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benzylchloride1
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I prepared some acetic anhydride from sodium acetate, bromine and sulfur today. 20ml of bromine was placed in a 100ml beaker and 3.5g of sulfur powder
was added slowly while stirring with a glass rod. 66.5g of anhydrous sodium acetate was placed in a 500ml rbf. The sodium acetate was not fused. A
pressure equalizing funnel was attached and the sulfur bromide- bromine solution was added to the funnel. The S2Br2/Br2 solution was slowly added to
the sodium acetate. The mixture fumed and an orange liquid refluxed on the walls of the flask. After the addition the funnel was removed and the
mixture was stirred with a glass rod. The mixture turned into a suspension of white crystals in a clearish liquid. A distillation set up was assembled
and the mixture was heated with a heating mantle to distill over the product. The product distilled between 120 C-125C @ 580mm Hg. The distillation
was stopped because of charring of the flask contents. A considerable amount of liquid remained in the flask. Approximatly 16g of a clear liquid was
obtained. A small quantity of o-toluidine was acylated with the acetic anhydride in aqueous solution. Upon quencing the reaction mixture with water,
white crystals were obtained. The derivative was recrystallized from water and formed white needles. The derivative is drying and a melting point will
be taken.
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panziandi
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Nice work well done! Be interesting to get the mp. 
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Sauron
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Use a batter pump and distill at c.25 mm Hg not 580 mm on a water bath (a rotav is ideal) and you will get no charring and a much better yield
Then redistill the crude Ac2) at ordinary pressure.
Sic gorgeamus a los subjectatus nunc.
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benzylchloride1
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Another experiment was conducted today using S2Cl2 instead of S and Br2. 100g of anhydrous sodium acetate was placed in a 500ml RBF equipped with a
Claisen adaptor, reflux condenser with a CaCl2 tube and a additon funnel. 38ml of S2Cl2 was placed in the addition funnel and slowly added to the
mixture. The mixture became very hot. After the mixture cooled some what, it was stirred with a glass stirring rod. The mixture was heated with a
heating mantle and periodically stirred with the glass rod. Magnetic stirring will not work because of the semi-solid nature of the reaction mixture.
The mixture was yellowish in color, but melted to a liquid with a tan colored solid suspended in it. After about 45 minutes of heating, the mixture
was allowed to cool and a distillation head attached and the mixture was vacuum distilled using a water pump. About 30- 40 ml of a clear colored
liquid was obtained that acetylated o-toluidine in aqueous solution. The crude acetic anhydride will be distilled from potassium permanganate to
remove sulfur compounds. The anhydride will then be weighed so as to obtain the percentage yield. I scaled down this procedure 4 times due to the fact
that I did not have 400g od sodium acetate and enough S2Cl2 today. I made the S2Cl2 today as well. The synthesis of acetic anhydride can be conducted
in one day from sodium acetate, sulfur, hydrochloric acid and trichloroisocyanuric acid. The vacuum distillation really improves the yields, thanks
for the advice. This method works extremely well and is suitable for the preparation of acetic anhydride by amateur chemists that have a fair amount
of equipment. A properly functioning fume hood is essential for making the disulfur dichloride and the anhydride due to the poisonous nature of the
S2Cl2 and chlorine. I wonder if a method could be adapted from this for synthesizing benzoyl chloride. I am looking for a cheaper source of the
anhydrous sodium acetate, since I pay around $10 per pound with shipping.
[Edited on 28-4-2009 by benzylchloride1]
[Edited on 28-4-2009 by benzylchloride1]
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Sauron
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Well done!
You were smart to buy the anhydrous NaOAc as this is the point so many others got stuck on, trying to dry the trihydrate.
Benzoyl chloride is readily prepeared:
1) from TCT and the acid in acetone and in presence of TEA
2) from benzotrichloride and phthalic anhydride using ZnCl2 catalyst at 120 C for 20 hrs reflux. You get a nearly quantitative mixture of phthaloyl
chloride and benzoyl chloride. Both very useful. You can use the phthaloyl chloride to make SOCl2 from SO2 gas.
You can make the trichloride from toluene or benzyl chloride.
Sic gorgeamus a los subjectatus nunc.
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benzylchloride1
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The sulfur bromide/ bromine method gives a cleaner product then the disulfur dichloride method, but is considerably more expensive due the amount of
bromine required. I obtained a 56% yield of acetic anhydride boiling between 110 C and 130 C, upon distilling from 0.5g of potassium permangante to
remove sulfurous contaminants. I live at a very high altitude and boiling points are way lower then those at 760 mm. My thermometer is not very good.
