Menschutkin reaction ammonium salts

Heterocyclic amines have also been used as phase transfer catalysts. However, because these amines quaternize easily, the question is whether the operative catalyst is the tertiary amine or the quaternary ammonium salt formed in situ Furukawa et al.286 have shown that a methyl 2-pyridyl sulfoxide may be used as a phase transfer catalyst and promote substitution reactions between lithium chloride or sodium cyanide and benzyl bromide. According to the authors, the catalyst behaves as a cation complexer and not as a quaternary ammonium salt formed in situ by a Menschutkin reaction. 

An example of reaction type (c) in Table 5-4 is the well-known Menschutkin reaction [30] between tertiary amines and primary haloalkanes yielding quaternary ammonium salts. Its solvent dependence was studied very thoroughly by a number of investigators [51-65, 491-496, 786-789]. For instance, the reaction of tri-n-propylamine with iodomethane at 20 °C is 120 times faster in diethyl ether, 13000 times faster in chloroform, and 110000 times faster in nitromethane than in -hexane [60]. It has been estimated that the activated complex of this Menschutkin reaction should have a dipole moment of ca. 29 10 Cm (8.7 D) [23, 64], which is much larger than the dipole moments of the reactant molecules (tris- -propylamine 2.3 10 Cm = 0.70 D iodomethane 5.5 10-3 1 64 D) [64]. 

The influence of the solvent on the rate at which a chemical reaction takes place was aheady made clear, in the final stages of the XIX century, with the reaction of Menschutkin between tertiary amines and primary haloalkanes to obtain quaternary ammonium salts. The reaction of Menschutkin between triethylamine and iodoethane carried out in different media shows this effect (Table 2.1.3) ... 

Figure 6. Ammonium salt (6) synthesised by the Menschutkin reaction of triethyl amine with 5-norbomene-2 -exo-ylmethyl 6-bromohexyl ether. The norbomene compounds used and produced are racemates.

As noted earlier, the replacement of halogen by an amino group (a substitution reaction at carbon and at nitrogen [ ]) is generally not useful for the preparation of primary (RNH2) or secondary (R2NH) amines since the alkylamines are stronger bases than ammonia. However, the substitution reaction is useful for tertiary (R3N) amines, for example, the A-methylation of pyridine with methyl iodide (Equation 10.48) and the formation of other quaternary ammonium salts (cf. the Menschutkin reaction. Table 7.7, item h). 

Our compatriot N. A. Menshutkin made a great contribution to the development of the kinetics. In 1877 he studied in detail the reaction of formation and Iqrdrolysis of esters from various acids and alcohols and was the first to formulate the problem of the dependence of the reactivity of reactants on flieir chemical structure. Five years later when he studied the hydrolysis of tert-zmy acetate, he discovered and described the autocatalysis phenomenon (acetic acid formed in ester hydrolysis accelerates the hydrolysis). In 1887-, studying the formation of quaternary ammonium salts from amines and alkyl halides, he found a strong influence of the solvoit on the rate of this reaction (Menschutkin reaction) and stated the problem of studying the medium effect on the reaction rate in a solution. In 1888 N. A. Menschutkin introduced the term chmical kinetics in his monograph Outlines of Development of Chemical Views. ... 

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