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acetochloroglucose : 6

" "\OH ' C H ^ C A)A + 4C 2 H 5 .OH =


C 6 H/ + 4C.,H 5 OC 2 H 3 + KC1.

\OC 6 H n 5

It is reduced to salicin by the action of sodium amalgam
and water. 7 It forms a compound with acid sodium sulphite,

Perkin, Journ. Chem. Soc. xxi. 122.

Ibid. xxi. 181.

Ibid cx\v. 295. 4 Piria ibid lvi 64

Schiff, . cliv. 14.

Michael, Amcr. Chem. Journ. i. 309.

Liscuko, Jahresbcr. Chem. 1864, 588.


which has the formula C 13 H 16 7 .S0 3 HNa, and forms a dazzling
white, hygroscopic, crystalline mass. 1

When it is moistened with one per cent, nitric acid, dried and
heated to 110 115, it is converted into parahelicin, which is
without doubt a polymeride; this substance is an amorphous,
starchy, tasteless powder, which is scarcely soluble in water and
alcohol, and has no action upon a solution of rosaniline reduced
by sulphurous acid, whereas helicin forms a reddish violet
crystalline compound with it. It dissolves in very dilute
hydrochloric acid which has been slightly warmed, and is thus
reconverted into helicin. 2

Tetracetylhelicin, C 13 H 12 (C 2 H 3 O) 4 , was obtained by Schiff
by heating helicin with acetyl chloride or acetic anhydride ; it
crystallizes from hot alcohol in long, silky needles or prisms.

Benzoylhdicin, C 13 H 15 (CO.C 6 H 5 )O 7 . Piria prepared this com-
pound by the action of nitric acid on populin (p. 282), 3 and Schiff
by heating helicin with benzoyl chloride.* It crystallizes in silky
needles, which are slightly soluble in water, more readily in
alcohol. Sodium amalgam and water reduce it again to populin ;
on boiling with water and magnesia it is decomposed into helicin
and benzoic acid.

Helicoldin, C 26 H 34 O U , is formed by dissolving salicin in nitric
acid of sp. gr. 1'085 :

It crystallizes from hot water in needles, and is very similar to
helicin, from which it differs in being resolved by acids, &c., into
glucose, salicylaldehyde, and saligenin (Piria).

Odacetylhdicoulin, C 26 H 26 (C 2 H 3 O) 8 O 14 , is obtained by heating
helicoidin to 100 with acetic anhydride ; it is insoluble in water,
and crystallizes from alcohol in druse-like aggregates, melting
at 80 (Schiff).

Ortho-aklehydophenoxyacetic acid, C 6 H 4 (COH)OCH 2 .CO 2 H, is
formed when equal molecules of salicylaldehyde and chloracetic
acid are heated together and the fused mass treated with
an excess of caustic soda solution of sp. gr. 1'2 1'3; the
mixture is then heated on the water-bath until it has become
almost solid, the acid precipitated by hydrochloric acid and

1 Schiff, Ann. Chcm. Pharm. ccx. 126.

- Ibid. Bcr. Deutsch. Chcm. ,. xiv. 317
3 Ann. Chcm. Pharm. xcvi. 379.

* Ibid. cliv. 23.



re-crystallized from hot water. It forms large, yellow plates,
which melt at 132, and sublime when gradually heated.
Like other aldehydes it reduces Fehling's solution and am-
moniacal silver solution, and combines with phenylhydra-
zine and acid sodium sulphite. Its salts are readily soluble
and crystallize well; its ethyl ether forms needles melting
at 114 . 1

2166 Ortlwhydroxybenzidene compounds. These are obtained
in a similar manner to the benzidene compounds.


Ortlwliydroxylenzidene acetate, C 6 H.<f is formed

\CH(OCO.CH 3 ) 2 ,

when salicylaldehyde is herated to 150 with acetic anhydride;
it crystallizes from alcohol in thick, hard, transparent tablets,
which melt at 103 104, and distil with slight decom-
position. 2

Perkin has obtained the following compounds in a similar
manner :

xOCH 3 Melting-point.

