Henry E. (Henry Enfield) Roscoe.

A treatise on chemistry (Volume 3) online

. (page 44 of 50)
Online LibraryHenry E. (Henry Enfield) RoscoeA treatise on chemistry (Volume 3) → online text (page 44 of 50)
Font size
QR-code for this ebook


lodo-isophthalic acid, C 6 H 3 I(CO 2 H) 2 (4:3:1), is formed by
the oxidation of acetyliodotoluene, CH 3 .CO.C H 3 I.CH 3 , which
will be subsequently described. It is scarcely soluble in cold,
only very slightly in boiling water, and crystallizes from hot
acetic acid in small, white needles, which melt at 203 204,
but sublime in white, lustrous flocks, without previously melting,
when carefully heated. On fusion with caustic potash, para-

1 Miiller, Ber. Deutsch. Chem. Oes. xix. 1491.

- Barth and Senhofer, ibid. viii. 1481 ; Ann. Chem. Pharm. elxxiv. 235.
3 Limpricht, ibid, clxxx. 92.

* Baeyer, Ber. Deutsch. Chem. Oes. xix. 1806.

VOL. III. PART IV. l J



482 AROMATIC COMPOUNDS.

hydroxybenzoic acid is formed, while it yields benzoic acid when
reduced in alcoholic solution by sodium amalgam. 1

Nitro-isopUlmlic acid, 2C C H,(NO 2 )(C0 2 H) 2 + 3H 2 O, is pre-
pared by heating isophthalic acid with fuming nitric acid for
some time ; 2 it is slightly soluble in cold, very readily in boiling
water and alcohol, and crystallizes in thin, lustrous plates, re-
sembling those of benzoic acid, which readily lose their water
and melt with slight decomposition at 248 249.

Its salts, some of which crystallize well, have been fully
examined by Beyer.

Methyl nitro-isophtkalate, C 6 H 3 (NO 2 )(CO 2 .CH 3 ) 2 , is formed
when hydrochloric acid is pissed into an alcoholic solution of
the acid, and crystallizes in fine, lustrous needles, which melt at
121'5, and yield a vapour which smells like aniseed.

Ethyl nitro-isophthalate, C C H 3 (N0 2 )(CO 2 .C 2 H 5 ) 2 , forms fine
needles or transparent prisms, which melt at 83'5.

Amido-isophthalicacid, C 6 H 3 (NH 9 )(GO 2 H).,, is readily obtained
from the nitro-acid by reduction with tin and hydrochloric acid.
It is only slightly soluble in cold water and alcohol, crystallizing
from hot water in lustrous plates and from alcohol in prisms.
It combines with acids and bases forming compounds which
have been investigated by Beyer. Its ethers are obtained by
the reduction of the corresponding nitro-compounds.

Methyl amido-isophthalatc, CeH 3 (NH 2 )(CO 2 .CH 3 ) 2) crystallizes
from wood-spirit in thin, yellowish plates or tablets, which melt
at 176.

Ethyl amido-isophthalate, C 6 H 3 (NH 2 )(C0 2 .C 2 H 5 ) 2 , forms thin
plates or fascicular needles, melting at 118. Its ethereal
solution has a splendid violet fluorescence.

s-Sutyho-isophthalic W, CH 3 (CO 2 H) 2 S0 3 H + 2H 2 O (1:3:5),
is prepared by the action of sulphur trioxide on isophthalic acid, 3
and by heating the latter to 200 with fuming sulphuric acid. 4
It is very readily soluble in water, but only slightly in dilute
sulphuric acid, and crystallizes in long needles or transparent,
four-sided, pointed, rhombic columns, which effloresce in dry
air, but deliquesce in very damp air. The anhydrous acid melts
at 257 258, a slight discolouration taking place.

a-Sulpho-isophthalicacid, C C H 3 (CO 2 H) 2 SO 3 H + 2H 2 O (1:3: 4),
is obtained by the oxidation of an alkaline solution of a-meta-

1 Klingcl, Bcr. Deutsch. Chtm. Gcs. xviii. 2701.

- Fittig and Storss, ibid, cliii. 285 ; Beyer, Journ. Prakt. Chem. [2] xxv. 465.

