Nov., 1920
T H E J O U R N A L O F I N D U S T R I A L A N D EiVGINEERING C H E M I S T R Y
Diagnostic features-The habit of this substance is characteristic, and, when taken in connection with the indices as listed, renders the identification of the substance a n easy matter. The lowest refractive index, a, is approximately matched by a mixture Qf equal parts of monobromobenzene and a-monochloronaphthalene (n, = I .600), and the intermediate one, 0, by a-monochloronaphthalene (n, = I .640). CY-SAPHTHYLAMINE
NAPHTHALENE-2,7-DISULFOIiATE1
( G o H7"z)z. CIOH~(SO~H)~ This salt separates very slowly in the form of groups of long needles, when the hot solution is cooled. It is soluble in hot water, in hot and cold 95 per cent alcohol, and in cold alcohol diluted with one-quarter of its volume of water, but practically insoluble in cold water and in acetone. It decomposes gradually without melting when heated above 220'. It gave on analysis 11.01 and 11.24 per cent sulfur (theory 11.16). CRYSTALLOGRAPHIC-OPTICAL PROPERTIES. Crystal habitRods, the more slender ones slightly curved. Refractive indices (D)- a = 1.560, 6 = 1.650, y = 1.675, y - CY = 0 . 1 1 5 , all *o.Wj; index a usually shown lengthwise, and means of the others crosswise. In parallel polarized light-Double refraction extreme, the colors being third order on even slender rods; extinction parallel; elongation In convergent polarized light-Partial biaxial figure rarely shown, the sign being Diagnostic features-The features most useful in identifying this substance are the value of the lowest refractive index, CY, and the parallel extinction. Monochlorobenzene (n, = I 361) matches the index in question, and the rods disappear when their long direction lies parallel with the plane of vibration of t h e polarizer. Between crossed nicols the extinction is parallel, a property which distinguishes this compound sharply from the (one likely t o be confused with it, the I ,6-disulfonate.
-.
+.
@ - N A P H T H Y L A M I N E NAPHTHALENE-2,7-DISULFONATE,
(C~~H?NHZ)Z.C~OH~(SO~H)Z This salt forms a mass of, long, slender needles on cooling a hot solution. It is soluble in hot water and 95 per cent alcohol, practically insoluble in cold water and alcohol and in acetone, and appreciably soluble in a cold mixture of 4 volumes of alcohol and I of water. It does not melt when heated t o 280'. Analysis gave 11.07 and 11.16 per cent sulfur. CRYSTALLOGRAPHIC-OPTICAL PROPERTIES. Crystal habitRods, in part plate-like; sometimes showing a 130' termination; often twinned, that is, grown together in groups of two in definite crystallographic relationship. Refractive indices (D)- a = 1.530, p = 1.700, y = 1.740, y - CY = 0.210, all *o.005; index CY is often shown lengthwise on the twins, but crosswise on rods with parallel extinction; p is shown lengthwise on the latter. In parallel polarized light-Double refraction extreme, colors being second or third order even on thin plates, down t o first on parallel-extinguishing rods; extinction inclined, on twins making a n angle of 8' * I' with the twinning plane, often parallel on untwinned rods; elongation variable, but usually on untwinned rods. I n conoergent polarized light-A biaxial interference figure often shown, the obtuse bisectrix being perpendicular t o the plates; 2 E is evidently large and sign -. Diagnostic features-The features most useful for identifying this substance are the habit, especially the frequent twinning;
+
108j
the unusually low value of the lowest refractive index, a, and the extinction relations. The lowest index is matched by methyl salicylate ( n = 1.530 t o 1.535); and crystals immersed in this liquid disappear in one direction or another with reference to the plane of the polarizer. SUMMARY
The -a- and @-naphthylamine salts of the naphthalene-a-, p-, 1,5-, 1,6-, 2,6- and z,7-sulfonic acids and the ferrous salt of naphthalene-@-sulfonic acid are described. Their characteristic relative solubilities are shown in Table I and their optical properties in Table 11. TABLEI-RELATIVE SOLUBILITIES O F SUBSTANCES DESCRIBED (Except the ferrous salt of the @-acid) NOTE: d. = difficultly soluble: v. d. = very difficultly soluble. sol. = soluble; s. sol. = slightly soluble: mod. moderately 'soluble; insol. = insoluble: v. s. = very slightly soluble.
