C-Arylcalix[4]pyrogallolarene Sulfonic Acid: A Novel and Efficient Organocatalyst Material for Biodiesel Production

Abstract

The synthesis of C-arylcalix[4]pyrogallolarene sulfonic acid derivatives and their application as an organocatalyst material for biodiesel production were investigated. The C-arylcalix[4]pyrogallolarene derivatives were prepared in high yields through a two-step reaction: condensation between pyrogallol and aromatic aldehydes (i.e. benzaldehyde, 4-hydroxy-3-methoxybenzaldehyde and 4-ethoxy-3-methoxy benzaldehyde) and then followed by a sulfonation reaction with sulfuric acid. They were evaluated as the organocatalyst for the esterification reaction of palmitic acid with methanol as a representation of biodiesel production. Using 4 mol% of C-4-hydroxy-3-methoxyphenylcalix[4]pyrogallolarene sulfonic acid, methyl palmitate was generated in up to 91.9% yield after 4 h at 65 °C, making it similarly efficient to sulfuric acid that is used as the catalyst in the conventional reaction under similar conditions. However, different from sulfuric acid, the C-4-hydroxy-3-methoxyphenylcalix[4]pyrogallolarene sulfonic acid could be recovered by using a simple filtration technique making it better than sulfuric acid from industrial and environmental points of view. These results demonstrate that the C-arylcalix[4]pyrogallolarene sulfonic acid derivatives are a novel and potential organocatalyst for methyl palmitate biodiesel production.

Preliminary Investigation of Organocatalyst Activity Based on C‐Arylcalix[4]‐2‐Methylresorcinarene Sulfonic Acid Materials for Biodiesel Production

“…However, the presence of the sulfonic acid group was confirmed from the 1 H NMR spectrum of compound 4 by two singlet peaks at 7.45 and 7.47 ppm with an integration ratio of four protons. The position of the sulfonic acid on the aromatic ring was on the para position because the protons of benzaldehyde found as doublet and doublet at 7.08–7.11 ppm as previously reported 12…”

“…The acid catalyst is able to speed up the reaction rate by protonation of carboxylic acid group; thus, it is easily attacked by the hydroxyl group of methanol through nuchleophilic acyl substitution reaction 9 . Based on our previous work, the optimum reaction temperature for methyl palmitate production was 338 K 12 …”

“…H‐beta zeolite material has been used to increase the yield of methyl palmitate to 54.0% only. As H‐beta zeolite inorganic catalyst seems insufficiently efficient for methyl palmitate production, researchers are also evaluating the potential of organic‐based catalysts (organocatalysts) 12 …”

“…According to a previous study, p ‐sulfonic acid calixarenes can produce methyl palmitate of up to 91.0% yield 14 . Our previous work showed that calix[4]pyrogallolarene sulfonic acids due to 12 hydroxyl groups could have higher catalytic activity than calix[4]arene sulfonic acids 12 . However, the catalytic activity of calix[4]pyrogallolarene sulfonic acids (up to 91.9%) was not significantly different from that of calix[4]arene sulfonic acids.…”

Preparation and evaluation of alpha‐cellulose sulfate based new heterogeneous catalyst for production of biodiesel

“…This trend agrees with the previous work that stated that the acid catalysis process depends on the amount of Bronsted acid sites. 27 Furthermore, as shown in Figure 5c, the reaction yield also increased by increasing the amount of alpha-cellulose sulfate catalyst.…”