Hydrofluoric acid interpretation

Newer and more complex humus extractions have been developed. These typically involve more steps such as both physical separation on the basis of density and particle size (related to the size of soil inorganic components), and chemical separation based on extractions and washings with hydrofluoric acid (HF), hydrochloric acid (HC1), and sodium hydroxide (NaOH). The products of such separations are then subjected to spectroscopic analysis and interpretation [22,23],... 

In their studies of conductance of the methylbenzenes in anhydrous hydrofluoric acid, Kilpatrick and Luborsky (96) found that the specific conductance of solutions of prehnitene and durene changed with time, and additional experiments indicated this was due to rearrangement toward isodurene. It should be noted that the symmetrical configuration 1,2,4,5- is the strongest base of the three tetramethylbenzenes. The concentration and stability of the ArH+ ions are the important factors in the isomerization. With the xylenes and trimethylbenzenes in anhydrous hydrofluoric acid, no reaction was observed at 20°, but isomerization did take place upon addition of boron trifluoride. This is interpreted to be due to an increase in the concentration of ArH+ by the reaction... 

The authors concluded that the observed complexation was caused because there were also increased amounts of aluminium released at low pH conditions. For Compoglass F, for example, the aluminium level increased from 4.68 ppm in neutral water to 104 ppm in lactic acid solution, so this interpretation was consistent with all of the observations. There is the alternative possibihty, that at low pH, molecules of hydrofluoric acid (HF) formed which are predominantly un-dissociated, but the pH of the lactic acid solution was such that only very small amounts of HF could have been present, which again points to aluminium is the cause of fluoride complexation. 

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