The heating was conducted with a heating mantle and aluminum foil was used as insulation. All of the distillate had the characteristic odor of acetic
anhydride. The product acetylates amines at room temperature. The acetyl toludine derivative melted at 145 C, indicating that it is the para
derivative. The toluidine was a mixture of ortho and para isomers obtained from the reduction of crude mono nitrotoluene. I now have a vacuum
distillation setup, I nitrated around 150g of toluene and separted the isomers by fractional vacuum distillation and then freezing the residue to
obtained the crude p-nitrotoluene. I now will have some pure o and p-toluidines to work with once I run the reduction reaction. I plan on running the
acetic anhydride synthesis full scale when I get some more anhydrous sodium acetate. I have a 2L reaction kettle with a removable flange head. This
will be ideal because I can mix the disulfur dichloride and sodium acetate with a glass stirring rod and then place the flange head on the kettle with
a reflux condenser protected with a CaCl2 tube. The heating and distillation will be conducted with a Buchi water bath because I do not have a mantle
for the reaction kettle. Now we have a confirmed method of producing acetic anhydride of reasonable purity from readily available chemicals.
[Edited on 1-5-2009 by benzylchloride1]
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Magpie
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Very nice, and thanks for sharing this with the forum.
In one of your earlier posts you said that you distilled your product at reduced pressure using a water pump (aspirator). Since S2Cl2 and Ac2O are
sensitive to water I was wondering if the ~25mmHG vapor pressure of water from the pump causes any problem?
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Sauron
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Tjis is my 3rd trt at posting this, I will copy this tome before hitting the button.
IMO there's a reason why you get a cleaner product with Br than Cl. Your S2Cl2 is contaminated with SCl2 and S. I am assuming that you made the S2Cl2
from the elements and that you did not perform heroic procedures to purify it.
It is very hard to obtain pure S2Cl2. See Vrauer's monographs on S2Cl2 and SCl2. The former is stable, the latter is now.
2 SCl2 (equilibrium) S2Cl2 + Cl2
S2Cl2 is a great solvent for S and if you add more Cl2 to try to react all the S you wll make more SCl2 instead.
Why not same hassle with Br2?
Br2 forms only S2Br2. The lit. is divided on whether SBr2 exists at all, the consensus seems to be either no or it is so unstable that for practical
purposes it is not there. See Mellor, Gmelin and ATBOIC.
This reaction requires the S2X2 which has a disulfide structure X-S-S-X in order to metathetize with sodium acetate to AcO-S-S-OAc.
SCl2 does not work, and if you had some you could prove it.
There's your source of contamination.
The S + Br2 procedure was first published in a Russian journal and reprinted in late 40s in Chemistry & Industry (London) so it really needed no
confirmation.
Members here got all hung up trying to do the double fusion of NaOAc.3H2O which is tricky. You wisely cut the Gordian knot by purchasing commerial
anhydrous NaOAc. Tell me, did you use it as is or did you fuse it once? If you used it out of the bottle, fusing it once at 135 C then powdering the
melt and using it at once, may boost your yields.
Sic gorgeamus a los subjectatus nunc.
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benzylchloride1
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I did not fuse the anhydrous sodium acetate before reacting it with the S2Cl2. I currently do not have a suitable drying oven for that purpose, but I
plan to buy one in the next few months. The S2Cl2 was directly prepared from sulfur and dry chlorine. The flask containing the sulfur was heated with
a mantle to a temperature slightly above the melting point of the sulfur and chlorine was passed into the mixture. After an initial lag period, the
S2Cl2 distilled as orange colored drops. The sulfur chloride in the receiving flask was reddish in color due to SCl2. The sulfur chloride in my
opinion is more unpleasant then either chlorine or benzyl chloride.The fume hood does a good job at taking care of the chlorine gas during the
chlorination phase, but the odor of sulfur chloride is barely noticable when the apparatus is disassembled. During the reaction between the S2Cl2 and
sodium acetate, the odor is worse because the mixture is exposed to the air during the stirring process. A warning to others; do not repeat this
experiment without a properly functioning fume hood. The residue in the flask after distilling the acetic anhydride can be dissolved with water, much
brown colored collodial sulfur is present that wash formed during the reaction. I should place a CaCl2 tube between the aspirator and vacuum adaptor
to prevent the ingress of moisture.
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Polverone
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The section on acetic anhydride in the 1921 edition of the first volume of Thorpe's Dictionary of Applied Chemistry, available here, is quite interesting. Earlier and later editions do not have such a wealth of information about processes employing sulfur chlorides and
oxychlorides, but this was apparently the dominant industrial mode at the time of this edition and Thorpe's devotes a corresponding amount of space to
the topic. There's also information about purification and avoiding side-products that may be useful. Sulfur monochloride and dichloride have both
been employed, as has sulfuryl chloride. The chlorides may be generated in situ.
