Electrolysis of concentrated hydrochloric acid

Predict the products of the electrolysis of concentrated hydrochloric acid using platinum electrodes. 

Conduct electrolysis until the pH of the solution in the anode compartment becomes equal to 3 take samples every hour. Check the completeness of converting the tungstate into the metatungstate by means of the Scheele reaction. To do this, add 1 ml of concentrated hydrochloric acid dropwise to 5 ml of a sample. The absence... 

Sometimes it is necessaiy to hold the electrolysis of diluted hydrochloric acid, which concentration is less or equal to 17%. Graphite electrodes being rather stable in the concentrated HCl, begin to destroy catastrophically in the diluted acid solutions. The graphite corrosion reaches the value of 50 kg per 1 ton of chlorine, that is 10 times more than that of NaOl electrolysis [5]. 

Both mathematical modeling and optimization of the process were made for aromatic compounds chlorination by the concentrated hydrochloric acid electrolysis. It was stated, that declination of experimental data from the rated values didn t exceed 2-1058. 

Electrolysis of hydrochloric acid yields hydrogen at the cathode and oxygen at the anode from the dilute acid, but chlorine at the anode (of carbon) from the concentrated acid. Electrolysis of the concentrated acid is used on the large scale to recover chlorine. 

The electrolysis of asymmetric ketones 43 led to the formation of isomers and stereoisomers. Kinetic measurements for the formation of ketimine 43 in saturated ammoniacal methanol indicated that at least 12 h of the reaction time were required to reach the equilibrium in which approximately 40% of 42 was converted into the ketimine 43. However, the electrolysis was completed within 2.5 h and the products 44 were isolated in 50-76% yields. It seems that the sluggish equilibrium gives a significant concentration of ketimine 43 which is oxidized by the 1 generated at the anode, and the equilibrium is shifted towards formation of the product 44. 2,5-Dihydro-IH-imidazols of type 44, which were unsubstituted on nitrogen, are rare compounds. They can be hydrolyzed with hydrochloric acid to afford the corresponding a-amino ketones as versatile synthetic intermediates for a wide variety of heterocyclic compounds, that are otherwise difficult to prepare. 

When cold aqueous sulphuric acid of suitable concentration is electrolysed in a divided cell, a solution of perdisulphuric acid is obtained at the anode.1 The most favourable concentration of sulphuric acid is 45 to 60 per cent., but even with this the yield is far from quantitative, and, indeed, after a time further electrolysis actually effects a decrease in the quantity of perdisulphuric acid. If the sulphuric acid is too weak the anodic product may be only oxygen, whilst with too concentrated an acid the perdisulphuric acid will undergo conversion into permonosulphuric acid, which decomposes readily. The addition to the electrolyte of a few drops of hydrochloric acid,2 or of a solution of perchloric acid, or of an alkali perchlorate,8 has been found to favour the formation of the perdisulphuric acid it is also advisable that the platinum anode should be smooth or polished and not rough or platinised. 

With a rising voltage across the electrolyzer the back electromotive force will rise in proportion, because gases will be evolved and dissolved at a higher pressure in the platinum electrodes. When this pressure rises to 1 atm., the gases will be able to overcome the ambient atmospheric pressure and begin to escape freely into the atmosphere in the form of bubbles. Should this process proceed under reversible conditions and should the concentration of hydrochloric acid during electrolysis remain constant, the back electromotive force... 

The chemical change occurring during the course of electrolysis is observable on or in the vicinity of the electrodes. In many cases such a change is a simple decomposition. If for example a dilute solution of hydrochloric acid is electrolysed (between platinum electrodes), hydrogen gas is liberated on the cathode and chlorine on the anode the concentration of hydrochloric acid in the solution decreases. 

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