Amines, relative nucleophilic

One potential problem with this procedure is that the product can sometimes act as a nitrogen nucleophile, and multiple substitutions may then occur. It is useful, therefore, to be able to distinguish the relative nucleophilicity of different amines. 

The amine-catalyzed mercaptan-epoxide reaction (Equation 4) proceeds exothermally at room temperature (27. 28). The order of average relative nucleophile-displacement rates (Table II) further suggests that mercaptans react significantly faster than amines and that the addition of the mercaptlde (RS ) ion to the epoxide group is the rate determining step (30). 

The pattern of base catalysis of reactions with amine nucleophiles provides additional evidence. These reactions are catalyzed by bases only when a relatively poor leaving group (such as OR) is present (not Cl or Br) and only when relatively bulky amines are nucleophiles. Bases could not catalyze step 1, but if amines are nucleophiles, bases can catalyze step 2. Base catalysis is found precisely in those cases where the amine moiety cleaves easily... 

The problem of water in ionic ring-opening polymerization is much less critical than in vinyl polymerization, because, if present, water in the former system has to compete with relatively nucleophilic monomer present in large excess. Thus, certain polymerizations (e.g., polymerization of cyclic amine-conidine) can be conducted even in alcohols as solvents. 

Reaction with silyl enol ethers. Derivatives from ketones and esters behave to- ards arenediazonium salts according to their relative nucleophilicities. a-Arylation, 9 ketones by a free radical pathway and nonradical a-amination of esters are. bserved. 

In principle, the interaction of a phosphorus(III) ester with an co-haloalkylamine should lead to an (co-aminoalkyl)phosphonic diester or a phosphinic acid analogue (Scheme 11). Such examples in the classical Michaelis-Arbuzov mould have been widely reported, but success in their outcome depends on the relative nucleophilicities of nitrogen and phos-phorus(III) centres towards the displacement of halogen. The interaction of triethyl phosphite and a halogen-substituted tertiary amine, such as 2-chloroethyldiethylamine, does not lead to a phosphonic diester, and in this particular case the product is a piperazinium diquaternary salt. However, successful Michaelis-Arbuzov reactions have been carried out between the bis(bromomethyl)phthalazines 130 (to both the mono- and di-phosphonic acid stages) and the series of [co-(2-cyano-4-pyridine)alkyl]phosphonic diesters 132 (n = 1-4) have been prepared from the 4-pyridinealkyl bromides 131 as precursors to the phosphonoalkylpiperidinecarboxylic acids 133 . ... 

The enhanced activity of the ruthenium and the ruthenium/iron catalysts in the amine solutions over those in alkali base solutions may be the result of several perturbations. Certainly, the solvent effects alone can play a role in this case given that the amine concentrations are suflS-cient to change markedly the properties of the medium. Thus solvation effects on a rate-determining step or key equilibrium in a cycle such as Scheme 1 would have major consequences on the catalytic activity. If CO activation in steps such as Reactions 8 or 9 can be affected instead by other nucleophiles (for example. Reactions 10, 11, 12), then the high concentrations of the amines, higher even than [H2O] under these conditions, plus the relative nucleophilicity of these species may accelerate the CO activation step. 

Generally, isolated olefinic bonds will not escape attack by these reagents. However, in certain cases where the rate of hydroxyl oxidation is relatively fast, as with allylic alcohols, an isolated double bond will survive. Thepresence of other nucleophilic centers in the molecule, such as primary and secondary amines, sulfides, enol ethers and activated aromatic systems, will generate undesirable side reactions, but aldehydes, esters, ethers, ketals and acetals are generally stable under neutral or basic conditions. Halogenation of the product ketone can become but is not always a problem when base is not included in the reaction mixture. The generated acid can promote formation of an enol which in turn may compete favorably with the alcohol for the oxidant. 

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