Types of Weak Bases

Anions of weak acids make up the second general category of weak bases. In an aqueous solution of sodium hypochlorite (NaClO), for example, NaClO dissociates to Na and CIO ions. The Na ion is always a spectator ion in acid-base reactions. 000 (Section 4.3) The CIO ion, however, is the conjugate base of a weak acid, hypo-chlorous acid. Consequently, the CIO ion acts as a weak base in water  

A solution made by adding solid sodium hypochlorite (NaQO) to enough water to make 2.00 L of solution has a pH of 10.50. Using the information in Equation 16.37, calculate the number of moles of NaClO added 

As such, it is a strong electrolyte that completely dissociates in solution into Na, a spectator ion, and CIO ion, a weak base with = 3.3 X 10  

Plan From the pH, we can determine the equilibrium concentration of OH . We can then constract a table of initial and equiUbrium concentrations in which the initial concentration of CIO is our unknown. We can calculate [CIO ] using the expression for K.  

Solve We can calculate [OH ] by using either Equation 16.16 or Equation 16.20 we will use the latter method here  

When hydroxylamine acts as a base, which atom accepts the proton  

Analyze NaClO is an ionic compound consisting of Na and CIO ions. As such, it is a strong electrolyte that completely dissociates in solution into Na, a spectator ion, and CIO ion, a weak base with Ky = 3.3 X 10 (Equation 16.37). Given this information we must calculate the number of moles of NaClO needed to raise the basicity of 2.00-L of water to 10.50. 

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It was soon realized that there are problems with this approach.24,25 Log ionization ratios for weak bases that are not primary aromatic amines, while linear in H0, do not give the unit slope required by equation (8). This soon led to many other acidity functions, defined for other types of weak base, HA for amides,24 Hq for tertiary aromatic amines,25 C0 or HR for carbocations,26,27 and so on. In a recent review of addity functions,28 28 different ones were listed... 

The second type of weak bases for imine ligations are 1,2- or 1,3-heterosubstituted amines of amino thiols and amino alcohols. Of the two, the amino thiols appear to be the more suitable choice because they form stable thiazolidine derivatives under very mild reaction condi-tions 84"89,114 121 140 Furthermore, the 1,2-and 1,3-aminothiol moieties are found in cysteines and homocysteines that form a stable heterocyclic ring with an aldehyde within ten minutes at pH 4-5. Thiazolidine ring formation has been successfully used to ligate both linear and constrained peptides to K2K dendron types of cores and proteins containing a-oxoacyl groups. 

A common type of weak-base exchanger uses the same polystyrene-DVB polymer but contains tertiary amine groups (Figure 8.5) [6]. 

Fig. 1. Extrapolation of indicator data for various types of weak bases to standard state of infinite dilution in water to give (supposedly) thermodynamic pKa s. (1) Theoretical plot for ideal Hammett Base with pK =—6.0. Solid lines represent observable region of indicator change and dotted lines represent extrapolation. All ideal Hammett indicators should lie on line 1 of this plot with appropriate change of left-hand scale, to correspond to their pKa s. (2) Theoretical plot of ideal weak base that gives slope of 1.10. Note that it does not extrapolate to standard state in water (pH = 7) and so observed value of pHa does not refer to same standard state as ideal Hammett base. (3) Actual behavior of benzoic acid (half-protonated at Ht, = —7.38). Note that although it follows ideal Hammett base behavior in observable region of indicator change, it departs sharply from it at lower acidities as shown by activity measurements. At present there is no way of telling how many supposedly ideal Hammett bases behave in this way over part of the acidity region and what standard state they finally extrapolate to.

Strategy Decide whether the add and base are strong or weak. Then decide which of the three types of acid-base reactions is involved. Finally, use Table 4.2 to derive the proper equation. 

Because of certain misconceptions with regard to the choice of solvent and the occurrence of sulfur-oxygen bond fission in hydroxylic solvents - , it is important to emphasize that one can greatly reduce the rate of this competing process by the use of weak bases. In systems which can undergo facile C—O as well as S—O bond fission, it is possible to control the type of bond cleavage by choosing the appropriate base . A remarkable illustration of this behavior is found in the ethanolysis of sulfinate 6a. In anhydrous ethanol at 90.0° with acetate ion as the added base, 6a yielded ethyl 2, 6-dimethylbenzenesulfinate plus a trace of sulfone 7a. Under the same conditions but with 2,6-lutidine the reaction was slower and sulfone 7a was the only detectable reaction product . ... 

Reasonably reliable pATbh+ values for the protonation of weak bases or of weakly basic substrates can be obtained via equation (17), together with m slope parameters that can be used to classify basic molecules as to type, and for an estimate of the solvation requirements of the protonated base. Measurements at temperatures other than 25°C can be handled using equation (22), and enthalpies and entropies for the protonation can be obtained. Protonation-dehydration processes are covered by equation (26). Medium effects on the... 

Two types of probe molecules have been used for the detection of Lewis and Bronsted acid sites. The first involves the adsorption of relatively strong basic molecules such as pyridine, ammonia, quinoline, and diazines. The second kind involves the adsorption of weak base molecules such as CO, NO, acetone, acetonitrile, and olefins. The pioneering works of Parry27 and Hughes and... 

Neutralization of a weak acid-weak base solution is a complex type of acid-base solution. If the weak acid and weak base have the same strength, the solution is neutral. If the strength of an acid and the strength of a base are not equal, the solution will be either acidic or basic, depending on the strength of either. 

