INDUSTRIAL AND ENGINEERING CHEMISTRY
910
FISSIO% PRODUCTS
On alkaline fusion of the tannin and t>he phlobapherie oiily prot,ocatechuic acid and catechol werr isolated. Other phenolic residues may be present, hut it has not, been possible to isolatt, othrr fission products. .Ukaline fusion of methylated tannin and methylated phlobaphene yie1dt:d veratric acid. Oxidatioir of the methylated tannin also g:tw veratric': acid. V;iciium di-tillation of the phlobapherie gavc catechol and a sm:ill :imoiinl ot p ti r no1.
~IsctissIoxOF
iiroxylated. The small amount of methoxyl which is present is bc'licved to be attached to the 3' position. The small amount of phenolic hydroxyl groups suggests t'hat the other aromatic ring is hydroxylatcd to a much lesser degree, if a t all, than are the other phlobatannins. The carbon cont>entis too low and the hydrogctri too high for a structure similar to th:it pict,urc: by Russell but containing fewer hydroxyl groups. The ultraviolet absorption spectra of both redwood tannin m d piilohapheno are somewhat similar to that of lignin. .iCKNOWLEDGllENT
RESULTS
Redwood tannin belongs t o thr. phlobatanriiii class. It coiit,aiiic soruca.hat less phenolic groups than d? other members of this c1:tss. It contains a small hut appreciable amount of methoxyl. The phlobaphene fraction appoars t,o contain 30-35% of native lignin in addition to the true phlobaphene. This is not surprising, i n view of the similar solubility hehavior of the two matc:rialrj. If the results are correctcd for thts presence of lignin, the (rut. phlobaphene contains only R *dightly higher methoxyl contwit and less phenolic and aliphatic hydroxyl groups than docs 1ht' tannin. The true phlobaphene thus appears to be a c0ndens:tliori product of the tannin, in which both the aliphatic and the phtwolii~ hydroxyl groups are involved. Attempts have been macle to t,>tablizh a formula for redivouii 1annin on the basis ' of Ruswll's general type forinula for thr phlobatannins ( 6 ) . However, it has not heen possible t o fit any single formula to all of the known d a h . This suggrrts that) the t,:mnin fraction is not, homogencwi-; but consiqts of txinins 01' slightly different compositions a.hirh, hoiwvor, po solubility characteristics. Reriiusc: protocatechuic :rid is o b tained on fusion, it appears thr{t the 3', 1' ptwitiotis :in' ti>,-
Vol. 36, No. 10
'rhe authors are indebted to A. Russell for supplying the sample of mimosa tannin and Cor suggestions and comments relative to this work, and to J. A. Van don Alcker for determina,tion of the absorption spectra. Appreciation is expressed to The Pacific TJumber Company for permission to publish this work. LITERATURE CITED
(1) Brauns, F. E., J. .4m.Chem. SOC.,61, 2120 (1989). (2) Freudenberg, K., "Tannin. Cellulose. Lignin", pp. 4, 15, 18.
;3)
(4) (5) (6)
(7)
Berlin, Julius Springer, 1933; "Handbuch der Pflanzenanalyse", Vol. 3, pp. 345, 353, 355, Vienna, Julius Springer, 1932. Glading, R. E., Paper Trade J., 111, No. 2 3 , 32 ( h e . 5 , 1940). Nierenstein, M., in "Allen's Commercial Organic Analysis", Vol. V, pp. 2, 4, 13, 60, Philadelphia, P. Rlakiston's Son & Co., 1927. Patterson, R. F,,and Hihbert, H., J . Am. Chem. Soc., 65, 1863 (1913). Russell, A, Chem. Rev., 17, 155 (1935). Russell, :I., Todd. J., and, Wilson, C1. L., J . Chem. Soc., 1934, 1940.
;8) Van den
Akker, J. h.,U.8.Patent 2,312,010 (Feb. 23, 1943).
hefore the Iliviiion uf Celiulose Chemistry ;it t h e 107th ?deetirig 01 t h e 4vrnr~-,\.vC ! n E u I r , . \ L S O C I E T Y Cleveland, , Ohio. t'REsEa1,r.u
us an
r ra
s
Specific heats of ferrous chromik a i d atiaguesbrn chromite have been measured throughout the temperature range 52 ' to 298' K. Ferrous chromite has two anomalies in its bpecific heat curve, one pralc occurring at 75" and the other at 135" K. The f~llowiiaigmolal entropies at 288.16" IC. were computed: ferrous rhromite, 34.9 * 0 . t E.['.; ~iiagncsiurra rhromite, 25.3 II: 0.2 E.V.
