1591
BIDENTATE CHELATE COMPOVNDS
April 5, 1958 [CONTRIBUTION FROM THE
DEPARTMENT OF
ORGANIC CHEMISTRY O F THE UNIVERSITY OF SYDNEY]
Bidentate Chelate Compounds. I BY FRANCIS LIONSAND KENNETH V. MARTIN’ RECEIVED OCTOBER2, 1957 Some new a-thiopicolinamides have been synthesized and shown to function as bidentate chelate compounds.
Diehl,2 in his review of chelate compounds, has pointed out that the bidentate chelate compounds constitute the largest group and are the most thoroughly studied. A recent report3 of a convenient method for the preparation of a-thiopicolinanilide suggested that this substance and some of its analogs should be able to function as bidentate chelate compounds. Because, further, there do not appear to be any reports of studies of similarly constituted bidentates i t was thought of value a t least to make some preliminary studies of such compounds. a-Thiopicolinanilide (I, R = phenyl) was prepared according to the method described by Porter3 and was obtained as an orange crystalline solid. This procedure involves heating excess a-picoline with sulfur and aniline for many hours. The reaction proceeded readily also when such bases as o-toluidine, m-toluidine, p-anisidine, a-naphthylamine and 2-aminopyridine were substituted for aniline (see Table I). However, the reaction apparently failed with o-anisidine and P-naphthylamine. I t is interesting to note that if excess sulfur was used, then on attempted isolation of the product by vacuum distillation, the corresponding benzothiazole I1 was obtained. Similarly, the benzothiazoles could be prepared readily by distilling a mixture of the pure a-thiopicolinamide and sulfur in ‘JUCUO.
9
111
A dH I V
composition of the organic molecule and formation of the metal sulfide as a precipitate. Alterations in the type of amine used to prepare the a-thiopicolinamide do not apparently affect the coordinating power : a-thiopicolin-o-toluidide, athiopicolin-m-toluidide, a-thiopicolin-p-t.oluidide, a-thiopicolin-p-anisylamide and a-thiopicolin-cunaphthylamide formed similar metal complexes (see Table 11). When a-thiopicolinanilide and ethylenediamine were heated together under reflux the solution acquired a deep red color and hydrogen sulfide was evolved. Vacuum distillation produced 2- (CY-pyridy1)-imidazoline (VI) in 71% yield. This reaction of ethylenediamine with thioamides was first utilized by Forsel14f5and provides a convenient method for synthesis of imidazolines. VI is of
fi
/KH-CHn
vI I
I1
interest in that i t functions as a bidentate chelate compound in a similar manner to dipyridirie and ophenanthroline.6 The preparation described above represents a very convenient method for the synthesis of VI. This could be of value since methods for the colorimetric determination of iron have been evolved using VI as reagent.6
When a methanol solution of copper(I1) acetate was added to an alcoholic solution of a-thiopicolinanilide a dull red color developed and bis-(a-thiopicolinani1ide)-copper(I1) crystallized from solution in lustrous bronze-red plates, m.p. 205’. The Experimental’ copper(I1) complex behaved as a typical uncharged a-Thiopicolinamides (see Table I ) were prepared accordcomplex and could be recrystallized from a chloro- ing to the method described by P ~ r t e r . The ~ amine (2 form-ethanol mixture. Since the copper(I1) com- moles), a-picoline (1 mole) and sulfur (1.5 moles) were plex is non-charged and contains two moles of I (R heated for from 6 t o 48 hours in an oil-bath maintained a t 160-180”. The product usually was isolated by vacuum = CcHs-) it can be formulated as V. a-Thiopicodistillation. When the amine used was m-toluidine, p-toluilinanilide, in its reaction, functions as either of the dine or p-anisidine this treatment resulted in formation of the tautomeric forms I11 or IV. The thiol form IV re- corresponding benzthiazole. However the a-thiopicolinacts with copper(I1) ions to form v. Similar com- amide could be isolated by careful crystallization of the plexes (involving two moles of I V coordinated to crude reaction product from ethanol. of Bis-a-thiopicolinamido-Metal Complexes. one atom of the metal) can be prepared containing -ToPreparation a solution of the a-thiopicolinamide ( 2 mole) in ethanol coordinated nickel(II), zinc(T1) and mercury(I1). was added a methanol solution of the metal acetate (1 mole). Silver(1) and lead(I1) salts apparently cause de- Generally the metal complex separated immediately. This (1) University Research F u n d S t u d e n t of t h e University of Sydney. Inquiries regarding this paper should be sent t o K V. M a r t i n , Polychemicals D e p a r t m e n t , E. I. d u P o u t d e Nemours a n d C o . , Wilmington, Del. (2) H. Diehl, Chem. Reus., 21, 39 (1937). (3) H. D. Porter, THISJ O U R N A L , 76, 127 (1954).
was collected and recrystallized from a chloroforin-ethanol mixture. (4) (5) (6) (7)
Forsell, Ber., 24, 1846 (1891). Forsell, ibid., 25, 2135 (1892). J. L. Walter a n d H. Frieser, Anal. Chem., 26, 217 (1954). All melting points are uncorrected.
