New Class of Ionic Associates for the Nonaqueous Standardization of Acids and Bases James 7 . Alessi, David G. Bush, and James A. Van Allan Research Laboratories, Eastman Kodak Company, Rochester, N.Y . 74650
Bis(l,5-dimethyl-2-phenyl-3-pyrazolone) perchlorate (I), developed as a primary standard by Busev and others (I, Z ) , will find wide use by workers in the field of nonaqueous titrimetry. This product does not have the usual limitations of low solubility in nonaqueous solvents that restricts the number of materials available a t present for use in standardizing nonaqueous acids and bases (3-5). Compound I has the additional advantage that it can be used for the standardization of both acids and bases since it is an "ionic associate" of two moles of 1,5-dimethyl-2phenyl-3-pyrazolone (antipyrine) and one mole of perchloric acid. Some recent synthetic work in our Laboratories has produced several substituted pyridones, which form a similar class of "ionic associates" (6). A comparison has been made of one of these pyridones, perchlorate (11), with bis( l-butyl-2,6-dimethyl-4-pyridone) I as a nonaqueous primary standard. EXPERIMENTAL
grams) was stirred for 1h hr with 600 ml of water and 186 ml of 70% perchloric acid. To the resulting solution was added 115 grams of sodium carbonate in 300 ml of water, followed by 100 ml of acetic acid. The solid was collected and crystallized from water to give 90 grams (68% yield) of I1 (mp 161-162 "C). Anal. Calcd for C22H3&1N206: C, 57.6; H, 7.7; C1, 7.8; N, 6.1; 0,20.8. Found: C, 57.8; H, 7.7;C1,7.7; N, 6.1; 0,20.4. &agents and Procedures. The titrations were made with a Metrohm Potentiograph, Model E336, using a glass indicator electrode (Beckman 40495) and a modified sleeve-type calomel reference electrode (Beckman 40463) in which a methanolic 0.1M tetramethylammonium chloride fill was used to replace the usual aqueous saturated KCl solution. Hexadecyltrimethylammonium hydroxide (HDTMAH), O.lN, in 9:l benzene:methanol was obtained from Eastman Organic Chemicals, EK A10904. Perchloric acid titrant, O.IN, was made by diluting 8.5 ml of 70% perchloric acid to 1liter with glacial acetic acid. Bis(l,5-dimethyl-2-phenyl-3-pyrazolone) perchlorate, commonly called antipyrine perchlorate (I) (100.00 f 0.18% pure), was obtained from Eastman Organic Chemicals, EK X10891, as was bis(1butyl-2,6-dimethyl-4-pyridone) perchlorate (11),EK 11311. All solvents used were Eastman Spectro Grade.
Synthesis. The scheme for the synthesis of I1 from dehydroace-
RESULTS AND DISCUSSION
tic acid follows:
One possible structure of I1 is:
0 COCH,
+ C4HgNH2
A
0
CH, &OH
II
L
C
HC' C4HgHN-C
II
I CH3
C 'H
II 1 CH,
HCIO,
CH,
CH, mol wt 459.0 (2.18 mequiv/gram
A
C-NHCIH,
Similar half salts (or ionic associates) have been synthesized by Thyagarajan and his coworkers (7) who postulate this type of dimer with a proton shared between two carbonyl oxygen atoms. Katritzky and his coworkers (8) did extensive work in the area of protonation of amides and their heterocyclic analogs and results of their work would tend to support the above structure. Infrared studies performed in our Laboratories, on the other hand, do not support the above structure, but support a structure such as the following:
A mixture of 100 grams of dehydroacetic acid and 233 ml of nbutylamine was heated on a steam bath for 3 hr. The solution was evaporated to dryness in vacuo and the residue was crystallized from ligroin (bp 100-115 T I . This bisamine adduct (125 A. I . Busev, B. E. Zaitsen, V. K. Akisnov, Ya. Chellkhovskii,and F. Kopetski. Zh. Obshch. Khim., 38, 534 (1968); English Translation, p 523. A. I . Busev, V. K . Akimov, and I. A. Emel'yanova, Zh. Anal. Khim., 23,616 (1968);English Translation, p 525.
W. H u b e r , "Titrations in Nonaqueous Solvents," Academic Press, New York, N.Y., 1967, p 9 4 .
J. Kucharsky and L. Safarik, "Titrations in Nonaqueous Solvents," Elsevier. N e w York, N.Y.. 1965, p 109. I. Gyenes. "Titration in Nonaqueous Media," lliffe Books, Ltd., Princeton, N.J., 1967, p 160. J. A. Van Allan, G. A. Reynolds, J. T. Alessi, S. Chie Chang, and R . C. J0ines.J. HeterocycL Chem., 8,919 (1971).
mol wt 476.9 (2.10 mequivlgram
No loss in carbonyl absorption (-1635 cm-l) is noted in going from the free base to the half salt, indicating protonation a t the nitrogen atom. Moreover, a completely (7) B. S. Thyagarajan, K . Rajagopalan, and P . V . Gopalakrishan, Chem. Ind. ( L o n d o n ) , 1887 (1966). (8) A. R. Katritzky and R. A. Y . Jones, C h e m . Ind. ( L o n d o n ) , 722 (1961).
