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same time sweet taste ; it dissolves slightly in cold, more readily
in hot water, from which it crystallizes in fine needles, while it
is deposited in mouoclinic prisms from an alcoholic solution
which is allowed to evaporate spontaneously.

100 parts of water dissolve at :

15 100

0-085 0-225 7-925 parts.

Absolute alcohol and ether dissolve about half their weight of
the acid ; 2 it is also readily soluble in chloroform, differing in
this respect from its isomerides, and is dissolved by solutions
of the acetates and citrates of the alkali metals. 3

Its aqueous solution is coloured deep violet by ferric chloride ;
free acids, especially acetic and hydrochloric acids, hinder the re-
action. 4 It prevents the precipitation of copper salts by alkalis,
while its isomerides have not this property. 5 Strong boiling
nitric acid converts it into picric acid, and chromic acid oxidizes
it to water, carbon dioxide and a little formic acid. 6

It melts at 155 156 , 7 and sublimes on gradual heating, but
partially decomposes into carbon dioxide and phenol when
rapidly heated. It is completely split up when heated to
250 260 for two hours in a sealed tube ; on cooling, the
compound of these two substances, which has already been
described, separates out (Part III. p. 115). 8 This decomposition
also occurs when the acid is heated for a long time to 220 230
with water, and more rapidly in presence of hydrochloric acid at
140 150 . 9 Sodium amalgam only acts upon it in acid solu-
tion ; a resinous substance, probably saliretin, being formed. 10 In
order to test the purity of salicylic acid, a piece the size of a pea

1 Bar. Dcutech. Chem. Ges. xvii. Ref. 624 ; Schmitt, loc. cit.
- On Solubility, &c., see Ost, Juurn. Prakt. Chem. [2] xvii. 232; Bourgoin,
Bull. Soc. Chim. xxix. 247 ; xxxi. 57.

3 Rother, Pharm. Journ. Trans. 1886, 323.

4 Pagliani, Ber. Deutsch. Chem. Gcs. xii. 385. 5 Weith, ibid. ix. 342.

6 Kraut, Ann. Chem. Pharm. cl. 9. 7 Hiibner, ibid, clxii. 74.

8 Klepl, Journ. Prakt. Chem. [2] xxv. 464
8 Griibe, ibid, cxxxix. 143.
10 Velden, Journ. Prakt. Chem. [2] xv. 164.



THE SALICYLATES. 301



is ground up with five cc. of concentrated sulphuric acid, in
which it should form a perfectly colourless solution. 1 Its alcoholic
solution evaporated on a watch-glass should yield perfectly
clear and colourless crystals : if they are yellow or brown, the
sample contains admixed resins or colouring matters, while if
they are pink or violet, iron is present.

As salicylic acid decomposes so readily into carbon dioxide and
phenol, Kolbe considered that it would, like the latter, be a
powerful antiseptic, and subsequently verified this conclusion by
experiment. It has very rapidly come into favour both for
technical and household purposes, and is preferable to phenol
because it has no smell and is not poisonous. Its isomerides,
according to Kolbe, are not antiseptics. 2 Salicylic acid is also
employed in medicine, both for external and internal application.
Several physicians have observed that the acid prepared from
winter-green oil acts more powerfully than that obtained
artificially, but this may possibly be due to the fact that the
acid which first came into the market contained a considerable
amount of impurity. 3

2173 The Salicylates. Salicylic acid was first thought to be a
monobasic acid, but was afterwards regarded as dibasic. Piria
observes on this point : " Salicylic acid differs in a most striking
manner from other monobasic acids in forming acid ethers, which
are more fitly compared with the acid ethers of polybasic acids
than with the neutral ethers. In the course of researches which
I have instituted upon this question, I have succeeded in finding
the cause of this exception, or rather in showing that the behaviour
of this acid is not exceptional. Salicylic acid, which has
hitherto been looked upon as monobasic, is actually dibasic, and
very markedly so ; it forms salts with two equivalents of a base
so readily that it is singular that they have remained so long
unnoticed. In the following, I shall call salts containing one
equivalent of base, which have been previously described, acid
salicylates, and those discovered by me, containing two equivalents
of base, neutral salicylates." 4

