Hydrogen bromide styrene

In the presence of peroxides hydrogen bromide adds to the double bond of styrene with a regioselechvity opposite to Markovmkov s rule The reachon is a free radical addi tion and the regiochemistry is governed by preferenhal formation of the more stable radical... 

Polypeptide Synthesis and Analysis. Sihca or controUed-pore glass supports treated with (chloromethyl)phenylethyltrimethoxysilane [68128-25-6] or its derivatives are replacing chloromethylated styrene—divinylbenzene (Merrifield resin) as supports in polypeptide synthesis. The sdylated support reacts with the triethyl ammonium salt of a protected amino acid. Once the initial amino acid residue has been coupled to the support, a variety of peptide synthesis methods can be used (34). At the completion of synthesis, the anchored peptide is separated from the support with hydrogen bromide in acetic acid (see Protein engineering Proteins). 

Methylene dichloride [6] and perchloric acid [7] were purified and dosed as described. Silver perchlorate (BDH) was treated in vacuo for a few hours before use. 1-Phenylethyl bromide (Eastman-Kodak) was fractionally distilled under high vacuum and the middle fraction was collected into breakable phials since this compound undergoes a slow decomposition, yielding hydrogen bromide and styrene, when kept in bulk, solutions of it in methylene dichloride were prepared from the original phials by the tipping technique [7]. Styrene was purified [8], dried, and stored [9] as described. Shortly before use it was vacuum-distilled into breakable phials from a microburette. 

This is manifest in the reactivity of 180/180-Z1 which was generated from 3-bromo-41-f-pyran (283) by /3-elimination of hydrogen bromide with KOtBu (Scheme 6.61). Whether or not this reaction was conducted in the presence of styrene or furan, the only product identified was tert-butyl 4H-pyran-4-yl ether (284). This is in line with the relationship of the intermediate to a pyrylium ion. Thus, the addition of the tert-butoxide ion to 180/180-Zj has to be expected at the 4-position with formation of the vinyl anion 285, which is then protonated to give 284. Likewise, the attack of the nucleophile is predicted at C2and C6 leading to the vinyl anions 286, which... 

A-8. Write the structures of the resonance forms that contribute to the stabilization of the intermediate in the reaction of styrene (C6H5CH=CH2) with hydrogen bromide in the absence of peroxides. 

The preparation of styrene from a saturated compound is analogous to that of ethylene and its derivatives. When ethylbenzene is treated with bromine, the first product of the reaction has the structure CeHs.CHBr.CHs. This substance loses hydrogen bromide, when warmed with alcoholic potash —... 

Reetz et al. reported on catalytically active solvent-stabilized colloids in propylene carbonate, which were prepared electrochemically or by thermal decomposition of [Pd(OAc)2 assisted by ultrasound. The colloidal particles had sizes of 8 to 10 nm, as determined by TEM. After addition of aryl bromide, styrene, and base to the colloid solution, satisfactory conversions were obtained within reaction times of 5-20 h. Isolation of the particles stabilized by propylene carbonate was not possible, however [16]. The same authors also reported Suzuki and Heck reactions with electrochemically prepared Pd or Pd/Ni colloids stabilized by tetraalkylammonium, as well as polyvinylpyrrolidone (PVP)-stabilized palladium colloids prepared by hydrogen reduction (Table 1) [17]. It was assumed that the reaction occurs on the nanopartide surfaces. 

Complex formation between a polycation and a polyanion is also called polysalt formation or coacervation. If, for example, a solution of poly(sodium styrene sulfonate) (III) is added to an equimolar solution of poly(4-vinyl pyridinium hydrogen bromide), then a stoichiometric complex with respect to the side groups is formed, and this occurs at every mixing ratio (Figure... 

Figure 23-7. Coacervate formation (A and B) or solubilization (C and D) on mixing the polyanion of poly(sodium styrene sulfonate) S with poly(4-vinyl pyridinium hydrogen bromide) P or the ionene Y, or vice versa.

Previously [8], the authors succeeded in achieving a strong chiral induction (88-100% ee) for the chlorination of methacrylic acid in the crystalline CD complexes. Here, we report on the asymmetric addition of gaseous bromine, chlorine, hydrogen bromide and hydrogen chloride to styrene in the crystalline complexes of a-CD (cyclohexa-amylose) or fi-CD (cyclohepta-amylose). 

The term regiospecific can be used when a single product is formed. The addition of hydrogen bromide to styrene, for example, is regiospecific because the phenyl group strongly stabilizes cationic character. 

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