Infrared spectra of 1,3-butadiene matrices containing some atomic metals

Low-temperature matrices of 1,3-butadiene containing Ni, Pd, Fe or Mg atoms were prepared by codeposition at − 190°C, and their i.r. spectra were examined as the matrices were warmed to various temperatures. With Ni atoms, a charge-transfer complex, NiC₄H₆, whose i.r. spectrum was indistinguishable from that of solid C₄H₆, was formed initially. It rearranged at about −130°C into a yellow π-complex Ni(C₄H₆)₂ which in turn transformed rapidly into a more stable red polymeric π-complex (NiC₄H₆)_n. The spectra of these π-complexes showed that the butadiene ligands were in the cis configuration. The polymer decomposed at about −80°C into butadiene, metallic nickel and traces of organonickel residues. It also reacted with water to give butane and butenes. Matrices with Pd or Fe atoms behaved similarly but only a charge-transfer complex was observed with Mg atoms.     

Study of the reactions of oxygen atoms with carbonothioicdichloride,carbonothioicdifluoride, and tetrafluoro-1,3-dithietane

The reactions of ground-state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro-1,3-dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast-flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants are??(O + C₂CS) =(3.09 ± 0.54) × 10^?11 exp(+115 ± 106 cal/mol/RT),??(O + F₂CS) = (1.22 ± 0.19) × 10^?11 exp(-747 ± 95 cal/mol/RT), and??(O + F₄C₂S₂) = (2.36 ± 0.52) × 10^?11 exp(-1700 ± 128 cal/mol/RT) cm³/molec˙sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy-rich adduct which then decomposes by C-S bond cleavage.     

Spectroscopic analysis of imidazolidines. Part II: 1H NMR spectroscopy and conformational analysis of 1,2 and 1,3‐diarylimidazolidines

¹H NMR spectra of a series of 1,2 and 1,3‐diarylimidazolidines are analyzed and correlated with their conformational features. Results were interpreted on the basis of chemical shifts and coupling constants of hydrogen atoms and confirmed by ID nOe difference experiments. 1,3‐Diarylimidazolidines ( 1–7 ) show a fast inversion of the N‐aryl nitrogen in all studied cases. 1,2‐Diaryl‐3‐methyl (or benzyl) imidazolidines ( 8–13 ) display a preferential conformation with a transoid orientation of N₃ and C₂ substituents.     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

31P-NMR-Daten heterocyclischer phosphine. Diastereomerenzuordnung an 1,3-Oxa-, 1,3-Aza- und 1,3-thiaphospholanen

The diastereomers of 16 1,3-oxa-, 1,3-aza- and 1,3- thiaphospholanes were assigned by means of the coupling constants ²J(P? C? H) and ³J(P? C? CH₃) and the linewidths of the ³¹P signals and ¹H chemical shifts of CH₃ groups. It is shown that the change in the ³¹P chemical shifts allows the estimation of the relative configuration in these compounds.     

1,3‐Bis(ethylamino)‐2‐nitrobenzene, 1,3‐bis(n‐octylamino)‐2‐nitrobenzene and 4‐ethylamino‐2‐methyl‐1H‐benzimidazole

1,3‐Bis(ethylamino)‐2‐nitrobenzene, C₁₀H₁₅N₃O₂, (I), and 1,3‐bis(n‐octylamino)‐2‐nitrobenzene, C₂₂H₃₉N₃O₂, (II), are the first structurally characterized 1,3‐bis(n‐alkylamino)‐2‐nitrobenzenes. Both molecules are bisected though the nitro N atom and the 2‐C and 5‐C atoms of the ring by twofold rotation axes. Both display intramolecular N—H...O hydrogen bonds between the amine and nitro groups, but no intermolecular hydrogen bonding. The nearly planar molecules pack into flat layers ca 3.4 Å apart that interact by hydrophobic interactions involving the n‐alkyl groups rather than by π–π interactions between the rings. The intra‐ and intermolecular interactions in these molecules are of interest in understanding the physical properties of polymers made from them. Upon heating in the presence of anhydrous potassium carbonate in dimethylacetamide, (I) and (II) cyclize with formal loss of hydrogen peroxide to form substituted benzimidazoles. Thus, 4‐ethylamino‐2‐methyl‐1H‐benzimidazole, C₁₀H₁₃N₃, (III), was obtained from (I) under these reaction conditions. Compound (III) contains two independent molecules with no imposed internal symmetry. The molecules are linked into chains via N—H...N hydrogen bonds involving the imidazole rings, while the ethylamino groups do not participate in any hydrogen bonding. This is the first reported structure of a benzimidazole derivative with 4‐amino and 2‐alkyl substituents.     

