Sauron
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Easy Route to Thionyl Chloride SOCl2
Thionyl chloride is not an easy compound to prepare. The classical method is a pressure reaction involving oxidation of SCl2 and/or S2Cl2 with SO3 or
oleum (60%) while chlorine is introduced, the reaction takes 40 hours. Not a bench scale proposition.
A more recent method involves cycling a mixture of SO2Cl2 and PCl3 through activated carbon at a controlled temperature to give POCl3 and SOCl2 which
can then be fractionated. It is possible to set this up on a bench scale but PCl3 is hard to come by.
I just ran across an old JACS article by a Monsanto chemist who mentions that SO2 reacts at elevated temperature with phthaloyl chloride to give
phthalic anhydride and SOCl2. This is catalyzed by a small amount of ZnCl2 and is the reverse of one prep of phthalyl chloride (from the anhydride
and SOCl2 w/same catalyst.) Isn't that nice?
I have spent a lot of time investigating workarounds for SOCl2 and found quite a few but for some reactions it is still the reagent of choice. As
phthaloyl chloride is cheap and available, and SO2 easy to generate, this should be useful.
Kyrides, JACS 59, 206 (1937)
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Ozone
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Howdy, Sauron!
I've been out for a while--attacked by wasps---ran like hell--tripped--fell--broke arm. Bummer.
One handed typing sucks.
COuld you not add the acid you want (to make an acid chloride) to your phthaloyl chloride to perform the shift? Or, is the phthaloyl chloride far more
stable than your desired product? Ifit is, your product is probably more volatile, and the equilibrium could be pushed by distilling off your product
under vac.
Still, you rxn is interesting (I love the old stuff).
\
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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solo
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Here is an old thread on the subject..........solo
https://sciencemadness.org/talk/viewthread.php?tid=1439&...
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Sauron
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Indeed, @O3, phthaloyl chloride has been used to make acid chlorides in just that way. However it is about 6X more expensive than another high boiling
acyl chloride (benzoyl chloride) that does same job. The cost difference is partially offset by the fact that you need 1.5 to 2 molar equivalents of
benzoyl chloride to get optimal (90%) yields, whereas the "excess" is built in as it were, to phthaloyl chloride.
I posted an H.C.Brown JACS article about this a while back.
Or someone did anyway.
The Kyrides article on phthaloyl chloride is referenced from it and also in JACS.
The benzoyl chloride route appears at first to be better of the two.
I am studying the economics of both methods now in comparison with three TCT routes to acetyl chloride.
Phthaloyl chloride is competitive in cost if and only if you prepare your own, which is best done from cheap phthalic anhydride and benzotrichloride.
This reaction catalyzed by 2% AnCl2 produced almost quant yld of phthaloyl chloride along with benzoyl chloride (!) as by product.
While that prep is relatively slow and best done overnight, the chlorination of volatile carboxylic acids with either benzoyl or phthaloyl chloride is
fast (1 hr or less) and in fact best yields are obtained when distillation (through a short column) is done rapidly. As rapidly as possible without
letting temp at stillhead exceed the bp of the acyl chloride being formed.
Also in both cases the pot reside can be recovered efficiently and is benzoic acid, or phthalic anhydride.
While benzoic acid can be chlorinated with TCT benzoyl chloride is so cheap that it is hardly worthwhile to do so. Just save the benzoic acid for a
rainy day.
Phthalic anyhydride though is rife for reacting with benzotrichloride again.
So you see these are rather neat processes.
And quite general.
My economics comparion with TCT methods for AcCl is not yet complete. TCT appears to be the winner hands down but, other factors will tend to level
things off. Two of the three TCT methods (the solventless ones) are slow (8 hrs) and require 100 C so electricity costs will need to be factored in.
The third uses acetone as solvent, TEA as acid trap, and proceeds without heating at RT in 3 hours. However large reactors will be needed to produce
the quantities needed (by @hector2000 anyway) and while the acetone and TEA can be recovered and reused this does impose some cap.costs.
Finally I need to get @hector to obtain bulk quotes at his location before I can make meaningful comparisons because 1 L and 2 L prices mean little
compared with price per L when you buy a 55 gal drum. He buys Merck for synth grade AcCl that way for $6/L while 1 L from Acros is $70. If I do my
calcls on basis of small pack, I'll just scare him off.
