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the action of hydrochloric acid gas on an alcoholic solution of the
acid, 1 or by heating the normal potassium salt with ethyl iodide. 2
^ It crystallizes from ether in tablets, melts at 72, boils at 282,
and is converted by caustic soda into a crystalline mass
of C 6 H 4 (ONa)C0 2 .C 2 H 5 , which is readily soluble in water
and alcohol.

Metamethoxybenzoic acid, C fi H 4 (OCH 3 )CO 2 H, is obtained by
heating metahydroxybenzoic acid with the calculated quantity of
caustic potash and methyl iodide, and decomposing the ethereal
salt thus formed with a solution of caustic potash in wood-spirit
(Griibe and Schultzen). It is also formed by the oxidation of
nietacresyl methyl ether with potassium permanganate, 3 and by

1 Griibe and Schultzen, Ann. Chcm. Pharm. cxlii. 351.

- Heintz, ibid, cliii. 337.

3 Oppenheim and Piall', Jicr. Deutsch. Glum. Ges. viii. 8b7.



the action of carbon dioxide on a mixture of metabromophenyl
methyl ether and sodium. 1 It crystallizes from hot water in
long needles, which melt at 106 107, and sublime without

Meta-ethoxylenzoic acid, C 6 H 4 (OC,H 5 )CO 2 H, was prepared by
Heintz from the ethyl ether ; it is also formed by the decom-
position of the sulphate of metadiazobenzoic acid with alcohol. 2
It crystallizes in small needles, melting at 137, which are
scarcely soluble in cold, slightly in hot water, but readily in
alcohol, and sublime undecomposed.

Ethyl meta-ethoxylenzoate, C 6 H 4 (OC 2 H 5 )CO 2 .C 2 H 5 , is obtained
by heating metahydroxybenzoic acid with two molecules of
caustic potash and ethyl iodide ; it is a liquid, boiling at 263.

Meta-acetoxylcnzoic acid, C 6 H 4 (OCO.CH 3 )C0 2 H, is produced
by the action of acetyl chloride on the acid (Heintz) ; it forms
granular crystals melting at 127, and gives amorphous salts.

2181 Metahydroxybenzoic acid behaves towards phosphorus
pentachloride in a very similar manner to salicylic acid.

Metacarlonylphenylphosphoryl chloride, C 6 H 4 (OPOC1 2 )COC1, is
a colourless liquid, which boils at 168 170 under a pressure
of 11 12 mm. A yield of 57'5 per cent, of the theoretical
quantity is obtained, and the unattacked acid may be extracted
from the residue in the retort by boiling water or alkalis.

Metacarloxyorthophosphoric acid-, C ? H 4 (CO 2 H)PO(OH) 2 , is
formed when the chloride is treated with water, a considerable
evolution of heat taking place, but no metahydroxybenzoic acid
being reformed. It crystallizes in fine, white scales, which melt
at 200 201, and are only decomposed by water at a tem-
perature of 150 160, phosphoric and metahydroxybenzoic
acids being formed.

When the chloride is submitted to slow distillation, a portion
passes over unchanged, together with phosphorus oxychloride,
no metachlorobenzoyl chloride, C 6 H 4 C1(COC1), or metachloro-
benzenyl trichloride, C 6 H 4 C1(CC1 3 ), being produced, and a black
syrupy residue is left, which yields metahydroxybenzoic acid on
boiling with water or alkalis, and therefore probably contains the
compounds (C 6 H 4 (COC1)0) 2 POC1 and (C 6 H 4 (COC1)0) 3 PO.

Metabenzenyltrichlorophosphoryl chloride, C 6 H 4 (OPOC1 2 )CC1 3 ,
is obtained in a similar manner to the corresponding salicylic acid
derivative. It boils at 178 under a pressure of 11 mm., and is

Korner, Jahresber. Chem. 1867, 414.
Griess, Zcitschr. Chem. 1866, 1.


converted by water into metacarboxyphenylphosphoric acid,
while on heating with phosphorus pentachloride to 180, a
portion is converted into metachlorobenzenyl trichloride. 1

Metahydroxylenzamide, C 6 H 4 (OH)CO.NH 2 , is formed when
diazobenzamide nitrate is boiled with water 2 as well as by the
action of ammonia on ethyl metahydroxybenzoate. It crystallizes
from water in thin plates, which have a bitter taste and melt
at 167.