This view was accepted by most chemists, tut Kolbe con-
sidered it to be a monobasic hydroxy-acid. Further researches
have shown that it is both a monobasic acid and a phenol, and



1 Hager, Fresenius' Zdtsclir xvi. 259.

2 Journ. Prakt. Chcm. [2] xi. 9.

3 Williams, Yearbook of Pharm. 1884, 424.

4 Ann. Chcm. Pharm. xciii. 262.



.302 AROMATIC COMPOUNDS.

therefore contains two hydrogen atoms which are easily replaced
by metals. The salts thus obtained are usually called basic
salicylates, while those formed by the replacement of the
hydrogen of the carboxyl group are known as normal salicylates.
The latter have recently been carefully examined by Milone. 1

Potassium salicylate, C 6 H 4 (OH)CO 2 K, is obtained by dissolving
the acid in potassium carbonate solution, evaporating and ex-
tracting the residue with alcohol. It is deposited in needles on
the spontaneous evaporation of its aqueous solution. When
heated to 210 220, it decomposes quantitatively into basic
potassium parahydroxybenzoate, phenol and carbon dioxide :

/OH /OK

2C 6 H 4 <( = C 6 H 4 < + C 6 H 5 .OH+C0 2 .

\C0 2 K \C0 2 K

If a solution of one molecule of the acid and two molecules
of caustic potash be evaporated to dryness, and the residue
heated to 220, the basic salt of parahydroxybenzoic acid is also
formed, together with phenol :

/OK /OK

2C 6 H 4 < + H 2 = C 6 H 4 < + C 6 H 5 .OH + K 2 C0 3 .



If, however, three or more molecules of potash are employed,
the salicylic acid is not changed ; if four are taken, complete
decomposition into carbon dioxide and phenol sets in at 300,
while in the presence of six molecules, the acid remains quite
unaltered even at this temperature. 2 Rubidium salicylate
behaves in a precisely similar manner on heating. 3

Sodium salicylate, C 6 H 4 (OH)CO 2 Na, forms silky tablets or a
crystalline powder, and has an unpleasant sweet taste. It
dissolves in its own weight of water and is used in medicine.
On heating to above 200, phenol and carbon dioxide are given
off, the basic salt remaining behind, but not a trace of the para-
acid is formed even at 300. When salicylic acid is heated to
this temperature with four molecules of caustic soda, it decom-
poses into phenol and carbon dioxide, while if eight molecules
are added the greater portion of it remains unaltered (Ost).

1 Oaz. Chim. Ital. xv. 219.

2 Ost, Journ. Prakt. Chcm. [2] xi. 391 .

3 v. d. Vclden, ibid. [2] xv. 151.



THE SALICYLATES. 303

Inversely, sodium parahydroxybenzoate is converted into
basic sodium salicylate, phenol and carbon dioxide, when it is
heated to 290 in a current of carbon dioxide, 1 while hydroxy-
isophthalic acid, C 6 H 3 (OH)(CO 2 H) 2 , and hydroxytrimesic acid,
C 6 H. 2 (OH)(C0 2 H) 3 , are formed at temperatures above 300.

When equal molecules of salicylic acid and its normal salt
are dissolved in alcohol and the solution concentrated, hard,
clear crystals of C 7 H 6 O 3 + C 7 H 5 NaO 3 are obtained, which are
converted by water into pseudomorphs of salicylic acid. 2

Lithium salicylate is converted into the basic salt at 300
without any formation of parahydroxybenzoic acid.

Thallium salicylate, C 6 H 4 (OH)CO 2 T1, is obtained by neutra-
lizing the acid with thallium carbonate ; its hot, concentrated
solution deposits coarse needles on cooling. If the calculated
quantity of thallium hydroxide be added to the solution, the
basic salt, C 6 H 4 (OT1)C0 2 T1, separates out in yellow, nacreous,
rhombic tablets, which are only very slightly soluble in water.
This compound is also formed, together with phenol, when the
normal salt is heated to 300, while at a higher temperature the
salicylic acid is partially converted into parahydroxybenzoic
acid and hydroxyisophthalic acid (v. d. Velden).

