[ccj]

what will happen if chlorine is passedthrough methylbenzene in the presence of sunlight and halogen carrier?

will both the side chain and the ring be substituted??

[Donaldson Tan]

Under correct conditions, the halogen carrier will transfer chlorine atoms to the benzene deriavative.

Sunlight will cleave the Cl-Cl bond to produce chlorine atoms (aka free radicals) to attack the benzene deriavative too.

After a prolonged period, the side chain and the ring will be substituted with chlorine

[Mitch]

I would suspect ortho para substitution first.

[jdurg]

I would suspect ortho para substitution first.

As would I.  Methylbenzene is simply another name for Toluene, and I know that substitutions on the Toluene ring generally occur before substitution on the methyl portion.  (As in the nitration of toluene, and phenol, and any other monosubstituted benzene ring).  

[hmx9123]

The o-, p- substitution that you're talking about is standard electrophilic substitution, though.  I seem to recall that the C-H bond on the methyl portion is easily cleaved and reacted with radicals.  Of course, I may be totally full of s#*$.

[Mitch]

lol, your right. So sp3 C-H bonds have a lower bond dissociation energy?

[nocommentes]

So sp3 C-H bonds have a lower bond dissociation energy?

Of course, not in saturated alkanes. But in toluene C-H bonds of methyl group can dissociate easily in any way to give benzyl radical, cation or anion. These particles are stabilized because of conjugation with pi-electron system of benzene ring. That's why radical chlorination of alkyl substituted benzen will led to substitution in benzyl position.

[Chris_Whewell]

Toluene + chlorine gives first benzyl chloride, then benzal chloride, and finally benzo tri-chloride.  After the uptake of 3 chlorine atoms on the alpha carbon, no further reaction will occur with u.v. light.

NO substitution of the hydrogen atoms of the ring will occur, unless the reaction is conducted in the presence of a Lewis acid catalyst.