Rubrocurcumin is a red colored dye that is formed by the reaction of curcumin

Curcumin

Curcumin is the principal curcuminoid of the popular Indian spice turmeric, which is a member of the ginger family . The other two curcuminoids are desmethoxycurcumin and bis-desmethoxycurcumin. The curcuminoids are natural phenols and are responsible for the yellow color of turmeric...

 and borate

Borate

Borates are chemical compounds which contain oxoanions of boron in oxidation state +3. The simplest borate ion, BO33−, has a trigonal planar structure. Other borates are made up of trigonal BO3 or tetrahedral BO4 structural units, sharing oxygen atoms...

s.

Synthesis

The reaction of curcumin with borates in presence of oxalic acid

Oxalic acid

Oxalic acid is an organic compound with the formula H2C2O4. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate , is a chelating agent for metal cations...

 produces rubrocurcumin.

Characteristics

Rubrocurcumin produces a red colored solution.

Rubrocurcumin is a neutrally charged composition, while rosocyanine

Rosocyanine

Rosocyanine and Rubrocurcumin are two red colored materials, which are formed by the reaction between curcumin and borates.-Application:The color reaction between borates and curcumin is used within the spectrophotometrical determination and quantification of boron present in food or materials...

 is build from ions. In rubrocurcumin, one molecule curcumin is replaced with oxalate

Oxalate

Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...

 compared to rosocyanine.

Complexes

Complex (chemistry)

In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...

 with boron

Boron

Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

such as rubrocurcumin are called 1,3,2-dioxaborines.

Literature

• G. S. Spicer, J. D. H. Strickland: Compounds of curcumin and boric acid. Part II. The structure of rubrocurcumin. Journal of the Chemical Society, London 1952, p. 4650–4653