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while its copper salt yields azobenzene on dry distillation. 6

Metaliydrazobenzoic acid was obtained by Strecker by adding
ferrous sulphate and then hydrochloric acid to an alkaline
solution of the azo-acid. It is also formed by the continued
action of sodium amalgam and other reducing agents. It is
amorphous, insoluble in water, and only slightly soluble in
alcohol. It is readily oxidized in alkaline solution to the
preceding compound and, like hydrazobenzene, undergoes an
intramolecular change (Part III., p. 357), when it is boiled
with concentrated hydrochloric acid, diamidodiphenic acid,
C 12 H 6 (NH 2 ) 2 (C0 2 H) 2 , being formed. 7

Parazdbenzoic acid 'is almost insoluble in alcohol, water and
ether, and forms a yellow or reddish precipitate, which becomes
granular on boiling and melts at about 240. 8 The barium salt
is a flesh-coloured precipitate; azophenylene is formed when
the calcium salt is distilled (Glaus).

Parahydrazolenzoic acid is insoluble in water and crystallizes .

Griess, Juhresber. 1864, 352. 2 Ann _ CJlcm p^ rm- cvi> 70-

nnd. cxxviii. 267. 4 Ibid _ cxxix> 129>

Sokolow, Journ. Prakt. Chem. xciii. 425 : Liebert, ibid, xciii 429
Claus, Ber. Dcutsch. Chcm. Ges. viii. 41
Griess, ibid. vii. 1609 ; Schultz, Ann. Chem. PJiarm. cxcvi. 18.

Beilstein ' Ann ' Chem - Ma- cxxix. 144 ; Bilfinger, ibul



DIAZOXYBENZOIC ACID. 267

from alcohol in needles; its alkaline solution absorbs oxygen
with formation of the azo-acid.

/ N \

Diazoxylenzoic acid, (V | ^>C 6 H 3 .CO 2 H. When S-dinitro-
\N/

benzoic acid is dissolved in caustic soda and treated with sodium
amalgam, the liquid becomes coloured black but remains perfectly
clear, appearing brown when diluted. Acids added to this solu-
tion precipitate diazoxybenzoic acid a& an amorphous, black
powder, which is insoluble in water, alcohol, ether, &c., and
detonates feebly on heating. The alkali salts form black solu-
tions in water ; the salts of other metals are black precipitates.
The barium salt, when dried at 70, becomes so strongly electrified
that the particles continue in motion for hours; it loses this
property at a higher temperature. Tin and hydrochloric acid
reduce the acid to 8-diamidobenzoic acid.

Isodiazoxybenzoic acid is obtained from /3-dinitrobenzoic acid
and resembles the preceding compound, but is not attacked by
tin and hydrochloric acid. 1

Azonitromethanebenzoic acid, N0 2 .CH 2 N NC 6 H 4 .CO 2 H, is
formed when an aqueous solution of pure metadiazobenzoic
acid nitrate is mixed with a- dilute solution of nitroniethane
in caustic potash, and the whole treated with an excess of
hydrochloric acid after standing for some time. It is readily
soluble in hot alcohol and ether, slightly in boiling water,
and crystallizes in stellate groups of yellowish-red plates,
which are almost tasteless and detonate on heating. Silver
nitrate added to its ammoniacal solution produces a deep red
precipitate. 2

N.C^.CO^H

Azo-aceto-acetic benzoic acid, \\ , is obtained

N.CH(CO.CH 3 )CO 2 H

by the action of metadiazobenzoic acid sulphate on aceto -acetic
ether, the method described for the preparation of the preceding
compound being followed. It is thrown down by hydrochloric
acid as a light yellow precipitate consisting of microscopic
spheres, and is insoluble in boiling water, crystallizing from hot
alcohol in narrow plates or small needles, which have a bitter
taste. On careful heating it fuses to an oil, which solidifies on
cooling to a waxy mass, but at a higher temperature it detonates

1 Meyer and Michler, Ann. Chcm. Phccrm. clxxv. 152 ; J3er. Deuisch. Chcm.
6V.S-. vi. 7-16, vii. 422.

2 Griass, ibid, xviik 961,



268 AROMATIC COMPOUNDS.

feebly, a large quantity of carbon separating out. Its silver salt
is a light yellow, amorphous precipitate.

