Isobutene dichloride

J. H. Beard, P. H. Plesch, P. P. Rutherford, The Low-temperature Polymerisation of Isobutene, Part V, Polymerisation by Aluminium Trichloride in Methylene Dichloride, J. Chem. Soc., 1964, 2566. 

A ubiquitous co-catalyst is water. This can be effective in extremely small quantities, as was first shown by Evans and Meadows [18] for the polymerisation of isobutene by boron fluoride at low temperatures, although they could give no quantitative estimate of the amount of water required to co-catalyse this reaction. Later [11, 13] it was shown that in methylene dichloride solution at temperatures below about -60° a few micromoles of water are sufficient to polymerise completely some decimoles of isobutene in the presence of millimolar quantities of titanium tetrachloride. With stannic chloride at -78° the maximum reaction rate is obtained with quantities of water equivalent to that of stannic chloride [31]. As far as aluminium chloride is concerned, there is no rigorous proof that it does require a co-catalyst in order to polymerise isobutene. However, the need for a co-catalyst in isomerisations and alkylations catalysed by aluminium bromide (which is more active than the chloride) has been proved [34-37], so that there is little doubt that even the polymerisations carried out by Kennedy and Thomas with aluminium chloride (see Section 5, iii, (a)) under fairly rigorous conditions depended critically on the presence of a co-catalyst - though whether this was water, or hydrogen chloride, or some other substance, cannot be decided at present. 

The results are presented as plots of DP against mole fraction of isobutene. With methyl chloride, methylene dichloride, or vinyl chloride as diluent the DP rises very steeply to a sharp peak with increasing monomer concentration, and then falls off in a curve of exponential type (Figure 4). With ethyl chloride there is apparently no maximum, the... 

Table 6 Polymerisation of isobutene by titanium tetrachloride and water in methylene dichloride [80, 87] ...

The technique and apparatus used in this work have been described in detail [81]. The reaction vessel was made hydrophobic by exposure to the vapour of trimethylchlorosilane and evacuated for several hours. Then isobutene, dried by sodium, and methylene dichloride, stored over calcium hydride, were distilled into it, the temperature adjusted, and the reaction started by the breaking of a phial containing a solution of titanium tetrachloride in methylene dichloride and one containing water. These could be broken in this, or the reverse, order, or simultaneously. The ensuing reaction was registered as a time-temperature curve by an automatic recorder. The range of conditions studied was [C4H8] = 0.05 -0.6 mole/1, [TiClJ = (0.1-5) x 10 3 mole/1, [H20] = (0.05-5) x 10 4 mole/1, T= 18°- -95°. 

Chain-Transfer with anisole. The phenomenon of chain-transfer, especially with aromatic compounds, has been extensively investigated for the polymerisation of styrene, but there is only one such study with isobutene [13]. Isobutene (0.1 mole/l) was polymerised by titanium tetrachloride (3 x 10 3 mole/l) in methylene dichloride with a constant, low, but unknown concentration of water in the presence of anisole (0.02 to 0.15 mole/l) over the temperature range -9° to -90°. The reactions were stopped at 10-20 per cent conversion by the addition of methanol. 

When we tried to interpret our experiments on the polymerisation of isobutene by aluminium chloride in methylene dichloride [10], in which the irrelevance of water had been demonstrated, we rejected (for good reasons) the theory of co-initiation by an impurity RfX (more reactive than the solvent RX) according to scheme (2), and put up for consideration the following three reaction schemes ... 

Detailed study [18] of the system isobutene-titanium tetrachloride-water-methylene dichloride showed it to be highly complex, but the kinetics and the temperature-dependence of rate and DP could be explained, at least qualitatively, on the hypotheses that the chain-carriers are ions, that paired and free cations have appreciably different reactivities, and that the degree of dissociation of the ion-pairs increases with decreasing temperature. 

The Polymerisation of Isobutene by Titanium Tetrachloride in Methylene Dichloride, R.H. Biddulph, P.H. Plesch and P.P. Rutherford, International Symposium on Macromolecules, Wiesbaden, 1959, Paper No.III.A.10. 

