Thermal Cyclodimerization Research Articles

Thermal cyclodimerization of isoprene for the production of high-performance sustainable aviation fuel

Isoprene is converted to cycloalkanes by thermal dimerization followed by hydrogenation. The resulting blend exhibits outstanding jet fuel properties.

The spin delocalization substituent parameter σ˙. 7. Meta-substituent effects on the cyclodimerization of trifluorostyrenes. A test for the σ˙JJ approach

Rate constants (k's) of the thermal cyclodimerization of ten meta-substituted trifluorostyrenes (m-Y-TFS's) have been measured in the temperature range 110–160°C. On the basis of these k's and the σmb values derived from 19F NMR data the spin-delocalization substituent constant σ˙m values of these ten meta-substituents have been calculated. The averaged σ˙m values are: m-Et, 0.09; m-t-Bu, 0.11; m-F, 0.03; m-Cl,−0.05; m-Br, 0.12: m-CF3, −0.07; m-OMe, 0.10; m-NO2, −0.002; m-CN, 0.11 and m-CO2Me, 0.08. Both the smallness of these values and the nonexistence of correlation between Hammett-Type polar σX and these σ˙m values support our belief that the σjJ approach is reliable and trustworthy.

Sulfonated poly(fluorenyl ether) membranes containing perfluorocyclobutane groups for fuel cell applications

This paper describes the preparation and electrochemical properties of new proton conducting polymer membranes, sulfonated poly(fluorenyl ether) membrane-containing perfluorocyclobutane (PFCB) moieties for fuel cell applications. The sulfonated polymers were prepared via thermal cyclodimerization of 9,9-bis(4-trifluorovinyloxyphenyl)fluorene and subsequent post-sulfonation using chlorosulfonic acid (CSA) as a sulfonating agent. The post-sulfonation reaction was carried out by changing the molar ratio of CSA/repeating unit of the polymer at room temperature for 5 h and the resulting sulfonated polymers showed different degrees of sulfonation (DS) and ion exchange capacities (IEC). With the increment of CSA content, the DS, IEC and water uptake of the sulfonated polymer membranes increased. Their proton conductivity was investigated as a function of temperature. The polymer membrane with an IEC value of 1.86 mmol/g showed a water content of 25% similar to Nafion-115's but showed higher proton conductivity than Nafion-115 over the temperature 25–80 °C. The polymer membrane with lower water uptake and higher IEC showed similar proton conductivity and methanol permeability to Nafion-115. These results confirmed that the sulfonated poly(fluorenyl ether)-containing PFCB groups could be a promising material for fuel cell membranes.

High-Temperature Chromophores and Perfluorocyclobutyl Copolymers for Electro-optic Applications

The synthesis and hyperpolarizabilities of a series of push−pull chromophores containing a bis-(4-methoxyphenyl) amine donor and efficient acceptor bridges with thiophene and ring-locked polyene are presented. The chromophores are readily soluble in common organic solvents and exhibit high thermal decomposition temperatures (highest Td was 358 °C). Molecular hyperpolarizabilities (β) of the chromophores were measured by hyper-Raleigh scattering at 1604 nm (highest β was 20 000 × 10−30 esu). The electrochemical behavior of the chromophores was studied by cyclic voltammetry and agreed well with the observed intrinsic nonlinearities. In addition, preliminary results of conjugated polyene chromophores containing aryl trifluorovinyl ether monomers were synthesized and copolymerized via thermal cyclodimerization, affording perfluorocyclobutyl aryl ether polymers with high glass transitions (highest Tg was 224 °C) and a good thermal stability (typical Td was >350 °C). These chromophores can be used to develop electro-optic materials due to their large optical nonlinearities, good absorption characteristics, high thermal stability, and excellent solubility with organic solvents and polymeric materials.

Synthesis and Electronic Factors in Thermal Cyclodimerization of Functionalized Aromatic Trifluorovinyl Ethers

A series of 19 p-substituted aromatic trifluorovinyl ether compounds were prepared from versatile intermediate p-Br-C(6)H(4)-O-CF=CF(2) and underwent thermal radical mediated cyclodimerization to new difunctional compounds containing the 1,2-disubstituted perfluorocyclobutyl (PFCB) linkage. The synthetic scope demonstrates the functional group transformation tolerance of the fluorovinyl ether, and the dimers are useful as monomers for traditional step-growth polymerization methods. (19)F NMR spectra confirmed that p-substitution affects the trifluorovinyl ether group chemical shifts. The first kinetic studies and substituent effects on thermal cyclodimerization were performed, and the results indicated that electron-withdrawing groups slow the rate of cyclodimerization. The data were further analyzed using the Hammett equation, and reaction constants (rho) of -0.46 at 120 degrees C and -0.59 at 130 degrees C were calculated. This study presents the first liner free energy relationship reported for the cyclodimerization of aromatic trifluorovinyl ethers to PFCB compounds.

