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Author: Subject: Acetic anhydride preparation
Sauron
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[*] posted on 26-2-2008 at 17:53


count on Aldrich applying a packing surcharge, and doubtless, Hazmat charges will also be applied.

Anyway the online price at Aldrich Singapore is $142 Sg$ which is over $100 US and that would just increase again by the time it gets to Bangkok, Aldrich is way overpriced here and I never buy from them if I can get it elsewhere. Acros and Merck are much more reasonable.

Let me reiterate: SiCl4 is NOT a general chlorinating reagent for acid chlorides. Yields are competitive only for acetyl and benzoyl chlorides (85% and 77%). With other acids yields were less than 50%, often 30%. For pyruvic acid and all tested dicarboxylic acids no reaction occurred.

SiCl4 reacts with anhydrous sodium acetate to give acetic anhydride directly, in 75% yield, but only in presence of a substantial amount of Ac2O as diluent. If benzene is substituted as diluent, yield drops to 50%. So, benzene can be used in initial procedures, and Ac2O so obtained can be used in subsequent runs.

[Edited on 27-2-2008 by Sauron]




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[*] posted on 26-2-2008 at 19:09


The article is here, I think it has actually even been referred to in this topic (if anyone wants to look)

Montonna, 'Silicon Tetrachloride as a Reagent for the Preparation of Acid Chlorides' (1927) 49(8) JACS2114: http://tinyurl.com/2l7u56

Quote:
Preparation of Acetyl Chloride.-Three hundred and sixty g. (six moles) of glacial acetic acid and 672 g. (six moles) of toluene are placed in a liter, round-bottomed, Pyrex flask fitted with a rubber stopper through which passed a dropping funnel and a reflux condenser. The upper portion of the latter is filled with glass beads and the condenser itself is, in turn, connected to an absorption system consisting of two washbottles containing acetic acid. The mixture is heated to 50' and at that temperature 510 g. (three moles) of silicon tetrachloride is added from the dropping funnel during a period of 30 minutes. The same temperature is maintained until the vigorous evolution of hydrochloric acid almost ceases. The upright condenser is then replaced by a Glinsky or Hempel column carrying a thermometer and attached to a downward condenser, and the product fractionated over a free flame until the thermometer registers 80-85 ".

The product on redistillation gives 400 g. of acetyl chloride, b. p., 50-55"; yield, 85%.



[Edited on 26-2-2008 by LSD25]




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[*] posted on 26-2-2008 at 21:42


The article was cited upthread by S.C.Wack, requested by me, and posted in References by jokull. There is no need to cite it again. Anyway the more interesting reaction contained in same article, giving Ac2O directly, rather than AcCl, is as follows:



130 g (1.6 mols) anhydrous sodium acetate in 300 ml acetic anhydride as diluent is warmed to 50 C, and 67 g (400 mmol)SiCl4 is added with stirring over a period of one hour. The temperature rises to 80 C. Heating and stirring are continued for three hours at 90 C.

Yield 75% of 96% acetic anhydride.

Same reaction with benzene as diluent: stirred 5 hours at 50-60 C, 50% yield.

I would be inclined to try a higher boiling diluent than benzene, such as toluene or xylene, and see whether yield improves.

The usual cavetas apply regarding anhydrous sodium acetate. It is preferable to start with a freshly opened bottle of commercial anhydrous NaOAc, in which case a single melting will suffice. Starting with the trihydrate, the material must be fused twice, the second fusion being done cautiosly so as to avoid charring (loss of material.) A forced air, temperature controlled drying oven is a major convenience in this process.

If you use your SiCl4 to make AcCl, you still need to react that with anhydrous NaOAc to obtain Ac2O.

Better to go straight for the anhydride.

If you have no Ac2O to use as diluent, then do a couple runs using benzene (or IMO, better toluene or xylene.) Then you will you have some of the preferred diluent.

I'm going to have a look at S.C.Wack's other citation, re Si2OCl6 ("silicon oxychloride" but without any real hope of practical advantage over SiCl4.

This material is much more difficult to come by, as far as I can determine it is commercially unavailable. As the paper states on its first page, its preparation is far from easy, yields are low, and seperation of the desired product from higher oxychlorides of silicon very difficult. The claimed yield of 82% of acetic anhydride from sodium acetate (anhydrous) is only a little better than that obtained from SiCl4. So unless there are some surprises in the paper, it's a non-starter.

[Edited on 27-2-2008 by Sauron]




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[*] posted on 27-2-2008 at 03:22


The reason why I said "if you happen to have some around" was because AFAIK it is no easier to prepare than SiCl4. It seems that in the preparation of mixed oxychlorides in the article, SiCl4 was in fact the main product. Just mentioned it as summing up what I've got on acetic anhydride from Si cpds.