Metahydroxybcnzanilidc, C 6 H 4 (OH)CO.NH(C 6 H 5 ), is obtained
in the same way as salicylanilide ; it crystallizes from dilute
alcohol in needles, melting at 154 155, and combines with
alkalis to form salts which crystallize well. It is not attacked
by boiling alkalis, but is decomposed by them on fusion

Metalydroxylcnzuric acid, C 6 H 4 (OH)CO.NH.CH 2 .CO 2 H, occurs
in the urine of the dog after metahydroxybenzoic acid has been
administered ; it crystallizes in needles. 3

Metahydroxylenzonitril, C 6 H 4 (OH)CN, is formed by boiling
diazobenzonitril sulphate with water 4 and by heating meta-
hydroxybenzoic acid in a current of ammonia, first to 220 230
and then to 300 320 ; the isomeric compounds are decomposed
by this treatment into phenol and carbon dioxide, but yield no
nitril/' Metahydroxybenzonitril crystallizes from hot water in
small plates and from alcohol in small, rhombic prisms ; it has
an intensely sweet and at the same time sharp taste, melts at
82, and decomposes on heating with hydrochloric acid into
ammonia and metahydroxvbenzoic acid.


2182 Iodomctahydroxybcnzoicacid,Q^^(QT&}QO.JA.. Weselsky
obtained this substance by the action of iodine and mercuric
oxide on an alcoholic solution of metahydroxybenzoic acid. It cry-
stallizes in needles, which are only slightly soluble in cold water.

Nitrometdkydroxybenzmc acwfo,C 6 H 3 (NO 2 )(OH)CO 2 H. Gerland
found that the direct nitration of metahydroxybenzoic acid yields

1 Anschiitz, private communication.
- Oriess, Zeitschr. Chem. 1566, 1.

3 Baumann and Heitpr, ffoppe-Sei/Ier's Zefachrifi, i. 260.

4 Griess, Ber. Dentsch. Chem. Gfa*. viii. 859.
s Smith, Journ. Prakt. Chem. [2] xvi. 218.

V 'I


a nitrohydroxybenzoic acid, which forms yellow, rhombic crystals,
and has a repulsive, bitter taste ; it must be identical with
one of those described below, since inetahydroxybenzoic acid can
only yield four mononitro-derivatives. The first three were
prepared by Griess by boiling the corresponding nitro-amido-
benzoic acids with caustic potash. 1

a-Nitrometahydroxylenzoic acid, (CO 2 H : OH : NO 2 = 1:3:6),
is readily soluble in water, and crystallizes in thick, honey-yellow
prisms or in needles containing one molecule of water, which is
given off at a few degrees above 100. It melts nt 169, has a
slightly acid taste, and is coloured a faint reddish brown by ferric
chloride. The barium salt, C 7 H 3 ~NO 5 Ba + GH 2 O, forms yellowish
red prisms, which are readily soluble in water.

P-Nitromdahydroxy'bcnzoic acid (1 : 3 : 4), is slightly soluble in
hot water, and crystallizes in long, yellow, four- or six-sided
plates, melting at 230. The barium salt, C 7 H 3 NO 5 Ba + H 2 O, is
almost insoluble and crystallizes in yellowish red plates.

<y-Nitrometahydroxybenzoic acid (1:3: 2) : is less soluble in water
than the a-acid, has an intensely sweet taste, and crystallizes
with one mo'ecule of water in long, four-sided plates or large
tablets, which melt at 178 and give a faint reddish brown
colouration with ferric chloride. The barium salt, 2C 7 H 3 NO 5 Ba
+ 3H 2 O, also has a very sweet taste, and forms tolerably soluble
reddish brown plates.