1
0 40
1
090t
- 0.20
8
-0.40
0 60
HNP
: ,500V
-- 0O 80 6OI
L
0
1
I
I
2
,
3
I
4
5
I
6
HDTMAH (mls)
Figure 1. Titration of I
and I I with HDTMAH
in acetonitrile
I
I , Antipyrine perchlorate, I I, Bis(l-butyl-2,6-dimethyl-4-pyridone) perchlorate
protonated sample (full salt) of the material displayed the same carbcnyl absorbance with an additional absorption band ( -2700 c m - l ) indicating N-H bonding. If protonation occurs a t the oxygen atom, neither the carbonyl nor the N-H absorption bands would be present. It is beyond the scope of this paper to resolve this structure question. Ionic associate I1 exists as a monohydrate under normal room conditions (determined by both gravimetry and Karl Fischer titration), but drying under vacuum a t 60 "C for 24 hr effectively removes the water of hydration. The dried sample must be stored over such desiccants as phosphorous pentoxide or calcium hydride to ensure the anhydrous state. Ionic associate I1 is a monobasic acid, and its titration by a tetraalkylammonium hydroxide can be expressed by the equation [(C, H,-NO),H]ClO,
+ R,NOH
= 2 C,,H,-NO
+ R,NC10, + H,O
In four titrations in acetonitrile using HDTMAH as titrant, the equivalent weight of I1 as an acid was found to be 99.6 f 0.2% of the calculated value. Antipyrine perchlorate (I) was used to standardize the HDTMAH titrant. The titrimetric results showed no solute concentration dependence in the range of sample sizes employed (20-400 mg). In Figure 1, the titration curves of I and I1 in acetonitrile are compared. Although I is more acidic than 11, [ i . e . , compared to the half neutralization potential, HNP, for benzoic acid (-0.090 V), AHNP (acid) for I is 0.460 V, while AHNP (acid) for I1 is 0.180 VI, both materials display very sharp end points in their titration curves. Other nonaqueous solvents tried and in which stoichiometric results were obtained on titration of I1 with base include acetone, methanol, ethanol, methyl ethyl ketone, dimethylformamide, dimethylsulfoxide, and pyridine. Ionic associate I1 is a monoacidic base and its titration by perchloric acid can be expressed by the equation [ ( C ,H,-NO)HICIO,
+ HC10, = 2 (C,,H,-NO.H) C10,
In three titrations in acetonitrile using HClOd as titrant, the equivalent weight of I1 as a base was found to be 99.9 f 0.1% of the calculated value. Antipyrine perchlorate (I) was used to standardize the perchloric acid titrant. Again, no solute concentration dependence was found on results in the range of sample sizes employed (20-400 mg) .
444
0
I
I
1
I
I
2
3
4
HCIOl (mls)
Figure 2. Titration of I
and I I with HClO4 in acetonitrile
I , Antipyrine perchlorate; I I , Bis(l-butyl-2,6-dirnethyl-4-pyridone) perchlorate
In Figure 2, the titration curves of I and 'I1 in acetonitrile are compared. Since I1 is a stronger base than I, I1 has a larger potential jump at its end point [Compared to benzoic acid (HNP = -0.090 V), 4HNP (base) for I is 0.590 V, while AHNP (base) for I1 is 0.390 VI. Other nonaqueous solvents tried and in which stoichiometric results were obtained on titration of I1 with acid include acetone, methanol, ethanol, methyl ethyl ketone, and acetic acid. We have found no evidence that unusual hazards are involved in the handling and use of this material. In thermal analysis, a strong exotherm is observed which initiates a t about 225 "C. Shock tests showed no shock sensitivity a t 550 inch-pounds. However, as with all organic perchlorates, due care should be exercised in handling this material, especially in the presence of organic materials and other oxidizable substances.
CONCLUSIONS Bis( l-butyl-2,6-dimethyl-4-pyridone) perchlorate, [(CllH17NO)2H]C1O4, represents a new class of ionic associates, which are suitable for use as primary standards for nonaqueous titrimetry. Along with antipyrine perchlorate, bis( l-butyl-2,6-dimethyl-4-pyridone) perchlorate is recommended as a nonaqueous primary standard because it can be obtained as a product of high purity (available from Eastman Organic Chemicals, EK 11311); the single product can be used to standardize both acids and bases; it has a high equivalent weight (459.0); it titrates stoichiometrically in the common nonaqueous titration solvents; and it displays a sharp inflection in the equivalence-point region as both an acid and a base.
ACKNOWLEDGMENT We acknowledge the aid of D. C. Batesky of the Synthetic Chemicals Division of the Eastman Kodak Company in making the first sample of both ionic associates mentioned in this paper. We would also like to thank T. J. Davis, T. H. Regan, and G. A. Reynolds of our Laboratories for their helpful suggestions and interest in this work. Received for review June 25, 1973. Accepted October 10, 1973.
A N A L Y T I C A L CHEMISTRY, VOL. 46, NO. 3, M A R C H 1974