3 Heine, Be,: Deutsch. Chem. Gcs. xiii. 491. 4 Lonnies, ibid. xiii. 7o3.



TEREPHTHALIC ACID. 4 83



xylenesulphonic acid, 1 or metatoluylsulphamic acid 2 with potas-
sium permanganate. It is readily soluble in water, and crystallizes
from dilute sulphuric acid in flat, very hygroscopic needles
melting at 235 240.



TEREPHTHALIC ACID.

2252 Parapbthatic acid is readily formed by the oxidition of
those para- compounds which possess two side-chains containing
carbon, such as paraxylene, 3 cymene, or methylisopropylbenzene,
OH 3 .C 6 H 4 .C 3 H 7 , cuminol or cuminaldehyde, COH.C fl H 4 .C 3 H 7 ,"
paratoluic acid, 5 &c. Caillot, as already mentioned, obtained it
from oil of turpentine, C 10 H 16 , which is closely related to cymene.
The isomerides of this, oil of cajeput, oil of citron, and the
tliymene contained in thymian, all yield terephthalic acid on
oxidation, 6 and it is also formed when potassium parasulpho-
benzoate is fused with sodium formate. 7

In order to prepare it, a mixture of 100 grms. of paraxylene,
which need not be pure, 400 grms. of potassium dichromate and
550 grms. of sulphuric acid, diluted with two volumes of water,
is heated for several days in a flask connected with a reflux
condenser until the solution has become coloured a pure green ;
the unattacked xylene is then distilled off, and the solution
filtered from the precipitated acid, which is dissolved in dilute
carbonate of soda and precipitated by hydrochloric acid. The
acid is obtained pure by repeating this process two or three
times.

Cymene, which is easily prepared by distilling camphor with
phosphorus pentoxide, may be employed instead of paraxylene,
or Roman cumin oil, a mixture of cymene and cuminol, may
be used.

Terephthalic acid is a tasteless powder, which appears crystal-
line Tinder the microscope, is insoluble in ether and chloroform,
and scarcely soluble in water and alcohol ; the hot, saturated,
aqueous solution has an acid reaction, and deposits the acid on

Jacobscn and Lonnies, Ber. Dcutsch. Chem.Gcs. xiii. 1556.

Coalc and Remsen, Amcr. Chem. Journ. iii. 214.

Beilstein, Ann. Chcm. Pharm. cxxxiii. 40.

Miiller and Warren dela Rue, ibid. cxxi. 8<.

Beilstc-in and Yssel de Schepper, ibid, cxxxvn. 308.

Schwanert, ibid, cxxxii. 260.

Remsen Bcr Dcutsch. Chcm. Ges. v. 3/9.

I I 2



484 AROMATIC COMPOUNDS.

cooling as an indistinctly crystalline powder. It sublimes when
heated without previously melting.

Ammonium, terephthalate, C 8 H 4 O 4 (NH 4 ) 2 , is deposited on the
evaporation of its solution in small, lustrous crystals.

Calcium terephthalate, C 8 H 4 O 4 Ca + 3H 2 O, separates from hot
water in small crystals, which dissolve in 1,214 parts of water
at 6 C .

Barium terephthalate, C 8 H 4 O 4 Ba + 4H 2 O, is deposited from a
rapidly cooled solution as a white, granular powder ; by gradual
evaporation it is obtained in small, concentrically arranged tablets,
which dissolve in 355 parts of water at 5.

Silver -terephthalate, C 8 H 4 O 4 Ag 2 , is an amorphous precipitate,
which blackens in the light.

Methyl terephthalate, C 8 H 4 O 4 (CH 3 ) 2 , is formed by the action of
the chloride on methyl alcohol, 1 and crystallizes from hot alcohol
in large flat prisms, which melt at 140 and are volatile without
decomposition. By means of this compound the smallest quantity
of terephthalic acid can be detected. The substance is treated
with phosphorus chloride and then with methyl alcohol, water
being finally added and the methyl compound extracted with
ether. On the evaporation of the latter characteristic crystals
of the compound are obtained.

Ethyl terephthalate, C 6 H 4 (CO 2 .C 2 H 5 ) 2 , forms white odourless
prisms, which resemble those of urea and melt at 44-.

