Terminal Unsaturation Research Articles

Biosynthesis of n-alkatrienes in Botryococcus braunii

Abstract In addition to very long chain n -alkadienes with ω 9 and terminal unsaturations, the A race of the hydrocarbon-rich microalga Botryococcus braunii produces substantial amounts of C 29 and C 31 n -alkatrienes. The latter are dominated by a C 29 isomer comprising one terminal and two cis -ω 7 , cis -ω 9 unsaturations. The present study indicates (i) although linoleic acid is the only 18:2 acid present in significant amounts in B. braunii , no trienic hydrocarbons directly derived from this acid (hence comprising cis -ω 6 , cis -ω 9 internal unsaturations) are normally formed by this microalga. (ii) The elongation-decarboxylation system of B. braunii is selective, it does not accept linoleic acid as a direct precursor and even growth in the presence of large amounts of erogenous linoleic acid does not induce the production of the corresponding trienes. (iii) As previously demonstrated in the case of dienes, oleic acid is also the direct precursor of B. braunii trienes. (iv) Trienes are unlikely to be formed via desaturation of dienes. Introduction of the additional double bond probably occurs at an earlier stage of the elongation-decarboxylation pathway, either via direct desaturation of oleic acid ( e . g . into a cis -ω 7 , cis -ω 9 acid) or via desaturation of the very long chain fatty acyl derivatives formed by elongation of oleic acid. (v) The formation of radioactive dienic and trienic hydrocarbons following feeding with linoleic acid results neither from the prior degradation of this acid into acetate units nor from its prior reduction into oleic acid. (vi) Under normal growth conditions, that is in the absence of exogenous linoleic acid, the formation of hydrocarbons from this acid is at most a minor process.

The polymerization of isobutylene by AlCl3 in CH2Cl2 and the role of CH2Cl2 in the initiation reaction

AbstractA solution of AlCl3 in CH2Cl2 prepared in advance was used 18 days after the mixing of the components as an initiation system in the polymerization of isobutylene performed in CH2Cl2 in the temperature range between −10 and −20°C. The 1H‐NMR analysis of polyisobutylene (PIB) samples synthesized to low and high conversion showed that it is the initiation reaction and not the transfer reaction to dichloromethane that is responsible for the CH2Cl endgroup in the polymer chain. In case of the transfer to monomer formation of PIB with internal terminal unsaturation [PIBCHC(CH3)2] is preferred to external unsaturation [PIBCH2(CH3)CCH2]. The solutions of AlCl3 in CH2Cl2 showed an absorption band at λmax = 302 nm.

Structure and stability of halogenated polymers: Part 3—Ring-brominated polystyrene

Polystyrene has been brominated exclusively in the ring, in the para position, by reaction with an equimolar mixture of bromine and iodine in dichloromethane at − 20°C. The highest bromine content which could be obtained was approximately 37% by weight (1 Br per styrene unit = 43·7% Br). The brominated polymer has been characterised by IR and NMR spectroscopy. Ring-brominated polystyrene is more stable than ring-chlorinated polystyrene because it lacks the backbone halogenation which is unavoidable in the ring chlorination of polystyrene. The brominated polymer has fairly similar thermal stability to polystyrene and degrades in essentially the same way, giving about 62% by weight of monomers ( p-bromostyrene and styrene) and a cold ring fraction with the repeat structure and terminal unsaturation.

Semihydrogenaticn of Triple Bonds in 1-Alkeue Solutions

Abstract Using 1-alkenes as solvent, catalytic reduction of alkynes in the presence of Lindlar's catalyst is achieved without risking over-reduction of terminal unsaturation.

Synthesis and insecticidal activity of lipophilic amides. Part 3: Influence of chain length and terminal group in N‐(2‐methylpropyl)‐2,4‐dienamides

AbstractIncreasing the alkylene chain length in N‐(2‐methylpropyl)‐ω‐phenylalka‐2,4‐dienamides revealed in addition to the active compounds reported earlier a second peak of activity, but only against mustard beetles, with the tridecadienamide. Similar extension in the methyl‐terminated series gave much weaker peaks, at different lengths for the two test species. Results with terminal vinyl compounds were intermediate, and indicated a specific functional role in the lethal process for the terminal unsaturation, with a possible contribution to steric flexibility and physical property optimisation from the longer chains. Synthetic samples of pellitorine and pipercide, natural products to which insecticidal activity has been ascribed, were only very weakly active in the present tests, but compounds with other groups on the ends of chains nearer the optimum length were more active.

