Polymerization of acetylenic derivatives. XXX. Isomers of polyphenylacetylene

Cis-transoidal (orange, soluble, and of low crystallinity) and cis-cisoidal (red, insoluble, and highly crystalline) polyphenylacetylenes (PPA) were prepared by Ziegler-Natta catalysts and trans-cisoidal (yellow, soluble, and amorphous) polyphenylacetylenes were prepared by using phosphine complexes, TiCl₄ and by thermal initiation. The cis-transoidal and cis-cisoidal structures isomerize thermally in the solid state above 100°C. In solution the cis-transoidal structure isomerizes above 80°C. The polymers obtained by thermal isomerization are soluble, amorphous, and have a trans-cisoidal structure. At temperatures higher than 120°C the cis–trans isomerization is accompanied by cyclization and by scission of the polymer chain. A method was developed for determination of cis content of cis-transoidal and cis-cisoidal polyphenylacetylenes.     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl₃ complexes under conventional laboratory conditions in various solvents from ?10 to ?50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear M _n versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DP _n obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (M _w/M _n = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (M _w/M _n = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at ?10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

Indolalkaloids of Pleiocarpa talbotii Wernham. 145. Alkaloids

Besides talbotine ( 1 ) three new indole alkaloids, talpinine ( 2 ), talcarpine ( 3 ) and 16-epi-affinine ( 4 ) were isolated from the stem bark of Pleiocarpa talbotii Wernham. The structure of 2 was deduced by chemical degradation and by analyses of the spectra of the alkaloid and its derivatives. One of these derivatives is identical with talcarpine ( 3 ). The structures 2 and 3 are similar to that of macroline ( 14 ), a splitting product of the bisindole alkaloid villalstonine from Alstonia species. 16-epi-Affinine ( 4 ) was chemically correlated with the known alkaloid vobasine ( 19 ). Talpinine ( 2 ) and 16-epi-affinine ( 4 ) were also isolated from the root bark of Pleiocarpa talbotii.     

Anionic dispersion polymerization. I. control of particle size

Studies on the mechanism for the formation of the stable dispersion polystyrene prepared by anionic dispersion polymerization of styrene in n-hexane using poly(t-butylstyrene) as the stabilizing moiety in steric stabilizer have been performed by a combination of size exclusion chromatographic (SEC) and transmission electron microscopic (TEM) analyses. When the molecular weight of poly(t-butylstyrene) as the stabilizing moiety exceeded 1.76 X 10⁴ g/mol, the formed polymer particles successfully retained a steric stability. Block copolymerization of t-butylstyrene and styrene in n-hexane has also provided the dispersion polymer particles with a relatively narrow size distribution. The stable dispersion polystyrenes have been produced in n-hexane by polymerization of styrene using the mixture of sec-butyllithium and poly(t-butylstyryl)lithium. The polymerization is called living dispersion polymerization (LDP), in which poly(t-butylstyrene-b-styrene) as the steric stabilizer and polystyrene can be formed simultaneously. The particle size was readily controlled by a combination of the concentration of monomer and the molar ratio of poly(t-butylstyryl)lithium to sec-butyllithium, for instance, [stabilizing moiety]/[RLi]. © 1996 John Wiley & Sons, Inc.     

Polymer reactions. V. Kinetics of autoxidation of polypropylene

The rate constants for the autoxidation of polypropylene were determined by a combined ESR, volumetric, and chemical method. The values of k_i, k_p, and k_t at 110°C. are 3 × 10^?4 sec.^?1, 1.9 l./mole-sec., and 3 × 10⁶ l./mole-sec., respectively. The values of k_i and its activation energy are the same as those for the decomposition of polypropylene hydroperoxide, thus identifying the latter as the principal initiation process. The values of the temperature-independent k_t suggest that secondary peroxy radicals are the terminating species. The rate constants are compared with rate constant ratios for initiated autoxidations of squalane and other related systems.     

Chemical composition and antimicrobial activity of the essential oils of Onychopetalum amazonicum R.E.Fr.