The following ethereal salts have been prepared by Beyer,
some by means of the chloride, the remainder from the silver
salt : "

Melting-
point.

Propyl terephthalate, C 6 H 4 (CO 2 .C 3 H 7 ) 2 , long needles .... 31 '0
Isopropyl terephthalate, C 6 H 4 (CO 2 .C 3 H 7 ) 2 , lustrous plates . 55'5
Isobutyl terephthalate, C 6 H 4 (CO 2 .C 4 H 9 ) 2 ," needles 52'5

The normal butyl ether is liquid, while the tertiary butyl
ether is only formed with great difficulty, and has not yet been
obtained in considerable amount. Miiller and Warren de la
Rue have prepared the amyl ether; it crystallizes in scales,
which are melted even by the warmth of the hand.

Phenyl terephthalate, C 6 H 4 (CO 2 .C H 5 ) 2 , crystallizes from alcohol
in fine needles, melting at 191 . 3

1 Warren de la Rue and Miiller ; Schwanert, loc. cit.
" Ber. Dcutsch. Chem. Ges. x. 1742.
3 Schreder, ibid. vii. 707.



TEREPHTHALAMIC ACID. 485

Terephthalyl chloride, C 6 H 4 (COC1.) 2 , is formed by the distilla-
tion of the acid with phosphorus pentachloride and is a crys-
talline mass, which has a somewhat sharp odour resembling
cinnamon, melts at 78 (Schreder) and boils at 259 (Beyer).

Terephthalamide, C 6 H 4 (CO.NH 2 ) 2 , is obtained by the action
of ammonia on the chloride, as a white amorphous powder,
which is insoluble in all solvents (Warren de la Rue and
Muller).

Tercphtkalamic acid, C H 4 (CO.NH 2 )CO 2 H, is obtained as the
product of all reactions by which paracyanobenzoic acid might be
prepared, as the elements of water are taken up by the latter
according to the following equation :

/ON /CO.NH 2

C 6 H/ + H 2 = C 6 H 4 <(

\C0 2 H \C0 2 H

Terephthalamic acid crystallizes in indistinct, microscopic
plates, which are slightly soluble in cold, readily in hot water
and alcohol, melt at 214, and are converted into terephthalic
acid by boiling with caustic soda (Sandmeyer).

Ethyl paracyanobenzoate, C 6 H 4 (CN)C0 2 .C 2 H 5 , is prepared from
ethyl paramidobenzoate and crystallizes in needles, melting at
54. On heating with an alcoholic solution of hydroxylamine,
tho ethyl ether of benzenylamidoximeparacarboxylic acid, C 6 H 4
(C0 2 H)C(NH 2 )NOH, is formed ; it melts at 135 and yields the
free acid which melts above 330. x The meta- and para-cyano-
benzoic acids and their ethers, therefore, behave towards hydro-
xylamine like other nitrils, while the ortho-compounds differ
from these.

Terephthalonitril, C 6 H 4 (CN) 2 , is prepared by heating terephtha-
lamide with phosphorus pentoxide (Warren de la Rue and
Muller) or by distilling potassium benzeneparadisulphonate, 2
potassium parachlorobenzenesulphonate, 3 or potassium para-
bromobenzenesulphonate 4 with potassium cyanide or dehydrated
potassium ferrocyanide. 5 It is insoluble in water, slightly soluble
in cold, readily in hot alcohol, and crystallizes in needles or
lustrous prisms, which melt at 215 and readily sublime. It is

1 Miiller, Bcr. Deutsch. diem. Oes. xviii. 2485 ; xix. 1491.

2 Garrick, Zcitschr. Ghern. 1869, 551.

3 Nolting, Bcr. Deutsch. C'kcm. Gcs. viii. 1110.

4 Irclan, Zcitschr. Chan. 1869, 164 ; Barth and Scuhofcr, Ann. Chan. 1'luifM.
clxxiv. 242.

6 Limprieht, ibid, clxxx. 88.



486 AROMATIC COMPOUNDS.

converted into terephtlmlic acid by boiling with an aqueous, or
more rapidly with an alcoholic, solution of potash. It is, how-
ever, better to decompose it by heating to 160 with hydrochloric
acid (Limpricht).



