Good Link detailing Fenton's Reagent courtesy of Organikum.
Today I decided that I would take the time to properly dispose of some organic wastes (acetonitrile, chloroform, tetrachloroethane, benzene, and
others) by destroying them with Fenton's Reagent. For those of you who are not familiar with this particular reagent it is basically a method by
which to make hydroxyl radicals in solution, which basically eat up everything organic around.
The usual method is to make an aqueous solution with a pH between 3 and 6 and add to this ferrous cations (usually ferrous sulfate) and a peroxide
source (usually hydrogen peroxide). And thus the reaction commences. I made a large batch today by dissolving some steel wool in some HCl and
pouring this into a large quantity of H2O2 and some more HCl was added (notice the scientific measurements here). Additionally some FeCl3 (circuit
etching) was also added as the reaction was going slow.
The solution was yellow and the organic liquids were added forming their own layer on the bottom. Occasionally some bubbles would rise off them but
nothing intense. The reaction temperature stayed low and the whole solution fizzed slightly for some time. About four hours later the solution was
still fizzing and the mixture was slightly warm, hardly noticeable. And all the organic layer was gone, the liquid had gotten darker. Now, here is
the odd part, once all the organic was gone the solution started heating up, really heating up. I was doing this in a spaghetti jar so I definitely
didn’t want it heating up. It got itself so hot it started boiling. I rushed off and dumped it on the ground and it really started freaking out,
burning fumes rose up quickly forcing me to close my eyes, and the ground started to heave and shoot out caustic shots of liquid that fizzled and
popped where they landed, it was incredibly destructive.
I flooded the area with water and let it die out.
So.... does anyone have a simple method by which they make Fenton's reagent on a normal basis, so I can follow a procedure next time instead of
mixing things like amounts don’t matter? Or maybe something easier, I mean, Fenton’s will eat chlorinated organics and such and seems safer then
piranha, the only other real method I know to take out chlorinated organics in solution is the reduction with aluminum/nickel alloy and HCl.
[Note, picture was taken before things started to get out of hand.]
chemoleo - 6-5-2005 at 20:05
Flat surface area on ice, broad reagent vessel, little catalyst, 'reasonable' or 'moderate' amounts of organic substance,
icecooling and patience next time?
I know you got plenty of all these!
Also
Quote:
adding slowly the H2O2. If the pH is too high, the iron precipitates as Fe(OH)3 and catalytically decomposes the H2O2 to oxygen -- potentially
creating a hazardous situation.
I suppose this didnt happen during the addition of copious amounts of solvents, i.e. pH change and so on? like, the generation of more HCl (due to
chlorinated solvents) might cause this.
[Edited on 7-5-2005 by chemoleo]Madandcrazy - 30-5-2005 at 06:29
quote:
---------------------------
pH change and so on ?
---------------------------
I thought some amounts of a organic catalyst canges the pH during the reaction in the Fenton’s and prepricate same Fe(OH)3 ?
The chlorination of Fe(OH)3 would gave
FeCl3 and H2O or Fe(OH)3 are someways a material for a alloy.BromicAcid - 30-5-2005 at 07:46
Well, I've been working a lot with Fenton's reagent, but on a much smaller scale. Nearly all of my reactions have been in test tubes with
10 ml of 6% H2O2 and 5 drops of insoluble organic compound.
I've found that OTC H2O2 has a pH of roughly 5.5 - 6.5 being that it is stabilized with phosphoric acid (a few brands were more acidic then
others). So there is acutally no need for acid addition. In the test tubes, addition of 1-3 drops of concentrated H2SO4 helped things but addition
of 4+ drops actually decreased the rate significantly (as is shown on the graph on that site I link to). I am also messing with using boric acid to
decrease the pH considering a saturated 5% solution has a pH of ~5.5 which would be great. Additionally, does anyone know any easy to prepare buffer
that I could use to keep the pH in the region from 3 - 6 ?
The rate of the reaction is directly determined by the amount of FeCl3 added (1 or 2 drops is good, three is fast and four is too fast and makes the
mixture too hot) and the reaction is also much much faster if the peroxide is more concentrated 3 - 6% works good.
I ran four tubes at a time, varying one reaction condition each time. I also noted as have other people working with this mixture that heavily
chlorinated organics (perchloroethylene) are decomposed with great difficulty with Fenton's reagent wereas aromatics and such are decomposed
readily. The most major item of importance though is the surface area of the insoluble organic compound (note that this of course does not apply to
soluble organic compounds). A large flat bottomed dish would be ideal.
