W ILLET F. W HITMORE A N D ARTHUR I. GEBIIART, Polytechnic In s titu te o f Brooklyn, Brooklyn, N. Y.
T
H E commercial importance of the naphthalenesulfonic acids has resulted in numerous methods for the identification of these difficultly characterized compounds.
In m ost cases their salt-forming properties have been utilized in preparing metallic or arylamine salts (1, 2, 3, 6 -8 ,1 0 , 12).
Chambers and Scherer (4) used the base benzylisothiourea for characterization of a - and |3-naphthalenesulfonic acids and the 1,5-, 1,6-, 2,6-, and 2,7-disulfonic acids. H ann and Keenan (11), using microscopic methods w ith this reagent, reported the optical d ata on the derivatives of these same acids. The lim itation of the above methods is their lack of applicability to large groups of the acids. By a combination of such procedures—metallic salt formation, benzylisothiourea salts, and free acids— Garner (9) outlined a procedure for the microscopic identification of tw enty substituted naphtha
lenesulfonic acids. His method requires the preparation and examination of a num ber of derivatives of each acid.
The method which is here reported is based upon the fact th a t benzoylation of a number of naphthylam ine-, naph- thol-, and aminonaphtholsulfonic acids yields characteristic, readily isolated test forms.
Photomicrographs of the derivatives and the free acids or their sodium salts are included (all of the same magnifica
tion, approximately 70). The la tte r two are generally poorly described in the literature and are in m any cases character
istic and serve as additional proof of identity. Optical data are given for the derivatives.
G e n e r a l P r o c e d u r e
P u r i f i c a t i o n o f S a m p l e s . All acids insoluble in water are dissolved in strong sodium carbonate solution and treated with activated carbon (Darco). The free acid precipitated with hy
drochloric acid is filtered by suction, washed with a little cold water, reprecipitated similarly a second or third time, and dried at 40° to 50° C. In what follows, unless otherwise noted, this is the purification procedure used.
P r e p a r a t i o n ' o f B e n z o y l D e r i v a t i v e s . For monosub
stituted acids—naphthylamine- or naphtholsulfonic acids—0.2 gram of the acid or its sodium salt is dissolved in 10 ml. of ap
proximately normal sodium carbonate solution in a 125-ml.
glass-stoppered Erlenmeyer flask and 0.2 ml. of benzoyl chloride (reagent quality) added. With disubstituted acids such as the aminonaphthol type the quantities of sodium carbonate and benzoyl chloride are doubled; otherwise the procedure is the same.
Contrary to usual procedure, sodium carbonate appears to serve better than sodium hydroxide for the benzoylation, the derivative frequently precipitating more easily when the car
bonate is used. No trouble is experienced from gaseous carbon dioxide, as it is absorbed in the excess of carbonate used.
The flask is stoppered and vigorously shaken until all odor of benzoyl chloride has disappeared. This may take as long as 5 minutes in some cases and a precipitate may or may not form, depending on the sulfonic acid.
NOVEMBER 15, 1938 ANALYTICAL EDITION 655
If a precipitate forms, it is filtered by suction. Sufficient fine solid c. p. sodium chloride is added to the filtrate to make about a 20 per cent saline solution. If more precipitate forms, it is collected with the original and the filtrate is discarded. This salting-out procedure is necessary only if it is desired to increase the yield; otherwise the original precipitate is used and the filtrate discarded immediately. If no precipitate forms during benzoylation, the above salting-out procedure is applied. Rarely is a concentration of more than 20 per cent of salt required for complete precipitation.
The derivative is removed from the filter and dissolved in 10 ml. of water, warming to 40° C. if necessary to aid solution. A small amount of Darco is added and the solution is filtered, cooled, and salted out as before. This reprecipitation is repeated (elimi
nating the Darco after the first time) until the filtrate is neutral to phenolphthalein. Usually two or three recrystallizations are sufficient. The precipitate is spread on a porous plate and dried in a desiccator. Oven drying tends to darken the derivatives in some cases.
R e c r y s t a l l i z a t i o n o f D e r i v a t i v e s f o r M i c r o s c o p i c
E x a m i n a t i o n . Tomake the method generally applicable,
a standard crystallization technic has been developed and is applied as far as possible. Adherence to this procedure gives consistently reproducible test forms. Appreciable deviations yield unsatisfactory or misleading results. Crystallizations on the slide do not generally permit of sufficient control of conditions.
