Pinacolin and retropinacolin rearrangements

The preparative importance of the pinacolin rearrangement is considerable it leads not only to ketones that are hard to prepare in other ways but also from them to triply substituted acetic acids. The reagent effecting the rearrangement is always acidic, either a moderately strong organic acid or. a mineral acid. 

Hill and Flosdorf145 have given details for conversion of 2,3-dimethyl-2,3-butanediol into pinacolin in 65-72% yield by hot 6N-sulfuric acid. 

Zaugg and his co-workers147 described the rearrangement of a mixed alkyl aryl glycol  

2-Methyl-l,l-diphenyl-1,2-propanediol (50 g) is added with stirring to concentrated sulfuric acid (300 ml) at 5°. The mixture is left at room temperature for 2 h, then poured on ice and diluted with water (to 3 1) the precipitated 3,3-diphenyl-2-butanone is distilled in a vacuum, then having b.p. 101-103°/0.3 mm and m.p. 40-41° (38 g). 

Disecondary glycols can also be rearranged they give aldehydes.148 

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