Thiophenes thermal activation

We Finally note that the MTR model is a priori more appropriate to disordered materials. It is not expected to give good results with single crystal OFET, especially when the mobility becomes temperature-independent (see Section 14.6.1.2). However, it has recently been invoked in the case of poly thiophene [112], the mobility of which is also thermally activated. 

Photoinitiated Cationic Polymerization of Unusual Monomers Recently, novel monomers and macromonomers (Chart 11.12), namely, benzoxazines, monothiocarbonates, thiophene, and epoxy and vinyl ether functional polymers were reported to undergo photoinitiated cationic polymerization [2,118], Among them, benzoxazine monomers deserves a special attention as they yield thermosets with several excellent characteristics including heat resistance good flame retardance stable dielectric constants low water absorption and perfect dimensional stability. This type of thermosets is also obtained by thermally activated ring-opening polymerization at elevated temperatures without catalysts [19]. 

In previous articles we hypothesized the existence of a high temperature back reaction of stabilized organic products with thermally activated sulfur such as S radical) (Aizenshtat et al, 1995 Krein and Aizenshtat, 1995). To experimentally evaluate this possibility we reacted, under autoclave inert conditions at 300°C, a mixture of hydrocarbons with elemental sulfur. The products and their GC/MS identification were presented in Stoler (1990). A similar experiment was performed without detailed analysis of the products distribution by Baker and Reed (1929). Most of the material polymerizes. Only 15-20% could be extracted by organic solvents (e.g. hexane or methylene chloride). The sulfur isotopes data for all products show that no isotopic discrimination occurred in this experiment (Stoler et al, 2003). All sulfur-containing isolated and identified compounds produced are thiophenes with the structure ... 

Aminothiophenes and 3-aminobenzo[Z)]thiophene undergo thermal [2 + 2] cycloaddi-tion reactions with activated alkynes. The reactions are solvent dependent thus in non-polar solvents at -30 °C, 3-pyrrolidinothiophene adds to DMAD to give a [2 + 2] cycloadduct which is ultimately converted into a phthalic ester. In methanol, however, a tricyclic product is formed (Scheme 54) (81JOC424. ... 

Qi et al. studied perovskite systems obtained by partially replacing La with Ce at the A-site of LaNi03 for ATR of gasoline and its subrogate n-octane with or without thiophene additive. They found similar activities and mechanical and thermal stabilities with both pellet and monolith Lao.8Ceo.2Ni03 [73]. 

The mechanism of the cycloaddition process was partly clarified on the basis of experiments with acetylenic dithio derivatives 102, which were found to be thermally transformable to allenic isomers 103.149 The latter gave expected 2/7-thiopyrans 104 in 41 to 78% yields under triethylamine catalysis, whereas isomeric thiophenes 105 were formed in the presence of protic acids (Scheme 5). The activation energies for some of the processes were also measured.149... 

An enantioselective synthesis of (+)-estradiol has been accomplished from 1,3-dihy-drobenzo[c]thiophene 2,2-dioxide (306) by successive thermal S02-extrusion and cycloaddition (80HCA1703). Treatment of the optically active iodide (307) with two mole equivalents of the masked quinodimethane (306) in the presence of two mole equivalents of sodium hydride gave (308) as a 1 1 mixture of diastereoisomers. Thermolysis of this alkenic sulfone in 1,2,4-trichlorobenzene furnished the trans-anti-trans steroid (309) in 80% yield. Treatment of (309) with methyllithium gave the methyl ketone, which was subjected to a Baeyer-Villiger oxidation and then silyl ether-acetate cleavage to afford (-l-)-estradiol (310 Scheme 66). 

Smectite-type materials containing transition metal divalent cations (Ni2+, Co2, and Zn2+) in octahedral sheets were synthesized. The synthetic smectites were thermally stable and had large surface areas and high pore volumes after evacuation at 873 K. Catalytic activities of synthetic smectites were investigated. The Ni2 -containing smectites were active for the isomerization of 1-butene and the oligomerization of ethylene. The Co2+-containing smectites were active for the hydrodesulfurization of thiophene. 

Diels-Alder reactivity of thiophene and benzothiophene remains poorly understood. AMI semiempirical studies examining the activation of thiophene for this thermally allowed [4+2] cycloaddition process have shown that the usual synthesis approaches (use of highly reactive dienophiles, substitution on thiophene, increased reaction pressures) have only small effects on rate enhancement. However, use of the corresponding S-methylthiophenium salts, which have little aromaticity, should provide excellent activation for Diels-Alder reactions of thiophenes even with poor dienophiles such as ethylene <95JHC483>. This AMI approach has been applied to examine Diels-Alder reactions of benzo[6] and benzo[c]thiophenes the theoretical data agree with experimental results <95JCS(P1)1217>. 

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