Formation of By‐products in Pure and Aqueous Acrylic Acid – Kinetic Measurements and Formation Mechanisms

Abstract

During acrylic acid (AA) storage, a quality loss occurs due to the formation of by-products such as diacrylic acid (DiAA), triacrylic acid (TriAA), and higher oligomers. This problem intensifies in the presence of water since the formation rate of oligomers increases and further by-products such as 3-hydroxypropionic acid (3-HPA) and 3-hydroxydiacrylic acid (3-HDiAA) are formed. However, water is often essential during storage and transport to raise the flash point or reduce the melting point. In this work, the formation kinetics are investigated for all mentioned components in pure and aqueous AA. The formation mechanisms of 3-HPA and 3-HDiAA are assumed as acid-catalyzed ester hydrolyses of DiAA or TriAA. The introduced reactions are modeled with the measured kinetic data in order to confirm the proposed reactions.

Does the oxa-Michael reaction of 2-trifluoromethacrylic acid lead to fluorinated polyesters?

“…The multiplicity of the latter signal was determined thanks to 1 H{ 19 F} NMR spectrum (Figure S12-bottom). The coupling atoms of previously mentionned J FF was confirmed because the corresponding doublets were observed on both 19 F{ 1 H} and 19 F{ 1 H}{ 13 C} NMR spectra (Figure S13-top), which have the same profile. Similar coupling constants are also noted in the 13 C NMR spectrum (Figure S14).…”

“…To the best of our knowledge, the oligomerisation of MAF by oxa-Michael addition leading to low molar mass-oligomers was claimed in Japanese patent 29 and an analytical publication. 30 However, only the descriptions from 1 H and 13 C NMR spectra of the dimer and trimer were reported. Thus, it was worth to confirm this formation by means of complementary techniques as 19 F, 2D NMR and IR spectrocopies, GC/MS and MALDI-TOF analyses, as well as to attempt increasing the average degree of polymerisation (DP n ).…”

“…The experimental conditions for recording 1 H [or 19 F] NMR spectra were as follows: angle 90° [or 30°], acquisition time 4.5 s [or 0.7 s], pulse delay 2 s [or 5 s], number of scans 36 [or 64], and a pulse width of 5 μs for 19 F NMR. 1 H decoupling is applied on all 13 C NMR analyses and almost on Attached Proton Test mode ( 13 C{ 1 H}-APT). In the details of NMR characterisation, s, d, t, q, and m stand for singlet, doublet, triplet, quintet, and multiplet, respectively.…”

“…One typical example is acrylic acid (AA) that easily polymerises under radical conditions by π orbital cleavage in C=C bond, but has also been involved in oxa-Michael addition, affording polyesters in low molar masses (Scheme 1). [9][10][11][12][13] In addition, dimer of AA was firstly observed under its storage conditions. 13,14 Scheme 1 : Oxa-Michael addition homopolymerisation of acrylic acid According to Matsuoka's group, 15 Lewis bases such as phosphines and N-heterocyclic carbene (NHC) underwent Michael addition to AA, followed by proton transfer as step-growth polymerisation, which produces a variety of polymers (random and telechelic ones).…”

“…[9][10][11][12][13] In addition, dimer of AA was firstly observed under its storage conditions. 13,14 Scheme 1 : Oxa-Michael addition homopolymerisation of acrylic acid According to Matsuoka's group, 15 Lewis bases such as phosphines and N-heterocyclic carbene (NHC) underwent Michael addition to AA, followed by proton transfer as step-growth polymerisation, which produces a variety of polymers (random and telechelic ones). On the other hand, strong Brønsted acid catalysts (especially sulfonic acids) activate the carbonyl group of AA, affording high molar mass polyesters.…”