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[*] posted on 24-1-2017 at 23:22
Isopropyl Acetate


I was hoping someone who has synthesized Isopropyl Acetate can tell me if my results are similar to theirs. Specifically, I am looking to know if the odor is similar.

In particular it smelled positively awful, similar to "Silly String" or solvents. Much different smell than the other ingredients such as Acetic Acid or iPrOH. The Wikipedia page states "It is a clear, colorless liquid with a characteristic fruity odor." citing "ChemVIP" for this, however, the website link is no longer available.

Further, "Fenaroli's Handbook of Flavor Ingredients, Fourth Edition" (page 900-901) states "Isopropyl acetate has an intense, fruity odor. On dilution, it has a sweet apple-like flavor."

I did indeed use the search function to look for other results of iPrOH Acetate, none were found of sufficient value. The general procedure I followed was from Vogel's practical organic chemistry page 383, however, I did adjust the procedure.


Quote:

Vogel's Practical Organic Chemistry 3rd Ed. Page 383:

n-Propyl Acetate. Use 40 g. (50 ml.) of n-propyl alcohol, 160 g. of glacial acetic acid and 2 g. of concentrated sulphuric acid. Reflux for 12 hours. Add an equal volume of water, saturate with salt to isolate the crude ester. Treat the crude ester with saturated sodium bicarbonate solution until effervescence ceases, saturate with salt, remove the ester and dry it with anhydrous sodium or magnesium sulphate. B.p. 101- 102°. Yield: 36 g.

iso-Propyl Acetate. Use 40 g. (51 ml.) of iso-propyl alcohol, 160 g. of glacial acetic acid and 2 g. of concentrated sulphuric acid. Reflux for 18 hours. Proceed as for n-propyl acetate. B.p. 87-88°. Yield : 31 g,


My procedure used 35mL isopropanol, 40ml Glacial Acetic Acid, and 3mL Concentrated Sulfuric Acid. Reflux time was approximately 3.5 hours.

I tried two different methods of separation. I first attempted salting out as suggested by Vogel, which did indeed form separate layers. This layer was removed and then neutralized with sodium bicarbonate. The second method of which I tried was directly neutralizing it with saturated sodium bicarbonate under strong stirring. It does have a tendency to foam up so stirring is advised, or, slow addition. Both of these methods gave me the same product, a foul nauseating solvent like odor reminiscent of silly string. The yields seemed quite favorable towards the ester, however, no attempt was made to store it. It was discarded by way of combustion as it was quite flammable. It was worth noting that the flame had a very faint red-purple color to it, however, this was not performed under analytical conditions.

The isopropanol I used was dried using the NaOH method starting with 91% following Lewis Gilson's paper "Note on the Preparation of Absolute Isopropanol" - 10.1021/ja01343a024

Further, if someone could also comment on the odor of n-propyl acetate I would also appreciate that.




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Amos
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[*] posted on 25-1-2017 at 15:56


With most low-molecular weight esters, the smell is going to be a big disappointment if you read the wiki entry and see "fruity"; only in very low concentrations could most of them be considered nice-smelling. To me, n-propyl acetate smells rather harsh and solvent-like, but if smelled in a lower concentration, like from a distance away after opening a freshly-shaken container, I think it smells sort of like apples, specifically the skin.
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[*] posted on 26-1-2017 at 01:15


I agree with Amos, having synthesised many over the years for shits and giggles pure compounds never smell awesome and especially not at high concentration.




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[*] posted on 26-1-2017 at 04:59


Some heavier esters such as methyl salicylate and benzyl benzoate can be smelled in pure form, but these have much lower volatility and hence your nose isn't hit with so much at once.
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[*] posted on 27-1-2017 at 03:33


From my experience isopropyl acetate smells vaguely like petrol or cyclohexane, not particularly fruity. n-propyl acetate does smell a bit like apples, but nowhere near as strongly as the butyl analogues do.



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[*] posted on 27-1-2017 at 10:37


I made n-amyl acetate. Whiffs smelled of banana as hoped. Smelling too much smelled of finger nail polish remover.



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[*] posted on 6-1-2021 at 01:53


I've made iPrOAc and I think the smell is just great, comparing to PrOAc and BuOAc. It is not so "plain" and "sweet", more noble one and becomes better on dilution. The smell can be characterised as "frutty" one but I didn't encounter any fruit with such smell, it is smell on its own. It doesn't smell like solvent and not like "sweet apple solvent" (BuOAc) either. I don't regret I've made it. I used almost 22hrs reflux.
But I must admit during the synthesis the smell was awful, also I detected some contamination during the washing process with awful "petrol" smell. The most contribution to the smell during the synthesis I think is from acetic acid and this combination of 2 smells creates a new one which is quite bad. I neutralised all the acid till pH=7 (by universal paper). After drying on MgSO4 the ester doesn't color the paper anymore, so I think making the mixture slightly alkaline during the process should not be the problem.
The smell in the concentrated form (from the bottle) has acetic acid notes. It is better to sniff a stopper, after few seconds these notes disappear and the smell becomes more characteristic. The same is true for other acetic acid esters.

