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tinued boiling with hydrochloric acid. 1

Schultzen and Naunyn, after taking coal-tar xylene, found in
the urine a toluric acid, which did not crystallize but was only
obtained as a colourless liquid ; 2 this substance probably con-
sists entirely or chiefly of the meta-compound.

Paratolunitril, CH 3 .C 6 H 4 .CN, is best prepared by distilling
paratoluic acid with potassium thiocyanate. It is a powerfully
refractive liquid, smelling like benzonitril, boils at 217'8
and solidifies at a low temperature to a mass, which melts
at 2S'5. 3

Chloroparatoluic acid, C 6 H 3 C1(CH 3 )C0 2 H (3:4: 1), is formed
by the oxidation of chlorocymene, C 6 H 3 C1(CH 3 )C 3 H 7 , with dilute
nitric acid. 4 It is slightly soluble in hot water, readily in alcohol,
and crystallizes in large plates melting at 194 196.

a-Bromoparatoluic acid, C 6 H 3 Br(CH 3 )CO 2 H (3:4: 1), has been
obtained by the oxidation of orthobromocymene, 5 brometbyl-
methylbenzene, 6 and bromoparaxylene, 7 and is also formed when
paratoluic acid is allowed to stand in contact with dry bromine. 8
It is almost insoluble in cold, slightly soluble in hot water and
readily in alcohol, crystallizing in needles, which melt at 204.

&-Bromoparatoluic acid, which is formed by the oxidation of
inetabromocymene, crystallizes from alcohol in plates melting at
196 C . 9

Dibromoparatoluic acid, C 6 H 2 Br 2 (CH 3 )C0 2 H (3:6:4:1), is
obtained by oxidizing solid dibromoparaxylene with a solution
of chromium trioxide in acetic acid. It is only very slightly
soluble in water, and crystallizes from alcohol in stellate
aggregates of needles, which melt at 195 . 10

lodoparatoluic acid, C 6 H 3 I(CH 3 )C0 2 H, was obtained by Griess
together with amidoparatoluic acid, by the action of hydriodic
acid on diazo-amidotoluic acid, it is slightly soluble in water,
readily in alcohol, and crystallizes in white plates or needles.

Kraut, Ann. Chcm. PJuirm. xcviii. 360.

Zeitschr. Chcm. 1868, 29.

Patern6 and Pisati, Ber. Dcutsch. Chcm. Ges. viii. 441 ; sec also Volrath,
/^ tschr. Chcm. 1866, 489 ; Hofmann, Ann. Chcm. Pharm. cxlii. 126 ; Merz,
Zc tschr. Chcm. 1868, 33 ; Weith, Ber. Dcutsch. Chcm. Gcs. vi. 421.

Kekule and Fleischer, ibid. vi. 1090 ; v. Gerichten, ibid. x. 1250 ; xi. 368.

Landolph, Ber. Deutsch. Chem. Ges. v. 268.

Fittica, Ann. Chem. Pharm. clxxii. 312.

Morse and Remsen, Ber. Deutsch. Chem. Ges. xi. 225.

Jannasch and Dieckmann, Ann. Chcm. Pharm. clxxi. 83.

Kelbe and Koschnitzky, ibid. xix. 1730.
1 Schultz, ibid, xviii. 1762.



NITROPARATOLUIC ACIDS. 421

a-Xitroparatoluic acid, C 6 H 3 (NO 2 )(CH 3 )CO 2 H (3:4:1), is
formed by the action of fuming nitric acid on cymene * or
paratoluic acid. 2 It is slightly soluble in cold, more readily in
hot water and readily in alcohol, from which it crystallizes in
light yellow, monoclinic prisms, which melt at 189 190.

fi-Nitroparatoluic acid (2 : 4 : 1) is obtained by the oxidation
of liquid nitrocymene with chromic acid solution (Landolph,
Fittica). It is scarcely soluble in cold, slightly in hot water, and
only with difficulty in alcohol, crystallizing in small plates or
needles, which sublime without melting when heated. Accord-
ing to Widman and Bladin, the so-called liquid nitrocymene
consists chiefly of paratolylmethylketone, 3 and the acid prepared
from it is therefore probably not a uitrotoluic acid.

