CRYSTALLOGRAPHI C DATA
No. 98. 4-Aminosalicylic Acid Contributed by JOHN KRC, JR., and W. C. MCCRONE, Armour Research Foundation of Illinois Institute of Technology, Chicago 16, 111.
Density. 1.545 (flotation in henzene-carhon tetrachloride, pycnometer); 1.582 (x-ray).
0
H 2 X a - C R
OPTICAL PROPERTIES
O 'H
B
Refractive Indices (5893 A,; 25' C.). a = 1.536 i 0.001. 1.695 i- 0.005. y = 1.99 0.02 (calculated from a,0, and
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=
,.
9TII II
Structural Formula for 4-Aminosalicylic Acid XCELLENT
Optic Axial Angles (5893 A , ; 25" C.). 2X = 100". 2V = 87 (calculrtted from p and 2 H ) .
:3?2{$
crystals of ?-aminosalicylic mid cain he obtained
p
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~
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g
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pressure apparently gives a decomposition product; hence this procedure cannot he used. There waR no evidenoe of polymorphism.
Acute Risertrix. A a = 26" ill scute 8. Extinction.
Firnure 2. Crystals o f 4-aminosalicylic acid recrystallized from henzyl alcohol on microscope slide
el
i
1. ).
1503
Figure 3. Crystals of decomposition product obtained on melting or suhliming 4-aminosalicylio acid
ANALYTICAL CHEMISTRY
1504 Principal Lines I/Il
d
5.03
4.09
3.75 3.63 3.53
Weak 2 2 5 Weak
d
2.05 1,992 1.955 1.920 1.840
AIolecular Refraction ( R )(5893 h.; 25" C). = 33.1; R (obsd.) = 38.8.
I/Ii
1 1 2 Weak 2
q z
d 3.45 3.35 3.24 3.04 2.99
I/II
2.79 2.74 2.60 2.50 2.46
1 1 4
9 10 7 4 3
3
3
1.606 1.581 1.540 1.606 1.440
1 Weak 2 1 Weak
1,735.
On warming, the crystal size and growth rate both increase. Bisectrix figures are possible with 2V about 90".
FUSION DATA.4-Aminosalicylic acid decomposes on melting (220" C.) to give a pure decomposition product melting, in turn, a t 122" C. The latter crystallizes spontaneously from the melt after considerable supercooling. The melt is fairly viscous, the crystallization velocity is very slow, and the crystals are small.
Irenecorvin is responsible for powder x-ray diffraction data.
R (calcd.)
ACKNOWLEDGMENT
CONTRIBUTIOKS of crystallographic d a t a for this section should be sent to Walter C. McCrone. Analytical Research. Arinour Research Foundation of Illinois Institute of techno log^-, Chicago 16, 111.
CORRESPONDENCE
Conductometric Titrations with Dimethy IgIyoxi me SIR: This note reports the conditions under which conductometric methods, including high-frkquency methods, may be used to determine the end point for the titration of solutions of nickel(11) ion and dimethylglyoxime and shows that for some recently reported titrations of dimethylglyoxime with cobalt, nickel, lead, and manganese (3),no changes that occur under the conditions specified permit detection of the claimed end points by two recognized types of high-frequency apparatus or by a conventional conductance method. Sakano, Hara, and Yashiro ( 3j report high-frequency titration curves having very abrupt changes of slope a t molar ratios 2 to 1 and 1 to 1 for the addition of O.OO5M nickel sulfate, cobalt nitrate, lead nitrate, or manganese chloride to 0.001M aqueous dimethylglyoxime in the absence of any buffer. It is the opinion of the present authors that their results must be related to factors other than the reported reactions and would not be substantiated over any considerable range of concentration and volume. The high-frequency titrations, using concentrations and conditions specified by Nakano, Hara, and Yashiro, have been repeated in this laboratory using the apparatus based on the General Radio Twin-T impedance measuring circuit (1j a t a number of frequencies from 2 to 10 Mc., and using a crystal oscillator apparatus (2) a t 5 Mc. A thorough study has also been made of these reactions, a t the same and other concentrations, with and without added ammonia and buffers. These titrations were followed with the highly precise 1000-cycle conductance bridge huilt around the Leeds and Northrup Co. No. 1553 ratio box, as well as with the radio-frequency apparatus just listed.
duced a t any point during the titration by addition of a few drops of ammonia. Similar conductance curves and color changes were produced over concentrations ranging from 0.001M to 0.005M. Similar color changes and converse conductance changes were produced by addition of dimethylglyoxime to nickel sulfate solution. More concentrated solutions of dimethylglyoxime were made by using a small amount of ethyl alcohol in the water, but this did not affect the nature of the results.
DIMETHY LGLYOXIME-NICKEL
Figure 1. Conductometric titration of dimethyl glyoxime with nickel ion in presence of ammonia
For all unbuffered solutions, a plot of instrument response against volume of nickel sulfate added to the aqueous dimethylglyoxime gave a smooth curve, indicating a continuous increase i n conductance with no abrupt changes. For the addition of O.OO5M nickel sulfate to 100 ml. of 0.001M aqueous dimethylglyoxime (for which the 2 to 1 and 1 to 1 ratios would occur a t 10 and 20 ml. of nickel sulfate, respectively), the first 1 or 2 ml. of salt solution resulted in a faint yellow color. More nickel sulfate gradually changed the color to a faint pink, with a slight turbidity increasing to a just visible precipitate at 15 to 25 ml. of added solution. Greatly increased precipitation may be pro-
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These observations suggest that in these unbuffered solutions a small amount of the usual 2 to 1 complex is formed and precipitated but that no reaction is completed. This conclusion was further supported by p H measurement as dimethylglyoxime was added to nickel sulfate solution. Upon addition to a 0.001M salt solution the pH falls continuously to well past the 2 to 1ratio, hydrogen ion being released as the 2 to 1 complex is formed. Prior addition of ammonia to the dimethylglyoxime solution
