Cyanide transfer reaction

It is well known that MPV type hydride transfer proceeds via six membered transition state with concerted mechanism. As shown in Figure 6.3, similar alkynyl transfer reaction and cyanide transfer reaction have also been reported. 

Ooi and Maruoka found that aluminum alkoxide (83) prepared from aluminum complex (82) and tertiary propargyl alcohol reacts with highly electrophilic aldehydes, such as chloral and pentafluorobenzaldehyde, to give alkynyl transfer products in good yield (Scheme 6.65) [84]. Bisphenol structure of ligands on aluminum center is the most important feature to obtain the alkynylated products, and thus, in reactions with (84) or (85) instead of (83) dramatical decrease in the yield of alkynyl product was observed. Same group also reported that cyanide transfer reaction with acetone cyanohydrin as a cyanide donor catalyzed by complex (82) [84]. 

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

One after the other, step through (or animate) the sequence of structures depicting the SN2 and proton transfer reactions shown above. Compare the two. From what direction does cyanide approach the hydrogen in HCl From the same side as Cl ( frontside ), or from the other side ( backside ) Does the Sn2 reaction follow a similar trajectory ... 

Another example of an acid is hydrogen cyanide, HCN, which transfers its proton to water when it dissolves to form the solution known as hydrocyanic acid, HCN(aq). However, only a small fraction of the HCN molecules donate their protons, and so we classify HCN as a weak acid in water. We write the proton transfer reaction with equilibrium half-arrows ... 

Tables IV and V list examples to show the effect of functional groups and substituents on the course and rate of reactions involving cleavage of the Co—C bond in acid, neutral, and alkaline solution in the absence of any other added reagent. Transfer reactions involving HO (see Section VI,C,2), cyanide insertion (VI,D,1), and irreversible reactions not involving cleavage of the Co—C bond (V,B) are also included in order to complete...

Despite intense study of the chemical reactivity of the inorganic NO donor SNP with a number of electrophiles and nucleophiles (in particular thiols), the mechanism of NO release from this drug also remains incompletely understood. In biological systems, both enzymatic and non-enzymatic pathways appear to be involved [28]. Nitric oxide release is thought to be preceded by a one-electron reduction step followed by release of cyanide, and an inner-sphere charge transfer reaction between the ni-trosonium ion (NO+) and the ferrous iron (Fe2+). Upon addition of SNP to tissues, formation of iron nitrosyl complexes, which are in equilibrium with S-nitrosothiols, has been observed. A membrane-bound enzyme may be involved in the generation of NO from SNP in vascular tissue [35], but the exact nature of this reducing activity is unknown. 

Probably the most important group of phase transfer reactions, and certainly the commonest, are those in which an anion is transferred from the aqueous phase into the organic solvent, where nucleophilic substitution occurs. These would once have been performed in a dipolar aprotic solvent such as DMF. A good example is the reaction between an alkyl halide (such as 1-chlorooctane), and aqueous sodium cyanide, shown in Scheme 5.5. Without PTC, the biphasic mixture can be stirred and heated together for 2 weeks and the only observable reaction will be hydrolysis of the cyanide group. Addition of a catalytic amount of a quaternary onium salt, or a crown ether, however, will lead to the quantitative conversion to the nitrile within 2 h. 

The Reissert reaction of 3,4-dihydro-p-carboline (213) has also been studied 47,48). It has been shown that 3,4-dihydro-p-carboline (213) afforded 1-cyano-2,9-dibenzoyl-l,2,3,4-tetrahydro-P-carboline (214) with a phase-transfer catalyst and trimethylsilyl cyanide (Scheme 27). However, the normal Reissert product 2-benzoyl-l-cyano-l,2,3,4-tetrahydro-p-carboline (215) was obtained when a catalytic amount of anhydrous aluminum chloride was used in addition to the trimethylsilyl cyanide reagent. Reaction of 214 with sodium... 

