Molecular Formula: C6H8O4
Density: 1.2 g/ml
Chemical Names: L-lactide
Appearance: white particle
Minimal order quantity: 100 gram
The initial lactide is about 80% pure, with a lot of yellow impurities. Then recrystallization, usually using ethanol or ethyl Acetate recrystallization for about 5 times, this time the purity can reach 99.5% . The environment and operation details of recrystallization are the most important factors. With regard to the purchase of Lactide, we advise customers to purchase directly for use, if not well preserved, subsequent use may also need to recrystallize, and most schools can not meet the environmental requirements of recrystallization.
Frequently Asking Questions
1. Is l-lactide levorotatory or dextrorotatory?
L-Lactide is levorotatory, D-Lactide is dextrorotatory.
2. Why actual l-lactide percent is less than theoretical l-lactide percent?
The actual l-lactide percent is related to the times of purification, solvents, operating environment, methods of purifications.
The theoretical l-lactide percent is about 80%. We use heat-stable lactic acid from Purac, the Lactic acid content is generally 80%-88%, when remove this part of water which forms in lactic acid condensation, oligomer pyrolysis to lactide and part of dimer trimer. The rough percent is 50%-60%. After recrystallization, the final percent is about 30-35%.
3. what is method of synthesis and purification of l-lactide?
The synthesis methods l-lactide include atmospheric pressure method and decompression method. The main problem of the two methods is how to reduce the dry distillation carbonization during the depolymerization of Lactide, then improve the yield of lactide.
The idea of atmospheric pressure method is to introduce “inert gas” into the reaction system, with the help of these inert gases, the Lactide will produce out of the reaction system. By injecting “inert gas” N2 or CO2 into the reaction system to reduce the partial pressure of lactide vapor and continuously remove the lactide from the reaction system.
The substitution of oxygen by inert gas in the reactor avoids the side reaction such as color change and coking caused by oxidation, and improves the yield and purity of lactide to a certain extent, the shortcoming of this method is long dehydration time, low production efficiency and product yield is not high.
At present, the most widely used method is the decompression method. The idea is that the whole reaction system is in the state of high vacuum, and the Lactide can be quickly distilled out. In addition, the Lactide can be isolated from oxygen under high vacuum, to reduce the occurrence of oxidation reaction and increase the yield of lactide.
On the basis of the decompression method, the researchers found that adding a certain amount of “inert solvent” to the reaction system could improve the coking and carbonization of the reaction solution. For example, Hotsuta and Linan respectively added glycerol and higher alcohol solvents to the vacuum system. It is considered that these inert solvents can not only bring out the Lactide, but also improve the viscosity of the reaction solution at the later stage of the reaction, so as not to overheat the local side effects.
Regarding to purification of Lactide, There are two main methods :
First one is the recrystallization process, which is cumbersome and solvent consumption. Solvent recrystallization method is widely used in the laboratory. The main solvents used are alcohols, ethers, esters, Ketones, benzene, haloalkanes and Oxolane etc. As the yield of single recrystallization of lactide in single solvent is generally not high, the multiple recrystallization of lactide in compound solvent was developed.
Researchers found that recrystallization with Ethyl Acetate for 3 times can effectively avoid the residue of hydroxyl in the product, but the yield of recrystallization is low, and the purity of lactide obtained by recrystallization with ethanol for 1 time can not meet the requirements. Therefore, ethanol was recrystallized twice to obtain higher yield of recrystallization, and then ethyl acetate was recrystallized once to remove the residual hydroxyl in Lactide, and the yield of refined lactide was 35.4% .
Although the solvent recrystallization method is easy to operate, the volatile, flammable, explosive and high pollution characteristics of organic solvents limit its application in industrial production.
The Second method is vacuum distillation, which need equipment investment and high technical requirements.
The advantage of distillation is that no other solvents are used, so that no new impurities are introduced into the purification process, and the equipment is easy to large-scale and continuous production.
4. What is the factors affecting the synthesis of lactide?
The depolymerization of lactic acid oligomers is reversible. If the temperature of the depolymerization process is too low, the lactic acid oligomer can not be easily depolymerized to form lactide, and if the temperature is too high, the lactic acid oligomer will decompose and oxidize, in addition, the lactide produced will change color and appear racemization due to coking and carbonization. The depolymerization temperature is generally controlled at 220 ~ 250 °C.
In order to promote the depolymerization to the positive reaction direction and avoid the discoloration of Lactide, the lactide should be separated from the reaction system in time.
The pressure of the reaction system should be lower than the vapor pressure of Lactide at the reaction temperature. The method of decompression reduces the oxygen content in the reaction system and can effectively avoid the discoloration of lactide caused by oxidation, but the method of decompression usually needs high vacuum equipment and the vacuum degree is not easy to control, and the energy consumption is large in the process.
The depolymerization of lactic acid oligomers is an intramolecular Transesterification, in which the empty orbitals of metal elements can form coordination bonds with the carbonyl oxygen atoms of lactic acid oligomers, thereby catalyzing the depolymerization reaction.
At present, many kinds of lactide synthesis catalysts have been developed, the main types are: Metal compound catalyst, main elements such as zinc, tin, aluminum, titanium, rare earth catalyst, main elements such as Yttrium, Lanthanum, etc. , such as sulfuric acid, Para-Toluene Sulfonate acid, solid super acid and so on; and by the above several kinds of catalyst combination compound catalyst.