T-butyl Vinyl Ether Research Articles

Mesomeric Acceleration Counters Slow Initiation of Ruthenium-CAAC Catalysts for Olefin Metathesis (CAAC = Cyclic (Alkyl)(Amino) Carbene).

Ruthenium catalysts bearing cyclic (alkyl)(amino)carbene (CAAC) ligands can attain very high productivities in olefin metathesis, owing to their resistance to unimolecular decomposition. Because the propagating methylidene species RuCl2(CAAC)(=CH2) is extremely susceptible to bimolecular decomposition, however, turnover numbers in the metathesis of terminal olefins are highly sensitive to catalyst concentration, and hence loadings. Understanding how, why, and how rapidly the CAAC complexes partition between the precatalyst and the active species is thus critical. Examined in a dual experimental-computational study are the rates and basis of initiation for phosphine-free catalysts containing the leading CAAC ligand C1 Ph , in which a CMePh group α to the carbene carbon helps retard degradation. The Hoveyda-class complex HC1 Ph (RuCl2(L)(=CHAr), where L = C1 Ph , Ar = C6H3-2-O i Pr-5-R; R = H) is compared with its nitro-Grela analogue (nG-C1 Ph ; R = NO2) and the classic Hoveyda catalyst HII (L = H2IMes; R = H). t-Butyl vinyl ether (tBuVE) was employed as substrate, to probe the reactivity of these catalysts toward olefins of realistic bulk. Initiation is ca. 100× slower for HC1 Ph than HII in C6D6, or 44× slower in CDCl3. The rate-limiting step for the CAAC catalyst is cycloaddition; for HII, it is tBuVE binding. Initiation is 10-13× faster for nG-C1 Ph than HC1 Ph in either solvent. DFT analysis reveals that this rate acceleration originates in an overlooked role of the nitro group. Rather than weakening the Ru-ether bond, as widely presumed, the NO2 group accelerates the ensuing, rate-limiting cycloaddition step. Faster reaction is caused by long-range mesomeric effects that modulate key bond orders and Ru-ligand distances, and thereby reduce the trans effect between the carbene and the trans-bound alkene in the transition state for cycloaddition. Mesomeric acceleration may plausibly be introduced via any of the ligands present, and hence offers a powerful, tunable control element for catalyst design.

Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers

Abstract. Formation of secondary organic aerosol has been observed in the gas phase ozonolysis of a series of enol ethers, among them several alkyl vinyl ethers (AVE, ROCH=CH2), such as ethyl, propyl, n-butyl, iso-butyl, t-butyl vinyl ether, and ethyl propenyl ether (EPE, C2H5OCH=CHCH3). The ozonolysis has been studied in a 570 l spherical glass reactor at ambient pressure (730 Torr) and room temperature (296 K). Gas phase reaction products were investigated by in-situ FTIR spectroscopy, and secondary organic aerosol (SOA) formation was monitored by a scanning mobility particle sizer (SMPS). The chemical composition of the formed SOA was analysed by a hybrid mass spectrometer using electrospray ionization (ESI). The main stable gas phase reaction product is the respective alkyl formate ROC(O)H, formed with yields of 60 to 80%, implying that similar yields of the corresponding excited Criegee Intermediates (CI) CH2O2 for the AVE and CH3CHO2 for EPE are generated. Measured SOA yields are between 2 to 4% for all enol ethers. Furthermore, SOA formation is strongly reduced or suppressed by the presence of an excess of formic acid, which acts as an efficient CI scavenger. Chemical analysis of the formed SOA by ESI(+)/MS-TOF allows to identify oligomeric compounds in the mass range 200 to 800 u as its major constituents. Repetitive chain units are identified as CH2O2 (mass 46) for the AVE and C2H4O2 (mass 60) for EPE and thus have the same chemical compositions as the respective major Criegee Intermediates formed during ozonolysis of these ethers. The oligomeric structure and chain unit identity are confirmed by HPLC/ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF experiments, whereby successive and systematic loss of a fragment with mass 46 for the AVE (and mass 60 for EPE) is observed. It is proposed that the oligomer has the following basic structure of an oligoperoxide, -[CH(R)-O-O]n-, where R=H for the AVE and R=CH3 for the EPE. Oligoperoxide formation is thus suggested to be another, so far unknown reaction of stabilized Criegee Intermediates in the gas phase ozonolysis of oxygen-containing alkenes leading to SOA formation.

