【文章內(nèi)容簡介】 reaction products. They proposed the initial formation of an organozinc halide which then deposed by an ionic process. In this laboratory the treatment of 1,4dibromobutane with a variety of metals in refluxing xylene and in butyl ether has bean found to produce the same gaseous products in each case (Table I)。 ethylene, butane, 1butene, traps and cis2butene, 1,3butadiene, and cyclohutane. Analysis of the plex reaction products was carried out by means of gas chromatography (Fig. 1).Direct parison of yields between reactions conducted in xylene aaid in butyl ether is plicated by the fact that butyl ether itself undergoes some cleavage when heated th the metals used in this study. The treatment of boiling butyl ether with sodium produced a large amount of propane and small amounts of C2 and C4 hydrocarbons. with the less active metals listed in Table I, the production of propane was negligible.While the distribution among the products observed on metallic dehalogenation of 1,4dibromobutane varied considerably with the reaction conditions,the overall consistency of products strongly supports the supposition of a mom mechanism for all of these reactions. In order to further clarify the question of whether the dehalogenations are free radical or ionic in nature, the reaction was carried out under conditions which would favor radical formation.Kharasch and coworkers[7] have carried out a number of reactions using a Grignard reagent and cobaltous halides as a source of free radicals in solution. It was proposed that radical formation takes place according to the following scheme. TIME IN MINUTES. Gas chromatography mixture of hydrocarbons (upper product of 1,4dibromobutane bromide and cobaltous bromide in tracings for a standard curve) and the reaction with methylmagnesium butyl ether (lower curve）When a mixture of 1,4dibromobutane and cobaltous bromide was treated with methylmagnesium bromide in a high boiling solvent, it was found that the same group of gaseous reaction products was observed as in the metal dehalogenation reactions The results of this series of reactions are also listed inTable I. At the lower temperature of refluxing ethyl ether, no cyclobutane was formed。 a not unexpected result in view of the observations of Cason and Way.[3]TABLE IDEHALOGENATION REACTIONS OF 1,4DIBROMOBUTANE （ MOLE)ReagentSolventYield,Ml.Products, Mole%C2H4C4H101—C4H8NaXylene8063165LiXylene90164615MgXylene90145112NaBu2Oa200High..MgBu2Oa190312419ZnBu2OaBu2Oa342816Zndioxane60274713Mg+CoBr2Bu2Oa20082416Mg+CoBr2Et2O7083342CH3MgBr+CoBr2Xyleneb…c2138CH3MgBr+CoBr2Bu2O…c231715CH3MgBr+CoBr2Et2O…c6351ReagentSolventYield,Ml.Products, Mole%2—C4H81,3—C4H6Cyclo C4H8NaXylene802311LiXylene905513MgXylene904613NaBu2Oa200..0MgBu2Oa190629ZnBu2Oa2601110Zndioxane601300Mg+CoBr2Bu2Oa2001331Mg+CoBr2Et2O701700CH3MgBr+CoBr2Xyleneb…c542CH3MgBr+CoBr2Bu2O…c3008CH3MgBr+CoBr2Et2O…c1700 a The high yields in butyl ether were due to the secondary reaction of the metal with the solvent。 the other product being propane. Small amount is abbreviated . b In addition, 53% ethane and 4% propane were found. C No yield of reaction products was measured here due to the large dilution by methane.The experimental results of this study support the view that the metal dehalogenation reactions of 1,4dibromobutane are free radical in nature. However, it should be born in mind that in any reactions as plex as these there is no difficulty in finding explanations of the experimental facts, but only in defending a preferred explanation selected from many. One reasonable reaction scheme which will acmodate the above observations is as follows:In the same fashion the 4bromolbutene (Equation 4) may depose to form 1,3butadiene and 1butene. The 4bromolbutyl radical (A) may be generated either by the direct abstraction of the halogen by the metal or by the thermal deposition of a metal alkyl intermediate.[8]The formation of cyclobutane as envisioned in Equation 2 above is a displacement of bromine atom from carbon by an attacking radical. The experimental evidence regarding radical displacement reactions has been summarized by The formation of a 1,4butyl diradical as suggested by Bawn and Milstead[2] is also a possibility. In order to test the proposal of the 4bromolbutyl radical (A) as:reaction intermediate, the deposition of 4phenoxybutyl bromide with magnesium and tobaltous bromide in refluxing xylene tv as carried out. Again a plex mixture of gaseous products was formed (Table II). Analysis of this mixture showed the same products as observed in the reactions of 1, was formed to the extent of 2 mole percent. Kharasch, Stampa, and Xudenburg[l0] have reported that treatment of 4phenoxybutyl bromide with phenylmagnesium bromide and cobaltous bromide in ether gave predominantly butyl phenyl ether and butenyl phenyl ether. TABLE IIREACTIONS OF nBUTYL BROMIDE AND 4PHENOXYBUTYL BROMIDEReagentSolventYield,Ml.Products, Mole%C2H4C4H101—C4H8 nButyl bromide, moleMg+CoBr2Et2O49005521CH3MgBr+CoBr2Et2O…a611204Phenoxybutyl bromide, .0052 moleMg+CoBr2Xylene255379ReagentSolventYield,Ml.Products, Mole%2—C4H81,3—C4H6Cyclo C4H8Mg+CoBr2Et2O49024……CH3MgBr+CoBr2Et2O…a………Mg+CoBr2Xylene251012 a No yield of reaction products was measured due to the high dilution with methane. The other major product (63%) was pentane.Both trans and cis 2butene