Crystal structure of (R,R)-lactide.
Crystal structure of meso-lactide. Positions of the hydrogen atoms were not reported.
|CAS number||[(S,S)-Lactide] , 25038-75-9 [(R,R)-Lactide], 13076-19-2 [(R,S)-Lactide = meso-Lactide], 26680-10-4 [mixture of three isomers]|
|Molar mass||144.13 g mol−1|
|Melting point||95 to 97 °C (203 to 207 °F; 368 to 370 K) [(S,S)-Lactide and (R,R)-Lactide]|
|Solubility in water||Hydrolyses to lactic acid|
|Solubility||soluble in chloroform, methanol
slightly soluble in benzene
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Lactide is the cyclic di-ester of lactic acid, i.e., 2-hydroxypropionic acid. Lactic acid cannot form a lactone as other hydroxy acids do because the hydroxy group is too close to the carboxylic group. Instead, lactic acid first forms a dimer, which is similar to a 5-hydroxyacid. The dimer contains a hydroxy group at a convenient distance from the carboxylic group for the formation of a lactone. Indeed, the dimer readily forms a six-membered cyclic diester known as lactide. Lactides may be prepared by heating lactic acid in the presence of an acid catalyst.
In general, a lactide is the cyclic diester, i.e., the di-lactone of two molecules of any 2-hydroxycarboxylic acid.
Lactic acid is chiral; two enantiomeric forms, (R)-lactic acid and (S)-lactic acid, may exist. Thus, lactide formed from two equivalents of lactic acid consists of two stereocenters. Three different stereoisomers of lactide are known:
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- Römpp Online Chemielexikon Version 3.3 aufgerufen am 25. März 2009
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