Online Encyclopedia

PHTHALIC ACIDS, or BENZENE DICARBOXYLIC

Online Encyclopedia
Originally appearing in Volume V21, Page 546 of the 1911 Encyclopedia Britannica.
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PHTHALIC ACIDS, or
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BENZENE DICARBOXYLIC
  Acme, C6H4(
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CO2H)2 . There are three isomers: (1) ortho, or
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phthalic acid; (2)
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meta, or isophthalic acid; (3) para5 or
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terephthalic acid . Phthalic acid was obtained by Laurent in 1836 by oxidizing naphthalene tetrachloride, and, believing it to be a naphthalene derivative, he named it naphthalenic acid; Marignac determined its formula and showed Laurent's supposition to be incorrect, upon which Laurent gave it its
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present name . It is manufactured by oxidizing naphthalene tetrachloride (prepared from naphthalene, potassium, chlorate and hydrochloric acid) with nitric acid, or, better, by oxidizing the
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hydrocarbon with fuming sulphuric acid, using mercury or mercuric sulphate as a catalyst (German pat . 91, 202)' . It also results on the oxidation of ortho . II diderivatives of
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benzene . It Corms white crystals, melting at 213° with decomposition into
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water and phthalic anhydride; the latter forms long white needles, melting at 128° and boiling at 284° . Heated with an excess of lime it gives benzene; calcium benzoate results when calcium phthalate is heated with one molecule of lime to 3300-350° . The acid (and anhydride) are largely used in the colour industry (see
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FLUORESCEIN; PHENOLPHTHALEIN) . Phthalyl chloride, C6H4(000I)2 or C6H4(CCl2)(CO)O, formed by
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heating the anhydride with phosphorus chloride, is an oil which solidifies at o° and boils at 275° . In some reactions it behaves as having the first formula, in others as having the second .

Phthalyl chloride with phosphorus pentachloride gives two phthalylene tetrachlorides, one melting at 88° and the other at 47° . They cannot be changed into one another, and have been given the formulae C6H4(CCI3)(000I) and C6H4(CC12)20 . Phthalimide, C6H4(CO)2NH, is formed by heating phthalic anhydride or chloride in

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ammonia
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gas or by molecular rearrangement of ortho-cyanbenzoic acid . It forms N-metallic and alkyl salts . Bromine and potash give anthranilic acid, C6H4(
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NH2)(CO2H) . (See INDIGO.) Isophthalic acid is obtained by oxidizing meta-xylene with chromic acid, or by fusing potassium meta-sulphobenzoate, or meta-brombenzoate with potassium formate (terephthalic acid is also formed in the last case) . It melts above 300°, and dissolves in 7800 parts of cold water and in 46o of boiling . The barium salt (+6H20) is very soluble (a distinction between phthalic and terephthalic acids) . Uvitic acid, 5-methyl isophthalic acid, is obtained by oxidizing mesitylene or by condensing pyroracemic acid with baryta water . Terephthalic acid, formed by oxidizing para-diderivatives of benzene, or best by oxidizing
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caraway oil, a mixture of cymene and cuminol, with chromic acid, as almost insoluble in water,
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alcohol and ether; it sublimes without melting when heated . For the reduced phthalic acids see POLYDSETHYLENES .

End of Article: PHTHALIC ACIDS, or BENZENE DICARBOXYLIC
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