NC 6 H 4 .C0 2 H
Azomalonic-benzoic acid, \ . Griess obtained this

NCH(C0 2 H) 2

compound in a similar manner from malonic ether. Hydrochloric
acid separates it from the product as an amorphous, fiery yellowish
red precipitate, which crystallizes from hot alcohol in microscopic
plates. On heating it froths up and chars.



/S0 3 H
MONOSULPHOBENZOIC ACIDS, C 6 H 4 <

\COOH.

2153 Orthosiilphobenzoic acid is formed, together with ortho-
sulphamidobenzoic acid, when orthotoluenesulphamide is oxidized
with potassium permanganate. On the addition of hydrochloric
acid to the filtrate, the anhydride of the sulphamide separates
out, while acid potassium orthosulphobenzoate remains in solu-
tion and is deposited in large monoclinic tablets. 1

It may also be obtained by heating the diazo-compound of
anthranihc acid with an alcoholic solution of sulphur dioxide. 2

It crystallizes from water in large, monoclinic tablets, which do
not deliquesce in the air and melt at 240 with decomposition.
On fusion with caustic potash salicylic acid is formed. 3

Acid barium orthosulphobenzoate, (C 7 H 5 SO 3 ) 2 Ba + 2H 2 O,
crystallizes in needles, and is less soluble in water than the
normal salt.

Orthosulphamidobenzoic acid is not known in the free state, as
when it is liberated from its salts by the addition of an acid it is
immediately converted into the anhydride :

/S 0,NH 2

= C 6 H/ >NH + H,0.
CO.OH NC3/



\



This body is slightly soluble in cold, more readily in hot water
and alcohol, and forms crystals which melt at 220 and are

1 Eemsen, Ann. Chem. Pharm. clxxviii. 293 ; Fahlberg and Remsen, Bcr.
Dcutsch. Chem. Oes. xii. 471.

2 Wiesinger, ibid. xii. 1349. 3 Bottinger, ibid. viii. 374.



SACCHAEIN. 269



sweeter than sugar. The salts, which are readily soluble in
water, have also a sweet taste. When the anhydride, which is
called Unzoylsulphimide, is heated to 150 with hydrochloric
acid, it is converted into orthosulphobenzoic acid. It is not
attacked by phosphorus pentachloride.

According to Fahlberg and List a it is a powerful antiseptic,
and, since a very dilute solution of it is as sweet as a concen-
trated solution of cane sugar, they believe that it may find an
extended application. It could thus be used as a sweetening
agent in the diet of patients suffering from diabetes and in
many other cases as a cheap substitute for sugar. They propose
for it the unsuitable name of saccharin, which has also been
given (Part II., p. 648) to the lactone of saccharinic acid.

2154 Metasulphdbenzoic acid. In 1834 Mitscherlich found
that benzoic acid combines with anhydrous sulphuric acid, SO 3 ,
to form an acid which can be heated to above 150, and boiled
with water without decomposition. Its barium salt can also be
boiled with caustic potash without losing sulphuric acid. He
says, " I propose to name it provisionally benzoylsulphuric acid,
since the complexity of its composition necessitates a name
which gives a clue to its constitution without indicating it
fully." 2

Fehling, who investigated its salts more closely, observed that
when heated with an excess of caustic potash until complete
decomposition has taken place, it yields a residue containing
both sulphite and sulphate of potassium, a behaviour which
is characteristic of the salts of hyposulphuric acid. " This acid,
therefore, contains hyposulphuric and not sulphuric acid," and he
therefore called it benzoylhyposulphuric acid. 3

It was then investigated with great care by Limpricht and
v. Uslar, who recognised it as a sulphonic acid. 4

