Pinacolines

A solution of 30 parts by weight of pinacolin alcohol in ether is saturated with hydrogen chloride at room temperature and the ether solution then agitated with bicarbonate. After concentration by evaporation it leaves behind the crude diethylstilbestrol [a,j3-(p,p -dihydroxy-diphenyl)-Oi, 3from benzene, melts at 170°C to 171 °C. The yield amounts to 75% of the calculated. The total y eld of diethylstilbestrol, calculated on p-hydroxypropiophenone, is 68% of the theoretical. 

Silver Pinacoline Nitraminic Acid, AgC5HuN202, is a weak expl which puffs off on rapid heating (Ref 2)... 

This is clearly demonstrated in the pinacolinic deamination (cf. p. 114) of an optically active form of the amino-alcohol (50). Such reactions proceed from a conformation (antiperiplanar 50a or 50b) in which the migrating (Ph) and leaving (NH2 as N2 cf. p. 114) groups are TRANS to each other. Rearrangement via a bridged carbocation would necessarily lead to 100% inversion at the migration terminus in the product ketone (5lab), whichever initial conformation, (50a) or (50b), was involved ... 

Tuulmets [Kinetics and Catalysis, 5 (59), 1964] has studied the kinetics of the reaction of ethyl magnesium bromide with pinacolin. He used a calorimetric technique to monitor the progress of the reaction. The overall temperature increase of the reaction mixture was less than a degree. Mixture temperatures were determined with a sensitive potentiometer. The data below... 

Changes in the potentiometer reading may be assumed to be proportional to the temperature change of the reaction mixture. Determine the order of the reaction with respect to pinacolin and the apparent reaction rate constant. 

A rearrangement which takes place in similar compounds, and has been much studied recently, may be briefly mentioned here. This rearrangement has been named—not quite correctly—the retro-pinacoline rearrangement. 

The next example deals with an effect of ferrous chloride addition (Galli and Gentili 1993). Phenyl iodide reacts with the potassium derivative of l,l-dimethyl-butan-2-one (pinacolin) in DMSO according to the following equations ... 

Di methyl-3,3-d in itrohutane, (H3C)3C.C(N02)2 CH3, crysts, having a strong camphor odor, very volatile, mp 173—74° easily sol in ether obtd in a small quantity from pinacoline oxime N2O4, in addn to pinacoline nitrimine (Ref 5)... 

Pinacol Rearrangement takes place when pinacol is heated with dilute acid, pinacolin formed ... 

It is suggested that the change of the a- to the /3-base takes place probably through an anhydride of the a-base by a molecular rearrangement almost identical with that of the pinacol-pinacolin type ... 

The reaction itself is called the pinacoline transformation. Ethers of the glycols also behave similarly, in some cases with particular ease (B., 39, 2288 A., Ch. (8), 9, 484). For a corresponding reaction among ketones, see p. Ill, See also Ann. Rep., 1930, 114. 

Reaction XXXII. Action of Alkalis on certain a-di-ketones. (A., 25, 25 31, 324 B., 14, 326 19, 1868 41, 1644.)—When benzil is fused with potassium hydroxide, or digested with alcoholic potash, or heated for a long time with aqueous potash, a molecular re-arrangement not unlike the pinacoline transformation (p. 79) takes place, and benzilic acid is formed. 

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