Recognition of 1,3‐Butadiene by a Porous Coordination Polymer

The separation of 1,3‐butadiene from C₄ hydrocarbon mixtures is imperative for the production of synthetic rubbers, and there is a need for a more economical separation method, such as a pressure swing adsorption process. With regard to adsorbents that enable C₄ gas separation, [Zn(NO₂ip)(dpe)]_n (SD‐65; NO₂ip=5‐nitroisophthalate, dpe=1,2‐di(4‐pyridyl)ethylene) is a promising porous material because of its structural flexibility and restricted voids, which provide unique guest‐responsive accommodation. The 1,3‐butadiene‐selective sorption profile of SD‐65 was elucidated by adsorption isotherms, in situ PXRD, and SSNMR studies and was further investigated by multigas separation and adsorption–desorption‐cycle experiments for its application to separation technology.     

Facile synthesis of blocky styrene(1,3)‐butadiene copolymers having stereoregular monomeric sequences

Half titanocenes (CpCH₂CH₂O)TiCl₂ 1 and (CpCH₂CH₂ OCH₃)TiCl₃ 2 , activated by methylaluminoxane are tested in styrene–1,3‐butadiene copolymerization. The titanocene 1 is able to copolymerize styrene and 1,3‐butadiene, with a facile procedure, to give products with high molecular weight. The analysis of microstructure by ¹³C‐NMR reveals that the styrene homosequences in copolymers are in syndiotactic arrangement, while the butadiene homosequences are, prevailingly, in 1,4‐cis configuration, according with behavior of 1 in the homopolymerizations of styrene and 1,3‐butadiene, respectively. The reactivity ratios of copolymerization are estimated by diad composition analysis. All obtained copolymers have r₁ × r₂ values much larger than 1, indicating blocky nature of homosequences. The structural characterization by wide‐angle X‐ray powder diffraction and differential scanning calorimetry indicates that all copolymers are crystalline, with T_m varying from 171 to 239 °C, depending on the styrene content. The titanocene 2 did not succeed in styrene–1,3‐butadiene copolymerization, giving rise to a blend of homopolymers. Compounds 1 and 2 were also tested in the polymerization of several conjugated dienes, and the obtained results were very useful to rationalize the behavior of both catalysts in the copolymerization of styrene and butadiene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 815–822, 2010     

Synthesis of New Chiral and Racemic 1,3‐Dioxolanes

A series of chiral 1,3‐dioxolanes, 3 – 12 , with >99% ee values, have been synthesized. This is the first study of chiral ketalization reaction starting from ketones with aryl, monosubstituted aryl, and long alkyl chains (C₁₁—AC₁₃). Their ee values were determined by chiral high‐performance liquid chromatography (HPLC) on Chiralcel OD column, using their racemic 1,3‐dioxolanes rac‐ 3 – 12 , which were also synthesized for the first time. These chiral and racemic 1,3‐dioxolanes were characterizated by infrared, NMR (¹H, ¹³C), mass spectrometry, elemental analysis, optical rotation, and chiral HPLC.     

Metal atom synthesis ofsyn(1-3-η-but-2-enyl)(η-buta-1,3-diene)(triethylphosphine)cobalt

Summary Cocondensation of buta-1,3-diene with cobalt vapor followed by addition of triethylphosphine gave a new complexsyn-Co(C₄H₇)(C₄H₆)(PEt₃) (1) in 43% yield. The reaction pathway leading to (1) was investigated by matrix isolation i.r. spectroscopy. The monodentate butadiene, which was found as a reaction intermediate in the –196 toca. 0° temperature range, rearranges into a -butenyl or bidentate butadiene. The reaction of (1) with bromoethane gave cycloocta-1,5-diene and 4-vinylcyclohex-1-ene in quantitative yield. Complex (1) catalyzes the cyclotrimerization of phenylacetylene to 1,3,5-triphenylbenzene.     

Reaction of hydrogen atoms with diethyldisulfide and ethylmethyldisulfide

H atoms react with C₂H₅SSC₂H₅ to give C₂H₅SH as the sole retrievable product with ? = 2.32 at 25°C and 2.84 at 145°C. The primary reaction is postulated to be H + C₂H₅SSC₂H₅ ← C₂H₅SH + C₂H₅S with k₁ = (4.73 ± 0.64) × 10¹³ exp [?(1710 ± 69)/RT] cm³/mol·s relative to the rate constant of the H + C₂H₄ ← C₂H₅ reaction. The high value of the entropy of activation suggests the presence of partial hydrogen bonding in diethyldisulfide which is broken in the transition state. Ethylmethyldisulfide reacts similarly: H + C₂H₅SSCH₃ ← C₂H₅SH + CH₃S or CH₃SH + C₂H₅S. The thiyl radicals propagate a chain of radical exchange reactions forming the symmetrical disulfides with exposure-time-dependent quantum yields. The overall kinetics conform to a 16-step mechanism from which the rate constants of the elementary reactions could be established by computer modeling. Thiyl radicals react considerably more slowly with disulfides than H atoms.     