N E oi the recent programs oi the Buleau of M1r1t.s lid5 t w . 1 1 a study of the beneficiation and utilization of low-pradc domestic chromite ores. A i part of this program the Yacific Experiment Station has made thermochemical atudies 01 rompounds of importance in the metallurgy of chromium. This paper presents low-temperature >pecific heat and entropl data for ferrous chromite and magnesium chromite. The chromite samples were prepared in thii laboratory b) F. R. Boericke and W. M. Bangert. Ferrous chromite way made by heating in a vacuum to 1300" C. a finely ground stoichiometric mixture of high-grade qponge iron, reagent-grade ferric oxide, and chromic oxide of high purit7 The re.nction I * rrprcasented by the equation Fe
+ Fe&
-
3< I Oo = dPe('rbO,
t h i , tirial pro(iiic.t slio\vwl 99.'25VG Fe('rz04 and
Magnesium chromite was prepared in a similar manner by rtha cting reagent-grade magnesium oxide nith t,hp chromir oxide :it L400"
C. according t o the reaction, SIgO
+ ( h O a = bTg(?r20,
saniple analyzed 99.5% illgC'rs04arid 0.5'l/OFeCrs04. X-ray analyses of the crystal etructures of the samples were imide by E. V. Potter of the Salt Lake Cit,y Station of the Bureau ,)i bIines. The feyoous chromite shos-ed a cubic lattice with a parcimetw of 8.358 A. The pattern for this sample checked well i v i t t i those previously reportwl for syntlirtic and natural chromito. Yo inipiirity was prv-f'iit i i i -uifii+nt qiia ntity to exhihit adtii'L'lit:
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1944
TABLE I. SPECIFICHEATS K. 53.3 56.9 60.7 64.7 68.6 72.8 76.9 80.3 83.9 94.3 104.2 114.7 123.3 123.9 126.2 128.9 131.0 133.0 134.8
T
FeCrzO4 (Mol. Wt. = 223.87) C p , cal./mole T O K. ~ p cel.imole , 134.9 7.000 136.8 7.642 138.9 8.381 145.3 9.155 9.929 155.3 10.50 165.3 175.3 10.48 185.2 10.65 11.02 195.8 205.8 12.42 216.6 14.00 226.0 15.83 235.6 17.44 246.1 17.56 255.9 18.06 265.8 18.67 19.24 276.4 286.0 19.87 20.22 296.2
MgCrzOr (Mol. Wt. = 192.34)-T ~ K .~ p cal./mole ,
I>(
D
91 1
p)+ D ( y )+ (F),
giving Ss3.0g =
4E
2
4.13 E.U. per mole
(F)+ 2 E (7) + 4 E (y),giving x
~= ~ . ~ ~
4.74U. per mole
The method of Kelley, Parks, and Huffman (2) also was used tuv extrapolate the normal curve to 0" K., using magnesium chromite as the standard substance in their extrapolation method. This extrapolation gives 8 6 3 . 0 9 = 4.28 E.U. per mole. A mean of these three values, 8 6 3 . w = 4.38 E.U. per mole, is adopted as t h e extrapolated portion of the entropy. The entropy associated with the hump a t 75" K. in the sperjfivheat curve of ferrous chromite was determined by actual summa-
y,
rn
of the seven lowest specifir heat determiiia-
tion, i= 1
tions. This was a series of determinations with little or no intervening temperature gaps. Minor corrections were applied f o bring the final temperature of each determination into exact coincidence with the initial temperature of the immediately following determination. The total entropy increase from 53.09' to 79.43" K. is 3.668 E.U. per mole, and the total heat absorption
in this interval, also obtained by summation, tional lines. The magnesium chromite also checked known spacings; its parameter was found tc be 8.31 A.
2
i-1
CpdA T , is 243.2
ralorirh per mole.
SPECIFIC HEATS
The method and apparatus used in the low-temperature specific heat measurements have been described previously (1, 9). The experimental results, expressed in defined calories (1 calorie = 4.1833 international joules), are listed in Table I and shown graphically in Figure 1. The molecular weights in Table I are in acrordance with 1941 International Atomic Weights. Corrections have been made in the Rprrifir heat results for the previously mentioned impurities, Magnesium chromite exhibited normal behavior throughout the temperature range studied. Two "humps", however, appear in the specific heat curve of ferrous chromite, the peaks being at 75' and 135' K. Anomalies such as these are not uncommon in ferrous iron compounds; similar humps have been reported in the specific heat curves of ferrous oxide, ferrous sulfide, ferrous chloride, and ferrous silicate. ENTROPIES AT 298.16O K.
The evaluation of the entropies at 298.16' K. is obtained by graphical integration of a plot of C p against log T. This necessitates the extrapolation of the specific heat curves from the temperature of the lowest measurements down to the absolute nero of temperature. It was found that the function sum,
D ( 7 )
+ 4 E (F)+ 2 E (q)
adequately represents the magnesium chromite specific heat data in the measured range up to 200' K.; symbols D and E denote, respectively, Debye and Einstein functions. These functionsowere used for extrapolating the data down to 0" K. to obtain 8298.16 = 25.3 * 0.2 entropy units (E.U.) per mole, of which 1.63 E.U. is extrapolation below 53.09' K. Extrapolation of the specific heat curve of ferrous chromite down to 0' K. is difficult by any method because of the abnormal specific heats in the vicinity of the lower hump. A smooth "normal" curve was drawn, connecting the points above 138' K. with the points a t 80.3' and 83.9" K., and with the lowest point a t 53.3" K. Two functions sums were found to represent adequately this normal curve up to 150' K.:
30
25 0
a
E
L 2o
10
5
c
50
100
150
I
I
200
250
I SO0
T OK. Figure 1. Specific Heats of Ferrous Chromite (A) and Magnesium Chromite (B)
A similar aet of specific heat deterniinations was made over the rrgion of the larger hump a t 135" K. I n addition, each of two determinations of the total heat absorption between 120' anti 140' K. gave 366.2 calories per mole. The entropy increase from 120' to 140' K. is 2.820 E.U. per mole. The'total measured entropy increase from 53.09' to 298.16' K. is 30.52 E.V. per mole. Adding to this the value adopted for the extrapolated portion of the entropy gives ~$98.16 = 34.9 * 0.4 E.TJ.per mole. LITERATURE CITED
(1) Kelley, J . Am. Chem. SOC.,63,1137 (1941). (2) Kelley, Parks, and Huffman, J . Phys. Chem., 33, 1802 (1929). (3) Shomate and Kelley, J. Am. Chem. SOC.,66, 1490 (1944). PUBLIERED by permission of the Director, U. S. Bureau of Mines.
