Propylene oxide, protonated

Propylene glycol, glycolysis of polyurethanes with, 572 Propylene oxide (PO), glycolysis of polyurethanes with, 572-573 Propylene oxide (PO) polyols, 211, 223 Proton exchange membrane fuel cells (PEMFCs), 272-273 Proton NMR integrations, 386. See also H NMR spectroscopy Protonic acids, reactions catalyzed by, 67-68... 

ATR-HP IR spectroscopy has also been used to follow the cobalt-catalysed carbonylation of epoxides to give lactones or polyesters [46]. Addition of excess propylene oxide to [HCo(CO)4] (generated in situ by protonation of [Co(CO)4] ) under 20 bar CO was found to give an acyl complex, [Co(C(0)CH2CH(OH)Me)(CO)4]. Depending... 

Excluding polymerizations with anionic coordination initiators, the polymer molecular weights are low for anionic polymerizations of propylene oxide (<6000) [Clinton and Matlock, 1986 Boileau, 1989 Gagnon, 1986 Ishii and Sakai, 1969 Sepulchre et al., 1979]. Polymerization is severely limited by chain transfer to monomer. This involves proton abstraction from the methyl group attached to the epoxide ring followed by rapid ring cleavage to form the allyl alkoxide anion VII, which isomerizes partially to the enolate anion VIII. Species VII and VIII reinitiate polymerization of propylene oxide as evidenced... 

Preparation of Poly (propylene ether) Polyols. The polymerization of propylene oxide with zinc hexacyanocobaltate complexes in the presence of proton donors results in the production of low-molecular-weight polymers. Table V shows the variety of types of compounds that have been found to act this way. Since these compounds end up in the polymer chains, it seems reasonable to call them chain initiators. Thus, in essence, each of these compounds is activated by the catalyst to react with propylene oxide to form a hydroxylpropyl derivative. Thereafter, the reaction continues on the same basis, with the proton of the hydroxyl group reacting with further propylene oxide. This sequence is shown here with 1,5-pentanediol as the initiator. The hydroxyl... 

Su, Borho and Xu have applied rotational spectroscopic and high-level ab initio studies to the 1 1 chiral molecular adduct of propylene oxide dimer [117], Six homochiral and six heterochiral conformers were predicted to be the most stable configurations where each monomer acts as a proton acceptor and a donor simultaneously, forming two 6- or 5-membered intermolecular hydrogen-bonded rings. Rotational spectra of six, that is, three homochiral and heterochiral conformer pairs, out of the eight conformers that were predicted to have sufficiently large permanent electric dipole moments were measured and analyzed. 

EXAMPLE Acid-catalyzed hydrolysis of propylene oxide (epoxypropane). Step 1 Protonation of the epoxide. 

There are two possible types of mechanism for the uncatalyzed hydrolysis of epoxides, a simple SN2 reaction of the substrate with water and a reaction of the protonated substrate with hydroxide ion. Another question to be answered concerns the position of attack of the nucleophile in substituted ethylene oxides. Experiments by Long and Pritchard [150] with H2180 indicate that in the uncatalyzed hydrolysis of propylene oxide two-thirds of the overall reaction occur via attack at the primary carbon. The corresponding percentage for the reaction of isobutylene oxide has not been determined precisely, but it is 20 % at least, probably much more. Attack at the primary carbon predominates also in the uncatalyzed reaction of propylene oxide with chloride ion [152]. 

The similar magnitudes of the rate coefficients k0 (Table 9) for three epoxides are in agreement with the simple SN 2 mechanism. Similar magnitudes of rate coefficients have been found also for the uncatalyzed reaction of ethylene oxide and the primary carbon in propylene oxide with chloride ion (Table 9). In the case of the two-step mechanism, methyl substitution would increase the basicity of the oxygen in the ring, favoring formation of the protonated intermediate, and exert a small influence on the Sn 2 reactivity of the primary carbon. The overall effect would be a rate increase. However, the experimental data do not agree with this expectation and, consequently, the two-step mechanism may be ruled out. 

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