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[*] posted on 27-2-2008 at 03:43


Yes, S.C> I figured that was what you meant. As it happens SiCl4 is rather easy to purchase, and not *too* expensive at $100 a kg. With a price like that I would not consider making it. After all I am paying a lot more for oxalyl chloride (a LOT more) and while I could make that, I don't bother.

The stoichiometry of SiCl4 in reaction with anhydrous NaOAc makes it attraactive, one mol SiCl4 plus 4 mols acetate giving theoretically 2 mols anhydride and in practice, 1.5 mols.

That helps compensate for the cost of reagent.

Si2OCl6 on the other hand seems to be unobtainium commercially.

Pity that SiCl4 is not more generally applicable to the preperation of acyl chlorides and anhydrides.

Anyway thanks for all the assistance.




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[*] posted on 27-2-2008 at 05:37


To S.C. Wack, I honestly thought that you were referring to and citing a different article

Here is the one I was thinking of:

Quig & WIlkinson, 'Preparation of Disilicon Hexachloride' (1926) 48(4) JACS 92: http://tinyurl.com/23fj3t

It does not actually fit here and I am more than happy to shift it if that is required, although I wanted to put it here as it fits (or so I thought) with the discussion.




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[*] posted on 27-2-2008 at 06:30


Silicon tetraacetate is, according to the first JACS paper above, the initial product of reaction of 4 parts glacial acetic acid and one part SiCl4, byproduct being 4 HCl.

Silicon tetraacetate is commercially available, but sold in small packaging only (10 g) for several dollars a gram.

Si(OAc)4 reacts with equimolar SiCl4 to give 4 AcCl. If this stuff were available in qty and not too expensive then the preperation of AcCl could be done without use of anhydrous NaOAc, with its tedious and persnickety fusions. Alas this seems unlikely.

Preparation of Si(OAc)4

Four moles glacial acetic acid and 1.5 moles SiCl4 in 200 ml abs. Et2O are refluxed 48 hrs in a dry apparatus with exclusion of moisture. After standing in the cold a further 48 hrs, the precipitated crystals are collected in a dry box, and a second crop collected after concentration of the mother liquor. Yield 70 g or 30% on GAA basis.

The product is extremely hygroscopic.

It can be efficiently prepared from Ac2O and SiCl4, but that is useless for making Ac2O. The byproduct is AcCl.

Si(OAc)4 reacts with SiCl4 to give 4 mols AcCl per mol.

So that is you have lots of SiCl4 and GAA this is a pretty good way to make AcCl.

Of course, you need not bother to isolate the tetraacetate at all, just proceed as in the JACS article and you get a much better yield in a single step.

[Edited on 28-2-2008 by Sauron]




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[*] posted on 27-2-2008 at 10:50


Hm, so to make this useful one would need a good source of dry chlorine, a tube furnace, and some silicon powder.
Silicon is fairly cheap, chlorine is easy to make, but some of us here do not have access to a tube furnace.

I am seriously considering running this reaction--it looks very easy to do.




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[*] posted on 27-2-2008 at 11:07


Tube furnaces are not that hard to make either. Basically, you wrap some resistance
wire around a tube and insulate it. What material is suitable for the tube and what
wire can be used are determined by the temperature you are trying to reach. (By the
way, what temperature is needed for your reaction between Si and Cl2?) Brauer's
Handbook of Preparative Inorganic Chemistry, which is available in the SM library, has
a detailed discussion of how to make a tube furnace. Also, since it is a resistive
device, you can use a lamp dimmer to control your tube furnace.
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[*] posted on 27-2-2008 at 14:13


:-) By some of us I did not mean me, I have several that I can use. Soon I'll have a very nice one at home too.
Brauer, which I have downloaded a long time ago (excellent text!!) should have information on SiCl4. If not, I can simply ramp up the heat until I see the SiCl4 condensing.


I need to get a kilogram of silicon powder first. I have already the reaction vessels.




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[*] posted on 27-2-2008 at 14:55


Quote:

:-) By some of us I did not mean me, I have several that I can use.


That comment was mean for those people you referred to as "some of us",
not for you :)

According to Brauer, the temperature required is 400C. Thus, heating it should
not be a problem --- even without a tube furnace, putting a burner under the tube
containing the silicon or some such thing should work. However, because
SiCl4 decomposes easily upon exposure to water, one must take care to
rigorously exclude water from the system. Brauer suggests drying the chlorine
by passing it through sulphuric acid and placing a tube of CaCl2 where the
system communicates with the atmosphere.
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[*] posted on 27-2-2008 at 19:54


I don't get excited about making something that only costs ten cents a gram, not if it is not the end product, and not if I can purchase it easily.