Polymerization of t-Butyl Vinyl Ether Mediated by an Aluminum Lewis Acid–TrF System and Its Complex Structure–Tacticity Correlation

Abstract A variety of aluminum (aryloxide)s were used with triphenylmethyl fluoride (TrF) initiator for the isoselective cationic polymerization of t-butyl vinyl ether. This contribution discusses the relationship between polymer tacticity and counteranion structure, which changed according to the bulkiness, strength and chirality of the Lewis acid combined with TrF so as to make the ionic pair more interactive in the polymerization process. Newly developed organoaluminum activators, 15 and 22, showed mm = 55–57%, which is a more than 10% increase in mm compared with achiral aluminum compounds.

Living cationic polymerization of vinyl ethers in the presence of iodomethyl methyl ether and zinc iodide

Living cationic polymerization behaviors of isobutyl vinyl ethers (IBVE), initiated by iodomethyl methyl ether (IMME)/zinc iodide (ZnI2) have been investigated. The polymerization was carried out at 0, −15, and −30°C in toluene. It was found that the rate of polymerization increased as the IMME concentration increased and decreased as temperature decreased. 100% conversion was always achieved without exception. Furthermore, the number-average molecular weight\((\bar M_n )\) of polymers increased in direct proportion to monomer conversion. The molecular weights of polymers were in good agreement with the theoretical values, calculated on the basis that one polymer chain was formed by one IMME molecule and the values of polydispersity index are always less than 1.2, revealing the living nature. The living nature was also confirmed by synthesis of poly(IBVE-b-TBVE) by subsequent monomer addition of t-butyl vinyl ether (TBVE).

Outgassing Issues in Acetal Resist Design.

The outgassing issues that have long plagued conventional acetal resist designs are shown to be significantly mitigated depending on the structure of the acetal-blocked polymer. Resists formulated with acetal-blocked polymers based on low molecular weight vinyl ethers such as ethyl vinyl ether and t-butyl vinyl ether deblock during exposure resulting in considerable outgassing inside the stepper and attendant film shrinkage. By modifying the acetal structure, deblocking can be completely prevented during exposure, in which case the resist requires post-exposure baking to initiate the deblocking reaction as with conventional high activation energy systems. Such systems also show superior plasma etch resistance compared to conventional lower molecular weight acetals.

Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals

A small quantity of 10-methylphenothiazine cation radical (MPT .+ ), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. 1 H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D 2 O indicated that electron transfer from the monomer to MPT .+ was involved in the initiation step

On the photolysis of acylphosphine oxides: 1. Laser flash photolysis studies with 2,4,6-trimethylbenzoyldiphenylphosphine oxide

2,4,6-trimethylbenzoyldiphenylphosphine oxide (TMDPO) was irradiated in dilute solutions of benzene, methanol and dichloromethane with 20 ns flashes of 347 nm light. By optical absorption measurements, a transient spectrum with a maximum at about 330 nm detected at the end of the flash was ascribed to the diphenyl phosphonyl radical ( Ph) 2 P ̇ =0 . This radical is formed by the reaction. Evidence was obtained for fragment radicals being formed, to some extent at least, from triplet states. Both the singlet and the triplet lifetimes were estimated as τ < 1 ns. The singlet energy was estimated as 288 kJ mol −1. In the absence of radical scavengers ( Ph) 2 P ̇ =0 radicals undergo a self reaction (2k 2≈5 × 10 9 l mol −1 s −1). Rather high rate constants (in l mol −1 s −1) were found for reactions of ( Ph) 2 P ̇ =0 radicals with oletinic compounds: 6.0 × 10 7 (styrene), 6.0 × 10 7 (methyl methacrylate), 2.3 × 10 7 (methacrylate), 1.8 × 10 7 (acrylonitrile), 5.0 × 10 6 (t-butyl vinyl ether), 2.0 × 10 6 (vinyl acetate). The quantum yield of radical formation is ø(-TMDPO) = 0.5 to 0.7. These results clearly show why TMDPO is highly appropriate to be applied as an initiator for photocuring of coatings of various compositions.

