Isatin test

Following a published procedure for converting substituted anilines to isatins by reaction with chloral hydrate and hydroxylamine [1], it was noticed that at the end of the first stage (formation of an isonitrosoacetanilide), the odour of hydrogen cyanide was present, and this was confirmed by a Prussian blue test [2], In related work, concentrations of 100-200 ppm of hydrogren cyanide were found [3]. A mechanism for its formation from chloral hydrate and hydroxylamine was proposed [2], and the need for appropriate precautions was stressed [2,3],... 

Pure commeroial benzene is shaken in a machine for six to eight hours with one-tenth of its volume of concentrated sulphurio acid j the liquids are separated with a funnel and the benzene, after being shaken with sodium hydroxide solution, is distilled. Test with isatin and sulphurio aoid. 

Isomeric thienothiophenes, selenophenoselenophenes, and seleno-phenothiophenes have an odor reminiscent of naphthalene. They all show the indophenin test with isatin and concentrated sulfuric acid. 

More rarely, ions of type (97) form dimeric products (possibly by initial loss of nuclear protons) thus, thiophenes with two free a-positions, or free adjacent a- and (3-positions, give indophenines (e.g. 103) with isatin (104). This reaction is used as a test for thiophene, the so-called indophenine test . 

Reaction of 164 with acetic anhydride, reaction of isatin with L-pipecolic acid, or reaction of pyrrolidine with isatin in acetic anhydride gives a substance known as isatin blue. Proline and isatin give the same product and the blue color is the basis of a color test for such compounds.463-468 The structure 166 has been proposed for isatin blue,461 and other related compounds have also been prepared.461... 

The reaction of isatin with thiophene in the presence of sulfuric acid gave a blue color. This indophenine test was reported to be sensitive to 0.025% of thiophene in benzene. 

Carbazole, Analytical Procedures, Carbazole gives with isatin in coned sulfuric acid a blue coloration(Ref 1). As an indole derivative, it gives a positive "pine-splinter test (formation of a red color when a pine-splinter soaked in HCI soln is held in the vapor of an ale soln of carbazole)(Refs la, 2 8). Carbazole may also be identified by a bluish-green coloration produced when a trace of carbazole is dissolved in coned sulfuric acid and a drop of nitric acid is then added(Ref 8,p 72). Various other colorimetric tests for carbazole are known, such as described in Refs 1,1a,2,5 6 and Addnl Refs a,e,g,h m... 

The benzene used should first be tested for thiophene with isatin and cone, sulphuric acid, and then redistilled and recrystallised traces of... 

The following three process factors were tested to determine the influence of conditions in the technology of isatin production ... 

In lab studies of isatin yield, conditions of the technological procedure in producing this product from isonitrozoacetylamine have been tested. The effects of three process factors have been assessed. 

When a Boc amino acid is being coupled to a N-tenninal proline, hydroxyproline, or other secondary amino group, the Kaiser test is negative or gives an inconclusive brownish color. Such N-terminal residues give a good blue color with isatin.P ... 

Properties of Benzene (SECTION 430).—(a) Test for thiophene in commercial benzene (SECTION 653).—To a few drops of sulphuric acid add a crystal of isatin, about 5 cc. of crude benzene, and shake. 

Add to a drop of the oil a trace of isatin and 1 cc. of concentrated sulphuric acid. Test a sample of commercial benzene and one of benzene purified by crystallization from thiophene. 

A more sensitive test for hydroxyproline (0.1 /xg/5 cm ) is performed by first dipping the plate in 0.2% isatin in acetone, drying, and then spraying with Ehrlich s reagent (Section 4.7.6). Only hydroxyproline among 200 amino compounds gives a purple-red spot. 

When thiophene is treated with isatin (667) and sulphuric acid a blue coloration is formed. The production of color in this way, the so-called indophenin reaction, led to the discovery of thiophene by Victor Meyer. Before thiophene was discovered it was thought that the reaction was characteristic of benzene. A certain sample of the hydrocarbon failed to give the test. On investigation it was found that the benzene used had been prepared from benzoic acid. As benzene obtained from coal-tar gave the test, it was evident that the color-reaction was produced by a substance mixed with the hydrocarbon. When benzene containing thiophene is shaken with concentrated sulphuric acid, the thiophene is more rapidly converted into a sulphonic acid than is the benzene. Thiophene is obtained from the sulphonic acid prepared in this way by heating the latter with water under pressure. 

A color test utilizing isatin for piperidine and pyrrolidine alkaloids containing the structural unit — NH—CH2—CH2— has been described (53). Coniine and conhydrine give a positive test but pseudoconhydrine, which lacks the above feature, does not. The Conium alkaloids have been separated by gas-liquid chromatography (54). 

---