No one is looking over anyone's shoulder for buying silicon tetrachloride. This is NOT true of:

thionyl chloride,
sulfuryl chloride
sulfur I or II chloride
phosphorus III or V chloride
phosphorus oxychloride
arsenic trichloride

Oxalyl chloride costs 6X as much

So SiCl4 is useful, but just about only for acetic anhydride/acetyl chloride. It's not very good for most other acids than acetic and benzoic. As general reagents for this purpose, benzoyl chloride, TCT, phthaloyl chloride and oxalyl chloride are still on top, and in approximately that order. Thionyl chloride, if you can get it, is a good general reagent for acid chlorides higher than C3. Same for POCl3, but you will have DHS breathing down your neck. Sniffing around for tabun nerve agent. Well, no one cares about SiCl4.

I noticed a peculiarity in the primary lit. on this reaction.

In the 1927 JACS article, the authors used 6 mols of glacial acetic acid to 3 mols SiCl4 in 6 mols toluene as diluent, and warmed the mixture to 50 C till HCl evolution was almost over. Fractionation then gave 85% acetyl chloride. The reaction was describedas occuring in two steps as follows:

4 AcOH + SiCl4 -> Si(OAc)4 + 4 HCl
Si(OAc)4 + SiCl4 -> 4 AcCl + 2 SiO2

Reaction time is not given but in the reaction of SiCl4 with anhydrous NaOAc, times of 3-5 hours were reported, with yields up to 75% of acetic anhydride.

Compare the procedure described in Brauer, p.701 for preparation of silicon tetraacetate from glacial acetic acid and SiCl4.

In this procedure, absolute Et2O was solvent, at reflux, time 48 hrs, followed by 48 htrs in the cold. Molar ratios 4 mols GAA to 1.5 mols SiCl4. Yield of 70 g from two crops is onoly 30% on GAA basis.

This is a large disparity in what should be the same reaction.

The use of 50% excess SiCl4 may have converted half the Si(OAc)4 to AcCl and SiO2 but that should have been obvious.

Or is the two step reaction accurately representing what is going on?

Why so long a reaction time in the Brauer procedure?

Would changing from ether to toluene be advantageous?

Reaction temperatures were only 15-or so degrees apart.

If the reaction of GAA and SiCl4 occurs as described, why not add only 1 mol SiCl4 to 4 mols GAA in solvent, then when HCl evolution ceases, add a second mol.

In the prep of Si(OAc)4, I'd be tempted to conclude that a lot of product must be left behind in the mother liquor still, if it wasn't converted to AcCl by that seemingly unnecessary 50% excess of SiCl4. I think I will look up Brauer's ref for that prep. I think it is Inorg.Syn. v.4.

[Edited on 28-2-2008 by Sauron]




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[*] posted on 27-2-2008 at 20:40


As not everybody has the time or the patience to go through the first half of the Brauer PDF book, The following quote was lifted from Braeur, Handbook of Preparative Inorganic Chemistry, pages 682-3 (pages 707-8 of the OCR PDF from the Library):

Quote:
Silicon Tetrachloride SiCl4

Si + 2C12 = SiCl4
28.1 141.8 169.9

Silicon (prepared as shown above) or coarsely ground ferrosilicon (which should contain as much Si as possible) is placed in a boat inserted into a Pyrex tube about 60 cm. long and 2-3 cm. in diameter, through which a stream of Cl2 is passed (Fig. 223). The Cl2 is predried over concentrated H2SO4. A condenser is attached to the other end of the tube by means of an adapter; the tube itself is heated in an electric furnace. The tube should incline toward the condenser to prevent the SiCl4 from backing up.

The condenser end of the reaction tube should project out of the furnace for some distance so that the invariable byproduct FeCl3 may deposit without plugging the condenser. The condenser discharges into a distilling flask which is set in an ice bath. All joints must be tight and the entire apparatus carefully dried before the start of the run. A CaCl2 tube is attached at the end of the side arm of the distilling flask. If this precaution is overlooked, the side arm will immediately be plugged with silicic acid produced by reaction with atmospheric moisture. The reaction tube is heated to about 400°C and the Cl2 flow is then started.

