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Author: Subject: Ester synthesis
Bedlasky
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[*] posted on 10-3-2020 at 14:34
Ester synthesis


Hi.

I've been thinking that I should try some organic preparations. I have access mostly to carboxylic acids and alcohols, so esters sounds like good idea.

I can somehow obtain these compounds:

Methanol

Ethanol

n-propanol

Isopropyl alcohol

n-butanol

sec-amyl alcohol

Propylene glycol

Glycerol

Formic acid (85%)

Acetic acid (99,5%)

Butyric acid

Valeric acid

Sorbic acid

Stearic acid

Oxalic acid

Tartaric acid

Lactic acid

Citric acid

Benzoic acid

What equipment should I have for esters preparations?

[Edited on 10-3-2020 by Bedlasky]
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Mr.StinkyGas
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[*] posted on 10-3-2020 at 14:42


You should also check out esterification with FeCl3 for reactions that are sensitive to conc. Sulfuric acid. I made littorine HCl with this method. I wonder if indium nitrate would work as well. I need to do more experiments...

Equipment would be a reflux apparatus consisting of the flask and condenser with the heating mantel or even better a sand bath with a hotplate stirrer. You will need a small water pump for the condenser.

[Edited on 10-3-2020 by Mr.StinkyGas]
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Syn the Sizer
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[*] posted on 10-3-2020 at 14:58


that's a nice list of acids and alcohols. There is a very nice table of esters and associated scents online, I will post the link.

https://jameskennedymonash.files.wordpress.com/2013/12/table...
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DraconicAcid
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[*] posted on 10-3-2020 at 22:19


I will point out that secondary alcohols don't work as well as primary ones for regular Fischer esterification. Tartaric acid, citric acid and lactic acid have their own hydroxyls, and will probably give you a mess in Fischer esterification.

I've had some good results with butyric and acetic acid, and I've managed a couple of benzoates, cinnamates, and anisates. The latter ones are very difficult to purify by distillation, though (methyl cinnamate has a high enough mp to be crystallized, though).

Oxalic acid should work. ( https://thosci.com/synthesis-of-diethyl-oxalate/ )




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Syn the Sizer
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[*] posted on 11-3-2020 at 05:01


I have been curious about esters with acids like citric acid since it has 3 carbonyl groups, If it was possible you would need 3 moles of alcohol for every mole of citric acid.
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[*] posted on 11-3-2020 at 05:28


One word of warning with butyric acid. I recently obtained some of this, but the smell is so bad and remains lingering around so much, that I still did not do any experiment with that. I only transferred the acid from its plastic bottle to a glass bottle with a very good cap. I descarded the plastic bottle. After this act of transferring the acid to another container, in which I accidently spilled a few drops (just a few drops, not more), I had the horrible smell (of vomit) around me for a few days, even after showering.



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Tsjerk
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[*] posted on 11-3-2020 at 06:11


If you do use butyric acid, make sure you dry the ester very well before storage, you will learn what hydrolysis is when you don't ;).

Citric acid condenses well with primary alcohols at least. The tertiary alcohol of citric acid is not very reactive.

Tartaric esterfications with primary alcohols should also be no problem as long as you use a lot of ethanol. You have to remember that these are equilibrium reactions. Even when a less reactive secondary alcohol from the tartaric acid reacts with another tartaric molecule, the reaction is reversible, so it doesn't really form a polymer, over time it will reverse and react with an primary alcohol.

[Edited on 11-3-2020 by Tsjerk]
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Bedlasky
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[*] posted on 11-3-2020 at 06:19


Thnaks for answers.

Woelen: I know that butyric, valeric and capronic acids smells horribly. I'll probably start with esters of formic, acetic and benzoic acids. When I have more experience, I'll start with ohters.

Syn the Sizer: I found some link about triethyl citrate synthesis.

Triethyl citrate and tributyl citrate are used as environment friendly plasticizers.

Tsjerk: Preparation of diethyl tartrate

[Edited on 11-3-2020 by Bedlasky]
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[*] posted on 11-3-2020 at 07:51


simple methyl and ethyl esters are easy to make with HCl, H2SO4, or toslic acid as a catalyst. Usually you just use an excess of the alcohol, since it is cheaper, and then use a Dean Stark trap to remove the water with toluene as a solvent. Or you can make the anhydride or activated ester and then couple to the alcohol. For hydroxyacids, the reactions are structure dependent, as some form internal esters, lactones (like caprolactone), while other form polymers, such as lactic acid. And remember that biological fats are simlpy triesters than can be cleaved (soap) or transesterified (biodiesel). Those are neat experiments to do at home, and easy to do with chemicals you can find readily. But they are very useful reactions.
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[*] posted on 11-3-2020 at 21:17


Quote: Originally posted by Bedlasky  

Syn the Sizer: I found some link about triethyl citrate synthesis.

Triethyl citrate and tributyl citrate are used as environment friendly plasticizers.
[Edited on 11-3-2020 by Bedlasky]


I meant to comment on this when I got home, that's interesting I downloaded a copy and will read it this weekend. Thanks.

