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Author: Subject: Acetic anhydride preparation
Sauron
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[*] posted on 14-10-2008 at 03:27


Well, I certainly concurr with your last remark.



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[*] posted on 14-10-2008 at 11:30


i know i am a bit late.
i read all the posts and just wanted to ask.
if i have some 500grams of red phophorus. a chlorine source and sodium acetate.
what should be my easiest route to acetic anhydride
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[*] posted on 14-10-2008 at 11:39


Save your red P for something else.

Is your sodium acetate anhydrous or is it the trihydrate?

If the latter you need to dry it. Honestly you are better off buying commercial anhydrous sodium acetate than messing with the trihydrate. The commercial anhydrous NaOAc needs minimal drying, or no drying. Do not open bottle till you are ready to use.

Now go back upthread and see my summary of your reaction options.

Next, do you have a fume hood?

You can prepare acetyl chloride from:

GAA and TCT (cyanuric chloride) in acetone in presence of TEA

GAA and benzoyl chloride (1.5 to 2 excess of reagent) per H.C.Brown in JACS

GAA and phthaloyl chloride per L.F.Kyrides in JACS

GAA or anhydrous sodium acetate and oxalyl chloride per Roger Adams in JACS

or from GAA and Ph3P in CCl4

Or you can go straight to Ac2) from anhydrous sodium acetate, bromine and sulfur; or from oxalyl chloride and anhydrous sodium acetate in different proportions than for preparing AcCl.

Most assuredly if I were to go to the trouble of making POCl3 I would not waste it on preparation of acetyl chloride for which so many other less precious reagents and simpler methods are at hand.

The same is true of thionyl chloride.

There arer several more mild neutral preps of acetyl chloride and other acyl chlorides, likewise described here previously.


With acetyl chloride and ANHYDROUS NaOAc you have the makings of Ac2O at hand.

[Edited on 15-10-2008 by Sauron]




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[*] posted on 14-10-2008 at 11:48


well yes first i have a fune hood, bought it from a friend who was moving. the sod acetate is anhydrous and unopened.
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[*] posted on 14-10-2008 at 11:52


yeah but i couldnt get my hands on any tct etc. i thought maybe since i had the phos i could use it . since i dont have any better use for it anyways
i might be able to get a bit of sulphur too
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[*] posted on 14-10-2008 at 11:56


In that case you have an ambarassment of choices of ways to make AcCl from GAA and then react AcCl with freshly fused anhydrous NaOAc.

Also a few ways to get directly to Ac2O from GAA or anhydrous NaOAc.

One of those is sulfur, bromine and anhydrous NaOAc. Details have been posted on here before. You get a pasty yellow muck but distilling gets you Ac2O out of that. It's an old Russian prep.




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[*] posted on 14-10-2008 at 12:03


could you come again on that one a little detailed
what are the expected yields etc
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[*] posted on 14-10-2008 at 12:06


If you insist on using your red P then with 500 g of that you can produce a few Kg of PCl5

With PCl5 you can produce oxalyl chloride from ANHYDROUS oxalic acid.

And with oxalyl chloride and anhydrous NaOAc (freshly fused) in the right proportions you can produce Ac2O.

Note that PCl5 and oxalyl chloride are no fun to handle. Gloves, goggles, hood.

[Edited on 15-10-2008 by Sauron]




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[*] posted on 14-10-2008 at 12:08


what about the Hell-Volhard-Zelinsky reaction , does it help and work here
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[*] posted on 14-10-2008 at 12:11


The HVZ reaction is for making alpha-haloacids not acid chlorides. Chloroacetic acid is of no use to you in making acetic anhydride. None at all.

Acetyl chloride is CH3C(=O)Cl

Chloroacetic acid is CH2ClC(=O)OH

The reaction you are after is CH3C(=O)Cl + NaOC(=O)CH3 -> (Ch3C(=O))2O + NaCl

[Edited on 15-10-2008 by Sauron]




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[*] posted on 14-10-2008 at 12:27


i just checked with a friend he has about 400grams sulphur powder. how do i go about from that
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[*] posted on 14-10-2008 at 12:36


You still need bromine.