^-Nilrometahydroxylenzoic acid (1 : 3 : 5), was prepared by
Grube from the corresponding nitro-amidobenzoic acid, 2 and is a
yellowish brown, crystalline precipitate. Its salts crystallize badly.

Trinitrometahydroxybenzoic acid, C 6 H(NO 2 ) 3 (OH)CO 2 H, is
formed by heating diazo-amidobenzoic acid with ordinary strong
nitric acid, 3 and by the action of fuming nitric acid on metamido-
benzoic acid. 4 It crystallizes in large, almost colourless, rhombic
prisms, which have a vitreous lustre, and are best obtained
from solution in concentrated nitric acid ; it is readily dissolved
by water, alcohol, and ether, forming intensely yellow solutions,
which dye animal fabrics in the same way as picric acid. It
melts when heated and then explodes.

The barium salt, C 7 HN 3 O 9 Ba + 3H. 2 O, is tolerably soluble in
water, but insoluble in alcohol, and crystallizes in thick, light
yellow needles, which are very explosive.

1 Bcr. Deutech Chem. Gcs. xi. 1729. 2 Ibid. x. 1701.

3 Griess, Ann. Chem. Phnnn. cxvii. 28.

4 Beilstein and Geitner, ibid, cxxxix. 11


When metahydroxy benzole acid is heated with sulphuric acid,
three compounds isomeric with alizarin, G 14 H 8 O 4 , are formed. 1 If
the product be boiled with strong nitric acid, a trinitrometahy-
droxybenzoic acid is produced among other products, which is
readily soluble in water, and crystallizes in tablets or prisms con-
taining one molecule of water, which is lost at 100. It melts at 105
and then commences to sublime ; when rapidly heated it detonates.
The barium salt, C 7 HN 3 O 9 Ba+ 2H 2 O, is readily soluble in water,
and crystallizes in yellow needles, which explode at 299 . 2

Thiomctahydroxybenzoic acid, C 6 H 4 (SH)CO 2 H, is formed by the
action of tin and hydrochloric acid on sulphobenzoyl chloride,
C 6 H 4 (SO 2 C1)COC1. It is tolerably soluble in water, more readily
in alcohol, and sublimes very easily in small plates, melting at
146 147.

Dithiometahydroxybenzoic acid, S 2 (C 6 H 4 .CO 2 H) 2 , is obtained by
exposing the monothio-compound to the air in the moist state,
or more rapidly by adding bromine water to its aqueous solution. 3
Griess prepared it by decomposing diazobenzoic acid aurichloride
with sulphuretted hydrogen : 4

3C1N 2 C C H 4 .C0 2 H + 2H 2 S =

S.C 6 H 4 .C0 H

| " +C 6 H 5 .CO.,H43HC1 + 3N,.

SC 6 H 4 .C0 2 H

It crystallizes in microscopic needles, which are scarcely soluble
in water, more readily in alcohol, and melt at 242 244.

Sulphometahydroxybc.nzoic acid, C 6 H 3 (SO 3 H)(OH)CO 2 H, is
formed by the action of sulphur trioxide on metahydroxybenzoic
acid ; it crystallizes in green, deliquescent needles, melting at
208, is almost insoluble in ether and is coloured wine-red by
ferric chloride. 5

hosidphomctahydroxybcnzoic acid is obtained by dissolving the
sulphate of diazobenzoic acid in warm sulphuric acid ; it crystal-
lizes in plates, which are readily soluble in water and alcohol. It
is decomposed by strong nitric acid into trinitrometahydroxy-
benzoic acid and sulphuric acid. 6

