Weak base types

Anion-exchangers comprise strong-base types incorporating quaternary ammonium groups (—N+R3) and weak-base types incorporating primary, secondary or tertiary amines. They are prepared by chloromethylating the resin followed by treatment with the appropriate amine. 

Nitrogen Concentrates. Table III lists the recovery of the heavy oil nitrogen in the two Florisil concentrates and also the concentration of nitrogen types in each of these two concentrates. The weak base and very weak base types are determined by nonaqueous potentiometric... 

The weak base type is without the hydroxide from. It contains tertiary amino groups and will absorb mineral acids, or release weak bases from their salts ... 

An aqueous solution of a salt of the weak acid-weak base type, for which Kha is much larger than ICboh, should show an acid reaction. We can not conclude, however, that — [BOH] as equation (25) would indicate, because most of the hydrogen ions unite with A ions to form HA. It is only when the hydrogen ion concentration does not deviate much from 10 , i.e. when it does not exceed 10 , that we may assume [BOH] = [HA]. According to equation (25), [H+] and [BOH] should always be equal. This is not true, however, since the hydrogen ions which are produced are used up in the formation of HA. Only when the initial hydrogen ion concentration remains undisturbed does [BOH] exactly equal [HA], for then the hydroxyl ions produced by hydrolysis are removed as a result of the formation of BOH. —... 

It has been shown that the pH of a solution of a salt of the strong acid-weak base type may be calculated in the following manner ... 

In solutions of salts of the weak acid-weak base type, both pH and pOH diminish equally with increasing temperature. 

Prior to the development of polystyrene resins, phenol-formaldehyde (P-F) condensates were used as matrices, but they have now been replaced. A few weak-base types still exist (e.g., Duolite ES562 of Rohm and Haas), which are made by adding an amine during polycondensation. These P-F condensates are used for enzyme fixation. 

A synthetically useful reaction known as the Michael reaction, or Michael addition, involves nucleophilic addition of carbanions to a p unsaturated ketones The most common types of carbanions used are enolate 10ns derived from p diketones These enolates are weak bases (Section 18 6) and react with a p unsaturated ketones by conjugate addition... 

Besides equilibrium constant equations, two other types of equations are used in the systematic approach to solving equilibrium problems. The first of these is a mass balance equation, which is simply a statement of the conservation of matter. In a solution of a monoprotic weak acid, for example, the combined concentrations of the conjugate weak acid, HA, and the conjugate weak base, A , must equal the weak acid s initial concentration, Cha- ... 

Ion-exchange resins are categorized by the nature of functional groups attached to a polymeric matrix, by the chemistry of the particular polymer in the matrix, and by the porosity of the polymeric matrix. There are four primary types of functionaHty strong acid, weak acid, strong base, and weak base. Another type consists of less common stmctures in specialty resins such as those which have chelating characteristics. 

The distribution of chlorine atoms along the polymer chain has been studied in great detail. The distribution in various functional types is shown in Table 4 (18). High density polyethylene chlorosulfonated to 35% G1 and 1% S has been found to contain only 1.7% highly active chlorines, ie, reactive to weak bases. AH of these are attributed to the chlorine in the sulfonyl chloride group and those in beta position to SO2GI. No vicinal chlorides groups were found (19). 

Ion-exchange resins swell in water to an extent which depends on the amount of crosslinking in the polymer, so that columns should be prepared from the wet material by adding it as a suspension in water to a tube already partially filled with water. (This also avoids trapping air bubbles.) The exchange capacity of a resin is commonly expressed as mg equiv./mL of wet resin. This quantity is pH-dependent for weak-acid or weak-base resins but is constant at about 0.6-2 for most strong-acid or strong-base types. 

Identify the type of aqueous reaction using the symbols PPT for pre-dpitation, SA/SB for strong acid-strong base, SA/WB for strong acid-weak base, WA/SB for weak acid-strong base, and NR for no reaction. 

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. 

Most acids and bases are weak. A solution of a weak acid contains the acid and water as major species, and a solution of a weak base contains the base and water as major species. Proton-transfer equilibria determine the concentrations of hydronium ions and hydroxide ions in these solutions. To determine the concentrations at equilibrium, we must apply the general equilibrium strategy to these types of solutions. 

Ammonia is an example of a weak base. A weak base generates hydroxide ions by accepting protons from water but reaches equilibrium when only a fraction of its molecules have done so. The equilibrium constant for this type... 

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 . ... 

Figure 5.1 shows a tetrad of equilibrium reactions related to the partitioning of a drug between an aqueous environment and that of the bilayer formed from phospholipids. (Only half of the bilayer is shown in Fig. 5.1.) By now, these reaction types might be quite familiar to the reader. The subscript mem designates the partitioning medium to be that of a vesicle formed from a phospholipid bilayer. Equations (4.1)-(4.4) apply. The pAi m in Fig. 5.1 refers to the membrane pKa. Its meaning is similar to that of pAi when the concentrations of the uncharged and the charged species in the membrane phase are equal, the aqueous pH at that point defines pAi em, which is described for a weak base as...

The case of a buffer consisting of a weak base and its acidic form (for example, NH3 and NH4) is treated in an analogous way. Equations of the type of (1.4.26) are sometimes called the Henderson-Hasselbalch equations. 

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