Synthesis of Secondary Amines with Long Chains Containing Ether Bonds

Abstract

A novel class of secondary amines with long chains containing ether bonds were synthesized by a three-step protection–etherification–deprotection process from diethanolamine. The optimum reaction conditions were examined. This method has the advantages of simplicity, low cost, and high yield. Furthermore, some new downstream products (diglycolamides) were prepared from the ether-containing long-chain secondary amines as reactants, and their loading capacities in extractions of several metal ions were evaluated.

Key words

amines - amino ethers - Williamson synthesis - diglycolamides - extractants

Publication History

Received: 22 February 2022

Accepted after revision: 01 April 2022

Article published online:
13 May 2022

• References and Notes

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• 17 2,2′-Oxybis[N,N-bis(2-alkoxyethyl)acetamides] 5a–d; General ProcedureThe appropriate [bis(2-alkoxyethyl)]amine 4b–e (45 mmol) and Et₃N (45 mmol) were dissolved in CH₂Cl₂ (200 mL), and the mixture was cooled in an ice–salt bath (<5 °C). A solution of 2,2′-oxydiacetyl chloride (20 mmol) in CH₂Cl₂ was slowly added and the reaction was continued for 2 h. The ice–salt bath was then removed and the reaction was allowed to continue at 25 °C for 10 h. The mixture was washed successively with 2.0 mol/L aq HCl, 1.0 mol/L aq NaOH, and deionized H₂O, and then the organic layer was dried (Na₂SO₄) and filtered. The solvent was removed by swirling evaporation to obtain a crude product that was purified by column chromatography [silica gel, PE–EtOAc (3:1 to 20:1)].2,2′-Oxybis{N,N-bis[2-(octyloxy)ethyl]acetamide} (5a)Light-yellow liquid; yield: 63%. FTIR (KBr): 2930, 2853 (–CH₃, –CH₂–, C–H), 1657 (C=O, ν), 1463, 1373 (–CH₃, –CH₂–, C–H, δ), 1115 (O–C, ν), 725 (–CH₂–, r) cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 4.42 (s, 4 H), 3.62–3.50 (m, 16 H), 3.40 (q, J = 6.5 Hz, 8 H), 1.55 (dq, J = 7.2, 3.7 Hz, 8 H), 1.29 (d, J = 5.9 Hz, 40 H), 0.90 (t, J = 6.7 Hz, 12 H). ¹³C NMR (101 MHz, CDCl₃): δ = 169.74, 71.58, 71.34, 69.36, 69.02, 68.74, 48.15, 46.47, 31.90, 29.75, 29.65, 29.58, 29.52, 29.49, 29.31, 26.17, 26.10, 22.69, 14.13. HRMS: m/z [M + H]⁺ calcd for C₄₄H₈₉N₂O₇: 757.6665; found 757.6672; [M + Na]⁺ calcd for C₄₄H₈₈N₂NaO₇: 779.6484; found: 779.6461.
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