Murexide reaction
The murexide reaction is a chemical detection reaction for purine , uric acid , xanthine and chemical compounds derived from them such as caffeine , theophylline and theobromine . The end product of the reaction is the deep purple colored ammonium salt of purple acid , murexide , or its N -methylated derivatives .
execution
The detection reaction is usually carried out in a small porcelain dish. 30% hydrogen peroxide solution in connection with concentrated hydrochloric acid are added to the substance sample as reagents and evaporated. The residue shows a violet color after being taken up with aqueous ammoniacal solution. The selectivity of the reaction can be changed by using nitric acid instead of hydrogen peroxide and hydrochloric acid .
Reaction sequence
Uric acid ( 1 ) is oxidized to various products with hydrogen peroxide and hydrochloric acid , including parabanic acid ( 2 ) and alloxan ( 3 ). At the same time, the reagents hydrolyze uric acid to pseudouric acid ( 4 ) , which then breaks down to uramil ( 5 ). Uramil and alloxan condense to form purple acid ( 6 ), which reacts with the addition of ammonia to form the intensely colored murexide ( 7 ). When using methylated xanthines, the corresponding methylated derivatives of murexide are formed.
literature
- Harry Auterhoff , Joachim Knabe, Hans-Dieter Höltje (1999). Pharmaceutical Chemistry Textbook . 14th edition, Wissenschaftliche Verlagsges., ISBN 3804716458 .