C 6 H 4 <( , lustrous prisms 75

\CH(OCO.CH 3 ) 2


C 6 H 4 <; , small prisms 88 89

\CH(OCO.CH 3 ) 2

C G H / , needles or pointed tablets 100 101

\CH(O.CO.CH 3 ) 2

The last compound may also be obtained by heating salicyl-
aldehyde to 180 with acetic anhydride. 3 Tolerably concentrated
caustic potash decomposes it into acetic acid and orthohydroxy-
benzidene acetate, while it splits up on distillation into acetyl-
salicylaldehyde and acetic anhydride. 4

Orthohydroxybenzidenoxime, or Salicylaldoxime, C 6 H 4 (OH)
CH=N.OH, is formed by the action of bydroxylamine on
salicylaldehyde, and forms white crystals which dissolve readily
in alcohol, ether and benzene, but are insoluble in petroleum
spirit, and melt at 57. 5 Its compounds resemble those of
benzaldoxime (p. 139).

Rbssing, Ber. Deutsch. Chem. Ges. xvii. 2988.
Perkin, Ann. Chem. Pha.rm. cxlvi. 371.
Barbier, Bull. Soc. Chim. xxxiii. 53.
Perkin, Ann. Chem. Pharm. cxlviii. 203.
Lach, Ber. Deutsch. Chem. Ges. xvi. 1782.



Hydroxylenzidene-amidobenzoic aeid, C 6 H 4 (OH)CH NC 6 H
C0 2 H, is prepared by mixing warm, dilute, aqueous solutions
of salicylaldehyde and metamidobenzoic acid. It crystallizes in
long, yellow needles, which are very soluble in alcohol and
benzene. Its aqueous solution gives off salicylaldehyde on
evaporation. 1

Helicin combines with metamidobenzoic acid to form the
analogous compound C 6 H 4 (OC 6 H n O 5 )CH=NC 6 H 4 .C0 2 H, which
crystallizes from alcohol in lustrous plates, melting at 142; 2 it
is resolved into the preceding compound and grape sugar by
heating with an aqueous solution of emulsin.

Hydrosalicylamide, N 2 (CH.C 6 H 4 .OH) 3 . This compound, cor-
responding to hydrobenzamide (p. 140), was prepared by Ettling
by the action of ammonia on an alcoholic solution of salicylalde-
hyde, and named by him salicylimide. 3 It forms heavy, light
yellow crystals, melting at 300, and is insoluble in water r slightly
in cold, more readily in hot alcohol, and decomposes into salicyl-
aldehyde and ammonia when heated with concentrated caustic
potash solution or strong acids. It absorbs three molecules
of hydrochloric acid, forming a compound which decomposes
in moist air into salicylaldehyde and ammonium chloride. 4

As a phenol it forms metallic salts ; when an ammoniacal
solution of copper acetate is added to its cold alcoholic solu-
tion, the liquid becomes coloured emerald-green, and after a
few minutes becomes decolourized, cruciform plates being de-
posited, which after drying have a strong satin lustre; their
composition is represented by the formula (C 21 H 15 N 2 O 3 ) 2 Cu 3
(NH 3 ) 2 . They are almost insoluble in water and alcohol, and
form a green solution in hydrochloric acid, from which they are
reprecipitated by alkalis. They are not attacked by cold caustic
potash, and decomposition only proceeds slowly on boiling ;
salicylaldehyde is formed when it is heated with strong acids.

Orthobenzidenephenylhydrazine, C 6 H 4 (OH)CH=N 2 H.C 6 H 5 ,
crystallizes from hot, dilute alcohol in yellow needles or plates,
melting at 142 143. When it is heated with chloracetic
acid, a colouring matter, C 9 H 7 NO 3 , is produced, which forms a
deep bluish green solution in alcohol and is coloured cherry-red
by alkalis. 5

Schiff, Ann. Chcm. Pharm. ccx. 114.