Ammonium salicylate, 2C 6 H 4 (OH)CO 2 NH 4 + H 2 0, forms
readily soluble, monoclinic crystals ; when heated in a current of
ammonia it decomposes into phenol and ammonium carbonate.
The methylamine and aniline salts behave in a similar manner,
while tetra-ethylammonium salicylate decomposes on heating
into tri-ethylamine and ethyl salicylate. 3

Calcium salicylate, (C 7 H 6 O 3 ) 2 Ca + 2H 2 O, is readily soluble in
water, and crystallizes in octohedra ; when it is heated with a
solution of calcium sucrate, or when salicylic acid is heated with
an excess of milk of lime, the basic salt, C 7 H 4 O 3 Ca -f- H 2 O, is
formed as a sandy, crystalline powder, which is almost insoluble
in water and has an alkaline reaction (Piria).

Barium salicylate, (C 7 H 5 3 ) 2 Ba + H 2 O, is obtained by boiling
the acid with water and barium carbonate ; it crystallizes in
stellate aggregates of silky needles. When baryta water is
added to its boiling concentrated solution, the slightly soluble,
alkaline, basic salt, C 7 H 4 O 3 Ba + 2H 2 O, separates out in small
plates or needles.

1 Kupferberg, Journ. Prakt. Chem. [2] xiii. 104.

2 Hofmann, Arch. Phann. [3] xii. 226.

8 Kupferberg, Journ. Prakt. Chem. [2] xvi. 437.



304 AROMATIC COMPOUNDS.

Lead salicylate, (C 7 H 5 O 3 ) 2 Pb + H 2 O, separates from boiling
water in transparent crystals ; when it is boiled with water, or
when lead acetate is added to its hot solution, a slightly soluble,
crystalline precipitate of C 7 H 4 O 3 Pb is formed. If, however,
ammonia be added, and the solution boiled, the basic salt,
2(C 7 H 4 O 3 )Pb + SP.bO, is formed ; it is a light powder consisting
of micaceous plates.

Copper salicylate, (C 7 H 5 O 3 ) 2 Cu + 4H 2 O, is best prepared by
decomposing the barium salt with copper sulphate ; it crystal-
lizes in long, bluish -green needles, which are readily soluble in
water, and on boiling with it form the basic salt, C 7 H 4 O 3 Cu + H 2 O,
which is a yellowish green powder.

Basic copper potassium salicylate, C 7 H 4 O 3 Cu + C 7 H 4 O 3 K 2 4-
4H 2 O, is formed by adding salicylic acid to a solution of copper
tartarate in tolerably strong caustic potash; a green mass of
crystals is formed, which is dried on a porous plate and re-
crystallized from a little lukewarm water. Small, emerald-green,
rhombic tablets are thus obtained, which are insoluble in alcohol,
and form a dark blue solution in caustic potash. When the
aqueous solution is boiled it becomes colourless and deposits
black copper oxide. Barium chloride produces, on standing, a
green, crystalline precipitate of C 7 H 4 O 3 Cu + C 7 H 4 O 3 Ba + 4H 2 O.

Silver salicylate, C 7 H 5 O 3 Ag, is a precipitate which crystallizes
from boiling water in very lustrous, transparent needles.

orondisalicylicacid,-B(OH)(OC 6 Ht.CO 2 W) 2 , is not known in
the free state ; its sodium salt is formed, along with free boric
acid, when four molecules of salicylic acid are added to a boiling
solution of one molecule of borax, as well as by dissolving a
mixture of equal molecules of boric acid, salicylic acid and
sodium salicylate :

/OH

HO - B< + HO.C 6 H 4 .C0 2 H + HO.C 6 H 4 .CO 2 Na =
\OH

/OC 6 H 4 .CO 2 H

HO-B< +2H 2 O.

