Thiocyanogen preparation

To a benzene solution (100 mL) of thiocyanogen, prepared from lead(II) thiocyanate (17.84 g, 0.055 mmol) and bromine (8.00 g, 50mmol), was added benzocyclopropene (3.83 g, 35.7 mmol) in benzene (6 inL). The mixture was irradiated with a medium-pressure Hg lamp (100 W) through a Pyrex filter at 20 C for 30 min. The resulting solution was filtered to remove orange precipitates (polymer of thiocyanogen) and concentrated. Chromatography (silica gel, hexane/EtjO 2 l)of the residual afforded 1 yield 4.70 g (64%) mp 78.5-79.5 C. 2-Thiocyanatobenzyl isothiocyanate was also isolated yield 1.62 g (22%). 

A soln. of p-nitrobenzyl mercaptan in methylene chloride added with stirring at 0° during 1.5 hrs. to a soln. of thiocyanogen prepared from Pb-thiocyanate and bromine in methylene chloride, stirring continued 15 min., anhydrous Na-acetate added in one portion, then N - (2 - tritylthioethyl) - 5 - phenyl - 4,5 - dithia-pentanamide added during 15 min., stirred 45 min. at 0 and 1 hr. at room temp. -> N- [5- (4-nitrophenyl) -3,4-dithiapentyl] -5-phenyl-4,5-dithiapentanamide. Y 50%. F. e. s. R. G. Hiskey and D. N. Harpp, Am. Soc. 87, 3965 (1965). 

Benzyl mercaptan added at —80° during 1 hr. to a soln. of thiocyanogen prepared from lead thiocyanate and bromine in ether, stirred 0.5 hr., the resulting crude benzylsulfenyl thiocyanate (Y 94.1%) dissolved in ether, immediately added at —10° to methyl mercaptoacetate in dry ether, and stirred 2.5 hrs. 

A soln. of thiocyanogen prepared by treatment of lead thiocyanate with bromine in GCI4 added at 0-5° to a stirred soln. of azulene in dry CCI4, stirring continued 1 hr. at 0°, then the solvent removed by an air stream 1-thiocyanoazulene. Y 93.5%.—Similarly with 2 equivalents of thiocyanogen 1,3-Dithiocyano-azulene (Y 77%) and 1-thiocyanoazulene (Y 23%). A. G. Anderson, Jr., and R. N. McDonald, Am. Soc. 81, 5669 (1959). 

In a similar way the use of the 2-methyl-3-isothiocyanato-4-thiocyanato-hept-3-ene (252) prepared from thiocyanogen and the oxoal-kylene phosphorane (251) yields the 2-anilino-4-propyl-5-isopropyl-thiazole (253) by condensation with aniline (Scheme 128). 

Thiazolidines have been prepared from /3-aminothiols—for example, cysteine—to protect the —SH and — NH groups during syntheses of peptides, including glu-tathione. Thiazolidines are oxidized to symmetrical disulfides with iodine they do not react with thiocyanogen in a neutral solution. 

It may also be prepared by electrolysis of the alkali thiocyanates in aqueous or alcoholic solution, using a platinum gauze anode and a silver cathode. On evaporation under reduced pressure, thiocyanogen is obtained as a viscous oil, solidifying at —70° C.4... 

A usual method for the preparation of a solution of thiocyanogen is to treat lead thiocyanate with a dry ethereal solution of bromine cooled in ice. 

Thiocyanatothiophene is prepared very conveniently by the A1C13 catalyzed reaction of thiophene with thiocyanogen (63AHC(l)l). 

All methods that have been suggested for the preparation of thiocyanogen solutions involve the use of strictly anhydrous solvents, since the presence of moisture causes rapid hydrolysis and decomposition to take place. It is possible, howeyer, to stabilize thiocyanogen in aqueous solution to a limited extent by the presence of large quantities of potassium thiocyanate. 

Preparation of Thiocyanogen Solutions. To a suspension of 30 g. of plumbous thiocyanate in 300 ml. of the acetic acid is added 5 ml. of the bromine solution. The mixture is agitated vigorously on a shaking machine until it is practically colorless, and another portion of the bromine solution is added. This procedure is continued until all the bromine solution has been added. The mixture is then rapidly filtered through a dry fluted filter paper. ... 

