Modification of Riemer Tieman reaction

[harini_5]

I’ve learned the modification of Riemer Tieman reaction in which carbon tetra chloride is added to phenol to get aromatic acids. What is the electrophile attacking phenol?

 

[GCT]

Although I don't know a lot about this reaction my guess is that it's the carbon tetra chloride with respect to the positively charged carbon.

 

[harini_5]

But carbontetrachloride as such is very stable and so it is very unreactive.So it possibly cannot attack phenol.It is due to this low reactivity that it is used as a solvent in most cases

 

[GCT]

The molecule does not have an overall dipole moment yet there's still that positive charge on the carbon - I've known of carbon chloride compounds which are useful for addition of carbon on the benzene although I am not recalling any at the moment.

P

 

[gravenewworld]

I’ve learned the modification of Riemer Tieman reaction in which carbon tetra chloride is added to phenol to get aromatic acids. What is the electrophile attacking phenol?

What are the exact conditions and reagents used in this reaction?

 

[chemisttree]

Although I don't know a lot about this reaction my guess is that it's the carbon tetra chloride with respect to the positively charged carbon.

The four chloro groups are pulling the electrons away from the carbon in carbon tet. That carbon cannot be nucleophilic. The missing reagent is a strong base, sometimes KOH and copper powder. Reimar and Tiemann placed phenol, sodium hydroxide, chloroform and some ethanol/water solution into a sealed tube and heated for 3 days at 100C to generate the mixture of o- and p-hydroxybenzoic acids. The KOH reacts with the phenol, deprotonating it and activating the ortho/para carbon on the ring to behave as a nucleophile. The KOH also reacts with the carbon tet to generate :CCl2. This is the electrophile or the substrate upon which the intermediate ion (o- or p-phenolate anion) adds to. The resulting dichloromethyl-substituted phenolate ion can further react with OH- to generate the aldehyde and ultimately the carboxylic acid.

 

[GCT]

I mentioned it as an electrophile not a nucleophile and I'm not quite certain why it has to be nucleophilic as you've pointed out since the dichlorocarbene is electrophilic. Regardless what a bizarre mechanism I just referenced it

http://en.wikipedia.org/wiki/Reimer-Tiemann_reaction

You've got
electrophilic aromatic substitution (technical name)
An SN reaction
carbenes
cyclic rearrangements

...all in "one pot"

 

[chemisttree]

The four chloro groups are pulling the electrons away from the carbon in carbon tet. That carbon cannot be nucleophilic. The missing reagent is a strong base, sometimes KOH and copper powder. Reimar and Tiemann placed phenol, sodium hydroxide, chloroform and some ethanol/water solution into a sealed tube and heated for 3 days at 100C to generate the mixture of o- and p-hydroxybenzoic acids. The KOH reacts with the phenol, deprotonating it and activating the ortho/para carbon on the ring to behave as a nucleophile. The KOH also reacts with the carbon tet to generate :CCl2. This is the electrophile or the substrate upon which the intermediate ion (o- or p-phenolate anion) adds to. The resulting dichloromethyl-substituted phenolate ion can further react with OH- to generate the aldehyde and ultimately the carboxylic acid.

Sorry, that should have been carbon tet, not chloroform. What happened to the edit function?

 

[GCT]

It should be located on the top right of your section - strange - it's not there.

 

[Borek]

What happened to the edit function?

Looks like you no longer can edit posts already answered.

 

[Borek]

No, it is slightly different situation. You can edit your posts only for 30 minutes since posting. So even if you have wrote "wether" instead of "whether" you can't correct it if you have waited for too long