Synthesis of High Purity Nonsymmetric Dialkylphosphinic Acid Extractants

Summary

A protocol for the synthesis of high purity nonsymmetric dialkylphosphinic acid extractants is presented, taking (2,3-dimethylbutyl)(2,4,4'-trimethylpentyl)phosphinic acid as an example.

Abstract

We present the synthesis of (2,3-dimethylbutyl)(2,4,4'-trimethylpentyl)phosphinic acid as an example to demonstrate a method for the synthesis of high purity nonsymmetric dialkylphosphinic acid extractants. Low toxic sodium hypophosphite was chosen as the phosphorus source to react with olefin A (2,3-dimethyl-1-butene) to generate a monoalkylphosphinic acid intermediate. Amantadine was adopted to remove the dialkylphosphinic acid byproduct, as only the monoalkylphosphinic acid can react with amantadine to form an amantadine∙mono-alkylphosphinic acid salt, while the dialkylphosphinic acid cannot react with amantadine due to its large steric hindrance. The purified monoalkylphosphinic acid was then reacted with olefin B (diisobutylene) to yield nonsymmetric dialkylphosphinic acid (NSDAPA). The unreacted monoalkylphosphinic acid can be easily removed by a simple base-acid post-treatment and other organic impurities can be separated out through the precipitation of the cobalt salt. The structure of the (2,3-dimethylbutyl)(2,4,4'-trimethylpentyl)phosphinic acid was confirmed by ³¹P NMR, ¹H NMR, ESI-MS, and FT-IR. The purity was determined by a potentiometric titration method, and the results indicate that the purity can exceed 96%.

Introduction

Acidic organophosphorus extractants are widely used in the traditional hydrometallurgy field for extraction and separation of rare earth ions^1,2, non-ferrous metals (like Co/Ni^3,4), rare metals (such as Hf/Zr⁵, V^6,7), actinides⁸, etc. In recent years, they have also attracted more attention in the fields of secondary resource recycling and high-level liquid waste disposal⁹. Di-(2-ethylhexyl)phosphoric acid (D2EHPA ....

Protocol

1. Synthesis of Mono-(2,3-dimethylbutyl)phosphinic acid ^18,19

1. Reaction
   1. Weigh 31.80 g sodium hypophosphite hydrate, 16.00 g acetic acid, 8.42 g 2,3-dimethyl-1-butene, 0.73 g di-tert-butylnperoxide (DTBP), and 25.00 g tetrahydrofuran (THF) into a 100 mL Teflon-lined stainless steel autoclave, put a magnetic stirrer into the autoclave, and seal it.
   2. Put the autoclave in a vertical tube furnace under which is a magnetic stirringapparatus.Start the magnetic stirring apparatus and set the speed at 800 rpm.
   3. Set the heating program of the temperatu....

Results

³¹P NMR spectra were collected for the mono-(2,3-dimethylbutyl)phosphinic acid before and after purification by the amantadine method (Figure 1a-b). ³¹P NMR spectra, ¹H NMR spectra, MS spectra, and FT-IR spectra were collected for (2,3-dimethylbutyl)(2,4,4'-trimethylpentyl)phosphinic acid (see Figure 3, Figure 4, Figure 5.......

Discussion

The most critical step within the protocol is the mono-alkylphosphinic acid synthesis (Figure 1a). In this reaction, a higher yield and less dialkylphosphinic acid by-product is better. Increasing the molar ratio of NaH₂PO₂/olefin A will improve the yield and inhibit the generation of dialkylphosphinic acid by-product. However, a large NaH₂PO₂ dosage will also increase the cost and cause a stirring problem. The preferred molar rati.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
2,3-dimethyl-1-butene	Adamas Reagent Co., Ltd.		Molecular formula: C6H12, purity ≥99%
diisobutylene	Shanghai Aladdin Bio-Chem Technology Co., LTD		Molecular formula: C8H16, purity 97%
acetic acid	Sinopharm Chemical Reagent Co., Ltd.		Molecular formula: C2H4O2, purity ≥99.5%
di-tert-butylnperoxide	Sinopharm Chemical Reagent Co., Ltd.		Molecular formula: C8H18O2, purity ≥97.0%
tetrahydrofuran	Beijing Chemical Works		Molecular formula: C4H8O, purity A.R.
ethyl ether	Sinopharm Chemical Reagent Co., Ltd.		Molecular formula: C4H10O, purity ≥99.7%
ethyl acetate	Xilong Chemical Co., Ltd.		Molecular formula: C4H8O2, purity ≥99.5%
acetone	Beijing Chemical Works		Molecular formula: C3H6O, purity ≥99.5%
sodium hydroxide	Xilong Chemical Co., Ltd.		Molecular formula: NaOH, purity ≥96.0%
concentrated sulfuric acid	Sinopharm Chemical Reagent Co., Ltd.		Molecular formula: H2SO4, purity 95-98%
hydrochloric acid	Beijing Chemical Works		Molecular formula: HCl, purity 36-38%
sodium chloride	Sinopharm Chemical Reagent Co., Ltd.		Molecular formula: NaCl, purity ≥99.5%
anhydrous magnesium sulfate	Tianjin Jinke Institute of Fine Chemical Industry		Molecular formula: MgSO4, purity ≥99.0%