1 S<-.hunck ami ttomcr, Bcr. Dcutsch. Chcm. Gcs. xL 1167.
- Schardiiiger, ibid. viii. 1490.

3 Huhner ami Upmann, Zcitschr. Cht.m. 1870, 291 ; Frericlis, Ler. DculscJt.
Chrm. Gcs. vii. 793.

4 Journ. Prakt. Chc.m. [2] i. 102.

5 I'.arth, Ann. Chf.m. Pharm. cxlviii. 38 ; Senhofer, ibid. clii. 102.
8 (Jries.s, Jahrcsbcr. Chcm. 1S6-1, 351.


Disulphomctahydroxybenzoic acid, C 6 H 2 (SO3H) 2 (OH)CO 2 H,
seems to be formed when metahydroxybenzonitril is heated with
fuming sulphuric acid ; l its barium salt is obtained by boiling
the following compound with baryta water. 2

Trisulphometahydroxytenzoic acid, C 6 H(SO 3 H) 3 (OH)CO. 2 H, is
obtained by heating metahydroxybenzoic acid to 250 with a mix-
ture of fuming sulphuric acid and phosphorus pentoxide. The
free acid is a honey-yellow syrup; it is coloured an intense
carmine-red by ferric chloride, and on fusion with caustic potash
undergoes complete oxidation.

Metahydroxybenzoylsulphuric acid, C 6 H 4 (SO 4 H)CO 2 H, is found
in the urine of men and dogs after the administration of meta-
hydroxybenzoic acid (Baumann and Heiter). Its potassium
salt is obtained in a similar manner to that of salicylsulphuric
acid ; it forms deliquescent needles, and decomposes on boiling
with hydrochloric acid or alcoholic potash into metahydroxy-
benzoic acid and sulphuric acid. 3


2183 Fischer obtained this acid by the action of nitrous acid
on an aqueous solution of paramidobenzoic acid, 4 and Saytzew
by heating anisic acid (methylparahydroxybenzoic acid) with
hydriodic acid. 5 It is also formed when para-compounds such as
anisic acid, 6 paracresol, 7 parasulphobenzoic acid, 8 &c., are fused
with caustic potash ; it may be obtained by the same method
from various resins, as gum benzoin, dragon's blood, aloes and
acaroid resin. 9

Kolbe prepared it synthetically by adding potassium to boiling
phenol and at the same time passing iii carbon dioxide ; para-
hydroxybenzoic acid alone is formed, while if the temperature be
not allowed to rise above 130 150, salicylic acid is obtained.

Parahydroxybenzoic acid may also be prepared by the action

1 Smith, Journ. Prakt. Glum. [2] xvi. 220.
Kretschy, Ber.. Deutsch. Chem. Gen. xi. 858.
Baumann, ibid, xi. 1915.
Ann. Chem. Pharm. cxxvii. 129.
Ibid, cxxvii. 145.

Barth, Zeitschrift. Chem. 1866, 650.
Bavth, Ann. Chem. Pharm. cliv. i>59.
Remsen, iUd clxxviii. 281.
Barth and Hlasiwetz, ibid, cxxxiv. 274 ; cxxxix. 78.


of carbon dioxide on potassium phenate at 170 210 ; l it is
formed in small quantities, together with salicylic acid, when
sodium phenate is treated in a similar manner at a lower
temperature. 2 The fact that normal potassium salicylate de-
composes at 220 into carbon dioxide, phenol and basic potassium
parahydroxybenzoate, has been already mentioned. Parahydroxy-
benzoic acid is further obtained, together with a smaller quantity
of salicylic acid, 3 by heating tetrachloromethane to 100 with
phenol and alcoholic soda. 4

It is formed in theoretical amount when the potassium salt
of paracresylsulphuric acid is oxidized with potassium per-
manganate in alkaline solution. 5 Paracresol is also converted
into parahydroxybenzoic acid in passing through the animal
organism, while metacresol is found in the urine as metacresyl-
sulphuric acid, and orthocresol is partly converted into ortho-
cresyl sulphuric acid and partly into hydrotoluquinone. 6