ADDITION PRODUCTS OF TEREPHTHALIC
ACID. 1

2253 Tdraliydrotcrcphthalic acid, C G H 8 (CO 2 H) 2 . In order to
prepare this substance, 5 grms. of terephthalic acid are dissolved
in a little caustic soda solution and boiled for twenty hours, 500
grms. of 4 per cent, sodium amalgam being gradually added.

It is scarcely soluble in cold water and requires 120 parts of
boiling water for solution, from which it crystallizes on cooling
in small, arborescent prisms, which melt above 300 and sublime.
Its silver salt is a white amorphous precipitate which blackens in
the light.

Methyl tetrahydroterepUJialatc, C C H 8 (C0 2 .CH 3 ) 2 , is formed by
the a,ction of methyl iodide on the silver salt, as well as by
passing hydrochloric acid into a solution of the acid in wood-
spirit. It is thus obtained as an oily liquid, which smells of
fennel and soon solidifies in large prisms, melting at 30. It
crystallizes from ether, in which it forms a blue fluorescent
solution, in long needles.

Hcxhydroterephthalic acid, C (! H 10 (CO 2 H) 2 ,is obtained by heating
the tetrahydro-acid to 240 for six hours with concentrated
hydriodic acid. It is even less soluble in water than the tetra-
hydro-compound and crystallizes from hot water in small prisms,
melting at about 295. It is very stable towards alkaline per-
manganate solution, while the tetrahydro-derivative is oxidized
to oxalic acid by this even in the cold. Its methyl ether melts
at 58 and resembles the preceding compound, but does not
give a fluorescent solution.

DHyromohcxhydrotereplitlmlic acid, C 6 H 8 Br 2 (CO 2 H) 2 4- H 2 0,
is best prepared by treating finely divided tetrahydroterephthalic
acid for several hours with an ethereal solution of bromine, the
mixture being agitated at intervals, and repeating this operation
until the acid is almost completely dissolved. The solution is
J Baeyer, Bcr. Detttteh. Chcm. Gcs. xix. 1805






TETRAHYDROTEREPHTHALIC ACID. 487

then decolourized with sulphur dioxide and the acid extracted
by carbonate of soda solution. It is precipitated from the latter
by hydrochloric acid in granular, cubic crystals. Its methyl ether
is formed by the combination of bromine with the ether of
tetrahydroterephthalic acid, and crystallizes in large prisms
melting at 73.

Tetrahydrophthalic acid behaves towards bromine in the same
manner as cinnamic and fumaric acids. When the brominated
acid is heated with caustic soda solution, a dihydroterephthalic
acid is formed, which resembles terephthalic acid very closely.
A syrupy acid is however formed by the action of freshly pre-
cipitated silver oxide, which is probably a clihydroxyhexhydro-
terephthalic acid, and is converted by the action of bromine into
tetrabromocatechol :

C 6 H 8 (OH) 2 (CO 2 H) 2 + 7Br 2 = C 6 Br 4 (OH) 2 + 2C0 2 + 1 OHBr.

The constitution of tetrahydrophthalic acid is proved by the
formation of this substance, and may also be deduced from the
following considerations.

Phthalic acid only assumes two atoms of hydrogen when acted
upon by sodium amalgam and water, while isophthalic and tere-
phthalic acids combine with four. The simplest explanation of
this fact is that the double linking of two carbon atoms is con-
verted into a single one, if at least one of these be combined with
a carboxyl group. The following formulas are thus arrived at :

Dihydrophthalic acid. Tetraliydro-isophthaltc acid.

CH CH C0 2 H



HC\ /CH C0 2 H HC\/CH-COJ f



CH CH

Tctrahydrotcrephtlialic acid. Diliydroxyliexhydrotm-ephtluaic acid.

CH-CCLH CH^-CO.H



H 2 C\/CH.OH
CH-CQ 2 H



488 AROMATIC COMPOUNDS.



SUBSTITUTION PRODUCTS OF TERE
PHTHALIC ACID.