\OC 6 H 4 .C0 2 Na

It forms crystalline crusts and is readily soluble in hot water
and alcohol. Its aqueous solution turns turmeric paper brown,
reddens litmus paper, and is coloured violet by ferric chloride ;
hydrochloric acid gives a precipitate of salicylic acid. Several



METHYLSALICYLIC ACID. 305

other of its salts have been prepared ; its barium salt is only
slightly soluble in boiling water. 1

2174 Methyl salicylate, C 6 H 4 (OH)C0 2 .CH 3 . Cahours, in 1843,
found that winter-green oil, obtained from Gaultherm procumbens
(Canadian tea), one of the Ericaceae, which occurs abundantly in
the north of the United States and in Canada, consists of this
compound together with small quantities of a terpene, and he
prepared the ether by distilling salicylic acid with wood-spirit
and sulphuric acid in order to compare the two products. 2 Since
as a phenol it forms metallic salts, it was called gaultheriaic
acid and methylsalicylic acid, the latter name being now given
to the following compound.

The ethereal oils of Gaultheria punctata and Gaultlieria
leucocarpa, which grow on the summits of extinct volcanoes
in Java, 3 and of Andromeda Lechenaultii, one of the Ericaceae,
which occurs abundantly in the Neilgherry Mountains in India, 4
consist almost entirely of methyl salicylate.

It is a liquid with a pleasant, refreshing odour, and boils at
217. Winter-green oil is largely used in America as a perfume ;
that obtained artificially, by heating salicylic acid with methyl
alcohol and sulphuric acid, does not possess the fine odour of the
natural product.

Methylsalicylic acid, C 6 H 4 (OCH 3 )CO 2 H. Cahours obtained
the methyl ether of this compound by the action of methyl
iodide and caustic potash on winter-green oil. It is a liquid
boiling at 244 246 (Schreiner). In order to prepare the acid,
two parts of methyl salicylate are heated to 100 120 with one
part of caustic potash and three or four parts of methyl iodide,
the product distilled in order to remove methyl alcohol and
methyl iodide, and the residue then extracted with caustic soda
and precipitated with hydrochloric acid. Any adhering salicylic
acid is removed by boiling with an excess of milk of lime,
insoluble basic calcium salicylate being precipitated, while
calcium methylsalicylate remains in solution, and is then
decomposed by hydrochloric acid. 5

Methylsalicylic acid crystallizes from hot water in large,
monoclinic tablets, and from alcohol in prisms, which melt at
98-5 and decompose above 200 into carbon dioxide and anisoil.

1 Jahns, Arch. Pharm. [3] xii. 212.

2 Ann. Chem. Phnrm. xlviii. 83 ; liii. 327.

3 de Vrii, Pharm. Journ. Trans. [3] ii. 503 ; Kohler, Ber. Deutsch. Chem. Ocs.
xii. 246. 4 Brougtiton, Pharm. Journ. Trans. [3] u. 281.

5 Grabe, Ann. Chem. Pharm. cxxxix. 137.
VOL. III. PART IV. x



306 AROMATIC COMPOUNDS.

On heating with concentrated hydrochloric acid, it is resolved
into salicylic acid and methyl chloride ; hydriodic acid has a
similar action.

The sodium salt of the acid is formed, together with a little
of the methyl ether and sodium salicylate, when winter-green
oil is heated with sodium :

C 6 H 4 .ONa C 6 H 4 .OH C 6 H 4 .OCH 3 C 6 H 4 .OH

I +1 =1 +1

C0 2 .CH 3 CO,.OH 3 CO 2 .CH 3 CO 2 Na.

Two molecules of the sodium compound then react in a
similar manner : l

C 6 H 4 .ONa C0 2 .CH 3 C 6 H 4 .OCH 3 CO.,Na

I + I =1 + I

C0 2 .CH 3 C 6 H 4 .ONa CO 2 Na C 6 H 4 .OCH 3 .



ETHEREAL SALTS OF SALICYLIC ACID.

Melting Boiling

point. point.

