The Reaction between Basic Aluminum Sulfate and Hide Substance

166

E. 0. WILSON AND S. C. YU

T H E REACTION BETWEEN BASIC ALUMINUM SULFATE AND HIDE SUBSTANCE E. 0.WILSON

AND

8. c. Y u

Department of Chemiatry, Yenching University, Peking, China

Downloaded by UNIV OF MANITOBA on August 26, 2015 | http://pubs.acs.org Publication Date: January 1, 1941 | doi: 10.1021/j150406a015

Received November 1 , 1090

Aluminum compounds are used t o some extent in tanning, and it has been shown that the reaction between basic aluminum sulfate and hide substance is similar to analogous reactions in chrome tanning. The chemistry of aluminum salt solutions has been very thoroughly investigated by Wilson (6, 7), Thomas and Whitehead (5), Kiintzel (2) and others, and the general conclusion may be drawn that the differences between the behavior of chromium and aluminum salts in solution are differences of degree rather :than kind. Werner’s coordination theory has been applied, and it is known that “olated” complexes are formed which are in all respects similar to chrome complexes. Basic aluminum sulfate is a less vigorous tanning agent than basic chromium sulfate, and less research work has been done oh the chemistry of aluminum tanning. This laboratory has had the problem under consideration for a number of years, and several minor investigations have been carried out. Recent work by Cameron and McLaughlin (1) indicates that chrome tanning is a reversible adsorption process. These workers also conclude that the extent of the reaction between basic chromium sulfate and hide substance is quantitatively related to the concentration of free acid present in the system, and that the chrome compound fixed by the skin (hide substance) is of 663 per cent basicity regardless of the basicity of the solution used for tanning. The authors of this paper have carried out an investigation with the purpose of determining whether these important conclusions can also be applied to alum tanning. EXPERIMENTAL

The hide substance used was from calf skin. The epidermis and other non-collagen materials were removed by methods similar to those used in the tannery, After “liming,” “scudding,” and “bating,” the skins were soaked and thoroughly washed with distilled water to which chloroform had been added to check bacterial action. After dehydration with acetone, the skins were air-dried and cut into pieces 1-in. square. In one series where the effect of the removal of certain amino groups was to be studied, the prepared skins were deaminized by treatment with nitrous acid, following the method of Thomas and Foster (4). The preparation of basic aluminum sulfate solutions presented some

BASIC ALUMINUM SULFATE AND HIDE SUBSTANCE

167

difficulty, as it was desired to prepare solutions free from neutral salts. This was accomplished by treating solutions of pure aluminum sulfate with sufficient barium hydroxide solution to produce a compound of the desired basicity. The reaction in the case of a 33;j per cent salt is:


2A12(SO&

+ Ba(0H)g * BaS04 + SAl(0H)SOd

The resulting solutions were allowed to stand 1 or 2 weeks before filtering, then aged for about 6 months, and again filtered. Clear stable solutions were formed in all cases. The exact basicity of the solutions was determined experimentally before use. Solutions of five different basicities were prepared+, 11.49, 22.5, 21.8, and 33.3 per cent. These are later referred to as series A, B, C, D, and E. Seven-gram samples of the prepared skin were weighed into 125-cc. conical flasks, and a sufficient quantity of the basic aluminum sulfate solution added to produce a solution of the desired concentration. The h a 1 volume of solution used in each case was 110 cc. The sealed flasks were placed in a constant-temperature bath and rotated for 48 hr. The experiments of series A, B, and E were carried out a t 25' C. ; those of series C and D were carried out during very hot weather and the temperature was kept a t 35OC. After tanning, the skins were removed from the flasks and the mechanically held liquor removed by pressing with a Carver laboratory press. A pressure of 10,000 lb. per square inch was used. The pressed skins were cut by hand into small pieces, dried, and analyzed. Moisture, aluminum, nitrogen, and sulfate were determined in the tanned skins, and alumina and sulfate in the equilibrium liquor. The determination of nitrogen made it possible to report the fixation of alumina in terms of collagen. The factor 5.58 was used to convert nitrogen to collagen. This factor was obtained directly from our experimental data. RESULTS