If, in addition to SiCl4, the higher Si chlorides are desired (Si2Cl6 and Si3Cl8), the temperature of the tube should be as low as possible, but no lower than just below 400°C. When the reaction is well established, heating may be sharply reduced since the reaction itself evolves considerable heat. The crude chloride, which is accumulated in the distilling flask, may be purified by fractional distillation. If an absolutely Cl-free preparation is desired, a second distillation over Cu turnings is performed. Both distillations must be run in absolutely dry equipment. The ampoules into which the SiCl4 is distilled should be fused to the distillation apparatus, since it is impossible to obtain a non-turbid product if this is not done. Yield is quantitative.

PROPERTIES:
Clear, colorless liquid; fumes heavily upon exposure to air. Rapidly hydrolyzes in water to form a SiO2 gel. Miscible with benzene, ether, chloroform and saturated hydrocarbons. Forms esters of silicic acid with alcohols. B.p. 57.5°C, m.p.-68C, d 1.52.


I could not get the picture, which simply shows the furnace (horizontal) connected to a condenser (vertical & orientated downward @ 45 degrees) to the receiver. The Cl2(g) coming in is dried in a vessel attached to the front of the furnace tube with H2SO4 and then comes into contact with the silicon in the furnace tube.

[EDIT] I wonder if the output from the tube-furnace could be led directly into a vessel containing NaOAc with toluene/xylene as diluent? This would save a whole lot of fucking around purifying the intermediates, which providing atmospheric water is excluded and the reagents are anhydrous to start with, should probably not interfere too much with the reaction itself.

[Edited on 27-2-2008 by LSD25]




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[*] posted on 27-2-2008 at 21:03


Quote:

As not everybody has the time or the patience to go through the first half of the Brauer PDF book


I didn't have the patience to go through it --- I simply looked up Silicon Tetrachloride
in the table of contents and jumped to that page. The total time required was under a minute.
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[*] posted on 27-2-2008 at 21:13


I have a very fucking slow connection (as do others) and simply had to wait for the pages to load and go through one at a fucking time. Talk about a headfuck.

PS The same slow-arse connection precludes me downloading the same and looking on the desktop - I have had 4 or 5 goes at downloading this particular book, all of which have been interupted as a result of the idiotic slow transfer rate.




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[*] posted on 27-2-2008 at 22:50


For silicon tetraacetate, the Brauer pages start at 701 and the original reference is to Inorg.Syn. IV P.45 for the prep from Ac2O, which is circular and therefore useless for purposes of this thread. The reference for the alternative prep from GAA is (I think) Z.Anorg.Allg.Chem. 272, p.313 (1953) the title of which is ON TRICHLOROSILICON ACETATE.

What we normally do when lifting a prep from a pdf is to use Acrobat to make a new pdf from the specific page range and then post that, the new relatively tiny pdf comes complete with the illustrations. For example, here's the SiCl4 section.

Brauer, and his references, also suggest that SiCl4 reacts with heavy metal acetates, such as thallium (I) acetate to give the silicon tetraacetate. Now, kiddies, don't muck around with thallium compounds. I am merely speculating that perhaps some less dramatically toxic heavy metal acetates such as those of Hg or Pb etc, might be more cost effective in this capacity and less likely to result in premature termination of life functions.

[Edited on 28-2-2008 by Sauron]

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[*] posted on 28-2-2008 at 04:12


When it was asked in the acetaldehyde synthesis thread lately what exactly acetaldehyde was good for, my first thought was of acetic anhydride. This was mentioned earlier this month in this thread, some patents are cited, and I just thought that I'd toss out three more patents for the hell of it.
DE699709
DE708822
US2259895
I don't look up many DE patents from 1933-1945, so just now noticed that the swastika on the documents is blotted out. Oh please.
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[*] posted on 28-2-2008 at 04:56


I remember reading an article on the production of acetic anhydride from acetaldehyde via peracetic acid somewhere once before.

I thought I had saved the article, but I cannot find it - although I can find references to it. Anyway, here is the stuff I do have:

Zeyer, et al, 'The behavior of the iron(III)-catalyzed oxidation of ethanol by hydrogen peroxide in a fed-batch reactor' (2000) 2 Phys. Chem. 3605: http://tinyurl.com/3cvbkq

Acetic Acid by oxidation with Peroxide over Iron Hydroxide: http://tinyurl.com/32zgq6 (this like the preceding article, gives a mixture of acetaldehyde and acetic acid)

Chemicals from Acetaldehyde (1959) 51(12) Ind Eng Chem: http://tinyurl.com/2rvhh9 (a quick overview of the chemicals produced from acetaldehyde)

Philips, et al, 'A New Synthesis of Peracetic Acid' (1957) 79(22) JACS 5982: http://tinyurl.com/2nabdc

Here is an overview of the industrial synthesis:

Klaus Weissermel & Hans-Jürgen Arpe, Industrial Organic Chemistry: http://tinyurl.com/363tty

Now, I suspect that I have lost (or at least cannot find - same thing) the article I was thinking of, although this one looks something like it:

C. E. H. Bawn, T. P. Hobin & L. Raphael, 'The Metal-Salt-Catalyzed Oxidation of Acetaldehyde' Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 237, No. 1210 (Nov. 6, 1956), pp. 313-324: JSTOR abstract is here: http://tinyurl.com/3528f6 (they also cite another article to a similar effect).

