Preparations of Thiocyanates

Preparation of Thiocyanates.—As in other sections of this Chapter, well-established preparative procedures have not been superseded, nor even tilted at, by new methods. Potassium thiocyanate gives (155) with l,4-diphenyl-l-chloro-2,3-diazabuta-l,3-diene in high yield treatment with acid in EtOH gives (156) + PhCHO, while thermal rearrangement gives (157). 

Thiocyanogen has been used for thiocyanation of porphyrin (as its copper complex), and for the conversion of 2-bromothiophen into 5-bromo-2-thiocyanatothiophen in the presence of AICI3, a procedure which results in conversion of 2-(methylthio)thiophen into 3,5-di(thio-cyanato)-2-(methylthio)thiophen. Continuation of studies of the 

Attack by cyanide at sulphur in 3-chloro-l,2-benzoisothiazole is implied by the production of o-cyanophenyl thiocyanate and of bis-(c -cyanophenyl) disulphide other nucleophiles (Bu Li, PhS ) also attack at sulphur, but EtO causes replacement of Cl without cleaving the isothiazole ring. 

Aryl thiocyanates are formed in high yields through pyrolysis of A-aryl-dithiocarbamates.  

Preparation of Thiocyanates.—Variations of standard methods for the synthesis of thiocyanates are illustrated in the addition of alkoxy- and thiocyanato-groups to alkenes using KSCN, CuClj (or other Cu salt), and an alcohol as solvent, to give a-alkoxy-alkyl thiocyanates and in the addition of pseudohalogens CISCN or (SCN)a to chalcones. A sulphonylthiocyanate RSOaSCN, prepared from (SCN)a and a sodium sulphinate, adds similarly to alkenes to give a-thio-cyanato-alkyl sulphones. Aryl selenocyanates may be prepared from the 

Uemura, and M. Okano, Bull. Chem. Soc. Japan, 1974, 47, 2818. 

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The synthetic method for the preparation of thiocyanate complexes of air- and water-unstable transition-metal oxidation states has been found suitable for the synthesis of K[Ta(NCS)6] and K2[M(NCS)6] (where M = Ti4+,2 (Zr4+, Nb4+, Mo4+, or W4+), as well as the compound described above. By use of different solvents (e.g., diethyl ether or nitromethane), it can be expanded to include metal halides which undergo reduction... 

There are also preparatively important methods for preparation of thiocyanic esters that start from dithiocyanogen, which behaves in its reactions as a pseudohalogen, so that it can add to olefinic double-bond systems and substitute aromatic compounds. Kaufmann362 and also Wood363 have reviewed the preparation of organic thiocyanates, which has been described previously (pages 203, 213 ) in the present volume. 

Nucleophilic substitution, e.g. the preparation of thiocyanates from lipophilic alcohols, can be facilitated by substrate hydrophilation via ammonioethanesulfonic acid esters (betylates)i . Mercaptans can be easily prepared from alcohols with inversion of configuration via thiolic esters prepared with thioacetic acid in the presence of 2-fluoro-pyridinium salts . C-Sulfenylation of / -dicarbonyl compounds with mercaptans by air oxidation in the presence of tetraethylammonium fluoride has been reported . Activated thiolic and selenolic esters can be prepared at room temperature from carboxylic acids and aryl thiocyanates or selenocyanates in the presence of tri-n-butylphosphine i. Phenylselenolactones have been obtained under very mild conditions from unsaturated acids and benzeneselenyl chloride. ... 

Perhaps the most widely used preparation of thiocyanates involves the reaction of an alkyl halide with either potassium thiocyanate or ammonium thiocyanate. The reaction is not confined to simple alkyl halides but has also been used for the preparations with dihalides, chlorohydrins, secondary alkyl halides, and acyl halides (in the preparation of acyl thiocyanates). The preparation of undecyl thiocyanate is a typical example of the procedure. 

Preparations of Thiocyanates.—Syntheses from metal thiocyanates have been described involving aryl thallium(iii) acetate perchlorates and cop-per(n) thiocyanate, and the Se analogue using KSeCN with alkyl... 

