Problems Hydrochloric acid

Hydrogen chloride in air can also be a phytotoxicant (88). Tomatoes, sugar beets, and fmit trees of the Pmnus family are sensitive to HCl in air. Exposure of concentrated hydrochloric acid to the skin can cause chemical bums or dermatitis. Whereas the irritation is noticed readily, the acid can be water flushed from the exposed area. Copious use of miming water is the only recommended safety procedure for any external exposure. Ingestion is seldom a problem because hydrochloric acid is a normal constituent of the stomach juices. If significant quantities are accidentally swallowed, it can be neutrali2ed by antacids. 

Cation exchangers are regenerated with mineral acids when used in the form. Sulfuric acid [8014-95-7] is preferred over hydrochloric acid [7647-01-0], HCl, in many countries because it is less expensive and less corrosive. However, the use of hydrochloric acid is the best method of overcoming precipitation problems in installations which deionize water with high concentrations of barium or calcium compared to other cations. A 4% acid concentration is common, although sulfuric acid regenerations may start as low as 0.8—1% to minimize calcium sulfate [7718-18-9] precipitation. 

Typical speciftcations of technical-grade phosphonic acid are given in Table 12. Because disposal of the by-product hydrochloric acid poses problems, several attempts have been made to produce phosphonic acid by a nonhalide route however, so far none of these efforts have been translated into an industrial process. 

Use of mercuric catalysts has created a serious pollution problem thereby limiting the manufacture of such acids. Other catalysts such as palladium or mthenium have been proposed (17). Nitration of anthraquinone has been studied intensively in an effort to obtain 1-nitroanthraquinone [82-34-8] suitable for the manufacture of 1-aminoanthraquinone [82-45-1]. However, the nitration proceeds so rapidly that a mixture of mono- and dinitroanthraquinone is produced. It has not been possible, economically, to separate from this mixture 1-nitroanthraquinone in a yield and purity suitable for the manufacture of 1-aminoanthraquinone. Chlorination of anthraquinone cannot be used to manufacture 1-chloroanthraquinone [82-44-0] since polychlorinated products are formed readily. Consequentiy, 1-chloroanthraquinone is manufactured by reaction of anthraquinone-l-sulfonic acid [82-49-5] with sodium chlorate and hydrochloric acid (18). 

There are two serious problems associated with continuous tar distillation. Coal tar contains two types of components highly corrosive to ferrous metals. The ammonium salts, mainly ammonium chloride, associated with the entrained Hquor remain in the tar after dehydration, tend to dissociate with the production of hydrochloric acid and cause rapid deterioration of any part of the plant in which these vapors and steam are present above 240°C. Condensers on the dehydration column and fractionation columns are also attacked. This form of corrosion is controlled by the addition of alkaU (10% sodium carbonate solution or 40% caustic soda) to the cmde tar in an amount equivalent to the fixed ammonia content. 

Chloroaluminate laboratory preparations proved to be easily extrapolated to large scale. These chloroaluminate salts are corrosive liquids in the presence of protons. When exposed to moisture, they produce hydrochloric acid, similarly to aluminium chloride. However, this can be avoided by the addition of some proton scavenger such as alkylaluminium derivatives. In Difasol technology, for example, carbon-steel reactors can be used with no corrosion problem. 

The importance of magnesium chloride has probably been exaggerated. There is little doubt that it can act as a catalyst in corrosion reactions by hydrolysing to form hydrochloric acid, being then regenerated by reaction between ferrous chloride and magnesium hydroxide. There is, however, little evidence that this reaction takes place in cold- or hot-water systems, and it is probably confined to steam boilers where it might be a cause of corrosive attack underneath scale deposits it does not constitute a problem in a properly conditioned boiler water. 

A particular problem in oil recovery arises in the acidising process for stimulating well production in limestone formations . For many years 15% hydrochloric acid for this process has been successfully inhibited with commercially available organic inhibitors to minimise attack on the... 

Summary Problem An aqueous solution of hydrogen chloride is called hydrochloric acid. It is widely used for a host of industrial... 

It is frequently necessary to convert from one concentration unit to another This problem arises, for example, in making up solutions of hydrochloric acid. Typically, the analysis or assay that appears on the label (Figure 10.2, p. 263) does not give the molarity or molality of the add. Instead, it lists the mass percent of solute and the density of the solution. 

