Styrenes, addition reactions

Phenyl-1,4-hcxadicnc (122) is obtained as a major product by the codimerization of butadiene and styrene in the presence of a Lewis acid[110]. Pd(0)-catalyzed addition reaction of butadiene and aiiene (1 2) proceeds at 120 C to give a 3 1 mixture of trans- and c -2-methyl-3-methylene-l,5.7-octatriene (123)[lll]. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

As the quinone stabilizer is consumed, the peroxy radicals initiate the addition chain propagation reactions through the formation of styryl radicals. In dilute solutions, the reaction between styrene and fumarate ester foUows an alternating sequence. However, in concentrated resin solutions, the alternating addition reaction is impeded at the onset of the physical gel. The Hquid resin forms an intractable gel when only 2% of the fumarate unsaturation is cross-linked with styrene. The gel is initiated through small micelles (12) that form the nuclei for the expansion of the cross-linked network. 

N-Unsubstituted pyrazoles and imidazoles add to unsaturated compounds in Michael reactions, for example acetylenecarboxylic esters and acrylonitrile readily form the expected addition products. Styrene oxide gives rise, for example, to 1-styrylimidazoles (76JCS(P1)545). Benzimidazole reacts with formaldehyde and secondary amines in the Mannich reaction to give 1-aminomethyl products. 

The reaction of ACPC with linear aliphatic amines has been investigated in a number of Ueda s papers [17,35,36]. Thus, ACPC was used for a interfacia] polycondensation with hexamethylene diamine at room temperature [17] yielding poly(amide)s. The polymeric material formed carried one azo group per repeating unit and exhibited a high thermal reactivity. By addition of styrene and methyl methacrylate to the MAI and heating, the respective block copolymers were formed. 

When an unsymmetrically substituted vinyl monomer such as propylene or styrene is polymerized, the radical addition steps can take place at either end of the double bond to yield either a primary radical intermediate (RCH2-) or a secondary radical (R2CH-). Just as in electrophilic addition reactions, however, we find that only the more highly substituted, secondary radical is formed. 

Addition of styrene to a green solution of naphthalene" Na+ in tetrahydrofuran leads to an instantaneous change of color from green to red. Styrene polymerizes rapidly and quantitatively within a few seconds, and when the reaction is completed, addition of water converts the red solution of polystyryl carbanions into colorless solution of polystyrene. After precipitation of the polymer it was shown spectroscopically25 that the residual solution contains an amount of naphthalene equal to that used in the preparation of the initiating catalyst. This observation confirms the proposed mechanism of initiation of the polymerization. 

Absolute rate constants for addition reactions of cyanoalkyl radicals are significantly lower than for unsubstituted alkyl radicals falling in the range 103-104 M V1.341 The relative reactivity data demonstrate that they possess some electrophilic character. The more electron-rich VAc is very much less reactive than the electron-deficient AN or MA. The relative reactivity of styrene and acrylonitrile towards cyanoisopropyl radicals would seem to show a remarkable temperature dependence that must, from the data shown (Table 3.6), be attributed to a variation in the reactivity of acrylonitrile with temperature and/or other conditions. 

Optically pure (S)-benzyl methyl sulfoxide 139 can be converted to the corresponding a-lithio-derivative, which upon reaction with acetone gave a diastereomeric mixture (15 1) of the /S-hydroxysulfoxide 140. This addition reaction gave preferentially the product in which the configuration of the original carbanion is maintained. By this reaction, an optically active epoxy compound 142 was prepared from the cyclohexanone adduct 141181. Johnson and Schroeck188,189 succeeded in obtaining optically active styrene oxide by recrystallization of the condensation product of (+ )-(S)-n-butyl methyl sulfoxide 143 with benzaldehyde. 

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 observation of Tsuji et al. 148) concerned with copolymerization of 1- or 2-phenyl butadiene with styrene or butadiene illustrates again the importance of the distinction between the classic, direct monomer addition to the carbanion, and the addition involving coordination with Li4. The living polymer of 1- or 2-phenyl butadiene initiated by sec-butyl lithium forms a block polymer on subsequent addition of styrene or butadiene provided that the reaction proceeds in toluene. However, these block polymers are not formed when the reaction takes place in THF. The relatively unreactive anions derived from phenyl butadienes do not add styrene or butadiene, while the addition eventually takes place in hydrocarbons on coordination of the monomers with Li4. The addition through the coordination route is more facile than the classic one. 

Alkyl radical addition reactions to styrene chromium tricarbonyl can be accomplished using alkyl halides (10 equiv) and (TMSlsSiH (5 equiv) in the presence of AIBN in refluxing benzene, for 18 h (Reaction 66). " These reactions are believed to proceed through intermediates in which the unpaired electron is interacting with the adjacent arene chromium tricarbonyl moiety since the analogous reaction with styrene affords only traces of addition products. 

Radical addition to conjugated systems is an important part of chain propagation reactions. The rate constants for addition of cyclohexyl radical to conjugated amides have been measured, and shown to be faster than addition to styrene. In additions to RCH=C(CN)2 systems, where the R group has a chiral center, the Felkin-Ahn rule (p. 148) is followed and the reaction proceeds with high selectivity. Addition of some radicals, such as (McsSijaSi-, is reversible and this can lead to poor selectivity or isomerization. ... 

The selectivity is 100% in this simple example, but do not believe it. Many things happen at 625°C, and the actual effluent contains substantial amounts of carbon dioxide, benzene, toluene, methane, and ethylene in addition to styrene, ethylbenzene, and hydrogen. It contains small but troublesome amounts of diethyl benzene, divinyl benzene, and phenyl acetylene. The actual selectivity is about 90%. A good kinetic model would account for aU the important by-products and would even reflect the age of the catalyst. A good reactor model would, at a minimum, include the temperature change due to reaction. 

