Henry E. (Henry Enfield) Roscoe.

A treatise on chemistry (Volume 3) online

. (page 41 of 50)
Online LibraryHenry E. (Henry Enfield) RoscoeA treatise on chemistry (Volume 3) → online text (page 41 of 50)
Font size
QR-code for this ebook


the alcohol with hydrochloric acid (Colson); it is also formed
when metaxylene is heated with phosphorus pentachloride,
the yield being, however, very poor (Colson and Gautier). It
crystallizes in pointed prisms, melts at 34 and boils at 250
25 5 . 1

Metaxylylene bromide, C 6 H 4 (CH 2 Br) 2 , forms long, prismatic
needles, melting at 77, and is obtained by heating metaxylene
with bromine (Cokon, Radziszewski and Wispek), as well as
by bringing these two substances together in the sunlight
(Schramm).

Paraxylylene alcohol, C 6 H 4 (CH 2 .OH) 2 , was prepared by Gri-
maux by heating the chloride or bromide with 30 parts
of water to 170 180, and was named tollylene glycol? It
crystallizes in lustrous needles, which melt at 112 113, are
readily soluble in water, alcohol and ether, and are converted by
oxidation into terephthalic acid.

Paraxylylene mono-ethyl ether, C 6 H 4 (CH 2 .OH)CH 2 .O.C 2 H 5 , is
formed when the chloride is heated with alcoholic potash ; it is
a pleasant-smelling liquid which boils at 250 252 . 3

Paraxylylene chloride, C 6 H 4 (CH 2 C1) 2 , is prepared by the action
of chlorine on boiling paraxylene, 4 or by heating the alcohol
with hydrochloric acid. It may also be obtained in a similar
manner to the ortho-compound by heating paraxylene with
phosphorus pentachloride (Colson and Gautier). It crystallizes
from alcohol in pointed, rhombic tablets, melts at 100 and
boils with decomposition at 240 250.

Paraxylylene Iromide, C 6 H 4 (CH 2 Br) 2 , is obtained by passing
bromine vapour into paraxylene or by heating the alcohol with
hydrobromic acid ; it boils at 240 250, and crystallizes from
chloroform in plates, which melt at 143'5, 5 and dissolve in about
50 parts of ether.

Paraxylylene iodide, C 6 H 4 (CH 2 I) 2 , is prepared by heating the
alcohol with hydriodic acid ; it forms fine needles, which melt
at 170, and rapidly become coloured yellow in the air.

Paraxylylene acetate, C 6 H 4 (CH 2 .O.CO.CH 3 ) 2 , is formed when
the chloride is heated to 150 with an alcoholic solution of
sodium acetate. It is readily soluble in alcohol and ether, and

Bull. Soc. Chim. xliii. 6. 2 Ann. Chcm. Pharm. civ. 888.

Grimaux, Ball. Soc. Chim. xvi. 193.

Grimaux, Zcitschr. Chcm. 1867, 381.

Radziszewski ami Wispek, Bcr. Dcutsch. Chcm. Oes. xviii. 1280 ; Low, iota.

1 2072.



442 AROMATIC COMPOUNDS.

crystallizes from the latter in hard, lustrous plates, which have a
pungent, camphor-like taste, and melt at 47.

Paraxylylene monobenzoate, C 6 H 4 .(CH 2 .OCO.C 6 H 5 )CH 2 .OH, is
obtained by heating the chloride with an alcoholic solution of
sodium benzoate, and crystallizes in long, thin needles, melting at
73 74.



HYDROXYMETHYLBENZOIC ACIDS,

X C0 2 H
C 6 H /

\CH 2 .OH

2237 These compounds are isomeric with the hydroxytoluic
acids, from which they differ in being alcohols while the latte
are phenols.

Parahydroxymethylbenzoic acid was prepared by Dittmar am
Kekule", who named it oxymethylphenylformic acid, by heating
paratoluic acid with bromine at 160 170, arid boiling the
product with baryta water. It crystallizes in white plates o
flat needles, which are more readily soluble in water than para
toluic acid, melt a few degrees higher and sublime in feathery
needles. 1

Orthohydroxymethylbenzoic acid was first prepared by Hessert,
who named it " Benzolorthoalcolwlsaure" by the action of alkalis
on phthalide, which is its anhydride. Acids precipitate it as a
fine powder, which is slightly soluble in cold water, readily in
alcohol, has a strongly acid reaction, and melts at 118, being
thus converted into the anhydride, which is also formed when
the acid is simply boiled with water.