C-13 NMR Spectra and Spin-Lattice Relaxation Times of Poly(alkyl vinyl ether)s

13C NMR spectra of isotactic-rich poly(alkyl vinyl ether)s were measured in toluene-d8 at 110°C, with some improvements on peak separation. The 13C spin-lattice relaxation times (T1’s) for syndiotactic sequences were consistently longer than those for isotactic ones, in contrast to the case of polypropylene and polymethacrylates, in which the T1’s for isotactic sequences are longer than those for syndiotactic sequences. The nuclear Overhauser enhancement factors for the polymers of methyl and t-butyl vinyl ethers were close to the theoretical maximum. These results indicate higher flexibility of the syndiotactic sequences in poly(alkyl vinyl ether)s.

The mechanisms of thermal eliminations. Part 12. Relative rates of pyrolysis of ethyl, isopropyl, t-butyl, and n-butyl vinyl ethers: rate spread as an index of elimination mechanisms

Rate coefficients have been measured between 594.5 and 681.0 K for pyrolysis of ethyl, isopropy, t-butyl, and n-butyl vinyl ethers. The relative rates of elimination at 600 K are : 1.0, 10.0, 178, and 1.52, the Arrhenius data [E/kJ mol–1, log (A/s–1)] being: ethyl, 185.92, 11.826; isopropyl, 182.51, 12.527; t-butyl, 164.05, 12.169; n-butyl, 177.64, 11.284. These results show that the literature data for t-butyl vinyl ether elimination are considerably in error, confirming the prediction based on statistical mechanics. The relative primary, secondary, and tertiary elimination rates are consistent with those obtained from a range of thermal eliminations, whereas the relative rates based on the literature data are not. Analysis of the relative primary, secondary, and tertiary elimination rates from this and other reactions permits prediction of rates for secondary and tertiary compounds as yet unmeasured, and also suggests that some literature data may be in error through the incursion of side reactions. A β-ethyl group increases the rate of elimination 2,3-fold per β-hydrogen at 600 K (cf. 1.62 for acetates) and may likewise be due to steric acceleration, though the possibility of electron acceptance by alkyl groups in the gas-phase cannot be excluded. The product distribution in pyrolysis of 1-methylpropylvinyl ether is shown to be accounted for by the nature of the transition state. Vinyl ethers do not pyrolyse 50° below the corresponding esters as recently claimed. Tertiary vinyl ethers are for example less reactive than tertiary esters.

The Steric Course of the Cationic Polymerization of Vinyl and Related Monomers. The Counterion Effect

Abstract Polymerization with many triphenylmethyl salts was conducted for α-methylstyrene, isobutyl vinyl ether, t-butyl vinyl ether, and spiro[2,4]hepta-4,6-diene (SHD). The variation of polymer structure (the isotactic unit content for the first three monomer systems and the amount of the 1,4-addition structure for SHD) showed fairly simple correlations with the counteranion size. The results can be interpreted in terms of the tightness of the propagating ion pair within the framework of a theory of the cationic propagation which had been proposed. When the counteranion radius was greater than 3.5 A, the counteranion exerts a parallel influence on the tightness of the growing ion pair without regard to the monomer structure. However, in the case of smaller counterions, the tightness appears to be determined by the relative sizes of counteranion and monomer. The penta-coordinated counteranions gave rise to the polymer structure which would arise from tighter ion pairs than expected from their sizes alone...