ft-Nitroparatolunitril, C 6 H 3 (NO 2 )(CH 3 )CN, is obtained by
heating the diazo-cornpound of metanitroparatoluidine with
potassium cuprocyanide ; it melts at 99 100. 4

a-Amidoparatoluic acid, C C H 3 (NH 2 )(CH 3 )C0 2 H (3:4: 1), is
tolerably soluble in water and crystallizes in hair-like needles,
which melt at 164 165 (Ahrens).

2)iazo-amidotoluicacid.,CO 2 R.C 6 E 3 (CH^'H..'N= NC 6 H 3 (CH 3 )
C0 2 H, is formed by the action of nitrogen trioxide on an alcoholic
solution of the amido-acid. It forms yellow microscopic prisms,
which are insoluble in water and alcohol, and is decomposed by
the haloid acids with formation of substituted toluic acids. 5

Sulphoparatoluic acid, C 6 H 3 (SO 3 H)(CH 3 )CO 2 H (2:1: 4), has
been prepared by the action of sulphur trioxide on paratoluic
acid, 6 and by the oxidation of thiocymene, C 6 H 3 (SH)(CH 3 )C 3 H 7 7
and cymene-orthosulphonic acid. 8 It crystallizes in small plates
which contain two molecules of water and are stable in the air.
Sulphamidoparatoluic acid, 6 H 3 (S0 2 .NH 2 )(Ctf 3 )C0 2 H, is
formed by the oxidation of paraxylenesulphamide 9 or cymene-
sulphamide, 10 and crystallizes from hot water in long needles
which melt at 167 . 11

I Noad, Chem. Soc. Mem. iii. 431 ; Ahrens, Zeitschr. Chcm. 1869, 102 ;
Landolph, Ber. Deutsch. Chcm. Ges. vi. 936 ; Fittica, ibid. vi. 938.

Ann. Chcm. Pharm. clxviii. 250. 8 Ber. Deutsch. Chem. Gcs. xix. 584.
Leukart, ibid. xix. 417. 5 Griess, Ann. Chem. Pharm. cxvii. 58.

Fischli, Ber. Dcufach. Chcm. Gat. xii. 615.

Flesch, ibid. vi. 478 ; Bechler, Journ. PraU. Chem. [2] viii. 170.
liemsen and Burney, Amcr. Chem. Journ. ii. 405 ; Baur and Meyer, Ann.
Chsm. Pharm. ccxx. 18.

" Ahrens, Zeitschr. Chem. 1869, 102 ; Landolph, Ber. Deutsch. Chcm. Ges.
vi. 936 ; Fittica, ibid. vi. 938.
10 Ann. Chcm. Pharm. clxviii. 250.

II lies and Remsen, Ber. Deutsch. Chcm. Ges. xi. 230 ; Hall and Reinsen, ibui.
xii. 1433.



422 AROMATIC COMPOUNDS.



HYDROXYTOLUALDEHYDES, C C H 4 (OH)(CH 3 )COH.

2225 These compounds are formed when the cresols are
heated with caustic soda solution and chloroform, homosalicyl-
aldehydes being formed, which are volatile with steam. Ortho-
and meta-cresol also yield homologues of parahydroxybenz-
aldehyde, which are not volatile with steam, but this is not the
case with paracresol, since in the chloroform reaction the alde-
hyde-group always takes up either the ortho- or para-position
with respect to the hydroxyl. 1

Parahomosalicylaldehyde or Orthohydroxymetatolualdchyde
(COH : OH : CH 3 = 1 : 2 : 5) is slightly soluble in water, readily
in alcohol, and crystallizes from dilute alcohol in six-sided plates
which have a nacreous lustre, and melt at 56. It boils at
217 218, has a powerful, almost repulsive aromatic odour, and
gives a deep blue colouration with ferric chloride.

