Phenes

Supplement (combined with Volumes XVIII and XIX) XVII, 2nd 1934 2359-3031 Hydroxy compounds Furfuryl alcohol, 112. Carbonyl compounds Butyrolactone, 234. Furfural, 272. 2-Aoetyl-thio-phene, 287. Xanfhone, 366. Succinic anhydride, 404. Phthalio anhydride, 469. 

The cross-coupling of aromatic and heteroaromatic rings has been carried out extensively[555]. Tin compounds of heterocycles such as oxazo-lines[556,557], thiophene[558,559], furans[558], pyridines[558], and seleno-phenes [560] can be coupled with aryl halides. The syntheses of the phenylo.xazoline 691[552], dithiophenopyridine 692[56l] and 3-(2-pyridyl)qui-noline 693[562] are typical examples. 

Analogous compounds derived by fusion of a benzene ring to a pyrrole furan or thio phene nucleus are called indole benzofuran and benzothiophene... 

An old name for benzene was phene and its hydroxyl derivative came to be called phe nol This like many other entrenched common names is an acceptable lUPAC name Likewise o m and p cresol are acceptable names for the various ring substituted hydroxyl derivatives of toluene More highly substituted compounds are named as deriv atives of phenol Numbering of the ring begins at the hydroxyl substituted carbon and proceeds m the direction that gives the lower number to the next substituted carbon Sub stituents are cited m alphabetical order... 

Halogens react with benzo[6]furan by an addition-elimination mechanism to give 2- and 3-substituted products (76JCS(P2)266). Treatment of benzo[6]thiophene with chlorine or bromine in acetic acid gives predominantly 3-substituted products (71JCS(B)79). 2,2,3,3,4,5,6,7-Octachloro-2,3-dihydrobenzothiophene is obtained when benzo[6]thio-phene is treated with chlorine in the presence of 1 mole of iodine (80JOC2l5l). 

JOC1537). The mechanisms of these transformations may involve homolytic or heterolytic C —S bond fission. A sulfur-walk mechanism has been proposed to account for isomerization or automerization of Dewar thiophenes and their 5-oxides e.g. 31 in Scheme 17) (76JA4325). Calculations show that a symmetrical pyramidal intermediate with the sulfur atom centered over the plane of the four carbon atoms is unlikely <79JOU140l). Reactions which may be mechanistically similar to that shown in Scheme 18 are the thermal isomerization of thiirane (32 Scheme 19) (70CB949) and the rearrangement of (6) to a benzothio-phene (80JOC4366). 

Figure 1 Plot of weathering ratio (C3-dibenzo thiophenes C3-ehrysenes) versus souree ratio (C3-dibenzothio-phenes C3-phenanthrenes) for fresh and degraded oil samples from three different erude oil spills (Reprinted with permission from Environ. Sci. Technol, 30, 2332. 1996 Ameriean Chemieal Soeiety)...

C4H6 1-BUTYNE (ETHYL- 164.525 1.1892E-01 2.1726E-05 202.09 PHENE ... 

The —I—M 3-substituted thiophenes in alcohol show only one band, and, as is found in the 2-isomer, this is displaced (with increased extinction) toward longer wavelength with increasing conjugating power of the substituent. It is probable that this is the displaced 235-m/A band of thiophene, since the spectra of 3-acetylthio-phene and 3-cyanothiophene also show a primary band at about 225 mju, in hexane solution. ... 

Thiophenes substituted with groups such as alkyl, halogens, OCH3, and SCH3 show small but characteristic differences between 2- and 3-substituted compounds. In these cases, however, it is the 2-isomer which shows the less complex spectrum. Thus, 2-substituted alkylthio-phenes and halothiophenes show a single band with greater extinction than the 3-isomers whose spectra exhibit two peaks in a broadened absorption band. These differences are also present in the spectra of 2,5- and 3,4-dihalosubstituted compounds. In 2-substituted thiophenes, the intensity of the band varies inversely as the electronega-... 

Dichlorothiophene has become easily available through chlorination and dehydrochlorination of tetrahydrothiophened Another example of the aromatization of tetrahydrothiophene derivatives is the preparation of 3-substituted thiophenes by the reaction of 3-ketotetrahydrothiophene with Grignard reagents followed by the aromatization of the intermediate dihydrothiophene. Recent gas chromatographic analysis showed, however, that 2,3-dichlorothio-phene is the main product from the dehydrochlorination of tetra-chlorotetrahydrothiophene. 

The ease of formation of the thiophene ring is also evident from the fruitless attempts to prepare 3,4-dimethylene tetrahydrothio-phene, which only lead to the formation of 3,4-dimethylthio-phene. 

