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for benzoic acid, but which he subsequently found to be identical
with the hippuric acid discovered by Liebig. 11 Under his direc-
tions Keller conducted a research on the subject, taking 2 grains
of benzoic acid in the evening and repeating the dose three times
daily during the following days. His urine, which now possessed
a strongly acid reaction, contained a considerable amount of
hippuric acid, and, as Wohler says, " since benzoic acid seems

Ann. Chc.m. Pharm. Ixxvii. 17. 2 Ibid. cv. 209.

Chem. Ccntralbl. 1858, 831.
Schwarz, Ann. Chcm. Pharm. liv. 31.

Henneberg, Stohmann and Rautenberg, ibtf. cxxiv. 201. 6 Ibid. xc. 378.
NewEdinb. Phil. Journ. xlv. 17.
Salkowski, Bcr. Dcutsch. Chcm. G-cs. xi. 500.

Boussingault, Ann. Chim. Phys. [3] xv. 97 ; von Bibra, Ann. Chcm. PJiarm.
liii. 98.

30 Invert. PJiarm. xxvii. 642.
11 Berzelius, Lehrb. Chcm. 1831, iv. 376.






HIPPUEIC ACID. 185



not to affect the health, large quantities of hippuric acid might
readily be prepared in this manner, the only requisite being a
man who would continue the manufacture for weeks. 1 These
observations were confirmed by Garrod,* Schwarz and others ;
Marchaud found 39 2 grains of hippuric acid in his urine after
eating 30 grains of benzoic acid. 3

Many other compounds, which are converted into benzoic acid
by oxidation, are changed into hippuric acid by their passage
through the organism ; such are benzaldehyde, 4 cinnamic
acid, 5 CgH^.CHzziCH.COgH, hydrocinnamic acid or phenylpro-
pionic acid, 6 C 6 H 5 .C 2 H 4 .GO 2 H, phenylglycollic acid, 7 C 6 H 5 .CH
(OH)CO 2 H, quinic acid, 8 C 6 H 7 (OH) 4 CO 2 H, and even toluene. 9
The substitution products of benzoic acid appear in the urine as
the corresponding derivatives of hippuric acid ; thus phenylacetic
acid, C (i H 5 .CH 2 .CO 2 H ; gives phenylaceturic acid 10 ; salicylic acid,
C 6 H 4 (OH)CO 2 H, is converted into salicyluric acid, 11 and toluic
acid, C 6 H 4 (CH 3 )C0 2 H, into toluyluric acid; 12 phthalic acid,
however, remains unchanged. 13 It follows from this, that the
monobasic aromatic acids, and hydroxy-acids, combine with
glycocoll with elimination of water in their passage through the
organism.

After Liebig had discovered hippuric acid, he raised the ques-
tion whether it must be considered as a compound of benzoic
acid with an unknown compound body, or as a peculiar acid by
the decomposition of which benzoic acid is formed, just as oxalic
and formic acids are formed when sugar or starch is treated with
nitric acid. He decided for the latter view, and says: "The
first view is rendered improbable by the fact that I have been
unable to prepare even the slightest trace of benzoic acid from
horses' fodder, which is the source of their urine, even if this
acid be contained in Anthoxanthum odoratum and Holcusodoratus )
as found by Vogel, its identity being rendered doubtful by its



1 Ann. Chcm. Pharm. xliii. 108.
" Phil. Mag. xx. 501.

Journ. Prakt. Chem. xxxv. 309.

Frcrichs and Wohler, Ann. Chcm. Pharm. Ixviii. 336.

Krdmaun and Marchaud, Journ. Prakt. Chcm. xxvi. 491.

K. and H. Salkowski, Ber. Deutsch. Chem. Ges. xii. 653.

Grabe and Schultzen, Ann. Chcm. Pharm. cxlii. 349.

Latitemann, ibid. cxxv. 12.

Nauyen and Schultzen, Zeitfchr. Chcm. 1868, 29.

