Organic II Q's - EAS, sulfur as protecting group, fischer esterification

[sumzup]

• My understanding is that for EAS, Friedel-Crafts Acylations/Alkylations will only work for halobenzenes or better (in terms of electron donating groups). Does this mean that F-C won't work for a halobenzene that also has a nitro group on it, due to the extreme withdrawing effects of the nitro group?
• I know that compounds like 1,2-ethanediol can be used to protect aldehydes and ketones; since sulfur is in the same group as oxygen and reacts similarly, can something like HOCH₂CH₂SH or HSCH₂CH₂SH be used to protect aldehydes/ketones?
• On a related note, is the protecting of aldehydes/ketones affected by the Khydrate (just like with addition of KCN or NaCN to a carbonyl group)?
• When performing fischer esterification for a lab recently, most people's reactions turned purple (although mine didn't, for some reason); my TA mentioned that it had something to do with the sulfuric acid. Why/how would this be the case?

Oh, and just to be clear, these aren't homework questions. Just stuff I want to know the answers to.

 

[Yanick]

[*]My understanding is that for EAS, Friedel-Crafts Acylations/Alkylations will only work for halobenzenes or better (in terms of electron donating groups). Does this mean that F-C won't work for a halobenzene that also has a nitro group on it, due to the extreme withdrawing effects of the nitro group?

I'd say yes, halogens don't really pi donate that much (and have sigma withdrawing properties) while NO₂ groups have a lot of sigma and pi withdrawal. I'm not 100% certain though, I'll see what I can dig up.

[*]I know that compounds like 1,2-ethanediol can be used to protect aldehydes and ketones; since sulfur is in the same group as oxygen and reacts similarly, can something like HOCH₂CH₂SH or HSCH₂CH₂SH be used to protect aldehydes/ketones?

Dithiol compounds definitely work and actually offer a very handy way to create carbanions, google Umpolung (I may have spelled that wrong but I'm sure you'll get to the appropriate site).

[*] On a related note, is the protecting of aldehydes/ketones affected by the Khydrate (just like with addition of KCN or NaCN to a carbonyl group)?

I don't really understand what you mean here?

[*]When performing fischer esterification for a lab recently, most people's reactions turned purple (although mine didn't, for some reason); my TA mentioned that it had something to do with the sulfuric acid. Why/how would this be the case?

Labs are funny things especially when you have 20-30 kids running around and a shelf of reagents prepared by someone you don't know, which may have been standing for god knows long. I'd wager some type of contamination or something along the lines of "someone screwed something up."

 

[sumzup]

I'd say yes, halogens don't really pi donate that much (and have sigma withdrawing properties) while NO₂ groups have a lot of sigma and pi withdrawal. I'm not 100% certain though, I'll see what I can dig up.

Thanks, I thought that might be the case.

Dithiol compounds definitely work and actually offer a very handy way to create carbanions, google Umpolung (I may have spelled that wrong but I'm sure you'll get to the appropriate site).

That is the most fascinating organic chemistry thing I have learned in some time. Do you know what would happen if you just used oxygen groups instead of sulfur groups? Would the base added to create the carbanion end up reacting with the acetal somehow?

I don't really understand what you mean here?

I'm just taking about the equilibrium constant between a carbonyl and the hydrate; our professor told us that NaCN is only likely to react with compounds that have that constant as 0.001 (acetone) or better.

Labs are funny things especially when you have 20-30 kids running around and a shelf of reagents prepared by someone you don't know, which may have been standing for god knows long. I'd wager some type of contamination or something along the lines of "someone screwed something up."

You're probably right. It was just really weird that mine was the only one that didn't turn purple (it still worked, although I was saddened that I didn't get banana ester).