Overberger studies

Overberger and Borchert (1960) were the first to report that the P3u olysis of vinylcyclopropane yielded cyclopentene as the major product. Independently Flowers and Frey (1961b) studied this isomerization and found that it was homogeneous and kinetically first order and almost certainly unimolecular. The Arrhenius equation for the isomerization was found to be... 

Apolar binding of substrates has been demonstrated with polymers of vinylimidazole. Overberger etal. (77) studied the hydrolysis ofp-nitrophenyl acetate and p-nitrophenylheptanoate by poly[4(5)-vinylimidazole] in ethanol water mixtures. 

Polymers of 4(5)-vinylimidazole and copolymers containing this monomer are usually studied with ethanol-buffer mixtures as solvent because of their insolubility in water. Overberger and Smith (82) found that poly(l-Me-5-vinylimidazole) was soluble in water. Negatively charged substrates with long apolar side chains were bound very strongly to this polymer. A rate enhancement of 106 over the monomeric analog, 1,5-dimethylimidazole, was observed. 

Electron-transfer initiation from other radical-anions, such as those formed by reaction of sodium with nonenolizable ketones, azomthines, nitriles, azo and azoxy compounds, has also been studied. In addition to radical-anions, initiation by electron transfer has been observed when one uses certain alkali metals in liquid ammonia. Polymerizations initiated by alkali metals in liquid ammonia proceed by two different mechanisms. In some systems, such as the polymerizations of styrene and methacrylonitrile by potassium, the initiation is due to amide ion formed in the system [Overberger et al., I960]. Such polymerizations are analogous to those initiated by alkali amides. Polymerization in other systems cannot be due to amide ion. Thus, polymerization of methacrylonitrile by lithium in liquid ammonia proceeds at a much faster rate than that initiated by lithium amide in liquid ammonia [Overberger et al., 1959]. The mechanism of polymerization is considered to involve the formation of a solvated electron ... 

Overberger and coworkers carried out an interesting study on the hydrolysis of various 3-nitro-4-acyloxybenzoic acid substrates (V) catalyzed by imidazole (VI) and poly[4(5)-vinylimidazole] (VII) in ethanol-water mixtures [Overberger et al., 1973]. 

In the course of an extensive study of the chemistry of azo compounds, Overberger et al. [47a] prepared 1-pyrazolines, which may be considered cyclic azo compounds, by the addition of diazoalkanes to styrene. The reaction is considered a stereospecific 1,3-dipolar addition and, in the reaction between />-methoxyphenyldiazomethane and />-methoxystyrene both trans-3,5-bis-(p-methoxyphenyl)pyrazoline (m.p. 129°C, dec.) and c/s-3,5-bis(/>-methoxy-phenyl)pyrazoline were prepared and separated [47b]. 

Ridd [5] and Kalatzis and Ridd [6] have written an interesting series of studies and reviews on the interrelationship of nitrosation, diazotization, and deamination. Other reviews covering various aspects of iV-nitroso chemistry are by Leotte [7], Overberger et al. [8], Dusenberg and Powell [9], Lashkarev and Vasyunas [10], Mannschreck et al. [11], Rademachereta/. [12]. Chapter 16 should also be reviewed for background material on nitrosations. 

The recent study by Overberger and Jarovitzky (37) shows clearly the cationic nature of the propagation step in the polymerization of alpha-D-styrene by Ziegler catalysis. 

Overberger, Yuki, and Urukawa (50) studied the polymerization of methacrylonitrile in the potassium-liquid ammonia system. The results obtained with potassium amide-ammonia were the same as with potassium-ammonia. Isobutyronitrile was detected in the reaction products, indicating that potassium amide was initiating the quantitative polymerization as in the styrene-potassium-ammonia system (93). It was also found that potassium hydroxide initiated polymerization of methacrylonitrile in liquid ammonia, but at a slower rate than potassium or potassium amide. 

Overberger, Yuki, and Urakawa (50) studied the polymerization of methacrylonitrile with potassium amide in liquid ammonia at — 78° and found that the molecular weight was independent of monomer concentration and catalyst concentration. It was shown that trace quantities of water had no effect on the degree of polymerization, but water in excess gave lower yield and degree of polymerization. Overberger, Pearce, and Mayes (49) found that lithium amide was ineffective as initiator for methacrylonitrile in liquid ammonia at — 78°. 

Overberger, Glowaky, and Vandewyer have studied the effects of flie acyl drain length in the substrate and of the volume precent of water in aqueous alcohol solvent systems on the rates of hydrolysis of a series of 3-nitro-4-acyioxybenzoic acid substrates (S ) 15 (59). 

The accumulation of the acyl intermediate (PVIm-Ac ) was established unequivocally by studying the acylation and deacylation behaviors of the polymer separately. Overberger and Glowaky (60) allowed polyvinylimidazole 1 to react with loi -chain acyl substrates SJJ" 15 and separated the partially acylated polymer by utilizing gel permeation chromatography (Sephadex LH-20). Table 4—3 gives first-order rate coie stants for acylation (kobs) and deacylation (ka) reactions, is larger than kobs fot... 