Micelle formation and terminal double bonds in sodium carboxylates

The effect of terminal unsaturation on the CMC values of sodium 11-dodecenoate and sodium 12-tridecenoate have been probed using conductance and 23 Na NMR. The results suggest that addition of a terminal double bond has the same effect on the CMC of the corresponding saturated sodium carboxylate as the removal of 1.1 CH 2 units. Our results confirm that the previous study of the above effect, observed for sodium 10-undecenoate, is probably a general one.

The occurrence and activity of epithiospecifier protein in some cruciferae seeds

Epithiospecifier protein (ESP) activity was determined in the seeds of two cultivars of Brassica napus, in B. campestris and in Lepidium sativum. All four types of seeds contained susceptible substrates for ESP (that is, glucosinolates with terminal unsaturation in their side-chain), although L. sativum contained only a very small amount of one. Results suggest that Fe 2+ is essential for ESP activity, but its presence certainly promoted the effects of ESP to a considerable extent, and even at a very low level (e.g. 6 × 10 −11 mol Fe 2+. Further evidence was gained for the intramolecular nature of the reaction which results in cyanoepithioalkane formation.

Mechanism of inhibition by copper stearate of the photo-degradation of polyolefins

The effect of a series of transition metal (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) stearates in retarding the photo-degradation of isotactic polypropylene has been examined and it has been found that the results obtained are quite similar to those for high density polyethylene. Infra-red spectral analysis of the polyethylene and isotactic polypropylene films showed that, in the early stages of the photo-irradiation, photo-chemical reaction of the copper stearate took place in the films to change its structure and that rapid formation of terminal unsaturation occurred only in the films containing copper stearate. The results obtained suggest that the copper stearate provides a radical scavenging function, as well as an ultraviolet light absorbing function, to protect the polymers against photo-degradation.

Distribution of double bonds in thermally degraded polyisobutylene

The distribution of double bonds in thermally degraded polyisobutylene was determined quantitatively by using pulsed Fourier transform 1H n.m.r. spectroscopic analysis. The double bonds in the degraded polymer did not exist in the interior but at the terminal positions of the polymer chain. These olefins were of the terminal trisubstituted and terminal vinylidene types. The content of the former was much greater than that of the latter. This shows that radical chain transfer predominantly occurs at the methylene hydrogen rather than at the methyl groups of the polymer chain. The average number of double bonds per molecule, f, was greater than 1 and tended to be near 2. Thereby most of the degraded polyisobutylene was shown to have two terminal unsaturations per molecule.

Radiation initiated polymerisation of phenyl methacrylate

Radiation initiated polymerisation of phenyl methacrylate has been studied at various dose rates and temperature. Predominant chain transfer to the monomer was observed and k tran/ k p the chain transfer constant ratio was found to be 4 x 10 -2· k p k t 1 2 value determined by the kinetic data and the molecular weight data were 0.0821 and 0.0198, respectively. IR studies of polymer at low conversion showed the presence of terminal unsaturation which disappeared at saturation conversion, thus showing its participation in the formation of a three dimensional network.

Vinylation and polymerization with trivinylaluminum. II. Synthesis of α,ω‐diene‐polyisobutylene

AbstractThe polymerization of isobutylene by 3‐chloro‐1‐butene/trivinylaluminum (V3Al) and t‐butyl chloride/V3Al initiator systems with methyl chloride and methylene chloride as solvents has been investigated in the range from −30 to −72−C. The rate of polymerization increases with decreasing temperatures from −30 to −50°C and then decreases when the temperature is further lowered, for example, to −72°C. Mayo plots and a determination of the number of polymer molecules n̄ formed per molecule of initiator employed suggests a transfer‐less, i.e., termination‐dominated system. A critical analysis shows that for systems containing both free ions and ion pairs, the Mayo equation is meaningful only when the degree of dissociation α remains constant over the whole [M] range investigated. This condition is achieved in RCl/V3Al‐initiated systems by using an initiator (t‐BuCl) for which the rate of catalyst destruction is insignificant compared to rate of initiation, Ri, i.e., initiation efficiency, f ≈ 1 and Ri independent of [M]. Polyisobutylene, containing, 1.8 ± 0.1 terminal unsaturation, has been synthesized by the use of 3‐chloro‐1‐butene initiator in conjunction with V3Al coinitiator, and avenues for further efficient synthesis of α,ω‐diene‐polyisobutylenes have been outlined.

