Synthesis and Borylation reaction of 2-Ethylhexyl bromide

2-Ethylhexyl bromide appears as a clear, colorless to yellowish liquid at ambient temperature and pressure. This compound is insoluble in water but miscible with most organic solvents. 2-Ethylhexyl bromide can be synthesized through the bromination of isooctanol. Primarily utilized as an intermediate in organic synthesis and as a raw material in fine chemical production, 2-Ethylhexyl bromide has also been reported in research for its application in the preparation of hole‑transport materials for perovskite solar cells.

Synthesis

Figure1: Synthesis of 2-Ethylhexyl bromide

Method 1

In a 250 mL round‑bottom flask equipped with a magnetic stir bar, 2‑ethyl‑1‑hexanol (7.82 g, 60.0 mmol) and triphenylphosphine (23.61 g, 90.0 mmol) were dissolved in dichloromethane (30 mL) and cooled to 0°C. Separately, N‑bromosuccinimide (13.88 g, 78.0 mmol) was dissolved in dichloromethane (60 mL), and the resulting slurry was slowly added to the flask. The mixture was stirred at room temperature for 5 h. After reaction, the solvent was removed by rotary evaporation, and the residue was dispersed in hexanes. The mixture was filtered and purified by flash column chromatography (silica gel). Finally, the eluted organic phase was concentrated to obtain the product 2-Ethylhexyl bromide. [1]

Method 2

In an ice bath, triphenylphosphine (12 mmol, 1.2 eq.) and N‑bromosuccinimide (12 mmol, 1.2 eq.) were added together to a solution of the alcohol (10 mmol) in dichloromethane (20 mL). The reaction was monitored by TLC until completion, then quenched with saturated aqueous NaHCO₃ solution. The aqueous layer was extracted three times with dichloromethane, and the combined organic phase was washed with brine (20 mL). After drying over anhydrous Na₂SO₄, the solution was filtered and concentrated under reduced pressure. The resulting residue was purified by flash column chromatography to obtain the product 2-Ethylhexyl bromide. [2]

Borylation reaction

In a 15 mL thick-walled reaction vial under a nitrogen atmosphere, Cu⁰ catalyst (10 mg, 7 mol%, based on Cu), B₂pin₂ (304 mg, 1.2 mmol, 1.2 equiv), KOMe (84 mg, 1.2 mmol, 1.2 equiv), 2-Ethylhexyl bromide (1 mmol), and DMF (4 mL) were combined. The reaction mixture was stirred at room temperature for 30 minutes. After completion, the crude mixture was transferred to a separatory funnel containing Et₂O (20 mL), followed by the addition of water (10 mL). The two layers were separated according to their densities. The aqueous layer was then extracted twice with Et₂O (2 × 5 mL). The combined organic layers were dried over Na₂SO₄, concentrated under reduced pressure, and the resulting residue was purified by column chromatography. [3]

Nucleophilic substitution reaction

Figure2: Nucleophilic substitution reaction of 2-Ethylhexyl bromide

To a mixture of 4‑iodophenol (2.20 g, 10.00 mmol), K₂CO₃ (5.25 g, 38.00 mmol), and DMF (60 mL), 2-Ethylhexyl bromide (1‑bromo‑2‑ethylhexane, 1.93 g, 10.00 mmol) was added. The resulting mixture was refluxed for 12 h. After cooling, the reaction mixture was poured into excess dichloromethane and washed three times with deionized water. The organic layer was separated, dried over Na₂SO₄, and concentrated by rotary evaporation. [4]

Application

A preparation method for allyldimethyl(iso‑octyl)ammonium bromide has been publicly reported, which involves the reaction of allyldimethylamine with 2‑ethylhexyl bromide. The molar ratio of allyldimethylamine to 2-Ethylhexyl bromide is specified as 1:1.1. Accordingly, allyldimethylamine and 2-Ethylhexyl bromide are weighed according to this stoichiometric ratio. Acetone is measured and used as the solvent. The acetone, allyldimethylamine, and 2‑ethylhexyl bromide are sequentially added into a single‑neck round‑bottom flask, followed by stirring in a constant‑temperature water bath for 30 hours. After completion of the reaction, the mixture is cooled to allow crystallization and then dried. When used as a hydrophobic monomer in copolymerization with acrylamide, 2-Ethylhexyl bromide eliminates the need for additional surfactants.  [5]

Reference

[1] Biro, Robert; et al, Polymeric ionic liquid absorbents for n-butanol recovery from aqueous solution, AIChE Journal 2022, 68, e17676.

[2] He, Yan; et al, Remote Functionalization of Inert C(sp3)-H Bonds via Dual Catalysis Driven by Alkene Hydrofluoroalkylation Using Industrial Feedstocks, Organic Letters (2024), 26(39), 8278-8283.

[3] Prakash, Aishwarya; et al, Synthesis of Cu(0) Catalyst for Borylation of Alkyl Halides and Hydroboration of Alkenes: Scalable Access to Alkyl Boronate Esters, Inorganic Chemistry 2025, 64, 15951-15960.

[4] Lv, Pin; et al, Synergistic p-doping and interface passivation of P3HT by oxidized organic small molecules toward efficient and stable perovskite solar modules, Journal of Energy Chemistry (2025), 108, 477-484.

[5] Tian, Y., et al. (2018). Allyl dimethyl isooctyl ammonium bromide and its preparation method (Chinese Patent No. CN108104098A).

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