-
a-NAPHTHYLAMINE SERIES
.............
a @ 1,s 1,6 2,6 Cold water.. . . . . . . . . . . . . d. d. v. d. d. d. Hot water . . . . . . . . . . . . . . . sol. s. sol. d. sol. mod. Cold 95 perzcent alcohol.. d. d. d. s. sol. d. H o t 95 per cent alcohol. s. sol. s. sol. sol. sol. s. sol. sol. s. sol. Cold 7 5 per cent alcohol'. sol. s. sol. d. Hot 75 per cent alcohol. . . sol. s. sol. d. sol. s. sol. Cold acetone ............. insol. insol. insol. insol. insol. Hot acetone., insol. insol. insol. insol. insol. @-NAPHTHYLAMINE SERIES d. v. d. Cold water d. v. d. v. d. mod. s. sol. sol. Hot water sol. s. sol. s. sol. v. d. s. sol. v. d. Cold 95 per cent alcohol.. d. mod. s . sol. sol. Y . s. Hot 95 percent alcohol. sol. mod. d. sol. d. Cold 75 per cent alcohol'.. sol. sol. s. sol. sol. Hot 75 per cent alcoholl.. sol. v. s. Cold acetone insol. insol. insol. insol. insol. insol. insol. insol. insol. Hot acetone.. ........... sol. 1 Four volumes of 95 per cent alcohol : 1 volume of water. SULFONATE.
..
........... .............. ...............
..
.............
2,7 d. sol. sol. sol. sol. sol. insol. insol. d. sol. d. sol. s. sol sol. insol. insol.
TABLE11-OPTICAL PROPERTIES OF SUBSTANCES. DESCRIBED --U-NAPHTHYLAMINE SERIES--F~RROUS SULFONATE a @ 1,s 1,6 2,6 2,7 @
Habit, .. , , . plates Indices : a 1.552
........ @ ........ ? y ........ 1.799 ya.. . 0.243 Usual. . . . a & Y
Colors. . . . . Extinction Elonrcation. Figure.. 2
...
E. . . . . . . .
S i g n , ,. . , . .
1-2 par. indet. 0 indet. indet.
needles plates 1.600 1.650 1.725 0.125 Y
1 par. C 0 indet.
+
1.600 ?
1.795 0.195
a&r
2 incl. indet. rare indet. indet.
rods
grains
rods
plates
1.583 1.730 1.770 0.187
1.583 1.640 1.690 0.107 means 2-3 incl. indet. occas. large
1.560 1.650 1.675 0.115
1.500 1.660 0.160
u
a & Y
a & Y
2-2
17 -
occas.
large -
-
---@-NAPHTHYLAMINE SERIES----1,6 2,6 SULFONATE a @ 1,s Habit, . , , plates plates plates needles plates Indices : 1.631 1.550 1.610 1.640 a ........ 1.620 1.647 1.700 1.634 1,670 ? 6. 1.755 1.755 1.830 l.850-I1.730 y 0.124 0.205 0.220 "4-ol.... 0.2304- 0 . 0 9 0 a Usual. a&@ a a&@ a&@ 1-2 _ 1-2 1 1-2 3-4 Colors. . . . . . indet. 40' par. Extinction. par. indet. indet. indet. Elongation. I usual usual occas. rare Figure. . . . . usual 750 700 large indet. 2 E ........ 8 5 O Sign.. . . . . indet. -I-
.. ....... ........ ...
-
+
+
+
-
3 par.
rare indet.