Ber. Deutsch. Chcm. Gcs. xii. 2032.

Ann. Chcm. Pharm. xxxv. 261.

Bode, Jahresb. Chcm. 1857, 318.

Fischer, Bcr. Deutsch. Chem. Ges. xvii. 575 ; Rossing, Hid. 3004.

u 2



2167 Chlorosalicylaldehyde, C 6 H 3 C1(OH)CHO, is formed by
the action of chlorine on salicylaldehyde. 1 It is insoluble in
water, and crystallizes from alcohol in rectangular tablets.

Branwsalicylaldeliyde, C 6 H 3 Br(OH)CHO, is not only formed by
the direct action of bromine 2 but also when salicylaldehyde is
treated with phosphorus pentabromide, the latter compound act-
ing in the same manner as a mixture of bromine and phosphorus
pentabromide. 3 It crystallizes from ether in small plates, melt-
ing at 98 99 ; its alcoholic solution is coloured violet by ferric


Methylbromosalicylaldehyde, flat prisms )-I-,QO -

C 6 H 3 Br(OCH 3 )CHO. J 1

Ethylbromosalicylaldehyde, 4 sharp prisms

C 6 H 3 Br(OC 2 H 5 )CHO.

a-Nitrosalicylaldehyde, C 6 H 3 (N0 2 )(OH)CHO, is formed, to-
gether with the /3-compound, by boiling salicylaldehyde with
dilute nitric acid ; 6 the two substances are separated by means
of their barium salts. a-Nitrosalicylaldehyde crystallizes in
small yellow prisms, which melt at 105 107, while its barium
salt, (C 7 H 4 NO 4 ) 2 Ba + 2H 2 O, forms slightly soluble, yellowish red

P-Nitrosalicylaldehyde forms needles, melting at 123 125;
its barium salt, (C 7 H 4 N0 4 ) 2 Ba + 6H 2 O, crystallizes in yellow

MethylnitrosalicylcddcJiyde, C 6 H 3 (N0 2 )(OCH 3 )CHO, forms fine,
white needles, melting at 88. 6

Piria, Ann. Chem. Pharm. xxx. 169 ; Lbwig, Berz. Jahrexb. xx. 311.

Piria ; Lbwig, Pogg. Ann. xlvi. 57 ; Heberlein, Berz. Jalresb. xxv. 484.

Henry, Ber. Deutsck. Chem. Ges. ii. 274.

Perkin, Ann. Chem. Pharm. cxlv. 304.

Mazzara, Gazz. Chim. Itiil. vi. 460.

Voswinkel, Ber. Dcutsch. Chem. Ges. xv. 2027 ; Schnell, ibid. xvii. 1381.



2168 This compound is formed, together with metahydroxy-
benzyl alcohol, by the action of sodium amalgam on a faintly
acid solution of metahydroxybenzoic acid. It can be more
readily obtained from metamidobenzaldehyde by treating its
well-cooled solution in hydrochloric acid with the calculated
quantity of sodium nitrite and then heating. 1 It crystallizes
from hot water in white needles, melting at 104; its aqueous
solution is coloured a faint violet by ferric chloride, and it differs
from the isomeric para-compound in giving a precipitate with
lead acetate.

MctTiylmetahydroxybenzaldehydc,, C 6 H 4 (OCH 3 )CHO, is obtained
by heating the aldehyde with caustic potash, methyl iodide and
wood-spirit. It is an oily liquid, which boils at 230 and has a
pleasant odour.

Acetylmetahydroxylenzaldehyde, C 6 H 4 (OCO.CH 3 )CHO, is
formed by the action of acetic anhydride on the potassium
compound of the aldehyde, and is an oily liquid, boiling
at 263.