During the past two decades many fine details of the decomposition mechanism of azonitriles have been delineated and interesting correlations between molecular structure and rate parameters brought to light, in particular by Overberger, Cohen, Wang and co-workers and others. In an elegant series of studies the intervention of free radicals in the reactions was demonstrated by the loss of stereoisomerism in the products diastereomeric azocompounds afforded identical mixtures of... 

Kinetic Studies. The previous work of Overberger(1,7) provided a rationale to this research. These investigators utilized the hydrophobic backbone of poly-4(5)-vinylimidazole in conjunction with hydrophobic substrates (Sn ) to demonstrate enhanced rates of esterolysis. In particular, a buildup of long-chain acylated imidazole residues, which increased hydrolysis rates dramatically, inspired the concept of using hydrophobic pol)rmer side chains. 

The hindrance of desorption does not affect the mobility of radical-anions on the metal surface. Hence, their dimerization with formation of still adsorbed dimeric dianions is very likely, and these may grow and form living oligomers. Degree of polymerization of the attached oligomers depends on their lifetime on the surface, and the lifetime is shortened by a cationsolvating solvent that facilitates removal of the cation from the metal lattice and therefore the desorption. This is demonstrated by Overberger (13), who studied the co-polymerization of styrene and methyl methacrylate initiated by a fine suspension of particles of metallic lithium. 

The action of many nucleophiles in initiating colour production is well known. The action of amines was reported by La Combe [131], the action of bases by McCartney [124], Schurz et al. [122, 123], Beaman [132] and Overberger et al. [133]. Acids were found, by Grassie and McNeill [134] to accelerate the colouration process. The catalytic effect of acids was studied with polyacrylonitrile containing a small amount of copolymerized acrylic acid units the mechanism proposed was... 

SSlimidzu et al. 83) also studied the c ytic solvolysis by copolymers of vinylimidazole and acrylic acid. The Michaelis-Menten type behavior was observed for the solvolysis of ANTI 32 but not for that of PNPA 3 in 100% aqueous systems, in contrast to the second-order kinetic behavior in 28.5% ethanol-water as reported by Overberger et al. 80). Substrate binding as given by 1/Am fias maximal at 25 to 30 mol% imidazole content, and the intracomplex rate for the neutral imidazole unit was minimal at 20 to 30 mol% imidazole contents. The resulting overall efficiency simply decreased with increasing imidazole contents. 

Although ft>-fluoroolefins were not included in the above investigations, Overberger and co-workers studied the polymerization of linear and branched a-olefins containing the trifluoromethyl group with various Ziegler—Natta systems. - 5,5,5-Trifluoro-... 

Overberger et al. (1949) studied the decomposition rates of a series of aliphatic azonitriles in toluene by measuring the volume of Nj evolved as a function of time, at constant temperature. A set of V,/(where V, and are the volumes at time t, and t = °o) data for the decomposition of the azo nitrile compound... 

In 1959, C. G. Overberger initiated a program to study various parameters which influenced the ordered conformation of polyproline type pol)nners the results demonstrate that substitution of a methyl group at the 2-posltion, poly-2-methylproline (P2MP), can perturb the conformation of the polymeric chains so that the resultant poljnner no longer behaves like a typical poly-L-proline system. However, substitution of a methyl group at the 5-position (cis- and trans-) resulted in only a small modification of... 

This insensitivity to solvent polarity and temperature may relate to early cationic copolymerization studies carried out by Overberger, Arnold and Taylor and by Marvel and Dunphy. These groups found reactivity ratios for the cationic copolymerization of styrene and a-methylstyrene with chlorostyrene to also be insensitive to solvent and temperature changes. 

Subsequently, Overberger and coworkers proposed that insensitivity of reactivity ratios of these experimental parameters resulted from preferential solvation of the propagating carbenium ion by the most polar component present in the system (either nitrobenzene from the mixed solvent system they employed or chlorostyrene monomer). The active center in m-DIPB/m-DMB copolymerizations could be preferentially solvated by free m-DMB thus screening any effect of changing bulk solvent. However, Overberger, Ekrig, and Tanner 1 noted no dependence of reactivity ratios on initiation system whereas m-DMB/ m-DIPB copolymerizations are very dependent on the nature of the initiation system. Obviously, a more detailed study is required. 

Nucleophiles such as imidazole, pyridine (Letsinger and Savereide, 1962), and hydroxylamine are known to be powerful catalysts of ester hydrolyses. An extensive study of polymeric analogs of these compounds has shown that they too act as effective esterolytic catalysts (Overberger et aL, 1965 Overberger and Smith, 1975). The topic has been reviewed (Overberger and Salamone, 1969 Morawitz, 1969 Manecke and Storck, 1978 Overberger et aL, 1978) and only important features of these polymeric catalysts will be discussed here. 

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