Thiocyanate ions reactions

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Iodide and thiocyanate ion are effective catalysts for inducing a related rearrangement (62AG(E)S28). This reaction can be envisioned as proceeding by nucleophilic attack on the lesser substituted aziridinyl carbon atom by iodide ion to give an iodoethyl intermediate such as (132) which is subsequently converted to the final product. 

The reactions of oxiranes with thiocyanate ion or with thiourea are usually done in homogeneous solution in water, alcohols or alcohol-acetic acid. The use of silica gel as a support for potassium thiocyanate in toluene solvent is advantageous for the simple work-up (filtration and evaporation of solvent) (80JOC4254). A crown ether has been used to catalyze reactions of potassium thiocyanate. 

Treatment of cyclic carbonates of 1,2-diols with thiocyanate ion at temperatures of 100 °C or higher yields thiiranes (Scheme 145) (66CRV297, 75RCR138). Thiourea cannot replace thiocyanate satisfactorily, and yields decrease as the carbonate becomes more sterically hindered. The reaction mechanism is similar to the reaction of oxiranes with thiocyanate (Scheme 139). As Scheme 145 shows, chiral thiiranes can be derived from chiral 1,2-diols (77T999, 75MI50600). 

In general, thiocyanate salts are used for the epoxide-thiirane conversions. The reaction proceeds by nucleophilic attack on the epoxide by thiocyanate ion followed by cyclization as shown for (121) (125). The formation of a... 

Consider the reaction you encountered in the laboratory—that between ferric ion (Fe+3) and thiocyanate ion (SCN ) ... 

By means of colorimetric determination in the laboratory you measured the concentration of FeSCN+i, which we shall designate [FeSCN+2], in solutions containing ferric and thiocyanate ions, Fe+3 and SCN. The reaction is... 

These reactions take place with sparingly soluble silver salts, and hence provide a method for the determination of the halide ions Cl", Br, I-, and the thiocyanate ion SCN ". The anion is first precipitated as the silver salt, the latter dissolved in a solution of [Ni(CN)4]2", and the equivalent amount of nickel thereby set free is determined by rapid titration with EDTA using an appropriate indicator (murexide, bromopyrogallol red). 

Disulfides can be prepared by treatment of alkyl halides with disulfide ions and also indirectly by the reaction of Bunte salts (see 10-41) with acid solutions of iodide, thiocyanate ion, or thiourea, or by pyrolysis or treatment with hydrogen peroxide. Alkyl halides also give disulfides when refluxed with sulfur and NaOH, and with piperidinium tetrathiotungstate or piperidinium tetrathiomolybdate. ... 

When the reagent is the thiocyanate ion, S-alkylation is an important side reaction (10-43), but the cyanate ion practically always gives exclusive N-alkylation. ° Primary alkyl halides have been converted to isocyanates by treatment with sodium nitrocyanamide (NaNCNN02) and m-chloroperoxybenzoic acid, followed by heating of the initially produced RN(N02)CN. ° When alkyl halides are treated with NCO in the presence of ethanol, carbamates can be prepared directly (see 16-7). ° Acyl halides give the corresponding acyl isocyanates and isothiocyanates. For the formation of isocyanides, see 10-111. 

Reaction between alkyl halides, ethanol, and thiocyanate ion... 

In its reactions SsO shows properties typical for both sulfur homocycles and sulfoxides. With elemental chlorine SOCI2 and S2CI2 are formed, with bromine SOBr2 and S2Br2 are obtained. Water decomposes SsO to H2S and SO2 besides elemental sulfur while cyanide ions expectedly produce thiocyanate. The reaction with iodide in the presence of formic acid is used for the iodometric determination of the oxygen content [70] ... 

The reaction between peroxysulphuric acid and thiocyanate ions was investigated by Smith and Wilson by a stopped-flow conductance method. Their results can be summarized as follows. If / and m are the numbers of moles of cyanate and sulphur dicyanide produced per mole of thiocyanate consumed, the overall stoichiometric equation is... 

The acid-catalyzed reaction between hydrogen peroxide and thiocyanate ions has been investigated by several authors, most thoroughly by Wilson and Harris. The rate law has the form... 

