Fery
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acetyl esters of longer chain alcohols by reacting alcohol with acetyl chloride
I did a lot of Fischer esterifications. In the beginnings classical method where equilibrium reached when the reaction water prevented the completion
of the reaction, these reactions were refluxed for hours and the distillation was necessary to separate unreacted alcohol if it was not soluble in
water enough for washing it out in separatory funnel prior the distillation. Later with azeotropic distilling out reaction water, these had much
better yields, also the reaction was completed in shorter time like 1 hour like this 1-octyl formate, it was possible to consume long chain alcohol completely as it is hard to separate if from the ester (insoluble in water, similar
boiling point of alcohol with ester, probably azeotropes of alcohol with its ester).
Recently I got a plastic barrel of old acetyl chloride and decided to divide it into glass bottles. I let it outside at winter -5 to 0 C to cool down
as its b.p. is only 52 C and I did not want to inhale its vapors too much. In the garden I filled glass bottles: 4 L, few 2,5 L, few 1 L leaving only
about 50-100 ml of empty space in every bottle. Finally I moved bottles inside and thought: well done, let's relax. But after warming to room
temperature they started to overfill and terrible stench hit my nose. Volume expansion from 0 C to room temperature seems to be significantly higher
than the small empty space I let in big bottles. I had to get rid of about 100 ml of acetyl chloride. I temporarily moved the glass bottles outside
again until removing part of the acetyl chloride with a pipette and balloon. Now they are back inside and the level of the acetyl chloride rose up
significantly again, but there is still empty space in every bottle.
I synthesized acetyl esters of n-hexanol and n-octanol, both at 0,50 mol scale.
The method was: 0,50 mol of the alcohol was put into 250 ml flat bottomed flask, magnetic stirbar was added, air condenser attached (it was enough
because I did the reaction outside during winter time with temperatures -5 to 0 C) and dropping funnel with 45 ml of acetyl chloride (26% excess, very
likely only about 2-5 % excess should be enough but my acetyl chloride was quite old with unknown quality after years in plastic barrel and I did not
want to redistill this nasty stuff). A hose was connected to the apparatus to lead HCl gas into water trap which was a beaker filled with 100 ml of
water into which an inverted funnel was immersed with connected hose. The dropwise addition of acetyl chloride lasted about 1 hour (it could be
probably performed faster) at the outside temperature, the reaction flask was quite cold when touching by hand. After all the acetyl chloride was
added the reaction was heated until slightly boiling to expell as much HCl as possible and after boiling started the heating was turned off and let to
cool down to 0 C outside temperature. 100 g of snow was charged into 500 ml beaker and the reaction was slowly poured onto the snow while stirring (to
prevent some HCl and unreacted acetyl chloride hydrolysing to HCl to cause hydrolysis of the ester and then contamination of the product with long
chain alcohol). The mixture was transferred into 250 ml separatory funnel, low acidic layer discarded and upper organic layer kept, washed 2x with 100
ml of ice cold water, 2x with 100 ml of 5% NaHCO3, 1x with 100 ml of ice cold water (organic was always the upper layer). Transferred into 250 ml flat
bottomed flask, added stirrbar, dried with about 1,0 g of anhydrous Na2SO4 while magnetically stirred for 3 hours the capped flask. Then poured into
labeled glass flask for storage.
The results are amazing, yields more than 97 %, products crystal clear colored so I did not distill them. I read somewhere even easier workup when
they just filtered the esterification product through a tube filled with anhydrous K2CO3 (I would rather use KHCO3 to prevent hydrolysis as K2CO3 is
much more alkaline than KHCO3) - but they did not use so big excess of acetyl chloride.
1-Hexyl acetate has nice floral scent, 1-octyl acetate orange + waxy. Limonene has much better orange scent, but the ester scent is also quite nice
and good.
Here amounts:
1-hexyl acetate:
51,1 g 1-hexanol = 0,50 mol
45 ml acetylchloride (26% excess) = 0,63 mol
after workup in separatory funnel: 71,3 g = 0,494 mol (M=144,2 g/mol)
after drying: 70,2 g (M=144,2 g/mol) = 0,487 mol = yield 97,4%
note boiling point on wikipedia seems to be wrong (but I did not distill)
https://en.wikipedia.org/wiki/Hexyl_acetate
Boiling point 155–156 °C wrong on wikipedia
(it seems they messed b.p. with 1-hexanol b.p. 157 C)
https://www.thegoodscentscompany.com/data/rw1003201.html#top...
Boiling Point: 170.00 to 172.00 °C. @ 760.00 mm Hg
Boiling Point: 61.00 to 62.00 °C. @ 12.00 mm Hg
1-octyl acetate:
65,1 g 1-octanol = 0,50 mol
45 ml acetyl chloride (26% excess), 0,50 mol is theoretically necessary, M=78,49 g/mol, density 1,104 g/ml = 0,63 mol = 126%, = in 26% excess
after workup in separatory funnel: 85,7 g, M=172,27 g/mol, n = 0,497 mol
after drying: 84,7 g, M=172,27 g/mol, n = 0,492 mol = 98,4% yield
https://www.thegoodscentscompany.com/data/rw1003462.html#top...