2254 Chloroterephthalic acid, C 6 H 3 C1(CO. 2 H), is prepared from
amidoterephthalic acid, and is slightly soluble in hot water, more
readily in alcohol. It is crystalline, and melts above 300. The
chloride, C 6 H 3 C1(COC1) 2 , obtained by the action of phosphorus
chloride, is also crystalline and boils at about 300. By treating
this with ammonium carbonate, the amide, C 6 H 3 C1(CO.NH 2 ).,,
is formed, and crystallizes from alcohol in crusts, melting above
300.

Methyl chlorotcrephthalatc, C 6 H 3 C1(CO 2 .CH 3 ) 2 , forms silky
plates, melting at 60. l

BromoterepUhalic acid, C 6 H 3 Br(CO 2 H) 2 + H 2 O, is formed by
the action of potassium permanganate on an alkaline solution
of bromoparatoluic acid. It is almost insoluble in cold water,
and crystallizes from hot water in dazzling white, microscopic
needles, which melt at 304 305. Phosphorus pentachloride
converts it into the chloride, C 6 H 3 Br(COCl) 2 , an oily liquid,
which boils at 304'D 305'5, is only gradually decomposed by
water, and combines with aqueous ammonia to form the amide,
C 6 H 3 Br(CO.NH 2 ) 2 , which crystallizes from hot water in small
needles, melting at 270.

Methyl Iromoterephthalatc, C 6 H 3 Br(CO 2 .CH 3 ) 2 , crystallizes in
concentrically arranged groups of needles, melts at 42 and boils
at above 300 . 2

Dilromoterephthalic acid, C 6 H 2 Br 2 (C0 2 H) 2 , is prepared by heat-
ing dibromocymene, C 6 H 2 Br 2 (CH 3 )C 3 H 7 , for some time with
nitric acid, 3 and by the oxidation of dibromotoluic acid with
potassium permanganate. 4 It crystallizes from hot, dilute alcohol
in small plates, which have a satin lustre, do not melt even at
320, and sublime at a higher temperature with decomposition.

Ethyl dibromoterephthalate crystallizes from alcohol in nacreous
plates, melts at 121 and boils at about 335.

Nitroterephthalic acid, C 6 H 3 (N0 2 )(C0 2 H) 2 , is formed by treat-
ing terephthalic acid with a mixture of fuming sulphuric arid

1 Ahrens, Ber. Dcutsch. Chem. Gcs. xix. 1634.

2 Fischli, ibid. xii. 619.

3 Glaus and Wimmel, ibid. xiii. 902.

4 Schultz, ibid, xviii. 1762.



CHLOROTEREPHTHALIC ACID.



nitric acids, and crystallizes in prisms ; it separates from hot
water in cauliflower-like masses, which melt at 270 . 1

Methyl nitroterephthalate, C (i H 3 (NO 2 )(CO 2 .CH 3 ) 2 , crystallizes
from ether in splendid prisms, which melt at 70. 2

Nitroterephthalamidc, C 6 H 3 (NO 2 )(CO.NH 2 ) 2 , was obtained by
Warren de la Rue and. Muller in well formed prisms by the
nitration of terephthalamide.

AmidoterephtJialic acid, C 6 H 3 (NH 2 )(CO 2 H) 2 , is formed by the
reduction of the nitro-acid with tin and hydrochloric acid, and
crystallizes in thin, lemon-yellow prisms or moss-like forms,
which are only slightly soluble in cold water and alcohol, and
decompose on heating without melting. Their aqueous or
alkaline solutions, and those of their salts and ethers, which
latter are crystalline bodies but have not been described in
detail, show a remarkable blue fluorescence, while acidified
solutions of the acid do not possess this property.

Methyl amidotercphthalate, C C H 3 (NH 2 )(CO 2 CH 3 ) 2 , forms crystals,
melting at 126; its alcoholic and ethereal solutions also show a
strong blue fluorescence (Ahrens).

