2,5-Diketopiperazine, also known as piperazine-2,5-dione and as the cyclodipeptide cyclo (Gly-Gly), is an organic compound and the smallest cyclic dipeptide that consists of a six-membered ring containing two amide linkages where the two nitrogen atoms and the two carbonyls are at opposite positions in the ring.
Piperazine-2,5-dione is prepared from glycine in the presence of ethylene glycol.
Place 100 gm (1.33 mol) of glycine and 500 ml of ethylene glycol in a 1-litre three-necked flask fitted with an air-cooled reflux condenser and a sealed mechanical stirrer; fit a thermometer so that the bulb is in the liquid. Heat the mixture in the fume cupboard to 175°C and maintain the temperature at this level with continuous stirring for 1 hour. Cool the dark brown reaction product to room temperature and leave overnight in the refrigerator. Centrifuge the resulting suspension and decant the mother-liquor. Transfer the solid to a Buchner funnel with the aid of cold methanol and wash on the filter with gentle suction with more methanol, using about 200 ml in all. Crystallise the product from 300ml of boiling water but do not attempt to filter the hot solution at this stage; collect the light brown crystals which separate on cooling in ice. Dissolve the crude material in 350 ml of hot water, add 4 g of decolourising carbon and boil for 3 minutes. Filter the hot suspension through a preheated Buchner funnel and cool the filtrate in ice. Collect the colourless crystals of pure piperazine-2,5-dione, wash with a little ice-cold water and dry in the oven at 50 °C; the yield is 34 gm (45%). The melting point of the product is 310-312°C.
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Piperazine-2,5-dione was synthesized from glycine. The practical yield and percentage yield was found to be …… and ……. respectively. The melting point was found to be ….. °C.