Isobutylene bromide

Certain olefinic halogen compounds are best prepared by this method. Isobutylene bromide is dehydrohalogenated by hot potassium hydroxide... 

The rate of addition depends on the concentration of both the butylene and the reagent HZ. The addition requires an acidic reagent and the orientation of the addition is regioselective (Markovnikov). The relative reactivities of the isomers are related to the relative stabiUty of the intermediate carbocation and are isobutylene 1 — butene > 2 — butenes. Addition to the 1-butene is less hindered than to the 2-butenes. For hydrogen bromide addition, the preferred orientation of the addition can be altered from Markovnikov to anti-Markovnikov by the presence of peroxides involving a free-radical mechanism. 

Isobutylene, methyl chloride, methyl bromide, ethyl chloride (Linde Div. Union Carbide Corp.) were obtained in high purity and were further purified by passing through a column containing barium oxide and molecular sieves. 

We also obtained evidence for the formation of complexes between isobutylene and the bromide and chloride of aluminium and we found that in sufficiently pure alkyl halides, polyisobutylium and tert-butylium tetrahaloaluminates are stable electrolytes. 

Isobutylene (Philips Research Grade) was purified as described [17] by distillation on a vacuum line through a trap containing sodium at 350 °C. It was stored as liquid on a sodium mirror. Solutions in methyl bromide were made up by distilling the required quantities of solvent and isobutylene from hanging burettes along a vacuum line into a reservoir with Teflon tap, which was subsequently cut from the vacuum line and fused to a burette with Teflon tap which was then fused to the main vacuum manifold as shown in Figure 1. 

A very rapid polymerisation accompanied each addition of monomer, and sometimes polymer precipitated out. The amount was exceedingly hard to judge, but with isobutylene and aluminium bromide it was normally very little. At -78 °C more polymer was seen to come out of solution than at -63 °C. Throughout the whole process the solutions always remained colourless, except in experiments with styrene, in which the solution and the precipitated polymer became yellow. 

Figure 2 The change in conductivity (k) during the polymerisation of isobutylene by a solution of aluminium bromide in methyl bromide. In each experiment the isobutylene was added in several similar doses, as a solution in methyl bromide (3.3 mohdm 3). The polymerisations were finally stopped with a large excess of tritiated water conditions are given in the following Table...

Several experiments were done at -63 and -78 °C with the bromide or the chloride as initiator, in which one large dose of isobutylene was added rapidly to the initiator solution. Most of the polymer was precipitated and the products had the relatively high DP of ca. 4.5 103. The conductivity showed little change in these experiments, (in one it actually decreased), presumably for the reasons which have been mentioned before. 

Figure 3 The final, equilibrium conductivity of polymerised mixtures of isobutylene and AlBr3 in methyl bromide as a function of the isobutylene concentration [IB]. Each point represents the conductivity resulting from an addition of isobutylene conditions...

In Experiment C9 (circular points in Figure 7) 0.75 mol of isobutylene was added at -80 °C to 3.3 mmol of aluminium bromide in 40 ml of methyl bromide over ca. 1.5 h. According to the ratio (kc - k /Kj, which was ca. 103, the initiator solution was very pure. No polymerisation took place the isobutylene was shown by GLC analysis to be unchanged and this showed no dimers. 

In order to find out what R+ is, we consider first the common experience that when a tert- mty halide is treated with an aluminium halide under ordinary conditions, there is a brisk evolution of hydrogen halide and a coloured solution containing oligo-isobutylenes and condensed allylic ions is formed. In the present experiments the solutions were colourless, no hydrogen halide was evolved, and the conductivity was stable and behaved reversibly. Further, the rectilinearity of the k-[A1X3] plots in Figures 9 and 10, and the smallness of the intercepts on the K-axis, showed that ions generated by reactions other than those of type (viii) must have been very scarce, and for the experiment with tert-butyl bromide this was borne out by the absence of any byproducts. 