Silver orthohydroxymethylbenzoate, C 8 H 7 O 3 Ag, crystallizes from
water in small octohedra.

Phthalide, C 8 H 6 O 2 , was obtained by Kolbe and Wischin, who
prepared it by the action of zinc and hydrochloric acid on
phthalyl chloride, C 8 H 4 O 2 C1 2 , and named it phtfialaldehyde,
C 6 H 4 (COH) 2 . 2 It is also formed by the action of phosphorus
and hydriodic acid on the chloride, 3 and when orthoxylidene
chloride is boiled with water and lead nitrate. 4 Hessert has proved

1 Ann. Chem. Pharm. clxii. 337.

2 Zeitschr. Chcm. 1866, 315.

3 Baeyer, Bcr. Dcutsch. Chem.. Gr.s. x. 123.

4 Raymanii, Bull. Soc. Chim. x. 1180.



PHTHALIDE. 443



that it is not the aldehyde of phthalic acid but the anhydride or
lactone of the preceding compound. 1 Its formation was explained
by the following reactions :



/COC1 /CH 2 .OH



+HC1.

COCI \coci

/CH 2 .OH /CH 2X

C.H/ = C 6 H 4 <; -\0 + HC1.

\COC1 \CO/

It has since been shown that phthalyl chloride has not
the constitution assumed above (p. 4GO), and the formation of
phthalide is now represented much more simply :



C 6 H >0 + 4H = C 6 H 4 < >0 + 2HC1.

NOO/ \co/

This is confirmed by the observation of Hjelt,who found that it
is also obtained when bromine is passed into orthotoluic acid heated
to 140; the brominated acid which is first formed being decom-
posed as follows : 2

./GHiJBr /CH 2 \

C 6 H 4 <; =C 6 H 4 < >0 + HBr.

\CO.OH \CO/

It crystallizes from boiling water in needles which smell like
cinnamon, melts at 73 and boils at 290 (Grabe). It does not
combine with hydroxylamine, 3 gives no compounds with the acid
sulphites of the alkalis and does not reduce ammoniacal silver
solution (Hessert). It is oxidized to phthalic acid by alkaline
permanganate, while it is reduced to orthotoluic acid on heating
with phosphorus and hydriodic acid, and to orthoxylene together
with a little toluene by heated zinc dust.

Monobromophthalide is formed by the action of bromine vapour
on heated phthalide ; it crystallizes in plates, melting at 86, and
is converted into phthalaldehydic acid (p. 447) when heated with
water ; it has, therefore, the following constitution : 4

/CHBr

ctr o.



1 Bcr. DcMtech. Chem. Gcs. x. 1445 ; xi. 237. 3 Ibid. xuc. 412.

3 Lach, ibid. xvi. 1782. 4 Racine, ibid. xix. /78.



AROMATIC COMPOUNDS.






DibromopUhalidc, C 8 H 4 Br 2 O. 2 , is obtained, together with
dibromonaphthoquinone, by the oxidation of a-dibromo-
naphthalene with chromic acid, and crystallizes from boiling
alcohol in hard, white prisms, which sublime in needles and melt
at 187'5 ; it does not reduce ammoniacal silver solution and only
dissolves slowly in boiling caustic soda solution. 1 It has the
following constitution :

CBr



HC C CH 2

I II >0.
HC C CO



CBr

Guareschi obtained dichlorophthalide in a similar manner
from dichloronaphthalene ; it resembles the bromine compound,
and melts at 163 . 2

Hydrophthalide, C 8 H 8 O 2 , is formed together with phthalyl-
pinacone, C 1C H 18 O 4 , by the action of sodium amalgam on an
acid solution of phthalide, and is a syrupy mass, extremely
soluble in all solvents ; it probably has the following constitution
(Hessert) :

