ANILINE AND ANILINE DYES.— Production of Aniline. 205
by a similar process. ( Vide article, Benzol .) Themain constituents of commercial aniline oils consistof the lower members of this series, viz,
Nome of Base.
Ratioral
Formula.
Dissected Formula.
Melting
Point.
Aniline, .
Meta-toluidine,. .
Various Xyli \dines, . j"
c 6 ii,n
o 7 it 9 n
c 7 ti 0 n
C 8 H u N
C 6 II, NIL
C TT4 I L
0cI1 1(CILL
C i] 1 ^ L 2
^ ( ou 3 )„,
\ Mil.C 6 II 3 CH»(CII 3
r nil,
r it I CI1 ’ci i,
Lulls
182°
200°
199°
(212°
1 to\ 216
—8°
+ 45°(liquid at
t—20"
Various Cumi- - )
dines,./
Ac., <tc.
^1)1^13^
About
225°
Some liquidttome solid,one meltsat G0°.
Just as various isomeric modifications of certainhomologues of benzene are known, the formulae ofwhich arc distinguished one from the other by specialdevices in their “dissection:” so various isomericmodifications of the higher aniline homologues areknown, denoted by analogous methods. Compara-tively few of these have as yet been submitted tospecial study ; but in the toluidine series all three ofthe isomerides predictable in accordance with thesymbolic system of Kekole for the notation ofbenzene derivatives are actually known (vide articleBenzol ), although only two (para- and meta- tolui-dine), have as yet been shown to exist in commer-cial aniline oils.
In addition to these bodies, the aniline oils ofcommerce usually contain small quantities of othersubstances, for the most part formed as bye-productsduring the manufacture of the oils; the chief of theseconstituents are :—Diamidobcnzene, C 6 II 4 (XII 2 ) 2 ,
{ CII
(NIJ 3 ) ’ homologues
thereof:—Baraniline, C 12 "lI ;l4 N 2 ; Azobenzene,C 12 IIi 0 N 2 ! higher homologues thereof:—Xcnyl-
amme, C^lX^j 6 ; Acetamlide, c '’ n ^ 0 l, N .
H I
Para acet-toluide,toluide,
c a n 4 (cn 3 v
C 2 II 3 o
II
N : Meta acet-
c„n 4 (cn,)„]
C 2 II 3 0 N, &c.II
Aniline (par excellence,'), Amidobenzene, orPiienylamine. —This base was first discovered byUnverdorben in 1826, as a product of the dry dis-tillation of indigo; on account of the facility withwhich its salts crystallize, he applied the term Crystal-line to it. In 1884, IIunge obtained from coal tar asubstance to which he gave the name Kyanol, on ac-count of its power of producing purple or violet-bluetints with bleaching powder. In 1840, Fritzsciiefound that a volatile liquid base is produced, byacting on indigo and certain of its derivatives,with caustic potash; to this he gave the nameaniline, from anil, the Portuguese for indigo.Soon after Zinin obtained a substance, which he
termed Benzulam, by reducing nitrobenzene by alco-holic ammonium sulphide, and Fritzsciie showedthat this substance was identical with his aniline.In 1848, Hofmann showed that crystalline, kyanol,aniline, and benzidam are one and the same sub-stance. In 1856, Perkin discovered the produc-tion of mauve by the oxidation of aniline sulphateby potassium dichromate ; this process he subse-quently patented. The manufacture of anilinespeedily became a recognized industrial operation,the cheapest source being nitrobenzene, which wasderived from the benzene occurring in coal tar.The distillation of the latter hydrocarbon fromthe waste products of gas works is now a distincttrade (vide article Coal Tar Distillation ). The dis-covery of fuchsine by Verguin, in 1858, as a pro-duct of the action of certain dehydrogenizing agentson commercial aniline oils, greatly stimulated thegrowth of this industry; and the subsequent dis-coveries of triphenyl rosaniline (Bleu de Lyons),ethylated and methylated rosanilincs (Hofmann’sblues and violets), aldehyde green, iodine green,violets de Paris, diphenylamine blue, &c., &e., addedrapidly in succession to the magnitude and impor-tance of the trade in colours derived from anilineoils as starting point. The value of the aniline dyesnow yearly manufactured, is estimated by Vers-mann to exceed £2,000,000 sterling.
The chief processes by which aniline can be formedare these :—
A. From Benzene.
1. By the passage of a mixture of benzene andammonia through red hot tubes—(Berthelot).
Benzene. Ammonia. Aniline.
t'G^O 4“ NII a — II 2 -f C a II 6l NH a .
2. By the conversion of benzene into nitrobenzeneand subsequent reduction by nascent hydrogen, orby other reducing agents equivalent thereto.
c G rr 6 -i- no.,, on = h,oii + cyr^NO,tyi^.NO, -p 31-1, = 2U a O + c 0 h 5 ;nii 2 .
The following are the principal methods by whichthe reduction may be effected:—
a Action of alcoholic sulphuretted hydrogen or sulphides—(Zinin),
b “ acetic acid and metallic iron—( Bechamp ).
c " zincandalcoholichydrochloricacid—( Hofmann ).
d ‘‘ zinc dust and hot water— (Kremev).
e “ tin and hydrochloric acid—( Seheurer Kestner).
/ “ hydriodic acid, at 104° C.— (Mills),
g “ caustic soda and grape sugar— (Void),
h alkaline arsenites— (Wohler .
i “ stannous chloride— (Kekule ). •
k Distillation with alcoholic potash, inter alia — (Mils-cherlich).
I Passage through the animal organism— (Lethehj).m Action of iron filings and very dilute hydrochloric acid—(Brimmeyr).
n Water and particles of iron covered superficially with cop-per, by means of a short immersion in copper sulphatesolution—( Coblentz).
o V ater and solution of cuprous oxide in ammonia--
( Wagner).
p Water and carbon disulphide at 1G0° G.~(Schlagdenhau-jjen).
B. From Phenol.