Thiophene acidity

Acylation. To achieve acylation of thiophenes, acid anhydrides with phosphoric acid, iodine, or other catalysts have been widely used. Acid chlorides with AlCl, SnCl, ZnCl2, and BF also give 2-thienylketones. AH reactions give between 0.5 and 2.0% of the 3-isomer. There has been much striving to find catalyst systems that minimize the 3-isomer content attempting to meet to customer specifications. The standard procedure for formylation is via the Vil smeier-H a ack reaction, using phosphoms o xycbl o ri de / /V, / V- dim e tb yl fo rm a m i de (POCl /DMF) or /V-m ethyl form an i1 i de. 

The base-catalyzed intramolecular condensation of the aldehyde-ester (171) led to the isomeric thieno[3,2-6]thiophene acid (172), which upon decarboxylation led to thieno[3,2-6]thiophene (3 Scheme 58) (76AHC(19)123). 

More intense bands in the 4f-4f region were observed with lanthanide complexes of mandelic, salicylic, thiosalicylic, furoic, and thiophenic acids than the acetate and haloacetate analogues [235]. Both increase in intensity and nephelauxetic effect have been observed. It seems plausible that the aromatic groups in the hydroxy acids such as benzene, thiophene or furan contribute significantly to the intensity of the hypersensitive bands of the complexes. It appears that pH has an important role in determining the stoichiometry of the complex formed. Only ML species is formed up to pH 4 and both ML2+ and ML2 are formed at a pH of 6.0. 

Just as in benzene chemistry, Wolff-Kischner or Clemmensen reduction of ketones is a much-used route to alkyl-thiophenes, hypochlorite oxidation of acetyl-thiophenes a good route to thiophene acids, Beckmann rearrangement of thiophene oximes is a useful route to acylamino-thiophenes and hence amino-thiophenes, and esters and acids are interconvertible without complications. 

Here, the parallels with benzenoid counterparts continue, for these compounds have no special properties - their reactivities are those typical of benzenoid aldehydes, ketones, acids, and esters. For example, in contrast to the easy decarboxylation of a-acids observed for pyrrole and furan, thiophene-2-acids do not easily decarboxylate. Just as in benzene chemistry, Wolff-Kischner or Clemmensen reduction of ketones is a much-used route to alkylthiophenes, hypochlorite oxidation of acetylthiophenes a good route to thiophene acids, Beckmann rearrangement of thiophene oximes is a useful route to acylaminoth-iophenes and hence aminothiophenes, and esters and acids are interconvertible with no complications. 

CAS 527-72-0 EINECS/ELINCS 208-423-4 Synonyms 2-Carboxythiophene Thiophene-2-carboxylic acid 2-Thiophenecarboxylic acid a-Thiophenecarboxylic acid 2-Thiophenic acid... 

Thiophenethiol. See 2-Thienyl mercaptan 2-Thiophenic acid. See 2-Thenoic acid Thiophenol... 

Bromo-a-thiophenic Acid (3-BronioAto-phene-2-carboxyUc a )... 

Bromo -thiophenic Acid 14-Bromothio. jdtene-2-carboxylic acid)... 

Chloro-a-thiophenic Acid (ShChJorofhio-phenc-2 carboxylic axid) ... 

Functions of zeolite, as a representative acidic support, have been discussed just from the viewpoint of enhanced hydrogenation and isomerization. In addition, zeoUte itself has been found to desulfurize some sulfur species, such as thiophene. Acidic C-S bond breakage and hydrogen transfer can be postulated over the acidic zeolite. More research is needed. 

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