A 1 per cent solution is made by dissolving 0.02 gram of the dry derivative in 2 ml. of water in a test tube, warming if neces
sary to elfect solution. After cooling to room temperature, fine or powdered c. p. sodium chloride is added in very small amounts (5 mg. at a time), shaking until the portion added has dissolved before adding more. This addition of salt is continued until the solution becomes slightly cloudy, indicating that precipitation of the derivative has begun. The solution is now warmed to re
dissolve the precipitate and set aside to cool. Crystallization occurs in from 15 minutes to an hour if the salting out has been properly performed.
If precipitated too rapidly—that is, if too much salt is added—
no characteristic crystals are obtained but merely an indefinite mass of poorly defined forms. If too little salt is added crystal
lization is unduly prolonged or does not occur at all.
Under ideal conditions a slight cloud of crystal nuclei appears 5 or 10 minutes after warming, growing in 10 or 20 minutes more to a small amount of crystalline precipitate that settles to the bottom of the tube. A small amount of the precipitated crystals and mother liquor is now transferred to a slide, using a glass tube of about 2-mm. bore. (This size of tube prevents breaking up some of the large spherulites frequently found.) Appearance is the final test of proper precipitation. If indefinite forms are obtained, a new precipitation should be made using less salt.
Any deviations from the above procedure will be noted.
B e n z y l i s o t h i o u r e a D e r i v a t i v e s . T w o of the fifteen acids studied (H and R acids) do not yield insoluble benzoyl deriva
tives but are readily characterized by means of benzylisothiourea.
(At the outset of this work attempts to make general use of this reagent for characterizing all the acids failed in the majority of cases.)
The reagent is prepared by the method used by Chambers and Scherer U) by adding, with stirring, 126.5 grams of benzyl chloride to a solution of 76 grams of thiourea in 200 ml. of 40 per cent alcohol and warming 15 minutes on the steam bath. On cooling, the benzylisothiourea separates and is recrystallized several times from 40 per cent alcohol (m. p. 176° C.).
The derivatives are prepared by dissolving 0.1 gram of the sulfonic acid, or its sodium salt, and 0.2 gram of benzylisothiourea separately in 5-ml. portions of approximately 0.2 N hydro
chloric acid. Both solutions are heated to boiling and mixed.
Upon cooling rapidly the derivative separates as a white crys
talline precipitate. I t is filtered, recrystallized once from 6 ml.
of hot 0.2 N hydrochloric acid, and dried.
For microscopic examination the derivative is crystallized from a hot 1 per cent solution in 0.2 N hydrochloric acid by cooling until crystal nuclei just form, then allowing to stand at room temperature until a moderate amount of crystals has formed.
The properties and description of the acids studied and their derivatives are given in Table I. The purification pro
cedure is that applied to the acid or its sodium salt
(which-F i g u r e 1 . 1 - Na p h t h y l a m i n e- 7 - Su l f o n i c Ac i d ( C l e v e ’s Ac i d 1 ,7 )
F r e e a c id fro m h o t s o lu t io n C e n ter . F r e e a cid fro m co ld s o lu tio n R ig h t. B en zo y l d e r iv a tiv e L eft.
Fi g u r e 2 . 1 - Na p h t h y l a m i n e- 6 - Su l f o n i c Ac i d ( C l e v e ’s Ac i d 1 ,6 )
L e ft. F r ee a cid fro m h o t s o lu tio n C e n te r . F r e e a cid fro m co ld s o lu t io n R ig h t. B e n z o y l d e r iv a tiv e
S u b s ta n c e
s u l f o n i c Ac i d s a n d Th e i k De r i v a t i v e s
658 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 10, NO. 11 ever is the more usually m et w ith or easily handled) before preparing the derivative.
The designation “usual” refers to precipi
tation from sodium carbonate solution w ith hydrochloric acid, referred to above.
The physical appearance of the pure acid or salt is stated in the third column.
Unless otherwise noted, the free acids were precipitated w ith dilute hydrochloric acid (1 to 3 of water) from their solution in sodium carbonate.
The microscopic appearance of the ben
zoyl derivatives is described, after recrys
tallization by the standard procedure out
lined, or as stated in the table.
In the section under Optical D a ta on D erivatives indices of refraction are taken in the two positions of extinction and are noted as na and n„. W hen the long di
rection of the crystal is aligned w ith the 6 to 12 o’clock cross hair, the refractive index has been designated as n. (ordi
nate) ; when aligned w ith the other cross hair, as na (abscissa). For crystals show
ing oblique extinction, the first position (15°) is n„ and the next (105°) is na.
These refractive indices do n o t neces
sarily correspond to w and e or a, (3, or y b u t are more readily obtained. They are taken in mixtures of methylene iodide and xylene w ith white light a t 20° C.
