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Sauron
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I wish it were that easy. No, P2O5 does not react with Cl2 at least not at ordinary temperature.
[Edited on 3-4-2008 by Sauron]
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Klute
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My bad. I though I had already read about it somewhere but i can't seem to find the post again... Too bad.
But is such a drying agent necessary? Wouldn't a deeper/second H2SO4 wash bottle suffice? I guess it depends on the flow of Cl2..
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Sauron
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How dry is dry?
As garage chemist pointed out if you are going to condense and bottle Cl2 in steel lecture bottles than the Cl2 must be scrupulously dry. Otherwise it
will attack the LB and eventually leak.
Also as others have pointed out, for some reactions Cl2 must be very dry or yields go to hell.
So it depends on your application. See Brauer for his drying train recommendations for chlorine.
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woelen
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| Quote: | Originally posted by Sauron
Thanks, woelen. Nice tips. So your advice is to just add the stoichiometric amount of conc HCl to TCCA at the start and let it go at that? You concurr
with len1 that stirring is unnecessary? |
My experience is best with half-concentrated HCl (15% or so), and then quite some excess must be used (two times as much as needed for the reaction).
If the TCCA is in the form of small granules (0.5 mm and smaller), then the production of gas is fairly constant, without the need to stir. The reason
that I use 15% and no 30% is the higher liquid volume, which allows the TCCA granules to move more freely (otherwise it is clogged and an unreactive
sludge covers underlying TCCA too much). Another advantage is that there is less HCl gas in the Cl2. I use the Cl2 directly after drying with CaCl2 (I
do not like to use expensive and rare stuff like P4O10, which costs me appr. EUR 20 per 500 gram, while anhydrous CaCl2 is just EUR 3 per kilo or so
and can be purchased at any hardware store).
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Sauron
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My TCCA is powdered not granular. I was given the choice, and chose powder. Did I upgefuck?
OK 50% conc HCl 50% water, and 2X excess, so with powder do I stir or not?
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evil_lurker
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Drop slooooowwwlly at first.
Once all added in start gentle heating.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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LSD25
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Do any of the links here suggest anything you'd like to explore:
http://tinyurl.com/38k7yo
Not sure if this one is here:
http://www.ics-ir.org/jics/vol4/n2/articles/jicsv4n2r1.pdf
Then there is also this one, the conversion of amines to nitriles (regardless of phenolic OH's):
http://www.organic-chemistry.org/abstracts/literature/275.sh...
Also, TBCA (I assume from the bromination of cyanuric acid?):
http://www.organic-chemistry.org/chemicals/oxidations/tribro...
Apparently it is good for forming bromohydrins, bromoethers and bromoacetates.
Also, if you find it - what about the claimed reaction of TCCA with GAA in the presence of catalytic PCl3 (? or was it POCl3) to give AcCl? With that
sort of quantity and given that you already have shitloads of GAA, P, PCl3, POCl3, etc. and your interest in AA, this should be right up your street?
Whhhoooppps, that sure didn't work
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Sauron
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Thanks for the links.
The first one is only mildly interesting, as I am not sure why acylation with acetic anhydride requires much in the way of catalysis, and if it does,
the standard reagent is DMAP usually on prill support.
The primary amine to nitrile paper is more intereting.
Tribromoisocyanuric acid, mildly interesting.
I have not read the review of N-halo reagents yet.
I never heard of a purported TCCA chlorination of GAA to AcCl catalyzed by PCl3 or POCl3. Given the difficulty for most of us in obtaining those
"catalysts" I'd look elsewhere.
Anyway I'll take another look at these when I have some time.
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woelen
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Hmmm... how fine is your powder Sauron. I can imagine that if it is a really fine free flowing powder, that the reaction will be too violent. I don't
have experience with that. I have tablets, which I crush (first hitting with a hammer and then making smaller granules, 1 .. 2 mm size).
With these granules I have a nice smooth not too fast evolution of Cl2.
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Sauron
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The drum just arrived a few hours ago. I haven't opened it yet.
I have to get a suitable powder funnel and a large scoop to transfer this to my 10 L GL45 reagent bottles. Then Ill open the drum and let you know.
I figure, dripping the half-strength HCl onto the powder ought to work, I can control the reaction by the drip rate.
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Sauron
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The chloral patent I am basing my initial experiments on, calls for a pot charge of 200 ml 95% ethanol being chlorinated for initially 2.5 hours with
a flow of 3.5 g/min Cl2.
That works out to 525 g Cl2 in the first phase, which takes the ethanol to dichloroacetaldehyde. This starts at room temperature and by the time the
mixture reaches the calculated increase in mass and specific gravity, the mixture is refluxing under autogenous heat.
That is about 15 gram-atoms of chlorine or 7.5 mols Cl2. The ethanol was 3.37 mols. So far stoichiometric, so good.
The required TCCA charge for the chlorine generator for this phase is 2.5 mols plus some excess, so let's say 750 g and the HCl (half-concentrated)
1800 ml. Only experiment will tell me the correct addition rate to achieve the flow rate and time.
How many liters of Cl2 is 210 g/hr? Cl2 at STP has mass 3.214 g/L so 210 g is 65.34 liters per hour or just a little over a liter a minute.
The second phase calls for a somewhat slower rate of 2.5 g/min, for 8 hours. This is the final chlorination step to trichloroacetaldehyde, requiring
external heating to maintain reflux. The average reflux temperature by end is 95 C.
This is 180 g Cl2 per hour for 8 hours 1440 g Cl2. Clearly a lot of this chlorine is going to end up in the scrubber, and I mean beyond the 50% of
the reacted Cl2 that ends up there as HCl. It strikes me that this excess Cl2 can be utilized to chlorinate a second stage-1 reactor or even a third
and fourth (in sequence) as these only need 2.5 hours while the stage 2 reaction is 8 hours. This is worth some thought.
The 1440 g Cl2 is 20 mols and so requires 6.7 mols TCCA let's say 1750 g to allow for some excess.
How many liter is 180 g/hr Cl2? As above, 3.324 g/L so right at 56 L/hr or just a little less than a liter a minute.
I like the exploitation of the excess Cl2 in second stage to chlorinate an additional stage 1 reactor, this reduces demands on the scrubber and
reduces usage of TCCA while maximizing chloral yield.
Once again the end points is determined by mass gain and density.
This looks like FUN.
[Edited on 12-4-2008 by Sauron]
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