E. and H. Salkowski, loc. cit.

Bertagnini, Ann. Chcm. Pharm. xcvii. 249.

Kraut, ibid, xcviii. 360.

Grabe and Sclmltzen, loc. cit.



186 AROMATIC COMPOUNDS.

different crystalline form." These fragrant grasses were after-
wards found to contain not benzoic acid but coumarin, C 9 H 6 0.,,
which is the anhydride of orthohydroxyphenylacrylic acid,
C 6 H 4 (OH)C 2 H 2 .C0. 2 H.

After it had been proved that benzoic acid and allied sub-
stances are converted into hippuric acid in the organism, it
seemed probable that that occurring in the urine of graminivora
would be derived from benzoic acid or other benzoyl compounds
occurring in the fodder. Hallwachs, therefore, investigated the
chief grasses and plants in question, but was unable to detect the
slightest trace of benzoic acid or any other compound which '
could yield hippuric acid ; he also showed that coumarin and j
chlorophyll, which might be looked upon as allies of the benzoyl
series, pass through the organism unchanged. 1

O. Loew found, however, that quinic acid, which occurs in i
many plants, is also present in hay, and considered it to be the i
source of the hippuric acid. 2 Although the latter acid can be
obtained from quinic acid, it passes through the organism
almost unchanged, only a very small portion being converted |
into hippuric acid. 3

The amount of hippuric acid in the urine is naturally greater ;
when such fruits as plums and cranberries, which contain benzoic i
acid, have been eaten ; 4 but Ducheck found a much larger quantity i
than would correspond to the amount of benzoic acid contained !
in the plums.

As already mentioned, hippuric acid occurs largely in the
urine of diabetic patients who subsist on a meat diet, and in
that of others who have passed several days without taking food, ; |
as well as in small quantity in the urine of dogs after a meat .j
diet or long fasting.

It follows from these facts with tolerable certainty that the
hippuric acid, or rather the aromatic group contained in it, is-. :
derived from the albuminoids, which are known to yield benz - 'i
aldehyde and benzoic acid on oxidation, while phenylpropionic
acid is formed from them by the pancreatic fermentation (E. and
H. Salkowski).

E. Salkowski has adduced a further proof for this in the fact
that phenylaceturic acid, (C 6 H 5 .CH 2 .CO)NH.CH 2 .CO 2 H, which
is the homologue of hippuric acid, occurs in horses' urine and

1 Ann. Chem. Pharm. cv. 207. - Journ. Prakt. Chem. [2] xix. 309.

3 Stadelmann, Jahresbcr. Chem. 1879, 082.

4 Ducheck, Gmclin's Orrj. CJicm. v. 332 ; Thudichum, Ja-hresbcr. Chem. 1863,
656.



PREPARATION OF HIPPURIC ACID. 187

can readily be split up into glycocoll and phenylacetic acid,
C (i H. v CH.,.CO.JI. The latter acid is also formed, together with
phenylpropionic acid, by the putrefraction of albumen. 1

The source of the hippuric acid is therefore identical with that
of the uric acid, which is especially formed in tho organism of
the carnivora.

2 no The acid is best prepared from the urine of cows or
<>\cn, which often contains such a large quantity that it is preci-
pitated by the addition of hydrochloric acid. If this be not the
case, the urine is boiled up with milk of lime, filtered, and the
filtrate neutralized with hydrochloric acid, evaporated, and then
treated with an excess of hydrochloric acid. 2 Putz proposes to
precipitate the neutral solution with ferric chloride and decom-
pose the washed precipitate with hydrochloric acid. 3 The acid
obtained by these methods is always discoloured, but the im-
purity may be removed by dissolving it in warm chlorine water, 4
or treating its aqueous solution with bleaching powder. 5 It is
more convenient to effect the purification by allowing 3 parts
of the acid to stand in contact with 1 part of nitric acid, of
sp. gr. T3, and filtering off' tho mother-liquor after twenty-
four hours. It can also be dissolved in hot, dilute caustic soda
solution and treated with potassium permanganate until yellow
crystals separate out on the addition of hydrochloric acid. 7
These are boiled with water and animal charcoal and then
finally re-crystallized from hot water.