It is also formed by the action of sulphuric acid on benzonitril 5
and benzoyl chloride, 6 as well as by heating the latter with silver
sulphate ; 7 and by treating metadiazo-amidobenzoic acid with
an alcoholic solution of sulphur dioxide. 8

1 Journ. Soc. Chem. Ind. iv. 608 ; Bcr. DeutscJi. Chem. Ges. xix. Ref. 374.

2 Ann. Chem. Pluirm. xii. 314.

3 Ibid, xxvii. 322.

4 Ibid. cii. 239 ; cvi. 27.

5 Buckton and Hofmann, ibid. c. 155.

6 Oppenheim, Ber. Deutsch. Chem. Ges. iii. 735.

7 Carius and Kammerer, Ann. Chem. Pliarm. cxxxi. 155 ; Ador and Oppenheim,
Ber. Dmitsch. Chem. Ges. iii. 738 ; Kiimmerer, ibid. iv. 219.

8 Vollbrecht and Wiesinger, ibid. x. 715.



270 AROMATIC COMPOUNDS.

In order to prepare metasulphobenzoic acid, the vapour of
sulphur trioxide is passed over benzoic acid, which has been
previously fused and powdered, until a transparent mass is
formed ; or two parts of benzoic acid are heated with one part
of fuming sulphuric acid for some time. The product then
contains some parasulphobenzoic acid in addition to metasulpho-
benzoic acid and free sulphuric acid. 1 It is diluted with water,
neutralized with barium carbonate and filtered, the nitrate being
then heated and treated with hydrochloric acid. The acid salt
of the para-acid crystallizes out first on cooling, and then that of
the meta-acid, which is purified by recrystallization. The product
of the reaction may also be saturated with milk of lime, the
filtrate treated with potassium carbonate, and the potassium salt
which is thus obtained, recrystallized. 2 Metasulphobenzoic acid is
a colourless, crystalline mass, which deliquesces in moist air, but
solidifies again in dry air. It is not altered by boiling nitric
acid. On fusion with potash, metahydroxy benzoic acid is formed
(Earth), while with sodium formate it yields isophthalic acid
(v. Meyer).

The MctasuJphobenzoates. Metasulphobenzoic acid is a power-
ful dibasic acid, which decomposes even barium chloride and
barium nitrate. Its normal salts are usually readily soluble,
while the acid salts dissolve much less easily.

Normal potassium metasulphobenzoate, C 7 H 4 S0 5 K 2 , forms de-
liquescent crystals ; the acid salt, C 7 H 5 SO 5 K, crystallizes in long
needles, which contain two and half or five molecules of water
and are readily soluble in water and alcohol. 3

Normal barium metasulphobenzoate, C 7 H 4 SO 5 Ba + 3H 2 0, is
very soluble, and can with difficulty be obtained in well-
developed crystals ; it is usually deposited in crusts. The acid
salt, (C 7 H 5 SO 5 ) 2 Ba + 3H 2 O, dissolves in 20 parts of cold water,
readily in hot water and alcohol, and crystallizes in monoclinic
prisms.

Normal lead metasulphobenzoate, C 7 H 4 S0 5 Pb + 2H 2 O, is much
more readily soluble in hot water than in cold, and forms fine,
radiating crystals, resembling those of wavellite.

Silver metasulphobenzoate, C 7 H 4 SO 5 Ag 2 4- H 2 0, crystallizes in
yellow prisms which readily dissolve.

Normal ethyl metasulphobenzoatc, C 7 H 4 SO 5 (C. 2 H 5 ) 2 , is prepared
from the chloride of the acid and absolute alcohol, and forms a

1 Ann. Chem. Pharm. clxxviii. 27 f>.

2 Earth, ibid, cxlviii. 33. 3 Otto, ibid, cxxii. 155.



MONOSULPHOBENZOIC ACIDS. 271

thick liquid which has a faint ethereal odour, and decomposes on
heating. It is soluble in water, and its solution decomposes
when heated into alcohol and the acid.

