Murexide

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Murexide
Murexide sample solutions.jpg
Murexide sample and as solution. From left to right: dissolved in distilled water, in distilled water with NaOH, in tap water, in tap water with NaOH and in tap water with NaOH end point titrated with EDTA.
Names
IUPAC name
Ammonium 2,6-dioxo-5-[(2,4,6-trioxo-5-hexahydropyrimidinylidene)amino]-3H-pyrimidin-4-olate
Other names
5,5'-Nitrilodibarbituric acid monoammonium salt
Ammonium purpurate
C.I. 56085
MX
Purpuric acid ammonium salt
Properties
C8H8N6O6
Molar mass 284.19 g/mol
Appearance Reddish-purple solid (dry)
Purple-brownish solid (old)
Odor Odorless
Melting point Decomposes above 300 °C
Boiling point Decomposes
Soluble
Vapor pressure ~0 mmHg
Hazards
Safety data sheet Sigma-Aldrich
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Murexide (NH4C8H4N5O6) or ammonium purpurate, is the ammonium salt of purpuric acid, used in analytical chemistry for determining the concentration of calcium in water samples, as well as rare earth metals.

Properties

Chemical

Murexide solutions change color in the presence of several metal ions, such as calcium or magnesium.

Murexide will slowly darken in air over long periods of time, due to oxidation.

Physical

Murexide is a reddish purple solid when dry, while older samples are more brownish in color. It is soluble in water,

Availability

Murexide can be purchased from chemical suppliers or online.

Preparation

There are several ways to synthesize murexide.

One route involves heating alloxantin in ammonia gas at 100 °C.

Another route involves refluxing uramil (5-aminobarbituric acid) with mercury oxide.

Projects

  • Complexometric indicator
  • Colorimetric reagent for calcium

Handling

Safety

Murexide is irritant, though no toxic or mutagen effects are known.

Storage

Murexide should be kept in closed bottles, away from light and corrosive vapors.

Disposal

No special disposal, can be poured down the drain.

References

Relevant Sciencemadness threads