Weak acids properties

Carboxylate exchangers contain —COOH groups which have weak acidic properties and will only function as cation exchangers when the pH is sufficiently high (pH > 6) to permit complete dissociation of the —COOH site. Outside this range the ion exchanger can be used only at the cost of reduced capacity. 

Phosphatidylcholine, commonly known as lecithin, is the most commonly occurring in natnre and consists of two fatty add moieties in each molecule. Phosphati-dylethanolamine, also known as cephahn, consists of an amine gronp that can be methylated to form other compounds. This is also one of the abundant phospholipids of animal, plant, and microbial origin. Phosphatidylserine, which has weakly acidic properties and is found in the brain tissues of mammals, is found in small amounts in microorganisms. Recent health claims indicate that phosphatidylserine can be used as a brain food for early Alzheimer s disease patients and for patients with cognitive dysfunctions. Lysophospholipids consist of only one fatty acid moiety attached either to sn-1 or sn-2 position in each molecule, and some of them are quite soluble in water. Lysophosphatidylchohne, lysophosphatidylserine, and lysophos-phatidylethanolamine are found in animal tissues in trace amounts, and they are mainly hydrolytic products of phospholipids. 

Alkalies, Action on Aliphatic Nitrocompounds. Compds with hydrogen atoms attached to a primary or secondary carbon atom linked to an NO, group show weakly acid properties. Such compds dissolve or react slowly in strong alkalies to form salts. This formation of salts is usually comparatively slow. 

The variation of a with formal concentration is shown in figure 9-2. Weak electrolytes (compounds that are only partially dissociated) dissociate more as they are diluted. o-Hydroxyben-zoic acid is more dissociated than p-hydroxybenzoic acid at the same formal concentration because the ortho isomer is a stronger acid. Box 9-2 and Demonstration 9-1 illustrate weak-acid properties. 

Tantalum pentoxide possesses only very weakly acidic properties. Its salts even with the strong alkalis are readily hydrolysed by boiling in aqueous solution. Its complex heteropoly-acids with other adds are ill-defined, but it takes up active oxygen to form a stable pertantalic acid, HTa04. H20. 

In the case of purification of triamidophosphites [51] the production of compound 3d requires a considerable amount of time the yields of the target compounds are increased by 10-18%. In this case, probably, the reaction takes place under the influence of the weakly acidic properties of indole. Protonation of the ambident system >P - N< of amidophosphite by the proton of indole clearly takes place initially with the formation of an intermediate, the dissociation of which leads to the formation of the target compound and amine. 

Tables 2.12 and 2.13 list the logarithm of the stability constants for the complexes of these chelating agents with various metal ions. Note that with the exception of Chel-138, calcium and magnesium form rather stable complexes with these chelating agents Fe3+ forms the most stable chelate of any metal listed. Generally, ferric iron is followed by Cu2+, Zn2+, Mn2+, Fe2+, Ca2+, and Mg2+. The weak acid properties of these chelating agents must be considered in any evaluation of their behavior. Because they are weak acids, the hydrogen ion tends to compete with the metal ions for association with the active groups.

The —C = C — carbon atoms in alkynes are very close to each other and this in turn weakens the C — H bond. This enables the H atom to leave easily from the R — C = C — H molecule. As a result, allqmes with the R — C C — H formula show weak acidic properties. Because of this acidity, alkynes can react with some metal salts to form all l metal acetylene salts. If an alkyne has the structure R — C = C — R, however, there is no reaction. 

C-H bonds in hydrocarbons have a very weak tendency to be ionized. Thus, alkanes, alkenes and alk5Ties show weak acid properties. Conjugate bases of hydrocarbons are called carbanions. 

Zn +aq has very weak acidic properties - the most favored value for its p/fa is 8.96, though values ranging from 8 to over 10 have been reported from determinations by various physical techniques in a variety of media of different ionic strengths and containing different counterions. ZnOH+aq is, like all hydroxo-metal ions, prone to polymerize species such as [Zu2(OH)] +, [Zu2(OH)6]2-, and [Zn4(OH)4] + (cf the well-established [Pb4(OH)4]" + and [Ni4(OH)4] +) have been postulated. 

The dissociation constants of. V-nitro derivatives of o, a>-dinitramincs also indicate their weak acid properties [ 12]. 

Dosage forms of APIs with high solubility at pH 6.8 but not at pH 1.2 or 4.5 and with high permeability (by definition, some but not all BCS Class 2 compounds with weak acidic properties) are eligible for a biowaiver based on BCS provided that criteria (b), (c) and (d) described in section 9.2. are met, that the API has high permeability (i.e. the fraction absorbed is 85% or greater) and a dose solubility ratio of 250 ml or less at pH 6.8, and that the multisource product ... 

For pharmaceutical products containing APIs with high solubility at pH 6.8 but not at pH 1.2 or 4.5 and with high permeability (by definition, BCS Class II compounds with weak acidic properties)... 

Phenolsulfonephthalein, Phenol red, C19H14O5S. W. R. Orndorff and F. W. Sherwood state that phenol red usually contains a red colored impurity possessing weakly acid properties and which is insoluble in water and sodium bicarbonate solutions although readily soluble in sodium hydroxide. They recommend that this indicator be purified by dissolving the sample in sodium bicarbonate and acidifying the filtrate. The air dried product always contains about 1-1.5% of water which may be removed completely by heating at 120-140°. Water is readsorbed from the atmosphere by the dry powder. 

The anilinium ion (CgH5NH ) in anilinium chloride shows weak acid properties. If NaOH is added to anilinium chloride solution (left tube), the anilinium ions loses a proton to give aniline (middle and right tube)... 

In contrast, germanium oxide was found to be appreciably soluble in the molten equimolar KCl-NaCl mixture and its solutions show weak acidic properties. Its acid-base titration using NaOH as a titrant results in the appearance of a small pO drop at the equivalence point ( 1 pO unit), which corresponds to the ligand number value —0.5. This allows us to conclude that the acid-base titration runs in one step, and the final product is di-germanate ion, Gc202... 

The use of BaO as a titrant in melts possessing weakly acidic properties cannot be recognized as correct at all, apart from its use for the titration of other alkaline-earth metal cations (since, in this case, the solid solutions... 

Class Ai. Compounds insoluble in water and in dilute sodium bicarbonate, but soluble in dilute sodium hydroxide solution. Weakly acidic compounds belong in this class. Weakly acidic properties are usually exhibited by oximes, imides, amino acids, sulfonamides of primary amines, primary and secondary nitro compounds, enols and phenols. Certain mercaptans also are weak acids. 

The hydrolysis reactions of Eq. 10.2 liberate H+ and lower the solution pH unless OH- is present. This stepwise production of hydrogen ions is similar to that which occurs during the dissociation of polyprotonated acids. It is the primary reason why early workers attributed weak-acid properties to acid soils and clays. 

ZrOa and Th02 show similar catali ic behaviors. Although their basic properties are not so strong, they possess weakly acidic properties, and, therefore, show the acid-base bifunctional catalysis. ZrOa and Th02 as well as rare earth oxides showed dehydration activity for alcohols. 

The accumulation of negative groups in tartaric acid brings about the development of weakly acidic properties in the alcoholic hydroxyl groups which it contains. Sodium hydroxide does not precipitate the hydroxides of copper and of certain other metals in the presence of potassium or sodium tartrate. A quantitative study of the reaction has shown that one molecule of sodium tartrate reacts with one molecule of copper hydroxide. The structure of the salt formed is represented by the following formula —... 

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