Phenyl, 4-methoxyphenyl, and 4-ethoxyphenyl tellurium thiocyanates are known only in the form of their complexes with thiourea1,2 ethylenethiourea3, triphenylarsine oxide, 3-methylpyridine, 3-methylpyridine /V-oxidc, or 4-methylpyridine Af-oxide2. These compounds were prepared from the diaryl ditellurium compounds, thiocyanogen, and the ligands2. 

Diphenyl Tellnrium Bis[thiocyanate] A solution of thiocyanogen is prepared by shaking 4.5 g (14 mmol) of lead thiocyanate with 1.8 g (12 mmol) of bromine in dry diethyl ether for 10 min and filtering the mixture. The filtrate is protected from light. 2.8 g (10 mmol) of diphenyl tellurium are dissolved in 20 ml of dry diethyl ether and the thiocyanogen solution is added dropwise to the stirred solution of diphenyl tellurium. The mixture is stirred for 1.5 h, and the colorless crystalline product is filtered, washed with hexane, dried, and recrystallized from benzene/hexane (1/1, v/v) yield 2.9 g (78%) m.p. 129-132° (dec.). 

Improved preparation. Thiocyanogen can be prepared in 85-90% yield by use of a two-solvent system (water and waler-immisciblc toluene) for the reaction between sodium thiocyanate and gaseous chlorine. The thiocyanogen formed in the aqueous phase is extracted into the toluene. The thiocyanogen solution can be stored at reduced temperatures. 

Also the trityl group was applied for the masking of SH functions. The sulfides were prepared by the reaction of the thiol with trityl chloride (75% yield) or from trityl alcohol and the thiol in the presence of anhydrous TFA (85-90% yield). The cleavage of this group can be carried out under several conditions (Scheme 58). It is sensitive to acids (e.g. trifluoroacetic acid/ethanethiol 1 1) and to heavy metals. Thiocyanogen (SCN)2 oxidizes 5-trityl ethers to the disulfides and iodine converts 5-tritylcy -teine derivatives to cystine structures. 

Sulfonyl thiocyanates6 (51) may be prepared by the action of thiocyanogen (42) on the appropriate sodium sulfinates (52) (Scheme 30). Sulfonyl thiocyanates (51) will undergo free radical addition to alkenes and alkynes to give the adducts (53) and (54) (Scheme 30). 

Preparation.1 Ethereal solutions of iodine thiocyanate are prepared essentially by the method of Raby.2 Bromine (0.025 mole) is added all at once to a slurry of lead thiocyanate (0.025 mole, Eastman). The mixture is stirred at room temperature until the bromine fades (several minutes). A solution of iodine (0.025 mole) in dry ether is then added to the solution of thiocyanogen, and the mixture is stirred for 15 min. at room temperature with protection from light. 

Thiocyanogen chloride, C1SC=N. A solution of the reagent is prepared by adding 1 mole of lead thiocyanate, Pb(SCN)2, mol. wt. 323.38 (Fisher supplies practical grade) to a solution of 2 moles of chlorine in acetic acid and filtering off the lead chloride. 

Thiocyanodimethylaniline has been prepared by the action of thiocyanogen on an ethereal solution of dimethylanilined and also by the action of chlorothiocyanogen on dhnethylaniline. ... 

Olefin synthesis. This reagent has an advantage over trialkyl phosphites (see Trimethyl phosphite, 1, 1233, and this volume) for stereospecific generation of olefins from trithio- and thionocarbonates in that the conditions are mild (30°)-s Thus optically active /rans-cyclooctene (6) has been prepared from cis-cyclooctene in the following way.3 Addition of thiocyanogen to cis-cyclooctene (3) affords trans-, 2-dithiocyanocyclooctane (4), which when refluxed with 47% hydrobromic acid affords the iminodithiocarbonate (5). This was resolved via the salt with (—)-l-phenyl-ethanesulfonic acid by thirteen recrystallizations from 2-butanone. The (+)-(5) was... 

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