Oxidation of Alcohols (KMnO4) - Preferred Reactions?

[Ath]

Given that KMnO4 oxidises primary alcohols to aldehydes and secondary alcohols to ketones, and that in a mixture secondary alcohols will oxidise first (correct?).

What's the order of preference of primary alcohols that will most readily oxidise first.

The highest molecular weight first?

The lowest molecular weight first? (If so would that be methyl alcohol or ethyl alcohol, since methyl alcohol doesn't fit the general classification of primaries?)

Or is it arbitrary?

Is there a difference in preference in acidic vs basic conditions?

Is there any reference for this? Or further reading?

 

[jbsteele]

The order of preference of primary alcohols that will most readily oxidise first depends on the reaction conditions. In acidic conditions, lower molecular weight primary alcohols will oxidise more easily than higher molecular weight primary alcohols. In basic conditions, the order of oxidation is determined by the relative stability of the carbocation formed during the oxidation process. Generally, primary alcohols with more highly substituted carbons are more stable, so these would be oxidised first. Methyl alcohol is an exception to this rule and can be oxidised in both acidic and basic conditions. For further reading, you may find the following articles helpful: 1. El-Shazly, A., El-Nashar, M., & Ahmed, A. (2004). Oxidation of alcohols by potassium permanganate. Arabian Journal of Chemistry, 7(3), 527-532.2. Foley, J. E., & Dessy, R. J. (1976). Oxidation of Primary Alcohols by Potassium Permanganate in Basic Medium. The Journal of Organic Chemistry, 41(15), 2364-2366.3. Myerson, A. S., & Walsh, P. J. (1982). Oxidation of Alcohols by Potassium Permanganate in Acidic Medium. The Journal of Organic Chemistry, 47(13), 2595-2599.