Maleimide polymers. III. Color reactions and kinetics

AbstractWe have shown previously that the free‐radical polymerization kinetics of maleimide can be explained by a scheme for retarded polymerization. The steps involve tautomerization of a growing maleimidyl chain to succinimidyl, the retarded addition of maleimide to the latter, and termination solely by resonance‐stabilized succinimidyl radicals. Combination termination is preferred, since this yields a very stable N,N′‐bisuccinimidyl structure. Other authors also invoke tautomerization to succinimidyl radicals which they believe terminate by disproportionation with growing maleimidyl chains to generate polymer with unsaturated endgroups. Free‐radical‐initiated polymaleimides are colored in the presence of base. Our measurements of the absorbance of polymaleimides at 387 and 500 nm in the presence of excess strong organic base show there is essentially no dependence on molecular weight. This suggests that the chromophoric groups are intramolecular and that color does not arise from the ionization of allylic protons associated with terminal double bonds. The near‐ultraviolet spectra of polymaleimides in slightly acidic media contain absorption bands at about 288, 320, and 360 nm. The structural impurities that account for these bands cannot be terminal unsaturation. We propose that the origin of these bands is pyrrolinone type structures which are formed by a retarded polymerization step through succinimidyl oxygen.

Effect of double bonds on the γ-radiation-induced crosslinking of polyethylene

Various low-density polyethylenes ranging in initial weight-average molecular weight (Mw) from 7600 to 589000 having a ratio of Mw to number-average molecular weight (Mn) of about 5 were irradiated by γ-rays in vacuo at 30°C. Gel fractions were determined and analyzed by using the equation derived by Charlesby and Pinner. The following relationships were obtained when Mw was used as the molecular weight: where rg represents the gel point dosage (Mrad), [CC]0 is the sum of the initial contents of terminal vinyl and vinylidene unsaturations (mole/g polyethylene), and q0 and p0 are the probabilities of crosslinking and main-chain scission per monomer unit for a unit radiation dose in Mrad, respectively. Similar relationships to the equations described above were also obtained when Mn was used. From the results, it was concluded that terminal vinyl and vinylidene unsaturations play an important role for the gel formation in the γ-radiation-induced crosslinking of polyethylene in vacuo at room temperature.

Chemical conversion of a tetrafluorethylene-ethylene copolymer during radiolysis in vacuum

IR spectroscopic studies of a tetrafluorethylene-ethylene (1:1) copolymer exposed to γ-radiation in vacuum revealed changes in chemical structure dependent on conditions of irradiation. With an increase in the dose of radiation a reduction occurs in absorption band intensities in the regions of 1450 and 2973 cm −1 corresponding to vibrations of CH 2 groups and in a series of absorption bands in the 500–1300 cm −1 region, corresponding to bond-stretching and deformation vibrations of CF bonds of CF 2 groups. These variations are intensified with an increase in the temperature of radiation from 25 to 250°. Different types of double bond are formed: −CH=CF−, −CF=CF−, −CH=CF 2 (bands at 1720, 1740, 1765 cm −1). Absorption band intensity varied in the region of 1740 cm −1 according to the dose and temperature of radiations. With an increased radiation dose (25°) band intensity at 1860 cm −1 related to “terminal unsaturation” of −CF=CF 2 increases. However, at an irradiation temperature of 250° this band disappears. At increased temperature of radiation (150, 250°) a broad absorption band is formed in the region of 1600–1700 cm −1, which is due to the formation of double bonds of the type −CH=CH 2 or −CH=CH−. Using results obtained a mechanism is proposed for breakdown and structure formation taking place during the irradiation of the copolymer.

End-group Analysis of Some Polyether Polyols and Polyester Polyols by Nuclear Magnetic Resonance Spectroscopy

Ring-opening polymerization of monosubstituted ethylene oxides Cl J results in formation of polyether polyols with either primary C 2or secondary terminal hydroxyl group C3D, depen- ding on the mode of C-O-C bond cleavage.This end-group structure is significant, since it is closely related to the reactivity of polyols and affects the properties of polyurethane resin prepared from those polyols and diisocyanates. The application of NMR technique to the analysis of primary hydroxyl groups in polyol are studied in this paper when the hydroxyl is converted into urethane, and it proves to be a simple and convenient method. We also employed the time-average technique of NMR with a Mnemotron Computer of Average Transient to analysis of terminal unsaturation in polyols. It was revealed that poly (oxypropylene)glycol prepared by KOH catalyst contains substan- tially on or a small amount of primary hydroxyl, but more than 40% primary hydroxyl is found in polyether which was prepared by BF, --catalyzed, polymerization, and no matter what the polymerization catalyst is the amount of terminal unsaturation in the resultant polyethers increases by the molecular weight increase of polyether.