Hippuric acid is also readily obtained when finely powdered,
dry amido-acetic acid is gradually added to an excess of heated
benzoic anhydride, and the mixture heated on an oil-bath until
it becomes coloured red. It is then allowed to cool, dissolved
in water and neutralized with caustic soda, the solution being
subsequently acidified with hydrochloric acid and allowed to
stand for several days. The precipitated hippuric acid is boiled
with water and animal charcoal, the filtrate concentrated on the
water-bath and then allowed to cool slowly. The large crystals
which are formed are then washed with petroleum spirit to
remove any adhering benzoic acid. 8

Ber. Dcutsch. Chem. Gcs. xvii. 3010.

Gregory, Ann. Chctn. Pharm. Ixiii. 125.

Jahrcsbcr. Chem. 1877. 795.

D.iuber, Ann. Chcm. Pharm. Ixxir. 202.

Conrad, Journ. Prakt. Chcm. [2] xv. 244.

Hutstein, Jahrcsb. 1854, 453

Gossmann, Ann. Churn. Pharm. xnix. 374 ; Conrad, loc. eit.

Curtins. />''/. Dnittch; Chem. GCS. xvii. 1662.



188



AROMATIC COMPOUNDS.



Properties. It forms long, lustrous, rhombic prisms or needles
(Fig. 1), which are sometimes opaque, and which dissolve in 600
parts of water at ; it is only slightly soluble in cold alcohol and
ether, but dissolves readily in warm water and alcohol. It is in-
soluble in petroleum spirit, and can be separated from benzoic
acid by means of this property. It reddens litmus, but has not
a sour taste, melts at 187'5 (Conrad) and decomposes at tem-
peratures above 240, with formation of hydrocyanic acid, benzoic
acid, benzonitril, and a black, resinous substance. 1 When it is
heated with caustic potash to 260, ammonia and benzonitril are
given off, while calcium carbonate, calcium benzoate and carbon
remain behind. Caustic baryta effects a similar decomposition,




FIG. i.



barium cyanate being formed in addition, while \\hen an excess
of baryta is employed, benzene, ammonia and methylamine are
given off and barium carbonate and benzoate formed, but no
cyanide. 2 It has been already mentioned that on heating with
strong acids or alkalis it decomposes into benzoic acid and
glycocoll ; these products are also formed when it is heated to
120 with a concentrated solution of zinc chloride ; when, how-
ever, it is distilled with anhydrous zinc chloride, benzonitril and
carbon dioxide are formed. 8

On oxidation with lead dioxide and sulphuric acid or with

1 Limpricht and Uslar, Ann. Chem. Pharm. Ixxxviii. 133.
- Kraut, Ja.hrr.sber 1863, 348 ; Conrad, loc. cit.
3 bossmann, Ann. diem. Pharm. c. 69.



THE HIPPURATES. 189



nitric acid, it is converted into hipparaffin or methylenedibenz-
araide (p. 175) :

CH 2 .NH(CO.C 6 H 5 )

2 | ' +40=CH 9 (NH.CO.C 6 H 5 ) 2 +3C0 2 +2H 2 0.

C0 2 H

The substitution products of hippuric acid will be described
among the corresponding derivatives of benzoic acid.

21 1 1 The Hippurates. Hippuric acid decomposes carbonates
and dissolves zinc with evolution of hydrogen. Its salts are for
the most part soluble in water and crystallize well ; they have
been investigated by Schwarz. 1

Potassium hippurate, C 9 H 8 KNO 3 + H 2 0, forms vermicular
crusts consisting of pointed rhombic prisms ; on heating it forms
a vapour which possesses a smell resembling that of JSatureja
hortcnsis. It combines with hippuric acid forming the acid salt,
C 9 H 8 KN0 3 + C 9 H 9 NO 3 + H 2 O, which crystallizes in quadratic
tablets possessing a satin lustre.

