Sciencemadness Discussion Board - Esters!

Esters!

Texium - 8-5-2015 at 19:22

Hello everyone, I decided to start a general thread about esters, because they are lovely things, and so simple to make.

First off, my favorite infographic on the subject:

I've made a few esters at home before (methyl salicylate, ethyl salicylate, ethyl acetate, isopropyl acetate), although I'm rather limited by my reagents. Today in AP Chemistry class though, we had an ester party, where we spent all class making a ton of different esters. We had methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 1-pentanol, benzyl alcohol, and 1-octanol available for alcohols, and formic, acetic, propanoic, butyric, and salicylic acids available for carboxylic acids. I was so excited! As such, I tried making a lot of the more interesting looking esters from the table that I could access today. A review of them follows...

n-propyl salicylate: Sort of minty but muddled

n-butyl salicylate: The !STRONG! blackberry smell noted in the table was very disappointing. It emulated the smell of Expo marker almost perfectly.

Benzyl salicylate: Something weird happened: an orange precipitate formed in the test tube, and there was no perceived smell after heating for a while

Benzyl propanoate: Floral, fruity, not unpleasant

Benzyl butyrate: subtle and fruity, very nice

n-octyl formate: Hints of grapefruit, but kind of detergenty, like a grapefruit scented soap or other cleaning product.

n-pentyl acetate: The classic super intense banana laffy-taffy smell.

n-pentyl propanoate: Very pleasant peach smell with notes of banana

I may be able to try a few more over the next couple of weeks, but I'm not sure. Anyway though, just thought I'd share that and open up the discussion.

aga - 9-5-2015 at 01:17

Cool ! Nice table.

My next forray into OC will definitely be another esterification, simply because the change of smell is a good sign that something happened.

papaya - 9-5-2015 at 04:27

Could you describe how did you isolate pure esters ? You mention synthesis being "easy" however without proper equipment all you can isolate is the smell, not bulk product.

diddi - 9-5-2015 at 04:34

you only need basic o-chem glassware for most.

Texium - 9-5-2015 at 06:02

Quote: Originally posted by papaya

Could you describe how did you isolate pure esters ? You mention synthesis being "easy" however without proper equipment all you can isolate is the smell, not bulk product.

I just said that the synthesis is easy, not the isolation. For the ones that we did at school, we did not isolate the pure esters. It was just a qualitative lab where we made test-tube scale amounts of a lot of different esters to smell. If I was making them at home, I'd do it larger scale with a nice reflux apparatus and either do a distillation or a solvent extraction to try and isolate the pure ester, like I did when I made methyl salicylate at home.

Amos - 9-5-2015 at 07:22

Quote: Originally posted by papaya

Could you describe how did you isolate pure esters ? You mention synthesis being "easy" however without proper equipment all you can isolate is the smell, not bulk product.

It's not really all that difficult to isolate them, generally. Generally, the procedure is, once you've boiled off most of the alcohol you've used as a solvent, the mixture can be dumped into water, where the ester forms a separate layer. It can then be washed with base and with saturated sodium chloride to remove acid and excess water, respectively, and distilled. So all that's really needed is distillation equipment and a separatory funnel.

[Edited on 5-9-2015 by Amos]

Texium - 9-5-2015 at 07:31

As long as your yield of the ester is high enough that is. If you don't do it on a large enough scale, you won't get a cohesive layer in the separatory funnel, just a bunch of little bubbles.

blargish - 9-5-2015 at 08:24

Really neat chart! I've only really made made methyl salicylate myself and didn't bother to isolate the product...

Definitely an area of chemistry that I want to delve into in the future!

DraconicAcid - 9-5-2015 at 08:43

We do a similar lab at our college, where we make iso-amyl acetate and methyl salicylate (along with aspirin and nylon). The iso-amyl acetate (3-methylbutyl acetate) smells strongly of artificial banana.

I've tried to do my own "ester party" and make a whole bunch of random esters the same way, but nothing ever works. Now I've got a condenser, I can do it right and isolate them (like I did with the methyl cinnamate). Just need to find the time.

[Edited on 9-5-2015 by DraconicAcid]

blogfast25 - 9-5-2015 at 09:51

Very nice chart, zts16! (any chance of formatting it a bit better?)

gdflp - 9-5-2015 at 09:54

One thing though, it's missing isopropyl esters! Other than that, nice chart.

Pumukli - 9-5-2015 at 11:15

And now I lost another illusion. Until looking at the chart above I tought that a given ester has a fairly unique smell. But look at those apples and green leaves and bottles! Seemingly unrelated esters share the same smell! I thought that if I smelled something like e.g. banana then I could identify the compound as a fairly pure isopentyl-acetate. Now it seems I can't save on a gas chromatographe. :-) (Which would otherwise be a handy item in my shed.)

