A Manual of the Chemistry of the Carbon Compounds

TBti CARBON COMPOUNDS. 381
PHTHAUC ACIDS C9H4 j QQ OH 1
TerepMhttlic Acid is easily obtained by oxidizing inethyl-toluene or
any other aromatic hydrocarbon, alcohol, acid, &c., containing two
side-chains in the position 1*4, by a solution, consisting of 2 parts
of potassium dichromate, 3 parts of sulphuric acid, and 15 parts of
water. It is a white crystalline powder, almost insoluble in water,
alcohol, and ether, and subliming without previously melting. It
forms crystallizable salts; calcium and barium terephthalate are but
sparingly soluble in water.
The smallest quantity of terephthalic acid can be easily recognized
by treating it with a little phosphorus pentachloride, and adding some
methyl alcohol, and then a little water, and shaking the whole with
ether. On evaporating the ethereal solution, methyl krephthalaU
separates in crystals, melting at 140°. In the same way ethyl terephfhalate,
melting at 44°, may be obtained.
Hydrotereplmalic Add C0H6(CO,H), is a white crystalline powder,
which, is formed by acting with sodium-amalgam on an alkaline
solution of terephthalic acid.
f CN
Tcre/pKthdomtrUe C6H4-< QJJ is produced by distilling a mixture ot
potassium benzene-disulphonate and potassium cyanide. It forms
prismatic needles, having an aromatic odour, and dissolving sparingly
m alcohol, but not in water. By boiling it with potash, it is converted
into terephthalic acid.
IsophthtUic Add is readily formed by boiling isoxylene with chromicacid
solution, and also by oxidizing colophony with nitric acid. It is
almost insoluble in cold water, only sparingly in boiling water, but
more freely in alcohol, and crystallizes in very thin, long needles,
melting above 800°, Isophthalic acid has also been produced by
fusing potassium sulphobenzoato with sodium formate :—
CaH41 JO*| + cOgNaH . C^ [ °°*| + SO8NaH
PhiJialie Add is not obtained by oxidizing orthoxylene or orthotoluic
acid with chromic acid, because tho latter acid burns the
phthalio acid completely to carbon dioxide and water, but is formed
by oxidizing naphthalene, anthracene, and several derivatives of these
hydrocarbons, which contain two carbon-atoms linked to two aborning
carbon-atoms of the aromatic nucleus. It is usually prepared by
acting with chlorine on naphthalene, and boiling the product with
nitric* acid It crystallizes from boiling water in plates or thick
prisms, melting at 175°, Above this temperature it is resolved into
water and phthalic anhydride C0H4'. (^)/O, which sublimes in long
needles, melting at 129°.