Acetometahydroxylenzidene acetate, C 6 H 4 (OCO.CH 3 )CH(O.
CO.CH 3 ) 2 , is produced when the aldehyde is boiled with an
excess of acetic anhydride. It is slightly soluble in water,
readily in alcohol, and crystallizes in lustrous, white plates,
melting at 76.

Nitro -substitution products. The three following compounds
are all formed by the direct nitration of the aldehyde ; they
may be separated by re -crystallization from hot water, chloro-
form, c.

a -Nitromctaliydroxylenzaldcliydc, C 6 H 3 (NO. J ) (OHjCHO, crys-
tal lizes in yellowish plates, melting at 128, which are slightly
soluble in cold, more readily in hot water, and readily in
chloroform and petroleum ether.

ft-Nitromctahydroxyl)enzal<1chyde forms needles which melt at
166, and is more readily soluble in water than the a-com pound,
but only very slightly soluble in chloroform and benzene.

"/-Nitromctahydroxylicnzaldchydc melts at 138, and crystallizes

1 Tiemaun and Ludwig, Bar. Deutech. Chem. Gcs. xv. 2043 and 3052.


in prisms, which dissolve readily in hot water, chloroform and
benzene, but only with difficulty in petroleum ether.

When these compounds are heated with caustic potash, wood-
spirit and methyl iodide, their methyl ethers, C 6 H 3 (NO 2 )(OCH 3 )
CHO, are formed (Tiernann and Ludwig) ; tbese can also be
obtained by the nitration of metamethoxybenzaldehyde. 1

a- Ortlionitromethylmetaliydroxybcnzaldehyde crystallizes from
chloroform in thick, yellow prisms, melting at 107.

P-Orthonitrwmthylmetahydroxybenzcddchyde forms white plates
or needles, which melt at 82 83.

These bodies are known to be orthonitro-compounds because
they give the indigo reaction (p. 146).

Metanitromathylmetahydroxybcnzaldehyde crystallizes in needles
or prisms, and melts at 98.

Paranitromethylmetahydroxybenzaldehyde was obtained by
Ulrich by the oxidation of paranitromethoxycinnamic acid ; it
crystallizes in hair-like needles and melts at 62.


2169 This body was first prepared by Bucking by heating the
methyl ether, anisaldehyde, with hydrochloric acid. 2 It may be
synthetically obtained by the action of chloroform on an alkaline
solution of phenol, salicylaldehyde being formed at the same time.

In order to prepare it, 30 parts of chloroform are gradually
added to a solution of 20 parts of phenol in 120 parts of water
heated to 50 60 ; the liquid becomes coloured blue and then
deep red, a considerable rise of temperature taking place, the
use of an inverted condenser being thus rendered necessary.
The mixture is finally boiled for half an hour, the excess of
chloroform distilled off, an excess of sulphuric acid added, and
the whole distilled in steam, salicylaldehyde passing over along
with any free phenol, from which it is subsequently separated by
means of acid sodium sulphite. The residual liquid is filtered while
hot from the deep red coloured resin which is formed, and after
cooling is extracted with ether ; on evaporation of the ether, the
parahydroxybenzaldehyde is left behind, and is then re-crystall-
ized from boiling water. 3 It is slightlys oluble in cold, more readily

1 M. Ulrich, Ber. Dcutsch. Chem. Ges. xviii. 2571. 2 Ibid. ix. 527.

3 Reimer and Tiemann, ibid. ix. 824 ; Tiemann and Herzfeld, ibid. x. 63.


in hot water, and readily in alcohol, ether, &c., and crystallizes
in fine needles, which have a faint but pleasant aromatic odour,
melt at 115 116, and sublime unaltered. Its aqueous solu-
tion is coloured a dirty violet by ferric chloride ; if its ethereal
solution be shaken up with a solution of acid sodium sulphite,
combination ensues, but the double compound is readily soluble.
Its solution is not easily attacked by oxidizing agents, but it is
converted into parahydroxybenzoic acid by fusion with caustic
potash at a low temperature.

