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Preparation and heat stability of a hydrogenated Schiff base chelate
J. Inorg. NBcl. Chem., 1961, Vol. 21, pp. 181 to 189. PergamonPress Ltd. Printed in Northern Ireland
NOTES
Preparation and heat stability of a hydrogenated Schiff base chelate (Received 16 March 1961)
There has been recent interest in metal chelate compounds as possible heat stable materials, both in their own right, m and as part of the structure of heat stable metal-organic polymersJ ~m Previous work in this laboratory has concerned the preparationCU ) and heat stabilities ~x) of the copper, nickel, and zinc Schiff base chelates I (R = an n-alkyl group).
CHiN ~R
/
C H~-N H~R
[~ilZ---NH~(CH2)5
O--M--O
CH3
R/N~CH / I 1o:
R=n-.-C6H,3, M~Zn
]l
rrr
"II o: R=n--C~;H3 , M~Zn
It has seemed of interest to compare the properties, and in particular the heat stabilities, of the closely analogous metal chelates II. The compounds II can be considered to be formed by means of the hydrogenation of the two C - - N bonds in I. No member of the series 11appears to have been previously synthesized. We now wish to report the preparation of one such chelate, the zinc chelate of N(n-hexyl)-o-hydroxybenzylamine (lla). We also report here the results of a comparison of the heat stability of lla with that of the corresponding Schiff base chelate la. Catalytic hydrogenation in ethanol of the Schiff base N-(n-hexyl) salicylaldimine readily yields the previously unreported secondary amine N-(n-hexyl)-o-hydroxybenzylamine (Ill). The latter compound is too heat sensitive to be vacuum distilled; attempts to do so lead to resin formation. This is in contrast with the corresponding Schiff base, N-(n-hexyl) salicylaldimine. The latter compound is readily purified by vacuum distillation. 111 can be obtained relatively pure simply by evaporating the filtered reaction mixture. The structure of I!I is evident from the Hz consumption, the elemental analyses, the presence in the infra-red spectrum of an N - H stretching absorption peak and the absence of one due to ~ N stretching. Reaction of Ill with zinc acetate in methanol-water solution yields the zinc chelate Ila which can be obtained in a beautifully crystalline form by recrystallization from methanol. Elemental analyses for the purified compound are in good agreement with the structure lla. Like the Schiff base chelate Ia, compound lla has been obtained only in the anhydrous form. Also like la, lIa can be melted, but it melts over 100~C higher than does la. Attempts to prepare the corresponding copper and nickel hexyl chelates It gave oily products which could not be purified adequately for characterization. (1) R. t=) C. ~) D. (4) R.
G. CHARLES,J. Inorg. Nucl. Chem. 9, 145 (1959). N. KENNEY, Chem. & Ind. (Rec.) 880 (1960). B. SOWERnYand L. F. At:DRIETH, J. Chem. Educ. 37, 134 (1960). G. CHARLES,J. Org. Chem. 22, 677 (1957). 181
182
Notes
Figure I shows the thermogravimetric curves obtained by heating the two zinc chelates la and IIa in an atmosphere of argon, lla began to lose weight rather abruptly, at about 250°C, somewhat above the melting point of the substance. Weight loss continued to 710~C, the highest temperature employed. The residue remaining in the sample container at 71ffC was found to contain 99.6 per cent of the zinc initially present in the compound lla taken. This is conclusive evidence that the weight losses observed are due to volatilization of pyrolysis products rather than to evaporation of unchanged fla.
1
I
I
1
I
I
I
A ~-,,,/CH_2-NHI(CHz)5CH3 E: E:n
T 20 mg .,~/CH =N/'(CH2)5 CH3
0
I
IOO
I
200
I
I
300 400 Ternpereture 2 °C
I
500
I
600
I
700
FiG. l.--Weight loss-temperature curves for zinc chelates heated in argon. Fifty mg samples. The curves are displaced along the ordinate. The thermogravimetric curve obtained for the Schiff base chelate la shows a more gradual onset of weight loss which first becomes detectable at about 250°C. A white solid gradually condensed on the cool portions of the furnace tube. This material was identified as la by its infra-red absorption spectrum. The residue remaining at 710~C contained only 50.2 per cent of the zinc present in the sample of la taken. In a separate experiment la was heated only to 310°C. The material remaining in the sample container had the same melting point as pure la. These bits of evidence show that la is not pyrolyzed at least to 310'C, under the conditions used, and that the initial weight losses for la in Fig. 1 are due to evaporation of unchanged chelate. The compound la is thus clearly more heat stable than is IIa. In separate experiments thermogravimetric curves were obtained for chelate Ila which were terminated at the points A, B, and C shown in Fig. I. Elemental analyses were determined for the residues obtained. The results are shown in Table 1. The initial decomposition of lla appears to involve the elimination of a fragment of composition CeH~sN (probably n-hexylamine). At higher temperatures the nitrogen content of the residue is further reduced and at 710°C the residue is nitrogen free. The residue at point A melted at 144-148'C and was soluble in toluene. The residues at B and C did not melt at 300:C. An X-ray powder pattern for the residue at C showed ZnO to be present as the only detectible crystalline component.