If the bulk of the iodate solution is added rapidly, atmospheric oxidation does not present a serious problem, but the method cannot be used in the presence of salts of antimony(III), copper(I), or iron(II). The solution, which should contain for example 0.15 g SnCl2,2H20 in 25 mL, is treated with 30mL of concentrated hydrochloric acid and 20 mL of water and is then titrated in the usual manner with standard potassium iodate solution. 

Proteins have been hydrolyzed by treatment with sulfuric acid, hydrochloric acid, barium hydroxide, proteolytic enzymes, and other hydrolytic reagents, but no condition has been found which avoids some destruction or incomplete liberation of tryptophan, cystine, and some other amino acids. The early work on this problem has been reviewed by Mitchell and Hamilton (194). The literature and their own excellent experiments on the hydrolysis problem in relation to the liberation and destruction of tryptophan have been presented recently by Spies and Chambers (269). 

Acid chlorides are very reactive and at room temperature react readily with amines. Synthesis by interfacial and solution methods is possible. However, care should be taken that the hydrochloric acid produced does not react with unreacted amine groups. With the strong basic aliphatic diamines, the acid binder must preferably be even more basic. The attainable molecular weights are strongly dependent on the concentrations this is particularly the case for easily precipitated terephthalamide polymers. Possible problems with the acid binder can be overcome by starting with silylated diamines.33,34 A typical example for interfacial polymerization of terephthalamides is PA-2,T.66... 

The parent hexathiaadamantane (185) is obtained preparatively when a solution of formic acid and hydrochloric acid in nitrobenzene is allowed to stand for several weeks in a hydrogen sulfide atmosphere the product which separated is almost insoluble in all common solvents and purification presents a problem. Only large volumes of dimethyl sulfoxide at reflux serve for recrystallization.224 The reaction of thioacetic acid with formic acid in the presence of zinc chloride gives tetramethyl-(186), monomethyl-, dimethyl-and trimethylhexathiaadamantane derivatives (187).225 Other variations include the reaction of thioacetic acid with a /i-diketone,226 and the use of boron trifluoride227 or aluminum chloride as a catalyst.228... 

Cranston and Murray [35,36] took samples in polyethylene bottles that had been pre-cleaned at 20 °C for four days with 1% distilled hydrochloric acid. Total chromium Cr(VI) + Cr(III) + Crp (Crp particulate chromium) was coprecipitated with iron (II) hydroxide, and reduced chromium Cr(III) + Crp was co-precipitated with iron (III) hydroxide. These co-precipitation steps were completed within minutes of the sample collection to minimise storage problems. The iron hydroxide precipitates were filtered through 0.4 pm Nu-cleopore filters and stored in polyethylene vials for later analysis in the laboratory. Particulate chromium was also obtained by filtering unaltered samples through 0.4 pm filters. In the laboratory the iron hydroxide co-precipitates were dissolved in 6 N distilled hydrochloric acid and analysed by flameless atomic absorption. The limit of detection of this method is about 0.1 to 0.2 nM. Precision is about 5%. 

Sato et al. carried out detailed studies on the possibilities of transformation of tetrazolo[l,5-tf]pyrazines 54 to 2-aminopyrazines 56 < 1994S931 >. These authors found that the generally used methods for this conversion fail because the starting compound exists in the stable bicyclic form 54, whereas partial formation of the azide valence bond isomer 55 would be necessary for the success of the transformation. Application of special reaction conditions succeeded, however hydrogenation over palladium catalyst in the presence of ammonium hydroxide or treatment with stannous chloride in a mixture of methanol and hydrochloric acid solved this problem. Thus, a great number of derivatives of 54 was reduced to the corresponding 2-aminopyrazine 56 in medium to high yields (45-100%). 

Hproblems associated with all the trihalides of this review of the presence of small amounts of hydrates or oxochlorides. While on the matter of possible impurities, it may be recalled that in Bommer and Hohmann s early work there is a discrepancy between enthalpies of solution of anhydrous trichlorides and of respective metals in hydrochloric acid. Here the more likely impurity to be responsible is unreacted potassium metal in the lanthanide metal used in the hydrochloric acid dissolution experiments. 

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