2 par. indet. occas. large
2,7 rods
@-Acid Salt 13 plates
-I-
1.530 1.700 1.740 0.210 a 2-$ 8
i
Gus1 large
-
+
1.550 1.700
1.850f
0.3004a & B 3-4 indet. indet. occas. large
+
NAPHTHALENE SULFONIC ACIDS. 11-A METHOD FOR THE QUALITATIVE DETECTION OF SOME OF THE NAPHTHALENE SULFONIC ACIDS By Joseph A. Ambler and Edgar T. Wherry COLOR
LABORATORY,
BUREAU OF CHEMISTRY,
AGRICULTURE, WASHINGTON,
D.
DEPARTMENT OF C.
During the course of experiments on t h e sulfonation of naphthalene it became desirable t o have a fairly rapid and convenient way of detecting the presence of the various sulfonic acids formed when naphthalene is subjected t o the action of sulfuric acid under varying conditions. No readily applicable method is t o be 1 Presented a t the 59th Meeting of the American Chemical Society, S t Louis, Mo., April 12 t o 16, 1920.
1086
T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol.
found in the literature. The identification has always been made by means of the chlorides or amides, which is unsatisfactory for rapid work when dealing with mixtures of two or more of the acids. The technical separations are effected by means of the different solubilities of their calcium or sodium salts, but this method is not adapted t o making a qualitative differentiation, for example, of naphthalene-1,6-sulfonic acid from the isomeric 2,7-sulfonic acid, or of naphthalene-&sulfonic acid from the 2,6-disulfonic acid, since the solubilities of the salts of these pairs of acids are similar. The use of the salts of these acids with organic bases for qualitative separations was not described by Erdmann and Suvernl who studied the solubilities of the aniline, benzidine, and o-tolidine salts of t h e a-, p-, 2,6- and 2,7-sulfonic acids of naphthalene. They state t h a t these salts are very valuable for t h e isolatipn of the easily soluble sulfonic acids. Their observation t h a t the aniline salts of the a- and 2,7acids are soluble in cold water, while the corresponding salts of the p- and 2,6-acids are insoluble, suggested the possibility t h a t salts with other organic bases may have properties suitable for a qualitative distinction of the acids. Accordingly, a large number of such salts were prepared and their properties studied. The most important of these salts have been described in the preceding article, and from a n examination of their properties the following method of analysis has been d'eveloped. Before attempting this method, the chemist should make and become familiar with the salts described in the preceding article or a t least with those which are used in this analytical method. If this is done, he will have very little difficulty in distinguishing the various acids by this method. ANALYTICAL M E T H O D
REAGENTS-(I) A freshly prepared solution of ferrous chloride. ( 2 ) A hot saturated solution of a-naphthylamine hydrochloride made fresh just before use by dissolving t h e free base in hot dilute hydrochloric acid. (3) A standard normal solution of sodium hydroxide. (4) A hot saturated solution of /3-naphthylamine hydrochloride. ( 5 ) Acetone. (6) Methyl salicylate (oil of wintergreen or birch). ( 7 ) Microscope fitted with two nicol prisms and a revolving stage. PREPARATION O F soLuTIoN--The sodium salts of the sulfonic acids are prepared free from sulfates by the usual method of treating the sulfonation mass with lime, filtering from calcium sulfate, and treating the calcium salts in solution with sodium carbonate. The solution is then filtered t o remove calcium carbonate, and the filtrate is acidified slightly with hydrochloric acid. The solution may be of any convenient strength. Twenty-five cc. of a 5 per cent solution are in most cases ample for a complete analysis. QUANTITIES usED-The tests may all be made on small quantities in test tubes; for example, 2 cc. of 1
Arrn., 276 (18931, 297.
12,
No.