X CH 2

C 6 H 4 < > O.
\CH.OH

Phthalimidine, C 8 H 7 NO, is obtained by heating phthalide
with zinc ammonium chloride, or by treating it at its boiling-
point with ammonia :

/CO /C=NH

C 6 H 4 < > O + NH 3 = C 6 H 4 < > O + H 2 0.
\CH 2 \CH 2

It may be more simply prepared by the action of tin and
hydrochloric acid on phthalimide, C 6 H 4 (C 2 O 2 )NH. It is readily
soluble in alcohol and hot water, crystallizes in prisms or
needles, melts at 150 and boils at 337. When sodium
nitrite is added to its solution in hydrochloric acid, yellow
needles of nitrosophthalimidine separate out; they melt at 156,

1 Guareschi, Ann. Chcm. Pharm. ccxxii. 282.

2 Bcr. Deutsch. Chcm. Ges. xix. 1155.



METHYLPHTHALIMIDINE. 445



and are rapidly converted into orthohydroxymethylbenzoic acid
by the action of aqueous caustic soda :

,C=N-NO ,C0 2 Na

4Xs CH 2 tXx CH. 2 .OH

Hydrochloric acid precipitates either the free acid or phthalide
from this solution according to the temperature, and the latter
substance is in fact most conveniently prepared in this way from
phthalimide, which can itself be readily obtained from phthalic
acid. 1

Mcthylpkthalimidine, C 8 H 6 O(NCH 3 ), is formed by the action
of tin and hydrochloric acid on methylphthalimide, and is readily
soluble in water, alcohol and ether, from which it crystallizes in
large tablets, melting at 120; it boils without decomposition at
about 300 . 2

Phenylphthalimidine or PhtJialide-anil is prepared by heating
phthalide to 200 220 with aniline :

i~*if\ /"I "M' f~1 TT

C e H 4<^ \O + H 9 N.C 6 H 5 = C 6 H/ >O +H 2 O.

\/~1TT / \/^TT

N OH 2 / ^M 2

It crystallizes from alcohol in silvery plates, melting at 160
(Hessert).

PUlialidehydrazide, C U H 12 N 2 O, is formed by heating phthalide
with phenylhydrazine for some time :

OTI r^w

A,1 2 /^^-i

C H 4 ^ >O + N 2 H 3 .C 6 H 5 = C 6 H 4 '/ >O +H 2 0.



It crystallizes from hot water or alcohol in needles, which
possess a silver lustre, and melt at 165 . 3

Paranitrophthalidc, C 8 H 5 (N0 2 )0 2 , is prepared by dissolving
20 grms. of phthalide in 200 grms. of sulphuric acid, and
running in a solution of rather more than the calculated
quantity of potassium nitrate in 80 grms. of sulphuric acid, the
solution being well cooled during the operation. It forms long
colourless needles, which melt at 141, and are almost insoluble in
cold water, but dissolve slightly on boiling, more readily in alcohol,

1 Grabe, Bcr. Deutsch. Cham. Gcs. xvii. 2598 ; xviii. 1408.

2 Grabe and Pictet, ibid, xviii. 1173.

3 V. Meyer and Miinchmeyer, Hid. xix. 1706 and 2132.



446 AROMATIC COMPOUNDS.

and readily in benzene. Alcoholic potash produces a charac-
teristic violet colouration, while aqueous potash forms a yellow
solution. Dilute sulphuric acid precipitates paranitrohydroxy-
methylbenzoic acid, C 6 H 3 (NO 2 )(CH 2 .OH)C0 2 H, from the cool
solution. This body crystallizes in microscopic needles united
in stellate forms, and is extremely soluble in ether, readily in
alcohol and hot water. It melts at 129, and decomposes at a
higher temperature into water and nitrophthalide.

Paramidophthalide, C 8 H 5 (NH 2 )O 2 , is obtained by the reduc-
tion of the preceding compound, and is almost insoluble in
water, but dissolves slightly in alcohol, and more readily in
chloroform, from which it crystallizes in short prisms, melting
at 178. Its hydrochloride forms needles which are readily
soluble in water. It also dissolves in alkalis, salts of para-
amidohydroxymethylbenzoic acid being formed. The free acid has
not yet been prepared.