The Russian prep of acetic anhydride takes Br2, freshly fused (melted then ground) NaOAc and sulfur,




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[*] posted on 14-10-2008 at 12:43


although i i think i can get oxalic acid, and proceed with the phos method. still what do you think about this method it does not require br.
synthesis, generating sulfur chloride in situ:Mix quickly and thoroughly 205-215 g of pulverized fine NaOAc and 10g dry sulfur powder, the mixture is quickly transferred to a wide-mouth 1 liter RBF and wetted w/25 ml acetic anhydride. Into the flask through the rubber cork extend 1) a wide tube for chlorine in-flow 2) an overhead stirrer, which is sealed with the aid of a piece of rubber tubing greased with vaseline and 3) an out-leading tube for excess Cl2 release. The flask is immersed in an ice-bath. Chlorine is initially passed in very carefully, with frequent stirring or shaking, over the passage of time the rxn gets hotter and more and more liquid, so the stirrer may bee after some time rotated with a motor. Chlorine stream should bee regulated so that almost all of it is absorbed. When the reaction mixture stops heating and Cl2 is no longer taken up, the rxn contents are distilled in vacuo at oil bath temp ~150-180°C, then redistilled at ordinary pressure, collecting the fraction boiling between 132 and 142°C. Yield ~90%.
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[*] posted on 14-10-2008 at 12:50


I think you would be better off preforming your sulfur chloride and I think you would be well advised knowing whether you need SCl2 or S2Cl2, and how to seperate these and convert one to the other. The in-situ proposition allows no such control.

S and Br2 do not share this problem as they can only combine one way.




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[*] posted on 14-10-2008 at 12:53


ok this i think is for s2cl2
Prepare 100g freshly fused NaOAc and 65g S2Cl2. A small quantity of NaOAc is placed in a thin-walled glass cooled in an ice bath. To this is added some sulfur chloride, the mixtr is vigorously stirred w/a wooden spatula, not allowing the temp to rise. Then some NaOAc is added again, and the process is repeated several times until all is mixed in. The semi-liquid mass is transferred into a 1 liter RBF. The previous operation is repeated 4 times, so that 400g NaOAc and 260 g S2Cl2 total are taken into work. The RBF is then equipped w/a reflux condenser and gently heated on a water bath to ~80-85°C. As soon as the rxn starts, the heating is removed, and in case the rxn gets too vigorous it's cooled w/cold water. After 20-30 min SO2 evolution ceases and the mixture is heated for 10 more min's on a boiling water bath. The rxn product is then distilled off under vacuum, then fractionally re-distilled at ordinary pressure, collecting the fraction boiling between 132-142°C.
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[*] posted on 14-10-2008 at 13:06


Yeah, people here read Rhodium too, you know?

I would advise you to do it all in a RBF and use mechanical stirring because the proposed transfer would be a nightmare.

And first you need to prepare S2Cl2 and purify it. See Brauer for details. It's no fun, you would be happier with Br2.




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[*] posted on 14-10-2008 at 13:17


ch3cooh+socl2=====ch3cocl +so2 +Hcl
The separation is simplified to an extent because the by-products are both gases. You would obviously still have to fractionally distil the mixture to separate the acyl chloride from any excess acid or sulphur dichloride oxide.
now the question is how do i make socl2
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[*] posted on 14-10-2008 at 17:56


Not one that I recommend. Did you come here for help, or to have some place to post these tired old hackneyed and half baked writeups from druggie sites? Like the page you drew all of these from?

http://www.erowid.org/archive/rhodium/chemistry/anhydrides.h...

Because this site is about chemistry not cookery.

Where do you intend to get SOCl2? It's not on anyone's "A" list for chlorinating reagents for the lower three acyl halides. See Vogel's remarks about this. SOCl2 is always used in excess, and the excess SOCl2 is too proximate to AcCl to easily fractionate. The same problem holds for PCl3 and POCl3, not that you can make PCl3 from your red P anyway, because you can't. Chlorination of red P gets you PCl5 only.

The government watches it closely in US because of its notorious use in production of certain chemical weapons. Making it is NOT easy, simple, or cheap.

Honestly, you sound like a ringer. Got 500 g red P huh? And a fume hood? But you can't get basic common and even OTC reagents.

Well, sunshine, go find another sandbox to play in. This one is foir the big kids.

I'm through with you.


[Edited on 15-10-2008 by Sauron]

[Edited on 15-10-2008 by Sauron]




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[*] posted on 15-10-2008 at 02:06


Quote:
Originally posted by Sauron "Fuming hydrochloric acid"? All hydrochloric acid (conc) fumes. The term is meaningless. Fuming sulfuric acid is any sort of oleum of which common concentrations of dissolved SO3 run 20 to 65 per cents. Fuming nitric acid is any sort of nitric acid above d.1.42 up to a bit over 1.50. Fuming hydrochloric? It's redundant.