Acid ethyl metasulphobenzoate or Ethyl metasulphdbenzoic acid,
C 7 H 5 S0 5 .C 2 H 5 . The ammonium salt of this acid, C 7 H 4 SO 5
(NH 4 ).C 2 H 5 , is obtained by passing ammonia into an alcoholic
solution of the normal ether or by the action of alcoholic
ammonia on the chloride. It crystallizes in large, four-sided,
transparent tablets. If the ammonia be precipitated with
platinum chloride, and the excess of platinum removed by
sulphuretted hydrogen, a solution of the free acid is obtained ;
its salts crystallize well and are readily soluble. Its constitution
is probably represented by the former of the two following
formulae :

S0H /SCLCpHs

C 6 H/
2 H 5 \CO 2 H

Metasulphobenzoyl chloride, C 7 H 4 SO 3 C1 2 , is obtained by heating
the dry acid with phosphorus pentachloride ; the phosphorus
oxychloride is then distilled off and the residue washed with
water. It is a thick, oily liquid, which has a faint but unpleasant
odour, and decomposes on distillation into sulphur dioxide and
metachlorobenzoyl chloride. The latter is also formed when the
compound is heated to 140 150 with phosphorus pentachloride.
When it is allowed to stand for some time in contact with water
or when the acid is acted upon by one molecule of phosphorus
pentachloride, the monochloride is formed :

/S0 2 .OH /S0 9 C1

/ or C 6 H 4 <

\COC1 \CO.OH

This separates from ether in warty masses, and is decomposed
by boiling water, &c., with formation of metasulphobenzoic
acid.

Metasulphobenzamide, C 7 H 4 SO 3 (NH 2 ) 2 , is formed by the action
of concentrated aqueous ammonia on the chloride. It is almost
insoluble in cold water and crystallizes from hot water or ordinary
alcohol in needles containing a molecule of water, while it
separates from absolute alcohol in small, vitreous, anhydrous
crystals.



272 AROMATIC COMPOUNDS.

When it is heated with phosphorus pentachloride the following
reaction takes place :

/SO 2 NH 2 . /SO 2 .NH 2

C 6 H 4 < + PC1 5 = C 6 H 4 < + POC1 3 + HC1.

\CC1=NH



The imido-chloride which is thus formed has not been obtained
pure ; l it decomposes on distillation with formation of meta-
chlorobenzonitril, while ammonia or water converts it into
sulp/iamidobenzonitril, CN.C 6 H 4 .S0 2 .NH 2 , which separates from
alcohol in crystals, melting at 152 153.

Metasulphamiddbenzoic acid, C 7 H 7 NS0 4 , is formed when the
nitril or amide is heated with caustic potash solution :

/S0 2 .NH 2 /SO 2 .NH 2

C 6 H 4 < + KOH = C 6 H 4 < + NH 3 .

\CO.NH 2 \CO.OK

It is slightly soluble in cold water, and crystallizes from a
hot solution in scales resembling those of potassium chlorate,
and melting above 200. It is a monobasic acid, and forms
crystallizable salts.

Ethyl metasulphamiddbenzoate, C 7 H 6 (C 2 H 5 )NSO 4 , is obtained
by heating the silver salt with ethyl iodide, or by passing hydro-
chloric acid into an alcoholic solution of the acid. It is also
formed when ammonia is passed into a solution of sulphobenzoyl
chloride in a mixture of alcohol and ether. It crystallizes from
alcohol in monoclinic prisms. 2

xSH

Metatkiohydrobenzoic acid, C 6 H 4 <^ , is prepared by the

X C0 2 H

action of tin and hydrochloric acid on metasulphobenzoyl chloride.
It is tolerably soluble in water, more readily in alcohol, and
sublimes, when heated in a current of carbon dioxide, in flat
needles, melting at 146 147. It oxidizes when exposed to the
air in a moist state, or more rapidly when acted upon by bromine
water, to metadithiobenzoic acid, S 2 (C 6 H 4 .C0 2 H) 2 , which is scarcely
soluble in water, and only slightly in alcohol, crystallizing from
the latter in short needles which melt at 24G 247 . 3

1 Huth and Wallacli, Ber. Dcutech. Chem. Gcs. ix. 427.

' Hart, Amer. Chem. Journ. i. 342.

