Benzene/thiophene

Examples of the hydroquinone inclusion compounds (91,93) are those formed with HCl, H2S, SO2, CH OH, HCOOH, CH CN (but not with C2H 0H, CH COOH or any other nitrile), benzene, thiophene, CH, noble gases, and other substances that can fit and remain inside the 0.4 nm cavities of the host crystals. That is, clathration of hydroquinone is essentially physical in nature, not chemical. A less than stoichiometric ratio of the guest may result, indicating that not all void spaces are occupied during formation of the framework. Hydroquinone clathrates are very stable at atmospheric pressure and room temperature. Thermodynamic studies suggest them to be entropic in nature (88). 

With its sextet of 7T electrons, thiophene possesses the typical aromatic character of benzene and other similarly related heterocycles. Decreasing orders of aromaticity have been suggested to reflect the strength of this aromatic character benzene > thiophene > pyrrole > furan (9) and benzene > thiophene > selenophene > teUurophene > fuian (10). 

In summary, all estimates of resonance energies indicate a decrease in aromaticity in the sequence benzene > thiophene > pyrrole > furan. Similar sequences are also found for the benzo[6] and dibenzo analogues. A somewhat different sequence is found for the benzo[c] fused heterocycles with isoindole > benzo[c]thiophene > benzo[c]furan. As would be anticipated, the resonance energies for the benzo[c] heterocycles are substantially lower than those for their benzo[6] isomers. 

In summary, most of the presently available criteria point to an order of decreasing aromaticity of benzene > thiophene > selenophene pyrrole > tellurophene > furan. 

By shaking the recovered benzene-thiophene mixture with a solution of 5.5 g. of mercuric chloride, 10 g. of sodium acetate, and ro cc. of alcohol in 80 cc. of water, the unchanged thiophene is converted to the 2-chloromercurithiophene (containing a small amount of the dimercurichloride) from this the free thiophene can be obtained by treatment with hydrochloric acid. The recovered thiophene amounts to 2-2.5 g-... 

The order of aromaticity of these compounds is benzene > thiophene > pyrrole > fiiran, as calculated by an aromaticity index based on bond-distance measurements. This index has been calculated for five- and six-membered monocyclic and bicyclic heterocycles Bird, C.W. Tetrahedron, 1985, 41, 1409 1986, 42, 89 1987, 43, 4725. 

Virus replication comprises numerous biochemieal transformations that might provide suitable targets for antiviral therapy. The antiviral effect of thiosemicarbazones was first demonstrated by Hamre et al. [53, 54], who showed that p-aminobenzaldehyde-3-thiosemicarbazone and several of its derivatives were active against vaccinia virus in mice. These studies were extended to include thiosemicarbazones of isatin, benzene, thiophene, pyridine, and quinoline derivatives, which also showed activity against vaccinia-induced encephalitis. The nature of the aldehyde/ketone moiety was not as significant as the presence of the thiosemicarbazide side chain the latter was deemed essential for antiviral activity. 

Also as noted above any substituents present have little effect upon such oxidations. In 2,2 -methylenedifuran (118) the rings are attacked simultaneously giving a tetramethoxy derivative.297 Even the bulk of the fert-butyl group has little effect.298 The only marked substituent effect is that exerted by an aromatic (benzene, thiophene, furan) residue which, if directly attached at the 2-position, promotes elimination instead of the addition of another methoxy group. The net process then becomes one of arylation, as when 2-(2-thienyl)furan (119) is oxidized to 120.298 There are reports that acetyl and carboxy groups can be ejected during oxidation, but that ester groups are usually retained.287... 

Tellurophene, the most important member of chalcogenophenes, is a light yellow, bad smelling and toxic oil, rather stable in air. Its aromaticity follows the order benzene>thiophene>selenophene>tellurophene>furan." ... 

In a commercially useful reaction, sulfuric acid can be used to sulfonate thiophene at room temperature Benzene is not attacked under these conditions, and needs a reaction with oleum at 60 °C before it is sulfonated. Thiophene-2-sulfonic acid, formed in this way, dissolves in dilute alkali, allowing thiophene in coal tar distillate to be easily removed from benzene. Thiophene can be generated from its sulfonic acid by heating the latter in steam. 

