Ethyl 4-((11-(Hexylamino)-11-oxoundecyl)oxy)benzoate

Abstract

Ethyl 4-((11-(hexylamino)-11-oxoundecyl)oxy)benzoate was synthesized using 11-bromoundecanoic acid hexylamide and commercially available ethyl 4-hydroxybenzoate through a Williamson etherification synthesis. The structural characterization was performed using UV-Vis, FT-IR, ¹H-NMR, ¹³C-NMR, and HRMS.

1. Introduction

Oil spills are frequent, particularly due to the intensive use of petroleum products in our daily lives. They have been occurring regularly for almost 75 years. Among the various techniques to remove oil spills at sea, the use of organogelators is the most promising [1,2]. An organogel is a viscoelastic system considered to be a semi-solid preparation, in which an external, generally non-polar, liquid phase is immobilized [3,4].

Since 2005, several organic compounds have been synthesized to form organogelators for removing oil spills in aqueous media. These molecules contain a diversity of functional groups such as alkanes, cycloalkanes, ethers, alcohols, aromatic compounds, carboxylic acids, amides, imines, etc., which provide intermolecular forces capable of trapping oil away from water. The most common intermolecular forces involved are hydrogen bonding, Van der Waals interactions, π-π stacking, and dipole–dipole interactions [5,6,7,8,9,10,11,12].

This work demonstrates the synthesis and characterization of ethyl 4-((11-(hexylamino)-11-oxoundecyl)oxy)benzoate (OAM2) (Figure 1), synthesized from 11-bromoundecanoic acid hexylamide and ethyl 4-hydroxybenzoate. This compound has the potential to be an effective organogelator for removing oil spills due to the presence of functional groups that facilitate the necessary intermolecular forces.

2. Results

Synthesis of Ethyl 4-((11-(Hexylamino)-11-oxoundecyl)oxy)benzoate (OAM2)

OAM2 was synthesized in two steps. First, 11-bromoundecanoic acid hexylamide was prepared according to a method identified in the literature (Scheme 1A) [13,14]. This starting material was then used for Williamson etherification with commercially available ethyl 4-hydroxybenzoate (Scheme 1B).

OAM2 was recrystallized via evaporation in acetonitrile. The product was analyzed using FT-IR, high-resolution ESI-MS, UV-Vis, and ¹H and ¹³C-NMR (for the spectra, see Supplementary Materials, Figures S1–S6).

3. Materials and Methods

3.1. Generals

11-bromoundecanoic acid (95%), silica gel (high purity grade) tetrabutylammonium bromide (95%), N-(3-dimethylamino-propyl)-N′-ethylcarboiimide hydrochloride (EDCI, ≥98%), 1-hydroxybenzotriazole (HBOt, ≥98%), hydrochloric acid (37%), ethyl-4-hydroxybenzoate (99%), and dichloromethane (CH₂CI₂, 99.5%) were purchased from Sigma-Aldrich; sodium bicarbonate (99.7%) was purchased from BDH. 11-bromoundecanoic acid hexylamide was synthesized as previously described in the literature [13,14]. The ¹H and ¹³C NMR analyses were performed using a Bruker ASCEND™ 400 MHz AVANCE III at 400 MHz and 100 MHz, respectively. Tetramethylsilane (TMS) was used as the standard, and deuterated chloroform (CDCl₃) was used as the solvent. Melting point analysis was conducted using a Fisher-Johns melting point apparatus. The FT-IR analyses were conducted on a PerkinElmer Spectrum One spectrophotometer. UV-Vis absorption studies were performed on a UV-Vis Cintra 303 GBC. High-resolution mass spectra (HRMS) were recorded with a microTOF II spectrometer obtained from Bruker Daltonics (Bremen, Germany) with an electrospray ionization (ESI) source. The solvent used was chloroform.