I've also tried other transition metal catalysts such as copper and nickel salts with limited success, even the journals state that reactions
using copper salts are less useful then using iron salts for the catalytic effect. Still though I need to try a number of other things in order to
fully acertain the best reaction conditions for applying Fenton's reagent for the disposal of waste materials generated at home and it is
extremely promising that OTC 3% H2O2 works so well.
Correction to my first post, it is a Ni/Al alloy under basic conditions that eats chlorinated organics.
[Edited on 5/30/2005 by BromicAcid]Nerro - 30-5-2005 at 11:20
Quote:
Correction to my first post, it is a Ni/Al alloy under basic conditions that eats chlorinated organics.
As in raney nickel?BromicAcid - 30-5-2005 at 16:46
Wouldn't the solid left after reaction of the alloy be raney nickel, and not the inital solid itself? It's the actual dissolution of this
alloy that reduces the organics as I understand it, something like carbon tetrachloride going to methane and sodium chloride for the most part.
Being that the reaction between nickel and aluminum is exothermic (for examples see the bimetallic fuse thread) wouldn't the preparation of this
alloy be simple providing one has nickel and aluminum powder?Pyridinium - 31-5-2005 at 07:20
Quote:
Originally posted by BromicAcid
Additionally, does anyone know any easy to prepare buffer that I could use to keep the pH in the region from 3 - 6 ?
[Edited on 5/30/2005 by BromicAcid]
hi Bromic,
Any buffer I could think of offhand would either be destroyed by Fenton's or would complex the iron and ruin the activity. Citrate, succinate,
propionate, acetate, etc...
Am going to have to see if there are any completely inorganic buffer systems that would work in the low range you want. Borate-boric acid is no good
for that range.
Then there's the problem that some of the inorganic buffer species would be oxidized and ruin the buffer anyway.
One of the phosphate combinations might work at a pH around 5.5 to 6. Maybe NaH2PO4 or something? Off the top of my head, however, I'd say
don't mix any more phosphates into that witches brew than are already in there at the get-go. Who knows what could volatilize...IPN - 18-6-2005 at 02:42
Into a 2000ml beaker was placed 10g of FeCl3 and 300ml water. pH was set to 2 by HCl and 200ml 35% H2O2 was added. This resulted in lots of fizzing
and the orange solution turned black. ~150ml of organic waste (mostly octanol, chloroform, benzene and toluene) was carefully poured in and the beaker
was put into a 20l plastic bucket. Vigorous bubbling started nearly immediately and lots of water vapour mixed probably with some of the organics
(there was the bad smell of octanol..) rose from the bucket. Water was poured into the bucket to cool down the beaker. After ~2min the bubbling
stopped and I was left with a very hot and clear orange solution. I’ll allow it to cool down and then make the pH basic to precipitate the iron.
This seems to be a good way to dispose of organic waste that can't be disposed in other ways (pouring down the drain is not that good idea..).
hydrargirum - 4-7-2005 at 17:45
With regard to reagent of Fenton, there am a small variation here that allows to prepare
Benzaldehyde from benzyl alcohol
H2SO4 to 20% with H2O2 to 9% is mixed and benzyl alcohol and soon begins the reaction with the aggregate of a piece of iron (nail). Vigorously shaking
(magnetic) the mixture it is warmed up spontaneously and it acquired a rusty color
If the mixture is necessary it cools if too much exotermic.Finished becomes the reaction great part of the iron dissolves and smells pleasantly of
benzaldehyde.
If more water to the solution is added and distills obtains the benzaldehyde one that can be saturated with NaHSO3 and shaking and cooling aduct of a
pearl-white color is obtained, by acidification of this one is obtained benzaldehyde pure.Organikum - 25-4-2006 at 01:21
hydrargirum would you kindly disclose the ratios, say the amounts of H2SO4, H2O2 and benzylalcohol used in your experiment?
regards
/ORGhydrargirum - 27-4-2006 at 20:43
The experiment was made to way of test or approach
Stoichiometric amounts according to:
C6H5CH2OH + H2O2--------> C6H5CHO + 2H2O
( ±14 cc C6H5CH2OH
±35 cc H2O2 9%
40 cc H2SO4 20% in excess )
piece of iron ±1.5g (nail)Sandmeyer - 29-4-2006 at 11:53
and prepricate same Fe(OH)3 ?