It is converted by the action of water and sodium amalgam
into homosaligenin or crthohydroxymetaxylyl alcohol, C 6 H 3 (OH)
(CH 3 )CH 2 .OH, which crystallizes from hot water in lustrous
plates, melts at 105 and, like saligenin, gives a deep blue
colouration with ferric chloride.

Orthohomosalicylaldehydc or Orthohydroxymetatolualdehyde (1 :
2 : 3) is an oily liquid, which has a smell resembling both salicyl-
aldehyde and oil of bitter almonds, solidifies on cooling to
crystals which melt at 17, and gives a bluish colouration with
ferric chloride.

Metahomosalicylaldehyde or Ortholiydroxyparatolualdehyde (1 :
2 : 4) forms crystals, which melt at 54 and have a pleasant
aromatic odour. It boils at 222 223 and gives a violet
colouration with ferric chloride,

Ortliohomoparahydroxylenzaldehyde or Paraliydroxymetatolu-
aldehyde (1:4:3) crystallizes from hot water in pointed prisms,
which occur chiefly in twinned forms, resembling gypsum. It
melts at 115 and gives a bluish violet colouration with ferric
chloride.

Metahomoparahydroxylenzaldehyde or Parahydroxyortliotolu-
aldehyde (1:4:2) crystallizes in lustrous plates, melts at 110
and gives a light rose-red colouration with ferric chloride.

1 Ticmann and Schotten, Bcr. Dcutsch. Ch-em. Ges. xi. 770.



HYDROXYTOLUIC ACIDS. 423

Mcnyanthol, ( ' 8 H 8 O. An amorphous substance, called meny-
anthin, C 30 H 46 O 14 , which has an intensely bitter taste, occurs in
the common buckbean (Mcnyanthes trtfoliata) and is decom-
posed by heating with dilute sulphuric acid into grape sugar
and menyanthol. This substance is a liquid which smells like
benzaldehyde, reduces ammoniacal silver solution, and is con-
verted into a crystalline acid on exposure to the air or on fusion
with caustic potash. 1 It is probably identical with orthohomo-
salicyl aldehyde.



HYDROXYTOLUIC ACIDS, C G H 3 (OH)(CH 3 )CO 2 H.

2226 Kolbe and Lautemann, after finding that salicylic acid is
formed by the action of carbon dioxide on a mixture of phenol and
sodium, prepared its homologue, cresotic acid, from the cresol
which boils at 120. 2 The three cresotic acids were then pre-
pared from the isomeric cresols, 3 and, on account of their
similarity to salicylic acid, were also called homosalicylic acids.
Ihle has shown that, like their lower homologue, they may
be obtained by passing carbon dioxide over the heated sodium
cresols. 4

These compounds and the other hydroxytoluic acids, the ten
of which are all known, are also formed by reactions similar to
those employed for the preparation of the hydroxybenzoic acids
and other hydroxy-acids (Part III., p. 36).

The dimethyl ethers, C 6 H 3 (CH 3 )(OCH 3 )CO. 2 .CH 3) are formed
by heating the acids with caustic potash and methyl iodide, and
these are converted by saponification into the methoxytoluic
acids, C 6 H 3 (CH 3 )(OCH 3 )C0 2 H. 5

The numbers appended in brackets give the position of the
side chains in the order CO 2 H : OH : CH 3 .

Parahomosalicylic acid, a-Crcsotic acid or a-Orthohydroxymcta-
loluic acid (1:2: 5), may be obtained, in addition to the methods
just described, by fusing /3-metaxylenol 6 or /9-bromometatoluic
acid 7 with caustic potash, by the action of nitrous acid on the

Kromaycr, Jahretb. Chcm. 1861, 749.
Ann. Chcm. Pharm. cxv. 203.

