2- Alkyl-4- thiophenes formation

The oxidation of thiophene and its derivatives with H202 was studied using a Ti-Beta molecular sieve. The oxidation product is very dependent from the aromaticity of model compounds. The thiophene oxidation product was mostly sulfates and the benzothiophene oxidation product was benzothiophene sulfone. Oxidation of mono and di-alkyl thiophenes also produced sulfates and sulfones. The diffusivity and aromaticity of the relevant sulfur compounds, intermediates and stable product, as well as the proposed new mechanism of oxidation will be discussed. This proposed new reaction pathway is different from current literature, which reports the formation of sulfones as a stable oxidation product. 

Figure 5 summarizes, in tabular form, the products of electrophilic substitution of various alkylated thiophenes. Note that in the case of 3-alkylated thiophenes a mixture of products may be obtained. The 2,3-isomer is the favoured product but steric effects may play a role here resulting in the formation of the 2,4-isomer. It should be mentioned in passing that under certain special conditions it is possible to obtain the unfavoured electrophilic substitution products (22). 

In field-effect transistors based on the thin films of poly(3-alkyl)thiophene derivatives, high field-effect mobility has been observed because of the formation of crystal-like grains [116]. The mobility depends strongly upon the crystallinity of the thin films. Introduction of liquid crystallinity into conjugated polymers is expected to be effective for enhancing microscopic crystallization of conjugated polymers to increase their carrier mobilities. It can also cause anisotropy in various physical properties if macroscopic molecular alignment is achieved. 

The use of HOPG substrates permits the formation of superstructures of alkylated thiophenes at the liquid-graphite interface by self-assembly, due to the absence of strong covalent interactions between the molecules and the substrate [33]. The choice of the relatively inert HOPG substrate is also beneficial because coniamination from the ambient atmosphere is limited and to investigate the correlation between the 2D and 3D structures of the molecules. 

The influence of polar groups on the formation of SAMNs of oligothiophenes has been investigated since the early STM studies of thiophene-based materials. In particular, self-assembly of fi-alkylated thiophenes substituted with formyl groups (lla-b) (deposited from a dodecane solution) was studied on graphite [43]. 

This facile and efficient thiophene formation can be rationahzed by primary S-alkylation of 33 to give the iminium cation 35 followed by deprotonation (HBr ehmination) to the ketene-S,N-acetal 36, which cyclizes by intramolecular enamine addition to the carbonyl group (36->-37) intermediate 37 aromatizes to the products 34 by H2O elimination. Thiomorpholides (33) are easily obtained by Willgerodt-Kindler reaction of acetophenones with sulfur/morphoHne [81]. 

The preparation of HT regioselective thiophene polymers results in an improvement of their electroconductivity, nonlinear optical and magnetic properties. Improved selectivity of the reaction of Zn with 2,5-dibromo-3-alkyl thiophenes was achieved by performing the reaction at -78 C and warming to 0 C (equation 81) (226). The reaction of 3-alkyl-2-bromo-5-iodothiophene with Zn at 0 C resulted in the quantitative formation of 3-alkyl-2-bromo-5-(iodozincio)thiophene (equation 82). 

The principal electrophiles to attack ring sulfur are either oxidants or alkylating reagents. Thiophene sulfoxide and sulfone formation is discussed in Section 3.02.2.6. Alkylating agents capable of forming thiophenium salts include trimethyloxonium tetrafluoroborate (MeaO BF ) and alkyl fluorosulfonates (ROSO2F). The salts e.g. 87) are conveniently isolated as hexafluorophosphates (88). 

The key intermediate 21 is in principle accessible in any of several ways. Thus reaction of thiophenecarbox-aldehyde with amninoacetal would lead to the Schiff base 20 treatment with acid would result in formation of the fused thiophene-pyridine ring (21). Alkylation of that intermediate with benzyl chloride gives the corresponding ternary imini urn salt 23. Treatment with sodium borohydride leads to reduction of the quinolinium ring and thus formation of ticlopidine (24). ... 

The thiophene synthesis described herein is related to the synthesis in solution reported by Laliberte, and Medawar4 but differs in some aspects from the procedure in homogeneous phase. Laliberte and Medawar succeeded in obtaining aminothio-phenes in a one-pot reaction from acceptor-substituted acetonitriles, isothiocyanates, a-haloketones, and sodium ethoxide. In contrast to their procedure, solid-phase S-alkylation of the intermediate thioamides under basic conditions led to the formation of product mixtures. We obtained pure aminothio-phenes only when conducting the S-alkylation under neutral or slightly acidic conditions. 

Alkyl-3-cyano-4-hydroxythiophenes 625 were obtained from the reaction of 2,3-allenenitriles 610 with mercaptoacetates 622. The presence of the ester group leads to the formation of cyclic ketones 623, which undergo migration of the C=C and C=0 bonds to form thiophenes 625 [276]. 

Challenger and Harrison found both thienothiophene 1 and its isomer 2 in the products of the reaction between acetylene and sulfur. To identify these compounds, Challenger et developed syntheses of unsubstituted and 2-alkyl-substituted thieno[3,2-f>]thiophene (2) from thiophene derivatives. Cyclization of (3-thienylthio)acetic acid in the presence of sulfuric acid gave 2,3-dihydrothieno[3,2-6]thiophen-3-one (22) (R = H) in 14% yield reducing the latter with lithium aluminum hydride resulted in thienothiophene (2) formation in 80% yield [Eq. (9)]. Similarly 2-methyl- and 2-ethyl-2,3-dihydrothieno[3,2-/>]thiophen-3-one were obtained from a-(3-thienylthio)propionic and a-(3-tWenylthio)-butyric acids in 30% and 27% yields, respectively their reduction yielded 2-methyl (32%) and 2-ethylthieno[3,2-6]thiophenes (52%). The parent acids were prepared from 3-mercaptothiophene. ... 

From the preceding discussion, it can be seen that the mathematical description of the chemical transformations involved in product formation can be extremely difficult. However, knowledge of the response of HDS reaction rates to different kinds of feed components and byproducts is extremely important for designing new processes that will allow refineries to meet the stringent standards of the future. The following text attempts to summarize the observations reported in the literature on the effects of inhibitors on the hydrodesulfurization rates of alkyl-substituted dibenzo-thiophenes. It is quite possible that many reports have been overlooked, and the present authors apologize for any oversights that may have occurred in this review. 

Secondary aliphatic amines reacted readily with mercaptoaldimines (279), which could be prepared readily by the action of Na/NH3 on the aldehyde diacetals (278). The resulting N,N- dialkyl derivatives (280) were alkylated on sulfur by a-halocarbonyl compounds such as bromoacetic acid the resulting products (281) underwent spontaneous ring closure and aromatization via loss of the secondary amine to yield the acids (282 Scheme 97). Decarboxylation of the acids (282) furnished the substituted thieno[2,3-6 ]thiophenes (283). The use of other a-halocarbonyl compounds, such as bromoacetone or phenacyl bromide for the alkylation, led to the formation of the 2-acetyl or 2-benzoyl derivatives, (284) and (285) respectively (76AHC(19)123). 

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