The fixation of alumina as a function of concentration is shown in figure 1, and figure 2 gives the results of the deaminization experiments, The various basicities used are shown on the graphs. Figure 3 shows the values taken from figure 1 plotted on a logarithmic scale. The curves indicate that the fixation of alumina by collagen is an adsorption process and may be represented by the Freundlich equation. The deaminization experiments show that the amino groups play an important part in alum tanning, fixation being greatly reduced by removal of a part of the nitrogen. This effect is especially noteworthy a t the higher basicities. The decrease in fixation as calculated from our experimental data is much greater than can be accounted for on the assumption of direct chemical combination of aluminum complexes with the amino

E. 0. WILSON AND 6. C. YU

I2 IO

8


6 4

2

0

04

OB

1 2

1.6

2.0

24

2.8

3.2

GRAMS Alz03 PER 100 CC. FIG.1. Alumina fixed by collagen plotted against the concentration of alumina in the equilibrium liquor. Curve A (e),A series, 0 per cent basic; curve B (A),B series, 11.49per cent basic; curve C (Oj, C series, 22.5 per cent basic; curve D ( X j , D series, 21.8 per cent basic; curve E (a),E series, 33.3 per cent basic.

GRAMS A1203 PER 100

CC.

FIG.2. Plot showing the effects of deaminization on alumina hxstion. Curve I, normal skin, 33.3 per cent basic; curve 11, deaminized skin, 33.3 per cent basic; curve 111, normal skin, 11.49per cent basic; curve IV,deaminized skin, 11.49per cent basic.


169


groups. No final conclusions as to the mechanism of the reaction can be drawn from the numerical results. In order to apply the methods which Cameron and McLaughlin used to ascertain the basicity of the deposited complex, we have recasl our analytical data and made calculations as shown in table 1. First the assumption is made that the compound fixed by the collagen is a 100 per cent basic aluminum hydroxide. The results are shown graphically in figure 4. The experimentally determined concentrations of sulfate in the

GRAMS AI203 PER 100 CC. FIG.3. Log-log plot of the same data shown in figure 1. Curve A ( O ) ,A series, 0 per cent basic; curve B ( A ) , B series, 11 49 per cent basic; curve C ( O ) , C series, 22.5 per cent basic; curve D ( X ) , D series, 21.8 per cent basic; curve E (a),E series, 33.3 per cent basic.

equilibrium liquor are plotted as abscissa versus the total sulfate found by analysis of the tanned skins. Logarithmic plots are shown in figure 5. For any one given basicity the points fall on a straight line, but a series of liquors of different basicities give a series of straight lines. Next the assumption is made that the aluminum complex fixed is 663 per cent basic, and the calculated values of acid sulfate potentially free in the equilibrium liquor are plotted as abscissa against the calculated values of proteinbound sulfate. The points are plotted on figure 6 to a uniform scale and on a logarithmic scale on figure 7. Jf smooth curves were drawn through the points on these two plots, one would obtain an approximate adsorption

