Isatin-5-sulfonic acid

Indigotine was separated from isatin-5-sulfonic acid (decomposition product), 5,7 -disulfoindigo (isomeric subsidiary color) and 5-sulfoindigo (lower sulfonated subsidiary color) by reverse-phase HPLC on Altex Ultraspher ODS using gradient elution (215). 

Isatin-5-sulfonic Acid Not more than 0.4%. 5-Sulfoanthranilic Acid Not more than 0.2%. 

THTOPHENE. [CAS 110-02-1]. (CH C.H)2)S, formula weight 84.H, colorless liquid resembling benzene in odor, mp —30°C, bp 84°C. sp gr 1,070. Thiophene and its derivatives closely resemble benzene and its derivatives in physical ancl chemical properties. Thiophene is present in coal tar and is recovered in the benzene distillation fraction (up to about 0.5% of the benzene present). Its removal from benzene is accomplished by mixing with concentrated sulfuric acid, soluble thiophene sulfonic acid being formed. Thiophene gives a characteristic blue coloration with isatin in concentrated sulfuric add. 

A four-component domino reaction of isatin 58, phenylhydrazine, 3-aminocrotononitrile 117, and cyclic 3-diketones/amide/thioamide 118 in an aqueous medium in the presence of ( )-camphor-10-sulfonic acid on heating at 100 °C for 2-3 h afforded the spiro-fused 2-oxindoles 119 (Scheme 39) [94]. The reaction was successfully extended to 5-chloro- and 5-nitroisatins. According to the proposed mechanism, an acid-catalyzed reaction of phenylhydrazine with nitrile 117 affords the 5-amino-3-methyl-l-phenyl pyrazole 111 that adds to the carbonyl carbon of isatin giving rise to an intermediate product 120. The acid-catalyzed reaction of this intermediate (that has been isolated) with carbonyl compounds 118 affords another intermediate compound 121, which eventually furnishes the final products 119 by cyclodehydration forming tetrahydropyridine ring followed by subsequent dehydration (Scheme 40). 

HB polyarylenes were synthesized by two research groups via different C-C coupling methods. Smet et. al [65]. studied the condensation of isatins with a trifiinctional phenyl ether (see Formula 10.3). Trifluoromethane sulfonic acid served as catalyst and the low monomer concentration prevented gelation. This approach is, in principle, a variant of the acid catalyzed aldehyde-phenol polycondensation developed more than 100 years before for the production of Novolac and Bakelite (see Chap. 2). Possum et al. [66]. studied Pd-catalyzed polycondensations of 1,4-benzene diboronic acid with tri(4-bromophenyl)phosphioxide (see Formula 10.3). 

The yield of isatin is lower than for some of its derivatives. The explanation given in the literature is that some sulfonation occurs during the treatment with sulfuric acid, with corresponding loss of product. 

The stereochemistry of isatin-3-thiosemicarbazone-5-sulfonate was studied in aqueous solution, and in acidic pH the Z isomer was determined to be the most stable, but after... 

Iron(III)sulfate, 223-224 Isatin, 331 Isatoic acid, 331 Isoatlantolactone, 263, 264 Isobutenyl acetate, 153 Isobutyronitrile, 110 Isocyanates, 14-15 Isoflavones, 410 Isopavine, 217 Isopenams, 325 Isophorone, 197, 198 Isopinocampheylborane, 224 Isoprene epoxide, 4 Isopropenyl phenyl sulfone, 316 Isopropenyltriphenylphosphonium bromide, 225... 

Amino acids are best detected with ninhydrin, isatin, or sodium l,2-naphthoquinone-4-sulfonate. For certain amino acids specific detections are suitable which are made possible by the presence of other functional groups in the molecule than the amino group. 

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