The essential oils from leaves, twigs and trunk bark of Onychopetalum amazonicum R.E. Fr. (Annonaceae), obtained by hydrodistillation, were analysed by GC and GC–MS, and also were evaluated for in vitro antimicrobial activity. Forty-one compounds, which correspond to 75.0–92.2% of the oil components, were identified. Major compounds were sesquiterpenes, including (E)-caryophyllene, caryophyllene oxide, spathulenol, α-gurjunene, allo-aromadendrene and α-epi-cadinol. The oils were evaluated for antimicrobial activities against four bacteria strains and five pathogenic fungi. The oil of the trunk bark exhibited good activity against Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 10538 and Kocuria rhizophila ATCC 9341, with a minimal inhibitory concentration of 62.5 μg/mL. The essential oil composition and the antimicrobial evaluation are reported for the first time for the genus Onychopetalum.     

Cyclopolymerization. XIX. Effect of N-substituents on cyclopolymerizability of N-allylmethacrylamides

The effect of bulky N-substitutents of N-t-butyl- and N-phenyl-N-allylmethacrylamides (BAMA and PAMA, respectively) on their cyclopolymerizability was investigated. BAMA yielded an almost completely cyclized polymer while the degree of cyclization of poly (PAMA) was about 95%. The latter value indicates that the effect of phenyl group is comparable with that of methyl group, since N-methyl-N-allylmethacrylamide was reported to give a polymer with a degree of cyclization of 93%. Structural investigation on telomerization products of BAMA and PAMA permitted the assignment of the repeating cyclic units of these polymers to that of a five-membered ring. This structural characteristic was also supported by the observation of five-membered cyclized radicals on ESR measurements of these monomers. Rotation around amide C? N bonds of these monomers and related compounds studied by ¹³C-NMR was found to be strongly dependent on N-substitutents. The mechanism of the cyclization was discussed in terms of the structure of the ring formed and rotation around amide C? N bonds of these monomers. The reactivity of the methacryloyl and allyl groups involved in these monomers were compared based on the information obtained by structural investigation of polymers and telomerization products and by ESR studies. © 1993 John Wiley & Sons, Inc.     

Head-to-head vinyl polymers. X. Cyclopolymerization of o-dimethacryloyloxybenzene

To clarify the possibility of preparing a polymer that contained head-to-head (h–h) methyl methacrylate (MMA) unit radical cyclopolymerization of o-dimethacryloyloxybenzene (o-DMB) was investigated. p-Dimethacryloyloxybenzene (p-DMB) was also used in comparison. When the polymerizations were carried out with higher monomer concentrations than ca. 0.5 mol/L, benzene-insoluble polymer was produced. The extent of cyclization (f_c) in benzene-soluble polymer increased with a decrease in the monomer concentration and an increase in the polymerization temperature. The ¹H-NMR and ¹³C-NMR spectra of poly(MMA) derived from poly(o-DMB) by hydrolysis and methylation were in fairly good agreement with those of ordinary head-to-tail (h–t) poly(MMA). Therefore, it was concluded that the intramolecular propagation in cyclopolymerization of o-DMB was mainly performed by a h–t mechanism. However, the initial and maximum degradation temperatures of the poly(MMA) were observed to be somewhat higher than those of the ordinary poly(MMA), which suggests that a minor amount of the h–h unit was formed.     

Hetero-Cope-Umlagerungen. 4. Mitteilung. Regiokontrollierte Indolsynthesen

Hetero-Cope-Rearrangements, Regio-Controlled Synthesis of Indoles The reaction of O-deprotonated N-phenylhydroxylamines 1 with various electron-deficient allenes 2 , 14 , 16 gives, via Michael addition and Cope-rearrangement, substituted anilines 5 , which are easily convertible into indoles 6 . In this manner, sulfoxides 17 , serve as equivalents of 2-vinylindoles. Diels-Alder reaction with this 2-vinylindole equivalent followed by indolisation affords isoquinuclidine derivative 21 which may be a useful precursor for the preparation of Iboga alkaloids.     