3 Frehrichs, Ber. Deutsch. Chem. Ges. vii. 792.



PARASULPHOBENZOIC ACID. 273

2155 Parasulphobcnzoic acid is obtained by the oxidation of
paratoluenesulphonic acid ; it is not necessary to employ pure
material for its preparation, and the mixture of the three isomeric
acids which is obtained by dissolving toluene in sulphuric acid
may be conveniently made use of. The para-compound is the
chief constituent of the mixture, and, together with the meta-
acid, is readily oxidized, while the ortho-acid remains unaltered
(Remsen).

Ono hundred grammes of toluene are dissolved in the smallest
possible quantity of fuming sulphuric acid, the solution made up
to five litres with water, and heated until it becomes colourless.
Hydrochloric acid and barium chloride are then added to the
filtrate and the precipitated acid barium salt purified by re-
crystallization ; 200 grammes of it are obtained in this way. 1

It is also formed by the action of alcoholic sulphurous acid on
paradiazobenzoic acid (Vollbrecht and Wiesinger).

Parasulphobenzoic acid is readily soluble in water, and
crystallizes in needles, which are not deliquescent and melt
with decomposition at about 200. On fusion with caustic
potash, parahydroxybenzoic acid is formed, while with potas-
sium formate it yields terephthalic acid.

. The potassium salt forms transparent needles which easily
dissolve.

Normal barium parasulphobenzoate, C 7 H 4 SO 5 Ba + 2H 2 O,
crystallizes in small, tolerably soluble needles. The acid salt,
(C 7 H 5 SO 5 ) 2 Ba + 3H 2 O, is slightly soluble in hot water, and
forms long, flat, lustrous needles.

X S0 2 .NH 2

Parasulphamidobenzoic acid, C,,H,\ , is formed by

\CO.OH

the oxidation of paratoluenesulphamide with chromic acid
solution. It is almost insoluble in cold, slightly soluble in hot
water, and readily in alcohol, crystallizing in long, flat, lustrous
prisms.

1 Hart, loc. cit.



III. PA11T IV



274 AROMATIC COMPOUNDS.



/SO,H
DISULPHOBENZOIC ACIDS, C 6 H,f-CO 2 H.

\S0 3 H

2156 a-Disulphobenzoic acid (2 : 4) is obtained by the oxida-
tion of a-toluenedisulphonic acid. 1 It is readily soluble in
water, insoluble in alcohol, and is deposited from solution in
concentrated hydrochloric acid in large crystals, melting above
285. On heating to 250 with caustic potash, the asymmetric
dihydroxybenzoic acid melting at 204 is formed ; at a higher
temperature resorcinol is obtained.

(3-Disulplwbenzoic acid. (3 : 5) is formed when benzoic acid is
heated to 250 with fuming sulphuric acid and phosphorus
pentoxide. It is a white, hygroscopic, crystalline mass, which
on fusion with potash yields the asymmetric dihydroxybenzoic
acid, which melts at 232 233, while resorcinol is formed when
it is heated to 350 with caustic soda. 2

Both compounds are strong tribasic acids.

S0 3 H
CHLOROSULPHOBENZOIC ACIDS, C r H q Cl<

\C0 2 H

2157 Four of these compounds are known. The first is obtained
by the oxidation of orthochlorotoluenesulphuric acid, 3 the second
by the action of sulphur trioxide on metachlorobenzoic acid, 4
and the last two, one of which only has been examined, from
parachlorobenzoic acid. 5



BROMOSULPHOBENZOIC ACIDS, CJELBr



One of these derivatives has been prepared by the oxidation
of orthobromotoluene, 6 a second from metabromobenzoic acid
and sulphur trioxide, 7 and two others by the oxidation of the
isomeric parabromotoluenesulphonic acids, 8 one of them having
been also obtained from parabromobenzoic acid. 9

1 Blomstrand, Her. Deutsch. Chem. Ges. v. 1084 ; Fahlberg, Amcr. Chcm.
Journ. ii. 181. 2 Barth and Senhofer, Ann. Chem. Pharm. clix. 271.