We review the subject of noncovalent interactions in proteins with particular emphasis on the so-called weakly polar interactions. First, the physical bases of the noncovalent electrostatic interactions that stabilize protein structure are discussed. Second, the four types of weakly polar interactions that have been shown to occur in proteins are described with reference to some biologically significant examples of protein structure stabilization and protein-ligand binding. Third, hydrophobic effects in proteins are discussed. Fourth, an hypothesis regarding the biological importance of the weakly polar interaction is advanced. Finally, we propose adoption of a systematic classification of electrostatic interactions in proteins. 

Aminoazo dyes with only one amino group (aminoazobenzene type) are weak bases giving, in general, difficultly soluble salts which are readily hydrolyzed. If the dye is to be isolated as one of its salts, for example, the hydrochloride, the salt is precipitated from the reactiorr mixture by means of a considerable excess of hydrochloric acid. The precipitate is filtered off and washed with dilute hydrochloric acid, not with water. On the other hand, if the dye is to be used in coloring oils, fats, etc., it must be isolated as the free base and must contain no salts. For this purpose, the coupling reaction mixture is made alkaline and the precipitated dye is filtered off and washed thoroughly with water. The dye can be purified further by.recrystallization from an organic solvent. 

This type of behavior has been demonstrated by Haag for H-ZSM-5 systems and by Lunsford and coworkers for mordenites and faujasites. Both groups reported linear correlations between the cracking rate of n-hexane and the aluminum content of the zeolites. Other studies by Gorte and cowoikers involving the adsoiption of weak bases. 

Salts of weak bases and weak acids are the fourth class of salts. Most are soluble. Salts of weak bases and weak acids contain cations that would give acidic solutions and anions that would give basic solutions. Will solutions of such salts be neutral, basic, or acidic They may be any one of the three depending on the relative strengths of the weak molecular acid and weak molecular base from which each salt is derived. Thus, salts of this class may be divided into three types that depend on the relative strengths of their parent weak bases and weak acids. 

Hydrolysis of conjugate base (A ) of weak acid > basic solution and Hydrolysis of conjugate acid (BH ) of weak base > acidic solution. This solution can be basic, neutral, or acidic, depending on which hydrolysis occurs to a greater extent use K, and K, values for the hydrolysis reactions to tell which ion wiU be the dominant fector. (We did not do calculations for this type of salt.)... 

Considering this new H+-transfer acid-base definition, take a look at the type of acid-base reaction in which the acid is weak and the base is strong. An example is the reaction of acetic acid, HC2H3O2, the weak acid present in vinegar, with sodium hydroxide. The equation of the overall reaction is similar to that of a strong acid-strong base reaction. 

The strong-strong reaction plus the two types of weak-strong reactions are the favorable acid-base reactions. Looking at an acid-base reaction as occurring by H+ transfer helps you to understand why the weak-weak... 

Types of Acid-Base Reactions Strong Acid -I- Strong Base Strong Acid -I- Weak Base A Broader Definition of Acids and Bases Weak Acid -I- Strong Base MiniLab 15.1 Acidic, Basic, or Neutral ... 

Lowry and co workers141,222 studied the mutarotation of tetra-O-methyl-a-D-glucopyranose, and found that the rate of reaction is low in dry pyridine or in dry cresol, but high in a mixture of the two solvents or in either solvent when moist. Lowry and Smith57 concluded that the mutarotation requires an acid catalyst and a base catalyst, and that amphoteric solvents are complete catalysts for the process, whereas aprotic solvents are not. They also showed that molecules of undissociated acids, cations of weak bases, and anions of weak acids have catalytic properties. Much the same concept was developed independently by Bronsted and Guggenheim,189,223 and came to be known as generalized acid and base catalysis. It was found that the rate of mutarotation of a sugar in the presence of a mixture of several catalysts may be represented by an equation of the type ... 

Chapters 2-6 describe the use of several different types of polymer-based sensors, i.e. chemiluminescent, fluorescent and optical, to detect explosive materials. In the optical case a large array of coated beads is employed to reduce the signal-to-noise ratio, and provide greater amplification of weak signals from trace levels of vapours. 

As an alternative to the highly specific catalysis indicated by formulas I, II, and III, it is possible that the metal chelate compound merely participates in a generalized type of acid-base catalysis. Thus, the function of the metal would be to increase the acidity of the substrate through molecular association and thereby increase its susceptibility toward attack by other bases present such as hydroxide ion or water molecules. Under these conditions the diaquo chelate A would be an acid catalyst, the monohydroxy chelate Bi would be considered to be bifunctional in its effect, and the dihydroxy chelate B2 would probably be a weak basic catalyst. 

Many different types of bases are used in organic chemistry. Common inorganic bases include the anions of weak bases such as water and ammonia (OH and NH2 ). Similar deprotonation of alcohols leads to the alkoxide bases (RO ). Methoxide (MeO ), ethoxide (EtO ), and ferf-butoxide (Me3C-0 ) are very common and are often used in the alcohol solvents from which they were made (methoxide in methanol, tert-butoxide in ferf-butanol, etc.). The bases used to deprotonate water (p fa = 15.8) or alcohols (pATa 18) are sodium hydride (NaH), potassium hydride (KH), sodium and potassium hydroxide (NaOH, KOH), sodium metal (Na°),... 

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