Sodium, hippurate, 4C 9 H 8 NaNO 3 -f H 2 O, is a crystalline mass
which readily dissolves in water and hot alcohol.

Acid ammonium hippurate, C 9 H 8 (NH 4 )NO 3 +C 9 H 9 NO 3 -1-H 2 O,
crystallizes in small, quadratic prisms ; the normal salt has not
been prepared.

Calcium hippurate, (C 9 H 8 NO 3 ) 2 Ca -f 3H 2 O, forms rhombic
prisms, 2 which are soluble in 18 parts of cold and 6 parts of
boiling water (Liebig).

Strontium hippurate, (C 9 H 8 NO 3 ) 2 Sr + 5H 2 O, crystallizes in
fascicular aggregates, composed of four-sided prisms ; it is only
slightly soluble in cold water and alcohol, but dissolves readily
in them when hot.

Barium hippurate, (C 9 H 8 N0 3 ) 2 Ba + H 2 0, crystallizes in crusts
made up of quadratic prisms. Schwarz, in endeavouring to
separate a mixture of hippuric and benzoic acids by means of
their barium salts, obtained, first, barium benzoate, then barium
hippurate, and, finally, from the mother-liquor, the double salt,
C 7 H-O 2 .Ba.C 9 H 8 NO 3 + 5H 2 0, in characteristic warty masses. 3

Magnesium hippurate, (C 9 H 8 NO 3 ) 2 Mg + 5H 2 O, forms warty
crystals.

Zinc hippurate, (C 9 H 8 N0 3 ) 2 Zn + 5H 2 O, crystallizes in small

1 Ann. CTtcm. Pli/trm. liv. 33.

- Schabus, JaJircsber. Cficm. 1850, 411.

3 Ann. Chcm. 1'harni. Ixxv. 192.



190 AROMATIC COMPOUNDS.



plates, which after dehydration dissolve in 53'2 parts of water at
17 '5, and in 4 parts at 100 . 1

Lead hippurate, (C 9 H 8 N0 3 ) 2 Pb + 2H 2 0, is a curdy precipitate
crystallizing from a large quantity of hot water in fine, silky
needles, which often suddenly take up a molecule of water
and change into lustrous, four- sided tablets.

Copper hippurate, (C 9 H 8 N0 3 ) 2 Cu + 3H 2 O, is slightly soluble
in cold water, more readily in hot alcohol, and crystallizes in
small, pointed, rhombic prisms of a blue colour.

Silver hippurate, 2C 9 H 8 AgN0 3 -j-H 2 O, is a curdy precipitate,
which crystallizes from hot water in aggregates of lustrous
needles. '

When ferric chloride is added to a solution of a normal
hippurate, a cream-coloured precipitate of ferric hippurate is
thrown down, which contains more or less basic salt according
to the greater or less dilution of the solution ; this fact was dis-
covered by Putz, who employed the compound for the prepara-
tion of hippuric acid from urine. It is almost insoluble in
pure water, but dissolves in presence of free hippuric acid, an
excess of ferric chloride and in alcohol. Wreden has proposed
to employ this reaction for the determination of hippuric acid in
urine. Heimeberg, Stohmaun, and Rautenberg, found that it is
most convenient for this purpose to make use of a solution of
ferric nitrate which has been standardized with pure hippuric
acid. The urine is acidified with nitric acid, heated to boiling
to remove carbon dioxide, neutralized with calcium carbonate,
treated with an excess of lead nitrate, and then diluted to a
known volume and filtered. An aliquot portion of the filtrate
is heated and titrated w r ith the ferric nitrate solution until a
drop of the clear liquid gives a blue colouration with potassium
ferrocyanide, the distinction between this and the white of the
lead ferrocyanide which is formed at first, being very sharp. 2

Methyl hippurate, C 9 H 8 (CH 3 )NO 3 , is obtained by the action
of hydrochloric acid on a hot solution of hippuric acid in methyl
alcohol. 3 It is slightly soluble in cold, more readily in hot water
and in alcohol, and crystallizes in long, white prisms, which melt
at 80'5, and decompose at 250 with formation of ammonia and
benzonitril.