[Edited on 6-1-2021 by teodor]

[Edited on 6-1-2021 by teodor]
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[*] posted on 6-1-2021 at 02:25


The petrol/"diesel engine" like smell could perhaps be diisopropyl ether, it always forms when IPA is refluxed under acidic conditions. Also when I did the procedure I had to painstakingly make H2SO4 myself, so glacial acetic acid was precious stuff to me, while IPA could be bought at electronics stores. So, I reversed the molar ratio and most likely ended up with an IPA/IPOAc azeotrope that may or may not have been successfully broken by shaking twice with a concentrated solution of a MgCl2/CaCl2-mix.

I expected the smell to be less "solventy", but then again even acetone smells like flowers if it is diluted enough.
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[*] posted on 6-1-2021 at 03:16


@Jome, By the way, I often notice appearing of "petrol" smell which is probably the same think as "unsaturated hydrocarbon smell" (which is similar to alkyl chloride smell) when drying different compounds on CaCl2. It appears after some time in the stoppered bottle containing CaCl2 and a compound. I never noticed this effect drying with magnesium sulphate.
The problem with propyl esters of AcOH is also that their boiling points are almost the same as the corresponding alcohols so I think when you use the excess of the alcohol separation becomes more challenging. I didn't study CaCl2 method yet. Thank you for noticing iPr20 formation, I didn't think about it (but well, it should be expected).
I did several experiments with separation BuOH and Bu2O with 50% H2SO4 and I think I managed the process. I am curious, does this method work for iPrOH and iPr2O (iso-propyl alcohol and iso-propyl ether) separation.
Following Vogel procedures for PrOAc and iPrOAc (salting out with NaCl) I found that 18%-36% of the initial volume of acetic acid should be neutralised but the rest of unreacted acid (mixed with water and NaCl) probably could be recovered with fractional distillation.
To get this loss less than 18% you have to combine the separation and neutralisation process, so separate the layers during NaHCO3 addition.


[Edited on 6-1-2021 by teodor]
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[*] posted on 6-1-2021 at 08:46


teodor 22 hours for this esterification, wow, so long :o
using Dean-Stark trap apparatus, hexane, only 5 drops of H2SO4 for 0,25 mol ester and after 1 hour my last esterification completed...
these short chain alcohols should be easily washed into water phase in sep. funnel so no azeotropes during distillation




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[*] posted on 6-1-2021 at 10:58


@Fery Interesting. How do you get separation of water and iso-propyl alcohol in Dean-Stark? Also what is hexane for?
Time of the reflux is not an issue for me, it doesn't require my attention. This type of synthesis costs mainly the time required for final product separation.


[Edited on 6-1-2021 by teodor]
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[*] posted on 6-1-2021 at 11:22


Quote: Originally posted by teodor  
@Fery Interesting. How do you get separation of water and iso-propyl alcohol in Dean-Stark? Also what is hexane for?
Time of the reflux is not an issue for me, it doesn't require my attention. This type of synthesis costs mainly the time required for final product separation.


[Edited on 6-1-2021 by teodor]


The hexane is so that you get two layers in the Dean-Stark trap, with some of the isopropanol being in the top layer (so that it can return for reflux).




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[*] posted on 6-1-2021 at 11:42


Hi teodor, it was in a synthesis of an ester of allyl alcohol. If neglecting the already present ester - the hexane boils with water and alcohol and on condensing the mixture separates in the trap apparatus into upper phase hexane + alcohol (and a little of H2O) and bottom phase H2O + some amount of alcohol (this bottom phase does not return back into the reactor so you remove water). I just wanted to say that the esterification is quite fast reaction and I'm only guessing that you wasted a lot of hours + energy for heating. There is no need to use a lot of acid... I used to use 5 ml for 1 mol ester synthesis like in heptyl butanoate where so much of H2SO4 only caused carbonization (and maybe side reactions with alcohol) and later I observed that it is enough to use 10 times less of the catalyst.



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[*] posted on 6-1-2021 at 12:39


Thanks Fery & DraconicAcid, I've got the idea. We drive-off both water and alcohol and when the water layer (with some alcohol in it) stops to grow that means the esterification is completed - at that point we have removed either all water or all the alcohol from reflux.

Which source of information can I use to figure out the possible distribution of an alcohol between water and organic layer (except experiment?)

@Fery I used about 1ml H2SO4 per 0.7mols of isopropanol, it was excess of acetic acid (4x to the alcohol) to drive the reaction. I believe the speed of secondary alcohols esterification is slower than that of primary ones.

Also I didn't observe separation of isopropyl acetate from water/acetic acid mixture. It needs enough NaCl to form a separated layer (here is the difference with n-propyl acetate)


[Edited on 6-1-2021 by teodor]
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[*] posted on 6-1-2021 at 12:42


You might be able to look up a partition function somewhere, or you could put a few mL of saturated sodium chloride sol'n in your DS trap to chase the alcohol out of the water layer.



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[*] posted on 10-1-2021 at 12:44


To me, isopropyl acetate has a "stereotypical" solvent smell, though sweeter than normal. It smells fruity in the same way that ammonia smells fishy. It doesn't actually, but that's how it's always described. It smells rather pleasant to me, though I tend to like the way most solvents smell.
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