PHTHALIC ACIDS, or BENZENE DICARBOXYLIC

This article appears in Volume V21, Page 546 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: PER-PIG

PHTHALIC ACIDS, or BENZENE DICARBOXYLIC Acme, C6H4(CO2H)2. There are three isomers: (1) ortho, or

phthalic

PHTHALIC

acid; (2) meta, or isophthalic acid; (3) para5 or terephthalic acid.

Phthalic

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

FORMULA
FORMULA (Lat. diminutive of forma, shape,
pattern
- PATTERN
, &c., especially used of rules of judicial
procedure
- PROCEDURE (Fr. procedure, from Lat. procedere, to go for-ward)
)

and showed Laurent's supposition to be incorrect, upon which Laurent gave it its 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 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 benzene. It Corms

white

crystals, melting at 213 with decomposition into water and phthalic anhydride; the latter forms

long

LONG, GEORGE (1800-1879)
LONG, JOHN DAVIS (1838– )

white

needles, melting at 128 and boiling at 284. Heated with an excess of lime it gives benzene;

calcium

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

benzoate results when

calcium

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

phthalate is heated with one molecule of lime to 3300-350. The acid (and anhydride) are largely used in the colour industry (see

FLUORESCEIN

FLUORESCEIN

; PHENOLPHTHALEIN).
Phthalyl chloride, C6H4(000I)2 or C6H4(CCl2)(CO)O, formed by

heating

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

FORMULA
FORMULA (Lat. diminutive of forma, shape,
pattern
- PATTERN
, &c., especially used of rules of judicial
procedure
- PROCEDURE (Fr. procedure, from Lat. procedere, to go for-ward)
)

, 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

HEATING

phthalic anhydride or chloride in ammonia gas or by molecular rearrangement of ortho-cyanbenzoic acid. It forms N-metallic and alkyl salts. Bromine and potash give anthranilic acid, C6H4(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 caraway oil, a mixture of cymene and cuminol, with chromic acid, as almost insoluble in water, alcohol and ether; it sublimes without melting when heated.
For the reduced phthalic acids see POLYDSETHYLENES.

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