Ammonia conjugate bases

When an acid and a base react, the products are a new acid and base. For example, the acetate ion, C1T3COO-, in reaction 6.7 is a base that reacts with the acidic ammonium ion, N1T45", to produce acetic acid and ammonia. We call the acetate ion the conjugate base of acetic acid, and the ammonium ion is the conjugate acid of ammonia. 

Addition of nucleophiles sueh as ammonia or alcohols or their conjugate bases to benzynes takes place very rapidly. These nueleophilie additions are believed to involve eapture of the nueleophile, followed by protonation to give the substituted benzene. ... 

Example A common misconception is that the conjugate base of a weak acid is strong. This is sometimes, but not always, true. It is tme, for exanple, for ammonia, which is a very weak acid (pK 36). Its conjugate base amide ion (H2N ) is a much stronger base than HO . It is not true, however, for acetic acid both acetic acid and its conjugate base acetate ion are weak. The conjugate base of a weak acid will be strong only when the acid is a weaker acid than water. 

The two-step procedure includes formation of a N-substituted phthalimide 3, and its subsequent cleavage to the primary amine 5. Phthalimide (which can be obtained from reaction of phthalic acid with ammonia) shows NH-acidity, since the negative charge of the phthalimide anion (the conjugated base) is stabilized... 

Problem 2.11 Nitric acid (HN03) reacts with ammonia (NH3) to yield ammonium nitrate. Write the reaction, and identify the acid, the base, the conjugate acid product, and the conjugate base product. 

Where do hydrocarbons lie on the acidity scale As the data in Table 8.1 show, both methane (pKa 60) and ethylene (plC, = 44) are very weak acids and thus do not react with any of the common bases. Acetylene, however, has piCa = 25 and can be deprotonated by the conjugate base of any acid whose pKa is greater than 25. Amide ion (NH2-), for example, the conjugate base of ammonia (pKa - 35), is often used to aeprotonate terminal aikynes. 

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. 

To express the relative strengths of an acid and its conjugate base (a conjugate acid-base pair ), we consider the special case of the ammonia proton transfer equilibrium, reaction C, for which the basicity constant was given earlier (Kb = [NH4+l[OH ]/ NH3]). Now let s consider the proton transfer equilibrium of ammonia s conjugate acid, NH4+, in water ... 

We have seen how to estimate the pH of a solution of a weak acid or base (Chapter 10), but suppose that a salt of the acid or base is also present. How does that salt affect the pH of the solution Suppose we have a dilute hydrochloric acid solution and add to it appreciable concentrations of the conjugate base, the Cl- ion, as sodium chloride. Because the acid is strong, its conjugate base is extremely weak and so has no measurable effect on pH. The pH of 0.10 M HCl(aq) is about 1.0, even after 0.10 mol NaCl has been added to a liter of the solution. Now suppose instead that the solution contains acetic acid to which sodium acetate has been added (the acetate ion, CH jC()2, is the conjugate base of CH COOH). Because the conjugate base of a weak acid is a base, we can predict that adding acetate ions (as sodium acetate) to a solution of acetic acid will increase the pH of the solution. Similarly, suppose we have a solution of ammonia and add ammonium chloride to it. The... 

The most important type of mixed solution is a buffer, a solution in which the pH resists change when small amounts of strong acids or bases are added. Buffers are used to calibrate pH meters, to culture bacteria, and to control the pH of solutions in which chemical reactions are taking place. They are also administered intravenously to hospital patients. Human blood plasma is buffered to pH = 7.4 the ocean is buffered to about pH = 8.4 by a complex buffering process that depends on the presence of hydrogen carbonates and silicates. A buffer consists of an aqueous solution of a weak acid and its conjugate base supplied as a salt, or a weak base and its conjugate acid supplied as a salt. Examples are a solution of acetic acid and sodium acetate and a solution of ammonia and ammonium chloride. 

The cyanide ion, CN-, is the conjugate base of hydrogen cyanide, HCN. This acid is made by heating ammonia, methane, and air in the presence of a platinum catalyst ... 

It works the same way for bases. Every base has a conjugate acid. The ammonium in the above equation, for example, is ammonias conjugate acid. The ammonium ion has an extra proton that it can donate, making it an acid. 

In this reaction, acetic acid donates a proton to produce its conjugate, the acetate ion, which is able to function as a proton acceptor. Ammonia accepts a proton to produce its conjugate, the ammonium ion, which can function as a proton donor. Two species that differ by the transfer of a proton are known as a conjugate pair. The conjugate acid of H20 is H30+, and the conjugate base of H20 is OH-. 

Formation of the conjugate base of phosphine under the conditions of aqueous dioxane and KOH with red phosphorus allows also for the formation of C-P bonds by attack of oxiranes.33 Under these conditions, mixtures of phosphines and phosphine oxides are formed. Using red phosphorus in liquid ammonia with sodium metal and f-butyl alcohol, good yields of primary (2-hydroxyalkyl)phos-phines are obtained.34... 

The conjugate acid of a base is formed when the base acquires a proton from the acid. In this reaction, water acts as an acid because it donates a proton to the ammonia molecule. The ammonium ion (NH4+) is the conjugate acid of ammonia (NH3), a base, which receives a proton from water. The hydroxide ion (OH ) is the conjugate base. 

There are two ways to solve this problem. Assume x = [OH ] = [NH4] that comes from the reaction of the ammonia. Ammonia is the conjugate base (A ) of the ammonium ion (HA). 

It has been postulated that in the hydrazine solution (pH 8) the N-amino-4,6-dimethylpyrimidinium ion is partly deprotonated into its conjugate base, the resonance-stabilized ylide 31, so that in fact in this solution two equilibrated active species, 30 and 31, are present (62TL387 63AG604).The formation of an ylide intermediate was experimentally supported by the isolation of the dimer 2,4,7,9-tetramethyldipyrimido[l,2-fe r,2 -c]hexahydrotetrazine (32), which is formed when the pyrimidinium salt 30 is treated with liquid ammonia (Scheme III. 19). 

Thus, in liqnid ammonia, the amide ion may be used to convert an acetylene to its acetylide ion conjugate base (see Section 6.3.4). 

A simple example follows from the reactions considered in Section 4.11.1. We saw that we needed to use a strong base such as the amide ion to form the conjugate base of an acetylene. This reaction was favoured, in that the products were the weaker base acetylide and the weaker acid ammonia. 

These compounds ionize and act as sources of hydride and amide ions respectively, which are able to remove a-protons from carbonyl compounds. These ions are actually the conjugate bases of hydrogen and ammonia respectively, compounds that are very weak acids indeed. What becomes important here is that enolate anion formation becomes essentially irreversible the enolate anion formed is insufficiently basic to be able to remove... 

This occurs because 3-pyridyne (3,4-didehydropyridine) is formed by an alternative mechanism is the ElcB process [elimination (first order) from the conjugate base], SowM 3-Pyridyne then adds ammonia the addition is not regiospecific and two second step, amino derivatives are formed. 

Proton removal for the purpose of preparing negatively charged conjugate bases in conditions suitable for direct NMR observation may be effected on exposure of the free amine to strongly basic conditions such as potassium amide in liquid ammonia for ben-zazonine (5c) and potassium mirror in THF for aza[13]annulene (37a). 

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