Reactivity of Trimethylsilyl Vinyl Ether in Cationic Copolymerization and Some Related Reactions

In order to ascertain the relative reactivity of trimethylsilyl vinyl ether among vinyl ethers, cationic copolymerizations were carried out. Relative rates in bromine addition to the double bonds of vinyl ethers and relative stabilities of the iodine complexes were also studied as related reactions.n-, i-, and t-Butyl vinyl ethers were increasingly reactive in this order in all of these reactions. The reactivity of trimethylsilyl vinyl ether was between the i- and t-butyl vinyl ethers in both the copolymerization and iodine-complex formations, and at its lowest in the bromine addition.The reactivities of trimethylsilyl vinyl ether are rationalized by considering the contribution of the inductive effect of the trimethylsilyl group as well as the various degrees of participation of silicon 3d orbital in stabilizing the transition states.

Preparation of Vinyl Ethers by Transetherification in the Presence of Molecular Sieves

Abstract The interchange reaction: CH3OCH=CH2+ROH \ightleftarrows ROCH=CH2+CH3OH, which is catalyzed by Hg(OAc)2, has been studied. It was found that the equilibrium could be smoothly shifted toward the product by the selective absorption of the produced methanol on molecular sieves of the type 4A (MS-4A) and that the yield of the desired vinyl ether could be increased. According to this method, we prepared various vinyl ethers, including ethyl, isopropyl, isobutyl, t-butyl vinyl ether, and benzyl vinyl ethers. The yields of the alkyl vinyl ethers decrease as their alkyl groups become more electron-donating. The effects of the reaction conditions and the pretreatment of the molecular sieves have been investigated.

A Convenient Method for the Preparation of Poly (Vinyl Alcohol) from Poly(t-Butyl Vinyl Ether)

A Convenient Method for the Preparation of Poly (Vinyl Alcohol) from Poly(<i>t</i>-Butyl Vinyl Ether)

The thermal decomposition of alkyl vinyl ethers. Part II. The inhibited decompositions of t-butyl, isopropyl, and 2-chloroethyl vinyl ethers

The kinetics of the thermal decompositions of t-butyl, isopropyl and 2-chloroethyl vinyl ethers into predominantly olefins and acetaldehyde in a seasoned vessel have been studied in a static system. These reactions are homogeneous and essentially unimolecular; they obey first-order kinetics in their early stages. The rate constants are: t-butyl vinyl ether (215–324°), k= 1010·86 exp(–36,184/RT); isopropyl vinyl ether (311·0–375·0°), k= 1012·12 exp(–42,557/RT); 2-chloroethyl vinyl ether (353·0–424·0°), k= 1011·49 exp(–44,752/RT) sec.–1.

NMR spectra of alkyl vinyl ether and its structures

The NMR spectra of some vinyl ethers at 16.2 and 40.0 MHz have been obtained by Feeney at room temperature (1) and correlated with the degree of resonance contributions in vinyl ethers (2). In this work we have measured the NMR spectra of alkyl vinyl ethers at various temperatures using 100 MHz spectrometer and studied on the resonance and the molecular conformation in alkyl vinyl ether. The spectral parameters of vinyl ethers are given in Table I, in which the vinyl ethers are arranged in increasing order of their reactivities in cationic polymerization (3) from top to the bottom. This order is generally in accordance with the increasing order of bulkiness of alkyl group in alkyl vinyl ether. From top to the bottom in this Table the geminal coupling constant of vinyl ether, J AB, generally increases and the chemical shifts of HA and HB, 6A and 6B, are to lower field and the difference, 6 -6 A B' increases. It has been suggested that alkyl vinyl ethers may take a following resonance form (1,4). ?H2-CH=&R Pople (5) has shown that the coupling constant between geminal hydrogen atoms increases as the s-character of the carbon atom between them increases. So the JAB value of alkyl vinyl ether can be used as an indication of the degree of resonance. Thus the contributions of the resonance form are greatest in methyl vinyl ether and least in t-butyl vinyl ether. On the other hand, the resonance in alkyl vinyl ether must lead to a reduction in the olefinic character of the vinyl group and consequently the terminal methylene protons will become more equivalent. The values of AA, 6B and hA-6B shows that the resonance contribution in alkyl vinyl ether decreases from top to the bottom in Table 1, that is, in the increasing order of the bulkiness of its