II
solution or a few milligrams of solid, unless otherwise stated in the directions. Also, except when removing a n acid from the solution, 2 or 3 cc. of the reagent employed are adequate, except as noted below. TEST F O R
NAPHTHALENE-P-SULFONIC ACID
Ferrous chloride added t o the cold solution produces a precipitate of glistening micaceous flakes of ferrous naphthalene-P-su1fonate.l This may be slow in forming if the amount is small. If this acid is detected, i t is removed from the entire solution by adding a slight excess of ferrous chloride and filtering off the iron salt precipitated. T h e filtrate is then concentrated t o its original volume before making the following test. T E S T F O R NAPHTHALENE-1,s-DISULFONIC ACID
To a portion of the filtrate, heated t o boiling, is added a n excess of boiling a-naphthylamine hydrochloride solution, and the solution boiled down t o i t s original volume. A granular precipitate of a-naphthylamine naphthalene-1 ,j-disulfonate,l formed while concentrating, indicates t h e presence of the acid. Difficulty is sometimes encountered here in causing the insoluble salt t o precipitate. If, however, t h e a-naphthylamine hydrochloride solution is made directly before using, by dissolving the free base in hok dilute hydrochloric acid (decolorizing with norit o r bone-black when necessary), and employing a large excess of this reagent, there is no difficulty in obtaining a reaction. The explanation of the fact t h a t a solution freshly prepared from the base is more efficacious t h a n one made, for example, by dissolving the d r y hydrochloride of the base in water, or t h a n a solution which has stood for some time, is not known. I n adding this solution, an excess over t h a t required t o combine with all the sulfonic acids present must b e used, as otherwise the insoluble salt does not form. A possible explanation of this fact may be t h a t t h e disulfonic acid may form a soluble acid salt with a-naphthylamine. If 1,S-acid is found, i t must be removed from t h e rest of the solution before making any subsequent tests. T o the boiling solution a n excess of a boiling solution of the base is added, the mixture is concentrated t o its original volume and filtered hot. The excess of t h e base is then removed from the filtrate by titrating t o alkalinity with sodium hydroxide, using phenolphthalein for indicator. After cooling, the free base is removed on a filter, and the filtrate acidified with hydrochloric acid. T E S T F O R NAPHTHALENE-2,6-DISULFONIC ACID
The entire solution which has been freed from both
P- and 1,S-acids is heated t o boiling, and a large excess of boiling @-naphthylamine hydrochloride solution is added. The amount used must be sufficient t o form neutral salts with all sulfonic acids present. The 2,6-acid is indicated by a white precipitate of P-nap hthylamine naphthalene- 2,6-disulf onate2 formed 1 See
p. 1083 of preceding paper.
* See p.
1084 of preceding paper.
~ o v . 1, 9 2 0
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
while boiling. T h e solution is filtered rapidly while hot, and t h e filtrate allowed t o cool. The formation of a crystalline precipitate in the filtrate on cooling does not necessarily indicate the presence of any of the remaining acids, since the pnaphthylamine naphthalene-z,6-disulfonate is not completely insoluble in hot water. However, the presence of other naphthalene sulfonic acids a t this point has a salting-out effect on the 2,6-salt, and hence its precipitation is more complete in hot water when some of the naphthalene sulfonic acids are present whose @-naphthylamine salts are soluble in boiling water (the a-, 1,6- or z,7-acids). When none of these acids are present, the salt separating on cooling is distinctivewhite, fine, and voluminous-and when once seen would never be mistaken for the salts of any of the other naphthalene sulfonic acids not yet removed. TEST F O R NAPHTHALENE-CY-SULFONIC A C I D
