Styrene substituted

Among the substituted styrenes, divinylbenzene, vinyltoluene and a-methylstyrene are of importance as building blocks for polymers. 

1 Reactor 2 Crude divinylbenzene column 3 Light ends column 4 Pure divinylbenzene column 

The demand for vinyltoluene is considerably higher than that for divinylbenzene, reaching around 30,000 to 35,000 tpa. Ethyltoluene is used as a raw material. It is produced by Friedel-Crafts alkylation of toluene with ethylene in the presence of AICI3 at 80 °C in the liquid phase, or in the gas phase, using zeolite catalysts. During the refining operation, care must be taken to ensure that the o-ethyl- 

A new method of synthesizing p-vinyltoluene (p-methylstyrene) is based on the reaction between toluene and acetaldehyde, whereby p-methylstyrene can be produced in over 90% yield at high conversion rates from the intermediate product 1,1-ditolylethane (DTE). 

A variety of substituted styrenes 73 have also been shown to undergo alternative copolymerization with 

Over a wide range of monomer mixtures and using typical free-radical initiators or radiation-induced methods, a-methylstyrene 73 (R = CH3, X = none) will copolymerize with MA to give 1 1 alternating materials. Copolymerizations may occur even without 

Peroxide-initiated, bulk copolymerization of MA with trifluoromethyl-, halo-trifluoromethyl-, halogen-, halo-alkyl-, etc., substituted styrene and a-methylstyrene monomers at 65-70°C, were studied briefly by Backman and 

Radiation-initiated copolymerizations, either bulk or in solution, exhibit no induction period for the a-methylstyrene-MA monomer pair. Standard free-radical inhibitors prevent or stopped the copolymerizations. Apparent activation energies of 6.7 and 5.4kcal/mol were obtained for the bulk (3.6 mol % MA in a-methylstyrene) and (8.0 wt. % chloroform solution of equimolar amounts of the monomer pair) copolymerizations, respectively. Composition and IR spectra studies indicated that homopolymerization of either of the two monomers did not occur, under conditions explored, and that alternating copolymerization occurred over a wide range of monomer concentration of one component. As pressures are raised from 1 bar to 3 bars, considerably enhanced rates of copolymerization are observed. Above 80 C random copolymer is obtained. 

The free-radical copolymerization of p-isopropyl-a-methylstyrene has been studied in chloroform solvent at 60 C, with BPO initiator. Copolymerization gave a 1 1 copolymer regardless of the feed ratios, with the highest rate of copolymerization being obtained at equimolar feed. Kinetic studies at 1 1 feed and various concentrations of BPO showed an order of 1.07 and 0.65 with respect to the concentrations of MA and BPO. The overall activation energy was of the order of 7.6 kcal/mol. The dependence of copolymerization rate on monomer concentration and feed ratio shows that the mechanism of copolymerization cannot be simply explained by the participation of charge-transfer complexes formed between the two monomers. 

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With the improvement of refining and purification techniques, many pure olefinic monomers are available for polymerization. Under Lewis acid polymerization, such as with boron trifluoride, very light colored resins are routinely produced. These resins are based on monomers such as styrene, a-methylstryene, and vinyltoluene (mixed meta- and i ra-methylstyrene). More recently, purified i ra-methylstyrene has become commercially available and is used in resin synthesis. Low molecular weight thermoplastic resins produced from pure styrene have been available since the mid-1940s resins obtained from substituted styrenes are more recent. 

Thermoplastic resins produced from pure monomers such as styrene, alkyl-substituted styrenes, and isobutylene are produced commercially. An advantage of these resins is the fact that they are typically lighter in color than Gardner 1 (water-white) without being hydrogenated. Among the earliest resins in this category were those made from styrene and sold as Piccolastic. Styrene and alkyl-substituted styrenes such as a-methylstyrene are very reactive toward Friedel-Crafts polymerization catalysts. 

Hydroxybenzaldehydes readily react with compounds containing methyl or methylene groups bonded to one or two carboxyl, carbonyl, nitro, or similar strong electron-withdrawing groups. The products are usually P-substituted styrenes. 4-Hydroxybenzaldehyde, for example, reacts with 2-methylquinazolines (where R = H, Cl) to give compounds which have anti-inflammatory activity (59). 

Polymers of Styrene Derivatives. Many styrene derivatives have been synthesized and the corresponding polymers and copolymers prepared (61). Glass-transition temperatures for a series of substituted styrene polymers are shown in Table 3. The highest T is that of... 

Florio et al. demonstrated that the lithiation/electrophile trapping of enantio-pure styrene oxide, as well as the (3-substituted styrene oxides 180 and 182, is totally stereoselective (Scheme 5.42) [66]. These results demonstrate that the intermediate benzylic anions are configurationally stable within the timescale of depro-tonation/electrophile trapping. 

Bartoli recently discovered that by switching from azide to p-anisidine as nucleophile, the ARO of racemic trans- 3-substituted styrene oxides could be catalyzed by the (salen)Cr-Cl complex 2 with complete regioselectivity and moderate selectivity factors (Scheme 7.36) [14]. The ability to access anti-P-amino alcohols nicely complements the existing methods for the preparation of syn-aryl isoserines and related compounds [67] by asymmetric oxidation of trans-cinnamate derivatives [68]. 