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Magpie
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After reading of the success of benzylchloride1 I was anxious to try the S2Br2 synthesis of Ac2O.
Working with Br2 is exciting enough for me but add in the preparation of a vicious looking reagent like S2Br2 and the stage is set for excitement.
Lacking a detailed procedure, not understanding the stoichiometry, and not able to find an MSDS for S2Br2, added to the anticipation. I prepared
carefully and wore full safety regalia: safety goggles, mid-arm rubber gloves, long-sleeved shirt, lab apron, and above all: hood fan ON.
I followed BZ1's procedure exactly, except I had the benefit of a newly purchased, but not yet used, overhead stirrer.
I had reason to believe that my NaOAc was of good quality so did not fuse it. I prepared my own bromine from NaBr and washed it with con H2SO4.
Sulfur was flowers of sulfur, USP grade.
Addition of the sulfur to the bromine was uneventful. I really saw no evidence of a reaction other than there was no sediment in the beaker after
stirring. This was placed in a pressure equalizing funnel.
The mixer was turned on and the S2Br2 + Br2 slowly added to the 500 ml RBF. Although the mixer was working well it only stirred the material within
the diameter of the blades. So most of the NaOAc just sat there as an annulus. But I kept adding the liquid until it was all in. Then I removed the
addition funnel and poked the unreacted material into the center using a glass stirring rod and the side-ports of the RBF. There was some minor
refluxing going on but not much. All of a sudden (within a few seconds) the NaOAc began reacting and the whole mass turned into a creamy liquid that
stirred well with the mixer alone! The temperature rose to possibly as high as 80C. I did not measure it but just felt the flask by hand. After
15-20 minutes of stirring it had cooled off.
Tommorrow I will vacuum distill to recover the putative Ac2O.
Here's 2 pictures. The first is before the breakup of the solids while the liquid was still being added:
Attachment: phpsApV52 (97kB)
This file has been downloaded 1944 times
[Edited on 30-5-2009 by Magpie]
The second is of the creamy product following the sudden breakup of the solids:
[Edited on 30-5-2009 by Magpie]
[Edited on 31-5-2009 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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My preparation of Ac2O via S2Br2, started 2 days ago, was completed today.
The reaction product formed previously was vacuum distilled at 170-180 mmHg with distillate temp as high as 70C. This went smoothly with grey,
slightly charred solids remaining in the pot. Crude distillate volume was about 30mL.
This was then redistilled at atmospheric pressure, obtaining 2 cuts. 1st cut: 128-135C, ~15mL; 2nd cut: 135-143C, ~10mL. I think a fractionation
could serve well here instead of the simple distillation I used.
To confirm identity of the Ac2O I mixed 1 mL of cut 2 with 2 mL of aniline, added 15 mL of water, and shook vigorously. There was an immediate and
massive formation of white crystals: putative acetanilide. These crystals were redissolved (by heating) and the solution then filtered. The
filtrate was cooled to recrystalize. The mp of the crystals was determined to be 113-114C in agreement with my handbook value for acetanilide.
Disscussion
Some things that I think would facilitate this preparation:
1. Figure out some way to add the solid material (NaOAc) last, a little at a time. This would greatly aid in stirring, thus preventing the
difficulties both chemrox and I experienced. It would also keep the reaction under control. Just before my reaction suddenly took off I thought I
had a failed reaction, then, in 5 seconds, I thought I had a runaway.
The good thing about adding it first is that you have good containment Once you get a whiff of S2Br2 you are glad of that!
Note: Because of the sudden and dramatic breakup and reaction of the NaOAc chunk I'm thinking Sauron may well be right about the formation of an acyl
halide that triggers the reaction. This also seems consistent with the requirement for initial Ac2O in one of the Rhodium procedures.
2. Acquire enough crude Ac2O to allow a fractional distillation, thus improving purity of the product.
3. Employ CaCl2 cartridges during the distillations to prevent or reduce moisture absorbtion from the atmosphere.
4. By all means have a fume hood, and consider your neighbors. Time it for when they aren't around.
Conclusions
Overall I like this synthesis - mostly because it gives you the goods! Thanks
to Rhodium, Sauron, and benzylchloride1 for leading the way.
[Edited on 1-6-2009 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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benzylchloride1
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Excellent work Magpie! The sulfur bromide solution almost looks like bromine, if the sulfur is added to fast, a slightly vigerous reaction occurs. The
reaction takes a while to initiate and then the mixture turns into a liquid that is easy to stirr. What type of stirrer shaft and bearing did you use?
I have 2 mechanical stirrers; one working and the other non working. I have been using rubber stoppers with glass tubing and rubber tubing to seal. I
think that these would have a hard time with the sulfur halides. I am planning on running the full scale synthesis involving sulfur chloride and
sodium acetate in my 2-liter reation kettle; this should yield around 250g of acetic anhydride
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Magpie
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Thanks BZ1.
