Sciencemadness Discussion Board - The synthesis of methyl sorbate

The synthesis of methyl sorbate

Syn the Sizer - 10-5-2020 at 20:50

The synthesis of methyl sorbate

Objective - To synthesize methyl sorbate using methanol, sorbic acid and catalyzed with sulfuric acid.

Experimental

Sorbic acid | CH₃(CH)₄COOH | 112.128g/mol
Methanol | CH₃OH | 99.9% | 32.04g/mol | b.p 64.7^oC
Sulfuric acid | H₂SO₄ | 98% | 98.079g/mol | b.p 300^oC
Sodium Bicarb | NaHCO_{3 (aq)} | Sat. | 84.006g/mol
Sodium chloride | NaCl | Sat. | 58.44g/mol

Hazards

Sorbic acid^[1]
-Skin and eye irritation

Methanol^[2]
-Flammable liquid and vapour
-Harmful if swallowed, inhaled or in contact with skin
-Organ damage

Sulfuric acid^[3]
-Corrosive to metals
-Damage to skin and eyes
-Respiratory irritant

Sodium bicarb^[4]
-May produce flammable dust

Sodium chloride^[5]
-Skin, eye, lung, digestive irritant

Equipment

Hotplate | Model: SH-2 | Brand: Topline | S/N 20190094444
Reflux apparatus

Procedure

A reflux apparatus was assembled using a 300mm 24/40 allihn condensor and a 250mL round bottom 2-neck flask. Water flow was attached to the condensor and test to ensure there was no leaks. A drying tube filled with calcium chloride was added to the top of the condensor.
6.02g of sorbic acid was added to the round bottom flask. Sorbic acid is a white crystalline powder.
10mL of methanol was added to the 250mL round bottom flash and stirring was initiated, Methanol is a clear thin liquid.
0.5mL of ice cold H₂SO₄ was added to the flask dropwise while stirring.
A water bath was prepared with boiling hot water and the hotplate was turned on. the solution was refluxed with stirring for 72 minutes.
The heat was removed and the flask allowed to come to room temperature before the apparatus was dismantled.
5mL of cold NaHCO_{3 (aq)} was added to the round bottom flask and shaken to mix, the contents of the flask were than decanted into a 250mL separator funnel and the layers allowed to separate. The bottom aqueous layer was then drained off. This was repeated in the sep funnel 2 more times.
The bottom half of the organic layer had a clear emulsification with water as there appeared to be a 3rd cloudy phase between the aqueous and organic layers.
5mL of NaCl was added to the sep funnel and shaken to absorb water that was present, the bottom aqueous layer was drained. This process was repeated 3 more time until the emulsification was clearly gone.
Methyl sorbate has a boiling point of ~180^oC^[6] so purification was achieved by heating the ester to just above 125^oC to ensure no more water was left and the acid was neutralized with bicarb solution.

Discussion

The ester took on a brownish-yellow hue as the reaction progressed. The oil produced was lighter that the methanol and floated on top. After the first addition of bicarb solution the ester became transparent. The ester has a familiar minty scent, unlike wintergreen. It is hard to pin point the scent. A yield was not determined for this reaction.

References

[1] - Sorbic acid SDS
[2] - Methanol SDS
[3] - Sulfuric acid SDS
[4] - Sodium Bacarb SDS
[5] - Sodium Chloride SDS
[6] - Methyl sorbate

[Edited on 11-5-2020 by Syn the Sizer]

Syn the Sizer - 10-5-2020 at 20:55

I see on the left hand side of this window it says HTML is Off. I was wondering if that is my option, and if turned on will html code work in the forum post window. I am picky about my formatting and would like to be able to use HTML styles, tables and whatnot.

Fery - 11-5-2020 at 04:10

Syn the Sizer - very nice, thx for sharing !

Metacelsus - 11-5-2020 at 04:18

Quote: Originally posted by Syn the Sizer

Sodium bicarb^[4]
-May produce flammable dust

???

Syn the Sizer - 11-5-2020 at 05:54

Quote: Originally posted by Metacelsus

Quote: Originally posted by Syn the Sizer

Sodium bicarb^[4]
-May produce flammable dust

???

That is what I thought too, but its in the SDS so I added it.

Edit:
I guess it does say (during processing), and it says combustible not flammable.

[Edited on 11-5-2020 by Syn the Sizer]

Syn the Sizer - 11-5-2020 at 06:01

Quote: Originally posted by Fery

Syn the Sizer - very nice, thx for sharing !

You're welcome. It's not a top calibre write-up but I am still fairly new to the field plus writing was never my strong point, I was always more of a science/electronics person.

Texium - 11-5-2020 at 06:18

Quote: Originally posted by Syn the Sizer

I see on the left hand side of this window it says HTML is Off. I was wondering if that is my option, and if turned on will html code work in the forum post window. I am picky about my formatting and would like to be able to use HTML styles, tables and whatnot.

Unfortunately, HTML code had to be disabled on the forum a few years ago because it was used in an exploit to gain unauthorized access to other user's accounts.

Syn the Sizer - 11-5-2020 at 06:20

Quote: Originally posted by Texium (zts16)

Quote: Originally posted by Syn the Sizer

Unfortunately, HTML code had to be disabled on the forum a few years ago because it was used in an exploit to gain unauthorized access to other user's accounts.

Alright, that is understandable. This formatting doesn't look bad and I can learn to like it lol.

Boffis - 25-5-2020 at 02:24

Hi Syn the Sizer, what sort of yield of crude product did you get.

Bedlasky - 25-5-2020 at 10:17

Nice preparation! Thanks for sharing, maybe I'll try it in future.

Syn the Sizer - 24-11-2020 at 10:03

Quote: Originally posted by Boffis

Hi Syn the Sizer, what sort of yield of crude product did you get.

