94 



In a somewhat stronger acid medium pinacone (pinacoliiie) was 

 also obtained exclusively. 



. For (his was used a mixture of 807o of alcohol and 207u of 

 glacial acetic acid; quantities of J 5 gi-ams of zinc dust and 75 cc. 

 of the acid mixture were chosen for 5 grams of benzophenone. 



The reaction takes phice more energeticall)- and much zinc acetate 

 is deposited. The liquid is therefore diluted with water and the 

 remaining zinc rapidly dissolved by means of dilute HCl. A solid 

 substance is now left which is shaken for a day with 100 cc. of 

 SO'Yo alcohol as directed above. 



On boiling for 2 and 6 hours, respectively only 0.45 and 0.35 

 gram of a substance readily soluble in 807o alcohol had formed ; 

 its melting point was, however, situated below 25°; it did not 

 crystallise in the shape of felt-like needles and had the typical odour 

 of diphenylmethane; the residue consisted of pinacone. 



Hence, the reduction proceeds in dilute acetic acid and zinc dust 

 much more rapidly than in a nearly neutral medium, but otherwise 

 in the same direction. 



This result agrees with that of Zagomenni^), who obtained 927o of 

 pinacone in glacial acetic acid solution. 



With sulphuric acid (80 cc. of 9(37, alcohol, 20 cc. of H^SO, 1—1) 

 exactly the same result was obtained. After boiling for 2 — 4 hours, 

 respectively there was obtained only 0.28 — 0.27 gram of a product 

 soluble in alcohol having the odour of orange j)eels and a veiy^ pale 

 yellow colour with a low melting point ; the part not soluble in alcohol 

 was, presumably, mainly pinacoline. 



B. Reduction in a faintly acid medium with aluminium. 



Aluminium grit was not attacked by the above acetic acid-alcohol 

 mixture (15 grams of Al, 75 cc. of acid mixture to 5 grams of 

 benzophenone). Therefore, a little HgCl2 was added which caused the 

 reaction to set in. After three hours' boiling the product was treated 

 as stated above; no hydrole could be detected, only a little of a 

 pale yellow product soluble in alcohol and having an odour of orange 

 peels, all the rest consisted of pinacone. The melting point 165° also 

 again pointed to formation of pinacoline. Contrary to the reduction 

 in a neutral solution no hydrole is formed. 



4. Reduction in a faintly alkaline medium. 



A. With zinc dust. 



For this was chosen a mixture of 50 cc. of 96 "/„ alcohol, 25 cc. 



1) B 14, 102 (1881), 