Loss of methyl from ionized 2-hydroxy-1,3-butadiene

The loss of methyl from unstable, metastable and collisionally activated [CH₂?CH? C(OH)?CH₂]⁺˙ ions (1⁺˙) was examined by means of deuterium and ¹³C labelling, appearance energy measurements and product identification. High-energy, short-lived 1⁺˙ lose methyl groups incorporating the original enolic methene (C(1)) and the hydroxyl hydrogen atom (H(0)). The eliminations of C(1)H(1)H(1)H(4) and C(4)H(4)H(4)H(0) are less frequent in high-energy ions. Metastable 1⁺˙ eliminate mainly C(1)H(1)H(1)H(4), the elimination being accompanied by incomplete randomization of the five carbon-bound hydrogen atoms. The resulting [C₃H₃O]⁺ ions have been identified as the most stable CH₂?CH? CO⁺ species. The appearance energy for the loss of methyl from 1 was measured as AE[C₃H₃O]⁺ = 10.47 ± 0.05 eV. The critical energy for 1⁺˙ → [C₃H₃O]⁺ + CH₃˙ is assessed as E_c ? 173 kJ mol^?1. Reaction mechanisms are proposed and discussed.     

(2S,3S)‐2,6‐Dimethylheptane‐1,3‐diol,the oxygenated side chain of 22(S)‐hydroxycholestrol,and its synthetic precursor (R)‐4‐benzyl‐3‐[(2R,3S)‐3‐hydroxy‐2,6‐dimethylheptanoyl]‐1,3‐oxazolidin‐2‐one

(2S,3S)‐2,6‐Dimethylheptane‐1,3‐diol, C₉H₂₀O₂, (I), was synthesized from the ketone (R)‐4‐benzyl‐3‐[(2R,3S)‐3‐hydroxy‐2,6‐dimethylheptanoyl]‐1,3‐oxazolidin‐2‐one, C₁₉H₂₇NO₄, (II), containing C atoms of known chirality. In both structures, strong hydrogen bonds between the hydroxy groups form tape motifs. The contribution from weaker C—H...O hydrogen bonds is much more evident in the structure of (II), which furthermore contains an example of a direct short Osp³...Csp² contact that represents a usually unrecognized type of intermolecular interaction.     

1,3‐Dimethyl­isoguanine

The structure of 1,3‐dimethyl­isoguanine [or 6‐amino‐1,3‐dimethyl‐1H‐purin‐2(3H)‐one], C₇H₉N₅O, has been redetermined and the correct assignment of H atoms on the heterocycle is now reported. Inter­molecular hydrogen‐bonding inter­actions confirm that this form is the correct mol­ecular structure; this form is also in agreement with an earlier reported structure of the trihydrate form.     

1,3‐Ninhydrin dihydrazone featuring an R44(12) motif with symmetry and comprising only N and H atoms

In the title compound [systematic name: (1Z,3Z)‐1,3‐dihydrazinylidene‐1H‐inden‐2(3H)‐one], C₉H₈N₄O, isolated molecules possess approximate noncrystallographic C_2v symmetry and their cis conformation and planarity are assisted by a pair of short intramolecular N—H...O hydrogen bonds. Each molecule is asymmetrically involved in an extensive three‐dimensional network of N—H...O and N—H...N hydrogen bonds, and the structure also exhibits weaker π–π and C=O...C interactions. The structure features an R₄⁴(12) motif consisting solely of N and H atoms and possessing crystallographic symmetry.     

Copolymerization of 1,3‐butadiene and isoprene with cobalt dichloride/methylaluminoxane in the presence of triphenylphosphine

The homopolymerization and copolymerization of 1,3‐butadiene and isoprene were achieved at 0 °C with cobalt dichloride in combination with methylaluminoxane and triphenylphosphine (Ph₃P). For 1,3‐butadiene, highly cis‐specific and 1,2‐syndiospecific polymerization proceeded in the absence or presence of Ph₃P, respectively, although the activity with Ph₃P was much higher than that without Ph₃P. Only a trace of the polymer was, however, obtained in isoprene polymerization when Ph₃P had been added. For copolymerization, the polymer yield in the presence of Ph₃P was about three times higher than that in its absence. Copolymerization in the presence of Ph₃P was, therefore, investigated in more detail. Unimodal gel permeation chromatography elution curves with narrower polydispersity (weight‐average molecular weight/number‐average molecular weight ≈ 1.5) indicated that the propagation reaction proceeded by single‐site active species. Both the yield and molecular weight of the copolymer decreased with an increasing amount of isoprene in the feed, and this was followed by an increase in the isoprene content in the copolymer. The monomer reactivity ratios, r₁ (1,3‐butadiene) and r₂ (isoprene), were estimated to be 2.8 and 0.15, respectively. Although the 1,3‐butadiene content in the copolymer was strongly dependent on the comonomer composition in the feed, the ratio of 1,2‐inserted units to 1,4‐inserted units of 1,3‐butadiene was constant. Concerning the isoprene unit, the percentage of 1,2‐ and 3,4‐inserted units was increased at the expense of 1,4‐inserted units with an increasing isoprene content in the feed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3086–3092, 2002     