The stirrer I have is a 2-bladed, folding prop type. Both the prop/shaft and the bearing are made of PTFE. I bought these through an eBay store,
where the prices are much more reasonable than those of the scientific supply houses.
I make my Br2 using NaBr, 6% H2O2, and sulfuric acid. I'm still working on optimizing my procedure, but here is my method for the last batch:
2NaBr +H2SO4 + H2O2 --> Br2 + Na2SO4 + 2 H2O
1. Mix 51.5 g of NaBr with 125mL of 6% H2O2 in a 600 mL beaker. Pour this into a 250 mL RBF.
2. Assemble the RBF for simple distillation, no thermometer needed.
3. Add 16 mL of con H2SO4 and close up the system. Ice cold cooling water ON. No heat needed.
4. Turn hood fan ON. Some Br2 will escape through the vacuum adapter tubulation.
The bromine will be generated profusely. In fact it somewhat overhwelmed my 19/22 condenser.
Conclusion: The acid should not all be added at once so as not to overwhelm the condenser. Yield looks to be about 7mL, not that
great. Placed Br2 in a narrow-necked bottle with PTFE lined cap. Placed in freezer for short term storage. When rethawed most of the floating water
can be withdrawn with a Pasteur pipette. Right before using dry the Br2 by washing it with con H2SO4 using a sep funnel.
The single most important condition for a successful synthesis is good mixing - Nicodem
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benzylchloride1
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The method that I use produces bromine in high yield; around 90%. I use an excess of sulfuric acid and a slight excess of 35% hydrogen peroxide for
the bromine synthesis over the amount of sodium bromide used. The NaBr is dissolved in a 50% sulfuric acid solution and heated with a mantle. The H2O2
is slowly added, and the bromine distills. The receiving flask is chilled in an ice bath, hardly any of the bromine escapes. The reaction mixture is
carefully heated to boiling and boiled until most of the bromine has been expelled out of the distillation flask. Most of the bromine distills during
the addition of the H2O2; the reaction can get out of hand and contaminate the product. This happened to me the first time, add the H2O2 slowly,
around 2mL per minute. I typically use about 100g of sodium bromide, I typically get around 70g of bromine after drying with sulfuric acid. The
bromine can be distilled if desired, I did not distill it. I use a 500ml distilling flask and a 24/40 distillation setup. I produced around 200g of
bromine in one afternoon; I used 150g of it for a 1-bromonaphthalene synthesis and the other 50g of it for the acetic anhydride synthesis. Magpie,
could you U2U me the name of the Ebay seller that sells the stirrer setup; I am interested in purchasing one.
[Edited on 1-6-2009 by benzylchloride1]
[Edited on 1-6-2009 by benzylchloride1]
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Sauron
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At least no one os hung up on drying sodium acetate anymore.
Recommending the use of anhydrous NaOAc (commercial) seems to have been one of my better pieces of advice, though it took some time to take hold.
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Magpie
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from benzylchloride1:
| Quote: |
I am planning on running the full scale synthesis involving sulfur chloride and sodium acetate in my 2-liter reation kettle; this should yield around
250g of acetic anhydride
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Wow - that is definitely full-scale. I would think that you would need good agitation so that you never had anything approaching a runaway. It also
might be smart to have that kettle semi-immersed in a water bath with plenty of ice cubes handy! You even might want a reflux condenser.
I know some members have used dry powder feeders. It seems like that would be ideal, as good stirring and a controlled reaction could then be
achieved by adding the NaOAc slowly and in small portions.
I wonder how much trouble it would be to make one's own dry powder feeder - sealed to the reaction vessel, of course. You don't want S2Br2 and Br2
vapors running loose, even in a good hood. If someone could tell us about these and/or show a picture of one I would appreciate that.
Edit: It's amazing what a little searching will bring:
http://www.sciencemadness.org/talk/viewthread.php?tid=9623#p...
[Edited on 2-6-2009 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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benzylchloride1
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The reaction kettle will be placed in a Buchi water bath and chilled with ice. I plan on placing the sodium acetate into the kettle and slowly adding
the S2Cl2 through an addition funnel. I will need to purchase a 3-way Clasien adaptor because the reaction kettle lid has only one 24/40 neck. I use a
Fredreichs condenser with a CaCl2 drying tube. The S2Cl2 has a very foul odor and is toxic. A self contained powder addition funnel would help, but
they go for a lot of money on Ebay. The original procedure mentions preparing individual small batches of the reaction mixture, but this would be
wasteful due to losses during transfer and also exposes the chemist to large amounts of S2Cl2
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