Acid Behavior

Phosphoric acid, aside from its acidic behavior, is relatively unreactive at room temperature. It is sometimes substituted for sulfuric acid because of its lack of oxidising properties (see SuLFURic ACID AND SULFURTRIOXIDe). The reduction of phosphoric acid by strong reducing agents, eg, H2 or C, does not occur to any measurable degree below 350—400°C. At higher temperatures, the acid reacts with most metals and their oxides. Phosphoric acid is stronger than acetic, oxaUc, siUcic, and boric acids, but weaker than sulfuric, nitric, hydrochloric, and chromic acids. 

Oxidation—Reduction. Redox or oxidation—reduction reactions are often governed by the hard—soft base rule. For example, a metal in a low oxidation state (relatively soft) can be oxidized more easily if surrounded by hard ligands or a hard solvent. Metals tend toward hard-acid behavior on oxidation. Redox rates are often limited by substitution rates of the reactant so that direct electron transfer can occur (16). If substitution is very slow, an outer sphere or tunneling reaction may occur. One-electron transfers are normally favored over multielectron processes, especially when three or more species must aggregate prior to reaction. However, oxidative addition... 

In addition to this acidic behavior, an important characteristic of carboxylic acids is that the entire OH group can be replaced by other groups. The resulting compounds are called acid derivatives. We will consider only two types of acid derivatives, esters and amides. 

Prepd by treating methoxy picric acid with Pb hydroxide. It loses its OCH3 group thru hydrolysis to form normal Pb Styphnate. The OPbOH group displays acidic behavior in soln. 

There is nothing unusual about the acidic behavior of ammonium salts. In fact, any protonated amine can function as a proton donor. Because of this, many amine salts have been used as acids in synthetic reactions. If the chlorides are used, the amine salts are known as amine hydrochlorides. One of the earliest amine hydrochlorides studied with regard to its behavior as an acid is pyridine hydrochloride (pyridinium chloride), C5H5NH+C1. In the molten state, this compound undergoes many reactions of the type just shown. 

Another possibility for characterizing zeolite acid sites is the adsorption of basic probe molecules and subsequent spectroscopic investigation of the adsorbed species. Phosphines or phosphine oxides have been quite attractive candidates due to the high chemical shift sensitivity of 31P, when surface interactions take place [218-222]. This allows one to obtain information on the intrinsic accessibility and acidity behavior, as well as the existence of different sites in zeolite catalysts. 

Consider phosphoric acid, H3P04 (a triprotic acid), and phosphorous acid, H3P03 (a diprotic acid). Two structures that show this acidic behavior are ... 

Square pyramidal geometries and Lewis-acidic behavior were found in Sb(2,2,-Ci2Hg)PhBr2 51 and related compounds.252... 

According to Fraser (1975a), rare earth oxides may dissociate into the melt with both basic and acidic behavior—i.e.. 

However, it is evident that Bi(III) salts have a unique activation mode and a strong Lewis acidic behavior. In this context, Bi(III) salts are well known for being capable of activating both a-donors such as alcohols or amines and Ji-donors such as alkenes and alkynes. This fact makes Bi(III) a versatile Lewis acid for various alkylation reactions in which both alcohols and C-C multiple bonds can be utilized as an electrophilic component. 

Cr + ion forms many stable complex ions. In the aqueous medium, it forms the violet Cr(H20)e ion which is shghtly basic. Chromium(III) ion is amphoteric, exhibiting both base and acid behavior. 

The similarities between Tl+ and other M+ ions have led to the synthesis of many salts and complexes in which Tl+ serves as a balancing cation, but such compounds will not be included in the present review unless there is some feature of special interest. We may note immediately that the similarity of Tl+ to, say, K+ includes poor complexing (i.e. weak Lewis acid) behavior in both cases. 

Virtually no undissociated HC1 or KOH exists in aqueous solution. Demonstration 6-2 shows one consequence of the strong-acid behavior of HC1. 

B-strain can occur in Jmirex to lower their basicity Will B-strain inhibit or enhance the acidic behavior of borancs ... 

Rirthcrmore, molecules that show no acidic behavior at all in water may behave as weak adds in ammonia ... 

