Thermal esterification of cinnamic and p-methoxycinnamic acids with glycerol to cinnamate glycerides in solventless media: A kinetic model

• Use of glycerol as reactant and solvent is environmentally friendly.
• Best conditions for the synthesis of monoglycerides of two cinnamic acids are determined.
• Thorough kinetic modelling for both processes is performed.
• Esterification, glycerolysis and disproportionation reactions are involved.
• Removal of water is driven by high temperature and stripping by nitrogen.

The thermal processes of the esterification of glycerol with cinnamic acid and with p-methoxycinnamic acid in the absence of organic solvents to obtain monocinnamoyl glycerols were studied. Esterification runs were performed batchwise, changing the initial molar ratio of acid to glycerol from 1:3 to 1:9, and temperature from 150 to 200 °C. Under such conditions, systems proved to be monophasic, obtaining almost quantitative acid conversion and a significant selectivity to monoesters (80–90%). Apart from the esterification reactions, experimental conditions and data suggest the presence of glycerolysis and disproportionation reactions. Several kinetic models were fitted to experimental data and statistical and physical criteria were used to select the most adequate: a model with esterification and reversible glycerolysis reactions. When results and parameter values for both acids were compared, their kinetic behaviour in these processes resulted similar in the experimental conditions tested.