[Edited on 12-3-2020 by Syn the Sizer]
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[*] posted on 12-3-2020 at 16:19


Fischer esterification and fragrance collecting is a rewarding hobby. i like to explore the smells of the dozens of combinations of alcohols and carboxylic acids.

www.consolidated-chemical.com is a great source for many alcohols and carboxylic acids, such as 1-hexanol, 1-heptanol, 1-nonanol, isopentyl alcohol

list of esters i have made:
Methyl acetate
Ethyl acetate
Propyl acetate (pears)
Isopropyl acetate (pears)
Butyl acetate (apples)
Sec-butyl acetate (grape)
Isobutyl acetate (cherry)
Pentyl acetate (banana)
Isopentyl acetate (sweet banana candy)
Heptyl acetate (wood rum earthy)
Octyl acetate (orange fungal earthy)
Nonyl acetate (mushroom)

Methyl salicylate (root beer)
Isopropyl salicylate (leather vegetal herbal)


equipment i use for fischer esterifications:
* castor oil bath in crystallizing dish
* stirring hot plate
* round bottom flask
* stir bar
* liebig condenser (300 mm is overkill, even with room temperature circulating water the reflux line never goes above 10 mm)
* aquarium water pump and vinyl tubes
* CaCl2 drying tube on top of condenser

for the workup
* separatory funnel
* for esters that require a fractional distillation, a 200 mm hempel column packed with raschig rings works great
* distillation setup
* sand bath heating


Quote: Originally posted by DraconicAcid  
I will point out that secondary alcohols don't work as well as primary ones for regular Fischer esterification. Tartaric acid, citric acid and lactic acid have their own hydroxyls, and will probably give you a mess in Fischer esterification.



Secondary alcohols do work with fischer esterification, though you have to reflux for a really long time (up to 18 hours) because steric hinderance slows the reaction rate. Vogel's tells you to reflux for 18 hours when making isopropyl acetate. I thought that was absurd and unnecessary, since most esters only take a couple hours, so i just used a generous amount of H2SO4 and stopped after 5 hours. i barely had any ester layer in workup. sp i tried again with 18 hours, then i got a typical yield for fischer esterification.

Use fast stirring and slowly add the H2SO4 drop by drop. a 0.1 molar ratio of sulfuric acid to limiting reagent works for me; my first time trying to make isopropyl salicylate, i added a lot of sulfuric acid too fast, which made the whole mixture turn into a purple slush that smelled like gasoline (likely propene)

I have made isopropyl salicylate (leather vegetal smell), isopropyl acetate (pear), and sec-butyl acetate (funky grape smell) by simple fischer esterification.

For sec-butyl acetate, and all other secondary alcohols that dehydrate into di-alkyl substituted alkenes, you have to use anhydrous HCl as the catalyst instead of sulfuric acid, since sulfuric acid will dehydrate it to the stable but-2-ene. I used an HCl generator w/ an addition funnel dripping hydrochloric acid int 98% sulfuric acid, dried thru CaCl2 in a cold trap, and bubbled into a beaker of sec-butyl alcohol.

source: vogel's practical organic chemistry





20200312_192330[1].jpg - 3MB




[Edited on 13-3-2020 by Cou]
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DraconicAcid
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[*] posted on 12-3-2020 at 16:38


Nice!

I still say that there's only subtle differences between butyl acetate and propyl acetate and butyl butyrate. Apples? Pears? Bah- generic fruit.

I'm generally making these with a mind to having my students make them in a four-hour lab, so when I say the secondary ones don't work well, I mean that they aren't going to work in a reasonable amount of time (I've been planning to try the secondary ones using acetic anhydride, though).

I've managed propyl salicylate (celery, I swear), but butyl salicylate (which should smell of blackberries) has never, ever worked for me. I've tried a dozen times.

I have some isobutyl alcohol on order, along with some different acids (valeric and isovaleric).




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Cou
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[*] posted on 12-3-2020 at 17:04


Quote: Originally posted by DraconicAcid  
Nice!

I still say that there's only subtle differences between butyl acetate and propyl acetate and butyl butyrate. Apples? Pears? Bah- generic fruit.

I'm generally making these with a mind to having my students make them in a four-hour lab, so when I say the secondary ones don't work well, I mean that they aren't going to work in a reasonable amount of time (I've been planning to try the secondary ones using acetic anhydride, though).

I've managed propyl salicylate (celery, I swear), but butyl salicylate (which should smell of blackberries) has never, ever worked for me. I've tried a dozen times.

I have some isobutyl alcohol on order, along with some different acids (valeric and isovaleric).


i'm planning on trying to make butyl salicylate soon. i'm gonna do it in toluene solvent with a large excess of salicylic acid. After reflux, wash reaction mixture with lots of water and sodium bicarbonate solution so all you have left is organic layer w/ toluene and butyl salicylate. distill off toluene, then use vacuum to distill the butyl salicylate since its high boiling point is difficult (271 C)

EDIT: do you know if sulfuric acid is soluble enough to dissolve in toluene for fischer esterification catalysis? if you do that, then a dean stark trap is mandatory so the sulfuric acid doesnt transfer to water in reaction flask

[Edited on 13-3-2020 by Cou]
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