Properties of Amines

Keep in mind that we are comparing the boiling points of amines with comparable alkanes and alcohols. Among amines only primary and secondary amines can form hydrogen bonds. Lower amines are soluble in water. 

The bonding in alkylamines is similar to the bonding in ammonia. The nitrogen atom is sp -hybridized, with the three substituents occupying three corners of a tetrahedron and the lone pair of electrons occupying the fourth corner. As you might expect, the C-N-C bond angles are close to the 109° tetrahedral value—108° in trimethylamine, for example. 

One consequence of tetrahedral geometry is that an amine with three different snhstituents on nitrogen is chiral, as we saw in Section 5.10. Unlike chiral carbon compounds, however, chiral amines can t usually he resolved because the two enantiomeric forms rapidly interconvert by a pyramidal inversion, much as an alkyl halide inverts dming an Sn2 reaction. Pyramidal inversion occurs by a momentary rehybridization of the nitrogen atom to planar, sp geometry, followed by rehybridization of the planar intermediate to 

ACTIVE FIGURE 18.1 Pyramidal inversion rapidly interconverts the two mirror-image (enantiomeric) forms of an amine. 

Co to this book s student companion site at www.cengage. com/chemistry/mcmurry to explore an interactive version of this figure. 

Alkylamines have a variety of applications in the chemical industry as starting materials for the preparation of insecticides and pharmaceuticals. Lahetalol, for instance, a so-called 8-blocker used for the treatment of high blood pressure, is prepared by Sn2 reaction of an epoxide with a primary amine. The substance marketed for drug use is a mixture of all four possible stereoisomers, but the biological activity derives primarily from the [R,R] isomer. 

Problem 24.2 li)raw structures corresponding to the following lUPAC names  

Problem 24.3 Draw structures for the following heterocyclic amines  

Like alcohols, amines with fewer than five carbon atoms are generally water-soluble. Also like alcohols, primary and secondary amines form hydrogen bonds and are highly associated. As a result, amines have higher boiling points than alkanes of similar molecular weight. Diethylamine (MW = 73 amu) boils at 56.3 °C, for instance, while pentane (MW - 72 amu) lioils at 36.1 °C. 

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The noteworthy properties of amines are their basicity and their nucleophilicity The basicity of amines has been discussed m Section 22 4 Several reactions m which amines act as nucleophiles have already been encountered m earlier chapters These are sum marized m Table 22 4... 

The physical properties of amine oxides are attributed to the semipolar or coordinate bond between the oxygen and nitrogen atoms with high electron density residing on oxygen. 

BOILER AND FEED-WATER TREATMENT Table 17.4 Properties of amines... 

Information reflecting the various basicity properties of amines may be presented as Kb or as the pertinent dissociation constants pKJpK as shown in Table 11.5. 

From a practical perspective, DR (along with neutralization capacity and basicity) is one of the most important functional properties of amines and is always referred to when selecting amines for application in a steam-condensate system. Amine DR values vary considerably, however, and for each amine the DR value changes with variation of temperature and pressure. 

Amines are polar compounds. Primary and secondary amines can form hydrogen bonds, but tertiary amines cannot. Table 1.8 lists some common physical properties of amines. 

As noted earlier (see section 12.3.1), the Amex process, which uses long-chain amines, is preferred over the Dapex process, which uses HDEHP, for solvent extraction of uranium from H2SO4 leach solutions. Because the surfactant properties of amine sulfates are conducive to formation of objectionable emulsions, the Amex process is very sensitive to the presence of solids in the H2SO4 leachate. For acceptable phase coalescence in the Amex process, feeds should contain no more than 20 ppm solids. The Dapex process can tolerate feeds containing as much as 100 ppm solids. 

Ion pair extraction has also been used to extract polar analytes in bioanalytical procedures. Figure 15.2 exemplifies the determination of the amino acid taurine by gas chromatography-mass spectrometry (GC-MS) this figure also illustrates a useful property of amines (and phenols), which is that they will react more rapidly than water with an acylating reagent in an aqueous environment thus improving their organosolubility. After acylation and ion pair extraction with tetrabutyl ammonium sulphate the taurine is converted to an amide prior to analysis by GC-MS. 

Soliman EM. S3mthesis and Metal Collecting Properties of Amines, Mono, Di, Tii, and Tetraamine Based on a Silica Gel Matrix. Analytical Letters 1997 30 1739-1751. 

R.R. Eagan, J. Am. Oil. Chem. Soc. 45, 481-486 (1968) The Preparation and Properties of Amines and Cationic Surfactants from Fatty Acids". 

Hall, I.H., S.Y Chen, K.G. Rajendran, A. Sood, B.E. Spielvogel, and J. Shih. 1994. Hypolipidemic, antiobesity, anti-inflammatory, anti-osteoporotic, and anti-neoplastic properties of amine carboxyboranes. Environ. Health Perspec. 102(Suppl. 7) 21-30. 

Based on the excellent solubility and reducing properties of amine boranes, they are often used for the stabilization and purification of industrial materials. Further, they are applied as additives in hydrocarbon fuels and in lubricating oils, as polymerization catalysts, as ingredients in photographic processing and in the electroplating industry.169 High stability towards hydrolysis and oxidation makes cationic boron chelates useful as water-soluble dyes.170... 

The physical properties of amines depend in an important way on the extent of substitution at nitrogen. Thus primary amines, RNH2, and secondary amines, R2NH, are less volatile than hydrocarbons of similar size, weight, and shape, as the following examples show ... 

Perhaps the most characteristic property of amines is their ability to act as bases by accepting protons from a variety of acids ... 

Another route is based on the well-known property of amines to add to aldehydes to form aminals. The conversion of these intermediates provides entries to tertiary SMAs. For example, simple treatment of A-benzyl MSMA with formaldehyde gives the corresponding diaminomethane derivative in good yield.219... 

To show some physical and chemical properties of amines and amides. 

Q Describe the trends in the physical properties of amines, and contrast their physical properties with those of their salts. 

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