Shouldn't "benzanoate" be benzoate?

Texium - 9-5-2015 at 16:55

Quote: Originally posted by blogfast25

Very nice chart, zts16! (any chance of formatting it a bit better?)

Quote: Originally posted by gdflp

One thing though, it's missing isopropyl esters! Other than that, nice chart.

Thanks! Although I must say, I did not make that chart, it's just something that I found upon looking up "ester smells table." It came from here. The creator of the site made some other nice infographics also. I suppose it would be possible to create a modified, expanded version that is more detailed, with his permission. I don't see any copyright stuff anywhere, though I think it would still be polite to ask him first.
The lack of isopropyl esters is definitely the first thing that jumps out.

Quote: Originally posted by Pumukli

And now I lost another illusion. Until looking at the chart above I tought that a given ester has a fairly unique smell. But look at those apples and green leaves and bottles! Seemingly unrelated esters share the same smell! I thought that if I smelled something like e.g. banana then I could identify the compound as a fairly pure isopentyl-acetate. Now it seems I can't save on a gas chromatographe. :-) (Which would otherwise be a handy item in my shed.)

Shouldn't "benzanoate" be benzoate?

Many of the esters that have the same picture on the chart actually smell rather different from one another. The chart simplifies it, to give you a rather vague idea of what the esters smell like, but they're still quite unique. And yes, it should be benzoate.

[Edited on 5-10-2015 by zts16]

Etaoin Shrdlu - 9-5-2015 at 17:13

Okay guys, does ethyl formate really smell like rum? People keep insisting that to me and on the occasions I've smelled it I always without fail got a strong impression of apple. (Maybe I should start drinking?)

Also, propyl acetate. Pear or not pear? I know it's supposed to be pear. It's supposed to be quintessential pear. But it just smells horrid to me, even in small quantities. Horrid in a way that makes me understand what people mean when they say they can't stand organic solvents.

Texium - 9-5-2015 at 17:17

Quote: Originally posted by Etaoin Shrdlu

Also, propyl acetate. Pear or not pear? I know it's supposed to be pear. It's supposed to be quintessential pear. But it just smells horrid to me, even in small quantities. Horrid in a way that makes me understand what people mean when they say they can't stand organic solvents.

I agree. It's pretty terrible. When diluted a lot, it smells a bit more like pear, but still really harsh and fake smelling. The least offensive fruity ones that I smelled the other day were benzyl butyrate and pentyl propanoate.

DraconicAcid - 9-5-2015 at 17:25

I can't even tell what some of those pictures are supposed to be. What kind of flower is that? Is that some sort of spice?

Etaoin Shrdlu - 9-5-2015 at 17:28

Quote: Originally posted by DraconicAcid

I've tried to do my own "ester party" and make a whole bunch of random esters the same way, but nothing ever works. Now I've got a condenser, I can do it right and isolate them (like I did with the methyl cinnamate). Just need to find the time.

If you just want to smell them, mix approximately equimolar amounts of the alcohol and acid in a small test tube, add a few drops of concentrated sulfuric acid, then stuff the top with paper towel or otherwise loosely cover it to prevent rapid evaporation and let sit in a water bath at ~80C for ~30 minutes. Dump the contents of the test tube into a beaker with 10-20 times the volume of saturated bicarbonate solution. This will neutralize leftover carboxylic acid so it doesn't contribute to the smell. The alcohol is usually much less strongly scented than the ester, and some gets mopped up by the water so you can get a good idea of the smell by wafting over the beaker. It's a good way to try a whole bunch of different ones at once, and works especially well for the stronger ones.

zts, if you're interested in berry smells, isobutyl formate is a great raspberry.

EDIT: The ambiguous flower is jasmine. The kind of flowery kind of seedy looking thing is star anise.

[Edited on 5-10-2015 by Etaoin Shrdlu]

Texium - 9-5-2015 at 17:52

Really the 30 minutes aren't even necessary. When we did it at school it took maybe 10 minutes max to be able to clearly distinguish the smell of the ester. I hadn't thought about doing the bicarbonate wash before smelling them, that's a good idea. (Especially with butyrates!)
And I would have made isobutyl formate, but we don't have isobutanol at school

I love raspberries.
Edit: Wait a minute, it's n-butyl formate that has the raspberries according to the chart. I think I will try making some of that at school when I get a chance.