Diamidoterephthalic acid, C 6 H 2 (NH 2 ) 2 (CO 2 H) 2 , is not known
in the free state; its ethyl ether has been prepared from
succinosuccinic ether (Pt. II. p. 211). When the latter is
heated with ammonium acetate, a di-imide is formed, which
crystallizes in shining, yellow needles, melting at 181. Diethyl-
diamidotcrepJithalate is obtained by the action of bromine on its
solution in sulphuric acid :

C0 2 .C 2 H 5 C0 2 .C 2 H 6

H C



+ 2

\/- HC\/C-NH 8

CH C

C0 2 C 2 H 5 C0 2 C 2 H 6

It crystallizes from hot alcohol in lustrous golden needles of
the colour of potassium dichromate, which melt at 168. Its
brown alcoholic or ethereal solution shows a golden-yellow
fluorescence. It forms slightly soluble salts with hydrochloric
and sulphuric acids.

1 Wanm <!, la Rue and Mtiller, Ann. Ctiem. Pharm. cxxi. 00; Burckl.anlt,
Her. Uculsch. Chcm. Gc*. x. HI. 3 Ahrefls, ibid. xix. 1634.



490 AROMATIC COMPOUNDS.

When a solution of its diazo-compoimd in hydrochloric acid is
heated with an acid solution of cuprous chloride, an acid is
formed which is probably dichloroterephthalic acid, since it is
converted into tcrephthalic acid by the action of sodium amalgam
and water. 1

Sulphoterephthalic acid, C 6 H 3 (SO3H)(CO 2 H) 2 , is obtained by
heating terephthalic acid with fuming sulphuric acid, 2 and by
the oxidation of sulphoparatoluic acid, paratoluylsulphamic acid,
or paraxylenesulphonic acid with potassium permanganate. 3 It
forms a hygroscopic mass, and yields salts which are soluble in
water, but insoluble in alcohol.



HYDROXYMETHYLHYDROXYBENZOIC ACID,
/OH



C 6 H/-C0 H
\CH 2 .OH.



2255 These compounds, which are simultaneously alcohols and
phenols, are formed by the action of sodium amalgam on the
aldehydo-acids, which are described below. 4

Ortholiydroxymetliylsalicylic acid (1:2:6) is precipitated by
acids from its alkaline solution as an oil, which solidifies after
some time to hard, white crystals ; it is readily soluble in hot
water, alcohol and ether, and crystallizes from the latter in
transparent prisms, which melt at 142. Its aqueous solution
is coloured an intense bluish-violet by ferric chloride.

Parahydroxymethylsalicylic acid (1:2:4) is slightly soluble
in alcohol and ether, and crystallizes from the latter in long
prisms, which melt at 160 with decomposition. Ferric chloride
colours the solution violet.

Ortlwhydroxymethylparahydroxylcnzoic acid (1:4:2) is a
white powder, which does not melt below 270, and gives no
colouration with ferric chloride.

1 Baeyer, Her. Deutsch. Chem. Ges. xix. 428.

2 Ascher, Ann. Chem. PKarm. clxi. 2 ; Schoop, Ser. Deutsch. Chem. Ges. xiv.
223.

3 Hall and Reinsen, ibid. xii. 1434 : Buruey and Reinsen, Amcr. Chem. Journ.
ii. 405 and 413.

* Reimcr, Her. Deutsch. Chem. Ges. xi. 790.



ALDEHYDOHYDROXYBENZOJC ACIDS. 491



ALDEHYDOHYDROXYBENZOIC ACIDS

/OH

C 6 H/C0 2 H
\COH

2256 These are prepared by heating the hydroxybenzoic acids
with caustic soda and chloroform :

/ONa

C 6 H 4 < 4 SNaOH + CHC1, =

X C0 2 Na

/ONa

C.H-eOH + 3NaCl + 2H 2 O.
\C0 2 Na

They are converted by reduction into the preceding alcohol-
acids, and by fusion with caustic potash into the hydroxyphthalic
acids. They combine, like other aldehydes, with the sulphites of
the alkali metals.

Orlho-aldehydosalicylic acid (1 : 2 : 6) is obtained, together
with the following compound, from salicylic acid. It crystallizes
in fine, matted needles, which dissolve at 23 25 C in 1,500
1,600 parts, or at 100 in 15 16 parts of water. The aqueous
solution is coloured deep yellow by caustic soda, and red by
ferric chloride, and the alcoholic solution shows a faint, bluish
violet fluorescence. It melts at 179 and sublimes without
decomposition when carefully heated. On distillation with
slaked lime it decomposes into salicylaldehyde and carbon
dioxide. The copper salt is a gelatinous precipitate, Avhich
is soluble in ammonia; on boiling the solution a light blue
precipitate of C 8 H 4 O 4 Cu is thrown down.