Ethyl hippurate, C 9 H 8 (C 2 H 5 )NO 3 , is formed in a similar

1 Lowe, Jahresber. 1855, 536. 2 Ann. Chem. Pharm. cxxiv. 182.

3 Jaqucmin and Schlagdenhauffen, Compt. Bend, -x.lv. 1011 ; Coura 1, Jouni.
Prakt. Chem. [2] xv. 247.



THE HIPPURATES. 101



manner to the metlnl ether, 1 and also by allowing a saturated,
warm alcoholic solution of hippuric acid to stand for a month in
a warm place. 2

It may also be readily prepared by heating ethyl amido-acetate
with benzoic anhydride to 100. 3 It crystallizes from hot water
in long, white, silky needles, which melt at 60'5, have no odour,
but a sharp taste resembling that of oil of turpentine, and de-
compose on heating. On distillation with steam, it decomposes
into alcohol and the free acid.

The following ethers have also been prepared : 4

Melting-
Butyl hippurate, C 9 H 8 (C 4 H 9 )NO 3 , prisms ..... 40 41
Isobutyl hippurate, C 9 H 8 (C 4 H 9 )NO 3 small, rhombic

prisms 45 46

Amyl hippurate, C 9 H 8 (C 6 H n )NO s , small needles . . 27 28

When hippuric acid is distilled with phosphorus pentachloride,
hydrochloric acid is evolved and the distillate consists, first, of
phosphorus oxychloride, then of benzoyl chloride and finally of
the compound C 9 H 6 C1NO, which crystallizes from ether in flat,
four-sided, rnonoclinic prisms, melting at 40 50. It boils at
220, is not attacked by alcoholic potash, and on fusion with
potash yields benzoic acid and ammonia. 5 The formation of this
substance may be explained by the following equations :

CH 9 .NH.CO.C 6 H, CH 9 .NH.CO.C 6 H 5

| " +2PC1 6 = | +2POC1 3 +HC1.

CO.OH CC1 3

CH,.NH.CO.C 6 H 5 CR.
| =|| >N.CO.C 6 H 5 + 2HC1.

CC1 3 CGK

Hippuramide, (C 6 H 5 .CO)NH.C 2 H 2 O.NH 2 , is formed by the
action of aqueous ammonia on the ethyl ether; it separates
from hot water in short, thick crystals, melting at 183 (Jaque-
min and Schlagdenhauffen ; Conrad).

Hippuramido-acetic acid, C U H 12 N 2 O 4 , is formed, together
with hippuric acid, by the action of benzoyl chloride on silver

1 Rtenhouse, Ann. Chem. Pharm. ; xxL 148 ; Conrad, loc. cit.
" Liebig, Ann. Chem. Pharm. Ixv. 351.

3 Curtius, Ber. Dcutach. Chem. Ges. xvii. 1662.

4 Campani and Bizzarri, Ball. Soc. Chim. xxxv. 427 ; Campani, Ber Dcutsch.
< '/!. firs. xi. 1247.

5 Schwanert, Ann. Chem. Pharm. cxii 59.



102 AROMATIC COMPOUNDS.

amido-acetate, and is probably derived from the hippuric acid
which is first formed :



CH 2 NH.CO.C 6 H 5 CH 2 .NH.CO.C 6 H 5

CO.OH



+ NH 2 .CH 2 .CO.OH = |

CO.:



It crystallizes from hot water in rhombic tablets or needles,
melting at 206'5. On boiling with hydrochloric acid, it decom-
poses into amido-acetic acid and benzoic acid ; on heating with
dilute acids, on the other hand, both hippuric acid and amido-
acetic acid are formed. Its salts crystallize well; the ethyl
ether, which melts at 117, combines with ammonia forming
hippurglycollamide, which crystallizes in large, transparent plates,
melting at 202.