Complexation constants of crown ethers and cryptands for alkali metal salts depend on the cavity sizes of the macrocycles 152,153). ln phase transfer nucleophilic reactions catalyzed by polymer-supported crown ethers and cryptands, rates may vary with the alkali cation. When a catalyst 41 with an 18-membered ring was used for Br-I exchange reactions, rates decreased with a change in salt from KI to Nal, whereas catalyst 40 bearing a 15-membered ring gave the opposite effect (Table 10)l49). A similar rate difference was observed for cyanide displacement reactions with polymer-supported cryptands in which the size of the cavity was varied 141). Polymer-supported phosphonium salt 4, as expected, gave no cation dependence of rates (Table 10). 

Polymer-supported polyethylene glycol) analogues 50 145.156.l67-16H> anc[ 5/ 167> were effective catalysts for hydroxide, iodide, and phenoxide displacement reactions, but not for cyanide, chloride, and acetate displacementsI69). These catalysts are highly active for various solid/solid/liquid phase transfer reactions (Sect. 6). 

On the other hand, if it were possible to block the coordination sites of a metal by using a strongly attached ligand such as cyanide, then "outer-sphere electron transfer reactions should become more important (12). 

The radical cations generated in some electron-transfer reactions can often be trapped by nucleophiles. Many of these reactions are of synthetic value. It has been shown that many phenylalkenes react with electron acceptors under the influence of light to give styry] cations which can be trapped by nucleophilic alcohols or cyanide ions for example, 1-phenylcyclopentene... 

Carbene Complexes Carbonyl Complexes ofthe Transition Metals Cyanide Complexes of the Transition Metals Dinuclear Organometallic Cluster Complexes Electron Transfer in Coordination Compounds Electron Transfer Reactions Theory Electronic Structure of Organometallic Compounds Luminescence Nucleic Acid-Metal Ion Interactions Photochemistry of Transition Metal Complexes Photochemistry of Transition Metal Complexes Theory Polynuclear Organometallic Cluster Complexes. 

Stopped flow and continuous flow methods [11] have been used to follow proton transfer reactions with half-lives in the millisecond range. The stopped flow method which is more popular is essentially a device for mixing the reactants rapidly (typically in one millisecond) together with some means of observing the fast reaction which follows. Proton transfer from p-nitrobenzyl cyanide to ethoxide ion in ethanol/ether mixtures at —77 °C was studied in this way [12]. The reaction was followed spectrophotometrically. The most rapid reaction occurred with ti/2 ca. 2 x 10 2 sec although the equipment was suitable for following reactions with f1/2 ca. 2 x 10 3 sec. A similar method has been used to measure rates of proton transfer between weak carbon acids (for example, triphenylmethane) and bases (for example, alkoxide ions) in dimethyl sulphoxide [13], A continuous flow apparatus with spectrophotometric detection was used [14] to measure rates of ionization for substituted azulenes in aqueous solution (4), reactions for which half-lives between 2 and 70 msec were observed. 

Vitamin B12 (cyanocobalamin) 3 is, in fact, not a natural product as the cyanide ligand to the cobalt ion is added during the isolation procedure. Coenzyme B12 (adenosylcobalamin) 4 and methylcobalamin 5 are the true final products of the biosynthetic pathway. Coenzyme 0,2 is the cofactor for a number of enzymic rearrangement reactions, such as that catalysed by methylmalonyl CoA mutase, and methylcobalamin is the cofactor for certain methyl transfer reactions, including the synthesis of methionine. A number of anaerobic bacteria produce related corrinoids in which the dimethylbenzimidazole moiety of the cobalamins (3 - 5) is replaced by other groups which may or may not act as ligands to the cobalt ion, such as adenine orp-cresol [12]. 

These two methods involve the potential release of toxic HCN during the reaction and a cleaner as well as a safer method is to use acetone cyanohydrin 128 as a cyanide transfer reagent. The enzyme from the Brazilian rubber tree Hevea brasiliensis, called a hydroxynitrile lyase, catalyses cyanohydrin formation from aliphatic as well as aromatic aldehydes.40... 

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