" Hiibner and Majert, Ber. Deut.ch. Chcm. Gcs. vi. 792.
Otto, Ann. Chem. Pharm. cxxiii. 216.
Bottinger and Collen, ibid. cxci. 29.
Hiibner and Retschy, ibid, clxix. 45.

Hiibner and Upmann, Zeitsch. Chem. 1870, 295 ; Hiibner and Lcnnep, ibid.
1871, 67. s Hiibner and Post, Ann. Chcm. Pharm. clxix. 6.

u Bottinger, ibid. cxci. 13.



XITROSULPHOBENZOIC ACIDS. 275



NITROSULPHOBENZOIC ACIDS,



2158 Mulder, as early as the year 1840, prepared a nitro-
sulphobenzoic acid by the action of fuming sulphuric acid on
metanitrobenzoic acid, but did not investigate it. Limpricht
and v. Uslar then obtained one by the nitration of meta-
sulphobenzoic acid. 1 Remsen prepared another from parasulph-
amidobenzoic acid 2 in the same way, and Hart obtained the
same compound by nitrating parasulphobenzoic acid. He also
prepared another isomeride from orthosulphobenzoic acid and
two additional ones by the oxidation of the corresponding nitro-
toluenesulphonic acids.



AMIDOSULPHOBENZOIC ACIDS.

Two of these compounds have been obtained by the action of
sulphuric acid on metamidobenzoic acid. 3 One of these and
three others are formed when the corresponding nitrosulpho-
benzoic acids are reduced. 4



/PO(OH),
BENZOPHOSPHINIC ACID, C a H 4 <

X CO.OH

2159 This body may be readily obtained by dissolving 10
grams, of paratolylphosphinic acid in a litre of water, adding an
excess of caustic potash, heating to 50, and then running in a
solution of 18'4 grams, of potassium permanganate. The latter
is completely reduced after about a week, and the solution is
then filtered, acidified with acetic acid and evaporated. The
potassium acetate is extracted from the residue by alcohol, and
the residual acid potassium benzophosphinite dissolved in hot,
concentrated hydrochloric acid, the benzophosphinic acid being

1 Bbttinger, Ann. Cfwm. Pharm. cvi. 27.

2 Ibid, clxxviii. 288 ; Hart, Amr.r. Cham. Journ. i. 342.



:i Griess, Journ. Prakt. Chcm [2] v. 241.
4 Limpricht and v. Uslar ; Hart.



T '2



276 AEOMATIC COMPOUNDS.

deposited from this solution on cooling in transparent, lustrous.
striated tablets, which are readily soluble in water, and crystal-
lize from it in matted needles with a satin lustre.

It melts above 300, and decomposes when more strongly
heated, one portion becoming carbonized while the remainder
decomposes into benzoic and metaphosphoric acids. It is not
attacked by bromine and water at 130, while tolylphosphinic
acid is decomposed by these at the ordinary temperature into
phosphoric acid and bromotoluene.

It is a tribasic acid, but readily forms acid salts.

Acid potassium lenzophosphinale, C 6 H 4 (PO 3 H 2 )CO 2 K + H 2 O,
crystallizes in fine needles, which are readily soluble in water,
slightly in alcohol. When hydrochloric acid is added to its
solution, the double salt, C 6 H 4 (P0 3 H 2 )CO 2 K+C 6 H 4 (P0 3 H 2 )C0 2 H,
separates out ; it crystallizes from hot water in small prisms. It
may also be obtained as a precipitate resembling cream of tartar,
by adding the free acid to a tolerably concentrated solution of a
potassium salt.