TABLE 1


A series: 0 er cent basic

172.8 155.5 138.7 116.8 99.7 81.1 65.3 49.3 30.4 20.4 13.1 6.71

157.5 140.3 124.7 105.5 90.6 75.3 57.4 43.1 25.16 16.58 10.55 2.99

257.4 263.4 250.3 246.0 237.6 207.4 195 185 167 150 115

249 246

223 223 220 203 189 171 156 132 117 75

99.9 88.5 78.5 66.6 57.4 46.3 35.6 26.7 15.06 9.80 6.18 0.06

163.2 158.2 139.6 141 .O 140.8 120 106 94 76 67 37

42.3 36.7 32.3 27.7 24.2

77.4 70.4 56.2 59.0 61.6

13.8 50.9 10.3 41 5.0 32 3.0 20 1.82 17 Vegative Negative

B series: 11.49 per cent basic

156.9 140.7 124.7 105.0 90.7 71.7 56.1 38.5 22.84 13.0 7.81 1.93

192.5 172.8 150.2 130.7 111.3 89.4 70.5 49.3 30.0 17.4 11.1 5.65

447 421 378 374 347 331 312 280

217 180 124

329 323 292 266 243 235

224 197 169.5 142.4 115.8 71.3

92.7 83.1 74.6 61.4 53.6 41.9 32.6 22.1 7.2 4.1 0.05

180 183 168 141 127 125

im 104 70.1 55.8 30.0

28.5 25.5 24.5 17.8 16.4 12.1 9.1 5.7

31 43 40 16 11 15 16 11

1.4 Negative Negative 0.4 qegative Nega t I ve

C series: 22.6Der cent basic 91.7 82.0 73.4 62.6 52.8 42.2 31.2 22.3 13.3 9.04 5.03 1.77

123.8 111.6 95.8 82.4 67.8 53.8 38.8 27.1 15.45 10.45 6.15 2.35

464 418 413 411 383 380 351 313 256 207 152 116

304 264 266 262 237 212 194 173 140 129 98.2 59.8

50.4 44.8 41.5 35.1 30.2 24.3 18.3 13.6 8.2 5.5 3.0 1.0

149 115 128 125 109

85 77 69 55 60 47 20.8

9.1 7.6 9.6 7.6 7.6 6.4 5.4 4.6 3.15 2.0 0.95 0.22

-6

~

*

a b c d e

milliequivalents Alz08 per 100 cc. of equilibrium liquor. milliequivalents SO4per 100 cc. of equilibrium liquor. milliequivalents A1208 fixed by 100 g. collagen. milliequivalents so4 fixed by 100 g. collagen. available SO4in the equilibrium liquor if a 66t per cent complex is assumed ( b - )a). f = protein-bound SO,in leather if a 66t per cent complex is assumed (d - ) c ) . e’ = available SO,in the equilibrium liquor if a 334 per cent complex is assumed ( b %a). f’ = protein-bound SO,in leather if a 33) per cent complex is assumed (d tc). 170 = = = = =

-

-

171


8

.

1

b

]


TABLE 1-Concluded d

1

e

1

f

I

e’

D series: 21.8 Der cent basic

__ 83.8 74.3 62.7 53.7 42.3 35.6 25.4 18.4 10.5 6.88 2.94 2.71

I

D

65.1 58.2 49.8 43.6 35.8 29.6 22.3 15.9 9.31 6.52 5.74 1.67

269 263 250 2.33 22.3 215

397 388 386 375 366 361 338

200

225 186.5 138.3 83.6

171 139 118 91.1 59.3

37.2 33.4 28.9 25.7 21.7 17.7 13.5 9.8 5.8 4.23 4.76 0.77

137 134 121 108 101 95 87 64 46 45 31.4

9.3 8.6 8.0 7.8 7.6 5.8 4.7 3.7 2.3 1.94 3.78 Negative

1

f’

____ 5.0 5.0 Kegative Kegativc Negative Negative Negative Negative Negative Negative Negative Negative

E series: 33.3 per cent basic 78.6 69.3 52.0 46.7 30.3 27.6 20.2 14.24 5.58 3.06 6.47 2.24

53.6 47.8 37.1 34.5 23.1 20.8 15.24 10.63 3.45 1.69 5.31 0.326

664 662 645 658 593 515 447 373 225

209 299 75.8

315 305 286

281 219 195 166 97.0 74.2 124 22.3

27.4 94 1.2 Negative 24.7 1.6 Negative 84 19.8 71 Negative 2,5 62 18.9 3.3 Negative 13.0 2.9 Negative 11.6 47 2.4 Negative 8.5 46 1.8 Negative 42 5.88 1.13 Negative 1.59 22 Negative Negative 0.67 4.2 Negative Negative 3.15 24 2.99 Negative Negative Negative Negative Negative

