Jonctum,Merrell,France,1970
16.7 g (0.127 mol) of L-hydroxyproline are dissolved in 400 ml of pure boiling acetic acid. With vigorous boiling and agitation, a mixture of 13.7 ml (0.154 mol) of rectified acetic anhydride and 250 ml of pure acetic acid is added during 25 minutes. Without discontinuing the stirring, contents of the flask are cooled by simply causing fresh air to circulate externally round the flask until the temperature of the mixture is reduced to about 35°C. The acetic acid is removed by using a rotary evaporator without exceeding 35°C under a vacuum of about 15 mm Hg. After one hour, 20 ml of anhydrous toluene are added, then 10 ml of anhydrous acetone; the mixture is homogenized and concentrated again as above during 30 minutes. Then 25 ml of acetone are added again, and subsequently 20 ml of toluene, the product being concentrated again; gradually the solution is converted into an amber-colored crystallized paste. Finally, 30 ml of acetone are added to the residue, and stirring is carried out until the oily fraction surrounding the crystals is dissolved. The product is then cooled in an ice chamber, centrifuged, washed with anhydrous acetone and eventually dried, After recrystallization from acetone, crystals are obtained, melting point 132°C.