Fi g u r e 3 . 1 - Na p h t h y l a m i n e- 5 - Su l f o n i c Ac i d ( La u r e n t’s Ac i d) 1. F r ee a cid fro m co ld s o lu t io n 3 . B e n z o y l d e r iv a t iv e a fter s ta n d in g 2 . B e n z o y l d e r iv a t iv e a s first p r e c ip ita te d 4 . B e n z o y l d e r iv a tiv e , a n o th e r v ie w
Fi g u r e 4 . 2 - Na p h t h y l a m i n e- 6 - Su l f o n i c Ac i d ( Br o n n e r’s Ac i d) F r e e a cid fro m h o t s o lu t io n C e n te r. ^ B e n z o y l d e r iv a tiv e c r y sta lliz e d fro m s a lt s o lu tio n
R ig h t. B e n z o y l d e r iv a t iv e c r y sta lliz e d fro m w a ter
Fi g u r e 5 . 2 - Na p h t h y l a m i n e- 1 - Su l f o n i c Ac i d ( To b i a s Ac i d)
L e ft F r e e a cid fro m c o ld a cid s o lu tio n C e n ter . F r e e a cid fro m co ld a lm o a t n e u tr a l s o lu tio n R ig h t . B e n z o y l d e r iv a tiv e
NOVEMBER 15, 1938 ANALYTICAL EDITION In general, interference figures are not
readily observable in the orientations visible.
S e p a r a tio n s b y M e a n s o f B e n z o y l D e r iv a tiv e s
The varying solubilities of the deriva
tives suggested the possibility of separating various acids by this means. Table I I sum
marizes the solubilities of the benzoyl com
pounds studied.
A trial separation based upon the solu
bilities shown in Table I I was made by benzoylating a m ixture of 0.2 gram each of l-naplithylamine-7-sulfonic acid and 2- naphthol-6-sodium sulfonate in the usual m anner, using proportional am ounts of reagents.
Pr e c i p i t a t e. The precipitate was filtered by suction, washed with a little cold water, dissolved in 20 ml. of warm water, cooled, precipitated with the least possible amount of salt, and reprecipitated similarly a second time.
When recrystallized for microscopic examina
tion in the usual manner it showed the char
acteristic fan-shaped clusters of the benzoyl derivative of Schaeffer’s acid (Figure 7, 2).
Fi l t r a t e. Salt was added until a slight precipitate formed which was filtered off and discarded (to remove any residual derivative of Schaeffer’s acid). The bulk of the derivative was then salted out and recrystallized as usual until neutral. When recrystallized for mi
croscopic examination shield-shaped rosettes
Fi g u r e 6 . I - Na p i i t i i y l a m i n e- 4 - Su l f o n i c Ac i d ( Na p h t h i o n i c Ac i d) 1. F r e e a c id fro m c o ld s o lu tio n 2 . B e n z o y l d e r iv a tiv e
Fi g u r e 7 . 2 - Na p h t i i o l- 6 - Su l f o n i c Ac i d ( Sc h a e f f e r’s Ac i d) 1. S o d iu m s a lt fr o m co ld s a tu r a te d s o lu tio n 2 . B e n z o y l d e r iv a t iv e
Fi g u r e 8 . I - Na p h t h o l- 4 - Su l f o n i c Ac i d ( Ne v i l e a n d Wi n t h e r’s Ac i d)
F r ee a c id s a lt e d o u t fro m c o ld c o n c e n tr a te d s o lu tio n C e n te r . B e n z o y l d e r iv a t iv e as fir st p r e c ip ita te d R ig h t. B e n z o y l d e r iv a t iv e a fte r s ta n d in g
F i g u r e 9 . 1 ,8 - Am i n o n a p h t h o l- 4 - Su l f o n i c Ac i d (S Ac i d)
L e ft. F r e e a cid fr o m c o ld s o lu tio n # C en ter. D ib e n z o y l d e r iv a tiv e , o rd in a ry p r e c ip ita tio n R ig h t . D ib e n z o y l d e r iv a t iv e g ro w n s lo w ly fro m d ilu t e s o lu tio n
INDUSTRIAL AND ENGINEERING CHEMISTRY
of the benzoyl derivative of Cleve’s acid 1,7 were obtained (Figure 1, right).
This result indicates th a t clean-cut separations are possible.
In this study no unusual types of com
pounds were prepared or new or unusual syntheses involved in the preparation of derivatives. In addition, m any of the compounds which were made were iso
meric and consequently i t was felt th a t a n a ly s e s o f t y p e compounds would be satisfactory and representative of groups.
Analyses were made of the following types: a monobenzoyl compound, a di
benzoyl compound, and a benzylisothio- urea derivative. Nitrogen was deter
mined by the Kjeldahl method and sulfur w ith the P arr bomb.
