Thiocyanates, alkyl

Alkyl thiocyanates. From potassium or sodium thiocyanate and the alkyl halide in alcoholic solution, for example ... 

The organic chemistry of thiocyanates is notably that of nucleophilic displacement of alkyl haHdes by thiocyanate anion to form alkyl thiocyanates ... 

The action of potassium thiocyanate on tosylates derived from fluorohydnns gives the corresponding fluonnated alkyl thiocyanates [43] (equation 39)... 

Alkyl halides or sulfuric or sulfonic esters can be heated with sodium or potassium thiocyanate to give alkyl thiocyanates, though the attack by the analogous cyanate ion (10-66) gives exclusive N-alkylation. Primary amines can be converted to thiocyanates by the Katritzky pyrylium-pyridinium method (pp. 447, 489). "... 

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... 

Synthesis of thioethers from alkyl thiocyanates (Table 4.18)... 

Alkyl thiocyanates were reduced with lithium aluminum hydride to mercap-tans (yield 81%), and aryl thiocyanates to thiophenols (yield 94%) [680]. 

Alkyl thiocyanates can also be used as the cyano component for the cobalt-catalyzed cycloaddition (80MI1) [Eq.(28)] (experimental details in 84MI8). 

Ammonium thiocyanate reacts with alkyl hahdes forming alkyl thiocyanates, RSCN, which may also rearrange to alkyl isothiocyanates, RNCS ... 

Reactions with trialkylhoranes yield the corresponding alkyl thiocyanate, RSCN. 

Kamal and Chouhan prepared the TSIL [bmim][SCN] to convert alkyl halides to alkyl thiocyanates. This [bmim][SCN] was prepared by ion exchange of [bmim][Cl] with KSCN in acetone. Alkyl halides were reacted with this TSIL to give quantitative amounts of the corresponding alkyl thiocyanates with high yields. Scheme 31. The product was then easily extracted with ether. 

A number of volatile aliphatic compounds that contain nitrogen or sulfur atoms are important aroma constituents. Alkyl thiols, dialkyl sulfides and disulfides, and alkyl thiocyanates belong to this group. They occur widely in foods and spices and determine the odor of, for example, onions, garlic, and mustard. Because of their potent smell, they are used in high dilution and are often produced only in small quantities. The same is true for the following ... 

Sulphur compounds, such as alkyl thiocyanates (in mustard oil, garlic oil and the like). 

ThiocyanatesSodium arenesulfinates, ArS02Na, are converted into aryl thiocyanates, ArSCN in about 60-75% yield by reaction with diethyl phosphorocyanidate in THF, This reaction is also possible with benzyl and adamantyl sulfinates but yields are only about 40%. Alkyl thiocyanates cannot be obtained in this way. 

Alkyl thiocyanates are readily prepared, in high yields, by reaction of alkyl bromides with potassium thiocyanate under PTC294. Sulfonium salts have been found to be the catalysts of preference. 

Alkyl thiocyanates are obtained by the reaction of iron(III) thiocyanate on trialkylboranes in a fashion reminiscent of the reactions of iron(III) chloride (Section 4.1.11). It is not clear whether there is 60% usage of three alkyl groups or whether only two groups are in fact utilized. Equation (70) shows the reaction based on the assumption of usage of three groiq>s. 

Although extensive work with heteroatom-containing nitrile analogs has not been done, successful cycloadditions along these lines include the synthesis of 2-aminopyridine from cyanamide, and syntheses of 2-alkylthiopyridines from alkyl thiocyanates.However, nitriles containing strongly electron-withdrawing substituents are poor substrates. 

In contrast, the photolysis of these azides at 350 nm leads only to the corresponding nitriles and olefins in yields of 90 l-(Alkylthio)cyclopropyl azides (164), readily accessible from the corresponding chlorides and bromides, are smoothly decomposed at ITC with nitrogen evolution. The main process is a ring enlargement to 2-(alkylthio)azetines (165), accompanied by cleavage to an alkyl thiocyanate and an alkene (equation 114). ... 

Imidothioates are easily accessible frtxn nitriles (equation 26) or, in special cases, from alkyl thiocyanates (equation 27). Their hydrolysis represents a route to thiol caiiwxylic esters. - - However, the alternative, foimation of amides, is not easy to avoid and the yields are therefore often low. - ... 

Aminopyridine is prepared conventionally by the substitution of the pyridine ring via the so-called Chichibabin reaction using sodium amide in dimethylaniline [36]. 2-Aminopyridine is used in the manufacture of several chemotherapeutics and of dyes for acrylic fibers, and as an additive for lubricants [37]. Alkyl thiocyanates react [38] to give 2-alkylthiopyridines (eq. (12)) which are otherwise accessible only by multistep synthetic pathways [39]. The catalytic reaction (eq. (12)) seems to offer on easy entry into the pyrithione systems. 

Alkyl thiocyanates (39) are prepared by heating alkyl halides ortosylates with sodium or potassium thiocyanate (Scheme 21). The reaction may be performed in acetone, ethanol or water, but goes best in polar aprotic solvents like DMF or DMSO. The thiocyanate ion is an ambidentate nucleophile owing to resonance (Figure 1).4 In principle, therefore, the reaction shown in Scheme 21 may yield... 

Alkyl thiocyanates (39) are reasonably stable, volatile oils, with a slight garliclike odour. They are readily oxidised to either sulfonyl cyanates (40) or sulfonic acids (41), and by reduction they yield thiols (Scheme 22). 

---