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Author: Subject: Acetic anhydride preparation
Per
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[*] posted on 30-3-2007 at 04:18


Firstly I wanted to use CaCl2, but when there´s NOCl envolved I´d use MgSO4 as drying reagence.

Also I´d prepare the NO2 with lead nitrate which I´ve to produce in the next days.

Hope that 350°C are enought to make the NO2.
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Sauron
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[*] posted on 30-3-2007 at 05:24


Merck Index is silent regarding melting point, Brauser does not state reaction temperature for prodn of NO2, Acros says mp of lead nitrate is 470 C. So I would seek further information about decomposition to nitrogen dioxide if I were you.

Brauer did specify high melting glass, which is not very specific is it? Anything from Pyrex to Vycor could be implied.

Also you need a slow stream of O2.
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[*] posted on 31-3-2007 at 07:31


I don´t understand why I need a O2 stream, because O2 is already produced in this reaktion.

Also I still produced Pb(NO3)2 and there were little problems, in the first time just a white powder were produced, I think it has to be PbNO3 but heating the reaction mixture longer gaves a clear solution.
With that I´d try it out if 350°C are enougt, but firstly it has to be dry.
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[*] posted on 1-4-2007 at 02:00


I had until now forgotten that I have a 1913 patent on the N2O4 method.
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[*] posted on 2-4-2007 at 05:13


Now I’ve tried the method with Pb(NO3)2.
Firstly drying the lead nitrate solution was really nasty, and then I heated the white crystals (looking like TATP) to about 350°C and nothing happened.
Then I heated a few crystals in an reagence glass an heated them with an burner. It envolved a red gas looking like NO2, so this method was successful.
Soon I produce more Pb(NO3)2 then I can try the Ac2O synthesis.

Patente:
In the patente is mentioned that the NO2 + CH3COONa process is really successful to produce Ac2O and that it´s possible to produce a Ac ans Ac2O mix by heating concentrated HNO3 and lead the gases into sodium acetate.
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[*] posted on 5-4-2007 at 06:04


It took a long time but now I´m the proud owner of 401g dry lead nitrate.

In the morning I tried to produc Ac2O, I lead the brown NO2 gases over dry sodium acetate.
And what should I say, after a few minutes the cristals converted into white cristals and I coud recognice a small amount of a solid.
Now I need a good idea to recover the solid from the NaNO2.
Have anybody any ideas?
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[*] posted on 5-4-2007 at 06:16


Did you dry your NO2 as described in Brauser?

Cold trap for gross moisture then PbO2 then P2O5?

What do you reckon the solid might be and why is there no Ac2O formed?
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[*] posted on 5-4-2007 at 08:07


I don´t know if theres Ac2O formwed or not.
I just can say that there´s envolved a solid after I lead the dry NO2 gas into the sodium nitrate and that the layer of the sodium cristals changed.

But now I need a method to isolate the Ac2O from the NaNO2 which is formed while the reaction.

My feeling says that there´s formed Ac2O.
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[*] posted on 5-4-2007 at 08:47


@Per, wash the solid with a solvent that dissolves Ac2O but not NaNO2 or BaOAc. Filter. Then remove solvent. What's left is your product.

The lead nitrate method does not produce a whole lot of nitrogen dioxide per unit of weight.

What is your objection to the reaction of HNO3 with Cu metal? If you subject the gas stream to same rigorous drying as with lead nitrate won't this be just as satisfactory?
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[*] posted on 5-4-2007 at 09:01


Quote:
Mr per in what temp the leadnitate decompose to no2 and pbo?

At 350°C it decomposes definitively not, then I used a burner and it worked but I didn´t measure the temperature,
think that 470°C could be right.

What solvent would you suggest, maybe CHCl3?
But that would maybe react with the rest of the sodium acetate.

Quote:
The lead nitrate method does not produce a whole lot of nitrogen dioxide per unit of weight.

That´s right, but when I use Cu(NO3)2, I´ve very much copper nitrate which I don´t need and drying copper nitrate is very difficulty.
And PbO could easyly regenerate with HNO3.
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[*] posted on 5-4-2007 at 09:35


Try something more inert like petroleum ether or toluene. Look up to double check they won't dissolve the Na salts but I would not expect them to.

Also I don't know what rxn you would expect between NaOAc and chloroform?
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[*] posted on 5-4-2007 at 21:58


When I was a teenager I "discovered" a reaction that I have never bothered as an adult to elucidate.

Sodium thiosulphate (powder) and conc HNO3 -> lots of brown gas presumably NO2 + elemental S and apparently water.. Maybe some sodium nitrate.

Obviously some sort of redox, if anyone knows what the stoichiometry is I'd like to hear it. Also whether or not any other gases are evolved besides nitrogen oxides.
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[*] posted on 6-4-2007 at 01:26


S2O32−(aq) + 2H+(aq) → SO2(g) + S(s) + H2O

source Wikipedia
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[*] posted on 6-4-2007 at 01:47


SO2 is not rich dark red-brown. SO2 is colorless. I am well familiar with the smell of SO2 having made a lot of it and what I made was at least predominantly NO2.

