Synthesis and Metabolism of 1,3-Dibromopropane

1,3-Dibromopropane is a dihalogenated alkane compound that appears as a clear, colorless to yellow liquid under standard ambient conditions. It exhibits diverse chemical reactivity and possesses a relatively high density. While insoluble in water, it is miscible with common organic solvents. 1,3-Dibromopropane is primarily utilized as an intermediate in organic synthesis, particularly in the preparation of cyclopropane-based biologically active molecules, and is also well-regarded in fundamental research within organic synthetic methodology.

Synthesis

Figure1: Synthesis of 1,3-Dibromopropane

Charge the corresponding diol (1 equiv), 48% aqueous HBr (~3 equiv per OH group), and octane (~7:1 v/w ratio relative to the diol) into a one-neck round-bottom flask. Fit the flask with a fractionating column connected to a Dean-Stark trap, and heat it in an oil bath at 145–150 °C with rapid magnetic stirring. As the azeotrope distills (bp 89–92 °C), periodically drain the aqueous lower layer until approximately half the theoretical amount of water has been collected, at which point the azeotrope head temperature begins to rise. Then, set the condenser to total reflux for 6 hours, followed by reopening the system and collecting aqueous material for an additional hour (head temperature 96–100 °C). The pale tan octane phase, containing both dibromide and bromoalkanol, is washed with cold 85% v/v H2SO4 (10 mL, then 5 mL) to remove all color and bromoalkanol. The solvent is then stripped from the neutralized octane solution using a Vigreux column under reduced pressure, and the essentially pure residue (confirmed by 1H NMR) is Kugelrohr-distilled to obtain 1,3-dibromopropane. [1]

Metabolism

1,3-Dibromopropane is widely utilized in industrial chemical synthesis and has also been applied in the stabilization of wool through cross-linking to reduce its susceptibility to moth damage. Although the lowest lethal dose following intraperitoneal injection in mice has been reported as 750 mg/kg, the metabolism of this compound has not yet been documented, to the authors' knowledge. In contrast, the metabolic fate of its lower homologue, 1,2-dibromoethane, has been described in rats. The present study therefore investigates the metabolic disposition of 1,3-dibromo[14C]propane in the rat. The bromine content was measured in 24-hour urine samples collected both before and after administration of 1,3-dibromopropane. Urine samples were acidified to pH 1, extracted with ether, and the bromine content of the extracts was subsequently determined. In a separate analysis, air exhaled by rats during the 6-hour period following dosing was passed through a methanol-containing trap immersed in a freezing mixture; expired air from untreated rats was processed in the same manner. Aliquots of the methanolic solutions were then analyzed for bromine content. [2]

Voltammetric reduction

When 1,3-Dibromopropane is reduced at a glassy carbon electrode, an irreversible single two-electron step is generally observed in the presence of tetraalkylammo nium salts in DMF within the potential range from 2.3 to 2.5V vs. SCE depending on the salt and the solvent. Thus, the two C–Br linkages appear to behave quite iden tically at this kind of electrode. It was reported that the reduction, under these conditions, corresponds to a two electron process. The main product obtained by potentiostatic electrolysis was cyclopropane.

N-alkylation of heterocycles

The general procedure for the N-alkylation of heterocycles was carried out as follows. The heterocycle (1 mmol) was dissolved in 5 ml of anhydrous DMF. The complex (0.05 mmol) and K2CO3 were then added to the solution at room temperature. Shortly thereafter (20 min), 1,3-dibromopropane (1 mmol) was added in portions to the reaction mixture. The reaction was stirred at room temperature. The inorganic salt was removed by filtration and rinsed twice with dichloromethane. The solution was poured into water and extracted with dichloromethane (2 x 25 ml). The combined organic layers were washed with brine, dried over anhydrous sodium sulphate, filtered, and concentrated in vacuo, resulting in the formation of the product in 92% yield for the 1:1 coupling ratio and 78% yield for the 2:1 coupling ratio. In this process, 1,3-dibromopropane participates in both coupling proportions; however, N-alkylation of heterocycles with 1,3-dibromopropane in a 1:1 coupling proportion is easier than in the 2:1 coupling proportion. [3]

Reference

[1] Mekala, Shekar; et al, Process intensification-assisted conversion of α,ω-alkanediols to dibromides， Tetrahedron Letters 2015, 56, 630-632.

[2] James S P, Pue M A, Richards D H. Metabolism of 1, 3-dibromopropane[J]. Toxicology Letters, 1981, 8: 7-15.

[3] Hegade S, Jadhav Y, Chavan S, et al. Catalytic assay of Schiff base Co (II), Ni (II), Cu (II) and Zn (II) complexes for N-alkylation of heterocycles with 1, 3-dibromopropane[J]. Journal of Chemical Sciences, 2020, 132: 92.

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