Perchloric acids

Perchloric Acid. Historically, it was Conant s study1 of the protonating ability of weak bases (such as aldehydes and ketones) by perchloric acid that first called attention to the superacid behavior of certain acid systems. 

Superacid Chemistry, Second Edition, George A. Olah, G. K. Surya Prakash, Arpad Molnar, and Jean Sommer Copyright 2009 John Wiley Sons, Inc. 

Perchloric acid is extremely hygroscopic and is a very powerful oxidizer. Contact of organic materials with anhydrous or concentrated perchloric acid can lead to violent explosions. For this reason, the application of perchloric acid has serious limitations. The acid strength, although not reported, can be estimated to be around //0 —13 for 

Formation of various perchlorate salts such as N02+C104, CH3C0+C104, and R+C104, via ionization of their appropriate neutral precursors in perchloric acid can also lead to serious explosions. The probable reason is not necessarily the thermal instability of the ionic perchlorates but instead their equilibria with highly unstable and explosive covalent perchlorates [Eqs. (2.1)—(2.3)]. 

Actually, no specific advantage exists in using perchlorate salts, when comparable safe conjugate fluoride salts such as BF4, SbF6, and Sb2I i i are available. The use of perchlorate salts always necessitates extreme care and precautions. 

Hyperchloric Acid.—This acid may be obtained either by the distillation of chloric acid (see above), or by the distillation of hyperchlorate of potash with an equal weight of oil of vitriol, previously mixed ivith half as much water. It is purified from sulphuric acid by means of baryta, from chlorine by oxide of silver and is then concentrated by slow evaporation. 

It resembles the preceding acid, and when very concentrated, has a sp.g. of 1 65. It reddens litmus without bleaching it, boils at 412°, and may be distilled without change. It is veiy permanent, and has strong affinities. Its best known salt is the perchlorate of potash, which is so sparingly soluble, that the acid may be used as a test for potash, in aU liquids not too diluted. As the perchlorate of soda is very soluble, the use of this add enables us to distinguish, and to separate soda from potash. 

The perchlorate of potash is easily formed by melting chlorate of potash, and heating it till the mass becomes thick and pasty, which takes place when A of the oxygen is expelled. The residue is a mixture of chloride of potassium and perchlorate of potash, and the latter is easily purified by dissolving tbe whole in hot water, and allowing it to ciystallise on cooling. The action of heat on chlorate of potash is thus expressed  

It must here be observed, that our knowledge of the compounds of chlorine and oxygen is far from being complete or satisfactory, and that Gay-Lussac and Millon, since the discovery by Balard of hypochlorons add, have devoted attention to the subject. Millon, indeed, has published an elaborate 

Almost all of these compounds have properties so similar, that they are with difficulty distinguished from each other. Thus there are not less than 5 compounds, according to Millon, namely CIO, CIO, CIO, 01,0,3, and which are 

Hydrogen bromide is a noncombustible gas. The acid or the gas in contact with common metals and in the presence of moisture produces hydrogen. Violent reactions occur with ammonia and ozone (Mellor 1946, Suppl. 

Formula HI MW 127.91 CAS [10034-85-2] Composition The acid is a solution of hydrogen iodide gas in water, available in various concentrations (57%, 47%, and 10%). 

Hydriodic acid is used in the manufacture of iodides, as a reducing agent, and in disinfectants and pharmaceuticals. 

The acid is a colorless liquid, rapidly turning yellow or brown when exposed to light and air. The anhydrous hydriodic acid or hydrogen iodide is a colorless gas, fumes in moist air decomposed by light liquefies at -35 C (-3LF) freezes at -51°C (-59°F) extremely soluble in water, more so in cold water [900 g/100 mL at 0°C (32°F)], soluble in many organic solvents. Hydriodic acid is a strong acid (the pH of a 0.1 M solution is 1.0). 

Hydriodic acid is a corrosive liquid that can produce bums on contact with the skin. Contact of acid with the eyes can cause severe irritation. The gas, hydrogen iodide, is a strong irritant to the eyes, skin, and mucous membranes. No exposure limit has been set for this gas. 

The use of anhydrous perchloric acid as a catalyst for caticniic pdiymerisation dates from 1960, when Tauber and Eastham publidied a study of the interaction of this catalyst with 2-butene in 1,2-dichloroethane. The ccanplex behaviour of this stem did not permit any definite conclusion about the reactions invdved, but the possibility of initial formation of /so-butyl perchlorate was seriouriy considered. Today the formatiem of alkyl perchlorates is well documented as discussed in Sect. II-I, except for tertiary ones. Plesch and Westermann noticed that isotxitene did not pdymerise in CH2O2 when perchloric acid was mixed with it, but only gave r-hutyl perchlorate. 

