Amine tetraalkylammonium halide

The tetraalkylammonium halides formed by complete alkylation of amines are ionic compounds that resemble alkali-metal salts. When silver oxide is used to precipitate the halide ion, tetraalkylammonium halides are converted to tetraalkylammonium hydroxides, which are strongly basic substances similar to sodium or potassium hydroxide ... 

The nitrogen ylides (3.60) are formed as intermediates in the Sommelet rearrangement ". The method is used for the conversion of the tetraalkylammonium halides 3.59 (having hydrogen in an a-position to N) into tertiary aromatic amines 3.61 (Scheme 3.25). 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniate," MINI-lj),. is formed. Lanthanide elements with stable + 2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and tetraalkylammonium halides yields blue solutions, presumably containing Al, 3e Be", 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexamethylphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

The synthesis of quinoline derivatives using metal catalyzed processes continues to be of interest. A modified preparation of 2,3-dialkylquinolines was reported <04JHC423> from nitroarenes and tetraalkylammonium halides via an in situ ruthenium-catalyzed reduction followed by an intrinsic amine exchange reaction using tin(ll) chloride. One of the examples reported is shown below in Scheme 25. 

The final product from such a series of nucleophilic substitution and proton transfer reactions is a tetraalkylammonium halide. TTie relative proportions of the various alkylation products depend on the ratio of alkyl halide to ammonia in the reaction mixture. V atever the starting mixture, however, the product is almost invariably a mixture of alkylated products. For this reason, alkylation of ammonia or amines is not... 

Various sources of fluoride ion have been investigated, of which highly nucleophilic tetraalkylammonium fluorides ate the most effective Thuf, fluoro alkyl halides and N (fluoroalkyl)amines are efficiently synthesized by treatment of the corresponding trifluoromethanesulfonic esters with tetrabutylammonium fluoride trihydrate in aprotic solvents [5fl] (equation 34) The displacement reactions proceed quantitatively at room temperature within seconds, but tail with hydrogen fluoride-pyridine and give reasonable yields only with hydrogen fluo ride-alkylamine reagents... 

The disadvantage of direct alkylation lies in stopping it at the desired stage. Even if just one equivalent of the halide is added, some amine molecules will react once, some will react twice, and some will react three times (to give the tetraalkylammonium salt). Others will not react at all. A complex mixture results. 

Exhaustive alkylation to the tetraalkylammonium salt. Mixtures of different alkylated products are avoided if enough alkyl halide is added to alkylate the amine as many times as possible. This exhaustive alkylation gives a tetraalkylammonium salt. A mild base (often NaHC03 or dilute NaOH) is added to deprotonate the intermediate alkylated amines and to neutralize the large quantities of HX formed. 

Tetraalkylammonium salts, first synthesized by Hofmann in 1851 by the reaction of a tertiary amine with an alkyl halide, are soluble in various polar solvents. These salts form crystalline hydrates that contain large numbers of water of hydration molecules. The unusual physical properties of tetraalkylammonium salts and their effects on the structure of bulk water have been reported.2 3,4,5 currently, several theories exist as to the effects of the tetraalkylammonium cations on the structure or entropy of bulk water. Yet to be understood are the effects of the anions associated with the tetraalkylammonium ions on the overall structure of water. Not only Is the theory of interactions of such salts with water of interest to those engaged in basic chemistry, but the salts also are used in various applications. 

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