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Author: Subject: Isopropyl Salicylate
JHorace6p
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smile.gif posted on 21-2-2021 at 00:25
Isopropyl Salicylate


Hey there, I'm actively working on an isopropyl salicylate synthesis via isopropanol and salicylic acid.

Beginning with 10.5g of salicylic acid and 30.1mL of isopropanol in warm solution, while agitating I slowly added 10mL of concentrated H2SO4. The solution was set up for reflux at about 90 degrees C for 80 minutes.

Within 30 minutes there was a distinct and unusual odor being generated; very difficult to describe the actual smell, reviews were mixed.

After 80 minutes I let the solution cool to room temp and poured the mixture into a separatory funnel. Two layers clearly emerged.
This is the moment I found myself slightly confused... Possibly due to the somewhat offensive yet pleasant odor.

Something worth noting is that the stir bar I used, was by no means entirely clean, it had minor traces of a violet dye residue from a previous synthesis on it. What does this mean? (This should have no effect on the procedure itself) The solution was very colored (it should be colorlessish?) The top layer was very deep purple and the bottom layer was a pale red/orange.

I panicked, I decided to first perform a DCM extraction on both layers at once instead of isolating each and doing the extraction method on the single product layer.

I see now that I should have let the densities and other obvious properties guide my methodology here. However, I got confident in the face of ignorance. After adding the DCM I had the two same layers (the DCM seemed to go to the top layer) as described before. I isolated both layers and am not sure how to proceed.

I'm looking for guidance here with this situation and am thrilled for this to be my first post here. I honestly never communicate about these projects to anyone but myself and my wife; I am very excited to be hearing from others with the same passion and look forward to developing some scientifically motivated online-acquaintances.

I have pictures and better descriptions via note taking, if needed let me know and I will post them soon.
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Fery
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[*] posted on 21-2-2021 at 01:13


Hi JHorace6p and welcome to the forum.

Density of your ester 1,06 g/ml close to water
https://www.fishersci.com/shop/products/isopropyl-salicylate...
You used a lot of H2SO4 (personally I would use 10-50 times less of acid catalyst) which increased your water phase density but also unreacted isopropanol (you used excess which is good idea as it is cheaper than salicylic acid) which decreased density of your water phase and you increased density of the ester phase by adding dichloromethane.
The easy way to determine which phase is water you can paint a mark to the glass wall on the actual border of the 2 phases, add some water, mix thoroughly and observe which phase increased its volume (whether the new border is still at the mark). Sometimes densities of both phases are very close so separation is difficult and long lasting, in such cases you can change densities (e.g. add NaCl to increase density of water phase, add hexane to decrease density of organic layer, add dichloromethane to increase density of organic layer). You can increase yield of ester if it is more soluble in water by adding organic solvent for extraction, but for less water soluble ester there is no need to obtain extra few % from water phase by adding organic solvent and further lose more % of the product due to the necessity to separate the added solvent by distillation.

Scent of your ester: green, cortex clover orchid
http://www.thegoodscentscompany.com/data/rw1450281.html

Syntheses of these esters with pleasant scents could certainly attract also your wife to the chemistry.

[Edited on 21-2-2021 by Fery]




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Texium
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[*] posted on 21-2-2021 at 08:01


I tried making isopropyl salicylate once a long time ago and found the smell to be quite unpleasant. It is not the nice wintergreen aroma that you get from methyl salicylate. It’s very vegetal.

Now that you have the two layers, the next thing you’ll need to do is figure out which one is your organic layer. Take a small sample of each layer in test tubes, and add water to each of them. See which one takes up the water and which one won’t mix. Once you know which one is your organic layer, return it to your sep funnel and wash it with a saturated sodium bicarbonate solution to remove any unreacted salicylic acid and sulfuric acid that may be in there (make sure to vent frequently!). Then wash it with some saturated sodium chloride brine (it’s always nice to have a large bottle of this on hand). This will help remove water. After you’ve washed the organic layer with brine once or twice, you can transfer it to a beaker and add some anhydrous drying agent of your choice (sodium sulfate, magnesium sulfate, calcium chloride) and let it sit for 15-20 minutes. After that, evaporating the solution should yield your crude isopropyl salicylate.