1592
Vol. 30
FRANCIS LIONSASD KZNNETH V. MARTIN TABLE I a-THIOPICOLINAMIDES
M.p., OC.
No.
R
1 2
Phenyl o-Toluyl m-Toluyl P-Toluyl p-Anisyl a-Naphthyl a-Pyridyl
3
4 5 6
7
46.5 69.5 80 98.5 100.5 133 81.5
Yield.
%
Formula
71 75 44 55 86 22 22
Ci&IioN& CirHiYNrS CirHirNiS CiiHirNeS CirHirNO& CicHi&zS
Carbon, % Calcd. Found
Hydrogen, % Calcd. Found
68.4 68.4 68.4 63.8 61.4
5.3 5.3 5.3 5.0 4.2
68.6 68.4 68.4 63.9 61.8
5.5 5.2 5.2 5.0 4.3
CuHi*N&
Nitrogen, % Calcd. Found
12.3
11.8
11.4
11.2
19.5
18.7
TABLE I1 METALCOMPLEXES DERIVEDFROM U-THIOPICOLINAMIDES
No. (ace Table I)
Metal (M)
M.P., Form
OC.
Carbon, % Calcd. Found
Hydrogen. % Calcd. Found
Rletal, % Calcd. Found
1
Copper (11) Nickel (II) Mercury (11) Zinc (11)
Bronze plates Yellow needles Yellow needles Yellow tablets
205 242 174 265
58.8 59.4 46.0 58.6
58.9 59.2 46.2 58.5
3.7 3.7 2.9 3.7
3.7 3.6 2.9 3.7
13.0
12.8
2
Copper (11) Nickel (11) Mercury (11)
Brown flakes Bronze flakes Yellow prisms
220 271 173
60.2 60.8 47.6
60.2 60.5 47.6
4.3 4.3 3.4
4.3 4.5 3.5
12.4
12.5
3
Copper (11) Nickel (11) Mercury (11)
Brown plates Bronze plates Yellow prisms
174 229 122
60.2 60.8 47.6
59.9 60.5 47.6
4.3 4.3 3.4
4.3 4.4 8.5
4
Copper (11) Nickel (11) Mercury (11)
Brown plates Bronze plates Yellow prisms
209 258 163
60.2 60.8 47.6
60.2 60.8 47.5
4.3 4.3 3.4
4.3 4.3 3.4
12.4
12.6
5
Copper (11) Nickel (11) Mercury (11)
Brown plates Bronze plates Yellow powder
209 245 156
56.7 57.2 45.5
56.1 57.2 45.5
4.0 4.0 3.2
4.8
11.5
11.3
4.0
3.4
Copper (11) Xickel (11) Mercury (11)
Brown microcrystals Bronze pIates Yellow prisms
194 260 204
65.1 65.6 52.8
63.7 63.4 51.7
3.7 3.8 3.0
3.7 3.7 3.4
-
6
2-(cu-Pyridyl)-imidazoline.-a-Thiopicolinanilide (72.0g., 0.35 mole) and ethylenediamine (30 g., 0.5 mole) were heated together under reflux for 30 minutes. The reaction mixture colored deep red and hydrogen sulfide was evolved. Distillation in vacuo yielded 2-(a-pyridyl)-imidazoline (75 g., 71y0 of theory) as a colorless oil (b.p. 140" (1 mm.)) which soon solidified. It crystallized from a benzenepetroleum ether mixture in colorless plates, m.p. 100-101". Anal. Calcd. for CIH~NI: C, 65.3; H, 6.2. Found: C,65.1;H, 6.1.
The picrate crystallized in long yellow needles from a wateralcohol mixture, m.p. 228". Anal. Calcd. for CtrH12N~07: C, 44.7; H, 3.2. Found: C, 44.5; H, 3.4.
Acknowledgment.-The authors gratefully acknowledge the assistance of Miss B. Stevenson, who carried out all the C, H and N microanalyses, and Mr. J. Croft, who gave preparative assistance. SYDNEY, AUSTRALIA
