Stoichiometric cyanation reaction

Stoichiometric Cyanation Reaction. To elucidate the mechanism, the stoichiometric cyanation reaction of tram-chloro (aryl) bis (triphenylphos-phine) nickel (II) complexes 1 was studied. Arylnickel (II) complexes... 

A comparison of Figures 2 and 4 indicates that substituents have a qualitatively similar effect both on the oxidative addition reaction and on the catalytic cyanation. In both cases in fact there is a change in the slope on passing from electron-withdrawing to electron-releasing substituents. As to the effect of electron-withdrawing substituents, the sensitivity is lower in catalytic cyanation (p = 4.8) than in oxidative addition (p = 8.8) which is what is to be expected on the basis of the substituent effect in stoichiometric cyanation reaction of arylnickel complexes. 

Cyano(trimehyl)silane (TMSCN) serves as a cyanating agent for carbonyl groups in the presence of a catalytic or stoichiometric amount of a Lewis acid such as boron trifluoride, titanium(IV) chloride, tin(IV) chloride, etc. Thereby, a wide variety of chiral ligands was designed and used for asymmetric cyanation reactions. Among them, titanium complexes have mostly been employed as the catalysts. 

Kobayashi et al. disclosed reversed chemoselectivity of lanthanide Lewis acid over conventional Lewis acid in cyanation reaction. The comparitive reaction was performed with equimolar mixture of aldehydes, imines, and TMSCN, affording Strecker-type product exclusively with 20mol% of Yb(OTf)3 [10]. In sharp contrast, SnCU required more than a stoichiometric amount of reagent and gave cyanohydrin preferentially (Table 13.15). 

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 nickel-catalyzed transformation of aromatic halides into the corresponding nitriles by reaction with cyanide ions is reported. Both tris(triarylphosphine)nickel(0) complexes and tY2ins-chloro( aryl )bis( triarylphosphine )nickel(II) complexes catalyze the reaction. The influence of solvents, organophos-phines, and substituents on the aromatic nucleus on catalytic cyanation is studied. A mechanism of the catalytic process is suggested based on the study of stoichiometric cyanation of ti3ins-chloro(aryl)bis(triphenylphosphine)nickel-(II) complexes with NaCN and the oxidative addition reaction of Ni[P(C6H5)3]s with substituted aryl halides. 

As reported before, the reaction can be carried out in ethanol by adding quickly a stoichiometric quantity of NaCN after the catalyst and aryl halide additions. In methanol or in dimethylformamide the catalytic cyanation occurs only if the sodium cyanide is added slowly. In benzene, always in the presence of NaCN, the reaction does not occur and complexes 1 can be isolated. 

Chem. 29 (1967), pp. 1637-1642. Spectroscopic studies of die reaction of hexa-cyanoferrate(III) in water and ethanol. 3.3x 10 4 M Fe(NC>3)3 were exposed with a cyanide excess of likewise 3.3x10 mol l"1. With pH values of approximately 10, all the Fe2[Fe(CN)6] was converted into Iron Blue within 48 hours. Cyanate, die anticipated product of die oxidation of die CN-, could not, however, be proven. Perhaps this is further oxidized directly into C02. If this mechanism is assumed, die result, purely stoichiometrically, is that an alkaline environment must be favorable. This finding is supported by die known fact that hexacyan-oferrate(III) is a strong oxidation agent in alkaline medium and is even able to oxidize divalent chrome to hexavalent, therefore, that is, CN ions must have oxidized very quickly J.C. Bailar, Comprehensive Inorganic Chemistry, Vol. 3, Pergamon Press, Oxford 1973, p. 1047. An overly alkaline environment would, however, disturb die complexing of the Fe3+- ion by cyanide, which is then displaced by OH- (Fe(OH)3 then occurs as a by-product) and/or the latter can hardly be displaced from die iron. 

The palladium-catalyzed reaction of aryl halides with cyanides to give cyanobenzenes takes place under relatively mild conditions compared to the conventional method using a stoichiometric amount of CuCN [74]. Thus, palladium catalysis has been often employed. Recently, a number of effective methods for the cyanation have been reported. The reaction of aryl iodides with NaCN under two-phase conditions [75] and those of aryl triflates [76, 77] and aryl chlorides [78] with Zn(CN)2 occur with good efficiency, while these are considered to proceed via mechanism B. 

Employing a stoichiometric quantity of diphenylphospho-ryl azide as a carbon monoxide receptor allows the reaction to proceed at a lower temperature. The azide reacts with frani -[RhCl(CO)(PPh3)2] to form a cyanate at room temperature. Alkene formation is suppressed when this reagent is employed, but higher aldehydes are not decarbonylated in its presence. ... 

Potassium cyanate is readily hydrolyzed, and, for the stoichiometric reaction. 

A very recent study based on FTIR analysis of the isothermal co-reaction between tetrafunctional epoxy and cyanate ester resins at different stoichiometric ratios and temperatures substantiates some of these findings. Rheological char-... 

Cyanadons. Aluminum complexes of BINOLs (1) that are armed at C-3 and C-3 with diarylphosphine oxide groups possess both Lewis acid and base centers. Asymmetric cyanation of aldehydes and mines with MeaSiCN, and of quinolines and isoquinolines in a manner analogous to the Reissert reaction is successful (ee 70-90%). The asymmetric Strecker synthesis is applicable to conjugated aldimines and the higher reactivity of Me SiCN than HCN in the presence of 10 mol% of PhOH enables its use in catalytic amount while supplying stoichiometric HCN as the cyanide source. 

Consequently a process was developed where the required TAA salts are formed directly during the reaction and continuously regenerated via ion exchange with the aqueous phase. Since one TAA cation can transfer into the organic phase a great number of required anions via multiple ion exchange, the TAA salts can be used in much smaller than stoichiometric quantities, acting virtually as catalysts. The term phase-transfer catalysis is usied for this type of processes(3). This principle is conveniently explained when the cyanation of an alkyl halide, dissolved in a hydrocarbon with aqueous solution of sodium cyanide, is considered(3). 

We developed various catalytic enantioselective cyanation and azidation reactions using chiral poly rare earth metal (RE) complexes derived from ligands 5-8 and TMSCN or TMSN3 as a stoichiometric nucleophile [43, 44]. General mechanism for those asymmetric catalyses is shown in Scheme 11. First, polymetallic complexes 9 containing defined higher order strucmres are generated via a reaction... 

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