Factors Influencing the Course and Mechanism of Grignard Reactions. Xxi. The Reaction of Haloalkyl Phenyl Ethers With Grignard Reagents in the Presence of Cobaltous Halides

Abstract

It has been shown (1) that the cleavage of ethers by Grignard reagents and cobaltous halides is in many respects similar to the hydrogenolysis of ethers in the presence of Raney nickel (2). Furthermore,' Grignard reagents react with cobaltous halides to give unstable intermediates (sub-cobaltous halides) which abstract a halogen atom from an alkyl or aryl halide. It, therefore, seemed of interest to investigate the reaction of haloalkyl phenyl ethers with Grignard reagents in the presence of cobaltous halides.In most of the following experiments a solution of the haloalkyl phenyl ether was slowly added to two or three mole-equivalents of Grignard reagent containing two to five mole-% of the cobalt halide. The gases evolved mere collected in the usual way and analyzed as indicated in the experimental part. The reactions of Grignard reagents with the following ethers in the presence of cobaltous halides have been investigated: (a) C6H50CHzCH2Br, (b) CBH~OCHZCHZCHZB~, (e) C6H60CH2CH~CH2CHzBr, (d) C6H60CH2CH2CH2CHzC1, (e) C6H60CHz-CH2CH2CI-IzCH2Cl, (f) C6H60CH2CHzCHzCHzCHzCH2Br. The results are assembled in Table I. RESULTS' Table I shows that as the length of the haloalkyl chain is increased there is an abrupt change in the character of the reaction of the haloalkyl phenyl ethers [CaH60(CH2),Br] with the Grignard reagents modified by the addition of cobaltous halide, Thus, where n = 2, the over-all reaction may be represented by the following scheme:CoBrz (1-2 mole-%) + C G H~C G H~ + CeHsOMgX (50-90%) + CH2=CHz(65-81'%) f C~H S O C P H S (~~% ) .Phenol (60-70 %) and phenoxypropane (17-27 %) are also formed from y-bromopropoxybenzene (n = 3), but the gas (65-71 %) consists mainly of cyclopropane; there is also some propylene (maximum 10 % by infrared analyses). The yields 1 See earlier papers in this series. 575

The Detection of Free Radicals in Solution. I. The Reaction of Phenoxyethyl Bromide With Isopropyl-Magnesium Bromide (Or With Magnesium) in the Presence of Isoprene and Cobaltous Halides

“…Other papers in this series will deal with other types of radicals not recognizable by procedures previously employed. 1 It has been shown (1) that phenoxyethyl bromide reacts with certain Grignard reagents (say phenylmagnesium bromide) in the presence of a small amount of cobaltous bromide to yield the following products: CoBrs 1. 2C"HBMgBr + C6H6OCH2CH2Br ---> C6H6C6HB + C6HBOMgX (90%) +…”