curve from figure 6 and a straight line from figure 7. The deviation of the individual points from a straight line in the logarithmic plot is considerable. Cameron, McLaughlin, and Adams (3) have obtained similar results with a series of chrome liquors of different basicities, and since their points fall on a single common line, regardless of the basicity of the original liquor, conclude that their assumption of a deposited chrome complex of 663 per cent basicity is correct. We have replotted the curve obtained by these authors on an enlarged scale, as shown in figure 8. Inspection of this figure shows that we have a series of parallel lines for the different basicities, and that it is incorrect to state that all of the points fall on a single straight line. The above considerations have caused us to question the conclusion of Cameron and McLaughlin that the deposited chrome complex in the case of their experiments is a 663 per cent basic compound. The following mathematical treatment is given to show that if any given basicity such


MEQ. SULFATE PER 100 CC. FIG.4. Plot showing acid sulfate fixation if 100 per cent basicity of the compound fixed be assumed. Curve A (e),.4 series; curve B ( A ) , B series; curve C (O), C series; curve D (X), D series; curve E (a),E series.

MEQ. SULFATE PER 100 CC. FIG.5. Log-log plot of the same data as in figure 4. Curve A ( O ) ,A series; curve B ( A ) ,B series; curve C (O), C series; curve D (X), D series; curve E (a),E series. 172

0

U

U

I


z

MEQ. SULFATE PER 100 CC. FIG.6. Plot showing acid sulfate fixation if 663 per cent basicity of the compouna fixed be assumed.

MEQ. SULFATE PER 100 CC FIG. 7. Log-log plot of the same data as in figure 6 173

174

E. 0 . WILSON AND 0. C. YU


aa 66g per cent for the chrome (or aluminum) complex be arbitrarily assumed, and the calculated potentially available free sulfate be plotted against the protein-bound sulfate on a logarithmic scale, all of the points for different basicities will not fall on a single straight line if the fixation of chromium (or aluminum) follows the Freundlich adsorption isotherm.

FIG.8. Enlarged plot of the data of Cameron and McLaughlin for acid sulfate fixation on the assumption that the deposited chrome compound is 66# per cent basic. 0 , 0.4 per cent basic; 0 ,2.8 per cent basic; X, 15.8 per cent baaic; A, 17.5 per cent basic; 4, 33.2 per cent basic; Q , 36.7 per cent basic; 0 , 43 per cent basic; W, 46 per cent baeic. (Replotted from J. Am. Leather Chem. Assoc. S I , 104-5 (19371.)

In the following development the notation is similar to that used by Cameron and McLaughlin except that, for convenience, concentrations have been evressed in terms of eauivalents. L e t u = e&ivalents of cr203 gi;en, b = equivalents of CaO3 fixed, c = equivalents of C1-303 unfixed, d = total equivalents of acid sulfate present, e = equivalents of acid sulfate to make a to x acidity, f = equivalents of available acid (d - e), g = acid sulfate to make b same basicity as original liquor, h = acid sulfate to make b to z acidity, i = protein-bound acid sulfate (g - h ) ,


j = unfixed acid sulfate in system (f

175

- i), and

y = acidity of original liquor expressed as the fraction of total

chromium combined with sulfate. In terms of the Freundlich equation,

i

= k(j)m

From the above relations: Downloaded by UNIV OF MANITOBA on August 26, 2015 | http://pubs.acs.org Publication Date: January 1, 1941 | doi: 10.1021/j150406a015

- e) (9 - h)

e = az, f = (d

d = ay,

by, h

=:

bx, i =

j = (f

-

i)

- x) = b ( y - 2) = ( a - b)(y - 2) = a(y

Substituting in the Freundlich equation: b(y

- 2) = k [ ( y - ~ ) ( -a b)]“

For a certain liquor of y’ acidity, and 2’ as the assumed acidity of the fixed salt, then b(y’