Mcthylparahydroxybenzaldehyde, C 6 H 4 (OCH 3 )CHO. Cahours
prepared this compound by the oxidation of oil of anise seed, 1
while Cannizzaro and Bertagnini obtained it by oxidizing anise
alcohol (p. 284), and named it anisaldehyde. 2 Piria then showed
that it is also formed by distilling a mixture of calcium formate
and calcium anisate (methylparahydroxybenzoate) ; 3 and Tie-
mann and Herzfeld obtained it by heating parahydroxybenz-
aldehyde with methyl iodide, wood spirit and caustic potash.

It may be most readily prepared from oil of anise, which
consists for the most part of anethol, C 3 H 5 .C 6 H 5 .OCH 3 , the
methyl ether of allylphenol. One part of this is brought into a
cold solution of 2 parts of potassium dichromate, 3 parts of
sulphuric acid, and 8 parts of water. As soon as the temperature
ceases to rise, the mixture is diluted with half its volume of
water and distilled, the quantity of liquid in the distilling flask
being kept at its original volume by the gradual addition of
water. The distillate is repeatedly rectified, the aldehyde
coming over in the first portions, which are then shaken up with
a concentrated solution of acid sodium sulphite. The crystals,
which separate after some time, are washed with alcohol and
decomposed by carbonate of soda solution. 4

Anisaldehyde is a liquid which has an aromatic odour, boils at
24-7 248, and dissolves slightly in cold, more readily in hot
water ; it readily takes up oxygen from the air and is converted
by alcoholic potash into a mixture of anise alcohol and anisic
acid. When heated with dilute hydrochloric acid to 200, it
decomposes into parahydroxybenzaldehyde and methyl chloride

Acetylparahydroxybenzald&ydt, C 6 H 4 (OCO.CH 3 )CHO, is ob-
tained by dissolving 2 parts of parahydroxybenzaldehyde and
1 part of caustic potash in water, evaporating and treating the

1 Ann. Chcm. Pharm. Ivi. 307. - Ibid. xcViii. 189.

3 ibid. c. 105. 4 Rossel, ibid. cli. 28.


residue with acetic anhydride in presence of ether (Tiemanii
and Herzfeld).

It is also formed by the action of acetic anhydride on the
aldehyde, 1 and is a liquid, boiling at 264 265, which forms an
almost insoluble compound with acid sodium sulphite.

Acetylparahydroxybenzidene acetate, C 6 H 4 (OCO.CH 3 )CH(OCO.
CH 3 ) 2 , is prepared by heating the aldehyde with three times its
weight of acetic anhydride. It is readily soluble in hot water
and alcohol, and crystallizes from ether in flat prisms, melting
at 93 94 (Tiemann and Herzfeld).

Parahydroxybenzaldoxime, C 6 H 4 (OH)CHrz NOH, forms odour-
less, white needles. 2

Chloroparahydroxybenzaldehyde, C 6 H 3 C1(OH)CHO, crystallizes
from hot water in silky needles melting at 148 149 ; its aqueous
solution is coloured violet by ferric chloride.

Bromoparahydroxybenzaldehyde, C 6 H 3 Br(OH)CHO, is almost
insoluble in water, crystallizes from alcohol in long, strongly
refractive needles, melting at 179- 180, and does not give any
colouration with ferric chloride.

lodoparahydroxybenzaldehyde, C 6 H 3 I(OH)CHO, is formed
when parahydroxybenzaldehyde is boiled with iodine and dilute
alcohol. It is slightly soluble in water, readily in alcohol, and
separates from chloroform in white crystals, melting at 198
199. On heating with caustic potash it yields protocatechuic
acid. 3

Nitroparahydroxybenzaldehyde, C 6 H 3 (NO 2 )(OH)CHO. Maz-
zara obtained this substance by boiling the aldehyde with dilute
sulphuric acid, 4 and Herzfeld by adding concentrated nitric
acid to a solution of parahydroxybenzaldehyde in concentrated
sulphuric acid. 5 It is soluble in boiling water and alcohol, and
crystallizes in yellowish needles melting at 139 140. Its
aqueous solution gives a fugitive red colouration with ferric
chloride. It decomposes carbonates; the potassium salt, C 6 H 3
(N0 2 )(OK)CHO + H 2 O, forms golden-yellow tablets.

