CH3COCH3 + I2

2011-05-27 7:57 am

In the reaction : CH3COCH3 + I2 à CH3COCH2I + H+ + I-Why H+ is also used as catalyst?What kind of reaction is it? Is it only substitution? Substitution of alkane needs light (UV). Why we need H+ as catalyst in this case?

更新1:

May I ask : Is it the ethyl group in the ketone undergo substitution? Substitution needs light (UV). Why we need H+ as catalyst in this case?

回答 (1)

己式庚辛

2011-05-31 6:15 am

✔ 最佳答案

propanone is NOT alkane! you can see -CO- inside.

2011-05-30 22:15:38 補充：
THIS IS PROPANONE. CH3-C(=O)-CH3.
Not alkane. No ethyl group. is not free radical substitution.

this substitution is feasible due to the ketone group (C=O) in between.
proton activates propanone for further reaction.

for detailed mechanism, i'm too lazy to draw such a thing.
just adopt it from http://www.docbrown.info/page06/OrgMechs3.htm#iodination

2011-05-30 22:16:39 補充：
you can see that step 4 is fast, thus concentration of iodine doesn't matter;
step 1 is slow, so concentration of H(+) affects the reaction rate.

參考: http://www.docbrown.info/page06/OrgMechs3.htm#iodination

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