Kinetics of 1,3‐dipolar cycloaddition reaction between C,N‐diphenylnitrone and dimethyl fumarate in various solvents and aqueous solutions

Second‐order rate constants and activation parameters of 1,3‐dipolar cycloaddition reaction between C,N‐diphenylnitrone and dimethyl fumarate were obtained in various solvents and aqueous solutions at 65°C. Second‐order rate constants of the reaction in water and ethylene glycol are approximately 33 and 8 times faster than those expected from solvent polarity, respectively. Increase of the reaction rate in aqueous solutions of ethanol is higher than that of propan‐1‐ol. A multiparameter correlation of log k₂ vs Sp and E_T^N in various solvents and aqueous solutions of ethanol shows that solvophobicity and solvent polarity parameter are important factors in occurrence of the reaction. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 431–434, 2000     

Radical telomerization of 1,3‐butadiene with perfluoroalkyl iodides in the presence of potassium carbonate

The radical telomerization of 1,3‐butadiene with perfluoroalkyl iodides (C₆F₁₃I or merely C₈F₁₇I) initiated by di‐tert‐butyl peroxide was studied in the presence of various amounts of potassium carbonate at 145 °C in acetonitrile. The influence of this salt on both the kinetics and the telomer characteristics (color, molar mass, and functionality) was established. First, the determination of the chain‐transfer constant of C₈F₁₇I led to a value (2.52) similar to that obtained under the same conditions without any K₂CO₃ (2.59). Second, 1,3‐butadiene conversion was much faster, and the molar mass/time profiles were also quite different, revealing the formation of high molar mass polymers at the end of conversion, which was not observed in previous studies without any K₂CO₃. Moreover, great improvements in the functionality of the fluorinated telomers were achieved (closer to unity). The products were also not as colored as before (black in the absence of K₂CO₃), and this allowed valuable application tests. With electronic microscopy, K₂CO₃ was shown to neutralize hydrogen iodide (HI) produced in the course of the reaction, which caused major drawbacks (e.g., low functionality and dark color). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3743–3756, 2002     

Polymerization and copolymerization of 2-phthalimidomethyl 1,3-butadiene. I. Preliminary studies of free radical polymerization and polymerizations initiated by various transition metal allyl complexes

2-Phthalimidomethyl 1,3-butadiene was homopolymerized and copolymerized with butadiene by free radical initiators; r₁ and r₂ were close to 1. All the attempts to polymerize 2PMB anionically have been unsuccessful. Preliminary studies of various η³-allylic catalysts showed that η³-allyl M₀(CO)₃OOCCF₃ initiates the polymerization of butadiene and is not sensitive to N-methyl phthalimide (NMP); neither does it initiate the copolymerization of butadiene and 2PMB. On the other hand, a catalyst that results from the reaction of allyl trifluoroacetate with nickel tetracarbonyl is efficient for the copolymerization of butadiene and 2PMB. η³-Allyl nickel trifluoroacetate was prepared in heptane or benzene and used in benzene or methylene chloride. In all cases it initiated the copolymerization of butadiene with 2PMB     

A dynamic nuclear magnetic resonance spectroscopic study of conformational properties of 1,3-dioxepane and 4,4,7,7-tetramethyl-1,3-dioxepane

The 251 MHz ¹H and the natural abundance 63.1 MHz ¹³C NMR spectra of 1,3-dioxepane (1) and 4,4,7,7-tetramethyl-1,3-dioxepane (2) have been investigated over the temperature range of 5 to ?180 °C. While the spectra of 1 show no dynamic NMR effect, compound 2 exists in solution as a 1:1 mixture of a symmetrical (C₂) twist-chair and its mirror image conformation. The free energy barrier for the conformational racemization of 2 is 43 kJ mol^?1 (10.3 kcal mol^?1). Interconversion paths between various conformations of 2 are discussed. Compound 1 is suggested to have a symmetrical (C₂) twist-chair conformation which is rapidly pseudorotating via a chair conformation to achieve a time averaged symmetry of C_2v, even at ?180 °C.