Styrenes hydration

Aqueous mineral acids react with BF to yield the hydrates of BF or the hydroxyfluoroboric acids, fluoroboric acid, or boric acid. Solution in aqueous alkali gives the soluble salts of the hydroxyfluoroboric acids, fluoroboric acids, or boric acid. Boron trifluoride, slightly soluble in many organic solvents including saturated hydrocarbons (qv), halogenated hydrocarbons, and aromatic compounds, easily polymerizes unsaturated compounds such as butylenes (qv), styrene (qv), or vinyl esters, as well as easily cleaved cycHc molecules such as tetrahydrofuran (see Furan derivatives). Other molecules containing electron-donating atoms such as O, S, N, P, etc, eg, alcohols, acids, amines, phosphines, and ethers, may dissolve BF to produce soluble adducts. 

Fig. 7 Comparison of the X-dependence of the a-methyl effect in bromination and hydration of X-substituted styrenes (data from Ruasse et al, 1978).

Transition-state shifts with reactivity and selectivities in hydration and bromination of styrenes ArCY=CH2... 

A more extensive comparison between bromination and hydration has been carried out in the styrene series ArCY=CH2, where Y varies from H, Me... 

Fig. 13 Comparison of p values for bromination and hydration of styrenes XC6H4C(Y)=CH2 with variable Y. Selectivity coefficients for bromination depend on Y twice as much as for hydration (Ruasse and Dubois, 1984).

P. M. Dansette, V. B. Makedonska, D. M. Jerina, Mechanism of Catalysis for the Hydration of Substituted Styrene Oxides by Hepatic Epoxide Hydrase , Arch. Biochem. Biophys. 1978, 187, 290 - 298. 

Sulfonated poly(arylene ether)s have shown promise for durability in fuel cell systems, while poly-(styrene)- and poly(imide)-based systems serve as model systems for studying structure-relationship properties in PEMs because their questionable oxidative or hydrolytic stability limits their potential application in real fuel cell systems. Sulfonated high performance polymer backbones, such as poly(phe-nylquinoxaline), poly(phthalazinone ether ketone)s, polybenzimidazole, and other aromatic or heteroaromatic systems, have many of the advantages of poly-(imides) and poly(arylene ether sulfone)s and may offer another route to advanced PEMs. These high performance backbones would increase the hydrated Tg of PEMs while not being as hydrolytically sensitive as poly(imides). The synthetic schemes for these more exotic macromolecules are not as well-known, but the interest in novel PEMs will surely spur developments in this area. 

Ab initio MO calculations have been carried out for two carbocation-generating reactions the 6 nI reaction of protonated 1-phenylethanol (H2O leaving group) and the acid-catalysed hydration of styrene. Optimizations were done at the MP2/6-31G level. The 6 nI transition state lies half way between the reactant and the product with respect to the bond lengths, charge distribution, and secondary deuterium isotope effects. 

Methanol Formaldehyde Ethylene Propylene oxide Phenol 1,4-Butanediol Tetrahydrofuran Ethylene glycol Adipic acid Isocyanates Styrene Methyl methacrylate Methyl formate Two-step, via CH4 steam reforming Three-step, via methanol Cracking of naphtha Co-product with t-butyl alcohol or styrene Co-product with acetone Reppe acetylene chemistry Multi-step Hydration of ethylene oxide Multi-step Phosgene chemistry Co-product with propylene oxide Two-step, via methacrolein Three-step, via methanol... 

The Heck arylation of ethene with iodoarenes was investigated with a preformed [PdCl2(tppms)2] catalyst and gave the product styrenes in 60-100% yield (115). In contrast, when the in situ system Pd(OAc)2 -T 2tppms was used as a precursor, the conversion was less effective and yielded the hydration products. 

For example, the rate of hydration increases if the double bond hears electron-releasing snhsi-itiipnts. Schubert Lamm, and Keeffe have found that for a series of para-substituted styrenes (2), a linear correlation exists between... 

The question of which step of Equation 7.1 is rate-determining remains. Schubert found that when styrene-/, / -d2 (3) is hydrated, the recovered, unreacted 3 has not lost deuterons to the solvent.7 If the protonated species (1) were... 

The rate of acid-catalyzed hydration of styrenes can be enhanced photochemically (Scheme 2).293,294 Except for nitro-substituted styrenes, such photohydrations undergo exclusive Markovnikov addition. 

Analogous to the photohydration of styrenes, the acid-catalyzed hydration of phenylalkynes is also possible photochemically.293 294 307 Except for nitro-substituted arylalkynes, the reaction follows Mar-kovnikov s rule. This reaction has thus far received limited synthetic attention. 

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