[Edited on 5-10-2015 by zts16]

DraconicAcid - 9-5-2015 at 18:27

That's pretty much what I did, and I never managed to get it to work with the combinations I tried. No idea why it didn't go, when the methyl salicylate and isoamyl acetate work perfectly that way for the students. Maybe my lack of a green thumb applies to floral scents in addition to flowers.

DraconicAcid - 12-5-2015 at 08:41

I did manage to make (but not isolate) methyl vanillate (my students oxidized vanillin to vanillic acid a few years ago, and I still had some kicking around). Smelled a lot like nutmeg.

I've tried two esters this week, and adding ice-cold sodium carbonate gives a homogeneous mixture. I didn't think the ester would hydrolyze that quickly when cold.

ETA: Stupid! I needed to use sodium BIcarbonate!
[Edited on 12-5-2015 by DraconicAcid]

[Edited on 12-5-2015 by DraconicAcid]

smaerd - 13-5-2015 at 08:34

Ooo fun esters

. I have some nice alcohols which could be turned into carboxylic acids if I felt like dealing with dichromate. Hmmmm hmm hmm. Maybe I'll join in on some of the fun. Put my dean stark and molecular sieves to use.

Etaoin Shrdlu - 13-5-2015 at 10:00

Basic permanganate can take primary alcohols to carboxylic acids, if you don't feel like dealing with dichromate.

DraconicAcid - 13-5-2015 at 14:09

Methyl benzoate smells rather minty.

blogfast25 - 13-5-2015 at 18:11

Quote: Originally posted by DraconicAcid

ETA: Stupid! I needed to use sodium BIcarbonate!
[Edited on 12-5-2015 by DraconicAcid]

[Edited on 12-5-2015 by DraconicAcid]

Methinks you merely used too much carbonate. Calculate how much is needed and add it more slowly and alkaline de-esterification should not occur, I think. Bicar is fine too, of course.

Firmware21 - 28-8-2015 at 08:01

Has anyone tried to synthetize Isopropyl Salicylate ? I tried it recently, but couldn't isolate the product (Using wet solvent and overshooting either Sulfuric acid and sodium carbonate didn't help very much I guess).
it still had a very uncommon "green-scent" which now perfumes my leibig condenser. I might try it again if I manage to get my hands on anhydrous IPA.

[Edited on 28-8-2015 by Firmware21]

Praxichys - 28-8-2015 at 08:42

It doesn't really matter if your starting reagents are dry since the esterification reaction produces water anyway. To ensure completion, running the reaction with continuous removal of water (dean-stark trap or similar) will work well.

Try using excess salicylic acid. Reflux for a few hours (with water removal, if possible*), let cool, then drip saturated bicarbonate solution until exactly pH neutral or very slightly basic to convert the excess salicylate to the sodium salt. This will make the salicylate very soluble in what little water is in the mix, and will probably force the product to layer out. If not, saturate with a neutral salt like sodium chloride. If it still fails to layer out, extract with toluene.

Dry the product (or the extracted mixture) over a neutral drying agent (a vacuum desiccator would be ideal since the target has a high boiling point) and then vacuum distill.

That's how I'd do it. Of course, I'd be making like 100g of the stuff.

* Water removal drives the equilibrium and will greatly increase yield. Just be careful if you use sulfuric acid or you might sulfonate some things if the water content gets low. TsOH as a catalyst may be a better choice in that case, if you can make it.

Firmware21 - 28-8-2015 at 10:12

I'll try that next time (I'm not going for the 100g though).
However, unless I can improvise a dean stark with my current glassware set and figure out how to use it properly, I don't think I will be able to get a continuous water removal.

Also, I tried to extract the mixture with some ethylacetate, but I don't know yet if it catched anything.

Praxichys - 28-8-2015 at 10:49

The good news is that if you can distill, you probably already have one.

The main problem with this setup is joint leakage at the small flask. Grease it well and use your stiffest clip.

I sometimes use this setup when I know my dean-stark will need emptying every 10 minutes. You can trap a LOT of water with a setup like this. The drawback is that it needs a lot of solvent, and you have to shut down to empty it. (Calculate water yield and select an appropriately-sized flask)

For your ester synthesis, you should run with NaCl dust or something in the trap to "salt out" the isopropanol that will distill into it with the toluene, so the reactant gets returned to the flask but the heavier salt solution stays behind. You may be able to get away with just using isopropanol as the solvent since it has a 91% azeotrope, and the salt will trap the water in the "dean-stark" and return only isopropanol. Unfortunately you'd trade the use of toluene with having to fractionate the isopropanol from the final product, which is more difficult than removing salicylate but not terrible since their boiling points are so far apart. Use a neutral, alcohol compatible salt in the trap like NaCl. If not, the small amount of isopropyl salicylate that will come up with the toluene vapor (think: steam distillation) will be hydrolyzed if you use K2CO3 or something, and trap salicylate while returning isopropanol, reducing efficiency.