Eugellianlt and Latschinow, Zcitschr. Chcm. 1869, 622; Biedennaun, her
De ttach. Chcm. Ges. vi. 325 ; Kekule, ibid. vii. 1006.
Journ. Prakt. Chcm. [2] xiv. 454.
Sehall, Bcr. Dcutsch. Chem. Gcs. xii. 822.
Jacobin, Hid. xi. 874. 7 JW* X1V - 2347 '



424 AROMATIC COMPOUNDS.

amidometatoluic acid which melts at I72, 1 and by heating para-
cresol with caustic soda and tetrachloromethane. 2 It crystallizes
from hot water in very long needles or rhombic prisms, melting
at 151, and is readily volatile with steam. Its aqueous solution
is coloured an intense violet-blue by ferric chloride ; it decom-
poses into paracresol and carbon dioxide when heated to 180
with hydrochloric acid, while a remarkable reaction occurs when
its calcium salt is heated with lime, orthocresol being formed
(Jucobsen).

Mcthylparaliomosalicylic acid forms long, thin needles, melting
at 67.

Orthohomosalicylic acid, ft-Cresotic acid, or v-Orthohydroxymcta-
toluic acid (1 : 2 : 3) is also formed by fusing v-sulphamidometa-
toluic acid with caustic potash 3 and by the action of nitrous
acid on the amidometatoluic acid melting at 132 (Jacobsen).
It crystallizes from hob water in long, flat needles, which melt at
163 164. It decomposes into orthocresol and carbon dioxide
when heated with hydrochloric acid to 210; ferric chloride
colours its aqueous solution deep violet.

Methylorthohomosalicylic acid crystallizes in feathery needles
and melts at 81.

a-Metahomosalicylic acid, y-Crcsotic acid, or Ortlwhydroxypara-
tohiic acid (1 : 2 : 4) is also obtained by fusing paraxylenol with
caustic potash (Jacobsen), and, together with metahomopara-
hydroxybenzoic acid, when metacrcsol is heated with tetrachloro-
methane and caustic soda (Schall). It crystallizes from water
in needles and from alcohol in monoclinic prisms, which melt at
177, 4 and are volatile with steam. On heating with hydro-
chloric acid to 170, it decomposes into metacresol and carbon
dioxide ; ferric chloride produces a deep violet colouration in its
aqueous solution.

a-Methylmclatiomosalicylic acid crystallizes in plates, which
melt at 103 104.

(3-Metahomosalicylic acid (1:2:6) has been obtained from
/3-bromorthotoluic acid. It is slightly soluble in cold, readily
in hot water, very freely in alcohol, crystallizes in long
needles, melting at 168, and is tolerably volatile with steam.
Its solution is coloured a deep blue-violet by ferric chloride;

1 Ber. D".utsch. Chcm. Ges. xiv. 2352. ; Panaotovi6, Journ. Prakt. Ghem. [2]
xxxiii. 63. 2 Schall, ibid. xii. 821.

3 Bcr. Dcntsch. Chcm Gcs. xi. 902.

4 Oppenheimer and Pfaff, ibid. viii. 889.



PARAHOMOMETAHYDROXYBENZOIC ACID. 425



on heating to 200 with concentrated hydrochloric acid, it
decomposes into metacresol and carbon dioxide. 1

2227 Parahomomctaliydroxylicnzoic acid or Mctahydroxyortho-
toluic acid (1 : 5 : 2) is formed by fusing metasulphamido-ortho-
toluic acid, 2 a-bromorthotoluic acid, 3 or the chlororthotoluic acid
melting at 166 , 4 with caustic potash, and from /3-amidortho-
toluic acid by means of the diazo-reaction. 5 It is slightly
soluble in cold, readily in hot water, crystallizes in transparent
prisms, which melt at 172 and sublime in needles, and is also
volatile with steam. Ferric chloride, added to its cold saturated
solution or to that of its ammonium salt, produces a light
brown precipitate soluble in a large quantity of hot water.
It is not attacked by concentrated hydrochloric acid even
at 220.

Mdalwmomctaliydroxybcnzoic acid or s-Hydroxytoluic acid
(1:3: 5). Fuming sulphuric acid converts metatoluic acid into
two isomeric sulphonic acids, which yield a mixture of symmetric
hydroxymetatoluic acid and parahomosalicylic acid on fusion
with caustic potash ; the latter may be removed by distillation
with steam, while the former differs from all its isomerides in
not being volatile.

