[g8rgrl]

Ok, so my orgo book says that potassium permanganate will oxidize alkynes to side-by-side ketones in a neutral solution, and cleave the alkyne to form two carboxylic acids in a basic solution. What will it do in an acidic solution? Anyone know? My guess is that it would either favor the diol or alkene where the alkyne used to be. Thanks for the *delete me*

[leaftye]

An alkyne in an acidic solution would do the same thing as an alkene.  That is,

                                   Cl
CH3-C=-CH + HCl -> CH3-C-CH3
                                   Cl

Not sure how the permanganate would be affected.  Maybe it'd get protonated?

[408]

Your org book uses an oversimplification that started with Khan and Newman who had to control the pH very well to obtain the diketone.  Acid solution was unable to be used on their substrate because it was a carboxylic acid insoluble in water, and with very basic solution they got the cleaved product.
ref: http://pubs.acs.org/doi/abs/10.1021/jo01329a027
Without rigorous pH control they found the cleaved carb. acid was always the major product, and diketone was only present in trace amounts.  Likely because the diketone is cleaved faster than the alkyne is oxidized.
Said paper also indicates that under acid conditions the cleavage product carboxylic acid is formed.
Diketones can be formed only under anhydrous permanganate oxidation conditions such as in DCM.