Alkylamine basicity

Just as aniline is much less basic than alkylamines because the unshared electron parr of nitrogen is delocalized into the tt system of the nng p nitroamlme is even less basic because the extent of this delocahzahon is greater and involves the oxygens of the nitro group... 

Nonaromatic heterocyclic compounds piperidine for example are similar m basic ity to alkylamines When nitrogen is part of an aromatic ring however its basicity decreases markedly Pyridine for example resembles arylammes m being almost 1 mil lion times less basic than piperidine... 

Tetrahydroisoqumoline is a stronger base than tetrahydroquinohne The unshared electron pair of tetrahydroquinohne is delocalized into the aromatic nng and this substance resembles am line m its basicity whereas tetrahydroisoqumoline resembles an alkylamine... 

ALkylamines are corrosive to copper, copper-containing alloys (brass), aluminum, 2inc, 2inc alloy, and galvani2ed surfaces. Aqueous solutions of aLkylamines slowly etch glass as a consequence of the basic properties of the amines in water. Carbon or stainless steel vessels and piping have been used satisfactorily for handling aLkylamines and, as noted above, some aLkylamines can act as corrosion inhibitors in boiler appHcations. 

Amines. Although the chlorination of aqueous aLkylamines is analogous to that of ammonia, mono- and diaLkylarnines generally chlorinate faster because of their higher basicities (13). Bromination rates are significantly faster than chlorination rates, and in some cases, eg, (CH2)2NH... 

The small differences in basicity between fflumonia and alkylamines, and fflnong the various classes of alkylamines (primary, secondary, tertiary), come from a mix of effects. Replacing hydrogens of ammonia by alkyl groups affects both sides of the acid-base equilibrium in ways that largely cancel. 

In addition to being more basic than arylamines, alkylamines are also more nucleophilic. All the reactions in Table 22.4 take place faster with alkylamines than with arylanines. 

Table 24.1 lists pXa values of some ammonium ions and indicates that there is a substantial range of amine basicities. Most simple alkylainines are similar in their base strength, with p/q/s for their ammonium ions in the narrow range 10 to 11. Aiylctmines, however, are considerably less basic than alkylamines, as are the heterocyclic amines pyridine and pyurole. 

As noted previously, arylamines are generally less basic than alkylamines. Anilinium ion has pKa = 4.63, for instance, whereas methylammonium ion has pfCa = 10.64. Arylamines are less basic than alkylamines because the nitrogen lone-pair electrons are delocalized by interaction with the aromatic ring tt electron system and are less available for bonding to H+. In resonance terms, aryl-amines are stabilized relative to alkylamines because of their five resonance forms. 

Much of the resonance stabilization is lost on protonation, however, so the energy difference between protonated and nonprotonated forms is higher for arvlamines than it is for alkylamines. As a result, arylamines are less basic. Figure 24.3 illustrates the difference. 

Another fallacy to be refuted by PA data was the widespread belief that the low basicity of arylamines compared to alkylamines simply reflects delocalization of the lone pair of electrons on the nitrogen atom within the aromatic ring. Thus, the low basicity of aniline (pKa = 4.58) compared to ammonia (pKa = 9.27) is often attributed to such a conjugative... 

The gas-phase basicity order of alkylamines can be reproduced in terms of softness of the alkyl groups (using the Fukui function and local softness parameter ), this being far more important than group electronegativity58. 

Evans and co-workers demonstrated that rhodium-catalyzed allylic amination of enantiomerically enriched acyclic unsymmetrical allylic carbonates occurs with excellent regio- and enantiospedfidty (Tab. 10.5) [35]. Interestingly, while the classical nitrogen nucleophiles furnished allylic amination products in poor yield and with modest regioselectivity, the lithium anion of N-toluenesulfonyl-N-alkylamines proved optimal, in terms of nucleophilicity and basicity. 

Alkylamines differ very little among themselves in basicity. Their basicities cover a range of less than 10 in equilibrium constant (1 pK unit). 

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