Carminic acid structure

Cochineals contain several compounds with antraquinonic structures the most important is carminic acid. An nncommon chemical featnre of carminic acid and its derivatives is the presence of a C-glncosidic bond (Fignre 5.2.2). 

Figure 6.21 Examples of the structures of anthraquinone dyes (a) and azo dyes (b). a(n) is the natural dye carminic acid>...

The structure of kermisic acid is l,3,4,5-tetrahydroxy-7-carboxy-8-mcrhylanthraquinone. Carminic acid (Cl Natural Red 4 Cl 75470). is a red dye occurring as a glycoside in the body of the cochineal insect Dactylopius coccus of the order Homoptera. family Coecidae, Until the advent of synthetic dyes, the principal use for carminic acid was for dyeing tin-mordanted wool or silk. Its aluminum lake, carmine, finds use in Lhe coloring of foods. The structural formula of carminic acid is (2). 

Apart from its use as a valuable mordant dyestuff for textiles, cochineal (EEC 120) is still used as a colourant in cosmetics, foods, aperitif and beverages (ref. 194) and is one of the several permitted natural colourants which includes for example p-carotene, betanidin from Beta vulgaris, curcumin from Curcuma tonga, certain anthocyanins and chlorophyll complexes to quote a few structures. Commercial interest in natural products such as cochineal and carminic acid has been reactivated by the increasing pressures to avoid synthetic azo colours, their association with potential carcinogenic attributes and the increasing popularity of green issues. Carminic acid is reputed to possess some anticancer activity (ref. 195,196) and is a distant structural relative of the antibiotics, carminomycin and carminomycinone. 

Carminic acid was first obtained in crystalline form in 1858 (ref. 197) but its structure proved difficult to elucidate and was not finally established until 1965 through the work of two different groups while stereochemical detail was added in 1981. Some of the earlier work has been summarised (ref.198). 

Thus carminic acid can be represented by structure (D) as 7-(3-D-gluco-pyranosyl-3,5,6,8-tetrahydroxy-1-methylanthra-9,10-quinone-1-carboxylic acid, a formulation substantiated by its H NMR and C NMR spectra (ref. 210). By contrast, the detailed structure of the metal chelates of carminic acid is not known for certain (ref. 211) with regard to the possible competing role of the two chelating functions, namely the salicylic and the alizarin centres. 

Carminic acid and kermesic add can be regarded as more highly substituted derivatives of alizarin. In 1858, carminic acid was isolated in pure form, and in 1916, its structure was determined by Otto Dimroth (1872-1940). [55] The dyestuff, carminic acid, is distinguished from kermesic acid by a C-glucosyl residue in the former (Fig. 2.22). 

Kermesic acid an anthraquinone, m.p. 250 °C (d.), which occurs naturally as a bright red insect dye. It is structurally closely related to Carminic acid (see) it possesses the identical structure of a tetrahydroxyla-ted methylanthraquinone carboxylic acid, but there is no C-glycosidic glucose on C2. K.a. makes up 1-2% of kermes, the dried bodies of female scale insects Kermococcus ilicis. Kermes is one of the oldest known dyes and was used in ancient times as a scarlet mordant dye (Venetian scarlet), It was supplanted in the 16th century by cochineal. 

Cochineal is a red colorant derived from female scale-insects its chief coloring matter is carminic acid, the structure of which is shown in Table n. 

In order to explain the results shown in Fig. 2., the solution pH as a function of time was measured by a pH meter, and the results are displayed in Fig. 3. As can be seen from the data in the figure, when the initial solution pH is over 3.0, as reaction time increases, the solution pH decreases very fast to around 3.5 within 10 minutes, then reaches a lowest value of around 3.2 at 60 minutes, followed by a slight increase. What causes this interesting phenomenon We believed that the rapid decrease in solution pH is due to the fact that acidic intermediates are formed during the mineralization of 0.2 mM Indigo Carmine. Because of its complicated molecular structure, theoretically, it caimot be oxidized completely into CO2 and H2O in one step. 

Both HPLC and GC-MS were employed for the separation, identification and quantitation of the decomposition products of indigo and indigo carmine. The chemical structures of the dyes are shown in Fig. 3.73. Carboxylic acids were preconcentrated before HPLC analysis either by ion-exchange SPE or by solid-phase microextraction. HPLC measurements were performed in a Sarasep column (300 X 7.8 mm i.d.) using 5 mM H2S04 at a flow rate of 0.7 ml/min. Analytes were detected at 215 nm. The main intermediates formed during the photocatalytic decomposition are compiled in Table 3.26. The results demonstrated that... 

From classical degradative work on both carminic and kermesic acids (ref. 199, 200) the former was recognized as an anthraqinone resembling the latter and it was formulated (ref.201) as structure (A). This early work led to the surmise... 

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