Synthesis and characterization of perfluorocyclobutyl (PFCB) polymers containing pendent phenylphosphine oxide

Three phenylphosphine oxide (PPO) containing trifluorovinyl aryl ether monomers were synthesized and polymerized via thermal cyclodimerization affording perfluorocyclobutyl (PFCB) polymers containing PPO pendent groups. The new polymers exhibited moderate to high glass transition temperatures ( T g=145–217 °C) and good thermal stability in nitrogen (5% weight loss, T d>402 °C). Copolymerization with traditional PFCB forming monomers such as 4,4′-(trifluorovinyloxy)biphenyl resulted in film forming transparent thermoplastic copolymers with improved solubility and further enhanced thermal stability. Semi-fluorinated PPO containing polymers of this type may find potential application as space environment durable materials.

Synthesis and comparison of CF3 versus CH3 substituted perfluorocyclobutyl (PFCB) networks for optical applications

AbstractA novel aryl trifluorovinyl ether monomer, 1,1,1‐tris(4‐trifluorovinyloxyphenyl)‐2,2,2‐trifluoroethane (5), was prepared via a multistep reaction sequence adapted from previously reported procedures. Monomer 5 polymerizes by free‐radical mediated thermal cyclodimerization to produce a crosslinked perfluorocyclobutyl (PFCB) polymer. Substituting CH3 for CF3 did not affect the polymerization kinetics as measured by differential scanning calorimetry. Surprisingly, the refractive index of poly5 (1.4931 at 1550 nm) is slightly higher than that measured for poly6 (1.4876 at 1550 nm) despite the significant increase in fluorine content. Compared to the CH3‐containing monomer 6, fluorinated analogue 5 exhibits increased thermal and thermal oxidative stability and thus we expected lower optical loss for long‐term high performance applications. Copolymerization with existing aryl trifluorovinyl ether monomers should allow access to new PFCB network copolymers with a tailored performance. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5292–5300, 2004

Beyond butadiene II: thermal isomerization of the [2 + 2] photodimer of an all-trans tetraene, (R)-4,4abeta,5,6,10a-hexahydro-10abeta-methyl-2(3H)-methyleneanthracene, to a 16-membered [8 + 8] cycle.

Enthalpies of stabilization of polyenyl radicals of increasing order previously obtained by thermal geometrical isomerization are applied to the ethylene-cyclobutane paradigm. Progressively lower enthalpies of activation for thermal cyclodimerization and its reverse, cycloreversion, are predicted and realized. Photochemical dimerization at -75 degrees C of the optically pure tetraene of the title (1) at the semicyclic double bond produces in the main only one (4-axx) of the three allowed cyclobutanes (4), to which the tentative configuration anti-exo,exo is assigned. Equilibration among the three cyclobutanes (4), a slower rearrangement to a thermodynamically considerably more stable, [8 + 8] cyclohexadecahexaene (16), and a surprisingly slow fragmentation to 1 are studied kinetically between -42.3 and -8.2 degrees C. Cycloreversion of the dimer 16 to monomer 1 occurs in the range 60.4-86.6 degrees C (DeltaH = 31.7 kcal mol(-1), DeltaS = +10.8 cal mol(-1) K(-1)). The ratio of the rates of stereomutation and cycloreversion is significantly larger in these 1,2-dihexatrienylcyclobutanes than in two less strongly stabilized, previously published examples. The possible extension of Doubleday's calculational finding of entropic control of products from cyclobutane is considered.

The First Synthesis of α-Methylene Isophosphindoline Oxide

Over the last decade the intramolecular palladium-catalyzed coupling of haloarenes and haloalkenes with alkenes has proven to be a particularly valuable route to a wide variety of the structurally demanding cyclic and polycyclic systems We wish now to demonstrate its successhl application to the synthesis of the first parent representative of the five-membered ring carbon-phosphorus heterocycles possessing exocyclic unsaturation, a class of compounds remaining to date practically unexplored The effected synthesis of the a-methylene isophosphindoline oxide I is delineated in the equation which reveals also the optimized catalytic system and the prerequisite reaction conditions Of those, the reaction temperature is the most crucial parameter as the desired product undergoes unexpectedly facile thermal cyclodimerization to the spiropolycyclic system 2 frequently even precluding the isolation of 1.