Belated correction here. But in German "concentrated HCl" is 24-36% HCl (d = 1.12-1.18). "Fuming HCl" is 37-40% HCl (d=1.18-1.20). Both will work, but the latter is to the higher region of the concentration spectrum.

[Edited on 15-10-2008 by Formatik]
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[*] posted on 15-10-2008 at 02:44


Well, everywhere else, concentrated HCl is the solution of HCl and H20 as described in Merck Index, among other places, and the ACS documentation on their reagent grade chemicals. You will find that the concentrated acid is also defined by molar concentration. About 11.75M

Merck Index 12th Ed: Fumes in air. May be colored yellow by traces of iron, chlorine, and organic matter. Reagent grade concd hydro chloric acid contains close to 38.0% HCl. 83 ml of concd HCl poured into sufficient water to make 1 liter yields approx 1.0 N HCl. The pH of 1.0 N HCl is 0.10; of 0.1 N = 1.10; of 0.01 N = 2.02; of 0.001 N = 3.02; of 0.0001 N = 4.01. n D 18 (1.0 N soln) 1.34168 . d 4 15 1.05 (10.17% w/w soln); 1.10 (20%); 1.15 (29.57%); 1.20 (39.11%) . Freezing pt: minus17.14degrees (10.81% soln); minus62.25degrees (20.69%); minus46.2degrees (31.24%); minus25.4degrees (39.17%), Gmelin prime s, Chlorine (8th ed.) 6, 136-137 (1927). Constant boiling azeotrope with water bp 760 108.58degrees contg 20.22% HCl , d 4 15 1.096 . Boiling weaker or stronger aq solns results in loss of either component until the constant boiling acid is obtained. Density: d 4 15 1.05 (10.17% w/w soln); 1.10 (20%); 1.15 (29.57%); 1.20 (39.11%); d 4 15 1.096.

So if we follow your purported German standard then all reagent grade HCl is "fuming" hydrochloric acid" which is ridiculous, as in almost 50 years in chemistry that is a term I have never seen or heard till now. By the way Merck is a German company, isn't it? Ot should I say, nicht wahr?

[Edited on 15-10-2008 by Sauron]




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[*] posted on 15-10-2008 at 03:53


Quote:
Originally posted by Formatik
in German "concentrated HCl" is 24-36% HCl (d = 1.12-1.18). "Fuming HCl" is 37-40% HCl (d=1.18-1.20).


I also ran into that distinction. Some sellers (even OTC) seem to take it very seriously and like to specify the formal 'fumingness' of their product.
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[*] posted on 15-10-2008 at 04:09


The constant boiling (azeotropic) HCl/H2O system is only 20-22% HCl, so what the German "spec" means is anything over the azeotrope can be called "concentrated" while anything meeting or exceeding the reagent grade in rest of the world (where it is called concentrated)) is termed "fuming". ???

This is absurd and illogical. All hydrochloric acid over the azeotrope fumes, so what? Constant boiling HBr and HI certainly fume, nobody calls them "fuming hydrobromic acid" etc. Obviously the standard is for the convenience of the manufacturers, not for the chemists and technicians who use the stuff. I am not at all a jingoist but in this case the ACS standard serves the industry and the academic community better. 24 to 36 % concentrated? Nope!




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[*] posted on 15-10-2008 at 05:41


Beilstein has its own nomenclature and terminology for reagents, their properties and concentration. It is a German abstraction system from the end of the 19th century and as such it has its own peculiarities, but it is still the best there is. It is pointless and off topic to discuss about how logical it's terminology is in this thread. Please let's keep this thread short by posting only quality stuff and leave the details for U2U. Also, Sauron, please do not waste time with people who are too lazy to even use the shift key when writing down chemical formulas. It leads to nowhere and ends up in the usual manner.
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[*] posted on 15-10-2008 at 19:31


It's a subjective term just like some fuming acids. Concentrated nitric acid also gives off fumes, but the fuming strength of "fuming nitric acid" gives it its name. I've got a reference named Chemikalienkunde by H. Dietz, etc. that says fuming HCl fumes "very strongly". I've got 31.45% and it fumes, albeit not strongly. But I have noticed that its fumes are better visible in moist air, Germany is known by its humid weather.
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[*] posted on 28-10-2008 at 21:52


seems no one here has been able to carry out an easy synthesis as yet for anhydride. i read the previous posts and i tried the synthesis from vinyl acetate + h2so4 or hcl +acetic cid . and made a little aceticanhydride. but hte yield was pretty low.
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