This reaction includes modified acrylates with or without addition of styrenes in combination with one or more initiators in a solvent [126], In an example, tetrahydrofuran was used as solvent and the polymer concentrations amounted to about 5.6 g Thus, the polymerization is carried out as solvent process. 

In degree 2 only reactivity degrees are treated vis- i-vis exothermic polymerization in particular and addition reactions on the double bond (ethylene, butadiene, styrene, propylene), easy peroxidation (isopropyl oxide, acetaldehyde), hydrolysis (acetic anhydride). Possibly only propionitrile and substances with code 0 have an actual NFPA stability code. Every time one has to deal with the NFPA code one has to interpret it after carefully reading the paragraphs in Part Two. 

This study also gives a good account of the stereoselectivity of the 2-diazobut-3-enoate addition reaction with styrene. There is a preference for the ester group... 

Hexaepoxy squalene, HES (Scheme 70) was used as a multifunctional initiator in the presence of TiCU as a coinitiator, di-f-butylpyridine as a proton trap, and N,N-dimethylacetamide as an electron pair donor in methylcy-clohexane/methyl chloride solvent mixtures at - 80 °C for the synthesis of (PIB-fc-PS)n star-block copolymers [145]. IB was polymerized first followed by the addition of styrene. The efficiency and the functionality of the initiator were greatly influenced by both the HES/IB ratio and the concentration ofTiCL, thus indicating that all epoxy initiation sites were not equivalent for polymerization. Depending on the reaction conditions stars with 3 to 10 arms were synthesized. The molecular weight distribution of the initial PIB stars was fairly narrow (Mw/Mn < 1.2), but it was sufficiently increased after the polymerization of styrene (1.32 < Mw/Mn < 1.88). 

Numerous p-values for various electrophilic additions to styrene itself are available (Schmid and Garratt, 1977). Strictly speaking, the reaction constants measure only the sensitivity of the reaction to substituent effects they depend at the same time on the solvent, on the position of the transition state on the reaction coordinate (charge magnitude) and on the way in which substituent effects are transmitted (charge location). In particular, the observed trend of p-values for the chlorination ( — 3.22 Yates and Leung, 1980), bromination (—5.7 Ruasse et al, 1978) and sulfenylation ( — 2.41 ... 

Radicals also exhibit high activity in addition reactions. For example, the peroxyl radical of oxidizing styrene adds to the double bond of styrene with the rate constant k = 68 Lmol-1 s-1, and dioxygen adds with k = 5.6x 10-10Lmol-1 s-1 (298 K). As in the case of abstraction reactions, the distinction results from the fact that the first reaction is... 

Regio- and stereoselective addition of 9-(phenylthio)-9-BBN to terminal alkynes is catalyzed by Pd(PPh3)4 to produce 9-[(Z)-/ -(phenylthio)alkyenyl]-9-BBN (Scheme 73) 283 Addition of styrene avoids catalyst deactivation by trapping free thiophenol generated in the reaction mixture. The produced alkenylboranes exhibit high reactivities for protonolysis with MeOH to produce 2-phenylthio-l-alkenes. 

Palladium-catalyzed addition of the selenium-silicon bond of PhSe-SiMe3 to arylacetylenes proceeds in a regio- and stereoselective manner to afford (Z)-a-(phenylseleno)-/ -(trimethylsilyl)styrenes (Equation (123)).250 Aliphatic alkynes fails to undergo the addition reaction. Analogous addition of the Se-Ge bond to alkynes occurs under similar conditions. 

When the thiole derivatives are converted into the corresponding sulfenyl chloride such as 56, an addition reaction to styrene or /3-methylstyrene in nitromethane gives regioisomeric mixtures of adducts 57 and 58 (Scheme 11) <2001CHE702> as well as the cyclization products 59 which are generated in 47% (R = H) and 52% (R = OI I () yield, respectively. 

In the phosphonium salt synthesis, the addition reaction of tertiary phosphines to activated alkenes has been reported (Scheme 3). PPh3 is added to electron-deficient alkenes such as enones or enals at the p-position in the presence of acids.4 The reaction of styrenes with phosphine has recently been reported by Okuma, which gave Markovnikov adducts.5 Although no catalyzed reactions of... 

Addition of styrene at this stage instantaneously removes the colour and reduces the conductivity to its initial value, and polymerization sets in immediately with a rate constant equal to that of the first reaction. 

At the end of the polymerisation, when species IA has disappeared and ions are present, the addition of styrene makes the ions vanish instantaneously and they remain absent whilst polymerisation proceeds. Moreover, this polymerisation has the same rate constant as the first. This means that it cannot have been initiated only by the acid that was free at that time and that the acid bound as ions must also have become available. These facts are represented by the reaction paths leading to esters IB and IC, which complete the cycle whereby eventually ions are formed again, and can be destroyed again by addition of more monomer. Of course, reaction of the freshly added monomer with the then free acid leads to formation of ester IA. The maximum concentration of carbonium ions increases after each addition because of the increasing double bond concentration, as the polymer concentration increases. Thus the final value of the equivalent conductance and... 

In the simultaneous interpenetrating networks (SIN), the two reactions are run simultaneously. This reaction will be emphasized in the present paper. One reaction, for example, can be a polyesterification or a polyurethane stepwise reaction, while the other is an addition reaction using styrene to make polystyrene via free radical chemistry. 

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