When paranitrophthalide is heated with hydriodic acid and
phosphorus, <y-amido-orthotoluic acid is formed. 1

Orthonitrophthalide was prepared by Beilstein and Kurbatow,
together with the corresponding nitrophthalic acid, by oxidizing
a-nitronaphthalene with a solution of chromium trioxide in
acetic acid. They mention that the substance obtained has
the formula of nitrophthalaldehyde, but must possess a different
constitution, because it is only attacked with difficulty by the
oxidizing mixture just named. 2 Its properties prove that it is
actually orthonitrophthalide. 3

It crystallizes in small plates, melting at 136, is much more
readily soluble in alcohol and chloroform than the para-com-
pound, and forms a yellow solution in alkalis. On heating in a
sealed tube with dilute hydrochloric acid, it is smoothly con-
verted into v-nitrophthalic acid (Honig).

1 Hbnig, Ber. Dc,utsch. Chem. Ges. xviii. 3447.

2 Ann. Chem. Phann. ccii. 217.

3 Guareschi, ibid, ccxxii. 283 ; Honig, loc. tit.



PHTHALALDEHYDE. 447



ALDEHYDES, C 6 H 4 (CHO) 2 , AND ALDEHYDO-
ACIDS, C 6 H 4 (COH)(COOH).

2238 Phthalaldehyde. When orthoxylene is submitted at the
boiling-point to the continued action of chlorine, or is heated to
195 with eight parts of phosphorus pentachloride, orthoxylidcne
tetrachloride, C C H 4 (CHC1 2 ) 2 , is formed ; it crystallizes from ether
in large asymmetric prisms, melts at 89 and boils at 273 274.
On heating with water it is converted into phthalaldehyde, which
is also formed by the oxidation of phthal alcohol, and is an oily
liquid, which has not yet been prepared pure since it so readily
passes into the isomeric phthalide (Hjelt). According to Colson
and Gautier, phthalaldehyde is a yellow crystalline substance
melting at 52. Ammonia produces a deep blue or yellow
colouration, followed by a brown precipitate. 1

Phtholaldehydic acid is prepared by heating monobromo-
phthalide with water : 2

CHBrv CHO



C 6 H 4 < >0 + H 2 = C 6 H 4 < 4-HBr.

\ CO / \CO.OH

It may also be obtained by heating orthoxylene to 200 with
12-5 parts of phosphorus pentachloride and boiling the product,
xylidcnyl pentachloride, C 6 H 4 (CHC1 2 )CC1 3 , with water (Colson
and Gautier). It forms lemon-yellow crystals, which melt at 98
to 100, and are readily soluble in water. Its phenylhydrazine
compound crystallizes in fine, yellow needles.

Isophthalaldchyde is prepared in a similar manner from meta-
xyMene tetrachloride, C 6 H 4 (CHC1 2 ) 2 , which is a liquid boiling
at 273. It is an oily liquid which, as well as its solution in
water, gives a green colouration with ammonia, followed by a
brown precipitate (Colson and Gautier).

Tercphthalaldehyde, C 6 H 4 (CHO) 2 , was obtained by Grimaux
from paraxylylene chloride, C 6 H 4 (CH 2 C1) 2 , by boiling with lead
nitrate and water, 3 while Low prepared it by the same method
from paraxylylene bromide. 4

1 Hjelt, Bcr. Deutsch. Ghem. Ges. xviii. 2879 ; xix. 411 ; Colson and Gautier,

Bull. Soc. Chim. xlv. 6 and 506.

2 Racine, Ber. Deutsch. Chcm. Ges. xix. 778.

3 Jahrsber. Chcm. 1876, 490 ; Colson and Gautier, loc. tit.

4 Ann. Chcm. Pharm. ccxxxi. 361.



448 AROMATIC COMPOUNDS.

It is also formed when paraxylene is heated to 190 with
eight parts of phosphorus pentachloride, and the paraxylidene
tetrachloride which is thus formed boiled with water for
some time. The latter forms well-developed crystals, melting
at 93.