Symmetric hydroxytoluic acid is tolerably soluble in cold, readily
in hot water, and crystallizes in fascicular aggregates of needles,
which melt at 208; it solidifies to hard, transparent prisms
and sublimes in stellate groups of needles. Solutions of the
acid and of its salts give a fawn-coloured precipitate with ferric
chloride, which dissolves in a large excess of the reagent, forming
a dark brown solution. It is not attacked by concentrated
hydrochloric acid at 230, and yields metacresol when distilled
with lime. 6

s-Trinitrohydroxytoluicacid, C 6 (NO. 2 ) 3 (OH)(CH 3 )C0 2 H + H 2 O
Wan-en de la Rue, by heating the colouring matter of cochineal
with nitric acid, obtained nitrococcusio acid, which possesses the
same composition as the trinitro-anisic acid prepared by Cahours,
but is obviously not identical with it. 7 Gmelin states that it is
isomeric with the latter and also with methyltrinitrosalicylic
acid. 8 It differs from both of these by being dibasic, and Strecker
on this account suggested that it might be trinitrocresotic acid. 9

1 Jacobsen, Bcr. Dcutsch. Chem. Ges. xvi. 1962.

Ibid. xiv. 38. 3 Ibid. xvii. 2375.

4 Krii^er, ibid, xviii. 1758. 8 Jacobsen and Wierss, ibid. xvi. 1959.

6 Jacobsen, ibid. xiv. 2357. 7 Ann. Chem. Phartn. Ixiv 23.

8 Ilandb. Org. Chem. iii. 398. 9 Lchrb. Org. Chem. v. Aufl. /27.



426 AROMATIC COMPOUNDS.

Liebermann and Dorp found that it decomposes into carbon
dioxide and trinitrometacresol when heated with water to ISO , 1
and therefore considered it to be a trinitro-derivative of the
then unknown symmetric hydroxytoluic acid. After the dis-
covery of the latter, Kostanecki and Niementowski showed that
on solution in warm nitric acid it is converted into nitrococcusic
acid. 2

It crystallizes from hot water in colourless, rhombic plates,
which are yellow when not perfectly pure, and form a yellow
solution in water which dyes animal fabrics and the skin an
intense yellow. It melts with decomposition between 170 and
ISO , and detonates at a higher temperature. Its salts are
soluble in water and detonate violently on heating.

a-Orthohomomctahydroxybenzoic acid or Metahydroxyparatoluic
acid (1:3:4) is formed by fusing paratolulylsulphonic acid, 3
chloroparatoluic acid, bromoparatoluic acid 4 or sulphamidopara-
toluic acid 5 with caustic potash, as well as by the action of
nitrous acid on amidoparatoluic acid. 6 It crystallizes in long
needles, melting at 206 207, is slightly soluble in cold, readily
in hot water, and volatilizes with steam. Ferric chloride gives
no colouration, and hydrochloric acid has no action upon it at
270. On distillation with lime it decomposes into orthocresol
and carbon dioxide.

fi-Ort.hdiomometahydrQxy'benzoic acid (1:3:2) was obtained by
Jacobsen from sulphorthotoluic acid. It crystallizes from hot
water in long needles with a vitreous lustre, which melt at
183. are volatile with steam, and are not attacked by hydro-
chloric acid at 200 210. It yields orthocresol on distillation
with lime. Ferric chloride, added to an aqueous solution of the
acid or one of its salts, produces a heavy, bulky, light brown
precipitate.

(3-Methylorthohomomctaliydroxybenzoic acid crystallizes in long,
fine needles, and melts at 146. 7

2228 Mctahomcparahydroxylenzoic acid or Parahydroxyortho-
toluic acid (1:4:2) is obtained by fusing the aldehyde with
caustic potash. 8 It is also formed, together with a small
quantity of metahomosalicylic acid, when metacresol is heated

Ann. Ohcm. Pharm. clxiii. 99. 2 Ber. Dcutsch. Chcm. Gcs. xviii. 250.

Flesch, ibid. vi. 481. 4 v. Gerichten, ibid. xi. 368.