An acid, C 10 H 12 N 3 O 4 , is also formed by the reaction just men-
tioned, and crystallizes from hot water in microscopic needles
which melt at 240, and are decomposed by hot hydrochloric acid
into amido-acetic acid, benzoic acid, and a non-crystallizable,
nitrogenous compound. 1

Hydrobenzuric acid, C 18 H 24 N 2 O 6 , is obtained by the action of
sodium amalgam on a concentrated solution of hippuric acid in
caustic soda solution ; it forms a mass resembling turpentine,
and becomes crystalline after standing for months. When it is
treated with an excess of sodium amalgam and water, it decom-
poses into hydrobenzyluric acid, C 16 H 2I N0 4 , and amido-acetic
acid. The former is an oily liquid, which gradually solidifies ;
on boiling with alkalis it decomposes into hydrobenzoic acid,
benzyl alcohol and amido-acetic acid. Its alkaline solution
oxidizes in the air with formation of kydroxybenzyluric acid,
C 16 H 2] NO 5 , which is a crystalline mass melting at 60 70. 2

2 ii 2 Ornithuric acid, C 19 H 20 N 2 O 4 . Shepard found that ben-
zoic acid is not converted into hippuric acid in the organism of
birds, but into another nitrogenous compound, which was more
closely examined by Jaffe. 3 He obtained it from the excre-
ments of hens which were fed with benzoic acid ; it is very
slightly soluble in water and crystallizes from hot alcohol in
minute needles, melting at 182. Its solution reddens litmus.
The following salts are characteristic :

1 Curtius, Journ. Prakt. Chem. [2] xxvi. 145.

2 Otto, Ann. Chcm. Pharm. cxxxiv. 303.

3 Jnffe, Ber. Dcutsch. Chcm. Ges. x. 1925 ; xi. 406.



ORNITHINE. 193



Calcium ornithurate, (C 19 H 19 N 2 O 4 ) 2 Ca, is obtained by adding
the ammonium salt to a solution of calcium chloride and heating
the mixture ; it is a crystalline precipitate, which is only very
slightly soluble in water.

Barium ornithurate, (C 19 H 19 N 2 O 4 ) 2 Ba, is exceptionally soluble
in water and alcohol, and is deposited from its alcoholic solution
in opaque, crystalline flocks, which after drying form a snow-
white powder.

On boiling the acid with hydrochloric acid, it decomposes
almost immediately into benzoic acid and benzoylornithine,
C 12 H 16 N 2 O 3 , which is almost insoluble in alcohol and crystallizes
from water in very brittle needles, melting at 225 230. It
forms readily soluble salts with the mineral acids.

If the boiling with hydrochloric acid be continued for some
time, the acid decomposes into benzoic acid and ornithine,
C 5 H 12 N 2 O 2 , which is very deliquescent, has a strongly alkaline
reaction and a somewhat caustic taste. It combines with acids
to form salts which crystallize well.

Ornithine has the composition of a diamidovalerianic acid, and
the constitution of these compounds can therefore be expressed
by the following formulae :

Ornithine.



Benzoylornithine.


Ornithuric acid.


NH 2


NH.CO.C 6 H 5


C 4 H 7 .C0 2 H


C.Hy.CO.^


1


1


NH.CO.C 6 H 5


NH.CO.C 6 H 5 .



! 4 H 7 .C0 2 H
NH 2

Free ornithine, which has an alkaline reaction, will, of course,
have the following formula :

NH 2

C 4 H 7 .CO
NH 3 .0



VOL. III. PART IV



194 AROMATIC COMPOUNDS.



BENZENYL COMPOUNDS.

2113 These compounds are closely allied to the benzoyl deriva-
tives. Phosphorus chloride converts benzoic acid, C 6 H 5 .CO.OH,
first into benzoyl chloride, C 6 H 5 .COC1, and then by further
action into benzenyl chloride, C 6 H 5 .CC1 3 . The latter is also
formed by the continued action of chlorine on boiling toluene ;
on heating with caustic potash it is reconverted into benzoic
acid, which therefore bears the same relation to it as formic
acid to chloroform. The action of the potash is probably to form
benzenyl alcohol or orthobenzoic acid in the first instance :

C fl H 6 .CCl s +3KOH=C fl H 6 .C(OH) s + 3KCl.