ChemInform Abstract: Thermal Cyclodimerization of Aliphatic Secondary C,N‐ Dilithioallylamine Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The spin-delocalization substituent parameter σ jj. Part 10. The spin-delocalizing abilities of the para-trifluorovinyl and para-acetoxy groups. synthesis of para-trifluorovinyl-, para-vinyland para-acetoxy- α,β,β-trifluorostyrenes

para-Trifluorovinyl α,β,β-trifluorostyrene ( 1-CF=CF 2 ), p-acetoxy α,β,β-trifluorostyrene ( 1-AcO) and p-vinyl α,β,β-trifluorostyrene ( 1-CH=CH 2 ) have been synthesized. The rate constants ( k) for the thermal cyclodimerization of 1-CF=CF 2 and 1-AcO have been measured over the temperature range 90–130 °C for 1-CF=CF 2 and 110–160 °C for 1-AcO. The σ mb polar substituent constants of the p-CF=CF 2, pCH=CH 2 and p-AcO groups calculated from the 19F NMR chemical shifts are: for p-CF=CF 2, 0.40; for p-CH=CH 2, 0.03; and for p-AcO, −0.14, and the σ JJ spin-delocalization substituent constants of the p-CF=CF 2 and b p-AcO groups are 0.86 and 0.35, respectively, i.e., the former is a highly effective spin-stabilizer while the latter is moderately effective. Owing to the occurrence of a small amount of side-reaction, the σ JJ value of the p-CH=CH 2 group could not be accurately measured, but it was very roughly estimated to be in the range of 0.50–0.66.

Thermal Cyclodimerization of Aliphatic Secondary C,N-Dilithioallylamine Derivatives.

beta-Nitrogen-functionalized vinylic organolithium compounds derived from secondary aliphatic allylamines have been found to undergo upon heating (reflux of THF) either a dimerization or a regio- and stereoselective cyclodimerization reaction affording diamino 1,4-dienes or cis-2,3-disubstituted 4-methylenepyrrolidines, respectively, according to reaction time. In contrast, the corresponding dianions derived from aromatic allylamines underwent protonation by the solvent under analogous thermal treatment. A mechanism accounting for all these results has been proposed, which involves a spontaneous beta-elimination of lithium hydride and an intramolecular nucleophilic cyclization by addition of a lithium amide to an alkene group as critical steps. In addition, experimental evidence is provided about the formation of 3-lithio-1-aza 1,3-dienes as intermediates in these unusual thermal transformations.

Perfluorocyclobutane aromatic ether polymers. II. Thermal/ oxidative stability and decomposition of a thermoset polymer

AbstractThe results of thermal and oxidative stability studies are reported for one perfluorocyclo‐butane aromatic ether thermoset polymer. The polymer was prepared from 1,1,1‐tris (4‐trifluorovinyloxyphenyl)ethane by the thermal cyclodimerization of the trifluorovinyl either functionality, resulting in a network polymer comprising alternating perfluorocy‐clobutane and aromatic either groups. The results of isothermal and dynamic thermal gravimetric analysis (TGA) studies are reported with kinetic approximations for de‐composition in nitrogen, along with FTIR studies of the oxidative process in air and TGA/mass spec determination of the gasses evolved from decomposition in air. Based on these results, thermal and oxidative decomposition mechanisms are proposed. © 1995 John Wiley & Sons, Inc.

The spin-delocalization substituent parameter σ ·JJ. 9. Cyclodimerization rates of para-methylsulfinyl and para-methylsulfonyl α,β,β-trifluorostyrenes

19F NMR data and rate constants for the thermal cyclodimerization of para-methylsulfinyl α,β,β-trifluorostyrene ( 1) and para-methylsulfonyl α,β,β-trifluorostyrene ( 2) have been measured. On the basis of these data, the σ mb and σ · JJ values for p-MeSO and p-MeSO 2 groups have been evaluated. Three methods for the calculation of the σ · JJ scale yielded the same set of σ · JJ constants.

The spin delocalization substituent parameter σ 6. The spin‐delocalizing abilities of the thiomethyl, cyclopropyl and t‐butyl groups. Synthesis of three substituted trifluorostyrenes

AbstractThree substituted α, β, β‐trifluorostyrenes (TFS's), i. e., p‐thiomethyltrifluorostyrene (4), p‐cyclopropyltrifluorostyrene (5) and p‐t‐butyltrifluorostyrene (6), have been synthesized. The rate constants (k2) of the thermal cyclodimerization of these compounds have been measured in the temperature range 120–160°C. The polar parameters σmb of these TFS's calculated from 19F NMR chemical shifts are: for p‐thiomethyl, ‐0.18; p‐cyclopropyl, ‐0.31 and p‐t‐butyl, ‐0.22. The spin delocalization substituent parameters σ′T (140°) of p‐thiomethyl, cyclopropyl and t‐butyl groups are 0.59, 0.27 and 0.30 respectively. Thus all of these groups act as electron‐donating groups which can also effectively stabilize a spin.

