Hydrocholoric acid

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

To an ethanolic suspension of cimetidine, concentrated hydrocholoric acid and ethyl acetate are added, the product is collected, washed with ethyl acetate, and dried. The schematic is illustrated belcw ... 

The precipitate is insoluble in dilute acids, but decomposes in concentrated hydrocholoric acid. A large excess of the reagent dissolves it partly or entirely, when an intensive blue solution is obtained. Sodium hydroxide turns the precipitate to red, as iron(III) oxide and hexacyanoferrate(II) ions are formed ... 

Unless otherwise noted, catalysts were prepared by coprecipitating the hydrous oxides of uranium, antimony, and a tetravalent metal from a hydrocholoric acid solution of their salts by the addition of ammonium hydroxide. The precipitates were washed, oven dried, then calcined at 910 C overnight or at 930 C for two hours to form crystalline phases. Attrition resistant catalysts, containing 50% by weight silica binder, were prepared by slurrying the washed precipitate with silica-sol prior to drying. In some cases, small amounts of molybdenum or vanadium were added by impregnating the oven dried material with ammonium paramolybdate or ammonium metavanadate solution. The details of these preparations may be found elsewhere (5-8). 

Blanched green beans stored in a hydrocholoric acid solution at a pH... 

Acid. Taurates, methyltaurates and alkyl sulphosuccinamates are hydrolysed by boiling for 6h under pressure at 150-160°C with 6M hydrocholoric acid. 

Protonic acids such as hydrocholoric and sulfuric acids are far less suitable as initiators. Their conjugate bases, being strong nucleophiles, react rapidly with the carbenium ion center and prevent propagation. The advantage of the Lewis acid system is the low nucleophilicity of the anion (AlCl OH" in the example above). 

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