The filtrate from the previous test is allowed t o cool and stand a t least one hour after i t is cold t o insure complete crystallization of the difficultly soluble salts. Should a jelly be formed, more water is added, and the solution heated t o boiling and cooled again. The salts are then filtered and dried in a vacuuni oven a t 100' C. The filtrate should be tested with more of the cold reagent t o be sure of complete precipitation. A small quantity of the dry salts is boiled with 2 or 3 cc. of acetone, filtered through a warm, dry funnel, and the filtrate cooled. The presence of a-sulfonic acid is shown i n the cold filtrate b y the separationof crystals of @-naphthylamine naphthalene-a-sulfonate.' If this acid is found, the whole mass of the salts is boiled with acetone, filtered hot through a warm, dry funnel, boiled again with acetone, filtered, and t h e residue washed with hot acetone. T h e insoluble salts are then dried and examined under the microscope. OPTICAL PROPERTIES-Immerse the salts in methyl salicylate or other oily liquid having a refractive index near 1.53. Turn the stage t o bring a clearcut crystal (rod or plate) into parallelism with t h e plane of vibration of t h e polarizing nicol prism (as indicated by one of the cross hairs; which cross hair must be determined in advance). If the crystal boundaries disappear, indicating the identity of refractive index of the liquid with t h a t of the crystal in the direction of elongation; and if, on inserting the analyzing nicol, in crossed position, the extinction is more or less inclined, i. e., if t h e crystal becomes dark when turned so as t o make a n angle of up t o nearly I O ' with a cross hair, the presence of naphthalene-z,7-disulfonicacid as its @-naphthylamine salt is indicated. This salt of the 2,7acid also shows a characteristic twinning habit, the two parts of t h e crystal plates showing extinction in different positions. These twinned plates also show a n approximately 1 2 0 ' termination. If t h e crystal boundaries remain distinct, and, on raising the microscope tube, a band of light appears t o enter t h e crystal, showing t h a t its refractive index 1
See p. 1082 of preceding paper
1087
exceeds t h a t of the liquid in the direction of elongation; and if, on inserting t h e analyzing nicol in crossed position, the extinction is' parallel, i. e., the crystal becomes dark when parallel t o a cross hair, the presence of naphthalene-1,6-disulfonicacid also as the @-naphthylamine salt is indicated. If salts of both acids are present, both behaviors can be readily recognized on separate crystals. These optical properties are very characteristic of these two salts, as may be seen by referring t o the table of optical properties given in t h e preceding article. The very small amounts of t h e salts of any of the other four naphthalene sulfonic acids which may be present a t this point of the analysis do not in any way interfere with these observations, and are readily recognized as impurities. D E L I C A C Y O F THE TESTS
Most of the above-described tests are as delicate as i t is necessary for them t o be when used for technical purposes. The precipitation of the @- and 2,6-acids is very nearly quantitative, so t h a t a rough estimate of the amounts of these present can be made by weighing t h e dried precipitates. The precipitation of the 1,sacid is not so complete, since a-naphthylamine naphthalene-I,5-sulfonate is slightly soluble in boiling water. The a-sulfonic acid salt is almost completely insoluble in cold water, and by evaporating t h e ace;tone extract, its weight may be obtained, since none of the other salts are appreciably soluble in acetone. A rough estimate of the relative amounts of the 2 , 7 and 1,6-salts may be made under the microscope.1 SUMMARY
A method is proposed for the qualitative examination of mixtures of the following naphthalene sulfonic acids: CY- and @-monosulfonic,and I,s-, 1,6-, 2,6-, and 2,7-disulfonic acids.
THE MECHANISM OF BATING2 By John Arthur Wilson LABORATORIES O F A. F. GALLUN&
SONS CO., MILWAUKEE, WISCONSIN Received August 25, 1920
Perhaps the most curious of all the processes involved in making leather is t h a t of bating. Little is known of its origin because i t was a secret process, b u t i t is a t least some centuries old. After t h e skins are taken from t h e lime liquors, unhaired, and washed, they are plump and rubbery, a condition not particularly suitable for putting them directly into the t a n liquors. The object of bating is t o prepare t h e unhaired skins for tanning, and originally consisted in keeping them in a warm infusion of t h e dung of dogs or fowls until all plumpness had disappeared and the skins had become so soft as t o retain the impression of thumb and finger when pinched and sufficiently 1 The authors wish to extend their thanks t o Messrs. G. 0. Oberhelman and D. F. J. Lynch for their kindness in checking and confirming this method, and for suggestions they have made for its improvement. 1 Presented before the Section of Leather Chemistry at the 60th Meeting of the American Chemical Society, Chicago, Ill., Sept. 6 to 10, 1920.
