Colour additives

T artrazine, 4,5-dihydro-5 -oxo-1 -(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-1// -pyrazole-3-carboxylic acid trisodium salt was discovered by Ziegler in 1884 and is used as a dye for wool and silk. It is used as a colour additive in foods, drugs and cosmetics, and is an adsorption-elution indicator for chloride estimations in biochemistry (B-76MI40404). 

The Library of Chemical Information is maintained by the US Food and Drug Administration s Center for Food Safety and Applied Nutrition and is an excellent database for multiple classes of chemicals including food additives, cosmetics, colour additives, pesticides and other chemicals. 

US Food and Drug Administration (1982) Toxicological principles for the safety assessment of direct food additives and colour additives used in food. US FDA, Rockville, pp 1-130... 

Bromine readily adds across an alkenic double bond by electrophilic addition (Figure 8.4). The brominated compound is usually colourless, but bromine in solution ( bromine water ) has a red colour. Addition of bromine water to an aikene is accompanied by a loss of the red colour as reaction proceeds. The stoichiometry of reaction is almost always 1 1, with one molecule of bromine reacting per double bond. 

Fig. 3.117. Separation of 6SA and 8SA from a certified lot of D C Yellow No. 10 by pH-zone-refining CCC. (a) HPLC analysis of colour additive and (b) HPLC analyses of the separated components. Reprinted with permission from A. Weisz et al. [172].

The addition of additives to food, including colour additives, is strictly regulated in the developed world, for example by the Food and Drug Administration in the USA." Colonr additives are classified by the FDA as either certifiable or exempt from certification . 

Addition of triethylamine to a stirred suspension of the salt 1 and potassium carbonate in toluene at room temperature resulted in formation of a yellow colour. Addition of 2.5 equivalents of DMAD produced a red colour, and the pyrazolo[l,5-u]pyridine 2 was obtained in 82% yield. 

Treatment of 1 with morpholine at room temperature results in an exothermic reaction and the reaction mixture turns dark red in colour. Addition of water results in the separation of 2 as yellowish-green needles in 54% yield. 

With sodium- or potassium methoxide, trinitroanisole reacts like sym-trinitro-benzene or a- trinitrotoluene, viz. it adds on an alcoholate molecule, forming a red-coloured addition product (I) ... 

Wet Tests.—The presence of iron in solution may readily be detected by a considerable number of sensitive reactions. Thus ferrous iron gives a green precipitate of ferrous hydroxide upon addition of excess of ammonium hydroxide. With potassium ferricyanide and a trace of acid, a deep blue precipitate—Turnbull s blue—is obtained. With potassium ferrocyanide a white precipitate is obtained in the entire absence of any ferric salt. Ferric iron, on the other hand, is usually characterised by its deep yellow or brown colour. Addition of concentrated hydrochloric acid deepens the colour. With excess of ammonium hydroxide, brown flocculent ferric hydroxide is precipitated. With potassium ferrocyanide solution, a deep blue colour is obtained in acid solution, whilst with potassium ferricyanide there is no action. Potassium thiocyanate gives in acid solution a deep red colour, which is not d troyed by heat. Salicylic acid gives a violet colour, provided no free mineral acid is present. 

Betalains have received much attention from the food industry as natural colour additives (Adams et at, 1976 Pourrat et at, 1983). The betacyanins from red beet are used for colouring ice cream, jam and fruit conserves. Earlier interest in betacyanins came from their use in colouring red wine, although this was prohibited by law in 1892 due to the use of the apparently harmful pokeberry Phytolacca americana, extract (Dreiding, 1961). 

Chromium forms trihalides with all four halogens. The colour of a CrClg solution varies with temperature and chloride ion concentration. In cold dilute solution the octahedral [Cr(H20)g] + ion gives a violet colour. Addition of chloride ion, particularly if accompanied by heat, produces a green solution due to the [Cr(H20)5Cl]2+ ion ... 

Colour additives Column (cellulose) Spectrophotometric [48, 49] SolkaFloc BW 40)... 

Some food and colour additives may have (generally recognised as safe) (GRAS) status, which also gives some assurance that they could be used in pharmaceutical products with minimal additional safety testing. This is especially the case if the excipient is not likely to be absorbed systemically from the formulation. 

Ion " Colour Addition of NaOH(aq) Excess NaOH(aq) Addition of NHjfaq) Excess NH,(aq)... 

Furthermore, powder dyestuffs which could only be used in a continuous system after prior dissolution can be added dry as sufBcient time exists for the powder to dissolve. Batch addition of colour has the disadvantage that any errors in colour addition cannot easily be corrected and the possibiUty of off-shade paper being produced is high. 

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