Basicity of Amines Amine Salts

A convenient way to compare the base strengths of amines is to compare the pA a values of their conjugate acids, the corresponding alkylaminium ions (Sections 3.6C and 20.3D). 

The equilibrium for an amine that is relatively more basic wiU lie more toward the left in the above chemical equation than for an amine that is less basic. 

When we compare aminium ion acidities in terms of this equilibrium, we see that most primary alkylaminium ions (RNH3+) are less acidic than ammonium ion (NH4+). In other words, primary alkylamines (RHN2) are more basic than ammonia (NH3)  

We can account for this on the basis of the electron-releasing ability of an alkyl group. An alkyl group releases electrons, and it stabilizes the alkylaminium ion that results from the acid-base reaction by dispersing its positive charge. It stabilizes the alkylaminium ion to a greater extent than it stabilizes the amine  

By releasing electrons, R stabilizes the alkylaminium ion through dispersal of charge. 

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Dialkyldimethyl and alkyltrknethyl quaternaries can be prepared direcdy from secondary and primary amines as shown ia equations 7 and 8, respectively. This process, known as exhaustive alkylation, is usually not the method of choice on a commercial scale. This technique requires the continuous addition of basic material over the course of the reaction to prevent the formation of amine salts (223,224). Furthermore, products such as inorganic salt and water must be removed from the quaternary. The salt represents a significant disposal problem. 

Basic Orange 1 (130) (aniline coupled to 2,4-diamiaotoluene) and Basic Orange 2 (22) (aniline coupled to y -phenylenediamiae) are examples of amine salt type cationic azo dyes. The cation is formed by protonation under acidic conditions. Under neutral or alkaline conditions, these dyes behave more like disperse dyes. In 1988 the U.S. production of Cl Basic Orange 2 amounted to 132 tons. 

By far the most important use of amine salt extractants is in the recovery of uranium from acidic leach liquors. The basic process was developed at the Oak Ridge National Laboratory in the USA,195 and essentially similar processes are currently in operation throughout the world. Examples of plant practice in the USA,196 Canada,197 Australia,198 South Africa199 200 and South West Africa201 have been described. 

Probably the most important chemical reaction of amines, at least in medical applications, is the basicity of amines. Most amines have a noticeable base strength and will accept a proton from a strong acid to form its conjugate acid. The conjugate acid of an amine is called an ammonium salt. The ionic salt is much more soluble in water than the electrically neutral freebase form. So, by... 

We can use the formation of amine salts to separate amines from less basic compounds (Figure 19-6). When shaken with a two-phase mixture of ether and water, the amine dissolves mostly in the ether layer. Drain the water (with inorganic impurities), add dilute... 

The preferred alkaline compounds for carrying out my invention are the alkali metal and alkaline earth metal oxides, hydroxides and carbonates, and these compounds are utilized in just sufficient amount to displace the desired amine or amines. It is obvious, of course, that if the mixture of amine salts also contains free mineral acid or an ammonium salt, an additional amoimt of alkali stoichiometrically equivalent to these substances must be added. I have also found that as alkaline reagents for accomplishing this separation it is possible to use other alkylamines or methylamines of different basicity. These amines may be used for displacement together with or in place of the alkalies above mentioned. For example, dimethylamine being more basic than trim-ethylamine may be utilized to displace triethylamine from its hydrohalide salts, when utilized in stoichiometrical proportions. Similarly, diethylamine may be utilized to displace mono and triethylamine from their hydrohalide combinations. 

In 1909, 4-amino-6-methyl-l,3,5-triazin-2-ol was obtained by cyclization of (acetylcarbamimi-doyl)urca under basic conditions.443 Subsequently, several new processes based on acylated dicyanodiamides were developed.444-447,449 Thus, when acyldicyanodiamides 1 are heated to reflux in 2-ethoxyethanol, 4-amino-1,3,5-triazin-2-ols 2 are obtained in crude yields of 60 to 100%.444,445 Catalytic amounts of amine salts significantly accelerate this reaction. After selective acid hydrolysis of acyldicyanodiamides, (acylcarbamimidoyl)ureas 3 are obtained which can also be cyclized to the 1,3,5-triazines 2. These reactions are carried out in excess sodium hydroxide solution and provide the triazines in 90 to 99% yield.443,444,446 447 Cyclization of 1-acylbiurets 4, prepared by acid hydrolysis of (acylcarbamimidoyl)ureas 3, is effected by treatment with potassium hydroxide solution.444,448 While the benzoyl derivative 3 (R = Ph) yields the corresponding l,3,5-triazine-2,4-diol 5 (R = Ph) in quantitative yield, the acetyl derivative 3 (R = Me) cyclizes only partially to the corresponding triazinediol 5 (R = Me).448... 

Possible surface treatment mechanisms include anodization [32-34], plasma and flame treatment [35], solution oxidation [36,37], gas phase oxidation, and high temperature oxidation. Some of these treatments have been reviewed 1 Donnet and coworkers [18,38]. The most practical surface treatment for commercial production of carbon fibers is anodization. This is because anodization (electrolytic oxidation) can be performed continuously on carbon fibers. Typical anodizations have been performed in aqueous acidic or basic solutions. Electrolytes include sodium hydroxide, potassium hydroxide, sulfuric add, nitric add, and solutions of amine salts. Amine salts have an added advantage in that, after treatment, excess electrolyte can be removed simply by heating the fiber to high temperatures (250 C). 

The basicity of amines and the solubility of amine salts in water can be used to separate amines from water-insoluble, nonbasic compounds. Shown in Figure 10.2 is a flowchart for the separation of aniline from anisole. Note that aniline is recovered from its salt by treatment with NaOH. 

The basicity of amines and the solubility of amine salts in water can be used to separate amines from water-insoluble, nonbasic compounds. 

The use of silver (II) salts, particularly argentic picolinate, as reagents for hydroxyl oxidation has also been disclosed recently. The reaction may be run in acid, neutral or basic media in aqueous or polar organic solvents at room or slightly elevated temperatures. Primary alcohols may be oxidized to aldehydes or acids depending on the conditions used. Amines and trivalent phosphorous compounds are more sensitive to oxidation with this reagent than are hydroxyl groups. 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

Either the iodo carbamate (96) or the iodo amine salt (94) from above can be converted to the aziridine by refluxing about 2.5 g of the respective product in 100 ml of ethanol which contains 10 ml of water and 10 g of potassium hydroxide for ca. 2 hr. The aziridine is then isolated by pouring the basic reaction mixture into 250 ml water and extracting with 200 ml ether. The ether extract is washed several times with water and dried (MgS04). Evaporation of the ether on a steam bath yields 2j5,3j5-iminocholestane (95, 25-95 %) as a clear oil which solidifies on standing mp 103-105°. This aziridine is not easily crystallized. 

Further substitution of benzoic acid leads to a drug with antiemetic activity. Alkylation of the sodium salt of p-hydroxy-benzaldehyde (8) with 2-dimethylaminoethyl chloride affords the so-called basic ether (9). Reductive amination of the aldehyde in the presence of ammonia gives diamine, 10. Acylation of that product with 3,4,5-trimethoxybenzoyl chloride affords trimetho-benzamide (11). ... 

The chemistry of amines ts dominated by the lone pair of electrons on nitrogen, which makes amines both basic and nucleophilic. They react with acids to form acid-base salts, and they react with electrophiles in many of the polar reactions seen in past chapters. Note in the following electrostatic potential map of trimethylamine how the negative (red) region corresponds to the lone-pair of electrons on nitrogen. 

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