Lactide

Lactide is the lactone cyclic ester derived by multiple esterification between two (usually) or more molecules from lactic acid (2-hydroxypropionic acid) or other hydroxy carboxylic acid. They are designated as dilactides, trilactides, etc., according to the number of hydroxy acid residues. The dilactide derived from lactic acid has the formula [CH(CH₃)CO₂]₂. All lactides are colorless or white solids. This lactide has attracted interest because it is derived from abundant renewable resources and is the precursor to a biodegradable plastic.^[3]

Lactide

Names
Preferred IUPAC name 3,6-Dimethyl-1,4-dioxan-2,5-dione
Other names Dilactid
Identifiers
CAS Number	4511-42-6 [(S,S)-Lactide] Y 25038-75-9 [(R,R)-Lactide] N 13076-19-2 [(R,S)-Lactide = meso-Lactide] N 26680-10-4 [mixture of three isomers] Y 95-96-5 [mixture of three isomers][1] Y
3D model (JSmol)	Interactive image
ChemSpider	7002
ECHA InfoCard	100.002.245
EC Number	202-468-3
PubChem CID	7272
UNII	IJ13TO4NO1 [(S,S)-Lactide] Y 9J7G894K2M [mixture of three isomers] Y 7EH08MWO6M [mixture of three isomers] Y
CompTox Dashboard (EPA)	DTXSID7041253
InChI InChI=1S/C6H8O4/c1-3-5(7)10-4(2)6(8)9-3/h3-4H,1-2H3 Key: JJTUDXZGHPGLLC-UHFFFAOYSA-N
SMILES CC1C(=O)OC(C(=O)O1)C
Properties
Chemical formula	C6H8O4
Molar mass	144.126 g·mol−1
Melting point	95 to 97 °C (203 to 207 °F; 368 to 370 K) [(S,S)-Lactide and (R,R)-Lactide][2]
Solubility in water	Hydrolyses to lactic acid[2]
Solubility	soluble in chloroform, methanol slightly soluble in benzene [2]
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H319
Precautionary statements	P264, P280, P305+P351+P338, P337+P313
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Stereoisomers

The dilactide derived from lactic acid can exist in three different stereoisomeric forms. This complexity arises because lactic acid is chiral. These enantiomers do not racemize readily.

(R,R)-Lactide (left above), (S,S)-lactide (right above) and meso-lactide (below)

All three stereoisomers undergo epimerisation in the presence of organic and inorganic bases in solution.^[4]

Polymerization

Lactide can be polymerized to polylactic acid (polylactide). Depending on the catalyst, syndiotactic or a heterotactic polymers can result. The resulting materials, polylactic acid, have many attractive properties.^[5][6]

References

1. Sigma Aldrich product page for lactide Retrieved 8th of July 2015
2. Römpp Online Chemielexikon Version 3.3 aufgerufen am 25. März 2009
3. Andreas Künkel; Johannes Becker; Lars Börger; Jens Hamprecht; Sebastian Koltzenburg; Robert Loos; Michael Bernhard Schick; Katharina Schlegel; Carsten Sinkel; Gabriel Skupin; Motonori Yamamoto (2016). "Polymers, Biodegradable". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 1–29. doi:10.1002/14356007.n21_n01.pub2. ISBN 978-3-527-30673-2.
4. Shuklov, Ivan A.; Jiao, Haijun; Schulze, Joachim; Tietz, Wolfgang; Kühlein, Klaus; Börner, Armin (2011-03-02). "Studies on the epimerization of diastereomeric lactides". Tetrahedron Letters. 52 (9): 1027–1030. doi:10.1016/j.tetlet.2010.12.094. ISSN 0040-4039.
5. R. Auras; L.-T. Lim; S. E. M. Selke; H. Tsuji (2010). Poly(lactic acid): Synthesis, Structures, Properties, Processing, and Applications. Wiley. ISBN 978-0-470-29366-9.
6. Odile Dechy-Cabaret; Blanca Martin-Vaca; Didier Bourissou (2004). "Controlled Ring-Opening Polymerization of Lactide and Glycolide". Chem. Rev. 104 (12): 6147–76. doi:10.1021/cr040002s. PMID 15584698.