If you decide to run with excess isopropanol (instead of salicylate), you will still need to neutralize the catalyst at the end, so the process for extraction is essentially the same, just with far less base. There will also be an added step of fractionating off the alcohol either before or after drying the mixture. I would recommend drying before fractionating since it may eliminate a lot of ternary/quaternary azeotropes that may form between the components and water, since they're all polar to some degree. MgSO4 may work, but I would probably reach for the 3A or 4A sieves.

Sorry if this is too much detail. I get carried away sometimes.

[Edited on 28-8-2015 by Praxichys]

Firmware21 - 28-8-2015 at 11:52

Thanks a lot ! I thought that I could distill the IPA as an azeotrope with water while adding anhydrous IPA with an addition funnel, but it should be good with the improvised dean stark and sodium chloride, we'll see anyway. I hope a good old Vigreux column will be enough to separate the azeotrope though.

Ps: IMO, there is no "excess details"

chemrox - 28-8-2015 at 15:08

phenethyl anthranillate smells like oil of musky rose. I would be an even cooler chart if the pictures were clickable.

chemrox - 28-8-2015 at 15:11

Quote: Originally posted by Praxichys

I sometimes use this setup when I know my dean-stark will need emptying every 10 minutes.

Praxichys I have a couple of Dean Starks with stopcocks. I'll sell one if you like. Say $20.

[Edited on 28-8-2015 by chemrox]

Praxichys - 29-8-2015 at 11:29

Mine has a stopcock, but it's a pain to keep draining 10ml of water every few minutes. I sometimes use the other type of setup because I can just get it going and leave it for a few hours, and it's done when I get back. Drying wet, deliquescent items I need upwards of ~150ml water capacity sometimes. It's nearly impossible to get the rate perfect and just leave the stopcock open slightly.

$20 is a good deal for one of those. Do you happen to have one with a capacity greater than 15ml? I'd take a 50 if they even make them that big.

Brain&Force - 22-1-2016 at 19:58

Quote: Originally posted by Etaoin Shrdlu

I have some n-amyl acetate and I find that to be the quintessential, unwashed, raw pear scent, with slight hints of banana, apple, and pear. It's dissolved in 1-pentanol, though, which might affect the scent enough to produce those other notes.

Firmware21 - 2-6-2016 at 16:24

Fellow chemists, i present you the magnificent derp-stark :p

I tested it on a citric acid/IPA esterification: the system works pretty well (no leaks or whatever) but I didn't get the expected separation (salting out) in the trap. Maybe there was too much IPA for the amount of water generated.

I used about 20 g of citric acid (monohydrate) and an extreme overkill of 150 ml IPA, knowing at least 70 ml were required to fill the trap ( + 3 drop of conc. H2SO4) The trap was half filled with table salt.
Refluxed it for 4 hours.

I then tried to neutralize it with NaHCO3, but it fizzed way too much for the amount of catalyst used. Either caused by unreacted acid and/or free carboxyl group in the mono/di isopropyl citrate...

UC235 - 2-6-2016 at 19:18

NaCl will only salt water out of IPA up to about 90%. After that point, the salt just sits there and stronger dessicants are needed.

chemrox - 8-6-2016 at 08:57

Attempted synthesis of deschloroloperamide propanoate. This is involves a hindered OH group. I dissolved 14 g deschloroloperamide in 300 ml DCM and refluxed at ~ 41*. I added 2.8 ml propionyl chloride and observed bubbling and a slight increase (~2*) in reflux temp. Continued reflux for another 3 hrs. Extracted with 1M NaOH and dried over NaSO4. Cryx in dish over night. Collected product and took mp.s; deschloroloperamde MP 102-104*C, product: 90-104 *C. I suspect partial esterification occurred but IR is down.

DraconicAcid - 8-6-2016 at 09:27

Extracted with sodium hydroxide? Wouldn't that likely hydrolyze the ester?

chemrox - 9-6-2016 at 12:41

No not 1M as a wash. Corrections: mp was wrong.. to high temp and too much of a hurry
mp was 92-94 vs 102-104 for the starting material. Separation by TLC was ok but mixed with the some of starting spot. Polar solvent mixture- the ester migrated more slowly-seems consistent with mp however the mixture is troubling so how to proceed? More acyl halide? longer time? catalyst? which one?

[Edited on 9-6-2016 by chemrox]