Styrene protonated

Fig. 20. NMR peak positions for methyl methacrylate-styrene copolymers and homopolymers in CHC13 or CCI4 (see text) as a function of fu the mole fraction of methyl methacrylate in the monomer feed open circles represent styrene protons filled circles represent methyl methacrylate protons half-moons are not yet assigned with certainty but are interpreted in the text as methyl methacrylate methoxyl protons...

In cationic polymerization the active species is the ion which is formed by the addition of a proton from the initiator system to a monomer. For vinyl monomers the type of substituents which promote this type of polymerization are those which are electron supplying, like alkyl, 1,1-dialkyl, aryl, and alkoxy. Isobutylene and a-methyl styrene are examples of monomers which have been polymerized via cationic intermediates. 

Friedel-Crafts alkylation using alkenes has important industrial appHcations. The ethylation of benzene with ethylene to ethylbenzene used in the manufacture of styrene, is one of the largest scale industrial processes. The reaction is done under the catalysis of AlCl in the presence of a proton source, ie, H2O, HCl, etc, although other catalysts have also gained significance. 

With 1-phenyl-1,3-butadiene, the addition is exclusively at the 3,4-double bond. This reflects the greater stability of this product, which retains styrene-type conjugation. Initial protonation at C-4 is favored by the feet that the resulting carbocation benefits from both allylic and ben2ylic stabilization. 

Chromatography by ion exchange on a sulfonated poly(styrene-co-divinyl benzene) phase has been proposed as a replacement for titrimetry.57 Eluted by a dilute solution of a neutral salt such as sodium ethanesulfonate, the conductance of the protons can be measured in the absence of a suppressor from sub-millimolar to molar concentration. The response factors of mono-, di-, and trichloroacetic acid and of o-phthalic acid were large and essentially equivalent to ethanesulfonic acid, while the response factor of acetic acid was far smaller. A syringe pump has generated pressures as high as 72,000 psi (5000 bar) in a capillary column packed with 1 p particles, generating a fraction capacity of 300 peaks in 30 minutes.58... 

Examination of the mass spectrum of P2VPY taken during the maximum decomposition rate reveals the major decomposition products as methylpyridine (93 a.m.u.), protonated vinyl pyridine (106 a.m.u.), and protonated dimer (211 a.m.u.) with ion ratios 74 100 59 respectively. Trimeric and tetrameric protonated species (316 and 421 a.m.u.) are also observed but in relatively small amounts. Protonated ions, rather than the simple monomers and dimers observed for the decomposition of poly(styrene) by MS11, may be created by a mechanism similar to that reported for the decomposition of 2-(4-heptyl)pyridine12 in the mass spectrometer. 

The formation of these compounds has been rationalized according to Scheme 6. The reaction of Os (E )-CH=C 11 Ph C1 (C())( P Pr3)2 with n-BuLi involves replacement of the chloride anion by a butyl group to afford the intermediate Os (/i> CH=CHPh ( -Bu)(CO)(P Pr3)2, which by subsequent hydrogen (3 elimination gives OsH ( >CI I=CHPh (CO)( P Pr3)2. The intramolecular reductive elimination of styrene from this compound followed by the C—H activation of the o-aryl proton leads to the hydride-aryl species via the styrene-osmium(O) intermediate Os r 2-CH2=CHPh (CO)(P Pr3)2. In spite of the fact that the hydride-aryl complex is the only species detected in solution, the formation of OsH ( )-CH=CHPh L(CO)(P Pr3)2 and 0s ( )-CH=CHPh (K2-02CH)(C0)(P,Pr3)2 suggests that in solution the hydride-aryl complex is in equilibrium with undetectable concentrations of OsH ( )-CH=CHPh (CO)(P,Pr3)2. This implies that the olehn-osmium(O) intermediate is easily accessible and can give rise to activation reactions at both the olefinic and the ortho phenyl C—H bonds of the... 

The disilanickela compound 21 is not effective in the nickel-catalyzed double silylation reaction with styrene. However, the stoichiometric reaction of 21 with styrene afforded 4,5-carboranylene-l,l,3,3-tetramethyl-2-phenylmethylene-1,3-disilacyclopentane 29. A key feature in the 111 NMR spectmm of 29 includes a singlet at 7.71 ppm assigned to the vinyl proton. A characteristic low-frequency 13C NMR resonance at 139.75 ppm provides evidence for a tethered carbon atom of the two silicon moieties. Unambiguous confirmation was provided by X-ray crystallographic analysis of 29. 

In view of these results the experiments using styrene were repeated at lower temperatures and the study extended to the more nucleophilic analogs, a-methyl styrene, tetraphenylethylene. No significant shifts of benzyl proton peaks were observed in any of these cases, even with a 500-Hz scale expansion. 

The spectrum of styrene in toluene was compared with that in toluene containing an equimolar quantity of Zr (benzyl) 4 at 0.06 M using a sweep of 2500 Hz. The methylene doublets of styrene were in identical positions (1115 and 1230 Hz) in these spectra. Experiment (b) (Table XIX) was repeated at — 60°C using 250-Hz expansion on a 100-MHz spectrometer. The benzyl resonance was observed to shift approximately 4 Hz (relative to toluene) upheld. The lack of splitting in the latter indicates equilibrium (if any occurs) is very rapid. Finally, the effect of temperature on the systems Zr (benzyl) 4 in styrene and Zr (benzyl) 4 toluene were examined and the results are given in Table XX. They show that no specific interaction of styrene with Zr (benzyl) 4 occurs. The interaction of toluene would probably be of the type (XXIV) whereas styrene would interact similarly or in a manner shown in (XXV), both interactions would affect the environment of the benzyl protons in Zr (benzyl) 4 if they occurred to any significant... 

Proton NMR Spectra of Zr(benzyl)t (0.06 M) in Styrene and Toluene,Respectively, Obtained with the 220-MHz Spectrometer. 600-Hz Expansion Relative to T.M.S. Accuracy S... 

Temperature (°C) Benzyl protons in toluene solution Benzyl protons in styrene only... 

---