Notes
183
Experimental N-(n-hexyl) salicylaldimhle. Twelve and two tenths g (0.1 mole) of salicylaldehyde was mixed at room temperature with 11 g (an excess) of n-hexylamine. The mixture evolved heat spontaneously and water was given off. After the initial reaction subsided, the mixture was heated a few minutes on the hot plate. The mixture was cooled, dissolved in 50 ml of benzene, and extracted with three 100 ml TABLE 1.--
Ab B C
DECOMPOSITION Rt-SII)UI'~S FROM THE PYROLYSIS OF
Pyrolysis Temp. (:C)
Colour
o{;C
265 340 710
white yellow black
62.9 60.1 62.6
a. By difference b. Calculated for
:.
lla
IN ARGON
o,,;H
3gN
~O ~
3~Zn
6.4 5.4 1.9
3"8 2"5 0"0
9"8 12"1 8'0
17"3 i 19"9 I= 27"5
CzoHz~NO2Zn: C, 63.75; H, 6.69; N, 3.72; O, 8.49; Zn, 17.35.
portions of water. The latter were discarded. The benzene was distilled off and the residue was fractionally distilled in vacuo. The product was collected as a series of small fractions. Those fractions having the same index of refraction were combined and taken as the purified compound. Yield 82 per cent, based on the salicylaldehyde; b.p. 130-131~C at 2.2 mm-Hg; n D zs 1.5318; ~ 0.9685. Analysis calculated for CIaH~9ON: C, 76.06; H, 9.33; N, 6.82. Found: C, 76.29; H, 9-31; N, 6.92. C = N infra-red stretching frequency at 6.13 t~ (determination for the liquid).
bis-[N-(n-hexyl) salicylaldimino] zinc(l I) The preparation of this compound was described previously, m M.p. 92.5-93-5~C.
N-(n-hexyl)-o-hydroxybenzylamine Fourteen and seven-tenths g (0.072 moles) N-(n-hexyl) salicylaldimine was dissolved in 150 ml absolute ethanol and 0.1 g PtO..,~Sj added. The mixture was shaken at room temperature with H2 at an initial pressure of 60 lbs/in. 2 for 1'75 hr in a Parr Pressure Reaction apparatus. The pressure decreased during the first 1-5 hr with over 90 per cent of the total pressure drop occurring during the first hour. The total hydrogen consumption, as determined by the pressure decrease, was 0-072 moles (theoretical 0.072 moles). The reaction mixture was filtered through sintered glass and the ethanol allowed to evaporate at room temperature. The residue was further dried in a vacuum desiccator. The residue consisted of 14"8 g of a light yellow oil. Analysis calculated for CIaH~ON: C, 75.32; H, 10.21; N, 6"76. Found: C, 74.74; H, 10.13; N, 6.62. N - H stretching frequency at 3.03t~ (detn. for the liquid).