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Amos
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[*] posted on 22-2-2021 at 07:02


Purple coloration usually means you have some small amount of iron contamination; it's very, very common in salicylate preps. I don't know if you've ever performed or witnessed column chromatography before, but I like to do my final drying stage by packing a burette or column, and sometimes even just a pasteur pipette, with granules of my drying agent (usually anhydrous sodium sulfate) and running all of my liquid product through that, forcing the last bit out with the squeeze of a pipette bulb. You get a clear, dry product almost instantaneously, and this method also gets rid of any remaining liquid emulsions, dust, or fibers you may have gotten into it during handling.

I concur with zts above that it is not at all a pleasant-smelling ester, it smells like an aggressively latexy plant, maybe even petrochemical-like to a degree. And welcome to the forum, I hope you'll let us in on your successes and your troubleshooting processes more.

[Edited on 2-22-2021 by Amos]
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JHorace6p
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[*] posted on 23-2-2021 at 20:42


Wow! I did not anticipate such quick and great responses.
You have all brought up great points.

Firstly, I should have used less acid, I was following an old procedure (for methyl salicylate) from an old lab book of mine. The acid recommended seemed very excessive and I sorta justified it by thinking, well isopropanol is a secondary alcohol... and yeah I justified it in the moment, but looking back... Yes, way too much acid!

Second, I've determined my product is in the deep purple layer, and Now I'm working on the washing and cleaning process that Texium suggested.

I have a lot more to say to all your post and I'll put some pictures up once I have a crude yield to show.

I'll be back with some values and yields, and I'll reach out if I run into any more issues. Thanks for the amazing welcome you all. Stay safe, stay healthy.
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[*] posted on 1-3-2021 at 04:00


i think isopropyl salicylate smells decent and unique. I have had my sample for over a year now. latex, vegetal, spinach, green, leather, floral, are good ways to describe it.

You are using too much sulfuric acid. You only need a 5 mol % sulfuric acid to the limiting alcohol or carboxylic acid. I once used way too much sulfuric acid while trying to make isopropyl salicylate. The result was immediate formation of a purple slush and a gasoline smell (probably from dehydration of isopropyl alcohol to propene). I tried again with 5 mol% of sulfuric acid and it worked

Secondary alcohols require a long reflux to make esters, 18 hours (source: vogel's practical organic chemistry)

[Edited on 3-1-2021 by Cou]




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digga
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[*] posted on 2-3-2021 at 13:34


Question: Did you use 100% isopropanol? Le Chattelier's principle is at the core of esterification. The reaction goes both ways. The rate and direction depend on the relative concentrations of the reactants and products.

Water is a product. The more there is, the slower she goes. If you can remove the water, then the reactions runs faster to the right. Lots of Sulfuric acid will hold onto the water. Too much forces side reactions, like dehydration of the IPA.

My two cents: Use a massive excess of dry IPA. Use a much smaller percentage of concentrated Sulfuric Acid, as measured against the salicylic acid, as a catalyst. Reflux it with a drying column. (A Vigreaux column with some glass wool in the bottom packed with your favorite desiccant will do nicely. )

As the reaction mixture boils, a water/IPA azeotrope will rise into the column. The desiccant will bind the water and the IPA will drip back. This should repeat until all the salicylic acid is used up.

What remains is product, IPA and the sulfuric acid. Neutralize the acid with a mild base. An aqueous layer should separate. Distill off the IPA from the organic layer. What remains will be the product.

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[*] posted on 3-3-2021 at 20:01


So I went and did what I suggested. I packed the column with anhydrous Mg2SO4. Bad move. Much of the IPA was trapped up there and I ended up replacing it. Sieves would have been better. The column packed up tight. I am sure it got some of the water.

I am at the laundry phase. Filmatleven.

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