Six ionic liquids based on pyridine (Py)

1-methylimidazole (MIM)

N-methyl-2-pyrrolidinone(NMP) cations were prepared by coupling corresponding SO3H-functionalized zwitterion ionic complex with different counterpart anions including H3PW12O40 and p-toluenesulfonic acid (PTSA). The obtained ionic liquids were well characterized by FT-IR

TG

1H NMR

13C NMR methods and then these ionic liquids were deployed in the esterification reaction of glycerol with lauric acid under the condition without organic solvent. The effects of various key reaction parameters including reaction temperature

glycerol/lauric acid molar ratio

molar ratio of ionic liquid to lauric acid and the type of catalysts on the acid conversion and yield of glycerol monolaurate were discussed. The results indicated that all the ionic liquids exhibit good thermal stability and compared with other ionic liquids

[MIMBS]3PW12O40 ionic liquid has the best thermal stability. When [MIMBS][PTSA] ionic liquid was used to optimize esterification reaction parameters

the optimum reaction conditions were established as follows: glycerol/lauric acid ratio of 4

amount of catalyst of 1% molar to lauric acid

reaction time of 3 h at 130℃. When used under the optimized reaction condition

all the ionic liquids exhibit excellent catalytic activity

the acid conversions are all above 92% and the highest yield of glycerol monolaurate of 64.6% has been achieved. In addition

comparing the structure of the investigated ionic liquids

it can be found that under the condition of lauric acid being catalyzed by the ionic liquids with PTSA anion

the conversion is higher than that when lauric acid was catalyzed by ionic liquids with H3PW12O40 anion. With respect to the yield of glycerol monolaurate

when the reaction was catalyzed by ionic liquids

[MIMBS][PTSA] gives the highest yield. As to the reusability behavior of these ionic liquids

the results indicated that all these catalysts can be reused up to five times without noticeable loss of catalytic activity.