The traditional means of assessment of the sensitivity of radical reactions to polar factors and establishing the electrophilicity or nucleophilieity of radicals is by way of a Hammett op correlation. Thus, the reactions of radicals with substituted styrene derivatives have been examined to demonstrate that simple alkyl radicals have nucleophilic character38,39 while haloalkyl radicals40 and oxygcn-ccntcrcd radicals " have electrophilic character (Tabic 1.4). It is anticipated that electron-withdrawing substituents (e.g. Cl, F, C02R, CN) will enhance overall reactivity towards nucleophilic radicals and reduce reactivity towards electrophilic radicals. Electron-donating substituents (alkyl) will have the opposite effect. 

Various substituted styrenes have been also polymerized by NMP. These include 1 03-1 07, p-chloromethylstyrene (108), p-halostyrenes, and p-aceloxystyrene. Vinyl pyridines (e.g. 109) are amenable to NMP21 and may be quaternized post-polymerization to provide water-soluble polymers. 

Waters61 have measured relative rates of p-toluenesulfonyl radical addition to substituted styrenes, deducing from the value of p + = — 0.50 in the Hammett plot that the sulfonyl radical has an electrophilic character (equation 21). Further indications that sulfonyl radicals are strongly electrophilic have been obtained by Takahara and coworkers62, who measured relative reactivities for the addition reactions of benzenesulfonyl radicals to various vinyl monomers and plotted rate constants versus Hammett s Alfrey-Price s e values these relative rates are spread over a wide range, for example, acrylonitrile (0.006), methyl methacrylate (0.08), styrene (1.00) and a-methylstyrene (3.21). The relative rates for the addition reaction of p-methylstyrene to styrene towards methane- and p-substituted benzenesulfonyl radicals are almost the same in accord with their type structure discussed earlier in this chapter. 

The copper-catalyzed additions of sulfonyl chlorides to conjugated dienes and trienes73 as well as to aryl-substituted cyclic olefins74 and substituted styrenes have been described75 for example, arenesulfonyl chlorides add to vinylarenes providing good to excellent yields75 of /J-chlorosulfones ... 

A5-hexenyl substituent, extensive cyclization occurs to yield the cyclopentylcarbinyl product from the yields of uncyclized and cyclized products for A5-hexenylmercury chloride, the rate constants for equation 50 have been estimated (vide supra). The SH2 reaction 49 has also been invoked to be the key step in the alkylation of -substituted styrenes by a free-radical addition-elimination sequence, namely96... 

Influence of Structure on the Cationic Polymerization of Substituted Styrenes... 

Substituted styrenes are often used for investigating influences of structure, solvent and initiators on the cationic polymerization 1,2). Under constant outer conditions,... 

When one compares the brutto polymerization rate constants, a measure of the reactivity of monomers during cationic homopolymerizations is obtained. It was found for p-substituted styrenes that lg kBr increased parallel to the reactivity, which the monomers show versus a constant acceptor 93). The reactivity graduation of the cationic chain ends is apparently overcomed by the structural influence on the monomers during the entire process of the cationic polymerization. The quantitative treatment of the substituent influences with the assistance of the LFE principle leads to the following Hammett-type equations for the brutto polymerization rate constants ... 

Phenanthrene-l,4-diones have been prepared [52] by cycloaddition of a-substituted styrenes with an excess of 1,4-benzoquinone (Equation 2.18). Initial cycloadducts are oxidized by 1,4-benzoquinone. 

In contrast, product mixtures were obtained [53] when a-substituted styrenes were reacted with dimethylacetylenedicarboxylate (Equation 2.19). The products were formed via aromatization of the primary cycloadducts or by ene addition of a second molecule of DM AD. 

Values of e are correlated by the Op constants in accord with eq. (61) (119, 120). Kawabata, Tsuruta, and Furukawa (121) have proposed a revised form of the Price-Alfrey equation based on the definition e = 0 for styrene. On the basis of this redefinition, they have calculated a new set of Q values. These Q values are linear in the Hammett 0 constants. It is not clear from their paper whether this linear relationship is for substituents directly bonded to the carbon-carbon double bond or whether it is applicable only to Q values for substituted styrenes. Charton and Capato (119) were unable to obtain significant correlations between any a constants and the q values of Schwan and Price (117). Zutty and Burkhart (122) have proposed a redefinition of the Price-Alfrey equation based on ethylene as the reference system with Qo and e defined as 1 and 0, respectively. 

Substituted styrenes, such as acid (14) are polymerised with styrene itself to make resins with functional groups... 

Chromyl chloride oxidation of alkenes proceeds via the formation of adducts at a rate necessitating stopped-flow techniques. At 15 °C the formation of 1 1 adduct from styrene and oxidant in CCI4 solution is simple second-order with 2 = 37.0 l.mole .sec . Measurements with substituted styrenes yielded = — 1.99. E = 9.0 kcal.mole and = —23.8eu for styrene itself. Hydrolysis of the styrene adduct yields mostly phenylacetaldehyde (76.5 %)and benzaldehyde (21.1 %). Essentially similar results were obtained with a set of 15 alkenes and... 

Table 10.7 Copper-free Wacker oxidation of substituted styrenes [41]...

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

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