I have wondered about whether this was something that could be harnessed before, but it appears to have been ignored.

Oh, here is the article I was thinking of:

Carpenter, 'Oxidation of Acetaldehyde to Acetic Anhydride' (1965) 4(1) J. Industrial Engineering & Process Design 105: http://tinyurl.com/2atk64 [Thanks due to Solo for this article]

[Edited on 28-2-2008 by LSD25]

[Edited on 28-2-2008 by LSD25]




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[*] posted on 28-2-2008 at 04:56


Ullmann's on SiCl4 is interesting. Anyone contemplating running this prep should have a look.

To recap this section on SiCl4 and its utility in making AcCl or Ac2O directly, SiCl4 is very efficient at chlorination of anhydrous acetic acid in high yield and almost as efficient in the preparation of acetic anhydride from anhydrous sodium acetate (or potassium acetate).

The best price I found for SiCl4 was from Alfa, who sell a liter for $70; a liter weights about 1500 g so this is somewhat less than $50 a Kg. That is about 9 mols SiCl4.

According to the stoichiometry and yields presented in the 1927 JACS paper cited upthread, that is sufficient to prepare about 1200 g of AcCl.

Or, by direct reaction with anhydrous sodium acetate, sufficient to obtain 13.5 mols acetic anhydride. Roughly 2 Kg.

The over all reaction of SiCl4 and AcOH is

2 SiCl4 + 4 AcOH -> 4 AcCl + 4 HCl + 2 SiO2

and it proceeds in 85% yield on AcOH basis

The reaction of SiCl4 with anhydr. NaOAc is

SiCl4 + 4 NaOAc -> 4 NaCl + 2 Ac2O + SiO2

and proceeds in 75% yield. So for every mol SiCl4 used, we get 1.5 mols Ac2O, when Ac2O is used as diluent, or 1 mol Ac2O when benzene is used as diluent.

It is obvious that if Ac2O is your target, it is better to get there in one step.

Commercial silicon tetraacetate hovers around $1 a gram in 100 g packing for tech grade (Fluorochem) and so is out of range of economical utility.



[Edited on 29-2-2008 by Sauron]




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[*] posted on 29-2-2008 at 00:50


Merck SICL4 is 56$ per liter(cheap than Alfa)
If you order drum(190kg) it will be cheaper.
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[*] posted on 29-2-2008 at 04:25


Good news for you, then.

If you get a quote for the drum, let me know what it is.

It's also good news for me since Alfa has no representation here but I buy from Merck regularly.

SiCl4 is quite moisture sensitive. You had best plan to handle it in such a fashion that it does not come into contact with any atmospheric moisture. For Kg quantities a dry box (glove box) with dessicant and a N2 purge would be best.

[Edited on 29-2-2008 by Sauron]




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[*] posted on 24-4-2008 at 07:58


http://v3.espacenet.com/origdoc?CY=gb&LG=en&DB=EPODOC&IDX=GB424573&DOC=ce973ee58c33eea7621edc965e05ac7c23&QPN=GB424573

Has anyone seen this?

It's basically acetic anhydride from sodium bi-sulphate and sodium acetate, via the pyrosulphate!

Na2S207 + 2Na0Ac = 2Na2S04 + Ac20

It looks kinda interesting!

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[*] posted on 24-4-2008 at 08:53


'Sorry, I'll try another link!


]http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=GB424573&F=0&QPN=GB424573

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[*] posted on 24-4-2008 at 12:45


Duh. . .I noticed the method above was discussed earlier. . . it is a long thread!
I think it was tried unsuccessfully by a couple of members!
'Pity, it looked good at first glance, and if it actually worked it'd be a simple route for Ac20.

This thread seems to contain all possible routes, and they're all awkward!

AA, so desirable, but, what a bitch!

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Mood: nucleophilic

[*] posted on 26-4-2008 at 09:47


Despite the hazards, I say ketene and GAA is the way to go for making Ac2O. It is something you can run all day.

If you have the equipment to do it, it works.




Neither flask nor beaker.


"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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