[Sis290025]

After adding the nitric/sulfuric acid mixture to the benzoate/sulfuric acid mixture and warming the reaction mixture at room temperature, the reaction mixture is poured over only crushed ice. I know this causes precipitate to form, and, then, one can perform suction filtration to isolate the product. Thus, this is why ice is used instead of just cold water?

Thanks.   

[russellm72]

It's just a way of controlling the workup. Remember adding H2SO4 to water causes an exotherm. Just adding cautiously to ice you can see if things are getting a bit hectic.

This is a typical school/university experiment whereupon the product of the reaction precipitates pure from the reaction. This is not normally the case but with your product being a solid and the starting material an oil it can be removed ok this way. In reality, on a small scale, you'd add to iced-water and extract into an organic solvent. Clearly this has more hazards and more expensive to run as a teaching experiment.

R.

[Sis290025]

Which method would yield more optimal results if one were to do this activity: pouring it over ice or using iced water and extracting?

[russellm72]

Depends on your substrate. Your product is a basic aromatic compound so e.g. at beginning of a synthesis you'd probably do it on a large scale so it precipitating out might be ideal. Also it may precipitate out pure not needing purifying apart from perhaps a recrystallisation which may not be necessary depending on what you need to do. The yield here might not be great but your using cheap readily available chemicals and aqueous conditions. So easy to do and most folks can do easily. Also if you dont have to purify your saving time so again a cost saving.

If your compound was more valuable e.g. several steps into a synthesis then clearly you'd want to maximise your yield. In this case extracting your product into a solvent, concentrating and purifiying by flash/HPLC might be more beneficial. Of course here the user will need to be more experienced and will take longer to isolate your product. With experience you'll learn whats better to do.  Remember the worst steps of a synthesis should ideally be at the beginning because normally the chemicals are cheaper and more readily available and your not so far into the synthesis if you need to bring more material through.

R.

[Sis290025]

In the preparation of the benzoate/sulfuric acid mixture, I just wanted to review what happens when methyl benzoate dissolves in sulfuric acid (the ionic species that arise).


After the ester in placed in the acid, the O atom double bonded to the C (C=O group) is protonated by the acid.

A series of resonance structures, such as

___OH
___|
Ph-C-OCH3

and

___O-H
___||
Ph-C-OCH3

result?


Before the O atom is actually protonated, can the following be considered as one of the ions, aside from HSO4-, that are produced?
___O-
___|
Ph-C-OCH3
--(+)

Are there any other ions that I am missing from this reaction?


Thanks.
   

[AhmedEzatAlzawalaty]

wouldnt the acid hydrolyse the ester?
isnt there better method by first doing nitration of benzene and then convert nitro to amino by SnCl2/HcL and then converting amino to acylamino by acylation then block para by sulfonation then add Cl2/Fe
then Mg/Ether then CH3Cl then you add the Methyl then oxidize it to acid and esterify then regenerate the amino oxidize it into nitro?
 i think starting with nitrobenzene is better

[Sis290025]

I have another question about this experiment. Would the crude product of methyl m-nitrobenzoate have a higher mass than the recrystallized product of methyl m-nitrobenzoate?

Thanks again.

[russellm72]

Well think about it.

If your compound was 90% pure containing 10% impurities and you recrystallised to get material >99% pure by e.g. HPLC what do you think?

R.