bis-[N-(n-hexyl)-o-hydroxybenzylamhlo] zinc(ll) N-(n-hexyl)-o-hydroxybenzylamine(2'28 g 0.011 moles) was dissolved in 25 ml methanol. Twentyfive ml of 0.20 M aqueous zinc acetate solution was added slowly while shaking the flask. A pale yellow flocculent precipitate separated during the addition. The mixture was stirred with a magnetic stirrer and 10 ml of 1.00 M aqueous KOH solution was added dropwise from a burette over a period of 0.5 hr. The mixture was cooled in the refrigerator and the solid collected by filtration. The product was dried in a vacuum oven for 2 hr at 100::C. Yield, 2.3 g. The crude chelate was purified by dissolving in 50 ml hot methanol followed by filtering through filter paper in a heated funnel. The cooled solution deposited delicate colourless needles. The purified product was collected by filtration and dried in the wtcuum oven at 10OC. Yield 1.35 g; m.p. 221-222 C. Analyses calculated for (CtaHo.~NO)2Zn: C, 65"33; H, 8"44; N, 5"86; Zn, 13.68. Found: C, 66.5; H, 8.7; N, 5.9: Zn, 13.60. c5~ R. ADAMS,V. VOORHEESand R. L. StruttER, Sons, Inc., New York (1941). p. 463.
Organic Syntheses, Collective Vol. I, Sec. Edition, J. Wiley &
184
Notes
Attempts to prepare the corresponding copper(II) nickel(II) chelates by substituting the respective acetates in the above procedure gave very viscous brown (Cu) or green (Ni) oils which were not characterized. Heat Stability Studies Thermogravimetric curves were obtained with a recording thermobalance of the type previously described, c6~ Fifty mg samples of the chelates were heated in a stream of argon (50 ml/min) at atmospheric pressure (ca. 730 mm-Hg). Temperature was raised linearly with time at 2"lcC/min. R. G. CHARLES Westinghouse Research Laboratories Beulah Road, Churchill Boro. Pittsburgh 35, Pennsylvania (6) R. G. CHARLESand A. LANGER,J. Phys. Chem. 63, 603 (1959).
The ion exchange separation of cis- and trans- dichlorobis-(ethylenediamine) c o b a l t ( I l l ) nitrate. (Received 7 March 1961 ; in revised form 29 June 1961) The bis-(ethylenediamine) dichlorocobaltic nitrate complex [Co(en)aCldNO3, can exist in two stereoisomeric forms, cis and trans. It has been shown in several publicationsC~.~.s, 4,5) that inert isomeric cationic octahedral complex ions can be separated by ion exchange. In this paper the complete separation of the two cobaltic stereoisomers by means of cation exchange is described. In spite of previous reports, a very short column (4 cm long) was used, which has the advantage of an easy cooling during the separation. We were obliged to do so because of the ready aquation of the two isomers at the ordinary temperature. The cis isomer aquates more, and the trans isomer less readily, the final product in each case is cis-[Co(en)~(HaO)z] 3-. EXPERIMENTAL The two isomers were prepared using the method of BAILARc6). The U.V.-visible spectra (Fig. 1) were taken dissolving the compounds in the least possible amount of water and diluting to the desired concentration with alcohol. 47) A Hilger spectrophotometer was used for this purpose as well as for the determination of the two isomers during the separation. In the latter case the trans isomer was determined at 6150 A and the cis at 5350 ,~.. Because of the interference of the absorption of the two isomers when both were present in the same sample, two calibration lines were prepared for each isomer, the first at 6150 and the second at 5350 A (Figs. 2 and 3). The column (4 cm long and 1 cm dia.) was prepared with the strong cation exchange (Dowex 50w × 8, 100-200 Mesh) and was activated by successive treatments with 2 N HCI, water, 2 N NaOH and finally was used in the hydrogen form. A number of preliminary experiments showed the best eluant to be a buffer solution of pH 5 (1) MOTOHICHI MORI,et al. Nippon Kagaku Zasshi, 76, 1003-7, (1955). ~1 SVEN L]NDE.~rORS, Arkiv Kemi, 10, 561-8, (1957). ts) JAHN T. HONGEN, et al.,J. Amer. Chem. Soc., 80, 5015-8, (1958). c4~p. GALLACER,unpublished work Univ. Wisconsin. c~l Inorganic Syntheses, Ed. by FERNELIUS,VOI. II. p. 222. t6) M. L. ERNSBERGERand W. R. BRODE,J. Amer. Chem. Sot., 56, 1842-3 (1934). t~ Modern Coordination Chemistry, J. LEWISand R. G. W~LKINS,p. 200, lnterscience, New York, 1960.
NOTES
Preparation and heat stability of a hydrogenated Schiff base chelate (Received 16 March 1961)
There has been recent interest in metal chelate compounds as possible heat stable materials, both in their own right, m and as part of the structure of heat stable metal-organic polymersJ ~m Previous work in this laboratory has concerned the preparationCU ) and heat stabilities ~x) of the copper, nickel, and zinc Schiff base chelates I (R = an n-alkyl group).
