Of a-methylstyrene

The yield of acetone from the cumene/phenol process is beUeved to average 94%. By-products include significant amounts of a-methylstyrene [98-83-9] and acetophenone [98-86-2] as well as small amounts of hydroxyacetone [116-09-6] and mesityl oxide [141-79-7]. By-product yields vary with the producer. The a-methylstyrene may be hydrogenated to cumene for recycle or recovered for monomer use. Yields of phenol and acetone decline by 3.5—5.5% when the a-methylstyrene is not recycled (21). 

G-5—G-9 Aromatic Modified Aliphatic Petroleum Resins. Compatibihty with base polymers is an essential aspect of hydrocarbon resins in whatever appHcation they are used. As an example, piperylene—2-methyl-2-butene based resins are substantially inadequate in enhancing the tack of 1,3-butadiene—styrene based random and block copolymers in pressure sensitive adhesive appHcations. The copolymerization of a-methylstyrene with piperylenes effectively enhances the tack properties of styrene—butadiene copolymers and styrene—isoprene copolymers in adhesive appHcations (40,41). Introduction of aromaticity into hydrocarbon resins serves to increase the solubiHty parameter of resins, resulting in improved compatibiHty with base polymers. However, the nature of the aromatic monomer also serves as a handle for molecular weight and softening point control. 

These reactions are usehil for the preparation of homogeneous difunctional initiators from a-methylstyrene in polar solvents such as tetrahydrofuran. Because of the low ceiling temperature of a-methylstyrene (T = 61° C) (26), dimers or tetramers can be formed depending on the alkaU metal system, temperature, and concentration. Thus the reduction of a-methylstyrene by sodium potassium alloy produces the dimeric dianionic initiators in THF (27), while the reduction with sodium metal forms the tetrameric dianions as the main products (28). The stmctures of the dimer and tetramer correspond to initial tail-to-tail addition to form the most stable dianion as shown in equations 6 and 7 (28). 

Gumylphenol. -Cumylphenol (PGP) or 4-(1-methyl-l-phenylethyl)phenol is produced by the alkylation of phenol with a-methylstyrene under acid catalysis. a-Methylstyrene is a by-product from the production of phenol via the cumene oxidation process. The principal by-products from the production of 4-cumylphenol result from the dimerization and intramolecular alkylation of a-methylstyrene to yield substituted indanes. 4-Cumylphenol [599-64-4] is purified by either fractional distillation or crystallization from a suitable solvent. Purification by crystallization results in the easy separation of the substituted indanes from the product and yields a soHd material which is packaged in plastic or paper bags (20 kg net weight). Purification of 4-cumylphenol by fractional distillation yields a product which is almost totally free of any dicumylphenol. The molten product resulting from purification by distillation can be flaked to yield a soHd form however, the soHd form of 4-cumylphenol sinters severely over time. PGP is best stored and transported as a molten material. 

OC-Methylstyrene. This compound is not a styrenic monomer in the strict sense. The methyl substitution on the side chain, rather than the aromatic ring, moderates its reactivity in polymerization. It is used as a specialty monomer in ABS resins, coatings, polyester resins, and hot-melt adhesives. As a copolymer in ABS and polystyrene, it increases the heat-distortion resistance of the product. In coatings and resins, it moderates reaction rates and improves clarity. Physical properties of a-methylstyrene [98-83-9] are shown in Table 12. 

Production of a-methylstyrene (AMS) from cumene by dehydrogenation was practiced commercially by Dow until 1977. It is now produced as a by-product in the production of phenol and acetone from cumene. Cumene is manufactured by alkylation of benzene with propylene. In the phenol—acetone process, cumene is oxidized in the Hquid phase thermally to cumene hydroperoxide. The hydroperoxide is spHt into phenol and acetone by a cleavage reaction catalyzed by sulfur dioxide. Up to 2% of the cumene is converted to a-methylstyrene. Phenol and acetone are large-volume chemicals and the supply of the by-product a-methylstyrene is weU in excess of its demand. Producers are forced to hydrogenate it back to cumene for recycle to the phenol—acetone plant. Estimated plant capacities of the U.S. producers of a-methylstyrene are Hsted in Table 13 (80). 

Polymers of a-methylstyrene have been marketed for various purposes but have not become of importance for mouldings and extrusions. On the other hand copolymers containing a-methylstyrene are currently marketed. Styrene-a -methylstyrene polymers are transparent, water-white materials with BS softening points of 104-106°C (c.f. 100°C for normal polystyrenes). These materials have melt viscosities slightly higher than that of heat-resistant polystyrene homopolymer. 

Table 3. Polymerization of a-methylstyrene by the ClSi(CH, )2CH,CH2[Pg.18]

Results of these orienting experiments compiled in Table 3 in regard to the effect of temperature, medium polarity, initiator concentration, monomer concentration, and coinitiator concentration are similar to those reported by others36"39 for cationic polymerization of a-methylstyrene. For example, decreasing temperature, the molecular weight increases and increasing medium polarity, the yield increases. 

Research described in this section concerns effects of solvent polarity, temperature, monomer and initiator concentration on the polymerization of a-methylstyrene with Si-H containing initiator/Me3Al system for the synthesis of HSi-PaMeSt and of desirable molecular weight. 

Farkas and Sherwood (FI, S5) have interpreted several sets of experimental data using a theoretical model in which account is taken of mass transfer across the gas-liquid interface, of mass transfer from the liquid to the catalyst particles, and of the catalytic reaction. The rates of these elementary process steps must be identical in the stationary state, and may, for the catalytic hydrogenation of a-methylstyrene, be expressed by ... 

Models of this type were used successfully in the interpretation of the kinetic data of Maennig and Kolbel as well as of kinetic data obtained for the hydrogenation of a-methylstyrene and cyclohexene. 