- 2’) = k[(y’ - z’)(a - b)]“

A plot of b(y’ - 2’) versus [(y’ - $’)(a - b ) ] on log-log paper will give straight lines regardless of the values of z’ and y’. Furthermore, the constants k and m can be interpolated from the graph. In general, the following equations could be written:

bdyj - 2’) = k , [ b j - 5’)(a1 - bJl”’ b 2 ( ~ 7- 2‘) = k 2 [ ( ~ : 2’)(a2 - ball”’

- 2’) = k 3 [ ( ~ 3- 2’)(a3 - bs)]“’

b3(~3

b,(y:

- 2’) = k:[(y:, - z’)(a, - b,)]””

If it be assumed that the log-log plots for the above equations representing liquors of different acidities y:, y:, . . . y: all lie on one common line:

kl = Itq = k3

= . . * . I . . .

....k,

ml = % = m a = . . . . . . . . . . . . m , then

b,(d - z‘) = k [ ( y : - z Y a , For any point on the straight line b,(y:

- bhl“

- 2’) = ba(yi - 2’) = b3(y: - z’)

=

... b,(y:, - 2’)

and (a1

- bl)(y: - 2’)

=

(m - b)(y: - 2’) =

(a3

- b&y: - 2’) = ........ (an - bn)(y: - z’)

176

,E.0 . WILSON AND S. C. YU

and therefore a1

- bl - a2 - bZ bi

bz

- as - bs bs

-b ..... a,bn

=

1/R (ratio)

or


b, = R(a, - b,) Since a, = total CrzOs, b, = fixed Cr203, a,

- b,

=

C,

= unfixed C r 2 0 ,

b, = RC,

It has been demonstrated experimentally that the fixation of chrome (or alumina) by hide substance may be represented by an exponential equation of the Freundlich type. The equation derived above, b, = RC,, however, is not in the form of the Freundlich equation. From the above considerations it would appear that the arbitrary assumption of 66) per cent or other basicity for the deposited chrome complex is not justifiable, and that the unfixed acid in the system m w not be calculated by the method of Cameron and McLaughlin. SUMMARY

1. A method is given for the preparation of basic aluminum sulfate solutions free from neutral salts. 2. The fixation of alumina by hide substance from basic aluminum sulfate solutions may be represented by exponential curves of the Freundlich isotherm type. 3. The amount of fixation for a liquor of any given concentration is profoundly influenced by the basicity of that liquor, high basicities giving greater fixation. 4. Deaminimtion of skins before tanning greatly reduces their capacity t o combine with alumina. 5. The method used by Cameron and McLaughlin to prove that the chrome compound fixed by hide substance from basic chrome sulfate solutions is of 66p per cent basicity has been shown t o be of doubtful validity.

The data on deaminizatioa are abstracted from a Senior thesis by K. H. Hsu; the other material in this paper is taken from a thesis presented by the junior author for the degree of Master of Science in Chemistry. REFERENCES

(1) CAMERON, D.H.,AND MCLAOQHLIN, G . D.: J. Phys. Chem. 41, 961 (1937). (2) K ~ N T Z E A L ,,, AND K ~ N I G F E L0.: D , Collegium 782, 257 (1935). (3) MCLAKIGHLIN, G.D.,CAMERON, D. H., AND ADAMS,R. S. : J. Am. Leather Chem. Assoc. 29, 657 (1934);82, 98 (1937).


177

FOSTER,S. B. J. Am. Chem. Soc. 48, 489 (lC26). A. W., A N D WHITEHEAD,T . H . : J. Am. Leather Chem. Assoc. 26, 127 (1930). (6) WILSON,E. O., A N D K U A X ,R. C . : ,J. A m . IdeatilerChem. .4S8oC. 26, 15 (193Oj. (7) WILSON,E.O . , PENO,63. L., .4ND LI, C. L . : J. Am. Leather Chem. Assoc. 30, 181 (1935). (4) THOMAS, A. W . , A N D


(5)

THoniAs,

The Reaction between Basic Aluminum Sulfate and Hide Substance

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