Barbier, Bull. Soc. Chim. xxxiii. 54.

Lach, Ber. Deutsch. Chem. Ges. xvi. 1785.

Herzfeld, ibid. x. 2196.

Gaz. Chim. Ital. vii. 285.

Ber. Deutsch. Chcm. Ges. x. 1269.



\C0 2 H.


2170 The history of this important substance is of special
interest because its genetic relations to the benzoyl and cinnamyl
groups and to indigo blue were known at a very early period.
Piria, who prepared it in 1838, by heating the aldehyde with
caustic potash, 1 pointed out that the radicals benzoyl and salicyl
are different oxidation products of the hydrocarbon or radical
C 7 H 5 (p. 285). Marchand 2 and Gerhardt 3 found that it is also
formed when salicin is melted with potash, and is converted by
dilute nitric acid into nitrosalicylic acid, which is identical with
indigotic or anilotic acid, a substance obtained by the action of
nitric acid on indigo which had long been familiar to chemists.
This compound on fusion with potash at a low temperature
yields anthranilic acid (p. 237), while Cahours, by carrying out
the operation at a higher temperature, obtained salicylic acid ; 4 it
was obtained, together with acetic acid, in a similar manner
from cumaric acid by Delalande, who remarked that this latter
compound bears the same relation to cinnamic acid as salicylic
to benzoic acid. 5 Ettling, who prepared salicylic acid by
oxidizing its aldehyde with potassium dichromate and sulphuric
acid, found that it can also be obtained by heating the copper
salt of this or of benzoic acid, and is therefore an oxidation
product of the latter. 6 Gerhardt had previously observed that
salicylic acid decomposes on heating into phenol and carbon
dioxide, just as anthranilic acid is split up into aniline and
carbon dioxide. A series of relations was thus established
among the following compounds :

Benzene Benzoic acid Cinnamic acid

C 6 H 6 C 7 H 6 2 C 9 H 8 2

Phenol Salicylic acid Cumaric acid

C 6 H 6 C 7 H 6 3 C 9 H 8 3

Aniline Anthranilic acid

C 6 H 7 N C 7 H 7 N0 2

1 Ann. Chim. Phys. Ixix. 298 ; Ann. Chcm. Pharm. xxx. 165.
- Journ. Prakt. Chcm. [1] xxvi. 396. 8 Ann. Chcm. Pi

4 Ibid. lii. 343. s Ibid. xlv. 336. Ibid. liii. 77.


Hofmann found that aniline is converted into phenol by the
action of nitrous acid, and suggested that anthranilic acid would
probably yield salicylic acid when treated in a similar manner,
this suggestion being experimentally verified by Gerland. 1

Salicylic acid was obtained synthetically by Kolbe and Laute-
mann by the action of carbon dioxide on a mixture of phenol
and sodium. 2 The former chemist found that it is also formed
when carbon dioxide is passed over heated sodium phenate, half
of the phenol being set free : 3


2C 6 H 5 .ONa + CO 2 = C 6 H 4 < + C 6 H 5 OH.

\CO 2 Na

Ethyl salicylate may be prepared by the action of sodium on
a mixture of phenol and ethyl chloroformate : 4


C 6 H 5 .ONa + C1C0 2 .C 2 H 5 = C 6 H 4 < + NaCl.