Try it for yourself but don't breathe the results.
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[*] posted on 6-4-2007 at 07:26


Quote:
Also I don't know what rxn you would expect between NaOAc and chloroform?

I thought that maybe NaCl could be formed but that´s just an idea.

Sure that toluene and petrol ether aren´t react with NaNO2 when I want to purify it by evaporating the rest of the solvent?
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[*] posted on 6-4-2007 at 07:49


No reaction I ever heard of.
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[*] posted on 6-4-2007 at 14:02


Quote:
Originally posted by Sauron
SO2 is not rich dark red-brown. SO2 is colorless. I am well familiar with the smell of SO2 having made a lot of it and what I made was at least predominantly NO2.

Try it for yourself but don't breathe the results.


Yeah Im sure SO2 also reduces nitric acid in the process. So there are 2 reactions happening. One forms sulfur and one forms NO2.
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[*] posted on 6-4-2007 at 20:57


That is perfectly resonable.

It is an extremely rapid process, as I recall, and not a slow evolution. If you throw thiosulfate crystals into HNO3 you get an instant large cloud of NO2 (at least mostly)

I never tried dripping HNO3 slowly onto thiosulfate but that might serve as a NO2 generator. If we can figure out the stoichiometry this might serve as basis for a NO2 generator, and have neither the large residue of Pb oxide nor copper nitrate that are the bugbears in the lead nitrate pyrolysis and the dissolving-copper processes.

Will there be any SO2 to scrub from the NO2 stream? I don't know.
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[*] posted on 8-4-2007 at 03:46


Is it also possible to use acetone as solvent?
It´s cheaper and it´s boiling point is more convenient, but I don´t know if it´s too reactive.

Also could somebody try the prepartion with Cl2 instead of NO2, when NaCl is formed the Ac2O could be easily distilled.
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[*] posted on 8-4-2007 at 11:21


how is acetic anhydride identified
like what are the basic tests for identifying or telling if a chemical is acetic anhydride or not
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[*] posted on 8-4-2007 at 11:45


Quote:
Originally posted by chemicalpower
how is acetic anhydride identified
like what are the basic tests for identifying or telling if a chemical is acetic anhydride or not


Boiling point
Density/Specific gravity
Refractive index
React it with an alcohol and verify the ester's boiling point
React it with aqueous ammonia to form acetamide, and with aniline to form acetanilide, recrystallise and confirm proper melting point.
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[*] posted on 8-4-2007 at 19:17


Boiling point is easy. AcCl boils low, AcOH 117, Ac2O 140.

AcOH is nonflammable, Ac2O is very flammable. Remember that.

Density is easy, even without a set of hydrometers

All you need is a scale and a volumetric flask

Refractive index you need a refractometer or access to one
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[*] posted on 9-4-2007 at 04:14


Quote:

Sure that toluene and petrol ether aren´t react with NaNO2 when I want to purify it by evaporating the rest of the solvent?


Only if you boil it down so vigorously your solvent catches fire...

Per, learn the basics before cluttering this thread with obsolete questions. Crawl first, then walk.




One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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[*] posted on 9-4-2007 at 10:22


Would P2O5 do the trick, I know it can be used to make some anydrides, however, I am unsure if it will do the trick with this one?

If it will, look up how to make Calcium Phosphide, as the phosphine given off by its reaction with water burns in oxygen to make P2O5... Or use the zinc phosphide method in this patent (which produces zinc phosphate as a byproduct - which is also the first stage of the synthesis)

http://www.freepatentsonline.com/4128620.html

In a related area, if H3PO4 is dehydrated (at a low red heat) with charcoal, it is transformed (at around 250C) to pyrophosphate and then at the low red heat to metaphosphate (HPO3) which is supposed to be almost as good a dessicant as phosphorus pentoxide.

http://www.freepatentsonline.com/4082677.html (A patent for drying phosphoric acid by absorbing into wood shavings and heating to 200C in the oven - turning the wood to carbon in the process).

I think the phosphoric/phosphorus acids are soluble in some organic solvents too aren't they?

If so, make the metaphosphate - using dry everything extract it with an organic solvent (dry for preference) and mix that with the glacial acetic acid. Presumably the acetic anhydride could be distilled off the pyrophosphoric acid (made by absorbing water into metaphosphoric acid).

However, Nicodem has already said that these acids aren't nice to glassware.... be quick, be careful.

tup

PS I have no idea if this works, I believe it very well might, however, finding out is up to whomever wants to try it out. If the metaphosphoric acid works (metaphosphoric acid is what reacts with iodine to make HI in the synthesis on Rhodiums page - thus the 400C temperature from phosphoric acid before the reaction starts), and it COULD being an acid anhydride itself, that would be great - if it does not, the pentoxide is supposed to work.



[Edited on 10-4-2007 by tupence_hapeny]




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[*] posted on 9-4-2007 at 11:41


The short answer is no, theose won't work, or aren't practicable, and anyway they have already been discussed in detail in this thread and elsewhere.
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