Babcock et al. (Bl) examined the hydrogenation of a-methylstyrene catalyzed by palladium and platinum catalysts in a reactor of 1 -in. diameter under countercurrent flow. Flow rates were above 1500 kg/m2-hr for the liquid phase and above 15 kg/m2-hr for the gas, and it was concluded from the experimental results that mass transfer was not of rate-determining influence under these conditions. 

Johnson et al. (J4) investigated the hydrogenation of a-methylstyrene catalyzed by a palladium-alumina catalyst suspended in a stirred reactor. The experimental data have recently been reinterpreted in a paper by Polejes and Hougen (P4), in which the original treatment is extended to take account of variations in catalyst loading, variations in impeller type, and variations of gas-phase composition. Empirical correlations for liquid-side resistance to gas-liquid and liquid-solid mass transfer are presented. 

Johnson et al. (J5) have used the hydrogenation of a-methylstyrene catalyzed by palladium-alumina in powder form in agitated vessels. The physical diffusion of hydrogen through the liquid is the rate-controlling step. The total resistance of this transfer consisted of two separate resistances, one in the liquid adjoining the bubbles and another in the liquid adjoining the suspended solid particles. 

The observation (Porter ef a ., 1972) that added BrCCla almost completely suppresses the polarization of the olefin, while leaving the polarization of trans-4 unalfected, points to the secondary radical pair as the principal immediate precursor of a-methylstyrene. A rate constant for the decomposition of thediazenyl radical of 10 -10 sec has been estimated. Cage collapse and free-radical formation are also thought to occur and appropriately polarized products have been identified (see above). 

When double bonds are reduced by lithium in ammonia or amines, the mechanism is similar to that of the Birch reduction (15-14). ° The reduction with trifluoro-acetic acid and EtsSiH has an ionic mechanism, with H coming in from the acid and H from the silane. In accord with this mechanism, the reaction can be applied only to those alkenes that when protonated can form a tertiary carbocation or one stabilized in some other way (e.g., by a OR substitution). It has been shown, by the detection of CIDNP, that reduction of a-methylstyrene by hydridopenta-carbonylmanganese(I) HMn(CO)5 involves free-radical addition. ... 

The results obtained in reactions involving the two first examples showed a reduced catalytic activity compared to the homogeneous catalyst, a situation that may be due to diffusion problems. Enantioselectivity was similar or slightly lower than in solution, with 80% ee [21] and 58% ee [22] in the epox-idation of ds-/l-methylstyrene with NaOCl providing the best results. Only in the last example was an improvement in enantioselectivity reported from 51% to 91% ee in the epoxidation of a-methylstyrene. Recovery of the catalyst was only considered in one case [21] and a significant decrease in enantioselectivity was observed on reuse. 

As a second process, the hydrogenation of a-methylstyrene is a standard process for elucidating mass transfer effects in catalyst pellets and in fixed-bed reactors... 

Living" carbocationic polymerizations are most difficult to achieve mainly because of chain transfer to monomer and termination processes both of which frequently occur in carbocationic polymerizations. It has recently been demonstrated (JL) that "quasiliving" polymerization of a-methylstyrene (aMeSt) can be achieved by slow and continuous monomer addition and that the number-average molecular weight (Mn) of PaMeSt increases linearly with the weight of added monomer. A theory for quasiliving polymerizations has been developed (2). 

Hyperbranched polymers have also been prepared via living anionic polymerization. The reaction of poly(4-methylstyrene)-fo-polystyrene lithium with a small amount of divinylbenzene, afforded a star-block copolymer with 4-methylstyrene units in the periphery [200]. The methyl groups were subsequently metalated with s-butyllithium/tetramethylethylenediamine. The produced anions initiated the polymerization of a-methylstyrene (Scheme 109). From the radius of gyration to hydrodynamic radius ratio (0.96-1.1) it was concluded that the second generation polymers behaved like soft spheres. 

Reported vapor pressures of a-methylstyrene at various temperatures and the coefficients for the vapor pressure equations... 

The extent of asymmetric induction was low. L 1 was the most effective to induce asymmetry in the adduct of a-methylstyrene and methyl-... 

Methyldichlorosilane was by far the most reactive in hydrosilation of 1,1-disubstituted olefins. Trialkylsilanes did not add at all, even at 120°C. Trichlorosilane gave complicated results involving isomerization of olefins and dimerization of a-methylstyrene, and products were not optically active. 2-Methylbutene-2 and trichlorosilane gave two adducts, 2-meth-ylbutyltrichlorosilane and 3-methylbutyltrichlorosilane. The latter required isomerization of the olefin. 2,3-Dimethylbutene-l gave one adduct in 70% yield, and it was optically slightly active [0.8% (R) isomer]. 

Kumada and his co-workers (33) later showed that a chiral Ni(II) complex induced asymmetric hydrosilation of a-methylstyrene by meth-yldichlorosilane at 90°C for 60 hours. By use of the trans-(R) isomer of (PhCH2—PhMeP )2NiCl2, they isolated 8% PhMeC HCH2SiMeClH with [a]D + 6.43°and 31% PhMeC HCH2SiMeCl2 with [a] > + 6.50°. The latter compound was treated with methyllithium to prepare PhMeC HCH2SiMe3, [a], + 10°, which they estimated as 17.6% optically pure. 

The experiment with CS2 showed up another extremely interesting effect. Over almost the whole range of compositions the DPs obtained were very significantly greater than those obtained without carbon bisulphide - with methyl chloride as sole diluent. This CS2 effect has been reported previously for the cationic polymerisation of a-methylstyrene [57] and of isobutene [50]. It seems likely that it is due (at least partly) to the fact that CS2 does not act as a transfer agent, whereas most alkyl halides do. 

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