Eosins

Fluorescein is obtained by condensing phthahc anhydride (1 mol) with resorcinol (2 mols) in the presence of anhydrous zinc chloride. The tetra-bromo derivative, readily prepared by the addition of the calculated quantity of bromine, is eosin. 

Eosin (Tetrabromofluorescein). Place 16 5 g. of powdered fluorescein and 80 ml. of rectified (or methylated) spirit in a 250 ml. flask. Support a small dropping funnel, containing 36 g. (12 ml.) of bromine, above the flask make sure that the stopcock of the funnel is well lubricated before charging the latter with bromine. Add the bromine diopwise during about 20 minutes. When half the bromine has been introduced, and the fluorescein has been converted into dibromofluor-escein, all the solid material disappears temporarily since the dibromo derivative is soluble in alcohol with further addition of bromine the tetrabromofluorescein (sparingly soluble in alcohol) separates out. Allow the reaction mixture to stand for 2 hours, filter ofiF the eosin at the pump, wash it with alcohol, and dry at 100°. The yield of eosin (orange-coloured powder) is 25 g. 

Sodium salt of eosin. Grind together in a mortar 12 g. of eosin with 2 g. of anhydrous sodium carbonate. Transfer the mixture to a 250 ml. conical flask, moisten it with 10 ml. of rectified spirit, add 10 ml. of water and warm on a water bath, with stirring, until the evolution of carbon dioxide ceases. Add 50 ml. of ethyl alcohol, heat to boiling, and filter the hot solution through a fluted filter paper (supported in a short-stemmed funnel) into a beaker, and allow to stand overnight. Filter ofiF the browiiish-red crystals of sodium eosin, wash with a little alcohol, and dry. The yield is 10 g. 

This solution may also be employed in the test for bromine. If iodine has been found, add small amounts of sodium nitrite solution, warm shghtly and shake with fresh 1 ml. portions of carbon tetrachloride until the last extract is colourless boil the acid solution until no more nitrous fumes are evolved and cool. If iodine is absent, use 1 ml. of the fusion solution which has been strongly acidified with glacial acetic acid. Add a small amount of lead dioxide, place a strip of fluorescein paper across the mouth of the tube, and warm the solution. If bromine is present, it will colour the test paper rose-pink (eosin). 

Bromophenol blue 2, 7 -DichIorofluorescein Eosin, tetrabromofluorescein Fluorescein Potassium rhodizonate, C404(0K)2 Rhodamine 6G Sodium 3-aIizarinsuIfonate Thorin Dissolve 0.1 g of the acid in 200 mL 95% ethanol. Dissolve 0.1 g of the acid in 100 mL 70% ethanol. Use 1 mL for 100 mL of initial solution. See Dichlorofluorescein. Dissolve 0.4 g of the acid in 200 mL 70% ethanol. Use 10 drops. Prepare fresh as required by dissolving 15 mg in 5 mL of water. Use 10 drops for each titration. Dissolve 0.1 g in 200 mL 70% ethanol. Prepare a 0.2% aqueous solution. Use 5 drops per 120 mL endpoint volume. Prepare a 0.025% aqueous solution. Use 5 drops. 

Chugaev reaction glacial acetic acid plus acetyl eosin-red greenish yellow 1 80,000 sensitivity... 

Bromine and bromides can be detected quaUtatively by a number of methods. In higher concentrations bromine forms colored solutions in solvents such as carbon tetrachloride [56-23-5] and carbon disulfide [75-15-0]. Bromine reacts with yeUow disodium fluorescein [518-47-8] to form red disodium tetrabromofluorescein (eosin) [548-26-5] C2QH Br4Na20. As Httle as 0.3 p.g of bromide can be detected and chlorides do not interfere (56). Bromine reacts with platinum sulfate [7446-29-9] Pt(S0 2> solution to form red to brown crystals of potassium hexabromoplatinate [16920-93-7] K PtBr ( )-... 

Eosin [15086-94-9] (tetrabromofluorescein), C2QHgBi40, made by the bromination of fluorescein, is both a dye and an adsorption indicator. Eosin Y /7 7372-87-17, C2QH Br40 2Na, the disodium salt, is a biological stain. 475 -Dibromofluorescein [596-03-2], C2QH2QBr20, is used in D C Orange No. 

Dyes, xanthene used for eosin, fluorescein-type phthaleins, rhodamines, and rose Bengal. 

Eosin B (Bluish, Eosin Scarlet, 4, 5 -dibromo-2, 7 -dinitrofluorescein disodium salt)... 

Eosin Y (as di-Na salt) [17372-87-1] M 691.9. Dissolved in water and ppted by addition of dilute HCl. The ppte was washed with water, crystd from ethanol, then dissolved in the minimum amount of dilute NaOH soln and evaporated to dryness on a water-bath. The purified disodium salt was then crystd twice from ethanol [Parker and Hatchard Trans Faraday Soc SI 1894 7967]. 

In equation (4.88) the amplitude of the sine term is small, eompared with the eosine term, and ean be ignored. Henee... 

Eosin Flavonoids Morin Flavonol, fisetin, robinetin Quercetin Rutin condensation products of urea, formaldehyde and methanol [126], pesticide derivatives [127] sweetening agents [128, 129] anion-active and nonionogenic surface-active agents [130] steroids, pesticides [29,132, 133] pesticides [134—137] vanadium in various oxidation states [138] uracil derivatives [139]... 

The treatment of unsaturated substances with halogen leads to addition to these molecules. This is true not only of bromine and chlorine vapor but also of the less reactive iodine. Substitution also occurs in the presence of light. Examples of such halogenations are listed in Table 12. Figure 32 illustrates the characterization of fluorescein in a bubble bath preparation. Bromination of the fluorescein in the start zone yields eosin. 

Fig. 32 Characterization of fluorescein in a foam bath by bromination. 1 = fluorescein, 2 = foam bath brominated, 3 = foam bath, 4 = eosin.

Fluorescein Apply sample solution, lead bromine vapor over it or apply 0.1% bromine in chloroform. Various intermediate bromination products are formed with eosin as the final product (Fig. 32). [46]... 

EbuUioscopic method, 37 Electrolytic reduction, oxalic acid, 102 nitrobenzene, 144, 145 Eosin, 187 Epichlorhydrin, in Estimation of carbon and hydrogen, 4 halogens, 22 nitrogen, 13 sulphur, 28 Ether, 59... 

---