Terephthalaldehyde is only very slightly soluble in cold ether,
but readily in alcohol and tolerably freely in hot water, from
which it crystallizes in fine needles, melting at 116. It forms
a readily soluble compound with acid sodium sulphite. Con-
centrated caustic soda solution decomposes it with formation of
parahydroxymethylbenzoie acid, paraxylylene alcohol and tere-
phthalic acid :

/CHO /CH 2 .OH

|"1 TT / , TT i~\ /~1 TT f

4 \CHO 4N \CO.OH.

/CH 2 .OH /CH 2 .OH /CO.OH

e\r\ TT/ O TT / i ft TT /

^ 6 *1 4 \ ^ 6 tL 4 x -f^ 6 l 4 v

\CO.OH \CH 2 .OH \CO.OH.

Terephthalaldehyde is also obtained when paraxylylene bro-
mide is dissolved in cold, concentrated nitric acid. The com-
pound C 24 H 20 Br 2 O 4 is simultaneously formed ; it is insoluble in
water, but dissolves readily in ether, from which it crystallizes in
stunted needles, which melt at 80 and are converted into tere-
phthalaldehyde, paraxylylene alcohol and hydrobromic acid, by
heating with water :

/CHO
C 6 H 4 <

\CHBr.O.CH 2V



Q.H

\



CHBr.O.CH
CHO



/CHO HO.CH 2V

2C 6 H 4 < + >C 6 H 4 +2HBr.

\



CHO HO.CH



It is noteworthy that concentrated nitric acid exerts an
oxidizing action upon paraxylylene bromide, and does not effect
nitration as in the case of benzyl chloride. 1

Xylylidenediaminc, C 8 H 8 N 2 , is deposited in very brittle,

1 Low, Ber. Dcutsch. Chcm. Ges. xviii. 2072.



HYDROBENZAMIDE TRIALDEHYDE. 449

vitreous crystals when an alcoholic solution of tercphthalaldehyde
is saturated with ammonia and allowed to stand :

/CHO /CH NH

C C H 4 < + 2NH 3 = C 6 H 4 < + 2H 2 0.



It is also formed when dry ammonia is passed over the
aldehyde, but is decomposed again by acids, or even on boiling
with water, into ammonia and the aldehyde.

Hydrobcnzamide trialdehyde, N 2 (CH.C 6 H 4 .CHO) 3 , is formed
by the action of aqueous ammonia on terephthalaldehyde, as a
white powder consisting of matted microscopic needles, which is
insoluble in water and alcohol and is dissolved by acids, the
aldehyde being set free. 1

Nitrot&rephthalaldehyde, C C H 3 (NO 2 )(CHO) 2 . In order to pre-
pare this substance, a solution- of the aldehyde heated to 150 is
treated with an equal quantity of potassium nitrate dissolved in
sulphuric acid, kept at a temperature of 110 115 for 10 15
minutes, poured into water and then extracted with ether. It
is very readily soluble in alcohol, with greater difficulty in hot
water and ether, crystallizing from the latter in rhombohedra,
which melt at 86 and sublime in large needles. A blue indigo
derivative is formed when it is heated with caustic soda and
acetone (p. 146) (Low).

Terepkthalaldehydic acid, C H 4 (CHO)CO 2 H, is formed, together
with terephthalic acid, by the oxidation of the aldehyde with
chromic acid solution. It is only slightly soluble in ether and
chloroform, and still less readily in hot water, from which it
crystallizes in needles, which melt at 246 and sublime in well-
formed needles. It forms a barium salt which is readily soluble
in water, as well as a scarcely soluble silver salt, and only
reduces ammoniacal silver solution after continued boiling.

The ethyl ether, C 6 H 4 (CHO)CO 2 .C 2 H 5 , forms groups of pointed
needles, easily reduces ammoniacal silver solution on heating,
and gives all the reactions of benzaldehyde (Low).

Hydrolenzamidetricarboxylic acid, N,(CH.C 6 H 4 .CO 2 H) 3 is not
formed by the action of ammonia on the aldehydo-acid, but by
the oxidation of the trialdehyde with potassium permanganate.
It crystallizes in nacreous, rhombohedral tablets (Oppenheimer).