Electrophilic substitution is much easier than in benzene. Thiophene reacts about as readily as mesitylene pyrrole and furan react as readily as phenol or even resorcinol. Electrophilic substitution of heterocycles has been reviewed (86HC(44/2)l), (90AHC(47)87), and the following conclusions were reached ... 

Not all clathrates are hydrates. Other well-known examples have host lattices formed from hydrogen bonded aggregates of hydroquinone, phenol, and similar organic compounds. Non-hydrogen bonded host structures are also known. One example is a cyclotriphosphazene. (C6H402PN). that traps molecules such as benzene in tunnels in the crystal.2 In addition, coordination polymers are formed by ambidentate ligands, such as CN and SCN, which coordinate to metal ions at both ends (Chapter 12). Perhaps the best known of this type of compound is the series of Ni(CN)2NHj M compounds, where M may be benzene, thiophene, furon. pyrrole, aniline, or phenol. 

The variety of aromaticity indices based upon structural or magnetic molecular properties along with their values for pyrrole, the other five-membered heterocycles, benzene and cyclopentadiene are summarized in Table 31 in Section 3.01.5.2. Of these indices, the majority predict the aromaticity order benzene >thiophen>pyrrole >furan, in agreement with resonance energy calculations (Section 3.01.5.2). 

Benzene (thiophene-free) is refluxed for several hours with pelletized sodium and then distilled directly from the metal, rejecting a small fore-run and the residue in the pot... 

Another particularly interesting class of amine complex that has had relatively little recent attentionistheclathrateseriesM(X)2(A) Y,whereM = Ni11 orCdu,X = CN orNCS, A = NH3 or KNHjfCHj NHj) and Y is the host, e.g. benzene, thiophene, furan, pyrrole, aniline or phenol.44,45... 

C. Aromatic Hydrocarbons. The methods listed for saturated hydrocarbons may be used with benzene. Thiophene and similar sulfur-containing impurities are removed by sulfuric acid washes. Very-high-purity benzene may be prepared by fractional crystallization from ethanol followed by distillation. 

Benzene (thiophene-free, 99+%, 900 mL) was obtained from Aldrich Chemical Company, Inc., and washed with concentrated sulfuric acid (5 x 100 mL), distilled water (100 mL), aqueous 2% sodium hydroxide solution (100 mL), distilled water (100 mL), and dried over anhydrous magnesium sulfate. It was then allowed to reflux over calcium hydride for 24 hr. The checkers found that the benzene only needed to be distilled from calcium hydride. 

Leonid Belen kii was born in Moscow, and he graduated from M. V. Lomonosov Moscow State University in 1953 with Professor A. P. Terentiev as supervisor in organic chemistry. Since 1955, he has worked as junior, senior (since 1966), and leading scientist (since 1988) at N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, where he obtained his Ph.D. degree (1963) under the direction of Professor Ya. L. Gol dfarb and his Degree of Dr. Chem. Sci. (1974) and rank of Professor in Chemistry (1991). His scientific interests include all aspects of chemistry of heterocyclic and aromatic compounds, particularly electrophilic substitution in benzene, thiophene, furan, and azole series as well as organosulfur chemistry. 

To sum up, although each criterion has limits of validity, nevertheless all the criteria agree in establishing the following order of decreasing ground state aromaticities benzene > thiophene > pyrrole > furan. 

On the basis of these qualitative criteria the following order of reactivity was universally established benzene[Pg.263]

The main reaction i.e, benzene hydrogenation occuring inside porous Ni-catalyst pellets is accompanied by poisoning reaction in which the thiophene presented in the feed stream reacts irtevcrsibly with the catalytic active sites. An analysis was made assuming isothermal behaviour [7], the same effective diffusivity for reactant and poison and that the steady-state continuity equation represents a good approximation at all times [8,9]. Under these conditions the mass balances for benzene, thiophene and catalyst activity are... 

Rate coefficients k(E) have been obtained in this way for decompositions of benzene, thiophene and benzonitrile over an energy range of some electron volts. These were the first direct experimental determinations of rate coefficients, k(E), for ionic decompositions. Moreover, a range of energies was accessible, since the times at which rates were measured extended over the 3 orders of magnitude, which contrasts with the later PIPECO experiments in which rates have been measured only in the microsecond time-frame. 

The 77Se NMR spectral data for five isoselenazoles ortho fused with benzene, thiophene and selenophene (2, 7-10) are reported in Table 1 (80BSB773). 

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