In order to prepare parahydroxybenzoic acid, a mixture of
equal molecules of caustic potash and phenol is heated in a
current of hydrogen, the temperature being finally raised to 180 ;
carbon dioxide is then passed in until the theoretical quantity of
phenol has distilled over, and the residue is then dissolved in water
and decomposed by hydrochloric acid. The parahydroxybenzoic
acid is boiled with animal charcoal and crystallized from hot
water. It is thus obtained in small, monoclinic prisms, while it
is deposited from dilute alcohol in larger crystals, 7 containing
one molecule of water, which is lost at 100; it dissolves in 580
parts of water at 0, and in 126 parts at 15, and is readily soluble
in hot water, alcohol and ether, but only slightly in chloroform,
which is therefore employed to free it from salicylic acid. Its
slight solubility in carbon disulphide is made use of in separating
it from benzoic acid. It melts at 200 and when rapidly heated
decomposes partly into carbon dioxide and phenol, and partly
into other products, which will be described below. It decom-
poses completely and readily into phenol and carbon dioxide on
heating with dilute sulphuric acid in a sealed tube. 8 Its aqueous
solution gives an amorphous, yellow precipitate with ferric

1 Kolbe, Joiirn. Prakl. Chew. [2] x. 100.

2 Ost, ibid. [2] xx. 208.

Hasse, Ber. Deutsch. Chem. Gcs. ix. 2186.
Reimer and Tiemann, ibid. ix. 1285.
Heymann and Kbnigs, ibid. xix. 704.
Baumann and Preusse, ibid. xix. 706.
Hartmann, Journ. Prakt. Chem. [2] xvi. 35.
Klepl, ibid. [2] xxv. 464.


chloride. Phosphorus pentachloride converts it into parachloro-
benzoyl chloride.

The Par ahy droxybenzoatcs. The normal sodium salt decom-
poses completely at 240 250 into carbon dioxide, phenol and
the basic salt ; when, however, it is heated to 280 295 in a
current of carbon dioxide, salicylic acid is obtained, while both
hydroxyisophthalic acid and hydro xytrimesic acid are formed
at temperatures above 340 (Kupferberg). When, on the other
hand, the acid is heated with eight to ten parts of caustic soda,
a partial decomposition into phenol and carbon dioxide sets in at
355 (Earth and Schreder), The salts of methylamine and
aniline decompose at a higher temperature into phenol, carbon
dioxide and the base, while that of tetra-ethylammonium
decomposes on distillation into tri-ethylamine and ethyl para-
hydro xybenzoate, the latter of which is then partially resolved
into carbon dioxide and phenetoil.

tiodium parahydroxybenzoate, C 6 H 4 (OH)C0 2 Na + 5H 2 O, crys-
tallizes from concentrated solutions in transparent tablets, which
effloresce in the air.

Potassium parahydroxybenzoate, C 6 H 4 (OH)CO 2 K + 3H 2 O, is
similar to the sodium salt, but is stable in the air.

Ammonium parahydroxybenzoate, C 6 H 4 (OH)CO 2 NH 4 + H 2 O,
crystallizes in long prisms.

Calcium parahydroxybenzoate, (C 7 H 5 O 3 ) 2 Ca -f 4H 2 O, forms line
needles grouped in stellate forms, and is very soluble.

Jtarium parahydroxybenzoate, (C 7 H 5 O 3 ) Ba -f H 2 O, crystallizes
in flat, lustrous needles or with two molecules of water in
pointed rhombohedra ; baryta water added to its solution pro-
duces a precipitate of the basic salt, C 7 H 4 O 3 Ba, as a sandy,
crystalline powder, which is scarcely soluble in cold water.

Lead parahydroxybenzoate, (C 7 H 5 O 3 ) 2 Pb -f 2H 2 0, is a very
characteristic salt, and is obtained by neutralizing the boiling
aqueous solution of the acid with lead carbonate. It separates
out on cooling in thin, iridescent plates which take a silver
lustre on drying, and resemble those of benzoic acid.

Copper parahydrozybcnzcatc, (C 7 H 5 O 3 ). 2 Cu + 6H 2 O, crystal-
lizes in small, bluish green needles, which become dull and
insoluble on boiling with water.