2 Ethyl salicylate, C 6 H 4 (OH)C0 2 .C 2 H 5 , liquid 223

3 Propyl salicylate, C 6 H 4 (OH)CO 2 .C 3 H 7 , liquid 239

4 Amyl salicylate, C 6 H 4 (OH)C0 2 .C 5 H 11 , liquid 270

5 Ethylene salicylate, (C 6 H 4 (OH)CO 2 ) 2 C 2 H 4 , needles 83

6 Propenyl salicylate, C 6 H 4 (OH)CO 2 C 3 H/OH) 2 , liquid



SALICYLIC ETHERS.

Melting-point.

7 Ethysalicylic acid, C 6 H 4 (OC 2 H 5 )C0 2 H, gradually) 19 . 4 o

solidifying oil j

8 Isopropylsalicylic acid, C 6 H 4 (OC 3 H 7 )C0 2 H, liquid .

9 Benzylsalicylic acid, C 6 H 4 (OC 7 H 7 )CO 2 H, small tablets 75

10 Ethylenesalicylic acid, C C) H 4 (OC 6 H 4 .C0 2 H) 2 , long ) 15r _ 152 c

needles \

1 Ann. Chcm. Pharm. cxlii. 327.

2 Baly, ibid. Ixx. 269 ; Schreiner, ibid, cxcvii. 17 ; Gottig, Ber. Deutsch.
Chcm. Ges. ix. 1473. 3 Cahours, Jahrenb. Chem. 1874, 333.

4 Drion, Ann. Chem. Pharm. xcii. 313. B Gilmer, ibid, cxxvii. 377.
fi Gottig, Ber. Deutsch. Chem. Ges. x. 1817.

7 Kraut, Ann. Chcm. Pharm. cl. 1 ; Gottig, Ber. Deutsch. Chcm. Ges. ix. 1474.

8 Kraut. 9 Perkin, Journ. Chem. Soc. xxi. 125.
10 Weddige, Journ. Prakt. Chcm. [2] xxi. 128.



ETHYL METHYLSALICYLATE. 307

ETHEREAL SALTS OF SALICYLIC ETHERS.

Boiling-point.

1 Ethyl methylsalicylate, C 6 H 4 (OCH 3 )CO 2 .C 2 H 5 , . 260

2 Methyl ethylsalicylate, C 6 H 4 (OC 2 H 5 )CO 2 .CH 3 , . 256 257

3 Ethyl ethylsalicylate, C 6 H 4 (OC 2 H 5 )CO 2 .C 2 H 5 , . 258 259

4 Methyl isopropylsalicylate, C 6 H 4 (OC 3 H 7 )CO 2 .CH 3 , 250

5 Methyl benzylsalicylate,C 6 H 4 (OC 7 H 7 )CO 2 .CH 3 , above 320

Melting-point.

6 Ethyl ethylenesalicylate, C 2 H 4 (OC 6 H 4 .C0 2 C 2 H 5 ) 2 , \ a fi _q-

thick plates - . . . . . . j

Phenyl salicylate, C 6 H 4 (OH)CO 2 .C 6 H 5 . Seifert 7 obtained this
compound by heating salicylic acid and phenol with phosphorus
oxychloride :

2C 6 H 4 (OH)CO 2 H + 2C 6 H 5 .OH + POC1 3 =

2C 6 H 4 (OH)CO,.C 6 H S + 3HC1 + HP0 3 .

A better yield is obtained by employing the sodium salts ; this
ethereal salt, known as salol, is manufactured by heating the
product of the action of carbon dioxide on sodium phenate with
phosphorus pentachloride or oxychloride :

C H 4 (OH)C0 2 Na + C 6 H 5 .ONa + PC1 5 =

C 6 H 4 (OH)C0 2 .C 6 H 5 + 2NaCl + POC1 3 .
2C 6 H 4 (OH)CO 2 Na + 2C 6 H 5 .ONa + POC1 3 =

2C 6 H 4 (OH)C0 2 .C 6 H 5 + SNaCl + NaPO 3 .

