Triethylamine reaction rate with methyl iodide

Similar to other tertiary aliphatic amines, quinuclidine easily forms salts with mineral and organic acids, and quaternary derivatives with alkyl halides. However, the rates of reaction of alkyl iodides with quinuclidine are significantly higher than with tertiary aliphatic amines.32 For example, quinuclidine reacts with methyl iodide 50 times faster, and with isopropyl iodide 700 times faster, than does triethylamine. The addition compound of trimethylborane with quinuclidine is more stable than the corresponding adducts of tri-alkylamines. These results can be explained by the almost total... 

In the last chapter we saw that there is no single measure of acidity and basicity. Similarly, there is no single measure of nucleophilicity and electrophilicity—the rank order of nucleophiles is totally upset when the reference electrophile is changed. A hard nucleophile like a fluoride ion reacts fast with a silyl ether in an SN2 reaction at the silicon atom, which is relatively hard, but a soft nucleophile like triethylamine does not. In contrast, triethylamine reacts with methyl iodide in an SN2 reaction at a carbon atom but fluoride ion does not. These examples, which are all equilibria, are governed by thermodynamics, but there are similar examples illustrating divergent patterns of nucleophilicity in the rates of reactions. 

The role of solvent effects in quaternization is one of the first physical organic studies and this is due to Menschutkin (1879LA334). It shows an increase in relative rate from 1 to 742 on going from benzene to benzyl alcohol, which suggests no simple explanation. Typical ranges of solvent-dependent rate ratios are 15,700/1 (nitromethane/cyclohexane) in the alkylation of triethylamine by methyl iodide (68BSF2678), 1660/1 [dimethylsulfoxide (DMSO)/carbon tetrachloride] in the reaction of l,4-diazabicyclo[2,2,2]-octane (DABCO) (5) with (2-bromoethyl)benzene (75JA7433) (Scheme 5),... 

Wetzler and coworkers123 employed 4-aminophthalimide (63) and 4-amino-lV-methyl-phthalimide (64) as solvatochromic (and thermochromic) fluorescent probes in solvent mixtures. A bathochromic shift of the emission spectra was found in mixtures of toluene with ethanol and with acetonitrile123 when the more polar solvent was added to toluene, but raising the temperature causes a relative hypsochromic effect. Mixtures of benzene and acetonitrile were studied by Nevecna and coworkers124 for their polarity by means of the probes 46 and 47 and with respect to the correlation of this with the rate constants of the reaction of triethylamine with ethyl iodide. The fluorescence of the ammonium salt of 4-(l-naphthylsulfonate)aniline (84) in dioxane and water mixtures was studied by Hiittenhain and Balzer125. 

The rate of reaction of methyl iodide with quinuclidine was measured in nitrobenzene, and then the rate of reaction of methyl iodide with triethylamine was measured in the same solvent. 

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