Pentamethylene dibromide

Trimethylene dibromide (Section 111,35) is easily prepared from commercial trimethj lene glycol, whilst hexamethylene dibromide (1 O dibromohexane) is obtained by the red P - Br reaction upon the glycol 1 6-hexanediol is prepared by the reduction of diethyl adipate (sodium and alcohol lithium aluminium hydride or copper-chromium oxide and hydrogen under pressure). Penta-methylene dibromide (1 5-dibromopentane) is readily produced by the red P-Brj method from the commercially available 1 5 pentanediol or tetra-hydropyran (Section 111,37). Pentamethylene dibromide is also formed by the action of phosphorus pentabromide upon benzoyl piperidine (I) (from benzoyl chloride and piperidine) ... 

Pentamethylene dibromide, see 1 5-Dibromopentane Pentamethylene dicyanide, 493 2-Pentene, 239 4-Pentyn-l-ol, 896, 901 Peracetic acid oxidation, 755, 768, 893 Perbenzoic acid, 807, 808, 894 analysis of, 809 Performic acid, 893, 894 Periodic acid, 1070 reagent, 1070 ... 

The preparation and purification of this compound is identical with that of cycZoselenobutane, the aS-tetramethylene dibromide in the latter case now being replaced by 27 grams of ae-pentamethylene dibromide. The product need only be distilled under ordinary pressure in a stream of carbon dioxide to effect purification. It is a colourless or very faintly yellow liquid, B.pt. 158° C. at 759 mm., nv 1 5475 at 18° C., density 1 409 at 12 5° C., 1 899 at 20° C., 1 892 at 26° C., and 1 884 at 32 2° C., whence d ° - 1 424 0-001236f. The compound has similar properties to those described for o/cZoselenobutane. The mercurichloride, C6H10Se. HgCl2, forms white, feathery needles, M.pt. 175° to 176° C. cycloSelenipentane I 1 -dichloride,... 

The ring system embodied in these cyclic derivatives is produced by condensing aluminium telluride with ae-pentamethylene dibromide ... 

Bromine is added with cooling to a mixture of N-benzoylpiperidine and phosphorus tribromide, the temperature is gradually raised, at reduced pressure, and a mixture of pentamethylene dibromide and POBr and benzonitrile is distilled at 20 mm. The organic layer is refluxed with hydrobromic acid to hydrolyze the benzonitrile, and the dibromide is separated by steam distillation, collected by ether extraction, and distilled. 

Dibromopentane (pentamethylene dibromide) is prepared by boiling a mixture of 48% HBr (1.5 moles), concentrated H2S04 (74 g), and tetrahydropyran (0.25 mole) for 3 h deteails are given in Organic Syntheses.10 9... 

Pentamethylene dibromide allowed to react with Mg in abs. tetrahydrofuran under argon, stirring continued 2 hrs. at room temp., ethyl acetate-[1- G] in tetrahydrofuran added dropwise, stirred 12 hrs. and allowed to stand 24 hrs. at ca. 20° 1-methylcyclohexanol-fl- G] (Y 77% purity 87%) refluxed 3 hrs. with pentachlorophenol j -methylcyclohexene-l- G (Y 90% containing ca. 18% startg. m.) passed repeatedly at 350° through a Pt-on-Al203 catalyst until Hg-elimination ceases -> toluene-[1- G] (Y 84-87% purity 97-99%). A. Rieker, K. Scheffler, and E. Muller, A. 670, 23 (1963). 

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