Ok, what else could I do but try it myself?
To a 500 ml roundbottom flask equipped with a magnetic stirrer, a thermometer and a addition funnel was added 250 mmol propiophenone (33,5 g), 350 mmol HCl (70 ml of a 5N HCl/IPA) and 100 ml IPA. The addition funnel was charged with a solution of 300 mmol sodium nitrite (20,7 g) dissolved in 30 ml water. The sodium nitrite solution was added dropwise during two hours while the temperature was kept at 25°C by mild cooling. Immediately when the nitrite solution was added sodium chloride started to preciptitate and the temperature rose mildly. The color of the reaction mixture changed from almost colorless to clear yellow. There was never any red fumes from NO2
visible throughout the reaction.
The reaction mixture was allowed to stir for a additional two hours after the addition was complete and was then left over night without stirring at room temp. In the morning the two phases was separated first by decantation then with the aid of a separatory funnel.
The acidic solution was slowly poured poured into 750 mmol NaOH (30 g) dissolved in 200 ml water with cooling and violent stirring. The alkaline solution was extracted with 3x50 ml toluene and the toluene discarded. The alkaline aqueous solution was cooled to 10°C and slowly added to a ice cold solution of 800 mmol HCl in 500 ml water. Isonitrosopropiophenone precipitated out immediately as white crystals and was isolated by filtration.
The still wet isonitrosopropiophenone was divided in two equal portions. One portion (A) was set aside to dry and the other portion (B) hydrolyzed in the following manner:
The wet isonitrosopropiophenone (B) was added to a solution of 400 mmol sulfuric acid (40 g) in 300 ml water and steam distilled until no more oily drops came over. This took about 2 hours. The distillate (little less than 1L) was saturated with NaCl and extracted with 2x100 ml toluene. The combined toluene extracts was dried over MgSO4
and the solvent removed by distillation.
Portion B gave 12,6 g 1-phenyl-1,2-propanedione (68% calculated from propiophenone)
Portion A is not dry yet but I'll add the yield tomorrow.
Ok what have we learned by this?
The alkyl nitrite can very well be generated in situ
. Since the yield of the 1,2-diketone isn't too shabby I don't see any reason whatsoever to make any alkyl nitrite separately and add it to the reaction. Unless one wants some amyl nitrite to sniff right before orgasm
Now with 1-phenyl-1,2-propanedione in hand I will give in to my curiosity of the effects of alpha-pyrrolidinopropiophenone and 2-tert-butylamino-1-phenylpropan-1-one.