Nucleophilic aliphatic salt effects

In 5 nI reactions of aliphatic substrates it is important to note that the electrophile is a carbonium ion and this is much less discriminating towards nucleophiles than are less reactive electrophilic species. In such reactions the nucleophilic strength of azide ion has no direct effect on rates, but is involved in determining product ratios in competitive reactions with other nucleophiles, including the solvent. Concentration factors are therefore important and salt effects of dissolved azides may also be significant -. 

Reaction with Nitrogen Nucleophiles. The acid-catalyzed reaction of primary, secondary, and tertiary amines with ethyleneimine yields asymmetrically substituted ethylenediamines (71). Steric effects dominate basicity in the relative reactivity of various amines in the ring-opening reaction with ethyleneimine (72). The use of carbon dioxide as catalyst in the aminoethylation of aliphatic amines, for which a patent application has been filed (73), has two advantages. First, the corrosive salts produced when mineral acids are used as catalysts (74,75) are no longer formed, and second, the reaction proceeds with good yields under atmospheric pressure. 

Studies on thiamine (vitamin Bi) catalyzed formation of acyloins from aliphatic aldehydes and on thiamine or thiamine diphosphate catalyzed decarboxylation of pyruvate have established the mechanism for the catalytic activity of 1,3-thiazolium salts in carbonyl condensation reactions. In the presence of bases, quaternary thiazolium salts are transformed into the ylide structure (2), the ylide being able to exert a cat ytic effect resembling that of the cyanide ion in the benzoin condensation (Scheme 2). Like cyanide, the zwitterion (2), formed by the reaction of thiazolium salts with base, is nucleophilic and reacts at the carbonyl group of aldehy s. The resultant intermediate can undergo base-catalyzed proton... 

Landini, D., A. Maia, and F. Montanari, Dehydrating Effect of Concentrated Aqueous Alkaline Solutions in Aliphatic Nucleophilic Substitutions Carried Out in Aqueous-Organic Two-Phase Systems The Different Behavior of Various Phase Transfer Catalysts Quaternary Salts, Crown Ethers and Cryptands, Isr.J. Chem., 26, 263 (1985). 

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