How is lactic acid converted to lactide?

Lactide is a cyclic lactide derived from multiple esterifications between two (usually) or more molecules of lactic acid or other hydroxy acids. Depending on the number of hydroxy acid residues, it can be named dilactide, trilactide, etc. Dilactide derived from lactic acid has the molecular formula (OCHMeCO2)2. All lactides are colorless or white solids. Lactide comes from abundant renewable resources and is a precursor to biodegradable plastics.

Dilactide derived from lactic acid exists in three different stereoisomeric forms:

Unilong’s Lactide can be polymerized into polylactic acid. Syndiotactic or heterotactic polymers can be produced, depending on the catalyst. The resulting material, polylactic acid, has many properties.

Judging from the raw materials for synthesizing lactide, lactide is generally synthesized from lactate or lactic acid.

When lactate is used as the raw material for the reaction, although the reaction time is faster and the product purity is high, the cost of lactate is too high, and the product is generally mixed with impurities such as acetic acid, making it difficult to purify, and the product yield is very low. This method is widely used in Laboratory research and industrial applications are rare.

It is more economical to use lactic acid obtained by biological fermentation as raw material for reaction, and the product yield is higher. Currently, research is more in-depth. The process flow is to first esterify and dehydrate lactic acid to generate lactic acid oligomers, and then perform catalytic depolymerization at a higher temperature to obtain lactide. The reaction formula is as follows:

Lactide is a cyclic dimer of lactic acid. There are four types of lactide based on optical rotation.

(1) The lactide formed by dehydration of two L-lactic acid molecules is called L, L-lactide (or simply L-lactide);

(2) The lactide formed by the dehydration of two D-lactic acid molecules is called D, D-lactide (or simply D-lactide);

(3) The lactide formed by dehydration of one L-lactic acid molecule and one D-lactic acid molecule is called meso-D, L-lactide (also known as Meso-lactide);

(4) Equal amounts of L- and D-lactide (both melting points are 96°C) are mixed to form racemic D, L-lactide (melting point is 127°C, hereinafter referred to as D, L-lactide)

What are the applications?

Lactide is an important intermediate in the synthesis of polylactic acid. Polylactic acid (PLA) is a new semi-crystalline polymer with biodegradability. It is a green and environmentally friendly bio-based material that can be widely used in many areas of life, such as medical materials, construction industry, food packaging, etc.

 

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