217
V O L U M E 26, NO. 1, J A N U A R Y 1 9 5 4 Group I Ammonium Potassium
Group I1 Barium Cadmium Calcium Lead Lithium 3Iagnesium
Sickel Silver Sodium Strontium Zinc
An interesting aspect of these experiments is the fact that ammonium acetate behaves as a base of strength comparable to potassium acetate in acetic acid-chloroform solution, while in water ammonium hydroxide is a much weaker base than potassium, sodium, or lithium hydroxide. I n another series of experiments, alkali metal salts were differentially titrated in the presence of organic bases. In one example, a solution containing 15 mg. of potassium acetate, 15 mg. of pyridine, and 4 mg. of n-butylamine was prepared in 10 ml. of glacial acetic acid and 100 ml. of chloroform. This mixture was titrated poteiitiometrically with 0.01.Y perchloric acid in p-dioxane (Figure 6 ) . I t is evident from this graph that potassium acetate is a stronger base than either n-butylamine or pyridine. When ammonium acetate was qubstituted for potassium acetate, a similar curve was obtained. Hon-ever, when cations of group I1 were used instead of thow of gioup I, the basicity of their acetate silt‘ was
found equal t o that of n-but?-laniine but stronger than pyridine (Figure 6). CONCLUSIONS
The experiments described have shown that ammonium and potassium acetates behave as stronger bases than other inorganic acetates studied in the nonaqueous solvent system of acetic acid-chloroform. Thua, a differential titration of sodium acetates and potassium acetates was accomplished. ACKNON LEDGMENT
The authors are indebted to E. G. E. Shafer for his valuable suggestions, and to Esther Critelli for preparing the graphs. LITERATURE CITED
(1) Beukenkamp, J., and Riemann, K , 111, ANAL. CHEW.,22, 582 (1950). (2) Hall, N. F., J Chem. Educ., 17, 125 (1940). (3) Kolthoff, I. hl., and Willman, &4., J . A m . Chem. Soc., 56, 1014 (1934). 14) Pifer, C. W., and Wolhsh, E. G., ANAL.CHEM.,24, 519 (1952) RECEIYED for review July 27, 1953. Accepted October 20, 1953. Presented a t the Pittsburgh Conference on Analytical Chemistry and Applied SpectrosC O P > , March 1-5, 1953
Analytical As peck of Reactions of 2- (2-P y ridy I)-benzimidazole And 2-(2=Pyridyl)-imidazoline with Iron( II) JOSEPH
L. W A L T E R
and
H E N R Y FREISER
Department o f Chemistry, University o f Pittsburgh, Pittsburgh, P a .
The compounds, 2(2-pyridyl)-benzimidazole and 2(2-pyridyl)-imidazoline, of interest because of their structural similarity to 2,2’-bipyridine and o-phenanthroline, were prepared and their reactions with metal cations tested. Both were found to give color reactions with copper(I), copper(II), cobalt(II), iron(II), and iron(II1). Most notable were those with iron(II), with which deep red-purple colored complexes were formed. These complexes were studied spectrophotometrically and found to have maximum absorbances at 490 mp for 2-(2-pyridyl)-benzimidazole at pH 5.7 and 560 mp for 2-(2-pyridyl)-imidazoline at pH 9.0. The molar extinction coefficients for the 2-(2-pyridyl)-benzimidazole and 2-(2-pyridyl)imidazoline are 3800, and 7800, respectively. The iron complexes could also be extracted with isoamyl alcohol, thus increasing the sensitivity of the color reaction.
I N T H E course of a study of analytical reagents of the type
where X = 0, S, XH and I’ = C-OH, C-SH, and l\j (7’-9), 2-(2-pyridyl)-benzimidazole(I) and 2-(Z-pyridyl)-imidazoline(II) were prepared and tested. These compounds were of interest because of their structural similarity to bipyridine and o-phenanthroline, reagents for iron. Also, because certain substituted phenanthrolines and diquinolyl did not exhibit reaction w-ith iron, ostensibly because of steric hindrance of the groups adjacent to
the nitrogens, the question arose whether the benz- portion of the benzimidazole would exert sufficient hindrance to prevent complex formation. I n this, comparison with the imidazoline with no steric hindrance should be revealing.
I
I1
111 2-( 2-Pyridyl)-benaoxazole(lIII)\\-as also prepared for purposes of comparison because it was felt that the benz- portion of the benzoxazole would offer less hindrance to coordination reactions of the nitrogen than would occur in the corresponding benzimidazole nitrogen ( 8 ) . The reactions of 2-(2-pyrid> 1)-benzimidazole and 2-(2-pyridyl)imidazoline with metal ions were found to be quite similar to those of bipyridine and o-phenanthroline in that a red complex with iron(I1) was formed ieadily. The colored complex was readily extractable with isoamj 1 alcohol. That the analogous benzoxazole(II1) did not give any reaction with iron(I1) was attributed to the lower basicity of the oxazole nitrogen as compared to the imidazole nitrogen. REAGENTS AND APPARATUS
Preparation of Z-(t-Pyridyl)ybenzimidazole. The procedure outlined here is essentially that of Leko and Vlajinats (3).
218
ANALYTICAL CHEMISTRY
One mole (123 grams) of cr-picolinic acid and 1 mole (108 r m s ) of o-phenylenediamine were allowed to react in a distilling ask immersed in an oil bath kept a t a temperature of 175' to 185" C. for.3 hours. The flask was then stoppered and the product distilled under atmospheric pressure a t a temperature of about 310" C. Direct heat rather than immersion in an oil bath was used for heating the flask for distillation. The resultant product, recrystallized twice from an alcohol-water mixture, gave a melting point of 216" to 219" C. (literature melting point, 216" to 218" C.). The compound was slightly soluble in water and very soluble in ethyl alcohol, isoamyl alcohol, chloroform, cirbon tetrachloride, benzene, and ether. Preparation of 2 4 2-Pyridy1)-imidazoline. The procedure outlined here is essentially the same as that for 2-(2-pyridyl)-benzimidazole with few exce tions. One mole (123 grams7 of a-picolinic acid and 1mole (60 grams) of ethylenediamine were allowed to react in a distilling flask immersed in an oil bath kept a t a temperature of 150' to 160' C. for 4 hours. The flask was then stoppered and the product distilled under atmospheric pressure using direct heat. The resultant product was a thick, green, oil which was induced, by scratching the side of its container, to crystallize as white crystals. The conipound was recrystallized twice from petroleum ether (boiling point 90" to 100' C.), giving a melting point of 96" to 98" C. Oxley and Short give 97" to 98" C. (6). The compound is soluble in wnter and virtually all organic solvents. 70-
n
Hydroxylamine Reducing Solution. -4 10% aqueous solution C.P. hydroxylamine hydrochloride was used as the reducing agent in all of the runs. One milliliter of this solution was added in each determination to keep the iron in a reduced state. Isoamyl Alcohol. The isoamyl alcohol used as the extracting solvent was dried over calcium chloride and fractionated through a %foot helices-packed distilling column. Apparatus. .411 pII niea.