Salol crystallizes in rhombic prisms, which are odourless and
melt at 42 42'5 ; the dilute alcoholic solution, however, has
a smell resembling that of winter-green oil. It is employed in
medicine as a substitute for salicylic acid, because, as it is not
decomposed until it reaches the duodenum, it does not attack
the stomach like the former : when applied externally it has no
corrosive action, and, on account of its lower melting-point, it
can be more conveniently used for dressings, &c., than salicylic
acid.

1 Grabe ; Schreiner ; loc. tit. 2 Schreiner ; loe. cit.

3 Gottig ; Schreiner ; loc. cit. * Kraut ; loc. cit.

8 Ferkiii ; loc. cit. 6 Wcddige ; loc. cit.

7 Journ. Prafct. Chcm. [2] xxxi. 462.

x 2



308 AROMATIC COMPOUNDS.



Phcnyl methylsalicylatc, C 6 H 4 (OCH 3 )C0 2 .C 6 H 5 , was prepared by
Seifert in a similar manner ; it crystallizes in six-sided prisms,
melting at 59.

Acetylsalicylic acid, C 6 H 4 (O.CO.CH 3 )CO 2 H, is formed by the
action of acetyl chloride on salicylic acid or its sodium salt, and
crystallizes from hot water in fine needles, melting at 118
118'5. Its aqueous solution gives a violet colouration with
ferric chloride ; when the acid is heated with ammonia, ammo-
nium salicylate is formed, but no salicylamide (Kraut).

/\

Salicyl Moraldidc, C 6 H / >CH.CC1 3 , is formed when

\CCK

salicylic acid is heated to 130 150 for a long time with an
excess of chloral. It is insoluble in water, slightly soluble in
alcohol and ether, and crystallizes from the latter in prisms,
melting at 124 125 . 1

Disalicylic acid, (C 6 H 4 .C0 2 H) 2 O. This compound, which is
also called salicylic anhydride, or salicylosalicylic acid, was ob-
tained by Gerhardt by the action of phosphorus oxychloride on
sodium salicylate. 2

It is also formed when acetylsalicylic acid is heated, or when
salicylic acid is heated for a long time to 130 140 with acetyJ
chloride. 3 It is an amorphous mass, which dissolves in the
alkaline carbonates and is reprecipitated by acids. It gives no
colouration with ferric chloride ; aqueous ammonia converts it
into salicylamide and ammonium salicylate, while potassium
salicylate is formed by the action of caustic potash.

Salicylide, C 7 H 4 O 2 , is formed by heating salicylic acid with
phosphorus oxychloride :



= C 6 H 4 + H 2 0.



It crystallizes from absolute alcohol in spherical aggregates of
lustrous plates, which melt at 195 200; it gives no colour-
ation with ferric chloride, and is converted into salicylic acid by
the action of caustic potash. 4

Tetrasalicylidc, C 28 H 18 9 , is formed at the same time as the
preceding compound, and is a resinous mass insoluble in
alcohol.

1 Wallach, Ann. Chem. Pharm. cxcvii. 41. " Ibid. Ixxxvii. 159.

3 Kraut, ibid. cl. 13. 4 Schiffj ibid _ clxilL 2 20.



SALICYLHYDROXYACETIC ACID.



Salicylhydroxyacetic acid, C 6 H 4 (OCH 2 CO 2 H)CO 2 H, is obtained
by oxidizing ortho-aldehydophenox-yacetic acid (p. 289) with
potassium permanganate. It crystallizes from hot water in
white needles, melting at 186 187. It forms readily soluble
salts which crystallize well. 1

21 75 The Action of Phosphorus Pentachloride upon Salicylic
Acid. As already mentioned, Chiozza found, in 1852, that when
salicylic acid is treated with phosphorus pentachloride and
the product distilled, the distillate yields orthochlorobenzoic
acid when treated with water (p. 217). Gerhardt repeated this
experiment, and found that the liquid before distillation is
salicyl chloride, C 7 H 5 O 2 C1, as it is converted by water into sali-
cylic acid, and by alcohol into an ethereal salt of this ; he also
obtained it together with methyl alcohol by treating winter-green
oil with phosphorus pentachloride. 2 Drion made the further
observations that only a trace of phosphorus oxychloride is
formed in this reaction, and that a portion of the product is
converted into chlorobenzoyl chloride by distillation. 3

Couper, however, obtained different results. He acted upon
one molecule of methyl salicylate with two molecules of phos-
phorus chloride, and distilled the resulting liquid ; the excess of
the chloride came over first, followed by a liquid distilling between
285 295, to which he gave the name of salicyl trichlorophos-
phate, explaining its formation by the following equation :

C 8 H 8 3 f PC1 5 = HC1 + CH 3 C1 + C 7 H 4 C1 3 P0 3 .

