Thiocyanates, reduction

Probably first obtained by Hantzsch and Arapides (105) by condensation of a,/3-dichlorether with barium thiocyanate, and identified by its pyridine-like odor, thiazole was first prepared in 1889 by G. Popp (104) with a yield of 10% by the reduction in boiling ethanol of thiazol-2-yldiazonium sulfate resulting from the diazotization of 2-aminothiazole. prepared the year before by Traumann (103). The unique cyclization reaction affording directly the thiazole molecule was described in 1914 by Gabriel and Bachstez (106). They applied the method of cyclization, developed by Gabriel (107, 108), to the diethylacetal of 2-formylamino-ethanal and obtained thiazole with a yield of 62% - Thiazole was also formed in the course of a study on the ease of decarboxylation of the three possible monocarboxylic acids derived from it (109). On the other... 

Bromide ndIodide. The spectrophotometric determination of trace bromide concentration is based on the bromide catalysis of iodine oxidation to iodate by permanganate in acidic solution. Iodide can also be measured spectrophotometricaHy by selective oxidation to iodine by potassium peroxymonosulfate (KHSO ). The iodine reacts with colorless leucocrystal violet to produce the highly colored leucocrystal violet dye. Greater than 200 mg/L of chloride interferes with the color development. Trace concentrations of iodide are determined by its abiUty to cataly2e ceric ion reduction by arsenous acid. The reduction reaction is stopped at a specific time by the addition of ferrous ammonium sulfate. The ferrous ion is oxidi2ed to ferric ion, which then reacts with thiocyanate to produce a deep red complex. 

Pyrrolethiols, readily obtained from the corresponding thiocyanates by reduction or treatment with alkali, rapidly oxidize to the corresponding disulfides. They are converted into thioethers by reaction with alkyl halides in the presence of base. Both furan- and thiophene-thiols exist predominantly as such rather than in tautomeric thione forms. 

Silver fluoborate, reaction with ethyl bromide in ether, 46, 114 Silver nitrate, complexing with phenyl-acetylene, 46, 40 Silver oxide, 46, 83 Silver thiocyanate, 45, 71 Sodium amide, in alkylation of ethyl phenylacetate w ith (2-bromo-ethyl)benzene, 47, 72 in condensation of 2,4-pentanedione and 1 bromobutane to give 2,4-nonanedione, 47, 92 Sodium 2 ammobenzenesulfinate, from reduction of 2 mtrobenzenesul-finic acid, 47, 5... 

Bromo-6,7,8,9-tetrahydro-l//-3-benzazepin-2-amine(6) with thiocyanate ion undergoes substitution of bromide to give the thiocyanatotetrahydro-l//-3-benzazepine 7.105 Attempts to replace bromide by azide ion failed, as did diazotization of the amine group with sodium nitrite in 6 M sulfuric acid. Oddly, treatment of the aminobromo compound with sodium borohydride in methanol results not in reduction, but in methoxy-debromination to give the 2-methoxy derivative which, on the basis of HNMR spectral data, is best represented as the 2-imino tautomer 8. 

Cobalt, pentaamminecyano-isomerization, 1,186 Cobalt, pentaamminehydroxy-thiocyanate isomerization, 1,185 Cobalt, pentaammineisonicotinamido-electron transfer, 1,373 with hexaaquachromium, 1,369 reduction... 

These and similar results can be explained if the simultaneous reduction of hydrogen peroxide is due to an induced reaction. To show the characteristic features of this reaction some results are presented in Table 19 and Table 20. The procedure for these measurements was as follows. The solution of peroxy compounds given in columns 1 and 2 was made up to 20 ml and the pH was adjusted to the given value. Then potassium thiocyanate solution was added and, after the reaction time noted, the process was quenched by adding potassium iodide solution (0.3 g KI). After 5 sec the solution was acidified with 1 ml 2 iV sulphuric acid then using, molybdate catalyst solution, the iodine liberated was titrated with standard thiosulphate. 

The data in Tables 19 and 20 show that both peroxysulphuric and peroxyacetic acid give the induced reduction of hydrogen peroxide by thiocyanate. The induced reduction depends strongly on the pH of the solution and on the concentration of thiocyanate. At pH > 3 both peroxy acids reacts more slowly... 

On the basis of these results it can be stated that the fast oxidation of thiocyanate by peroxy acids gives rise to the induced reduction of hydrogen peroxide. In order to elucidate the mechanism of this interesting reaction let us have a look at reactions of thiocyanate with peroxy compounds of different types. 

A variety of solvents was investigated for this reaction, as shown in Table 15.1. As inferred from Table 15.1, the hydrogenolysis performance is best in more polar solvents snch as acetonitrile, acetone, ethyl acetate, and acetic acid. Only in o-dichlorobenzene is the rate of reaction ranch lower than predicted by the dielectric constant. The presence of nonpolar solvents snch as hexane and the thiol product resulted in large amonnts of the disnlfide intermediate. It has been shown that the disnlfide is the intermediate in stoichiometric rednctions such as samarium diiodide reduction of alkyl thiocyanates to thiols (11) so it is reasonable to expect it as the... 

It is well known that palladium on carbon catalysts are poisoned by hydrogen cyanide and thiol products or hydrogen sulfide (6). Therefore, it was of interest to investigate the reduction of perfluoroalkyl thiocyanates as a function of tin concentration, keeping the concentration of palladium and reaction conditions constant. Figure 15.1 delineates the % conversion vs. Sn/Pd ratio, under the same reaction conditions of 175°C, 700 psig H2 for 2 hours with 5% Pd on carbon catalysts in ethyl acetate solvent at a 1000 1 substrate catalyst molar ratio. The increase in... 

An azide group can be transformed into a thiocyanate group by reduction with LiAlH4 followed by treatment with NJSl -thiocarbonyldiimidazole.[ 14]... 

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