Nitroterephthalaldekydic acid, C 6 H 3 (N0 2 )(CHO)CO 2 H(2:1:4,

1 Oppenheimer, Her. Deutsck. Glum. Ges. xix. 574.
VOL. III. PART IV.



450 AROMATIC COMPOUNDS.



is prepared in a similar manner to nitrophthalaldehyde. It is
readily soluble in hot water, and crystallizes from it in large,
four-sided needles, which melt at 160. On heating with caustic
soda solution and acetone it is converted into indigocarboxylic
acid, C 16 H 8 N 2 O 2 (C0 2 H.) 2 , a reaction which proves that the
nitroxylyl-group stands in the ortho-position with respect to
the aldehyde group.

In its preparation a small quantity of the isomeric acid
(N0. 2 :COH:G0 2 H^3:1 : 4), which melts at 184, is also
formed (Low).



/CO,H

THE PHTHALIC ACIDS, 6 H,<

X C0 2 H.

2239 In the year 183G, Laurent prepared naphthalic acid (acide
naplitalique), C 10 H ( .O 5 , by boiling naphthalene tetrachloride,
C 10 H 8 C1 4 , with nitric acid, 1 and Marignac, who was subsequently
confirmed by Laurent, proposed for it the formula C 8 H 6 O 4 . The
latter chemist found that it is also obtained, together with other
products, by boiling naphthalene with nitric acid, oxalic acid
being always simultaneously formed. 2 Since it no longer
belongs to the naphthalene series, he named it phthalic acid
(acide phtalique). 3 It decomposes on distillation with lime, as
was shown by Marignac, into carbon dioxide and benzene .*

During his investigation of the colouring matter of madder
root, Schunck found that alizarin is converted by oxidation into
alizaric acid, C 14 H 10 O 7 , 5 which, according to Gerhardt, 6 con-
firmed by Strecker and Wolff, 7 is identical with phthalic acid.
The napJithesic acid (acide naphtesique), C 10 H C O 4> which Laurent
had obtained by the action of potassium dichromate and
sulphuric acid on naphthalene, 8 was also recognized as phthalic
acid by Scheibler 9 and F. Lessen, the latter of whom found that
it is also formed by the action of potassium permanganate on
naphthalene. 10 An isomeric substance was prepared by Cailletet

Ann. Chim. Phys. Ixi. 114 ; Ann. Chcm. Pharm. xix. 38.
Ibid, xxxviii. 13. 3 Ibid. xli. 107.

Ibid. xlii. 215. 5 Ibid. Ixvi. 197.

Compt. Rend. Trav. Chim. 1849, 222.
Ann. Chcm. Pharm. Ixxv. 12.
Revue Scicnt. xiv. 560 ; Compt. Rend. xxi. 36.
Bar. Deutsch. Chcm. Gas. i. 125.
10 Zeitschr. Chcm. x. 419 ; Ann. Chcm. Pharm. cxliv. 71.



THE PHTHALTC ACIDS. 451

in 1847, by heating oil of turpentine (essence de tdrtbenthine)
with dilute nitric acid, and named on this account terephthalic
acid (acide terephtalique). 1 Five years previously, Persoz had
obtained cumino-cyminic acid (acide cnmino-cyminique) by the
oxidation of the ethereal oil contained in the seeds of
Roman cumin (Cuminum Cyminum\ but had not analysed it. 2
Hofmann, in attempting to purify cumic acid, C 10 H 10 2 , by
treatment with dilute sulphuric acid and potassium dichromate,
found that it is thus oxidized to insolinic acid, C 9 H 8 4 , which lie
also obtained from Roman cumin oil, and which, as he pointed
out, is very similar to terephthalic acid, 3 these being afterwards
shown by H. Miiller and Warren de la Rue to be identical. 4

Fittig then prepared a third acid by the oxidation of isoxylene
and named it isophthalic acid. 5