Silver parahydroxybenzoate, C 7 H 5 O 3 Ag + 2H 2 O, crystallizes
from hot water in small, lustrous plates.

Methyl parahydroxybenzoate, C 6 H 4 (OH)CO>CH 3 , is formed by
heating together equal molecules of parahydroxyberizoic acid,


caustic potash and methyl iodide ; it crystallizes from ether in
large tablets, melts at 17 and boils at 283 . 1

2 184 Paramethoxybenzoic acid, or Anisic acid, C 6 H 4 (OCH 3 )CO,H.
Cahours obtained this compound in 1839 by the oxidation of oil of
anise-seed, and showed at the same time that it is formed from the
"camphor" (anethol or allylphenol, C 6 H 4 (OH)C 3 H 5 ), contained
in this substance. 2 Laurent, in 1841, prepared from tarragon oil
(from Artemisia dracunculus), the so-called dragonic acid (acicle
draconique), which, according to Gerhardt, is identical with anisic
acid. This view was subsequently confirmed by Laurent, who
also accurately determined its composition. 3

At about the same time Persoz submitted oil of anise seed,
fennel oil, and star-anise oil (huile de badiane, from Illicium
anisatum) to oxidation, and obtained two acids, which he named
umbellic acid (acide ombellique) and badianic acid (acide
badianique)* Hempel showed, however, that these are both
anisic acid, 5 the formation of which might have been expected,
since the oils employed contain anethol. 6

Anisic acid was at first looked upon as the homologue of
salicylic acid ; Kolbe, however, considered it to be methoxy-
benzoic acid, since it behaves very similarly to benzoic acid, and
decomposes into anisoil (phenyl methyl ether) and carbon
dioxide when distilled with caustic b-iryt:i. 7

In order to determine from which of the hydroxybenzoic
acids it is derived, Saytzew heated it with hydriodic acid, and
found that the product consists of parahydroxybenzoic acid. It
was then thought probable that anisic acid and winter-green oil
would have similar constitutions, but Grabe showed that the
latter is the methyl ether of salicylic acid, while Ladenburg
proved that in anisic acid the methyl group replaces the
hydrogen of the phenol hydroxyl ; by heating equal molecules of
potassium parahydroxybenzoate and caustic potash with two
molecules of methyl iodide, he obtained the methyl ether of
paramethoxybenzoic acid (anisic acid) and prepared the free acid
by saponifying with potash and decomposing the product with
hydrochloric acid. 8 Anisic acid may also be obtained by
! oxidizing orthocresyl methyl ether with chromic acid Folution. 9

1 Ladenburg and Fitz, Ann. Cfunn. Pharm. cxli. 247.

- Ibid. xli. 66. 3 Ibid. xliv. 313. * Ibid. xliv. 311.

5 Ibid. lix. 104. 6 Cahours, ibid. xxxv. 812.

7 Lchrb. d. Organ. Chcm. ii. 135.

8 Ann. Chcm. Plwrm. cxli. 241.

!1 Konior, '/cit*el<r. <'!>. 1868, 3-2(1.


In order to prepare it, 1 part of oil of anise seed is poured
into a solution of 5 parts of potassium dichromate in 10 parts
of sulphuric acid and 20 parts of water, which is heated to 50.
The reaction is completed in a few minutes and the solution is
then allowed to cool, the anisic acid filtered off and purified by
precipitation with hydrochloric acid from solution in ammonia
(Ladenburg and Fitz).

