Oxidizing Primary Alcohol to Aldehyde in Methylenechloride & DMF

[Mop]

My problem is to describe the reason why a primary alcohol with
PDC in Methylenechloride is oxidized to the aldehyde, but in DMF further to the Acid. Would the only reason be that DMF is hygroscopic and contents usally some water to give the aldehydehydrate?

 

[GCT]

Probably

 

[ravenprp]

The reason for the difference in the oxidation product of a primary alcohol in methylenechloride and DMF is not solely due to the hygroscopic nature of DMF. While the presence of water in DMF can lead to the formation of the aldehydehydrate, there are other factors at play.

Firstly, the choice of solvent can greatly influence the reaction mechanism and the stability of intermediates. Methylenechloride is a non-polar solvent, while DMF is a polar aprotic solvent. This means that DMF has a higher polarity and can better solvate charged intermediates, leading to a different reaction pathway. In the presence of PDC (pyridinium dichromate), a strong oxidizing agent, the polar environment of DMF may favor the formation of the more stable carboxylic acid over the aldehyde.

Additionally, the stability of the aldehyde intermediate can also play a role. In methylenechloride, the aldehyde intermediate may be more stable due to the absence of polar solvents that can attack it. However, in DMF, the polar environment can lead to the formation of a hemiacetal intermediate, which is more susceptible to further oxidation to the carboxylic acid.

In summary, the difference in the oxidation product of a primary alcohol in methylenechloride and DMF is a result of the combined effects of solvent polarity, stability of intermediates, and the presence of water in DMF. It is important to carefully consider these factors when choosing a solvent for a specific reaction, as they can greatly impact the outcome of the reaction.