Para-ahlcliydosalicylic acid (1:2:4) forms long, fine needles,
which melt at 248 249, and dissolve in 2,6002,700 parts of
water at 25, and in 145150 parts at 100. Its aqueous
solution is not coloured by caustic soda, while ferric chloride
produces a deep cherry-red colouration. On distillation with
lime, parahydroxybenzaldehyde is formed; its copper salt is
also soluble in ammonia, but is not precipitated on boiling. 1

Ortho-aldeliydoparaliydroxybenzoic acid (1:4:2), was obtained
by Keiiner and Tiemann from parahydroxybenzoic acid;
1 Reimerand Tiemann, Ber. Dculsch. Cliem. Gcs. ix. 1268, x. 1562.



492 AROMATIC COMPOUNDS.

crystallizes from hot water in thin, arborescent prisms, which
melt at 243 244, and sublime in splendid, white needles.
Its aqueous solution is coloured deep yellow by caustic soda and
brownish red by ferric chloride. Salicylaldehyde is formed when
it is distilled with caustic lime.

Ortho-aldchydomdahydroxybenzoic acid (1:3:6) is obtained,
together with the following compound, from metahydroxybenzoic
acid. It crystallizes in needles, which melt at 234, and are
slightly soluble in hot water and readily in alcohol. Its aqueous
solution is coloured violet by ferric chloride and deep yellow by
caustic soda. On boiling with caustic soda it is only decomposed
at a high temperature, phenol being formed.

Para-aldehydometahydroxylcnzoic acid (1 : 3 : 4) has only been
obtained as a syrup; it is very unstable and reduces Feh ling's
solution readily. On fusion with caustic potash it is converted
into a-hydroxyisophthalic acid. 1



/OH

HYDROXYPHTHALIC ACIDS, C 6 H 3 ^CO,H.

\C0 2 H

2257 a-Hydroxyphthalic acid (4:1: 2). When the ethyl ether
of a-amidophthalic acid is dissolved in dilute sulphuric acid,
treated with sodium nitrite and then heated to 100, the ether
of a-hydroxyphthalic acid separates out as a yellowish oil, which
yields the free acid on saponifying with potash ; it is purified
by precipitating the neutral solution with basic lead acetate
and removing the lead by sulphuretted hydrogen. 2 It is also
obtained by oxidizing the sulphamido-orthotoluic acids with
potassium permanganate and fusing the residue with potash, 3
and is formed when para-aldehydometahydroxybenzoic acid, 4
a-chlorophthalic acid, 5 and a-sulphophthalic acid 6 are fused with
caustic potash or soda.

It is tolerably soluble in cold, very readily in hot water and
alcohol, and crystallizes in large stellate groups of pointed prisms
which melt at about 185, the anhydride being formed ; on
heating with dilute hydrochloric acid to 180, it decomposes

1 Landshoff and Tiemann, Bcr . Dcutsch. Chcm. Ges. xii. 1334.

2 Baeyer, ibid. x. 1079. 3 Jacobsen, ibid. xiv. 42.

4 Tiemann and Landshoff, ibid. xii. 1337.

5 Kriigcr, ibid, xviii. 1759.

6 Griibe, ibid, xviii. 1130 ; Kee, Inaugurate. Bern. 1886.



HYDROXYPHTHALIC ACIDS. 493

into carbon dioxide and metahydroxybenzoic acid (Ree). Its
aqueous solution is coloured reddish yellow by ferric chloride.
When the acid is heated with resorcinol, hydroxyfluorescein is
obtained, which forms a dark, yellowish red solution in caustic
potash, and is slightly soluble in water with a yellowish green
fluorescence ; acids separate it from its alkaline solution as a
yellow precipitate.

a-Hydroxyplithalic anhydride, 'C 8 H 4 O 4 , sublimes in feathery



Online LibraryHenry E. (Henry Enfield) RoscoeA treatise on chemistry (Volume 3) → online text (page 44 of 50)