It crystallizes in long monoclinic prisms or needles, melting
at 184, which dissolve in 2500 parts of water at 18. It is
tolerably soluble in boiling water and very readily in alcohol.
On heating with hydriodic or concentrated hydrochloric acid, or
on fusion with potash, it is converted into parahydroxybenzoic

Its salts, which crystallize well, have been chiefly investigated
by Engelhardt and by Borella. 1

Melting-point. Boiling-point.
Methyl paramethoxybenzoate, 2

C 6 H 4 (OCH 3 )CO. J .CH 3) scales . . 45 46 255

Ethyl paramethoxybenzoate, 3

C 6 H 4 (OCH 3 )C0 2 .C.,H 5 , liquid . . 250 255

Ethyl parahydroxybenzoate, 4

C 6 H 4 (OH)CO 2 .C,H 5 , crystals . . 116 297 298
Para-ethoxybenzoic acid, 5

C 6 H 4 (OC 2 H 5 )C0 2 H, needles . . 195
Ethyl para-ethoxybenzoate, 6

C 6 H 4 (OC 2 H 5 )CO 2 .C 2 H 5 , liquid . . 275

Para-acetoxylenzoic acid, C 6 H 4 (OCO.CH 3 )CO. 2 H, is formed
when parahydroxybenzoic acid is heated with acetic anhy-
dride. It is slightly soluble in water, and crystallizes from
chloroform in large plates, which have a silver lustre and melt
at 185 (Klepl).

Phenyl parahydroxylenzoate, C 6 H 4 (OH)CO 2 .C 6 H 5 , occurs in the
products which are formed by the dry distillation of the acid. It
is insoluble in water, but readily soluble in alcohol and chloro-
form, from which it crystallizes in compact, rhombic tablets, which
melt at 176, dissolve readily in caustic soda, and are decom-

Ctaz. Chim. Ital. xv. 304 ; Ann. Chcm. Pharm. cviii. 2-10.

Ladenburg and Fitz, ibid. cxli. 252.

Cahours, ibid. Ivi. 310.

Grabe, ibid, cxxxix. 146 ; Hartmann, Journ. Prakt. Chcm. [2] xvi. 50.

Ladenburg and Fitz ; Fuchs, Her. L/cutsch. Chcm. Gcs. ii. 624.'

Ladenburg and Fitz.


posed by it even in the cold with formation of phenol and
parahydroxybenzoic acid (Klepl).

Paraphcnoxybenzoic acid, C 6 H 4 (OC 6 H 5 )C0 2 H, is obtained by
boiling the following compound with alcoholic potash, or by heat-
ing it to 200 with concentrated hydrochloric acid. It is readily
soluble in alcohol and ether, and crystallizes from chloroform in
long prisms melting at 159'5. When heated with caustic baryta
it decomposes into carbon dioxide and diphenyl ether.

Phenyl parapkenoxybenzoate, C 6 H 4 (OC 6 H 5 )C0 2 .C 6 H 5 , is formed
when parahydroxybenzide, which is described below, is heated
to about 400, preferably in a current of carbon dioxide. It
crystallizes from dilute alcohol in fatty scales, which melt at
73 78, and sublime at a higher temperature, forming a vapour
which smells like the geranium.

2185 ^Anhydrides of parahydroxybenzoic acid. When para-
hydroxybenzoic acid is submitted to dry distillation, only half
of it is decomposed into carbon dioxide and phenol, which distils
over accompanied by water, and phenyl parahydroxybenzoate ;
as the distillation is continued, the boiling acid suddenly
becomes turbid, and a milky liquid settles in the retort, until
at 350 the residue solidifies to a white amorphous mass. 1

Parahydroxybenzoylparahydroxybemoic acid,

C 6 H/^ . In order to prepare this compound, the

\C0 2 H

distillation is stopped as soon as the acid has lost about 15 per
cent, of its weight and before any turbidity has appeared. The
residue is boiled with chloroform and water, and the compound
then extracted with dilute alcohol and purified by re-crystal-
lization. It forms short, microscopic needles, which melt at
261 and are rapidly converted into parahydroxybenzoic acid in
alkaline solution. As a monobasic acid it forms a barium salt,
(C u H 9 5 ) 2 Ba, which crystallizes in long plates containing water
of crystallization. On heating with acetic anhydride, the mono-
acetyl compound, C 14 H 9 (C 2 H 3 O)O 5 , is formed ; it crystallizes in
small plates, melting at 216'5.

Diparahydroxybenzoylparahydroxybenzoic acid,

C 6 H 4 <^ , is contained in the residue ob-

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