Hydrolysis in Concentrated Acid

Acid hydrolysis is the most generally used method of degrading proteins, and it is almost universally employed when amino acids are to be isolated or estimated, since it leads to complete hydrolysis with a minimum of destruction. The only amino acid that is extensively destroyed is tryptophan, the destruction of which may be largely due to the presence of traces of heavy metals during hydrolysis and may be reduced by using very pure HCl and quartz vessels (Jacobsen, 1949 Monnier and Jutisz, 1950). 

Slight destruction of serine and threonine (Rees, 1946) also takes place, but in partial hydrolyzates this would be almost negligible. No synthetic reactions or rearrangements have been shown to take place under the action of strong acids. 

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There appears to be little evidence of decomposition of unhydrolyzed cellulose in acid solution, but the products of hydrolysis decompose at almost the same rate that cellulose is hydrolyzed by dilute acid. The use of high concentrations of acid at low temperatures, as in the hydrolysis with fuming hydrochloric acid, favors hydrolysis over sugar decomposition and, therefore, higher yields of sugar are obtained. For that reason hydrolysis in concentrated acid is made the basis for determination of the carbohydrate content of wood. ... 

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