Amines basic properties

Although NF is an amine, it exhibits virtually no basic properties and is not protonated by the HSO F—SbF —SO superacid medium at 20°C (19). Commercial scmbbing systems for unwanted NF are available (20) and work on the principle of pyrolysis of the NF over reactive substrates at high temperatures. 

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. 

On the above basis it is, in principle, unnecessary to treat the strength of bases separately from acids, since any protolytic reaction involving an acid must also involve its conjugate base. The basic properties of ammonia and various amines in water are readily understood on the Bronsted-Lowry concept. 

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, amine basicity is clearly an important functional property because (as has been noted) when temperatures rise and Kb decreases, amine concentration must increase simply to maintain pH level. Often a sharp increase in concentration is needed to actually raise the pH. 

The structures of the amino acids reveal any functional groups that result In acidic or basic properties. To determine the acid-base properties of these compounds, look for carboxyl groups and amine groups. 

However, in more complicated amines, this straight correlation is violated. The bicyclic tertiary amine l-azabicyclo[4.4.4]tetradecane (22) and the acyclic tertiary amine n-Bu3N have nearly the same first IP (7.84 and 7.90 eV, respectively), but the proton affinity of the bicyclic amine is 20 kcal mol 1 lower than that of the acyclic52. On the other hand, for other bridge-head tertiary amines like l-azabicyclo[2.2.2]octane (quinuclidine, 20) and l-azabicyclo[3.3.3]undecane (manxine, 21) the expected relation between proton affinities and IP values is observed. The extraordinary properties of l-azabicyclo[4.4.4]tetradecane (22) are caused by its unusual conformation the nitrogen lone-pair is directed inward into the bicycle where protonation is not possible. In the protonated form, the strained out-conformation is adopted. This makes it the least basic known tertiary amine with purely saturated alkyl substituents. Its pKa, measured in ethanol/water, is only +0.693. Strain effects on amine basicities have been reviewed by Alder88. 

Heptamethylbiguanide catalyses the addition of phenyl isocyanate to alcohols more powerfully than do other amines, a property that is ascribed to its high basic strength (211). 

Alkaloids are found mainly in plants, and are nitrogenous bases, typically primary, secondary, or tertiary amines. The basic properties facilitate their isolation and purification. Water-soluble salts are formed in the presence of mineral acids (see Section 4.11.1), and this allows separation of the alkaloids from any other compounds that are neutral or acidic. It is a simple matter to take a plant extract in a water-immiscible organic solvent, and to extract this solution with aqueous acid. Salts of the alkaloids are formed, and, being water soluble, these transfer to the aqueous acid phase. On basifying the acid phase, the alkaloids revert back to an uncharged form, and may be extracted into fresh organic solvent. 

Opium contains over 40 different alkaloids, all of which will be exuacted from opium by the procedure just described. It then remains to separate morphine from this mixture. Of the main opium alkaloids, only morphine displays some acidic properties as well as basic properties. Although a tertiary amine, morphine also contains a... 

Ethanolamine nitric ester nitrate (ethanolamine dinitrate) N03NH3CH2CH20N02 is a solid melting at 103°C. According to Naoum this compound can be prepared by nitrating ethanolamine [68], Aubry [69] has reported that a yield of 90-96% can be achieved in this reaction. This method of preparation has not been confirmed by some authors. Serious disadvantages of the substance include its inclination to absorb moisture, and the readiness with which it loses nitric acid owing to the wealdy basic properties of the amine [70],... 

Unlike amines, imides do not have basic properties in water solution the electron pair of nitrogen is partly delocalized over the carbonyl groups,... 

The basic properties of the aromatic amines decrease with the number of radicles introduced the primary aromatic amines are stable the secondary aromatic amines are decomposed by water and the tertiary aromatic amines are unstable. In organic chemistry, compounds containing the monadic group NH2 are called amines or amides and compounds with the dyadic group NH are called imides. The existence of compounds like... 

Typical recipes of compositions, widely used in the electrical industry and in the production of reinforced plastics, are given in Table 1.2, while the basic properties of epoxy plastics cured by amine and anhydride hardeners can be found in Table 1.1. 

Eyal, A.M. Canari, R. pH dependence of carboxylic and mineral acid extraction by amine-based extractants Effects of pKa, amine basicity, and diluent properties, Ind. Eng. Chem. Res. 34 (1995) 1789-1798. 