The methods employed in the determination of the position of
the carboxyl groups in these three acids have already been
described in detail (Part III., p. 42). Quite recently, however,
Nolting has added a very simple proof of their constitution.
The three acids can be quantitatively obtained by the oxidation
of the three dimethylbenzenes with an alkaline solution of
potassium permanganate. Paraxylene yields terephthalic acid
and on nitration gives only one mononitroxylene, while ortho-
xylene is oxidized to phthalic acid and yields two nitro-deriva-
tives. Finally, three nitroxylenes can be obtained from isoxylene,
which corresponds to isophthalic acid. The position of the
carboxyls is, therefore, in :

Phthalic acid 1:2

Isophthalic acid 1:3

Terephthalic acid 1:4

This proof is exactly analogous to that employed by Kb'rner
to determine the positions of the bromine atoms in the three
dibromobenzenes, and by Griess in ascertaining the constitution
of the diamidobenzenes (Part III., pp. 52, 53). 6

Ann. Cltim. Phys. [3] xxi. 28.

Journ. Prakt. Chem. xxiv. 55 ; CompL Rend, xxxiii. 433.

Ann. Chcm. Pfuirm. xcvii. 197.

Ibid. cxxi. 86. 8 Ibid, cxlviii. 11.

Ber. Dcutsch. Chem. Ges. xviii. 2687.



G



452 AROMATIC COMPOUNDS.



PHTHALIC ACID.

2240 This acid is most simply formed by the oxidation of
orthoxylene or orthotoluic acid l with potassium permanganate
or dilute nitric acid. 2 Carius found that it is also obtained in
small quantity when benzene or benzoic acid is treated with
manganese dioxide and concentrated sulphuric acid in the cold, 3
diphenylbenzene, C C H 4 (C 6 H 5 ) 2 , being probably the intermediate
product (Part III., p. 87). According to Guyard, it is also formed
when a mixture of salicylic, formic and sulphuric acids is
heated. 4

Phthalic acid is manufactured from naphthalene, C 10 H 8 ,
which is first converted into the tetrachloride, C 10 H 8 C1 4 , by
passing chlorine through the fused hydrocarbon, the plant shown
in section and elevation in Figs. 2 and 3 being employed. The
mass becomes heated to such an extent that the iron vessel
containing it has to be cooled by water, the temperature being
kept below 160 170, above which carbonization takes place.
The tetrachloride is also manufactured by grinding naphthalene
with water and potassium chlorate, making up the paste into
balls, and bringing these, after drying, into concentrated hydro-
chloric acid. The chlorate may be replaced by bleaching
powder which is mixed with naphthalene and pressed into
cakes.

One part of the chloride is then heated with 5 6 parts of
nitric acid of sp. gr. 1*35 in flat stoneware retorts placed in an
air-bath (Figs. 4 and 5).

The vapours which are evolved are condensed and employed
in a subsequent operation. The acid may be finally purified
by crystallization, but the product is usually distilled and thus
immediately converted into the anhydride. The yield amounts
to 30 per cent, on the naphthalene. 5

Phthalic acid is also formed when naphthalene is heated to
130 with 20 parts of nitric acid of sp. gr. 1'15, 40 percent of
the theoretical yield being obtained. 6

1 Weith, Ber. Deutsch. Chem. Ges. vii. 1057. 2 Pircard, ibid. xii. 579.
3 Ann. Chem. Pharm. cxlviii 60. * Bull. Soc. Chim. xxix. 248.

p Schultz, Stcinkohlcnthtcr, S. 540 ; a. E. Fischer, Ber, Deutsch. Chem. Gcs.
xi. 735 ; Depouilly, Ann. Chem. Pharm. cxxxvii. 373.
Beilsteiu and Kurbatow, Ann. Chem. Phann. ceil. 215.



PHTHALIC ACID.



453




454



AROMATIC COMPOUNDS.




PHTHALIC ACID.



455



Properties. It crystallizes from hot water in thin plates or
lustrous, rhombic prisms, 1 which dissolve in 130 parts of water
at 11-5.



100 parts of

dissolve at 15 C



ether absolute alcohol 90 per cent, alcohol,

0-684 10-08 11-70 parts. 2




FIG. 4.



Varying statements have been made as to the melting-point



Online LibraryHenry E. (Henry Enfield) RoscoeA treatise on chemistry (Volume 3) → online text (page 41 of 50)