphuric acid, and pre formed nitronium ion for reaction.

2. For the directing part:
Chlorine is o,p directing. The synthesis of 1,3-dichlorobenzene is rather complicated. I am sorry but I do not know how they do it in the industry. Surely, they have some route, but not that I know of.

Another suggestion is that perhaps we can use free radical substitution of Cl to attack the C on benzene and subsitute H. I am not too sure about the outcomes of the exact product though.

[madscientist]

I am stuck on how to get Cl to bond at a meta position on the 1-chlorobenzene ring.

[movies]

You could convert a nitro group to a Cl by Sandmeyer reaction.

[madscientist]

You could convert a nitro group to a Cl by Sandmeyer reaction.

But wouldn't the Sandmeyer reaction involve an arenediazonium salt C6H5(N2), which is formed from the compound p-methylaniline. In this case it would be the NH2 (ortho-para directing) that acts as the leaving group. I havn't been able to find any examples of the sandmeyer reaction involving the substitution of a nitro group (or any other meta directing substituent) as you suggested?

The way im seeing it is that to use a sandmeyer reaction i would need to start with 3-chloroaniline which gives the same problem that both NH2 and Cl are ortho-para directing, i.e forming 3-chloroaniline from benzene is just as hard for me to visualise as forming 1,3-dichlorobenzene from benzene.

Is it a simple matter that the sandmeyer reaction can involve a nitro substituted benzene?

e.g:

1-chloro-3-nitrobenzene ----HNO2/H2SO4---> 3-chlorobenzenediazonium bisulfate ---HCl/CuCl ---> 1,3-dichlorobenzene

Im realy lost with this one any more help is greatly appreciated,

cheers

madscientist

[Yggdrasil]

You can reduce the nitro group to an amino group and then proceed with the Sandmeyer reaction.

[madscientist]

OMG! I cant beleive i didnt think to do that (forest for the trees n that...), Your a legend Yggdrasil thankyou for your help mate.

Cheers,

madscientist