\C0 2 .C 2 H 5

The acid is also formed, together with parahydroxybenzoic
acid, when a mixture of tetrachloromethane and phenol is heated
to 100 with alcoholic potash (Part III. p. 37 ). 5

It may also be obtained by fusing orthocresol, 6 toluene-
orthosul phonic acid, 7 &c., with caustic potash, as well as by
heating copper benzoate to 180 with water, 8 and when sodium
is allowed to remain in contact with ethyl succinate for a long
time. 9 It has also been observed as a product of the action
of hydrogen dioxide on a solution of benzoic acid in sulphuric
acid. 10

Salicylic acid also occurs in nature. Lowig and Weidmann
detected it in the flowers of Spircea Ulmaria, accompanied by
salicylaldehyde, but did not actually identify it. Its methyl
ether is contained in the ethereal oils of the various species of

21 7 1 It was formerly prepared exclusively from the winter-

Ann. Chem. Pharm. Ixxxvi. 147.

Ibid. cxv. 201.

Jvurn. Prakt. Chem. [2] x. 89.

Wilm and Wischin, Zeitschr. Chem. 1868, 6.

Reimer and Tiemann, Ber. Deutsch. Chem. Gcs. ix. 1285.

Earth, Ann. Chem. Pharm. cliv. 360.

Wolkow, Zeitschr. Chem. 1870, 326.

Smith, Amer. Chem. Journ. ii. 338.

Herrmann, Ber. Dcutsch. Chem. Gcs. x. 646.

Hauriot, Compt. Rind. cii. 1250.


green oil obtained from Gaultheria procumbens by saponifying
with potash and decomposing the product with hydrochloric
acid. It is now manufactured by Kolbe's process.

The calculated quantity of pure phenol is dissolved in strong
caustic soda solution, the whole evaporated to dryness and the
residue rubbed into a dry powder ; this is then gradually heated
up to 180 in a metal retort in a current of carbon dioxide which
has been previously warmed. After some time phenol com-
mences to distil over, and is subsequently given off in larger
quantity; the temperature is then raised to 200, and the
operation continued until no more phenol comes over. The
residue is dissolved in water and fractionally precipitated with
hydrochloric acid ; resinous and colouring matters are first thrown
down, followed by tolerably pure acid, which is re-crystallized
from water and purified by distillation with superheated steam. 1

According to another patented process, carbonyl chloride,
which is now manufactured on a large scale, is passed into a
mixture of sodium carbonate and phenate heated to 140, the
temperature being finally raised to 200 . 2

Various hypotheses were proposed to explain the course of
the reaction which occurs when sodium phenate is heated in a
stream of carbon dioxide. The correct explanation was found
by R. Schmitt. 3 Pure dry sodium phenate absorbs carbon
dioxide with formation of sodium phenylcarbonate,C 6 H. 5 O.CO.O'^a,,
as a white powder which is instantly decomposed by water,
phenol and sodium bicarbonate being formed. When heated in
a closed tube to 120 130, it is converted quantitatively into
monosodium salicylate. In Kolbe's reaction, this complete decom-
position does not take place, and the monosodium salicylate
reacts with the sodium phenate at a higher temperature, phenol
being liberated :

O.C 6 H 5 C 6 H 4 .OH

NaO.C 6 H 5 + C0 2 =

C0 2

CO 2 Na C0 2 Na.

C 6 H 4 .OH C 6 H 4 ONa

| +NaO.C 6 H 6 = | +C 6 H 5 .OH.

CO 2 Na CO 2 Na

Salicylic acid is, therefore, best prepared by bringing abso-
lutely dry sodium phenate into an autoclave, pumping in rather

1 Rautert, Compt. Rend. viii. 537.

2 Ibid, xviii. Ref. 90.

3 Journ. Prakt. Ghcm. [2] xxxi. 397.


more than the calculated quantity of carbon dioxide, the mass
being kept cool during the absorption, or, better, adding it in
the solid form, agitating for some time and then heating to
120 ISO . 1

2172 Salicylic acid has a slightly acid, astringent and at the

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