M o n o b e n z o y l D e r i v a t i v e . 2-Benzoyl- naphthylamine-l-sodium sulfonate (CioHe.- SOsNa.NH.CO.CeHt):
Nitrogen calculated, 4.02 per cent; found, 3.89 per cent. Sulfur calculated, 9.17 per cent; found, 8.99 per cent.
D i b e n z o y l D e r i v a t i v e . 2,5-Dibenzoyl- aminonaphthol-7-sodium sulfonate [CioHt.- S05Na.N H .0.(C0.C6H6)2].
Nitrogen calculated, 2.98 per cent; found, 3.08 per cent. Sulfur calculated, 6.8 per cent;
found, 6.63 per cent.
F i g u r e 1 0 . 2 ,5 - Am i n o n a p h t h o l- 7 - Su l f o n i c Ac i d ( J Ac i d) F r e e a cid fro m h o t d ilu te s o lu t io n 3 . D ib e n z o y l d e r iv a t iv e t
F r ee a c id fro m co ld d ilu t e s o lu t io n 4 . D ib e n z o y l d e r iv a t iv e p r e c ip ita te d m ore s lo w ly
F i g u r e 1 2 ( R i g h t ) . 2 - Na p h t h y l a m i n e- 6 , 8 - Di- s u l f o n i c A c i d ( A m i n o G A c i d )
1 . F r e e a c id fro m c o ld s o lu tio n 2. B e n z o y l d e r iv a tiv e
2
NOVEMBER 15, 1938 ANALYTICAL EDITION 661
B e n z y l i s o t h i o u r e a D e r i v a t i v e o f 2 - N a p h t h o l - 3 , 6 - D i - s u l f o n i c A c i d [CioH6.O H (S 03H .N H 2.N iI:C S.C H 2.C Ji5)2l.
Nitrogen calculated, 8 .8 1 per cent; found, 8 .7 0 per cent.
Sulfur calculated, 2 0 .0 0 per cent; found, 2 0 .1 2 per cent.
S u m m a r y a n d C o n c lu s io n s
A rapid and relatively simple method has been developed for the microscopic identification of a num ber of im portant naphthylam ine, naphthol, and aminonaphthol sulfonic acids by means of their benzoyl derivatives.
The procedure has been standardized so as to be applicable to the entire group of acids; only small am ounts of m aterial are required.
T he benzoyl derivatives offer a possible method of separation of some of the acids.
The characteristics and microscopic ap
pearance of fifteen of these sulfonic acids and their derivatives have been tabulated, including optical d ata for the latter, and photomicrographs of characteristic forms have been prepared.
Fi g u r e 1 4 . 2 - Na p h t h o l- 6 , 8 - Di s u l f o n i c Ac i d ( G Ac i d)
S o d iu m s a lt from s a tu r a te d a q u e o u s s o lu tio n 2 . B e n z o y l d e r iv a tiv L it e r a t u r e C ite d
(1) A m bler, J . In d. En q. Chem ., 12,1080 (1920).
(2) Ib id ., 12, 1194 (1920).
(3) A m bler and W herry, Ibid., 12, 1085 (1920).
(4) C ham bers an d Scherer, Ibid., 16, 1272 (1924).
(5) F o rster, H anson, an d W atson, J . Soc. Chem.
In d ., 47, 155T (1928).
(6) F o rs te r a n d K eyw orth, Ibid., 43, 165T (1924).
(7) Ib id ., 46, 25T (1927).
(8) G arner, J . Soc. Dyers Colourists, 43, 12 (1927).
(9) Ibid., 52, 302 (1936).
(10) G reen and V akil, J . Chem. Soc., 113, 35 (1918).
(11) H a n n an d K eenan, J . Phya. Chem., 31, 1082 (1927).
(12) L ynch, J . I n d . E n o . C hem ., 14, 964 (1922).
Re c e i v e d M a r ch 2 8 ,1 9 3 8 . A n a b str a c t o f a theaia a u b
-1 2
Fi g u r e 1 5 . 1 ,8 - Am i n o n a p h t h o l- 3 , 6 - Di s u l f o n i c Ac i d (H Ac i d) 1. A c id s o d iu m a a lt fro m h o t w a ter 2 . B e n z y lia o th io u r e a d e r iv a t iv e
m it t e d t o th e fa c u lt y o f t h e P o ly t e c h n ic I n s t it u t e of B r o o k ly n in J u n e , 1 9 3 7 , b y M r . G e b h a r t in p a rtia l fu lfillm e n t o f th e re q u ir e m e n ts fo r th e d e g re e o f m a s te r o f s c ie n c e in ch e m istr y .