Also in 1960, Asami and Tokura showed that 60% perchloric acid was a very effective catalyst for the polymerisation of styrene in sulphur dioxide But it was the now classic study of Pepper and Reilly on the pdiymerisation of styrene by the anhydrous acid in various solvents that initiated a Icrng series of investigations on the rde of this promoter in the cationic polymerisation of arcmatic defins and more recently of cyclopentadiene. 

On the basis of the above kinetic observations a mechanism was proposed which involved fast and complete initiation followed by standard bimolecular propagation (transfer reactions wiU be ignored in this ccmtext)  

if kj kp, the experimentally determined second-order rate constant is the propagation rate constant k . At 25 °C in 1,2-dichloroethane (e = 9.7) kp = 17.0 sec and Ep = 8.3 kcal mole.  

The nature of the active species was also investigated spectrcficopically. An absorption peak at 415 nm was errcmeoudy attributed to the prince of 1-phenylethylium i(Mis during the polymerisaticm. Pepper and Reilly prqiosed therefore that the chain carriers were ionic, and more specifically icm pairs  

CONTACT WITH COMBUSTIBLE MATERIAL MAY CAUSE FIRE, CAUSES BURNS 

Colorless, volatile, very hygroscopic liquid miscible with water sold commercially only as 60-70%.  

Anhydrous acid (which may be formed with strong dehydrating agents) decomposes at ordinary temperatures and explodes on contact with most organic materials. Extinguish fire with water spray.2 

Very hygroscopic. Combines vigorously with water with evolution of heat. Undergoes spontaneous and explosive decomposition. Very caustic.1 

Exceptionally powerful oxidizing agent that readily forms explosive salts. Safe handling procedures have been described. 4 

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Kolics A, Thomas A E and Wieckowski A 1996 CI-labelled and electrochemical study of chloride adsorption on a gold electrode from perchloric acid media J. Chem. See. Faraday Trans. 92 3727-36... 

Dichlorine h ptoxide, CljO, is the most stable of the chlorine oxides. It is a yellow oil at room temperature, b.p. 353 K, which will explode on heating or when subjected to shock. It is the anhydride of chloric(VlI) acid (perchloric acid) from which it is prepared by dehydration using phosphorus(V) oxide, the acid being slowly reformed when water is added. 

Thiele acetylation. Quinones, when treated with acetic anhydride in the presence of perchloric acid or of concentrated sulphuric acid, undergo simultaneous r uctive acetylation and substitution to yield triacetoxy derivatives, e.g., benzoquinone gives 1 2 4-triacetoxybenzene. 

Add 0-1 ml. of concentrated sulphuric acid or of 72 per cent, perchloric acid cautiously to a cold solution of 0 01 mol (or 1 0 g.) of the quinone in 3-5 ml. of acetic anhydride. Do not permit the temperature to rise above 50°. AUow to stand for 15-30 minutes and pour into 15 ml, of water. Collect the precipitated sohd and recrystaUise it from alcohol. 

The metal has a silvery appearance and takes on a yellow tarnish when slightly oxidized. It is chemically reactive. A relatively large piece of plutonium is warm to the touch because of the energy given off in alpha decay. Larger pieces will produce enough heat to boil water. The metal readily dissolves in concentrated hydrochloric acid, hydroiodic acid, or perchloric acid. The metal exhibits six allotropic modifications having various crystalline structures. The densities of these vary from 16.00 to 19.86 g/cms. 

Perchloric acid (HCIO4 Ho —13.0), fluorosulfuric acid (HSO3F Ho — 15.1), and trifluoromethanesulfonic acid (CF3SO3H Ho —14.1) are considered to be superacids, as is truly anhydrous hydrogen fluoride. Complexing with Lewis acidic metal fluorides of higher valence, such as antimony, tantalum, or niobium pentafluoride, greatly enhances the acidity of all these acids. 

The rates of nitration of mesitylene-a-sulphonate anion (iii) and iso-durene-a -sulphonate anion (iv) in mixtures of aqueous nitric and perchloric acid followed a zeroth-order rate law. Although the rate of exchange of oxygen could not be measured because of the presence of perchloric acid, these results again show that, under conditions most amenable to its existence and involvement, the nitric acidium ion is ineffective in nitration. 

Related studies have been made using perchloric acid. From mixtures of anhydrous nitric and perchloric acids in the appropriate proportions, Hantzsch " claimed to have isolated two salts whose structures supported his hypothesis concerning the nature of nitric acid in strong mineral acids. He represented the formation of the salts by the following... 

Practical difficulties in using concentrated (> 72 % perchloric acid) and the fact that the/f function is known only up to 60 % perchloric acid, reduce the value of these media for the study of nitration. 

