Optical Isomerism: Levorotatory Tartric Acid Reduction

[smack_whore]

hi,
if levo tartric acid was reduced to its ketone derivative would it produce exclusivly the levo form or would a racemic mix be formed or even the dextro form be formed?
(any examples you give me don't have to be for tartric acid i was just using it as an example as I've been reading the pasteur section of my book )
really I am asking if anyone has any links/book suggestions pertaining to this question but info will be appreciated a lot :!) thanks

 

[movies]

If you were to just reduce the two acids in tartaric acid, then the product should still be the same enantiomer that you started with. The reduction, in principle , shouldn't affect the alcohols which are the chiral centers. You can't predict with 100% certainty that the sign of optical rotation will stay the same, however. The ketone form will be more prone to epimerization of the chiral centers than they would be in the acid, but this would require strong acid or base. Some reducing agents may be acidic enough (or basic enough) to cause this epimerization, but I am fairly certain that you could find conditions to reduce the acid without affecting the stereochemistry of the alcohols.

The first idea that comes to mind is to convert the acids to the corresponding Weinreb amides and then add an alkyl Grignard reagent to form the ketones. I think that those conditions would be okay.

 

[chem_tr]

hi,
if levo tartric acid was reduced to its ketone derivative would it produce exclusivly the levo form or would a racemic mix be formed or even the dextro form be formed?
(any examples you give me don't have to be for tartric acid i was just using it as an example as I've been reading the pasteur section of my book )
really I am asking if anyone has any links/book suggestions pertaining to this question but info will be appreciated a lot :!) thanks

Movies has answered the question already, it is not my style to add same things, so I will mention of different things here.

You are asking about if one enantiomer is reacted with one reactant, say, an oxidizing agent in the case of tartaric acid (as the compound has double \displaystyle -CHOH- bonds; this is much easier than using Grignard reagents on an acid), the optical configuration will change or not... Well, my opinion here is that you may have to use specialized reactants, which approaches from just ONE direction to yield an enantiomer again, otherwise, the reaction will proceed in BOTH directions to give you a racemic mixture. This is my reasoning.

However, if you really want to obtain a ketone from an acid, Movies' idea is great already. If you are interested in this problem, I would recommend that you search some advanced organic chemistry textbooks like John March's to find if there are any solutions to this problem (I am also certain like Movies that there has to be an answer).

 

[smack_whore]

thanks, always a great help