The isolated substance was identified as bis(2-ethylhexyl) terephthalate (1) based on the spectroscopic and spectrometric data and comparison with previously published data. Below are the NMR data for the isolated compound (1).
Bis(2-ethylhexyl) terephthalate: White amorphous solids; 1H NMR (500 MHz, CD2Cl2): δH 8.12 (4H, s, H-2,3,5 & 6), 4.29 (4H, dd, J = 5.7, 4.4, H-1′/1″), 1.77 (2H, m, H-2′/2″), 1.46 (4H, m, H-3′/3″), 1.30 (4H, m, H-4′/4″), 1.38 (4H, m, H-5′/5″), 1.51(4H, m, H-7′/7″), 0.94 (6H, m, H-6′/6″) and 0.98 (6H, m, H-8′/8″). 13C NMR (125 MHz, CD2Cl2) δC 166.2 (2 ꓫ CO), 134.7 (C-1/4), 129.8 (C-2,3,5 & 6), 68.0 (C-1′/1″), 39.3 (C-2′/2″), 31.0 (3′/3″), 30.1 (4′/4″), 24.4 (7′/7″), 23.4 (5′/5″), 14.2 (6′/6″) and 11.3 (8′/8″); ESIMS m/z 391 [M + H]+; positive ion HRESIMS m/z 391 (calcd for C24H39O4 [M + H]+ , 391)
Compound 1 was obtained as white amorphous solids. The molecular formula for the compound was deduced through ES-MS spectrum, which showed a protonated molecular ion [M + H]+ peak at m/z 391 corresponding to the molecular formula C24H39O4 (calcd for C24H39O4, 391). A phthalate was presumed to be present based on the ES-MS diagnostic daughter peaks of 391 at m/z 167 and m/z 149 [13]. The proton 1H NMR spectrum showed a resonance signal in the aromatic region characteristic of a 1,4-disubstituted benzene ring, for the aryl protons H-2/H-5 and H-3/H-6 (δH 8.12 s, 4H). Further analysis of the proton-carbon HSQC spectrum showed that these protons were coupled to the corresponding carbon signal at δC 129.8 (C-2/C-5 and C-3/C-6). Another resonance attributable to oxygenated methylene protons was also observed further upfield in the 1H NMR spectrum at δH 4.29 (4H, dd, J = 5.7, 4.4), which was correlated to a carbon resonance at δC 68.0 (C-1′/1″) in the HSQC spectrum. The carbon signal at δC 39.3 (C-2′/2′′) displayed HSQC connection to the methine protons that were detected at δH 1.77 (2H, m, H-2′/2′′). The COSY spectrum showed a significant correlation between both H-1′/1″ and H-2′/2′′, owing to their close proximity, indicating the ester's branched alkyl chains as opposed to their straight chain [13]. Further signals at δH 0.94 (6H, s, H-6′/6″), 0.98 (6H, m, H-8′/8″), 1.51 (4H, m, H-7′/7″), 1.38 (4H, m, H-5′/5″), 1.30 (4H, m, H-4′/4″) and 1.46 (4H, m, H-3′/3″) accounted for the protons in the remaining methyl and methylene groups. In addition, key three-bond HMBC correlations clearly linked the aromatic protons and the ox-methylene protons at H-1′/1″ to the ester carbonyl (δC 166.2) thus excluding the possibility of the 1-methylheptyl ester isomer. The oxygenated methylene groups were also correlated to methylene carbons at C-2′/2′′, C-3′/3″ and C-7′/7″, respectively. Analysis of the 13C NMR spectrum also indicated the presence of 24-carbon signals including ester carbonyl groups (δC 166.2, CO) and the C-1/4 quaternary carbons (δC 134.7). Thus, based on the spectrometric and spectroscopic data and by comparison with literature values, compound 1 was identified as bis(2-ethylhexyl) terephthalate, previously isolated from Capparis spinosa [14]. However, this is the first time it has been isolated from the Fabaceae family and the genus Acacia.
In the petrochemical and polymer industrial sectors, bis(2-ethylhexyl) terephthalate (DEHT), a general-purpose plasticizer and an isomeric compound of di-2-ethylhexyl phthalate (DEHP), is widely used [15]. It belongs to the chemical group of terephthalic acid esters, which are the primary plasticizers employed to give elasticity and flexibility to a variety of fiber and plastic products [16–18]. It has also been used to create a variety of synthetic materials for medical device manufacturing, such as intravenous administration devices [15]. Prior research has identified and isolated DEHT from a number of plant species, including; Grewia lasiocarpa [19], Uncaria rhynchophylla [20] and Alnus nitida [21] as well as the marine fungus Penicillium griseofulvum [22]. In addition, other widely used phthalic and terephthalic acid esters that have also been found in many different plants, such as tris(2-ethylhexyl) trimellitate obtained from Moringa oleifera [23], diethyl terephthalate derived from Mangifera indica [24], and dimethyl terephthalate secluded from Goniothalamus tapis [25]. Our research aids in the identification of plasticizers in our food and medication supply chains.