Guanidine salts can be prepared by reaction of thiocyanates and sulfamates (22). 

Uses. There may be some captive use of carbonyl sulfide for production of certain thiocarbamate herbicides (qv). One patent (38) describes the reaction of diethylamine with carbonyl sulfide to form a thiocarbamate salt which is then alkylated with 4-chloroben2yl haUde to produce 3 -(4-chloroben2yl) A[,A/-diethylthiocarbamate [28249-77-6] ie, benthiocarb [28249-77-6]. Carbonyl sulfide is also reported to be useful for the preparation of abphatic polyureas. In these preparations, potassium thiocyanate and sulfuric acid are used to first generate carbonyl sulfide, COS, which then reacts with a diamine ... 

Whereas sulfonyl halides have been known for a long time and, especially the chlorides, have become of great synthetic value, sulfonyl cyanides were unknown until 1968. They were first prepared by van Leusen and co-workers from the reaction of sulfonylmethylenephos-phoranes with nitrosyl chloride. The same group also investigated part of their chemistry. Since then, two more, completely different, methods of synthesis were published from sulfinates with cyanogen chloride,and by the oxidation of thiocyanates. ... 

The importance of solvent effects in the preparation of perfluoroalkyzinc reagents is further illustrated in the reaction of perfluoroalkyl iodides with zinc-copper couple. In DMSO, DMF, and HMPA, the main products are the fluo-roolefins The formation of the fluoroolefin is facilitated when the reaction is carried out in the presence of potassium thiocyanate [30] (equation 21)... 

It can be prepared artificially by the action of allyl iodide on an alcoholic solution of thiocyanate of potassium, the latter body being isomerised to the isothiocyanate under the influence of heat. 

Estimation The above medium is reinforced with lOg/i of thiocyanate, sulphur is omitted and it is prepared as pour plates by the addition of 3% agar. Organisms other than Thiobacilli will grow from spread samples, but the Thiobacilli are easily distinguished by sulphur haloes (see Fig. 2.19). 

There is virtually no recent literature on quinoxaline cyanates or isocyanates, and most of what little there is on quinoxaline thiocyanates, isothiocyanates, or nitrones has been covered already the preparation of thiocyanatoquinoxalines from halogenoquinoxalines (Section 4.4.1) the conversion of the thiocyanatoquinoxalines into alkoxyquinoxalines (Section 4.4.1), into quinoxalinethiones (Section... 

In a 1 litre round-bottomed flask provided with an efficient double surface condenser, place 40 g. (39 ml.) of aniline, 50 g. (40 ml.) of carbon sulphide CAUTION inflammable) (1), and 60 g. (63-6 ml.) of absolute ethyl alcohol (2). Set up the apparatus in the fume cupboard or attach an absorption device to the top of the condenser (see Fig. II, 8, 1) to absorb the hydrogen sulphide which is evolved. Heat upon an electrically-heated water bath or upon a steam bath for 8 hours or until the contents of the flask sohdify. When the reaction is complete, arrange the condenser for downward distillation (Fig. II, 13, 3), and remove the excess of carbon disulphide and alcohol (CAUTION inflammable there must be no flame near the receiver). Shake the residue in the flask with excess of dilute hydrochloric acid (1 10) to remove any aniline present, filter at the pump, wash with water, and drain well. Dry in the steam oven. The yield of crude product, which is quite satisfactory for the preparation of phenyl wo-thiocyanate (Section IV,95), is 40-46 g. RecrystaUise the crude thiocarbanihde by dissolving it, under reflux, in boiling rectified spirit (filter through a hot water funnel if the solution is not clear), and add hot water until the solution just becomes cloudy and allow to cool. Pure sym.-diphenylthiourea separates in colourless needles, m.p. 154°. 

The salt, prepared in carbon tetrachloride solution, exploded feebly several times as the reaction proceeded. Oxidation of thiocyanate by chromium(VI) is postulated. 

A mixture of the nitrite with sodium thiocyanate explodes on heating [1], Preparation of a molten salt bath from 0.45 kg of potassium thiocyanate (reducant) and 1.35 kg of sodium nitrite (oxidant) led to a violent explosion on melting, which... 

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