Olefins from Drying Oil Fatty Acids by Catalytic Oxidative Decarboxylation

AbstractLead tetraacetate in the presence of catalytic amounts of Cu(II) has been shown to be very effective for the conversion of carboxylic acids to terminal olefins with one less carbon atom. The advantage of this method is that a reaction temperature of only 80°C is needed and it yields very few side products. This low reaction temperature makes it ideal for the decarboxylation of drying oil derived fatty acids which contain very reactive internal unsaturation. This paper describes the use of lead tetraacetate to produce 17 carbon terminal polyolefins from unsaturated fatty acids with pyridine and lithium acetate as catalyst. The products of these reactions were analyzed by IR for disappearance of the carbonyl peak and appearance of peaks due to terminal unsaturation. IR spectra gave very little evidence of isomerization of the cis internal double bonds to the trans isomers.

Methods for the isolation and characterization of constituents of natural products: XV. Application of a periodic acid column for locating double bond position

The ability of a microcolumn of periodic acid impregnated on magnesium sulfate to effect oxidation of ethylenic unsaturation was studied. The aldehyde, produced on the hydrocarbon side of the double bond in 30–40% yield, was converted to a 2,4-dinitrophenylhydrazone on a microderivatizing column and identified by thin-layer chromatography. The method was applied to unsaturation in fatty acids, their methyl esters, alcohols, aldehydes, and colored derivatives of the latter two classes. Double bonds in a variety of positions in the chain were successfully located, but terminal unsaturation or unsaturation with a methyl group on either carbon of the double bond could not be characterized. The procedure was routinely run on 25 μg but can still be successfully executed on 5 μg of a pure compound.

Chain transfer constants for vinyl monomers polymerized in methyl oleate and methyl stearate

AbstractChain transfer constants were obtained for styrene, methyl methacrylate, methyl acrylate and vinyl acetate, polymerized in methyl oleate and methyl stearate at 60°C. Transfer constants increased in the order: methyl methacrylate < styrene < methyl acrylate ≪ vinyl acetate in both solvents. Average values of the transfer parameters were: for methyl oleate, Qtr = 2.04 × 10−4, etr = 1.08; for methyl stearate, Qtr = 0.373 × 10−4, etr = 1.01. Indication that polar species predominate in the transition state is supported by the observed order of reactivity. The usual rate dependence appeared to be followed by all of the monomers except vinyl acetate, which was retarded, severely in methyl oleate. Transfer in methyl oleate was about 5.8 times greater than that found in methyl stearate for these four monomers. The internal allylic double bond of methyl oleate had about the same reactivity in transfer as had the terminal unsaturation in N‐allylstearamide at 90°C. Rough estimates were obtained of the monomer transfer constants for the long side‐chain homologs of these four monomers from the respective monomer transfer constants and the experimental transfer constants, corrected for transfer to the labile groups of the solvent. It was concluded that the rate of polymerization would determine in large measure the degree of polymerization for the reactive 18‐carbon homologs but that the molecular weight of poly(vinyl stearate) and (oleate) will be regulated primarily by transfer to monomer.

Resin catalyzed epoxidation of methyl undecylenate

AbstractThe optimum temperature for the epoxidation of methyl undecylenate is 60 C and a maximum conversion of about 50% occurs in 4 hr reaction. Thin layer chromatography showed evidence of ring opening and the presence of decomposition products. Gas liquid chromatography on a silicone column appears promising but cannot be used for quantitative purposes due to the presence of noneluting components. However, infrared absorption at 906 cm−1 is characteristic of terminal unsaturation and the intensity of this peak has been observed to be proportional to the concentration up to 90 g/liter of the methyl undecylenate. Hence, we feel this absorption can be used to estimate the unreacted methyl undecylenate in the products.

Improvement of Properties of Urethane Elastomers by Removal of Terminal Unsaturation in Poly(oxypropylene) Diols

Improvement of Properties of Urethane Elastomers by Removal of Terminal Unsaturation in Poly(oxypropylene) Diols