Acidic aqueous solutions

The data in Tables 4.2 and 4.3 refer to ions in aqueous acid solution for cations, this means effectively [MlHjO), ]" species. However, we have already seen that the hydrated cations of elements such as aluminium or iron undergo hydrolysis when the pH is increased (p. 46). We may then assume (correctly), that the redox potential of the system... 

Convert iron(ll) to iron(lll) in aqueous acid solution. 

The oxide MnO is obtained by heating the earbonate MnCOj, Oxidation of manganesedli in aqueous acid solution requires a strong oxidising agent, for example... 

Aqueous acid solution (R,). Render alkaline with 10-20% NaOH and distil. 

Attack on the halogen is probably the starting point of the reaction between A-4-thiazoline-2-thione and chlorine in aqueous acid solution to yield thiazole-2-sulfonylchloride. which then gives 2-chlorothjazole (153). 

The yields with the lower alkyls rarely exceed 50%. For example, with R, =R2 = Me, the yield is 20% in an aqueous acidic solution (219) or 40% in an acetic solution acidified with sulfuric acid (369). 

Step 1 The enol is formed in aqueous acidic solution The first step of its transformation to a ketone is proton transfer to the carbon-carbon double bond... 

Preparation of phenols Heating its aqueous acidic solution converts a diazonium salt to a phenol This IS the most general method for the synthesis of phenols... 

Germanium tetrafluoride produces hydrogen fluoride in aqueous acidic solutions. Hydrogen fluoride is toxic and very corrosive. The OSHA permissible exposure limit (17) and the American Conference of Governmental Industrial Hygienists (ACGIH) TLV for fluoride is 2.5 mg/m of air (18). 

Silver difluoride [7783-95-1], AgF2, is a black crystalline powder. It has been classified as a hard fluorinating agent (3) which Hberates iodine from KI solutions and o2one from dilute aqueous acid solutions on heating. It spontaneously oxidizes xenon gas to Xe(II) in anhydrous hydrogen fluoride solutions (20). 

Primary aromatic amines react with aldehydes to form Schiff bases. Schiff bases formed from the reaction of lower aUphatic aldehydes, such as formaldehyde and acetaldehyde, with primary aromatic amines are often unstable and polymerize readily. Aniline reacts with formaldehyde in aqueous acid solutions to yield mixtures of a crystalline trimer of the Schiff base, methylenedianilines, and polymers. Reaction of aniline hydrochloride and formaldehyde also yields polymeric products and under certain conditions, the predominant product is 4,4 -methylenedianiline [101 -77-9] (26), an important intermediate for 4,4 -methylenebis(phenyhsocyanate) [101-68-8], or MDI (see Amines, aromatic amines, l thylenedianiline). 

The oxidation potentials for rhenium in aqueous acidic solution are summarized in the following diagram (6). 

Reactions in Water. The ionization potential for bromine is 11.8 eV and the electron affinity is 3.78 eV. The heat of dissociation of the Br2 molecule is 192 kj (46 kcal). The reduction potentials for bromine and oxybromide anions in aqueous acid solutions at 25°C are (21) ... 

Different polyamide fibers with varying affinities for anionic dyes are pretreated with aqueous acidic solution containing sulfated castor od to give uniform shade levels. Sulfated castor od is also used in compositions for treatment of fabrics, skins, and furs to clean and revive colors (115). 

Precipitation and Purification. During the hydrolysis, control tests are made by turbidimetric titration of samples taken intermittently. When the desired degree of hydrolysis is reached, the ester is precipitated from the reaction solution into water. It is important for the precipitate to have the proper texture for subsequent washing to remove acid and salts for thermal stabilization. Before precipitation, the reaction solution is usually diluted with additional aqueous acetic acid to reduce the viscosity. If a flake texture is desired, the solution is poured into a vigorously stirred, 10—15% aqueous acetic acid. To precipitate the acetate in powder form, dilute acetic acid is added to the stirred reaction solution. In both cases, the precipitated ester is suspended in 25—30% aqueous acid solutions and finally washed with deionized water. The dilution, precipitation temperature, agitation, and strength of the acid media must be controlled to ensure uniform texture. 

