378
J A M E B R. POUND
3. A method for estimating the free formaldehyde during the course of a ureaformaldehyde reaction is presented. In conclusion I wish to express my thanks to Dr. T. Iredale for valuable advice and discussion. REFERENCES (1) DE CHESNE,E.B . : Kolloid-Beihefte 36,387 (1932). (2) DIXON,A. E . : J. Chem. SOC.113,238 (1918). A., AND HAYBURQER, A . : Ber. 41,24 (1908). (3) EINHORN, (4) EINHORN, A.: Ann. 343.207 (1905);361, 113 (1908). S., LAIDLER, K . J., AND EYRING, H . : The Theory of Rate Processes, pp. 18(5) GLASSTONE, 20. (1941). (6) GOLDSCHYIDT, C.: Ber. 29, 2438 (1896);Chem.-Ztg. 46, 460 (1897);J. Chem. Soc., 74, 178 (1898). (7) LECHER, H.: Ann. 438,154 (1920); 446,35 (1925);466,139 (1927). (8) REDFARN, C. A , : Brit. Plastics 6,288 (1933). (9) SCHEIBLER, H.,ANDCOWORKERS: Z. angew. Chem. 41,1305 (1928). (10) WALTER, G., AND GEWING, M.:Xolloid-Beihefte 34, 163 (1936).
ANILINE FORMATE AND ITS CHANGES OK KEEPING
JAMES R. POUXD The School o j Mines, Ballarat, Victoria, Australnu
Received September 84,1046
A study of the system aniline-formic acid-water was made in 1934 by A. M. Wilson and the present writer (1). The conditions under which crystals of aniline formate were obtainable a t room temperatures were indicated, and also the changing of these crystals into formanilide and water. There are two equilibria involved : (1)
Aniline
+ formic acid S aniline formate
(2)
formanilide
+ water
These affect both the liquid mixtures and the solid crystals of aniline formate I. CHANGES Ih’ THE CRYSTALS OS KEEPIKG
The original colorless crystals of aniline formate become in a few days sticky, then they often completely liquefy, then crystals of formanilide separate, and finally the whole re-solidifies. These changes generally are retarded in the presence of a drying agent. After twelve years four sealed samples of such crystals were re-investigated. There were determined (a) the “free formic acid” (by direct titration with alkali), ( b ) the “combined formic acid” (by boiling with excess alkali and back-titration by acid), and (c) the total aniline (by the bromate method). (6) indicates the formanilide content, and ( a ) the aniline formate
379
ANILINE FORMATE
content (plus the excess actual formic acid, if any). The results are given in table 1. The designations of the samples are the same as given in the previous paper. (The per cent by weight of “free formic acid” in aniline formate is 33.1 per cent; formanilide gives per cent “combined formic acid” = 38.0 per cent and “combined aniline” = 76.8 per cent.) Samples F and G were from the same parent lot of crystals, and samples P and R from another such lot. Sample F had re-solidified some time before seven years; the final solid might have been expected to contain moisture, but the analysis showed that it was 100 per cent formanilide, and it had the highest melting point of the samples. TABLE 1 Changes in aniline formate crystals ouer a period of time “FPLE SAKPLE
KEPT
W I E P TILU
IOaalIC
CONDIIION OF SAXPLE
ACID”
per ccnt
F .......................
In sealed tube (by itself)
G. . . . . . . . . . . . . . . . . . . .
Over HZSO.
1 day 13 days 12 yr.
32.5 7.9 0
Colorless crystals Liquid White and gray crystals, fairly loose; m.p. 47%.
1 day
32.5 58.8 3.6
Colorless crystals Sticky Dry compact creamy solid; m.p. 33%.
33.8 31.2 2.0
Colorless crystals Slightly sticky D r y compact creamy solid; m.p. 42°C.
33.8 32.2 0
Colorless crystals Slightly sticky Very hard compact whitish lump; m.p. 44°C.
13 days 12 y r .
P. . . . . . . . . . . . . . . . . . . .
Over PzOl
0
9 days 12 yr.