Silver benzophosphinate, C 6 H 4 (PO 3 Ag. 2 )CO 2 Ag, is obtained as
an amorphous precipitate by adding silver nitrate to a
solution of the acid neutralized with ammonia. On heating
with methyl iodide, the methyl ether is formed as a thick liquid,
which decomposes on boiling.

BenzopJiosphine chloride, C 6 H 4 (POC1 2 )COC1, is formed by the
action of phosphorus chloride on the acid ; it is a crystalline
mass, melts at 83, boils at 315, and is attacked by cold water,
but is readily decomposed by boiling water. 1

TrimethylplwspJiobenzobetalne, C 6 H 4 (CO.O)P(CH 3 ) 3 + 3H 2 0.
The chloride of this compound is formed by the oxidation of
trimethylparatolylphosphonium chloride with potassium per-
manganate :

CR CO.OH



\P(CH 3 ) 3 C1 \P(CH 3 ) 3 C1

It crystallizes in short, lustrous prisms, which are readily
soluble in water, less so in alcohol. The base, which is liberated
by alkalis, crystallizes from hot alcohol in rhombohedra, which
deliquesce in the air. When the chloride is heated with an
excess of caustic potash solution it decomposes with formation
of benzoic acid and trimethylphosphine oxide.

1 Michoelu and Panek, Her. DeutmJi. Chcm. Ges. xiv. 405.



BENZ ARSENIC ACIDS. 277

Dimethylphosphine-oxide benzoic acid, C 6 H 4 .PO(CH 3 ) 2 .CO 2 H, is
formed by the oxidation of dimethyltolylphosphine oxide, and
crystallizes in prisms which have a feebly acid taste, melt at
243, sublime almost without decomposition, and are not easily
attacked by caustic potash solution. 1



BENZARSENIC ACIDS.

2160 Benzarsenic acid,, C 6 H 4 (As0 3 H 2 )CO 2 H, is obtained by
oxidizing paratolylarsenic acid in alkaline solution. It is only
slightly soluble in water, and crystallizes in large, transparent
tablets or nacreous plates. On heating the anhydride, arseno-
lenzoic acid, C 6 H 4 (AsO 2 )CO 2 H, is formed ; this compound, which
corresponds to paranitrobenzoic acid, is a yellowish powder,
soluble in hot alcohol.

Acid potassium benzarsenate, C e H 4 (AsO 3 H 2 )CO 2 K + C c H 4
(As0 3 H 2 )C0 2 H, crystallizes from hot water in transparent,
triclinic tablets.

.AsOCOHjCK

Acid calcium benzar 'senate, C 6 H 4 <^ ^>Ca + H,O>

\CO CK

forms nacreous plates, slightly soluble in water.

Silver benzarsenate, C 6 H 4 (As0 3 Ag 2 )CO 2 Ag, is an amorphous
precipitate, which yields the crystalline methyl ether on heating
with methyl iodide.

Benzarsene chloride, C H 4 (AsCl 2 )C0 2 H, is obtained by the
action of phosphorus trichloride on the acid :

C 6 H 4 (As0 3 H 2 )C0 2 H + 2PCl 3 =
G x 6 H 4 (AsCl 2 )COCl + POC1 3 + P(OH) 3 .

The product of the reaction is carefully treated with water,
and yields the chloride, crystallizing in needles, which melt at
157 158, and are decomposed by boiling water.

Benzarsene iodide, C 6 H 4 (AsI )CO H, is formed by the action of
hydriodic acid and phosphorus on the acid, and crystallizes from
chloroform in yellow needles, melting at 153.

Bcnzarsenious acid, G 6 H 4 As(OH) 2 CO 2 H, is prepared by dis-
solving the iodide in carbonate of soda and precipitating with
hydrochloric acid ; it is thrown down in crystals, and crystallizes
1 Miuluiclis and Czimatis, Bcr. Dcuteck. Chem. Gcs. xv. 201S.



978 AROMATIC COMPOUNDS.

from hot water in fine needles, which are converted into the
anhydride, C 6 H 4 (AsO)CO 2 H, at 160.



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