Poly([7,8-bis(trifluoromethyl)tetracyclo [4.2.0.02 8.05 7]octane-3,4-diyl]-1,2-ethenediyl), 3457 Poly[borane(l)], 0134 crs-Poly (butadiene), 1480 Poly(l,3-butadiene peroxide), 1528 Poly(butadiyne), 1382 Poly(carbon monofluoride), 0336 Poly(chlorotrifluoroethylene), 0589 Poly(l,3-cyclohexadiene peroxide), 2380 Poly(cyclopentadienyltitanium dichloride), 1837 Poly(diazidophosphazene), 4781 Poly(dibromosilylene), 0282 Poly(difluorosilylene), 4324 Poly(dihydroxydioxodisilane), 4474 Poly(dimercuryimmonium acetylide), 0665 Poly(dimercuryimmonium azide), 4606 Poly(dimercuryimmonium bromate), 0253 Poly (dimercury immonium iodide hydrate), 4449 Poly (dimercury immonium perchlorate), 4006 Poly(dimercuryimmonium permanganate), 4603 Poly (dime thylketene peroxide), see Poly(peroxyisobutyrolactone), 1531 Poly(dimethylsiloxane), 0918 Poly(disilicon nitride), 4752 Poly(ethenyl nitrate), see Poly(vinyl nitrate), 0760 Poly(ethylene), 0778 Poly(ethylene terephthalate), 3256 Poly(ethylidene peroxide), 0831 Poly(furan-2,5-diyl), 1398 Poly(germanium dihydride), 4409 Poly(germanium monohydride), 4407 Poly(isobutene), 1578 Poly(methyl methacrylate peroxide), 1913... 

The system ethylaluminium dichloride-isobutene- -heptane in the temperature range —55 to 21 °C was shovwi to initiate in the absense of any cocatalyst No mention was given in this paper about the pol3unerisation 5 ields, but from a figure giving the time-conversion curve for a typical mn it can be concluded that reactions did not reach 100% conversion, at least within the first few minutes. 

The work of Marek s group also encompasses an interesting study of the polymerisation of isobutene by ethylaluminium dichloride in heptane between —55 and 21 This system showed all the typical traits of direct initiation through selfionisation. Indeed, addition of small amounts of water produced a decrease in the rate of polymerisation with respect to the dry medium (5 x 10 M residual water claimed). The initial rate of monomer consumption was directly proportional to the monomer concentration and the square of the catalyst concentration. The course of the first part of the polymerisations (up to about 40% yield) was internally first order. As the reaction proceeded further, a sensible deceleration was noticed and indeed incomplete yields were often obtained, confirming a general feature of direct initiation. The authors discussed the mode of initiation in terms of selfionisation of the catalyst followed by the attack of the positive ion onto the isobutene molecule, but did not comment about the origin of the anomalous rate decreases and of the limited conversions. 

It has been pointed out that the initiating potential of the system MesAl-f-BuQ is hi in solvent methyl chloride, but nil in n entane. On the other hand, AIQ3 and alkylaluminium dichlorides can induce the polymerisation of isobutene in both solvents. These facts do not disprove our interpretation, since it can be readily argued that the chlorine-methyl exchanges between catalyst and cocatalyst are extremely slow in a medium of such alow dielectric constant as n-pentane and that the absence of polymerisation arises precisely from the lack of formation of di- and trichloride. 

Preparation from malonic acid, isobutene, and a catalytic amount of coned, sulfuric acid in ether at a pressure of about 40 p.s.i. " Preparation via malonyl dichloride the first step requires heating at 45-50° for 3 days. 

In an investigation of the reaction between isobutene and PCls, it has been shown that, as the temperature of reaction is raised, the proportion of unsaturated phosphonic dichloride (30) increases at the expense of the saturated compound (31) ... 

The weak point of this method is the supply of isobutene diacetate (2), which is expensive and difficult to find in bulk quantities, or can be prepared by a double nucleophilic displacement from the corresponding dichloride (5, Scheme 16.2). 

Triphenylphosphine-carbon tetrachloride converts epoxides into cisA, 2-dichlorides, a process already known to occur with triphenyldichloro-phosphorane. The in situ generation of hydrogen bromide and isobutene is a simple laboratory preparation of t-butyl bromide. ... 

The chromium complexes are CrCl3L3 and CrCl2L2(NO)2, wherein the ligand L are pyridine and tri-n-butylphosphine in conjunction with ethylaluminum dichloride, effect simple dimerization of ethylene at 50°C [133-135]. A conversion of 4700 g butenes per g of chromium complex is achieved with the catalyst CxCX i -Etpy),. The butene fraction consists of 1-butene (50%), trans-2-butene (32%), ds-2-butene (18%), and isobutene (0.1%). Cr or Cr species may be involved in the reaction. Here chromium atoms are probably associated with the organoalu-minum halides to form bridged chromium-halogen-aluminum species. 

Miscellaneous Reactions. Isobutene, as the carbenium ion source for Ritter reactions, produces Al-r-butyl amides (eq 34). Isobutene undergoes highly regioselective cycloaddition with isocyanate to form azetidinones and with nitrones to yield isox-azolidines (eqs 35 and 36). Allyl thioethers are formed by the electrophilic addition of Benzenesulfenyl Chloride to isobutene (eq 37). Alkenylphosphonous dichlorides and alkenylthionophosphonic dichlorides are also formed by addition of PCI5 and P2S5 (eqs 38 and 39). ... 

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