I< . . . . . . . . . . . . . . . . . Over HsSO, Over PzO,
0
7 days 12 yr.
Sample G became “damper” or stickier after several weeks, and slightly yellowish; “drier” and more opaque after twelve months, and there was a sublimate above the sample (possibly of aniline sulfate). The final solid contained 11 per cent of aniline formate and 89 per cent of formanilide. Sample P became “damper” for a couple of months, then drier and seemed dry after a year; the final solid contained 6 per cent of aniline formate and 94 per cent of formanilide. Sample R was kept over sulfuric acid for the first 9 days, then over phosphorus pentoxide; it became “damper” from the first day and was completely liquid on the tenth day, recrystallizing after two months; it remained solid thenceforth, but became slightly discolored with time. The final solid was 100 per cent formanilide.
380
JAMES R.. POGND
F and R, which a t one stage were completely liquid, had changed completely t o formanilide; but G and P , which were never completely liquid, had not done so. The rate of change to formanilide vas fastest for F. 11. CHAXGES
IN THE LIQUID MIXTURES OK ICEEPISG
These changes have been indicated in the previous paper. Certain mixtures of aniline, formic acid, and water separated on keeping into two layers; others remained homogeneous for periods up to a year (at least). (a) In the homogeneous mixtures the percentage of free formic acid diminished wit,h time and reached an equilibrium value after 15 or 20 days. In the mixtures 10, 32, 35, and 39 (ivhich are referred to in the previous paper) the percentages of free formic acid after one year (actually 314 to 369 days) were 24.2, 33.9, 40.6, and 62.1, respectively,-all being within a few tenths of 1 per cent of the values quoted before. Mixture 38, ivhich was originally 62.6 per cent formic acid, 17.7 per cent aniline, and 19.7 per cent water, gave after the days indicated in [ ] the following per cent free formic acid ( ) : [O], (62.6);[l], (61.0);[4], (58.0); [ l l ] , (33.1); [le], (55.6); and [319], (55.8). The last figures indicate that the liquid then had the composition: formanilide, 18.4 per cent; aniline formate, 5.4 per cent; actual formic acid, 53.8 per cent; water, 22.4 per cent. When equilibrium was reached in the above five mixtures and in mixtures 3 and 6 (q.0.) there were present finally 61-22 per cent actual formic acid, 2-6 per ceilt aniline formate, 18-49 per cent anilide, and 14-44 per cent water. The actual aniline in the solution was always taken as 0 ; or the aniline was present wholly as anilide and as formate, there being always formic acid in excess. I n the final solutions the ratio Per cent free formic acid Per cent combined formic acid varied from 2 t o 8. The ratio
Per cent anilide X per cent water Per cent aniline formate varied from 76 to 261 (mean 173), and this roughly subst'antiates the second equilibrium (equilibrium 2). The ratio Per cent actual formic acid Per cent aniline formate varied from 16 to 4.5, and this substantiates the first equilibrium (equilibrium I ) , assuming some small constant value for the per cent actual aniline. ( b ) Heterogeneous mistures: Many mixtures of aniline, formic acid, and water, though homogeneous a t first, separated in time into tyvo layers. This separation is associated with the formation of formanilide (see reference l), and it occurs in several days. Seven such separated systems \Yere analyzed: one, 37 days after separation; the other six, t\velve years after separation, all being kept in sealed glass tubes. The analyses of four of the six long-term samples are given in
381
ANILIKE FORMATE
