Re: MT chlorine spill also created aromatic O-Cl's (fwd)

[lshadoff@brazosport.cc.tx.us (Lewis A. Shadoff)]

>>
>> the likelyhood of large quantity of dioxin formation is quite high and
>> should soon be known.  cresol is phenol (which is benzene with an alcohol
>> group (-OH) attached), plus an attached methyl (CH3) group.  The compound
>> carried was potassium chrysolate, where an potassium cation is ionically
>> (loosely) bonded in place of the H of the alcohol group.  Reaction with
>> free Cl apparantly knocks off the methyl group as well as the potassium
>> (which -O picks up another H+ to become an alcohol group again), resulting
>> in a chlorophenol.
>>

The formation of dioxins from phenolic compounds is at least a three step
process.  If cresol is reacted with chlorine there is first a substitution
reaction in which a hydrogen on the benzene ring is replaced with chlorine
making a methyl chlorophenol.  If the methyl is ortho- or para- to the
hydroxy group (the common forms of cresol) then the ortho- and para-
hydrogens are easily replaced due to ring activation.  The meta chlorines
are replaced with difficulty, but certainly after the ortho and para
positions have been chlorinated.  (This is made even more difficult since
chlorine de-activates the ring.)

The hydrogens on the methyl group are replaced in a free radical process
which requires the presence of a free radical initiator (such as sunlight).
The replacement of the methyl on the ring requires a catalyst and heat and
goes with difficulty.

Thus I would expect that the major products of the first reaction to be
mono- and di-chloro cresol.  Lesser amounts of
(chloromethyl)chloro-phenols, tri-and tetra-chloro cresol, and even lesser
amounts of chlorophenols.

The next reaction is elimination of HCl between two of the cresol
molecules, linking them together creating substituted phenyl-ethers (also
called substituted diphenyl oxides).  This reaction is facilitated with
base and thus the potassium salts would react more readily than the
phenolic compounds.  These substances have been isolated and even dubbed
"pre-dioxins".  These molecules are two benzene rings linked together with
an oxygen in between.  One ring is substituted (in the case of cresol
starting material) with hydroxy, methyl, and chlorine and the other with
methyl and chlorine (for the major products of the chlorination described
above.)

The next reaction is an intra-molecular elimination of HCl which can only
take place if there is a hydroxy group on one ring next to the linking
oxygen and a chlorine on the other ring also next to the linking oxygen.
The product is a dioxin substituted with chlorine and methyl (for the major
products above).  It can have two, one or no chlorines depending on the
degree of chlorination of the cresols which linked together.

It is much easier to describe these reactions using diagrams.  Consult your
local chemist :>)

Dr. Al Poland studied the toxicity of methyl (and many other) substituted
chlorinated dioxins using an enzyme innuno-assay technique when he was at
the University of Rochester.  He found that the toxicity is much less when
a chlorine is substituted with a methyl.

>> if you went to drug store and asked for a dioxin start-up kit, you would
>> probably be given chlorine, oxygen, phenols and heat.  that is, there is no
>> better known way to create dioxins than from phenols (apparantly, dioxin
>> formation is favored if the Cl has no yet attached to the phenol).  di &
>> tri-chlorphenols have been detected on site.  what we do not yet know in
>> this instance is how much crysolate was released, and how hot things got in
>> this 'reactor vessel' (the spill).  acid-base reactions, such as some of
>> these (?), apparantly release heat (details, anyone?).  there was an
>> unexplained plume for hours after the accident, possibly a condensation
>> plume from a relatively hot reaction zone... finally, we are of course
>> pushing authorities for dioxin sampling.
>>
Since potassium cresolate is probably shipped as an aqueous solution, the
plume could be mostly steam.



Lewis A. Shadoff BS, PhD, Lake Jackson, Texas