AlBr3-HBr

Provided that the uncomplexed species is suceptible to destruction, while the complex is protected, the lifetime of living polymer increases at higher monomer concentrations. Cationic polymerization of propylene induced by AlBr3. HBr studied by Fontana and Kidder22) exemplifies perhaps such a system. 

An entirely different type of termination mechanism has been proposed to account for the cessation of polymerization in the system propene-AlBr3-HBr through exhaustion of the catalyst [9]. It is suggested that by the transfer of a hydride ion, and then of a proton, an allylic ion ... 

Tetrabromopyrazine, which shows bactericidal activity, is obtained from tetrachloropyrazine (HBr/HOAc)293 or from tetrafluoropyrazine (AlBr3/HBr).279... 

Actually this reaction does not occur at all unless a trace of olefin,41 oxygen,42 or water48 is present, or unless the experimental conditions are conducive to the formation of decomposition products.41 In AlBr3-HBr catalysis, the initial step in the reaction is believed to be the formation... 

Recently two ponderous papers appeared by Kriz and Marek which purported to be model studies of the cationic polymerization of isobutylene (11,12). In the first phase of their study (11) the authors chose 1,1 -dineopentyl ethylene, a trimer of isobutylene, as their model compound and worked with AlBr3, HBr (or DBr) in n-heptane at —70° (11). They mixed these reagents by the following sequence nC + HBr + trimer+AlBr3. The products were analyzed by gas chromatography, NMR (60 MHz), and mass spectroscopy. Useful, hard data of this research are as follows 1.1,1 -dineopentylethylene rapidly isomerizes... 

The present paper is an attempt to unravel a rather confused aspect of cationoid polymerisations. This concerns the phenomenon comprised in the term monomer complexation of the growing cation . The idea seems to have occurred for the first time in the work of Fontana and Kidder on the polymerisation of propene by AlBr3 and HBr in w-butane [3]. The kinetics indicated a reaction of zero order with respect to monomer, M to explain this, it was assumed that the growing end of the chain, written as a carbenium ion, Pn+, is complexed with M and that the rate-determining growth step is an isomerisation of this complex ... 

Fontana et al. (1948, 1952) showed that the kinetics of the cationic polymerization of C3H6 by AlBr3 and HBr in an hydrocarbon solvent can be explained on the assumption that the alkene forms complexes with the growing cations, which might be unpaired or paired ... 

Die tibrigen Halogenderivate des Monogermans entstehen aus GeH4 durch Reaktion mit HCl bzw. HBr in Gegenwart von A1C13 oder AlBr3 (55). 

Cycloalkanes possessing a tertiary carbon atom may be alkylated under conditions similar to those applied for the alkylation of isoalkanes. Methylcyclopentane and methylcyclohexane were studied most.5 Methylcyclopentane reacts with propylene and isobutylene in the presence of HF (23-25°C), and methylcyclohexane can also be reacted with isobutylene and 2-butene under the same conditions.20 Methylcyclopentane is alkylated with propylene in the presence of HBr—AlBr3 (—42°C) to produce l-ethyl-2-methylcyclohexane.21 C12H22 bicyclic compounds are also formed under alkylation conditions.21 22 Cyclohexane, in contrast, requires elevated temperature, and only strong catalysts are effective. HC1—AICI3 catalyzes the cyclohexane-ethylene reaction at 50-60°C to yield mainly dimethyl- and tetra-methylcyclohexanes (rather than mono- and diethylcyclohexanes). The relatively weak boron trifluoride, in turn, is not active in the alkylation of cyclohexane.23... 

It is possible to hydrogenate aromatics in the superacids HF-TaF5, HF-SbF5, or HBr-AlBr3 in the presence of hydrogen. The reduction of benzene was shown to give an equilibrium mixture of cyclohexane and methylcyclopentane.243 244 Reduction was postulated to proceed via initial protonation of benzene followed by hydride transfer ... 

Surprisingly, no work has apparently been carried out on the addition of HBr to simple dialkylalkynes. Hexafluom-2-butyne readily adds HBr in the presence of AlBr3 (equation 116).23... 

AlBr3 nNHs (c). Klemm and Tanke1 reported the following heats of dissociation tetradecammine, —7.72 nonammine, —8.4 heptammine, —10.7 hexammine, —16.2. Klemm and Tanke1 measured the following heats of solution in HBr(20) at 0° hexammine, 66.4 pentammine, 60.2 triammine, 57.7 monammine, 66.9. See also Ephraim and Millman.1... 

On the surface of the solid metal halide superacid HBr-AlBr3, benzene gives the benzenium cation (70), which was characterized in situ by 13C MAS NMR.120 All the methyl derivatives and one ethyl derivative were also studied.120 The aromatic substitution reactions occurring in the complexes between gaseous arenium ions and... 

Quinoline and isoquinoline react in an analogous manner with benzene in conjugated superacids (HCI-AICI3, HBr-AlBr3) to yield predominantly cis-5,1-diphenyl-5,6,7,8-tetrahydroquinoline and <7,v-6,8-diphenyl-5,6,7,8-tetrahydroisoqui-noline, respectively (75-94% yield).297 The regioselectivity observed corresponds to the most stable dicationic intermediates 73 and 74. Unsaturated imides298 exhibit similar behavior in triflic acid (Scheme 5.33). 

In other words, of the initial charge of isopropyl chloride, 34% of the carbon is converted to propane under these conditions. A comparable sample of 1-chloropropane under identical reaction conditions, of excess alkyl halide Lewis acid, was converted after five minutes to the extent of 18% to propane. After 15 minutes the relative amount of "propane" had decreased as a result of further acid catalyzed polycondensation reactions. Similarly, isopropyl chloride reacts in HBr-AlBr3 at room temperature to give a gas product which is entirely propane after 2 min. In this system we again begin to see a buildup of heavier hydrocarbon species with time. The fact that the reaction proceeds so rapidly here can probably be attributed to a homogeneous hydrocarbon/acid liquid phase. This last result and additional experiments are summarized in Table IV. 

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