Salts That Yield Basic Solutions

A salt consisting of the anion of a weak acid and the cation of a strong base yields a basic solution in water because the anion acts as a weak base, and the cation does not react. The anion of a weak acid accepts a proton from water to yield OH ion. Sodium acetate, for example, yields a basic solution because the Na ion, the cation of a strong base, does not react with water, and the CH3COO ion, the anion of the weak acid CH3COOH, acts as a weak base  

SAMPLE PROBLEM 18.10 Predicting Relative Acidity of Salt Solutions Problem Predict whether aqueous solutions of the following are acidic, basic, or neutral, and write an equation for the reaction of any ion with water  

Plan We examine the formulas to determine the cations and anions. Depending on the nature of these ions, the solution will be neutral (strong-acid anion and strong-base cation), acidic (weak-base cation and strong-acid anion, highly charged metal cation, or first anion of a polyprotic acid), or basic (weak-acid anion and strong-base cation). 

Solution (a) Neutral. The ions are K and C104 . The ion is from the strong base KOH, and the C104 anion is from the strong acid HCIO4. Neither ion reacts with water. 

FOLLOW-UP PROBLEM 18.10 Write equations to predict whether solutions of the following salts are acidic, basic, or neutral (a) KCIO2 (b) CH3NH3NO3 (c) Csl. 

SAMPLE PROBLEM 18.10 Predicting Relative Addity of Salt Solutions 

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Salts That Yield Neutral Solutions Salts That Yield Acidic Solutions Salts That Yield Basic Solutions Salts of Weakly Acidic Cations and Weakly Basic Anions... 

Salts such as NaCN that are derived from a strong base (NaOH) and a weak acid (HCN) yield basic solutions. In this case, the cation is neither an acid nor a base, but the anion is a weak base ... 

Most salts are strong electrolytes that dissociate completely into ions in solution. The reaction of these ions with water, called salt hydrolysis, can produce acidic or basic solutions. In salt hydrolysis, the conjugate bases of weak acids yield basic solutions, and the conjugate acids of weak bases yield acidic solutions. 

Salts that yield a neutral solution consist of ions that do not react with water. Salts that yield an acidic solution contain an unreactive anion and a cation that releases a proton to water. Salts that yield a basic solution contain an unreactive cation and an anion that accepts a proton from water. If both cation and anion react with water, the ion that reacts to the greater extent (higher K) determines the acidity or basicity of the salt solution. 

Irradiation of the phenolic diazonium salt 3 in basic solution produced glaziovine in 457o yield. This is an appreciably higher yield than that obtained by irradiation of the corresponding phenolic bromo compound 4. ... 

Salts that yield a basic solution contain an unreactive cation and an anion that accepts a proton from water. 

Tetrazolium salts are unstable in basic solutions yielding intense colors. This reaction is still little understood.233,234 In the reaction of 2,3,5-triphenyltetrazolium with hydroxide, it is postulated that a hydroxide ion is involved first as a counterion later leading to the hypothetical A-hydroxy-formazan (147).229 Weiner studied the kinetics of this reaction and identified 1,3,5-triphenylformazan in 10% yield. In concentrated alkaline solutions, the A-hydroxytetrazole (148) has been isolated from triphenyltetrazolium chloride (Scheme 19).235,236... 

The easiest way to 10 goes via the synthesis of KDNM (see Section n.C). Acidification of an aqueous solution of KDNM, which should be buffered with H3PO4 (pH = 6.5), followed by low-temperature extraction with diethyl ether, gives the monomeric emerald-green nitrosolic acid 10 dissolved in the ether phase. Slow removal of the solvent yields the yellowish dimeric form of 10. The acid (10) is only poorly characterized. It is known to slowly decompose into HCN and HNO2 in basic solution (decomposition of the anion DNM), while the free acid (10) rapidly decomposes to give fuhninic acid, HCNO and hyponitrous acid, HON=NOH. It should be noted that both the free acid and its metal DNM salts are highly explosive. 

Deprotection of the N-Boc group of piperidine 305 by TFA to afforded a TFA salt, followed by basic aqueous workup with aqueous NaHC03 solution gave a single racemate of perhydropyrido[2,l-c][l,4]oxazin-3-one 306, while that of the O-TBS protected piperidine 307 by TFA or TBAF yielded diastereomeric mixtures of 308 (09OBC655). 

Two series of compounds of arsenic are common that of arsenic(III) and arsenic(V). Arsenic(III) compounds can be derived from the amphoteric arsenic trioxide As203, which yields salts both with strong acids (e.g. arsenic(III) chloride, AsC13), and with strong bases (e.g. sodium arsenite, Na3As03). In strongly acidic solutions therefore the arsenic(III) ion As3+ is stable. In strongly basic solutions the arsenite ion, AsO is the stable one. Arsenic(V) compounds... 

As a result of the high ionic charge to radius ratio of titanium(IV), normal salts of titanium(IV) are difficult to prepare from aqueous solutions these often yield basic, hydrolyzed species. A tris-catechol species, [Ti(cat)3], prepared by Raymond etal. is one exception it is stable in aqueous solution up to pH 12. The catechol ligand is so stabilizing to Ti that the Ti ATi reduction potential is shifted from the value of -1-0.1V cited as the standard potential in acid in Scheme 1 to a value for [Ti(cat)3] of -1.14 V vs. NHE, affording a powerful example of ligand tuning of metal redox potential. 

In other cases the conductivities of redissolved hydroxide solutions are equal to those of alkali at the same concentration, suggesting that the solubility of the hydroxide is more probably due to the formation of a sol. For example, the freshly precipitated cream-coloured Ge(OH)j dissolves in strongly basic solutions to form reddish-brown colloidal solutions. ) Hydrolysis of metal-salt solutions often yields colloidal solutions of the hydroxides, as in the case of the trihydroxides of Fe and Cr and the tetrahydroxides of elements of the fourth Periodic Group such as Sn, Ti, Zr, and Th. It is unlikely that the hydroxides M(OH)4 of the latter elements are present in such solutions, for the water content of gels MO2. XH2O is very variable. 

Preliminary studies showed that 3 was unstable in acidic media at ambient temperature but was stable in basic solution or as a crystalline solid, hi order to overcome the instability of the free acid of 3 which would occur upon attempted isolation, a through process to prepare 5 was required. However, when 3 was formed in the presence of 3 equiv of i-Pr2NEt in 95% yield, and treated directly with 1.0 equiv of triazole HCl salt 4, the decarboxylation/aminolysis reaction was slow and resulted in incomplete reaction (even at 90°C for 24 h). The reaction stalled at about 80% conversion. 

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