Indenopyrene, see Indeno[l,2,3-crf pyrene l//-Indole, see Indole Indolene, see Indoline Inexit, see Lindane Inhibisol, see 1,1,1-Trichloroethane Insecticide 497, see Dieldrin Insecticide 4049, see Malathion Insectophene, see a-Endosulfan, p-Endosulfan Intox 8, see Chlordane Inverton 245, see 2,4,5-T lodomethane, see Methyl iodide IP, see Indeno[l,2,3-crf pyrene IP3, see Isoamyl alcohol Ipaner, see 2,4-D IPE, see Isopropyl ether IPH, see Phenol Ipersan, see Trifluralin Iphanon, see Camphor Isceon 11, see Trichlorofluoromethane Isceon 122, see Dichlorodifluoromethane Iscobrome, see Methyl bromide Iscobrome D, see Ethylene dibromide Isoacetophorone, see Isophorone a-Isoamylene, see 3-Methyl-l-butene Isoamyl ethanoate, see Isoamyl acetate Isoamylhydride, see 2-Methylbutane Isoamylol, see Isoamyl alcohol Isobac, see 2,4-Dichlorophenol Isobenzofuran-l,3-dione, see Phthalic anhydride 1,3-Isobenzofurandione, see Phthalic anhydride IsoBuAc, see Isobutyl acetate IsoBuBz, see Isobutylbenzene Isobutane, see 2-Methylpropane Isobutanol, see Isobutyl alcohol Isobutene, see 2-Methylpropene Isobutenyl methyl ketone, see Mesityl oxide Isobutyl carbinol, see Isoamyl alcohol Isobutylene, see 2-Methylpropene Isobutylethylene, see 4-Methyl-l-pentene Isobutyl ketone, see Diisobutyl ketone Isobutyl methyl ketone, see 4-Methyl-2-pentanone Isobutyltrimethylmethane, see 2,2,4-Trimethylpentane Isocumene, see Propylbenzene Isocyanatomethane, see Methyl isocyanate Isocyanic acid, methyl ester, see Methyl isocyanate Isocyanic acid, methylphenylene ester, see 2,4-Toluene-diisocyanate... 

The catalytic activity of certain of the Friedel-Crafts catalysts was shown to decrease over a very wide range in the series boron fluoride, aluminum bromide, titanium tetrachloride, titanium tetrabromide, boron chloride, boron bromide and stannic chloride (Fairbrother and Seymour, mentioned in Plesch al., 83). When boron fluoride is added to isobutylene at dry ice temperatures, the olefin is converted to a solid polymer within a very few seconds. The time required for complete polymerization with aluminum bromide hardly extends to a few minutes while reaction times of hours are required with titanium chloride and periods of days with stannic chloride. 

It has previously been shown that large changes can occur in the rate of a cationic polymerization by using a different solvent and/or different counterion (Sec. 5-2f). The monomer reactivity ratios are also affected by changes in the solvent or counterion. The effects are often complex and difficult to predict since changes in solvent or counterion often result in alterations in the relative amounts of the different types of propagating centers (free ion, ion pair, covalent), each of which may be differently affected by solvent. As many systems do not show an effect as do show an effect of solvent or counterion on r values [Kennedy and Marechal, 1983]. The dramatic effect that solvents can have on monomer reactivity ratios is illustrated by the data in Table 6-10 for isobutylene-p-chlorostyrene. The aluminum bromide-initiated copolymerization shows r — 1.01, r2 = 1.02 in n-hexane but... 

The product (benzyl f-butyl ether) is primary on the benzyl side and tertiary on the t-butyl side. So, an SN2 type displacement by potassium f-butoxide of benzyl bromide is one approach, and an acid-catalyzed (SN1) process of benzyl alcohol with isobutylene (2-methylpropene) is another method ... 

Lalancette et al. studied the catalytic activity of AlCl3-intercalated graphite for the alkylation of aromatics with ethyl bromide, ethylene, propylene, and isobutylene and compared it with pure A1C13 the intercalate was a milder catalyst than AICI3 and gave less polysubstituted products... 

Direct evidence for stepwise reduction was obtained in the electrolytic reduction of t-butyl bromide at a mercury cathode in DMF18,19. The polarogram or cyclic voltammogram shows two waves [E1/2 = -1.23 V, -1.46 V (see)] indicating stepwise reduction. Labelling experiments indicate that isobutylene and isobutane arise from disproportionation of t-butyl radicals, and the 2,2,3,3-tetramethylbutane arises from a coupling reaction (equation 2). Reduction at the second wave leads to a carbanion, evidence of which is provided by... 

The cyclic voltammograms at vitreous carbon electrodes for 2-iodooctane, r-butyl bromide and -butyl iodide show two waves [e.g., -1.6 V and -1.8 V (see) for r-butyl bromide] indicating stepwise generation of alkyl radicals and carbanions. The products of large-scale electrolyses of r-butyl bromide (isobutane, isobutylene, 2,2,3,3-tetramethyl-butane) are indicative of the involvement of both radical and carbanion species214. 

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