Boiling Point: 206.00 to 211.00 °C. @ 760.00 mm Hg
(I did not distill but I would certainly distill only under vacuum, not at atmospheric pressure at all)
apparatus and the reaction
ester after washing
drying ester
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DrDevice
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Not relevant to the ester as such, but rather than distilling dubious quality acetyl chloride to purify it, stir it for several minutes with Calcium
oxide. HCl and acetic acid in the acetyl chloride will react with the oxide and any water resulting from the reaction will be bound to the resulting
calcium chloride.
Then simply filter.
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Fery
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DrDevice, thank you, I did not know this purification method!
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teodor
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Hi Fery! Nice to hear you continue your experiments with esterification.
I used acetyl chloride to make meNthyl acetate and salicyloyl chloride to make several salicylic esters with different alcohols.
I store the acid chlorides in a freezer. This solves both problems: volatility and requirement for dry atmosphere. In my new lab I monitor the
humidity in a room as well as in the freezer and the difference in the air water contents is 5.7 g/m3 in a room vs 0.45 g/m3 at -25C and 0.77 g/m3 at
-18C in average. I put all the bottles inside a polyethylene zip packets to prevent condensation of water on a bottle when I take it out of freezer
for warming up. I bought one freezer second-hand for 35 eur and the second one I was lucky to get for free. The second one is a "deep freezer", it is
quite a big box on wheels and the door is on top (something like this one: https://www.coolblue.be/nl/product/942092/wisberg-wbcf120cw....). So it has no limit on bottle height and you even probably could put a barrel
inside. (I use inside plastic boxes with bottles sorted by groups).
My experiment with menthyl acetate was rather successfull but I didn't find a way to purify the result from menthol residue yet (by the way, it was
part of YOUR menthol).
The salicyloyl chloride I've made from salicylic acid by the reaction with SOCl2 (which I have double distilled by a classical method
quinoline/lineseed oil and it really made a great difference, most surprisingly making him less water-aggresive). I've dryed the acid over H2SO4 and
it also made a great difference. It seams after good drying the acid is not hygroscopic anymore, at least with short air contact.
So, I have made several salicylic esters just by mixing alcohol and chloride in test tubes just to get their smells. It was quite easy but I didn't
find a way to get rid of salicyloyl chloride residue in test tubes, so if I don't match stoihiometry the result is a bit spoiled.
Reading your report: I didn't get how pouring the reaction mixture in snow prevents hydrolisys, could you explain that?
[Edited on 13-12-2024 by teodor]
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Fery
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Hydrolysis runs faster at elevated temperature, preferably at reflux temperature. Using snow I was able to keep T very low. Snow melts much faster
than crushed ice. The HCl present (dissolved in reaction mixture) and also produced by hydrolysis of excess of acyl chloride when combined with
snow/ice produces even temperatures lower than zero (I saw crystallization of ice from air humidity on the outer side of beaker).
Another method for workup is using only very small excess of acyl chloride and filtering the reaction mixture through a column of K2CO3 or maybe
better KHCO3 which is less alkaline.
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Dr.Bob
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In some cases you may want to add a small amount of DMAP to speed up the acylation, especially for some sterically hindered or less reactive alcohols.
Even using DMAP on resin or silica gel works fine, and then be simply filtered away later. I have used that to help slower reactions, but not as
needed with the acyl chloride. Great work.
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Keras
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I’m not sure why you don’t use a simple dean-stark apparatus. For high boiling alcohols and acetic acid, running the reaction at 100 °C and
distilling off the water should work without sacrificing acetyl chloride.
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Fery
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Keras - I already did esterification in dean stark apparatus dozens of times. I wanted to try also another route of producing esters. I had to utilize
about 100 ml of acetyl chloride very quickly as I explained in the initial post (I used all my free bottles, the volume of acetylchloride was
expanding in flasks and leaking, I have never seen such a significant volume expansion from 0 C to 20 C).
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Texium
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Quote: Originally posted by Keras  | | I’m not sure why you don’t use a simple dean-stark apparatus. For high boiling alcohols and acetic acid, running the reaction at 100 °C and
distilling off the water should work without sacrificing acetyl chloride. |
Someone didn’t read the first
post
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teodor
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Regarding my report of usage freezer as a dry storage. I was curious how 0.45g/m3 is dry comparing with a dessicator charged with NaOH. So I did the
experiment. The humidity in the dessicator wis stabilized on 1.1 g/m3 at 18.4C. So, the cold storage wins. (Also it looks like storing over NaOH
increase the decomposition speed of compounds which produce HCl by reaction with water).
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