The aqueous acid solution is transferred to a i-l. round-bottomed flask provided with a separatory funnel and equipped for steam distillation. A solution of 125 g. of sodium hydroxide in 250 cc. of water is added through the funnel, and the mixture is distilled with steam (Note 4). The first liter of distillate contains most of the amine, but the distillate should be collected until it is only faintly alkaline. A small residue containing di-(a-phenylethyl)-amine and neutral substances remains in the flask and may be discarded. 

Alkynes can be hydrated in concentrated aqueous acid solutions. The initial product IS an enol, which isomerizes to the more stable ketone. 

The reactions are generally run at room temperature or below. With steroids the product is usually isolated by addition of the reaction mixture to water followed by filtration or extraction. The inorganic product of the reaction, chromium III, is soluble in neutral or aqueous acid solutions and can be removed by washing. When steroidal amines are oxidized, the work-up is usually modified such that the steroid may be extracted from the insoluble basic chromium III salts. °... 

This is the most general method for preparing phenols. It is easily performed the aqueous acidic solution in which the diazonium salt is prepared is heated and gives the phenol directly. An aryl cation is probably generated, which is then captured by water acting as a nucleophile. 

This is the so-called water-gas shift reaction (—AG29gl9.9kJmoP ) and it can also be effected by low-temperature homogeneous catalysts in aqueous acid solutions. The extent of subsequent purification of the hydrogen depends on the use to which it will be put. 

Because of the differing focus of interest in these elements their chemistries have not developed in parallel and the data on which strict comparisons might be based are not always available. Nevertheless many of the similarities and contrasts expected in the chemistry of transition elements are evident in this triad. The relative stabilities of different oxidation states in aqueous, acidic solutions are summarized in Table 24.2 and Fig. 24.1. 

Decomposition of the diazonium salt of 2-amino-iV-methyl-iV-3 -pyridylaniline (205) in aqueous acid solution with copper powder at room temperature gave overall yields of cyclized products consisting of a mixture of i id-iV-methyl-3-carboline (206) (47.5%) and ind-N-methyl-jS-carboUne (207) (25.5%), in agreement with the proposed homolytic character of the reaction under these conditions. This constituted the first unambiguous synthesis of a simple 3-carboline derivative. 

A useful diagnostic tool for investigating possible hydration of cations of bases for which pA is greater than about one is the measurement of their ultraviolet spectra in aqueous acid solutions and also in an anhydrous acidic solvent such as dichloroacetic acid (for which the Hammett acidity function, Hq, is — 0.9, and in which hydration of the cation cannot occur). This technique has been used with quinazoline to obtain spectra approximating those of the hydrated and anhydrous cations, respectively. For weaker bases, spectral measurements in sulfuric acid-water mixtures of increasing acid content may be used to reveal a progressive conversion of hydrated into anhydrous species as the thermodynamic activity of the water decreases. 

A current of density 5- amperes per square decimetre of cathode space and a potential of 3 volts is used, and the temperature is maintained at between 75° and 85° C. During the electrolytic action, the nitro-cymene is kept in thorough emulsion in the aqueous acid solution by means of the agitator. 

The crude benzhydryl ether was a clear reddish oil. It was dissolved in 75 ml of 20% hydrochloric acid and the aqueous acid solution then washed three times with 50 ml portions each of ethyl ether. The aqueous acid solution was then decolorized with activated carbon and thereafter slowly admixed with 75 ml of 28% aqueous ammonia. The benzhydryl ether separated as an oily material and was removed from the aqueous mixture by extraction with three 50 ml portions of ethyl ether. 

The aqueous acid solution is rendered alkaline by adding 2 N sodium hydroxide solution. After extracting with diethyl ether (3 times 100 cc), drying the extracts over potassium carbonate, treating them with decolorizing charcoal, filtering and evaporating the ether, a yellowish oil (0.9 g), identified as 5-methyl-10-methylamino-10,11 -dihydro-dibenzo[b,f] azepine, is obtained in a yield of 37.5%. 

