Phthaleins, general

The above simple experiments illustrate the more important properties of aliphatic acid chlorides. For characterisation, the general procedure is to hydrolyse the acid chloride by warming with dilute alkali solution, neutralise the resulting solution with dilute hydrochloric acid (phenol-phthalein), and evaporate to dryness on a water bath. The mixture of the sodium salt of the acid and sodium chloride thus obtained may be employed for the preparation of solid esters as detailed under Aliphatic Acids, Section 111,85. The anilide or p-toluidide may be prepared directly from the acid chloride (see (iii) above and Section III,85,i). 

Table 5.1 summarizes the details of some useful acid-base indicators. Exact agreement with the pH range expressed by equation (5.5) is by no means always observed. This is because some colour changes are easier to see than others and so the general approximation made in deriving equation (5.5) is not uniformly close. Structurally, the indicators form three groups phthaleins (e g. phenolphthalein) sulphonephthaleins (e.g. phenol red) and azo compounds (e.g. methyl orange). 

Indicator dyes for pH having the phthalide structure fall into two types, the phthaleins, shown in the lactone form of general structure (1.66) and the sulfoph-thaleins (1.67). The synthetic pathways to these products are very similar. The phthaleins (1.66) are made by reacting phenol with phthalic anhydride in the presence of Lewis acid catalyst, e.g. ZnCl, whilst (1.67) are obtained by using 2-sul-fobenzoic anhydride (Figure 1.20). 

Assay With the aid of 10 mL of water, quantitatively transfer about 500 mg of sample, accurately weighed, into a separator Add 2 mL of 2.7 A hydrochloric acid, and extract the precipitated saccharin, first with 30 mL, then with five 20-mL portions of a solvent comprising 9 1 (v/v) chloroform alcohol. Filter each extract through a small filter paper moistened with the solvent mixture, and evaporate the combined filtrates to dryness on a steam bath with the aid of a current of air. Dissolve the residue in 75 mL of hot water, cool, add phenol-phthalein TS, and titrate with 0.1 A sodium hydroxide. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1A sodium hydroxide is equivalent to 20.02 mg of C7H8N203S. Benzoate and Salicylate Add 3 drops of ferric chloride TS to 10 mL of a 1 20 aqueous solution previously acidified with 5 drops of glacial acetic acid. No precipitate or violet color appears. 

These derivatives are readily obtained by adding diazotised arsanilic acid to alkaline solutions of phthaleins, the general metliod of preparatioir... 

A number of other phthaleins such as o-cresolphthalein, pyro-gallolphthalein, etc., as well as halogen substitution products of certain of the above-mentioned compounds have been prepared and partially investigated. In general, however, these additional indicators offer few advantages over the compounds described in detail. 

M13. Mateer, J. G., Baltz, J. I., Marion, D. F., and MacMillan, J. M., Liver function tests general evaluation of liver function tests, and appraisal of comparative sensitivity and reliability of newer tests, with particular emphasis on cephalin-cholesterol flocculation test, intravenous hippuric acid test and improved bromsul-phthalein test with new normal standard. J. Am. Med. Assoc. 121, 723-728 (1943). 

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