Polymerization of acetylenic derivatives. XXVII. Synthesis and properties of isomeric poly-N-ethynylcarbazole

Poly-N-ethynylcarbazole (PEC) was prepared thermally, by using Ziegler-Natta catalysts, and also by using TiCl₄ and phosphine complexes for initiation. The spectral data (infrared, NMR, x-ray diffraction, and ultraviolet) were best interpreted based on a cis-transoidal/cis-cisoidal stereoblock structure for (both soluble and insoluble) polymers prepared by Ziegler-Natta catalysts and on a trans-cisoidal structure for the polymers prepared with the other catalysts. The cis-transoidal/cis-cisoidal stereoblock structure isomerized thermally into a trans-cisoidal structure, at temperatures which were dependent on the type of initiation.     

Mechanics of peeling of rubbery materials. II. Initiation and propagation of peeling

The peel strength of a joint with flexible materials bonded by an elastic adhesive was evaluated in relation to the fracture mechanism. It was found that initiation and propagation of peeling are governed by different mechanisms. Initiation (the formation of an initial crack) occurs when the maximum stress in the adhesive layer reaches a definite value. In this case, the strength f_i in a trousers-type peeling is given by 2f_i = y₀σ_b?_b, where y₀ is the half-thickness of the adhesive layer, σ_b is the tensile strength, and ?_b is the tensile elongation of the adhesive. On the other hand, propagation is governed by the surface energy of the adhesive. In this case, the peeling strength f_s is determined by a balance of energies. For trousers-type peeling it is given by 2f_s = Γ, where Γ is twice the surface energy. These results were verified experimentally.     

On the photodecomposition of chlorophyll in vitro. I. Reaction rates

Abstract— Chlorophyll solutions are irreversibly bleached by light in the presence of oxygen. The action spectra parallel the absorption spectra for both chlorophyll a and b. The reaction is of second order with a Q₁₀ of 1.26. The reaction rates for chlorophylls a and b are of the same order of magnitude. Depending upon the light source, the initial rate for chlorophyll a is slightly higher, by a factor of 1.15 to 1.30. The rate for pheophytin is lowe 3 by several orders of magnitude. No pheophytin has been detected in the reaction products of the irradiated chlorophyll solutions in the absence of water.     

Beckmann Fragmentation and Rearrangement. Part VII. Fragmentation and cyclization of α-methylthio-ketoximes. Fragmentation reactions no. 27

α-Methylthio-propiophenone anti-oxime p-toluenesulfonate (tosylate) ( 12b ) fragments quantitatively in 80% ethanol yielding benzonitrile and a methylidenesulfonium ion 15 . The syn-isomer, however, undergoes a Beckmann rearrangement. The fragmentation of α-methylthio-isobutyropher one anti-oxime tosylate ( 13b ) is accompanied by cyclization to the 1, 2-thiazetin-1-ium ion 27 , which is hydrolyzed via the sulfimine 29 to the keto sulfide 20 and the keto sulfoxide 30 . A comparison of the rates of the α-alkylthio anti-ketoxime tosylates 12b and 13b and of the homomorphous oxime tosylates 16b and 17b shows that fragmentation and cyclization are strongly assisted by the sulfur atom. Whereas both the anti- and syn-isomers of α-amino ketoxime derivatives fragment quantitatively, only the anti-isomers of α-alkylthio ketoxime derivatives undergo facile fragmentation.     

Metabolic products of microorganisms. 98. Phosphinothricin and phosphinothricyl-alanyl-analine

From cultures of Streptomyces viridochromogenes a new antibiotic, phosphinothricylalanyl-alanine, has been isolated. The new amino acid phosphinothricin is 2-amino-4-methyl-phosphino-butyric acid, its structure is confirmed by synthesis. The tripeptide is highly active against Gram-positive and Gram-negative bacteria and against the fungus Botrytis cinerea. Phosphinothricin is an active glutamine synthetase inhibitor.     

