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Author Topic: Chlorination of Toluene in presence of heat & light..  (Read 5004 times)

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uvcyclotron

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Chlorination of Toluene in presence of heat & light..
« on: June 24, 2010, 12:22:55 AM »

Hey.
I got this objective question which asks for the product obtained from chlorination of toluene in presence of light & heat, followed by treatment with aq.NaOH
Options:
A) o-cresol
B) p-cresol
C) 2,4-dihydroxytoluene
D) benzoic acid

I think the presence of light would lead to chlorination under free radical mechanism..resulting in substitution of all hydrogens on the benzene ring by chlorine,but that leads to nowhere, i mean what will happen on treatment with aq.NaOH then?

Further since this was an objective ques, i already know the answer which is Benzoic Acid but I am unable to conclude a plausible mechanism.
Thanks in advance!
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SVXX

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #1 on: June 24, 2010, 02:22:49 AM »

You are right about the free radical mechanism. However it takes much more than just light and heat to chlorinate the hydrogen groups present on benzene by that method.
Rather, light and heat will cause -CH3 to transform into -CCl3. Now think.... what does hydrolysis of -CCl3 in basic medium yield?
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typhoon2028

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #2 on: June 24, 2010, 03:57:03 AM »

Through irradiation crosslinking (beta) of our polymer product, we have found benzoic acid.

Somehow divinyl benzene reacts to benzoic acid and other similar structures, during irradiation.  There is ozone present too.
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SVXX

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #3 on: June 24, 2010, 04:05:13 AM »

Through irradiation crosslinking (beta) of our polymer product, we have found benzoic acid.

Somehow divinyl benzene reacts to benzoic acid and other similar structures, during irradiation.  There is ozone present too.
Is this relevant to the discussion at hand? Pardon me, I am only a student. I would love to know how this is related.
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uvcyclotron

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #4 on: June 24, 2010, 05:10:58 AM »

Through irradiation crosslinking (beta) of our polymer product, we have found benzoic acid.

Somehow divinyl benzene reacts to benzoic acid and other similar structures, during irradiation.  There is ozone present too.
Is this relevant to the discussion at hand? Pardon me, I am only a student. I would love to know how this is related.

haha..humor slipped in with an apology..i like it. makes the forum interesting..

Anyways, thanks for the help SVXX, I got the clues, and I think the -OH group would attack the trichloro-substituted carbon in succession, leading to substitution of -Cl groups followed by dehydration leading to the benzoic acid..

But I still have a few doubts, like u said
However it takes much more than just light and heat to chlorinate the hydrogen groups present on benzene by that method.

Could you please elaborate? What more does it take?
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SVXX

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #5 on: June 24, 2010, 06:39:16 AM »

Light and heat are the usual norms when it comes to radical halogenations. If I remember correctly you need to supply a lot more energy. Preferably drastic conditions involving high temperatures.
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typhoon2028

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #6 on: June 25, 2010, 03:23:29 AM »

Through irradiation crosslinking (beta) of our polymer product, we have found benzoic acid.

Somehow divinyl benzene reacts to benzoic acid and other similar structures, during irradiation.  There is ozone present too.
Is this relevant to the discussion at hand? Pardon me, I am only a student. I would love to know how this is related.

Relation as I see it is:

Exposing organics to ionizing radiation can result in numerous by-products.  Sometimes not everything will follow a nice linear pathway as they do in a text book. 
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SVXX

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Re: Chlorination of Toluene in presence of heat & light..
« Reply #7 on: June 26, 2010, 04:28:58 AM »

Through irradiation crosslinking (beta) of our polymer product, we have found benzoic acid.

Somehow divinyl benzene reacts to benzoic acid and other similar structures, during irradiation.  There is ozone present too.
Is this relevant to the discussion at hand? Pardon me, I am only a student. I would love to know how this is related.

Relation as I see it is:

Exposing organics to ionizing radiation can result in numerous by-products.  Sometimes not everything will follow a nice linear pathway as they do in a text book. 

Very true...but the thread starter also mentioned the use of aq NaOH after the chlorination. Which is why my mind followed a "nice linear pathway"(not akin to textbooks though :P) as you mentioned.
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