Finally, certain 3-substituted compounds can be prepared by utilizing the - meta) directing powet (cf. Section IV,B) of some groups in the 2-position which afterward can be removed. 3-Nitrothiophene is prepared by nitration of 2-thiophenesulfonyl chloride and by removal of the sulfonic acid group of the 4-nitro-2-sulfonyl chloride formed with superheated steam. Another approach to 3-nitrothio-phene is to nitrate 2-cyanothiophene, separate the 4-nitro-2-cyano-thiophene from the 5-isomer, hydrolyze, and decarboxylate. A final method of preparation of 3-nitrothiophene is by simultaneous de-bromination and decarboxylation of 5-bromo-4-nitro-2-thiophene-carboxylic acid obtained through the nitration of methyl 5-bromo-2-thiophenecarboxylate. 

In the reactions of 2,5-disubstituted thiophenes elimination of an a-substituent occurs to a much greater extent than in the benzene series. The Friedel-Crafts acetylation of 5-bromo-2-ethylthiophene in the presence of SnCE gives 2-ethyl-5-acetyIthiophene. Elimination of an a-bromine occurs also in the chloromethylation of 2,5-di-bromothiophene, leading to a mixture of 2-bromo-5-chloromethyIthio-phene and 2,5-dibromo-3-chloromethyIthiophene. Bromine atoms at both the and -position are exchanged for chlorine in the... 

When both a-positions are blocked, the highly specific reactivity toward organolithium compounds disappears and metalation depends on the kind of a-substituents present. Thus whereas 2,5-dimethylthio-phene is not metalated at all, 2-methoxy-5-methylthiophene is metalated in the 3-position, similar to the known ortho metalation of anisole. On the other hand, 5-methyl-2-methylthiothiophene is also metalated (in low yield) in the 3-position, in contrast to thioanisole... 

This is of great preparative importance as the Grig-nard reagent of 3-bromosubstituted thiophenes and the dibromothio-phenes can be obtained only by the entrainment method and with inferior The mechanism of the entrainment reaction... 

Dinitro-2-hydroxythiophene and 3-nitro-5-acetyl-2-hydroxythio-phene have been obtained from nitrochlorothiophenes through reaction with sodium formate in methanol. These compounds were colorless crystalline substances which decomposed with evolution of nitrogen oxides and formation of a dark resin even at —20°C. They gave, however, stable, colored, sodium salts, with ionization constants of the... 

Most aminothiophenes are prepared by the reduction of nitrothio-phenes. Aminothiophenes or their derivatives have also been obtained through the Hofmann rearrangement of the acid amides, which, however, fails with 2-thenamide, in contrast to the 3-isomer. The Beckmann rearrangement of the oxime of 2-acetylthiophene has been applied successfully to the preparation of 2-acetamidothiophene. The free aminothiophenes are very unstable compounds and it has not been possible to distil 3-aminothiophene. They are best stored as the stannic-chloride double salts and give stable acetyl derivatives. 

The Grignard reagent from 2-thenyl chloride can be obtained by the use of the "cyclic reactor.However, rearrangement occurs in its reaction with carbon dioxide, ethyl chlorocarbonate, acetyl chloride, formaldehyde, and ethylene oxide to 3-substituted 2-methylthio-phenes, Only in the case of carbon dioxide has the normal product also been isolated. 

Thiophenealdehyde has been used in the reductive alkylation of 2-aminopyridine and 2-aminopyrimidine. 2-Arylamino-4- (2-thienyl )thiazoles have been prepared by the reaction of 2-acetylthio-phene with A-arylthioureas in the presence of iodine, ... 

The base-catalyzed tautomerization of 4-methyl-4//-cyclopenta[c]thio-phenes 193 to the corresponding 6-methyl derivative 194 has been investigated quantitatively. Second-order rate constants and activation parameters have been determined (75CS42). 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

The System described in the previous section has been extended with a sulfur chemiluminescence detector (SCO) for the detection of Sulfur compounds (32). The separated fractions were thiols + sulfides + thiophenes (as one group), benzothio-phenes, dibenzothiophenes and benzonaphtho-thiophenes. These four groups have been subsequently injected on-line into and separated by the GC unit. Again, no overlap between these groups has been detected, as can be seen from Figure 14.20, in which the total sulfur compounds are shown and from Figure 14.21 in which the separated dibenzothiophenes fraction is presented. The lower limit of detection of this method proved to be 1 ppm (mg kg ) sulfur per compound. 

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