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Sauron
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@solo thanks. Having looked at that thread I see it petered out in 2005 and that it contained a lot of twaddle from clueless members no longer active,
si will resist the temptation to merge this with that. I did not see any mention of pthaloyl chloride. So this is virgin territory so far as I can
tell. Even though the refs are 70 years old.
*rant mode*
One poster said that thionyl chloride is made by mixing SO2 and Cl2 in camphor or GAC. That's sulfuryl chloride not thionyl chloride.
And he said the product slowly hydrolyzes to H2SO4. Wrong! SO2Cl2 is in equilibrium with its components. SOCl2 hydrolyzes to SO2 and HCl. Those are
also the products of its use to chlorinate acids.
Plus there was a lot of guff in that old thread about terrorists. The famous use of SOCl2 to make mustard was by NATIONS not terrorists (Germany WWI,
Iran/Iraq). The chlorination of thiodiglycol can and has been done by HCl conc (so ban muriatic acid, huh?) and many other reagents. The demonization
of thionyl chloride is silly shit. What it's about is quite a few countries feel guilty about having SOLD TDG and thionyl chloride in vast quantities
to Saddam and to the ayatollahs for years knowing perfectly well what they were doing with it. In fact it was POLICY to make sure both got all the
toys they wanted so that neither side could gain advantage. Balance of terror. War of attrition. Iran mostly was supplied out of Asia (Japan, China,
transshipped via Singapore) while Iraq was supplied out of Europe and USA. A now defunct Baltimore MD company was one of Saddam's biggest TDG
suppliers along with a French govt owned oil subsidiary (part of Total) that ironically owns the US company's assets. The Germans and Brits had a big
stake in this too. The gory details are all well known in the business.
*end rant mode*
Here's the lit. procedure:
107 g phthaloyl chloride (94% pure) and 2 g ZnCl2 are heated to 100 C. A slow stream of dry SO2 is bubbled through the mix for ten hours. Distillate
is collected using tapwater cooling. Almost 45 g SOCl2 is collected; which after redistillation amounts to 39 g (66% of theoretical) As the pthalic
anhydrice left in pot was found to be essentially chlorine free it is believes reaction was actually quantitative but balance of SOCl2 was lost.
I'd put a cold trap or two and a CaCl2 tube to exclude moisture and try to get that other 20 g product.
Scale this by 10x20X and you obtain a useful amount of SOCl2 maybe 600 g.
[Edited on 14-4-2007 by Sauron]
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chemrox
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The benzoyl chloride method is so easy to use that any other method seems wasteful, harsh and expensive in comparison. I was going to use SOCl2 to
make acid anhydrides simply because I have it. You sure do end up with a bunch of benzoic acid though .. can it be recystallized from EtOH?
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chemrox
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Following on that line .. isn't it true that acid chloride plus acid yields anhydride? I cna't find a clear, concise writeup on doing it this way.
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Sauron
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Acid chlorides + sodium salts of same carboxylic acid = acid anhydride and NaCl, yes, see Vogel's 3rd ed (Practical Organic Chemistry).
How general? Limitations?
Oxalyl chloride + acid -> acid chloride + CO2 + CO
Oxalyl chloride + acid chloride -> acid anhydride + CO2 + CO
Which means that depending on proportions you can prepare either the acid chloride or the anhydride in very pure form and quant yield from the acid
and oxalyl chloride, as demonstrated by the great Roger Adams in a classic series of articles in JACS between 1916 and 1920. This is a special case
of the rxn you are asking about due to th special nature of oxalyl chloride which is truly wonderful stuff. Costly though.
Oxalyl chloride is best at making acid chlorides and anhydrides from aryl carboxylic acids, this is nearly quantitative. It has trouble with certain
acids cintaining phenolic groups in the ring, and others with nitro groups in the ring. In some cases a workaround is to employ the Na salt of the
acid instead of the free acid.
With aliphatic carboxylic acids oxalyl chloride gives lower yields in 50-70% range and produces a mix of anhydride, acid chloride and unreacted acid
instead of a pure product.
--------------
Here is prep of phthaloyl chloride along with benzoyl chloride:
225 g phthalic anhydride and 290 g benzotrichloride are mixed with 20 g anhydr. fine ground ZnCl2 and heated on an oil bath at 110-120 C for 20 hours
(overnight).