Hall and Remsen, ibid. xii. 1433.

Fittica, ibid. vii. 927 ; v. Gerichten and Rossler, ibid. xi. 705.

Jacobsen, ibid. xvi. 1962.

Schrottcn and Ticmann, ibid. xi. 778.



D1HYDEOXYTOLUALDEHYDES. 427

with tetrachloromethane and concentrated caustic soda solution, 1
and when parasulphamido-orthotoluic acid 2 or the chlorortho-
toluic acid which melts at 130 3 is fused with caustic potash. It
crystallizes from hot water in small needles which contain half a
molecule of water of crystallization ; this is lost at 100 and
the anhydrous residue then melts at 177 178. Ferric chloride
produces no colouration, but gives a reddish brown precipitate
with its salts, which dissolves in an excess of the reagent forming
a dark -brown solution. On heating to 200 with hydrochloric
acid it decomposes into carbon dioxide and metacresol.

Mdliylmdahomoparahydroxy'bcnzoic acid crystallizes in long
needles and melts at 176.

Orthohomoparahydroxybenzoic acid or Pardhydroxymetatoluic
acid (1 : 4 : 3) is formed by fusing the aldehyde, 4 a-sulphamido-
toluic acid 5 a-bromometatoluic acid, 6 or chlorometatoluic acid 7
with caustic potash, and together with a small quantity of
orthohomosalicylic acid by heating orthocresol with tetrachloro-
methane and caustic soda (Schall). It crystallizes from hot
water in small needles, containing half a molecule of water,
which is lost at 100; the anhydrous acid melts at 171 173,
and is volatile with steam. Ferric chloride produces no coloura-
tion ; on heating with hydrochloric acid to 180 185 it
decomposes into carbon dioxide and orthocresol.

MethylortTwhorn&parahydrooMjbenzoiG acid forms microscopic
silky needles, melting at 102 193.



DIHYDROXYTOLUALDEHYDES,
C 6 H 2 (CH 3 )(OH) 2 CHO.

2229 Para-orsellinaldehyde,(CH.O : OH : OH : CH 3 = 1 : 2 : 4 : 6).

This compound, which is also known as orcylaldchydc, is formed
together with two orcendialdehydes, C 6 H(CH 3 )(OH) 2 (CHO) 2 , by
heating orcinol with caustic potash and chloroform ; it crystallizes
from hot water in fascicular or stellate aggregates of needles,
which melt at 177 178. Its aqueous solution is coloured
reddish brown by ferric chloride. 8 The constitution of this body

Schall, Bar. Deutsch. Chcm. Ges. xii. 819.
Jaeobsen, ibid. xiv. 40. 3 Kviiger, loc. cit.

Schotten and Tiemann. 5 Jacobsen, ibid. xi. 897.

Jaeobsen, ibid. xiv. 2351. 7 Ibid, xviii. 1760.

Tiemann and Helkenberg, ibid. xii. 999.



AROMATIC COMPOUNDS.



has not been determined, but since resorcinol is converted by
the above reaction into /3-resorcylaldehyde, in which the alde-
hyde group takes the para-position with regard to one hydroxyl
and the ortho-position to the other, this is probably also the case
with orcylaldehyde.

Metahomometho^salicylaldchyde (1:2:3:5) has been obtained
from creosol and chloroform, and forms an oily liquid, which
possesses a smell resembling that of salicylaldehyde, and, like
the latter, forms a deep yellow coloured solution in alkalis.
Ferric chloride produces a deep green colouration. 1



DIHYDROXYTOLUIC ACIDS, CH 3 .C 6 H 2 (OH) 2 C0 2 H.

2230 In the year 1830, Heeren investigated the lichens
Rocella tinctoria and Lccanora tartarea, which are employed in
Holland for the manufacture of litmus and archil, and found in
them a characteristic, colourless, crystalline substance, which is
converted into a red dye by the united action of air and
ammonia, and which he therefore named erythrin (epvbpos, red).
On boiling with a solution of ammonium carbonate, it was con-
verted into the amorphous erythrinbitter. In order to obtain
erythrin in larger quantities, he extracted the lichens with
alcohol, but found that the erythrin was thus converted into a
similar substance, which was, however, unsuitable for the pre-
paration of the dye, and which he named pseudoerythrin? He also
found rocellic acid in the lichens which he examined (Pt. II. p. 320).