Further chemistry of alkenes and alkynes is described in this chapter, with emphasis on addition reactions that lead to reduction and oxidation of carbon-carbon multiple bonds. First we explain what is meant by the terms reduction and oxidation as applied to carbon compounds. Then we emphasize hydrogenation, which is reduction through addition of hydrogen, and oxidative addition reactions with reagents such as ozone, peroxides, permanganate, and osmium tetroxide. We conclude with a section on the special nature of 1-alkynes— their acidic behavior and how the conjugate bases of alkynes can be used in synthesis to form carbon-carbon bonds. 

Spence W.Wild, JChemSoc 1934, 1588-93 (Thermal reaction between Cl gaseous formaldehyde) 4)D.G.Nicholson J-H.Reedy, JACS 57, 817-18 (1935) (Expl reaction of bismuth with perchloric acid) 5)O.Hackl, ZAnalChem 107, 385-87 (1936) CA 31, 2007 (1937) (Expln danger of perchloric acid) 6)J.Meyer W.Sporman, ZAnalChem 107, 387-88 (1936) CA 31, 2007 (1937) (Perchloric acid behavior) 7)E.C. 

P Martin, C Polo, MD Cabezudo, MV Dabrio. Dansyl amino acids behavior on a Radial-Pak C18 column. Derivatization of grape wine musts, wines, and wine vinegars. J Liq Chromatogr 7 539-558, 1984. 

The relation between acidic behavior and the presence of hydrogen in a compound was clarified in 1887 by the Swedish chemist Svante Arrhenius (1859-1927). Arrhenius proposed that acids are substances that dissociate in water to produce hydrogen ions (H + ) and that bases are substances that dissociate in water to yield hydroxide ions (OH -) ... 

To date, chemical properties have been reported mainly for 59 and 61. Occupancy of the silicon 3p orbital by electrons from nitrogen greatly reduces the electrophilicity of these silylenes. This, together with probable aromatic stabilization, significantly mutes the behavior of 59 and 61 as silylenes. For example, 59 does not insert into Si—H bonds, or react with alkynes such as PhC=CPh367, Moreover, 59 shows no Lewis acidic behavior, even toward bases as strong as pyridine. 

Lin, A. C. Chiang, Y. Dahlberg, D. B. Kresge, A. J. Base-catalyzed hydrogen exchange of phenylacetylene and chloroform. Bronsted relations and normal acid behavior. /. Am. Chem. Soc. 1983, 105, 5380-5386. 

Tea leaves consist primarily of cellulose this is the principle structural material of all plant cells. Fortunately, the cellulose is insoluble in water, so that by using a hot water extraction, more soluble caffeine can be separated. Also dissolved in water are complex substances called tannins. These are colored phenolic compounds of high molecular weight (500 to 3000) that have acidic behavior. If a basic salt such as Na2C03 is added to the water solution, the tannins can react to form a salt. These salts are insoluble in organic solvents, such as chloroform or dichloromethane, but are soluble in water. 

Acidic behavior is thus the acceptance of an electron pair from an electron donor, this donor being called a Lewis base. There are three classes of Lewis acids that are important the first class consists of compounds having less than a full octet of electrons. A typical member of this class is trimethyl boron, B(CH3)3. Boron trifluoride and sulfur trioxide may be drawn with less than a full octet of electrons on the respective central atoms and are Lewis acids also. 

The Lewis acid behavior of I2 is well known (see Chapter 5). Interhalogens are also capable of behaving in this way, and IC1 and IBr form complexes with bases such as pyridine ... 

Explain why the acidic behavior of chromium oxides increases in the order... 

C. For two cations with the same valence, but one a stronger acid than the other (e.g., Cu2+ versus Ca2+), the cation with stronger acid behavior or higher hydrolytic constant would be preferred if the surface behaved as a relatively strong base. 

E. Surfaces that exhibit weaker acid behavior (high pKJ show a stronger preference for heavy metals than hard metals in comparison to surfaces with stronger acid behavior (low pKa). For example, illite or kaolinite show a stronger preference for Cu2+ or Cd2+ than montmorillonite. 

There are also examples of acid behavior. Thus H3B03 reacts to give quite a strong acid ... 

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