The spin delocalization substituent parameters σ: 3. The spin-delocalizing abilities of the acetyl and trimethylsilyl groups. Synthesis of four substituted trifluorostyrenes

Four substituted α, β, β-trifluorostyrenes (TFSs) namely, ptrimethylsilyltrifluorostyrene (1), p-acetyltrifluorostyrene ethylene ketal (2), p-acetyltrifluorostyrene (3) and p-phenoxytrifluorostyrene (4), have been synthesized. The rate constants (k2) of the thermal cyclodimerization of 1 and 3 have been measured in the temperature range 120—160°C. The polar parameters σP of the four TFSs calculated from 19F NMR chemical shifts are: for p-trimethylsilyl-1, 0.21; 1-ethylenedioxy-ethyl-, —0.01; p-acetyl-, 0.61 and p-phenoxy-,—0.47. The spin de-localization substituent parameters σ•T of p-trimethylsilyl and p-acetyl groups are 0.29 and 0.52 respectively. Thus both the p-trimethylsilyl and the p-acetyl groups act as electron-attracting groups which can also effectively stabilize a spin.

Chemistry of trifluorostyrenes and their dimmers: 3. Solvent effect on the kinetic parameters of the thermal cyclodimerization of α, β, β-trifluorostyrene1

Rate constants for the thermal cyclodimerization of α, β, β-trifluorostyrene (TFS) were determined in six solvents at 393°K. The products of this reaction were mixtures of roughly equal amounts of cis-trans isomers. The rate constants in 3 solvents, were calculated according to Arrhenius equation. In n-hexane, log A = 6.02±0.18, Ea= 19.5±0.3 kcal.mol−1; in glyme, logA = 5.31 ± 0.19, Ea= 18.0±0.3 kcal.mol−1; in methanol, IogA=4.93±0.13, Ea=17.1±0.3 kcal mol−1. All data are consistent with a stepwise radical mechanism, and our reaction in this solvent series obeys an isokinetic relationship, with β = 478°K.

ChemInform Abstract: CRYSTAL AND MOLECULAR STRUCTURE OF TRICARBONYL((1R*,4S*,4AS*,9AR*)‐1,4‐EPOXY‐2,3‐DIMETHYLIDENE‐1,2,3,4,4A,9,9A,10‐OCTAHYDROANTHRACENE)IRON

The thermal cyclodimerization of 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene assisted by Fe2 (CO)9 gives the title complex 1, a precursor for the synthesis of antitumoral anthracyclinones. The crystal structure of 1 has been determined by X-ray diffraction: a = 11.188 (1); c = 26.968 (3) A; space group tetragonal, P41212, Z = 8; R = 0.041; RW = 0.033. The tricarbonyliron group is in the exo-position and the coordination polyhedron is tetragonal pyramidal. The NMR coupling constants are well-related to the observed dihedral angles between the non-aromatic protons and now give a reliable criterion for assigning the stereochemistry of the metal in d8-complexes of 2,3-dimethylidene-7-oxanorbornane derivatives.

Crystal and Molecular Structure of Tricarbonyl‐[(1R*, 4S*, 4aS*, 9aR*)‐1,4‐epoxy‐2, 3‐dimethylidene‐1,2,3,4,4a,9,9a,10‐octahydroanthracene]iron

AbstractThe thermal cyclodimerization of 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene assisted by Fe2 (CO)9 gives the title complex 1, a precursor for the synthesis of antitumoral anthracyclinones. The crystal structure of 1 has been determined by X‐ray diffraction: a = 11.188 (1); c = 26.968 (3) Å; space group tetragonal, P41212, Z = 8; R = 0.041; RW = 0.033. The tricarbonyliron group is in the exo‐position and the coordination polyhedron is tetragonal pyramidal. The NMR coupling constants are well‐related to the observed dihedral angles between the non‐aromatic protons and now give a reliable criterion for assigning the stereochemistry of the metal in d8‐complexes of 2,3‐dimethylidene‐7‐oxanorbornane derivatives.

ChemInform Abstract: SOME THERMAL TRANSFORMATIONS OF 2‐CYCLOPROPYL‐ AND 2,3‐DICYCLOPROPYL‐1,3‐BUTADIENES

AbstractBei der Thermolyse von 2‐Cyclopropyl‐l ,3‐butadien (I) entsteht bis 200°C durch Dimerisierung ein Gemisch der Cyclohexenderivate (II)‐(IV).