This compound, which he also obtained from salicylic acid, is
decomposed by water into hydrochloric acid, phosphoric acid
and salicylic acid :

C 7 H 4 C1 3 P0 3 + 4H 2 O = 3HC1 + H 3 PO 4 + C 7 H 6 O 3 .

When he submitted it to rapid distillation, a considerable
quantity of hydrochloric acid was evolved, and the distillate
consisted of a liquid boiling above 300, which deposited large
crystals of salicyl monochlorophosphatc, C 7 H 4 C1PO 4 , when pre-
served in a sealed tube ; this substance, like the trichlorophos-
phate, is converted into phosphosalicylic acid, C-H 7 P0 6 , in moist
air. He therefore considered that the existence of salicyl

1 Rossing, Bcr. Dcutsch. Chcm. Gc.. xvii. 2988.
3 Ann. Chcm. Pharm. Ixxxix. 363.
3 Ibid. xcii. 312.



310 AROMATIC COMPOUNDS.

chloride, no analyses of which, had been published, was very
doubtful. 1

Drion replied to this, that although the latter compound had
not been obtained in a state of purity, its existence was proved
by the fact that ethers of salicylic acid are formed by the action
of alcohol upon it. 2

Kolbe and Lautemann came to the same conclusion. Accord-
ing to them, a mixture of chlorobenzoyl chloride, salicyl chloride
and chlorosalicyl trichloride is obtained by distilling salicylic
acid with phosphorus pentachloride. 3 Kekule, who investigated
this reaction at about the same period, found that when the
product is heated to 180 200 to remove phosphorus chloride
and oxychloride, a liquid remained which yielded salicylic acid and
traces of chlorobenzoic acid when decomposed by water. It also
contained 3 per cent, of phosphorus, and considerably more chlorine
than corresponds with the composition of salicyl chloride ; on dis-
tillation he obtained considerable quantities of phosphorus
oxychloride and chlorobenzoyl chloride, but not Couper's com-
pound. 4

It therefore became the generally accepted view, that the
following compounds are formed by the action of phosphorus
pentachloride on salicylic acid :

Salicyl chloride. Chlorobenzoyl chloride. Chlorobenzenyl trichloride.

/OH /Cl /Cl

C 6 H / C 6 H 4 < C H 4 <

\COC1 \COC1 \CC] 3 .

The salicyl chloride could not be obtained pure because it
decomposed on distillation, and could not therefore be freed
from chlorobenzoyl chloride and phosphorus oxychloride ;
according to Miquel, it adheres most obstinately to the
latter. 5

The solution of the problem was found by Anschiitz, who, by
bringing together equal molecules of salicylic acid and phos-
phorus pentachloride, obtained an evolution of hydrochloric acid
and a yellow liquid, which distilled under a pressure of 11 mm.
as a colourless, refractive liquid, only a small quantity of residue
being left. This has the composition of Couper's salicyl tri-



Ann. Chem. Pharm. cix. 369. 3 JUd. cix. 373.

Ibid. cxv. 183. 4 Ibid, cxvii. 14S.

Ann. Chim. Phys. [5] xi. 30-1.



ORTHOCHLOROCARBONYLPHENYL METAPHOSPHATE. 311

chlorophosphate and is orthocarbonylphenylphosphoryl chloride,
formed according to the following equations :

/OH OH

C 6 H 4 < + PC1 5 = C 6 H 4 < + POOL + H 2 0.

\CO.OH \coci

The phosphorus oxychloride then acts upon the salicyl chloride



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