The mixture is then fractionated at 23mm and the following fractions obtained:
Benzoyl chloride 201 g 90-95 C (theor. 208 g)
small intermed. fract. 8.8 g <138 C
phthaloyl chloride 287 g mostly 150-152 C (theor. 308 g)
The pot residue (Zn catalyst) was found to still be active so a fresh charge of benzotrichloride and phthalic anhydride can be added and process
repeated.
It was found that zinc dust or zinc oxide could be used in place of zinc chloride as the latter is formed in situ.
If amount of zinc chloride is reduced from 20 g to 2 g the temp must be upped to 200 C to maintain same rate of reaction.
Since both benzoyl and phthaloyl chlorides can be used to convert acids into volatile acid chlorides, this is a very productive process. Phthaloyl
chloride is expensive to buy but phthalic anhydride is dirt cheap and benzotrichloride reasonable.
[
[Edited on 15-4-2007 by Sauron]
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Ozone
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Toward anhydrides, SOCl2 and pyridine is a legendary dehydration reagent. This is why you want to make doubly sure that all of the SOCl2 has been
removed from your acyl chloride before adding your pyridine and hydroxyl, amine, etc. (or, you get anhydrides and/or black crap).
See Fieser and Fieser 1st Ed.
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Sauron
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Volatile acid chlorides (those with bp's sufficiently under that of the benzpyl chloride or phthaloyl chloride, to seperate cheanly through a short
fract. column) prepared by those methods will contain a lot of dissolved HCl gas. They need to be refractionated, cautiously at first to get the HCl
out.
Oxalyl chloride is too bloody expensive to be practical most of the time. Acros wants $320 a Kg. By the time it is shipped and taxed into Thailand it
will cost me $600 a Kg. So I priced out making it myself. The cheapest route is from TCT and anhydrous oxalic acid in acetone w/TEA and yld is only
52%
Works out to about $200 a Kg product. A Kg anhydrous oxalic acid is $60 and is 11 mols. A Kg TCT is $35. 5 mols. So two of thpse are needed. (This
process only uses the two most labile chlorines.) 52% is only going to yield 450 g or so so I have to multiply $130 x 2.25 = $290 and that is still at
ex factory cost. That means there's no advantage to making your own, and this is by far the cheapest method. Want to price it out using PCl5?? No
thanks.
There are some things oxalyl chloride will do that few other things will do. So there's no choice.
But acid chlorides and anhydrides are not among them.
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Klute
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Slightly off topic, but could benzoyl chloride be used to make p.toluenesulfonic chloride? IIRC benzoyl chloride is easily made from benzoyl peroxide,
no? methyl/ethyl tosylate would be the target compound,, gentle less harmfull efficient methylation/ethylation compounds... The only way around is
with orthoformate :S
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Sauron
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I'd make benzoyl chloride from benzoic acid or sodium benzoate if the prices weren't so close as to make this absurd. Na benzoate anhydrous $20 Kg,
benzoyl chloride $30 Kg. You'd lose money chlorinating it, rather than buying it.
Never heard of making it from the peroxide.
p-tosyl chloride boils at what temp? Vogel has a prep for it but I forget his reagent. Hopefully not chlorosulfonic acid, which is unobtainium here.
Actually I think that was reagent of choice for sulfonyl chlorides...the reagents for acyl chlorides may not work.
Here chlorosulfonic is under military control, why? because of use as a smokescreening agent (called FS when combined with SO3) You can make it from
HCl anhydr and oleum but it's exothermic and nasty.
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Klute
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I think i remeber about it been a side product when making perbenzoic acid from benzoyl peroxide in cholorform with Na Mehtoxide, but I'm not sure.
Maybe I'm confusing with another procedure.
I did check the bp of ts chloride, but it's the key reagent to form methyl and other tosylate esters.. in pyridine IIRC, or with Et3N... It seems
unlikely that it could be made in small amounts form methanol and PTSA unfortunaly...
Yes, cholorsulfonic acid is watched here too, never really knew why execpt from it been dangerous, but there's worse.. It's needfull in the
synthesis of Silica Sulfuric Acid wich is a great versatil catlyst/reageant... I tried making some by refluxing silica gel in conc. H2SO4, as I found
a doc about "sulfruic treated silica" which basicly said it their anaylsed product had a sulfonic acid/sulfuric ester bond from NMR. I guessed it was
the same coupound, but it seems much less effective, as only a little amout actually reacts to give SSA, most of the white solid been unreacted
silica...
And I think it chlorosulfonic acid is used to prepare tosic chloride, maybe SOCl2 could work.
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