a method of purifying 1α - hydroxy - 20 - methyl - 2 - methylene - 19 , 24 , 25 , 26 , 27 - pentanorvitamin d 3 to obtain 1α - hydroxy - 20 - methyl - 2 - methylene - 19 , 24 , 25 , 26 , 27 - pentanorvitamin d 3 in crystalline form . the method includes the steps of preparing a solvent of either ethyl formate or a mixture of ethyl formate and hexane , dissolving a product containing 1α - hydroxy - 20 - methyl - 2 - methylene - 19 , 24 , 25 , 26 , 27 - pentanorvitamin d 3 to be purified in the solvent , cooling the solvent and dissolved product below ambient temperature for a sufficient amount of time to form a precipitate of 1α - hydroxy - 20 - methyl - 2 - methylene - 19 , 24 , 25 , 26 , 27 - pentanorvitamin d 3 crystals , and recovering the 1α - hydroxy - 20 - methyl - 2 - methylene - 19 , 24 , 25 , 26 , 27 - pentanorvitamin d 3 crystals .