GeoSmitty
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Need mechanism help with SOCl2
I've been working on a problem for a while now and have decided I am stumped. This is how it's worded: The compounds SO2 and SOCl2 undergo
an exchange of radioactive labeled sulfur. The exchange reaction is catalyzed by Cl- and SbCl5. Write mechanisms for both reactions. Does anyone
have any advice?
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Dr. Beaker
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antimony pentachloride+chloride?
does'nt SbCl5 a very strong lewis acid?
In that case it will react with Cl- to create
SbCl6- (isoelectronic with SF6 and very stable)
which is a very poor electrophile and nucleophile i.e "inert" in this matter.
in other words: it seems SbCl5 and Cl- are not competible.
also, if it resembles PCl5 then it is a strong chlorinating agent (for example: RCOOH or RCONH2 to RCOCl)
hope it helped.
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Dr. Beaker
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Solution
S* is the labeled one.
notice that Cl- is indeed a catalyst.
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Dr. Beaker
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plausible mechanism with SbCl5
I think SbCl5 (strong lewis acid) abstract chloride from SOCl2 to produce SOCl+ which is highly electrophilic and is being attacked by S*O2 (lone
pair of O) to produce O=S*(+)-O-SOCl
and now:
O=S(+)-O-SOCl <-----> OClS*-O-S(+)=O
(shifting of Cl- from one S to the other)
OClS*-O-S(+)=O <----> SO2 + O=S*(+)Cl
O=S*(+)Cl + SbCl6- <-----> O=S*Cl2 + SbCl5
scrambling of labeled S
Vuwalla! (read with french accent)
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