In acidic aqueous solution, protonation reactions of tetracyanodioxotech-netate(V) give a complicated equilibration, leading to formation of [TcO(OHXCN)4]- and [TcO(H2OXCN)4] . At pH values less than 1, these monomer species are fairly stable, while at pH 2-5, [Tc203(CN)8]4 is formed rapidly. This complicated feature is seen in a plot of /cobsd against pH (Fig. 4). When thiocyanate ion is added to this system at pH 1, it replaces a water molecule or hydroxy group in the coordination site. 

An important property of the S-nitroso thiourea derivatives is the ability to effect electrophilic nitrosation of any of the conventional nucleophilic centres. This is manifest kinet-ically by the catalysis of nitrous acid nitrosation effected by added thiourea (equation 29). The situation is completely analogous to the catalysis of the same reactions by added halide ion or thiocyanate ion. The catalytic efficiency of thiourea depends on both the equilibrium constant Xxno for the formation of the intermediate and also its rate constant k with typically a secondary amine65. Since Xxno is known (5000 dm6 mol-2), it is easy to obtain... 

When thiocyanate ions are added to nitrous acid in water, a pink colouration develops which is believed to be due to the formation of nitrosyl thiocyanate (equation 34), which is too unstable to be isolated but which can be used as a nitrosating agent in aqueous solution. Because the equilibrium constant for ONSCN formation81 is quite large (30 dm6mol 2) at 25 °C, thiocyanate ion is an excellent catalyst for aqueous electrophilic nitrosation. The well established82 series is Cl- < Br < SCN < (NH2)2CS. Thiocyanate ion is also a sufficiently powerful nucleophile to react in acid solution with nitrosamines in a denitrosation process (equation 35), which can only be driven to the right if the nitrosyl thiocyanate is removed by, e.g., reaction with a nitrite trap such as hydrazoic acid. 

There are numerous examples of the demonstration of the catalytic activity of thiocyanate ion for a wide variety of substrates. In general the reaction of ONSCN is rate-limiting, but in some cases (just as for the nitrosyl halides) with very reactive substrates the formation of ONSCN can be rate-limiting. 

Hence, nucleophilic reactions of the superoxide ion are typical. This ion can be compared with the thiophenoxide and thiocyanate ions with respect to nucleophilicity. The cause of such high nucleophilicity lies in a so-called a-effect In 0—0 ion, an attacking site (O ) adjoins directly to a site (O ) with a significant electronegativity. This effect usually confers special activity to nucleophiles. The effect can be additionally enhanced by including the 0—0 group in sulfenate. 

Photoindnced electron transfer in the presence of a sensitizer (9,10-diphenylanthracene) also generates the same anion-radical. However, its disintegration proceeds within the solvent (acetonitrile) cage. Inside the cage, the 4-nitrobenzyl radical and thiocyanate ion unite anew, but in this case, by their soft-to-soft ends. This nucleophilic reaction takes place faster than the back electron transfer does. The final, stable product of the whole process is 4-nitrobenzyl- o-thiocyanate (Wakamatsu et al. 2000) ... 

Similarly, it was found that GiYj) is independent of [S2] for the OH scavengers thiocyanate ion [57] and iodide ion [58]. Clearly, there is good evidence that back reactions such as reaction (25) can occur in the spur and thus modify G(P2). 

In the acid hydrolysis of the pentamminecobalt complexes where you have a leaving group, such as nitrato or bromo, H. Taube and A. Haim came out with some very interesting work, with which I am sure you are all familiar. They suggested that the five-coordinated pentamminecobalt species was formed which then discriminated between various nucleophilic reagents, sometimes reacting with water, sometimes with- thiocyanate ion. In fact, they were able to measure these nucleophilic discrimination factors in a number of cases, and they were able to correlate different types of reactions in which the pentamminecobalt would be generated in different ways. 

C-3 in the unsubstituted compound.176,177 However, at the time of these experiments, only C-3 substitution had been observed with 2,3-anhydropentofuranosides, and the results of investigation of this reaction suggest that the amino sugar substituted at C-2 is the major product.184 With thiocyanate ion, substitution also occurs at C-3, leading to the thietane derivative, namely, methyl 3,5-anhydro-3-thio-a-D-xylofuranoside (59) but, as this compound was obtained in only 25% yield, the major pathway may involve 2-substitution, leading to products not characterized.178... 

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