Since amines are organic bases, water solutions show weakly basic properties. If the basicity of aliphatic amines and aromatic amines are compared to ammonia, aliphatic amines are stronger than ammonia, while aromatic amines are weaker. Amines characteristically react with acids to form ammonium salts the nonbonded electron pair on nitrogen bonds the hydrogen ion. 

We met the amino group when we were discussing the amino acids we mentioned that it was this group that gave these compounds their basic properties. Amines often have powerful fishy smells the smell of putrescine is particularly foul. It is formed as meat decays. Many neurologically active compounds are also amines amphetamine is a notorious stimulant. 

The nitrogen atom, as in aliphatic amines, pyridine etc., exhibits basic properties, that is to say the nitrogen atom can bind a proton through its free electron pair. In pyrrole the resonance possibilities II and III are, however, lost on the addition of a proton, so that the positive ion is thus not stabilized by resonance, whereby the proton attraction, that is the basicity, is very small for pyrrole. The formation of a negative ion, as in pyrrole-potassium, gives no hindrance so that pyrrole does show acid properties. 

Sorption of amines on starch was recognized760 as early as 1910 in studies of the interactions between starch and piperidine. Experiments with starch and 1 -butylamine show extraordinarily high and fast adsorption. The equilibrium concentration of that amine reaches 1982 mg/g of starch, as compared to n-hexane (6 mg/g), ethyl acetate (27 mg/g), and ethanol (208 mg/ g). Desorption is, in fact, also significant, but is much lower than in the case of the other complexes just mentioned. Because of their basic properties, amines decompose their host molecule.674 Less-basic amines, such as aromatic trypoflavin761 and aliphatic amine salts,762 can be included into starch. 

General, Remarks. Primary aromatic amines, whose basic properties are not too strongly reduced by the presence of negative substituents, can often be nitrated smoothly without protecting the amino group by acetylation or the like. The nitration is carried out in the presence of a large amount (at least 10 parts) of concentrated sulfuric acid and at as low a temperature as possible, below 0 in any case. The nitric acid must be entirely free from HNO2. 

The observations that secondary amines, (Rf)2NH, do not react with boron trifluoride, hydrogen chloride or trifluoroacetic acid [13] also serve to indicate a lack of basic properties. Similarly, tertiary perfluoroalkylamines are quite without basic properties. Moreover, the oxygen atoms in perfluoroalkyl ethers and ketones are poor donors this is exemplified by the fact that hexafluoroacetone cannot be protonated by superacids in solution. Such findings parallel similar observations with unsaturated derivatives where the base strength is considerably reduced in, for example, perfluorop3Tidine or perfluoro-quinoline [14] in comparison with the parent compounds. 

Systems in which the nitrogen is attached to carbon bearing only perfluoroalkyl groups, rather than fluorine, are particularly stable but weak bases for example, perfluoro-f-butylamine is practically devoid of basic properties [269] (Figure 8.104). Diazotisation of the amine gives a mixture of the alcohol and the nitroso derivative [270] (Figure 8.105). 

Types of Solvent.—In order that a particular solvent may permit a substance dissolved in it to behave as an acid, the solvent itself ifiust be a base, or proton acceptor. A solvent of this kind is said to be proto-philic in character instances of protophilic solvents are water and alcohols, acetone, ether, liquid ammonia, amines and, to some extent, formic and acetic acids. On the other hand, solvents which permit the manifestation of basic properties by a dissolved substance must be proton donors, or acidic such solvents arc protogenic in nature. Water and alcohols arc examples of such solvents, but the most marked protogenic solvents are those of a strongly acidic character, e.g., pure acetic, formic and sulfuric acids, and liquid hydrogen chloride and fluoride. Certain solvents, water and alcohols, in particular, are amphiprotic, for they can act both as proton donors and acceptors these solvents permit substances to show both acidic and basic properties, whereas a purely protophilic solvent, e.g., ether, or a completely protogenic one, e.g., hydrogen fluoride, would permit the manifestation of either acidic or basic functions only. In addition to the types of solvent already considered, there is another class which can neither supply nor take up protons these are called aprotic solvents, and their neutral character makes them especially useful when it is desired to study the interaction of an acidic and a basic substance without interference by the solvent. 

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