table 2; and the other samples gave similar results. The equilibria then are attained in the course of days, rather than years. The first four columns of table 2 give the primary results, and the last five columns the calculated constituents. In all the layers the per cent actual formic acid and/or the per cent aniline is zero; in other words, as either the acid or the aniline is in excess, the calculation is so adjusted. By the method of analysis adopted it is not possible to discriminate more exactly beta-een the actual formic acid and the acid present as aniline formate,-both “acids” being included in the “free formic acid.” TABLE 2 Data regarding mizturcs o j formic acid, aniline, and water after separation into two layers
I
_ _ __ per cent
~
cent
16 Original mixture* Aqueous layer Aniline I a j e r
100 31 69
l i Original m x t u r e
100 19 5 2 5 ’ 0 6 1 2 75 0 2 1 2 4 8
Aqueuus layer 4niline layer
10 5
Ii per
I
F
per
ten1
58.4 4.1
R5.0 60.1 4.1 i6.5 I
18 Original mixture Aqueous layer Aniline layer 8 Original mixture
Aqueous lager Aniline layer
100 33
62
30 5 58 10 8
1 100 1 33 2 2LIl49 i 6 I 10 2
I
31 . ! I
2 2 27 2
37.6 6.9 57.2
l4.G 9.7
2 5 27 9
15.9 6.2 57.6
10 1 1 1.8 1 73.5
I
~
~
3.6 3.4
5.8 ’
il.6
~
1
0
iG.0
0
15.l
0
14.6
* By synthesis. The per cent of aniline formate is always small, and this carries the largest proportional error. In the “aqueous layers” the ratio per cent formanilide/per cent aniline formate averages 2, but in the “aniline layers” this ratio is 50 or more. In the aqueous layers the ratio Per cent formanilide X per cent water Per cent aniline formate averages 175 (as in the homogeneous mixtures), but in the “aniline” layers it is 300 and over. The formation of formanilide is thus most complete in the absence of water. The ratio Per cent actual formic acid in the aqueous layer
Per cent actual formic acid in the “aniline” layer
=
1.5
382
LAWREKCE HARBURY
The “total aniline” and the “combined formic acid’’ or “anilide” are ten to seventy times more abundant in the “aniline” layers than in the aqueous layers, but the “free formic acid” is more evenly distributed ( 1 : l to 2 : l ) . This work completes the previous investigation. It proves that the transformation of crystals of aniline formate to formanilide is often very slow, being retarded if free water is absent. I n the liquid mixtures of formic acid, aniline, and water the two equilibria concerned are completed in one or two weeks; thereafter the four or five constituents remain mixed indefinitely. When such liquid mixtures separate into tivo layers, equilibrium is again attained, with the formanilide and aniline preponderating in the lower layers. REFERESCE (1 j \YILSOS,
.I,M.,
l’ocsu, J . I t . : J. l’hys. Chem. 39, TOO (113351
. ~ s i i
soLmmrn- ASD
MELTISG IWST AS FUSCTIOSS OF PARTICLE SIZE. 11’
THE IXDCCTIOK PERIODOF CRYSTALLIZATIOS LAWRENCE HARBCRY Kentuckg Color and Chemical Co., Inc., Louisuille, h-enfucby Receiterl Sepleniber 17, 1946 I. IKTRODUCTIOX
Fischer (2) found for several easily soluble salts,Yas well as for poorly soluble salts3 and also for an organic acid such as oxalic acid, an induction period of crystallization from supersaturated solutions. This period of induction must be passed before the separation of a new phase becomes traceable. It varies from substance t o substance, but, when appropriate conditions are taken care of, it satisfies in each case the relation:
C d ? = const’ant
(1)
In this formula C stands for the degree of supersaturation, C/CO, and I for the corresponding period of induction. The function indicates a rapid decrease of the period of induction with increase of the degree of supersaturation. Such a behavior has also been found, for other substances, by Gapon (3). 11. SOXE THEORETICAL ASPECTS O F THE IXDUCTION LAW
When endeavoring to find out the reason for the behavior expressed by formula 1, let us restrict ourselves first to a consideration of the spontaneous formation of 1
For the first paper on this topic see Harbury (5). K&r20,, (KHJzCZOI.HZO, and (TH,j*S04,FeSO,.6HzO. Such as AgzCr04,BaSO,, SrSOd, CaSO4~2HzO, CaC03, P b L , i i g ~ s O 1PbSOc, , PbCrOd, and MgC20r.2H20.
* Such as &SO4, 3