This is, however, as unstable as orthoformic acid and immedi-
ately decomposes into water and benzoic acid ; ethers are, how-
ever, known, such as ethyl orthobenzoate, C 6 H 5 .C(OC 2 H 5 ) 3 ,
obtained by the action of sodium ethylate on benzenyl tri^
chloride.

Benzoic acid itself may, therefore, be looked upon as a benzenyl
compound, and this view was actually taken by Berzelius
(Part I., p. 12).

A large number of compounds which are formed by the
action of hydroxylamine on benzoyl chloride may also be in-
cluded among the benzenyl derivatives. The simplest of these is
benzyhydroxamic acid :

^N.OH

\OH.

Benzonitril, C 6 H 5 .CN, and its compounds with alcohols, such
as benzimido-ethyl ether :

^NH

'\OC 2 H 5 .

also belong to this class. The latter compound is converted
by ammonia into benzenylamidine or benzimido- amide :



BENZENYL TRICHLORIDE. 195

Benzenyl amidines which contain the radical phenyl, &c., are
obtained by heating benzonitril with the hydrochlorides of
amido-bases ; thus aniline yields phenylbenzenylamidine :

X NH

\N(C 6 H 5 )H.

Another series of amidines consists of the anhydro-bases,
which are formed from the orthoamido-compounds by the
elimination of water ; benzoylorthodiamidobenzene in this way
yields phenylenebenzenylamidine :

, N



Benzenyl trichloride or Benzo-trichloride-, C 6 H 5 .CC1 3 . Liebig
and Wohler found during their researches on the radical of
benzoic acid, that benzoyl chloride is converted by phosphorus
pentachloride into a strongly-smelling, oily substance, which they
did not investigate more closely. 1 It was made the subject of
research by Schischkow and Rosing 2 and also by Limpricht, 3
who found that it is also formed when benzidene dichloride,
C 6 H 5 .CHC1 2 , is treated with chlorine, and named it benzoic
trichloride. Benzenyl trichloride is most readily obtained by
passing chlorine into boiling toluene until no further increase in
weight takes place. 4 The product is then washed with caustic
soda solution, dried over ignited potassium carbonate and recti-
fied ; it is employed in the colour industry and is manufactured
on the large scale, being purified by distillation in a vacuum.

Benzenyl trichloride, which is also known as phenylchloroform,
is a powerfully refractive liquid, which has a characteristic
penetrating odour, boils at 213 214, and has a sp. gr. of
1'380 at 14. On heating with water to 150, it is converted
into benzoic acid, while benzoic anhydride is formed when it is
heated with sulphuric acid which contains 4'6 per cent, of water
(p. 166). It is decomposed by fuming nitric acid with formation
of metanitrobenzoic acid (Boils tein and Kuhlberg).

1 Ann. Chcm. Pharm. iii. 265.

2 Jahresber. Chcm. 1858, 279.

8 Ann. Chcm. Pharm. cxxxiv. 55 ; cxxxv. 80 ; cxxxix. 323.
4 Beilstein and Kuhlberg, ibid, cxlvi. 330.



19 6 AROMATIC COMPOUNDS.

Benzenyl tribromide, C 6 ~H. 5 .C~RT 3 , is formed by the action of
bromine on boiling toluene, and is a colourless liquid which has
an exceedingly violent action on the eyes and mucous mem-
brane. It cannot be distilled, since it decomposes at about
150 ; on heating with water it is readily converted into benzoic
acid, while it is only very slowly attacked by boiling alcohol. 1

Benzenyl ethyl ether, C 6 H 6 .C(OC 2 H 5 ) 3 . This compound, which
is also called ethyl orthobenzoate, was obtained by Limpricht,



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