3.2. Synthesis

A mixture of ethyl 4-hydroxybenzoate (0.7745 g, 4.66 mmol), 11-bromoundecanoic acid hexylamide (1.757 g, 5.215 mmol), potassium carbonate (1.820 g, 13.1717 mmol), and tetrabutylammonium bromide (0.34 g, 1.053 mmol) were dissolved in DMF (70 mL). The blend was agitated at 650 rpm and heated at 65 ± 5 °C for 10 h. The reaction mixture was poured into cold, deionized water (600 mL), and the pH level was adjusted to 1–2 using aqueous HCl (10% w/w). A white solid precipitated and was collected by vacuum filtration using a glass Büchner funnel. The wet product was then placed in a desiccator over 3 Å molecular sieves for 1–2 weeks. If the DMF signal persisted, repeated washes with cold deionized water were performed, followed by recrystallization in acetonitrile. Yield: 67.33% (1.34 g); mp: 80–90 °C. UV (ethanol) ${\lambda }_{max}$ 256 nm, (cyclohexane) ${\lambda }_{max}$ 253 nm, (n-hexane) ${\lambda }_{max}$ 253 nm, (acetonitrile) ${\lambda }_{max}$ 255 nm. FTIR (ATR-diamond) $v_{max}$ (cm⁻¹): 3302 (νN–H), 2921 (ν as C–H), 2854 (ν C–H), 1710 (ester νC=O), 1633 (amide I), 1541 (amide II), 1251 (ν as (ar)C-O–C(al)), 1174 (ester as νC–O), 1108 (ester sy νC–O), 1015 (ν (ar)C–O–C(al)), 843 (fpp Ar C–H), 768 (fpp Ar sust1,4), 696 (γ–(CH₂)_n–). ¹H NMR (400 MHz, CDCl₃/TMS): δ [ppm] 7.98 (d, J = 8.3 Hz, 2H, COO-(Ar)CCH), 6.90 (d, J = 9.0 Hz, 2H, O-(Ar)CCH), 5.51 (s, 1H, NH), 4.34 (q, J = 7.6 Hz, 2H, COOCH₂), 4.04–3.95 (m, 2H, Ar-O-CH₂), 3.23 (q, J = 7.1 Hz, 2H, CONHCH₂), 2.15 (t, J = 7.7 Hz, 2H, NHCOCH₂), 1.80 (dd, J = 15.1, 7.6 Hz, 3H, COOCH₂CH₃), 1.62 (t, J = 7.6 Hz, 2H, CONCH₂CH₂), 1.46 (dt, J = 14.5, 7.1 Hz, 4H, Ar-O(CH₂)₂CH₂, NHCOCH₂CH₂), 1.33 (m, 18H, CH₂), 0.88 (t, J = 6.4 Hz, 3H, CH₃). ¹³C NMR (100 MHz, CDCl₃/TMS) δ [ppm]: 173.11 (NHCO), 166.52 (COO), 162.87 (O-(Ar)C), 131.53 (OOC-(Ar)CCH), 122.60 (OO-(Ar)C), 114.00 (C3,5, O-(Ar)CCH), 68.16 (Ar-OCH₂), 60.65 (COOCH₂), 39.51 (CONHCH₂), 36.96 (NHCOCH₂), 31.51 (CONH(CH₂)₃CH₂), 29.66 (CONCH₂CH₂), 29.50 (Ar-OCH₂CH₂), 29.42 (Ar-O-(CH₂)₂CH₂), 29.38 (Ar-O(CH₂)₃CH₂), 29.35 (Ar-O(CH₂)₄CH₂), 29.32 (NHCO(CH₂)₄CH₂), 29.12 (NHCO(CH₂)₃CH₂), 26.62 (NHCO(CH₂)₂CH₂), 25.98 (NHCOCH₂CH₂), 25.86 (CONH(CH₂)₂CH₂), 22.60 (CONH(CH₂)₄CH₂), 14.42 (CONH(CH₂)₅CH₃), 14.07 (COOCH₂CH₃). HRMS (ESI+): m/z 434.3276 [M + H]⁺ C₂₆H₄₃NO₄ requires: 434.3265.

4. Conclusions

A new molecule, ethyl 4-((11-(hexylamino)-11-oxoundecyl)oxy)benzoate (OAM2), was synthesized with a good yield from 11-bromoundecanoic acid hexylamide and commercially available ethyl 4-hydroxybenzoate. This compound was characterized using various spectroscopic methods. OAM2 shows potential as a gelator for oil and fuels, indicating its possible application in oil/fuel-spill remediation. Further research is suggested.