Sorry for the late reply, no yield was taken, this was purely qualitative, I was just curious what the methyl ester smelled like.

Dr. Who - 24-11-2020 at 16:14

Very cool. Does it have any use besides smelling "minty"?

Syn the Sizer - 25-11-2020 at 00:14

Not as far as I know, I couldn't really find any information on it. I am sure it is probably used as a flavouring too. The smell was very familiar just not sure from where.

Pumukli - 26-11-2020 at 02:34

I always had the impression that sorbic acid with its conjugated diene structure was sensitive to sulfuric acid during such a Fisher esterification reaction. I thought it may end up producing various addition products (methyl-ethers) during the process. What do you think?

I read an article (long ago) about methyl-sorbate but it was made via the diazomethane route to avoid side reactions in that article. I understand that you didn't distilled the product but maybe a TLC run would be informative regarding the purity. Those (putative) ether-esters would also be smelly (most probably) so the minty smell of the product can come from such a mixture too.

Fery - 26-11-2020 at 04:11

Hi Pumukli, I tried Fisher esterification sorbic acid + allyl alcohol + H2SO4 (cat.) + hexane (dehydrat. agent) + Dean Stark trap adapter and ended up in a black tar mass with some crystalline structure. I suppose sorbic acid underwent cyclic lactonization to parasorbic acid in my experiment?
I added allyl alcohol only approx 1,5 times stochiometric amount... perhaps adding it 3-5 times more than stochiometric amount could prevent lactonization and keep esterification and everything nicely dissolved? Maybe H2SO4 in my case induced lactonization and other catalyst could be better?

Boffis - 26-11-2020 at 09:43

Hi Fery, won't sorbic acid react with allyl alcohol via a Diels-Alder type reaction initial to a methyl-hydroxymethyl-cyclohexene carboxylic acid?

Fery - 26-11-2020 at 11:04

Hi Boffis, very likely, my experiment with preparing allyl sorbate was a big fail. I was waiting when the mass liquifies (a lot of crystalline sorbic acid which I expected to react into liquid ester) but it ended up in a black crystalline tar. Perhaps I had to go via K sorbate + allyl bromide...

Boffis - 26-11-2020 at 11:46

Maybe silver sorbate and alkyl bromide /iodide, the old way. Go retro

I have been working away on the chemistry of sorbic acid and sorbate salts. Hmmm... interesting but it very difficult to get just one product. I always seem to get a complex mixture that is hard to purify. With maleic anhydride the Diels-Alder reaction is pretty exothermic.

AvBaeyer - 27-11-2020 at 19:39

Some time ago I prepared methyl sorbate using a procedure somewhat like that reported by the OP. It is important to use recrystallized sorbic acid (mp 132-134) as the commercial material usually contains oxidation products which give it a pale yellow or off white color. It is also important to distill the ester under reduced pressure to remove minor reaction by products. An example of one of my runs is:

Purified sorbic acid (5.61 g, 50 mmole) was dissolved in 40 ml of dry methanol. Sulfuric acid (0.5 ml, note that only a small amount is required) was added and the reaction immersed in a preheated 60C bath for one hour. The reaction was then allowed to stir at room temperature for 4 hours (dinner break), then poured into water (100 ml) and saturated NaHCO3 (50 ml). The aqueous mixture was extracted with hexane (3 x 30 ml), the combined extracts dried over CaCl2, filtered and concentrated by simple distillation. The crude product (ca 4.9 g) was distilled to provide a mobile, colorless oil (3.67 g, 58%) with bp 75-78C@20mm. A reported bp is 70C@20 mm, Dictionary of Organic Compounds.

After several months in a sample vial the product became very resinous.

My unrealized aim was to reduce the ester to sorbyl alcohol to use as an intermediate for some intramolecular Diels-Alder reactions. Someday perhaps.

AvB

Fery - 28-11-2020 at 05:06

AvBaeyer, here the method of reducing sorbate esters, it is in my language so you need a translator:
http://www.chemicke-listy.cz/ojs3/index.php/chemicke-listy/a...
Reduction of methyl sorbate to (E,E)-hexa-2,4-dien-1-ol very selectively using LiAlH4 in ether.

AvBaeyer - 28-11-2020 at 16:35

Fery,

Thank you for the reference. I have also several other references to a similar reduction as well as sodium borohydride in methanol.

AvB

Syn the Sizer - 14-12-2020 at 20:01

Quote: Originally posted by Pumukli

I always had the impression that sorbic acid with its conjugated diene structure was sensitive to sulfuric acid during such a Fisher esterification reaction. I thought it may end up producing various addition products (methyl-ethers) during the process. What do you think?

I read an article (long ago) about methyl-sorbate but it was made via the diazomethane route to avoid side reactions in that article. I understand that you didn't distilled the product but maybe a TLC run would be informative regarding the purity. Those (putative) ether-esters would also be smelly (most probably) so the minty smell of the product can come from such a mixture too.

You are probably right, I am sure it probably would to a certain extent.

Cou - 14-12-2020 at 20:29

epic x)

Syn the Sizer - 16-10-2024 at 21:32

Hey People,

It has been some time since I was last here.

I am hoping to revisit this at some point in the near future, I am getting some smaller glass and have PCl5, Methanol, just need the sorbic acid which is easy.

I will need to get a new stirring hotplate.

Syn'

Dr.Bob - 17-10-2024 at 05:03

Sounds great, your write up was great to read, as the details were very clear. I wish you great luck.

Bob

Syn the Sizer - 17-10-2024 at 08:34

Thanks Dr.Bob, I appreciate it.

It has been a while since I have done a write up. The past couple years I have not had a suitable place to do chemistry so I am out of practice.