Sciencemadness Discussion Board

Methyl tosylate from Trimethyl Borate

hippo - 12-8-2019 at 08:18

It's already fairly well established that trimethyl orthoformate and anhyd. tosylic acid can react to form methyl tosylate. Seeing as trimethyl borate also breaks down into methanol in water, I was wondering if it could react similarly with tosylic acid to form methyl tosylate. I have some tosylic acid on hand and I would like the opinion of someone who knows more than me on the feasibility of this reaction before I attempt it.
Regards,
hippo

AvBaeyer - 12-8-2019 at 16:13

You pose a very interesting question. At first glance, a couple of things are working against you. First is the extreme sensitivity of trialkylborate esters to water. Compounding this sensitivity is the fact that most tosic acid contains a mole of water of crystallization which is available to destroy your trimethylborate ester. You would need to ensure that your tosic acid, which is also quite hygroscopic, is anhydrous by utilizing some type of drying method. I think that if you can ensure anhydrous tosic acid and using a large excess of trimethylborate you might be able to isolate some of your target compound.

By the way, the use of trimethylorthoformate to make methyl tosylate is not as good as it seems.

AvB

hippo - 12-8-2019 at 16:36

Quote: Originally posted by AvBaeyer  
You pose a very interesting question. At first glance, a couple of things are working against you. First is the extreme sensitivity of trialkylborate esters to water. Compounding this sensitivity is the fact that most tosic acid contains a mole of water of crystallization which is available to destroy your trimethylborate ester. You would need to ensure that your tosic acid, which is also quite hygroscopic, is anhydrous by utilizing some type of drying method. I think that if you can ensure anhydrous tosic acid and using a large excess of trimethylborate you might be able to isolate some of your target compound.

By the way, the use of trimethylorthoformate to make methyl tosylate is not as good as it seems.

AvB

Thank you for your input!
In terms of drying the tosylic acid, I wonder if azeotropic drying may be used in the same way one would dry oxalic acid. If dehydrating the tosylic acid isn't feasible, a large excess of trimethyl borate could be used as it is fairly easy to make starting from OTC chemicals.

AvBaeyer - 12-8-2019 at 18:06

Using excess trimethyl borate to dry tosic acid will not be of much use. You will end up with an unworkable equilibrium between (hopefully) some methyl tosylate, methanol, tosic acid, boric acid and trimethyl borate. If you think about how trimethyl borate is prepared, you should see why this is so.

By the way, conc. sulfuric acid is used as a catalyst to form trimethyl borate from boric acid and methanol. Has anyone ever reported dimethyl sulfate as a by-product in that reaction? If not, this may not bode well for your proposal. The formation of monomethyl sulfate (aka methylsulfuric acid) is irrelevant because it readily forms when methanol and sulfuric acid are combined. In another vein, a quick (and incomplete) search also shows no useful carboxylic acid ester formation using trimethyl borate as a primary search result.

Think about this some more. If nothing else you will learn some more chemistry which is always good. Have fun!

AvB

Sigmatropic - 13-8-2019 at 08:47

IIRC, if you enter trialkyl borate and tosylic acid into reaxys you get a patent about preparation of butyl tosylate using these reagents.
But for butyl it actually makes sense, since you can distill off the product and then the water (or the other way around) reforming your tributyl borate.
Not so much with methanol and trimethyl borate...

AvB,
Esterferication of boric acid does not require sulfuric acid, where does that idea come from?

Tsjerk - 13-8-2019 at 09:24

How about dehydrating the tosylic acid by heating to about 120 degrees or so? That would melt the compound so you can indicate completion by the absence of bubbling. The second indicator for the anhydrous compound would be the difference in melting point, which is quite extreme in this case.

[Edited on 13-8-2019 by Tsjerk]

Tsjerk - 13-8-2019 at 23:11

You can also dissolve the tosic acid monohydrate in methanol, dry with magnesium sulfate, filter, boil down to the volume you want to run your reaction at and add the methyl borate. There reaction runs in methanol anyway.

Tosic acid is only hygroscopic when solid, so drying in solution should be no problem.

hippo - 14-8-2019 at 02:02

Quote: Originally posted by Sigmatropic  
IIRC, if you enter trialkyl borate and tosylic acid into reaxys you get a patent about preparation of butyl tosylate using these reagents.


If good results have been achieved with a similar compound I guess that justifies an attempt using trimethyl borate. Will try once I've got my hands on some borax.
Quote: Originally posted by Sigmatropic  
But for butyl it actually makes sense, since you can distill off the product and then the water (or the other way around) reforming your tributyl borate.
Not so much with methanol and trimethyl borate...


In what process would the borate be reformed?

hippo - 14-8-2019 at 02:04

Quote: Originally posted by Tsjerk  
You can also dissolve the tosic acid monohydrate in methanol, dry with magnesium sulfate, filter, boil down to the volume you want to run your reaction at and add the methyl borate. There reaction runs in methanol anyway.

Tosic acid is only hygroscopic when solid, so drying in solution should be no problem.


I hadn't even considered drying in organic solvent, I will definitely give that a go

Tsjerk - 14-8-2019 at 10:34

Cool, I haven't tried it but please let me know whether it works.