Step 2 To 494 grams of ethanolamine, heated to approximately 150°C in a 500 ml flask equipped with stirrer, condenser and dropping funnel, is added 465 grams of 1-phenoxy-2-chloropropane with mechanical stirring. The reaction mixture is then heated to reflux for 3 hours, cooled and poured into a liter of water. The organic layer is extracted into ether and the ether solution is extracted with dilute hydrochloric acid. The aqueous acid solution is then made alkaline with 40% sodium hydroxide solution and the organic base is extracted into ether. Removal of the ether leaves N-(phenoxyisopropyl)-ethanolamine which, after recrystallization from hexane, melts at 70.5°-72°C. 

A solution of 100 g (1.7 mols) of isopropylamine in 60 cc of water was stirred into a solution of 4-hydroxyphenoxypropylene oxide. After the exothermic reaction has subsided, the reaction mixture was heated for two hours at 60Thereafter, the aqueous ethanol was distilled off, and the solid residue was dissolved in aqueous hydrochloric acid comprising more than the theoretical stoichiometric molar equivalent of hydrochloric acid. The aqueous acid solution was extracted with ether and was then made alkaline with sodium hydroxide, whereby a solid crystalline precipitate was formed which was filtered off and dried over phosphorus pentoxide. The product was 1,1 -(4 -hvdroxvphenoxv)-2-hvdroxv-3-isopropylamino-pro-pane. Its hydrochloride had a melting point of 166°Cto 169°C. 

To a stirred suspension of 4.29 g (0.11 mol) of sodium amide in 100 ml of dry toluene was added 19.9 g (0.1 mol) of phenothiazine. The solution was heated at reflux for two hours, the sodium salt of phenothiazine precipitating from solution. The toluene suspension of the sodium salt of phenothiazine was cooled to room temperature, whereupon there was added dropwise with continued stirring 13.36 g (0.1 mol) of /3-pyrrolldinoethyl chloride in 50 ml of dry toluene. After addition was complete, the solution was heated under reflux, with stirring, for an additional 15 hours. Upon cooling, the toluene was extracted with dilute hydrochloric acid and the toluene then discarded. The aqueous acid solution was made alkaline with dilute sodium hydroxide, the crude N-(j3-pyrrolidinoethyl)-phenothiazine separating as a brownish oil. 

Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They have large dipole moments, are soluble in water but insoluble in hydrocarbons, and are crystalline substances with relatively high melting points. In addition, amino acids are amphiprotic they can react either as acids or as bases, depending on the circumstances. In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton to yield a cation in aqueous base solution, the zwitterion is an add that loses a proton to form an anion. Note that it is the carboxylate, -C02-, that acts as the basic site and accepts a proton in acid solution, and it is the ammonium cation, -NH3+, that acts as the acidic site and donates a proton in base solution. 

These solutions have similar properties and are called acid solutions. The common species in the solutions is the aqueous hydrogen ion, H+(ag), and the properties of aqueous acid solutions are attributed to this ion. We shall investigate these solutions in Chapter 11. 

Aluminum metal reacts with aqueous acidic solutions to liberate hydrogen gas. Write the two half-reactions and the net ionic reaction. 

H- and 3//-Azepines are generally unstable in aqueous acid solution and the few examples of simple azepinium salts, namely perchlorates,77 bromides,105 picrates35201 and a solitary iodide,105 have been prepared under nonaqueous conditions. The fractional crystallization of oxalate salts has been used for the separation of mixtures of 4- and 6-substituted 3f/-azepines,66 and 3,6-di-tm-butyl- and 2,5-di-tert-butyl-3//-azepine, on treatment with tetrafluoroboric acid in acetonitrile, are converted quantitatively into their crystalline tetrafluoroboratc salts.70... 

In 1882 Griess discovered that in aqueous acidic solution 4-diazobenzenesulfonate and 4-methylaniline react quantitatively to yield 4-toluenediazonium ion and 4-ami-nobenzenesulfonic acid. This phenomenon is called diazo migration or diazo exchange. We now know that it is a consequence of the tautomerism of the initially formed l-(4 -methylphenyl)-3-(4 -sulfophenyl)-triazene, as discussed above. Griess also found another reaction that could not be explained at his time, but which is based on the tautomerism of intermediate triazenes occasionally, the reaction of an arenediazonium salt with a primary aromatic amine in weakly acidic solution yields a mixture of two isomeric aminoazo compounds (Scheme 13-21). 

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