Uses of Hydrochloric Acid

Hydrochloric acid is stored in rubber lined steel storage tanks and shipped in rubber lined tank cars, pot cars or glass carboys. The following commercial grades of hydrochloric acid are known synthetic hydrochloric acid which is prepared by the reaction of hydrogen with chlorine sulphate acid obtained as a by-product in the manufacture of sodium sulphate hydrochloric acid used in the foodstuff industry and finally chemically pure hydrochloric acid. 

Contrary to the technical synthetic aeid the characteristic feature of the sulphate hydrochloric acid is a higher sulphate content. The content of impurities in synthetic hydrochloric acid depends chiefly on the degree of purity of the absorption water. For the manufacture of pure acids distilled water is used and cooling as well as the absorption of hydrogen chloride vapours takes place in a quartz equipment. Similarly, the hydrogen leaving the mercury cells is first of all thoroughly freed of all mercury. 

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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. 

An integrated process for producing chlorine dioxide that can consume chlorine (46) involves the use of hydrochloric acid as the reductant. The spent chlorine dioxide generator Hquor is used as feed for chlorate production, and hydrogen gas from chlorate production is burned with chlorine to produce hydrochloric acid. The principal disadvantage in the integrated hydrochloric acid-based processes is that the chlorine dioxide gas contains Y2 mole of chlorine for each mole of chlorine dioxide produced. A partial purification is achieved by absorption in chilled water in which the solubiHty of chlorine is less than chlorine dioxide however, this product stiU contains 10—15% chlorine on the basis of total chlorine and chlorine dioxide. 

The use of hydrochloric acid in neutralising the excess of alkali after saponification. 

Mention should also be made of glutamic acid and invert sugar which are used in foodstuffs and demand the use of hydrochloric acid-resistant material in manufacture, and of the essential flavouring oils which should preferably be stored and prepared in stainless steel and aluminium equipment. 

The method described differs from that given in Org. Syn. 3, 53 mainly in the use of hydrochloric acid in place of sulfuric acid, in the liberation of the cyanoacetic acid from the sodium salt and in the simplified esterification process. These are slight but very important differences and make the procedure much easier to carry out in the laboratory. Moreover, the yields are higher. 

About 3 billion kilograms of hydrochloric acid are produced each year, mostly as a by-product of the plastics industry. The largest single use of hydrochloric acid is the pickling of steel. The pickling process removes iron(III) oxide (FC2 O3, rust) from the surface of the metal. About a third of all hydrochloric acid is used to produce other chemicals, mostly ionic compounds. Other strong acids have specialized applications in indushy and research laboratories, but none approaches the importance of sulfuric, nitric, and hydrochloric acids. 

In the context of preparing potential inhibitors of dihydrofolate reductase (DHFR), the group of Organ has developed a rapid microwave-assisted method for the preparation of biguanide libraries (Scheme 6.174) [330]. Initial optimization work was centered around the acid-catalyzed addition of amines to dicyandiamide. It was discovered that 150 °C was the optimum temperature for reaction rate and product recovery, as heating beyond this point led to decomposition. While the use of hydrochloric acid as catalyst led to varying yields of product, evaluation of trimethylsilyl chloride in acetonitrile as solvent led to improved results. As compared to the protic... 

Dissolution of metallurgical or ore samples containing iron often requires the use of hydrochloric acid. Iron(II) is readily titrated with potassium permanganate = in strong acid solution. 

In some, more recent formulations, phosphoric acid replaced acetic acid as the acidic medium [46, 48]. The use of hydrochloric acid as a solvent for the Griess reagents had also been reported [45]. 

The uses of hydrochloric acid are given in Table 6.4. It is used in chemical manufacture especially for phenol and certain dyes and plastics. 

This is particularly likely to occur when halides are present, at the ashing or atomizing stage at temperatures too low to afford atomization, and can lead to losses of, for example, CaCl or PbCl j. The use of hydrochloric acid for sample dissolution should be avoided. If chloride is present, excess nitric... 

If the reaction is allowed to become warm, substantial protodesilylation of the product takes place to give 3-methyl-1 -phenyl-1,3-butadiene. The aqueous workup should be carried out rapidly to minimize this side reaction. The use of hydrochloric acid has particular advantage since all of the salts dissolve facilitating the extractions. 