Flavinyl peptides. I. Synthesis of flavinyl-aromatic amino acids

The syntheses of flavinyl peptides, in which L-tryptophan, L-tyrosine, or L-phenylalanine are attached via peptide linkage to the isoalloxazine system with ω-carboxyalkyl groups in position 3 or 10, are described. Lumiflavin was carboxymethylated by known methods to yield N-3-carboxymethyllumiflavin. Oxidation of 10-ω-hydroxyhexyl-, 10-ω-hydroxypentyl-, 10-ω-hydroxybutyl-, and 10-formylmethylflavins gave the corresponding 10-ω-carboxyalkylflavins. The 10-ω-carboxyethylflavin was obtained by condensation of 2-amino-4,5-dimethyl-N-ω-carboxyethylaniline with alloxan. Activations of the carboxyl group of the flavins were achieved with N,N′-carbonyldiimidazole and p-nitrophenyltrifluoroacetate to form the corresponding acyl imidazoles and p-nitrophenyl esters. 10-Carboxymethylflavin was hydrogenated to form 10-carboxymethyldihydroflavin and activated by carbodiimide. Reaction of the carboxy-activated flavins with the appropriate amino acid methyl esters, followed by air oxidation in the case of dihydroflavin, gave the corresponding flavinyl peptides. Interaction of the flavin with aromatic amino acids results in a broadening of the visible flavin absorption towards the green, without the appearance of discrete new maxima, and in quenching of the flavin fluorescence. The fluorescence efficiency increases with increasing numbers of methylene groups in the flavin side chain. The nonlinear dependency of fluorescence quenching versus number of methylene groups indicates that different types of intramolecular interactions are involved.     

Free-radical copolymerizations of N-arylmaleimides. II

Free-radical copolymerization of methyl acrylate (MA) with N-p-chlorophenylmaleimide (NPCMI) and N-p-bromophenylmaleimide (NPBMI) initiated by AIBN in cyclohexanone solution at 75°C was studied. The copolymer composition has been determined from the nitrogen content and NMR spectra of the copolymers. The reactivity ratios have been calculated by ML, FR, KT, and JJ methods. Q and e values of NPCMI and NPBMI have also been calculated by the Alfrey–Price Q-e scheme.     

Hormone-receptor interactions. Synthesis and conformational study of cyclo-L-cystathionine.

The purpose of this work was to see whether the replacement of a sulfur atom in a cystine disulfide bridge by a methylene group is an only superficial ‘isosteric’ substitution, i.e. with regard to size, hydrophobia, bond angles, etc., or whether it would also encompass such parameters as preferred conformations in solution (M- or P-helicity of the bridge). The methods involved the synthesis of a model compound, cyclo-L -cystathionine (cyclo-L -carbacystine), and its investigation by ¹H- and ¹³C-NMR. It is concluded that the conformations of the CH₂(β)? CH₂(γ)? S? CH₂(β') bridge, and of the diketopiperazine ring are closely similar to the analogous elements in cyclo-L -cystine (DMSO as solvent). This knowledge might help to explain the fact that carba analogs of heterodetic-cyclic polypeptide hormones are often biologically very active.     

Cyclopolymerization. II. Mechanism of the free-radical polymerization of N-n-propyldimethacrylamide

The mechanism of cyclopolymerization was investigated by using N-n-propyldimethacrylamide (PDMA). Completely cyclized polymers were formed on polymerization of PDMA by a radical initiator. Moreover, those copolymers of PDMA and various monomers, such as styrene, methyl methacrylate, and vinyl acetate, obtained did not contain any detectable pendent double bonds. The kinetic investigation showed that the termination reaction proceeded between the cyclized radicals. The attempted polymerization of N-n-propyl-N-isobutyrylmethacrylamide, the monofunctional counterpart of PDMA, was failed. These results appear to confirm that cyclopolymerization of PDMA proceeds through a concerted mechanism which has been proposed for the mechanism of the cyclopolymerization of various difunctional monomers. Measurement of the ESR spectra of propagating radical has, however, revealed that the rate-determining step of the cyclopolymerization of PDMA is not intermolecular propagation but intramolecular cyclization, which indicates that the cyclization reaction proceeds in a stepwise way. This apparent contradiction was explained based upon thermodynamic considerations.     

Thiophene systems. 13. The synthesis of novel thienopyranones

The syntheses and spectral properties of novel dimethyl-substituted thieno[3,2-b]-, [3,4-b]- and [2,3-b]pyran-ones are described. The uv spectra of the three systems are distinctly different as supported by HOMO/LUMO calculations. 5,6-Dihydro-5,5-dimethyl-7H-thieno[3,4-b]pyran-7-one ( 10 ) and 5,6-dihydro-6,6-dimethyl-4H-thieno[2,3-b]pyran-4-one ( 20 ) represent the first members of these thienopyranone ring systems.