ANILINE AND ANILINE DYES.— Manufacture of Aniline Oils. 213
tion for tlio purpose (</), and superheated steam (at5 to C atmospheres) blown in through the agitator;the heat effects the reduction of the last traces ofnitrobenzol, and when the cylinder is sufficientlyhot, aniline and water are condensed in the worm.The former being only sparingly soluble in water isreadily separable from the aqueous distillate; thesmall quantity of aniline dissolved in the latter isrecovered by adding salt to the liquor, from whichthe aniline then separates, being much less solublein brine than in plain water. The condensed watermay also be used for generating steam for a secondoperation, whereby the dissolved aniline is also re-covered. Bolley recommends the steam supply tobe so managed, that about 14 parts of water condensefor every 1 of aniline.
Various minor modifications in the shape and sizeof the aniline still, the kind of agitator used, &c.,&e., have been adopted by different manufacturers.Thus many manufacturers dispense with a cohobatingworm, using simply a still provided with an agitatorthrough which steam can be injected at the close ofthe operation ; the distillate which passes over duringthe first energetic action of the iron on the nitroben-zol is returned to the still, as it contains a good dealof unaltered nitrobenzol, which has been carried overwith the steam, &c.
The most important variations in Bicciiamp’s pro-cess as worked by different aniline makers lie in therelation between the quantities employed of nitro-benzol, acetic acid, and iron; if too much of the lattersubstance be used the reaction is apt to go -too far,more hydrogen being added on than is required toform aniline, and ammonia and benzol being formedinstead; thus with nitrobenzene itself;—
C,JT,,N0 2 3II 2 — O r> H 5 ,NIT. 2 + 2II 2 0
C 6 H 5 ,N0 2 + 4H 2 = C 6 H 6 + NII 3 + 2H 2 0
and so on for the higher liomologues. For this reasonit is preferable to conduct the reducing process asabove described (i.e., to add the iron gradually to thewhole of tlio nitrobenzol), rather than to do as somemanufacturers do, viz., put all the iron into the still,and then add the nitrobenzol in small portions at atime. In the latter way of working, the nitrobenzolis always in contact with excess of iron. The presenceof too much acetic acid gives rise to the productionof acetanilide and its liomologues,
C.IL1
C 0 n 6 ,NO„ + C„II 3 0,0II + 3II 2 =3H 2 0 + C 2 tI.jO f n.
HJ
On the other hand, the presence of too little aceticacid and iron is favourable to the production ofnzobenzide from the deficiency in nascent hydrogen:—
2C,jH 5 ,N0 a + 4II 2 = 4H 2 0 + C 12 H 10 N 2 .
The most divergent statements are made by variouswriters as regards the proportions of iron filings,acetic acid, and nitrobenzol to be used in order togain the best result; thus the following propor-tions have been given by the respective authoritiesnamed:
Girard andDe Laire(1873).
Bolley
(1870).
Reimann
(1867).
Koi>p(1864).
Used byRunard andFranc inI860 .
(Girard andDe Laire).
100
100
100
100
100
Acetic acid,.
10- 2
5-10
50
90-100
100
Iron filings,.
140-140
200
150
140-150
200
Water,.
50- GO
—
_
_
—
Hydrochloric acid,
10
—
—
—
—
The following proportions are those actually em-ployed in some large aniline factories with goodresults :—
Of these proportions A corresponds more nearly withthose given by Girard and De Laire (1873), andB with those given by Reimann (18G7).
The yield of aniline oil necessarily varies with thenature of the nitrobenzol used; pure nitrobenzeneshould theoretically yield 75'6 per cent, of aniline;pure nitrotoluene, 78T per cent, of toluidine. Inpractice somewhat less than the theoretical amount isobtained, owing to the formation of bye products andto the presence of impurities in the nitrobenzol, &c.;something like GG parts of aniline oil per 100 of nitro-benzol is a fair average yield. Kremer’s process(see ante ) yields about G5 parts from 100 of goodnitrobenzol, if properly conducted.
It was formerly supposed that the reduction ofnitrobenzol to aniline occurred in virtue of thereaction—
C 6 II 5 ,N0 2 + 2 Fe + II 2 0 = Fe 2 0 3 + C 0 H 5 ,NII 2peroxide of iron being formed; but Sfiller hasrecently shown (British Association Reports, 1873)that magnetic oxide of iron is produced, thus:—4C 6 H 5 ,N0 2 + 9 Fe + 4H 2 0 = 3F 3 0 4 + 4C 6 H 3 ,NII 2The crude aniline oil is next subjected to a processof fractional distillation; the lowest portions of dis-tillate frequently contain benzene and its liomologues,acetone, odorine, &c., &c. Usually the oils are puri-fied by the colour maker himself, that he may obtainthe particular mixtures he prefers. In some cases,however, the oils are prepared for the market accord-ing to contracts, specifying the proportion of thesubstance that shall distil between certain fixedlimits. Light aniline oils distil for the most partbelow, and heavy aniline oils chiefly above 200° C.The term queues d'aniline (aniline tailings) is appliedto the highest boiling heavy oils.
Reimann distinguishes the light and heavy oils bythe names hupbaniUne and baraniline respectively,and gives the following tables as to the compositionof various kinds of commercial oils:—
Knphaniliue.
Baraniline.
Water, odorine, &c.,.
5
Aniline,.
90
Toluidine {para- and meta-h.
70
Higher liomologues,.
30
100
100