Procedures for THP-ether formation. Use of hydrochloric acid. Concentrated hydrochloric acid (0.3 ml) was added to a mixture of 2,3-dihydropyran (0.75 mol) and the alcohol (0.5 mol). Reaction commenced immediately on shaking and was moderated by cooling in an ice-water bath. The mixture was shaken for a further 30 minutes, allowed to stand overnight, diluted with ether (150 ml), and the solution washed twice with aqueous sodium hydrogen carbonate solution. The ethereal solution was dried and evaporated, and the residue distilled under reduced pressure. 

An example of the use of hydrochloric acid in reactions of thiourea with unsaturated ketone 39, based on 5-chloro-3-methyl-l-phenylpyrazole, leads to the formation of dihydropyrimidinethione 40 as mentioned in [51] (Scheme 3.12). Acetic acid, in particular, was used to carry out the reaction of thiourea 28 with 2-benzylideneindene-l,3-dione 41 to synthesize heterocycle 42 [58] (Scheme 3.12). 

The industrial manufacture of hydrogen peroxide can be traced back to its isolation in 1818 by L. J. Thenard.1 Thenard reacted barium peroxide with nitric acid to produce a low concentration of aqueous hydrogen peroxide the process can, however, be significantly improved by the use of hydrochloric acid. The hydrogen peroxide is formed in conjunction with barium chloride, both of which are soluble in water. The barium chloride is subsequently removed by precipitation with sulfuric acid (Figure 1.1). 

A mild procedure for the conversion of 2-(acylamino)benzonitriles 18 to quinazolin-4(3/f)-ones 19 makes use of hydrochloric acid instead of a base. Brief exposure of 2-(acy-lamino)benzonitriles to 5 M hydrochloric acid followed by basification gives quinazolin-4(3//)-ones generally in good yield. The use of 5 M acid appears to be critical, as more dilute acid produces a mixture of the required quinazolinone and the corresponding 2-(acetamido)-benzamide. The conversion does not proceed via 2-(acylamino)benzamides. ... 

Figure 4.20. Determination of the Amino-Terminal Residue of a Peptide. Dabsyl chloride labels the peptide, which is then hydrolyzed with the use of hydrochloric acid. The dabsyl-amino acid (dabsy 1-alanine in this example) is identified by its chromatographic characteristics.

Use of hydrochloric acid instead of hydrobromic acid in the procedure described above leads to the corresponding rrani-dichloro complex. 

This example illustrates the more energetic action of the phosphorus halide as compared with the corresponding hydrogen halide it is impossible to replace the third hydroxyl group of glycerol with chlorine by the use of hydrochloric acid. 

Buffer Mixtures Prepared without the Use of Hydrochloric Acid or... 

The size of the blank can be reduced in various ways. The equipment used for sampling and for commination of the sample should be made, if possible, from material which does not contain the element to be determined. In some cases the admixtures can be removed by the use of an appropriate solvent, which does not react with the sample but dissolves the impurities (e.g., the use of hydrochloric acid to remove iron from a sample of silicon comminuted in a steel mortar). Quartz, polyethylene or Teflon vessels are used instead of glassware. To prevent contact of the sample with laboratory air, certain chemical operations may be conducted in closed chambers (dry boxes) flushed with purified air or inert gas [95, 96]. 

Dehydration of epoxides. When the triterpenoid epoxide (1), or the isomeric < -oxide, is refluxed with pyridine hydrochloride in pyridine it is converted in high yield into the diene (2). Use of hydrochloric acid in ethanol is attended with re-... 

R4 = R6 = H R3 = OH). A study of the Schmidt rearrangement of the diketone 136 (R = H, Me) showed that by choosing catalysts of different acidities either of the carbonyl groups can be made to react with hydrazoic acid to give all three isomeric benzazepines.166 Thus, sulfuric acid and sodium azide converted 136 (R = H, Me) into 137 (R = H, Me), while the use of hydrochloric acid afforded only the tetrazole 138 (R = H,... 

It is noteworthy that, in all those cases where L-arabinose residues have been reported to be few or absent, the yield of the xylan was only 1% or less (see Table XII). These preparations can scarcely be deemed representative of the entire xylan portion of the wood, but have to be regarded as fractions, modified to an unknown extent during lengthy processes of isolation and purification. Use of hydrochloric acid for destroying the... 

Patents by Raschig and his associates describe processes whereby chlorobenzene is prepared from benzene by use of hydrochloric acid and oxygen at temperatures above 200 C, the chlorobenzene then being hydrolyzed by steam at temperatures above 350 C. The phenol and hydrochloric acid formed are s arated from the reaction products while they are still in the gaseous state. 

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