Rates of nitration in perchloric acid of mesitylene, luphthalene and phenol (57 I-6i-i %), and benzene (57 i-64 4%) have been deter-mined. The activated compounds are considered below ( 2.5). A plot of the logarithms of the second-order rate coefficients for the nitration of benzene against — ( f + log over the range of acidity... 

NITRATION AT THE ENCOUNTER RATE IN AQUEOUS SULPHURIC AND PERCHLORIC ACIDS... 

This consideration prompted an investigation of the nitration of benzene and some more reactive compounds in aqueous sulphuric and perchloric acids, to establish to what extent the reactions of these compounds were affected by the speed of diffusion together of the active species. ... 

The phenomenon was established firmly by determining the rates of reaction in 68-3 % sulphuric acid and 61-05 % perchloric acid of a series of compounds which, from their behaviour in other reactions, and from predictions made using the additivity principle ( 9.2), might be expected to be very reactive in nitration. The second-order rate coefficients for nitration of these compounds, their rates relative to that of benzene and, where possible, an estimate of their expected relative rates are listed in table 2.6. 

The rates of nitration, under a variety of conditions (56-80% sulphuric acid, 57-62% perchloric acid), of mesitylene and benzene... 

TABLE 2.6 Second-order rate coefficients and relative rates for nitration at 2 -0 °C in 68- % sulphuric acid and 6i-o % perchloric acid ° ... 

For nitrations in sulphuric and perchloric acids an increase in the reactivity of the aromatic compound being nitrated beyond the level of about 38 times the reactivity of benzene cannot be detected. At this level, and with compounds which might be expected to surpass it, a roughly constant value of the second-order rate constant is found (table 2.6) because aromatic molecules and nitronium ions are reacting upon encounter. The encounter rate is measurable, and recognisable, because the concentration of the effective electrophile is so small. 

Compound nitrated t5% aqueous sulpholan (K) Sulpho- lan (C) 15% aqueous nitromethane (K) Nitromethane (C) 61-05 % perchloric acid (K) 68-3% sulphuric acid (K) 68-3 % sulphuric acid (C) Estimated relative rates ... 

In aqueous solutions of sulphuric (< 50%) and perchloric acid (< 45 %) nitrous acid is present predominantly in the molecular form, although some dehydration to dinitrogen trioxide does occur.In solutions contairdng more than 60 % and 65 % of perchloric and sulphuric acid respectively, the stoichiometric concentration of nitrous acid is present entirely as the nitrosonium ion (see the discussion of dinitrogen trioxide 4.1). Evidence for the formation of this ion comes from the occurrence of an absorption band in the Raman spectrum almost identical with the relevant absorption observed in crystalline nitrosonium perchlorate. Under conditions in which molecular nitrous... 

Under these first-order conditions the rates of nitration of a number of compounds with acetyl nitrate in acetic anhydride have been determined. The data show that the rates of nitration of compounds bearing activating substituents reach a limit by analogy with the similar phenomenon shown in nitration in aqueous sulphuric and perchloric acids ( 2.5) and in solutions of nitric acid in sulpholan and nitro-methane ( 3.3), this limit has been taken to be the rate of encounter of the nitrating entity with the aromatic molecule. 

HCIO4 perchloric acid HPH2O2 phosphinic acid (formerly... 

Key properties are its flexibility, translucency, and resistance to all known chemicals except molten alkali metals, elemental fluorine and fluorine precursors at elevated temperatures, and concentrated perchloric acid. It withstands temperatures from —270° to 250°C and may be sterilized repeatedly by all known chemical and thermal methods. 

Acetic acid Chromium(VI) oxide, chlorosulfonic acid, ethylene glycol, ethyleneimine, hydroxyl compounds, nitric acid, oleum, perchloric acid, peroxides, permanganates, potasssium r rf-butoxide, PCI3... 

Ethyl ether Eiquid air, chlorine, chromium(VI) oxide, lithium aluminum hydride, ozone, perchloric acid, peroxides... 

Hydrogen chloride Acetic anhydride, aluminum, 2-aminoethanol, ammonia, chlorosulfonic acid, ethylenediamine, fluorine, metal acetylides and carbides, oleum, perchloric acid, potassium permanganate, sodium, sulfuric acid... 

Ketones Aldehydes, nitric acid, perchloric acid... 

Lead(ll) oxide Chlorinated rubber, chlorine, ethylene, fluorine, glycerol, metal acetylides, perchloric acid... 

Perchloric acid Acetic acid, acetic anhydride, alcohols, antimony compounds, azo pigments, bismuth and its alloys, methanol, carbonaceous materials, carbon tetrachloride, cellulose, dehydrating agents, diethyl ether, glycols and glycolethers, HCl, HI, hypophosphites, ketones, nitric acid, pyridine, steel, sulfoxides, sulfuric acid... 

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