Kane, however, obtained different results ; in extracting the
lichens with hot alcohol he obtained erytlirylin, insoluble in water,
and a soluble crystalline compound, which is identical with
pseudoerythrin and is not an accidental product, but one of the
most important of the whole series. He therefore transferred
the name erythrin to this substance and assumed that Heeren's
erythrin was a mixture of erytlirylin with other bodies. When
its solution is exposed to the air, erythrinbitter or amarylhrin
is formed, and this converted after several months' exposure into
crystalline telcrythrin, to which he gave this name in contradis-
tinction to erytlirylin, since the word reX,o9 denotes the end,
and v\rj the beginning of the series. 3



1 Tiemann and Koppe, Bcr. DeutscJi. Chem. Gcs. xiv. 2026.

2 Schwcigycrs Journ. Hx. 313. 3 Phil. Trans. 1840, 273.






DIHYDROXYTOLUIC ACIDS. 429

Schunck then investigated many varieties of Lccanora and
Variolaria from the Vogelsberg, and found, in them a crystalline
compound, which, like Heeren's erythrin, is converted into a red
dye by exposure to the air, but has a different composition, and
which he therefore named lecanorin. 1 On boiling with baryta
water, it decomposed into carbon dioxide and orcinol, which had
already been prepared from these species of lichens by Robiquet,
while on boiling with alcohol it was converted into Heeren's
pseudoerythrin. 2

Eochleder and Heldt, who detected lecanorin in Evernia
P-runastri, showed that it is also converted into pseudo-
erythrin by the action of hydrochloric acid and alcohol;
the latter substance must therefore be looked upon as the ethyl
ether of lecanorin, or as it is more suitably called, lecanoric
acid?

This compound was then carefully examined by Schunck, 4
who also submitted the substances contained in Rocella tindoria
var. fuciformis from Madagascar and Angola to a new investiga-
tion. The most important of these is erythric acid, which
yields the colouring matter. This is so readily converted into
the ethyl ether or pseudoerythrin by boiling with alcohol, that
the latter is always obtained when the lichens are extracted
with boiling alcohol. This compound has the same composition
as ethyl-lecanoric acid, and appears to be identical with it a
fact which admits of the simple explanation that erythric acid is
a copulated compound of lecanoric acid and orcinol. On boiling
with alcohol, orcinol is set free and the lecanoric acid combines
with the ethoxyl residue. 5

Erythric acid is converted by boiling with water into picro-
erythrin, the properties of which are not identical either with
those of Heeren's erythrinbitter or of Kane's amarythrin ; they
approach most closely to those of telerythrin.

Stenhouse, who investigated a South American sample of
Rocella tindoria, found in it a-orsellic acid, which is decomposed
by boiling with milk of lime or baryta into orcinol and a-orsellinic
acid, while Schunck's lichen, which is K Montagnei, contains
erythric acid, which yields picroerythrin and crythrelinic acid,
which is very similar to a-orsellinic acid. According to Schunck,
picroerythrin is decomposed by boiling with an excess of lime or

1 Ann. Chem. Pharm. xli. 157.

2 Ibid. xlv. 250. 3 /M* xlvin. 1.
4 Ibid. liv. 261. 5 /*** l xi - 64 -



430 AROMATIC COMPOUNDS.

baryta into carbon dioxide and orcinol, but Stenhouse has shown
that erytliroglucin is also formed. 1

Stenhouse also discovered a @-orsellic acid in liocdla lin-doria
from the Cape of Good Hope, but this was shown by Gerhard t,
who was subsequently confirmed by Stenhouse himself, to be
identical with the a -acid.

In " Remarks on the Preceding Communication," Strecker
observes : Stenhouse has made us acquainted with a series of



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