Recipes for making murexide from uric acid


The translation was performed with the help of Babel Fish

Preparation of the murexide(1).
On a large scale as well as in the laboratory, this operation is delicate and undoubtedly difficult to carry out. The conditions for success must be determined with care and precision, because of the extreme facility with which this substance changes, as soon as one exceeds the suitable proportions of the reacting bodies and the desired degree of heat.

We will speak here only about the industrial process. In the beginning, the murexide was sold as paste, then as powder, but currently it is delivered as crystals.

Murexide as paste, dyes with carmine purple.
One lays out in a row a series of sandstone pots from 5 to 6 liters of capacity, by pouring in each one 1 liter of nitric acid. One at the same time adds the uric acid by small portions, by employing the precautions indicated in connection with the preparation of the alloxane. The size is much larger than contents, so that the abundant foam which is formed does not overflow. Each pot requires approximately 1 kg. of uric acid. The operation is finished at the end of 10 to 12 hours and gives a brown liquid which contains urea nitrate, alloxane, alloxantine and parabanic acid, with a deposit of unmodified uric acid. The simultaneous presence of the alloxane and the alloxantine is very favourable to the development of the red. These two bodies form on the surface of the liquid a crystal crust.

This acid solution is evaporated with the water bath, in enamelled cast iron boilers, at a temperature which should not exceed 80. It is coloured little by little in red and finishes, while thickening, by becoming of brown dark. The paste hardens on cooling.

During the concentration, the urea breaks up, and the incipient ammonia which is formed reacts on the mixture of alloxane and alloxantine, to give the murexide. It is more advantageous to neutralise the free nitric acid, before heating, either by ammonia, or by soda carbonate; in this last case it is formed soda purpurate.

Powder Murexide.
Mr. Lauth proposed the following process: One dissolves 1 kilog. of acid in 900 grams of nitric acid; one neutralizes by 200 grams of ammonia, then one heats with the water bath. When the temperature reached 70 to 75, one adds to the mixture 125 grams of soda sulphite. It is formed alloxantine, and immediately after murexide. The product is washed carefully and is dried with the drying oven. 1 kg. of uric acid gives by this process 400 grams of murexide to lay some, costing approximately 30 Fr. the kg.

Crystal Murexide.
One forms a solution of alloxane with 30 Baume, and one saturates it by ammonia by having care to add the latter only little by little and while waiting for each time the bath is become again acid. When saturation is complete, which requires approximately 30 percent by volume, one heats. The solution reddens promptly, and becomes of a splendid crimson. At this time one cuts down fire and one lets cool. The murexide separates then out of crystals.

Paul Schützenberger, Traité des matières colorantes, comprenant leurs applications à la teinture et à l'impression et des notices sur les fibres textiles les épaississants et les mordants publié sous les auspices de la Société industriele de Mulhouse et avec le concours de son comité de chimie, vol 1 pp 408-409, Paris, 1867.



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