CHiN ~R
/
C H~-N H~R
[~ilZ---NH~(CH2)5
O--M--O
CH3
R/N~CH / I 1o:
R=n-.-C6H,3, M~Zn
]l
rrr
"II o: R=n--C~;H3 , M~Zn
It has seemed of interest to compare the properties, and in particular the heat stabilities, of the closely analogous metal chelates II. The compounds II can be considered to be formed by means of the hydrogenation of the two C - - N bonds in I. No member of the series 11appears to have been previously synthesized. We now wish to report the preparation of one such chelate, the zinc chelate of N(n-hexyl)-o-hydroxybenzylamine (lla). We also report here the results of a comparison of the heat stability of lla with that of the corresponding Schiff base chelate la. Catalytic hydrogenation in ethanol of the Schiff base N-(n-hexyl) salicylaldimine readily yields the previously unreported secondary amine N-(n-hexyl)-o-hydroxybenzylamine (Ill). The latter compound is too heat sensitive to be vacuum distilled; attempts to do so lead to resin formation. This is in contrast with the corresponding Schiff base, N-(n-hexyl) salicylaldimine. The latter compound is readily purified by vacuum distillation. 111 can be obtained relatively pure simply by evaporating the filtered reaction mixture. The structure of I!I is evident from the Hz consumption, the elemental analyses, the presence in the infra-red spectrum of an N - H stretching absorption peak and the absence of one due to ~ N stretching. Reaction of Ill with zinc acetate in methanol-water solution yields the zinc chelate Ila which can be obtained in a beautifully crystalline form by recrystallization from methanol. Elemental analyses for the purified compound are in good agreement with the structure lla. Like the Schiff base chelate Ia, compound lla has been obtained only in the anhydrous form. Also like la, lIa can be melted, but it melts over 100~C higher than does la. Attempts to prepare the corresponding copper and nickel hexyl chelates It gave oily products which could not be purified adequately for characterization. (1) R. t=) C. ~) D. (4) R.
G. CHARLES,J. Inorg. Nucl. Chem. 9, 145 (1959). N. KENNEY, Chem. & Ind. (Rec.) 880 (1960). B. SOWERnYand L. F. At:DRIETH, J. Chem. Educ. 37, 134 (1960). G. CHARLES,J. Org. Chem. 22, 677 (1957). 181
182
Notes
Figure I shows the thermogravimetric curves obtained by heating the two zinc chelates la and IIa in an atmosphere of argon, lla began to lose weight rather abruptly, at about 250°C, somewhat above the melting point of the substance. Weight loss continued to 710~C, the highest temperature employed. The residue remaining in the sample container at 71ffC was found to contain 99.6 per cent of the zinc initially present in the compound lla taken. This is conclusive evidence that the weight losses observed are due to volatilization of pyrolysis products rather than to evaporation of unchanged fla.
1
I
I
1
I
I
I
A ~-,,,/CH_2-NHI(CHz)5CH3 E: E:n
T 20 mg .,~/CH =N/'(CH2)5 CH3
0
I
IOO
I
200
I
I
300 400 Ternpereture 2 °C
I
500
I
600
I
700
FiG. l.--Weight loss-temperature curves for zinc chelates heated in argon. Fifty mg samples. The curves are displaced along the ordinate. The thermogravimetric curve obtained for the Schiff base chelate la shows a more gradual onset of weight loss which first becomes detectable at about 250°C. A white solid gradually condensed on the cool portions of the furnace tube. This material was identified as la by its infra-red absorption spectrum. The residue remaining at 710~C contained only 50.2 per cent of the zinc present in the sample of la taken. In a separate experiment la was heated only to 310°C. The material remaining in the sample container had the same melting point as pure la. These bits of evidence show that la is not pyrolyzed at least to 310'C, under the conditions used, and that the initial weight losses for la in Fig. 1 are due to evaporation of unchanged chelate. The compound la is thus clearly more heat stable than is IIa. In separate experiments thermogravimetric curves were obtained for chelate Ila which were terminated at the points A, B, and C shown in Fig. I. Elemental analyses were determined for the residues obtained. The results are shown in Table 1. The initial decomposition of lla appears to involve the elimination of a fragment of composition CeH~sN (probably n-hexylamine). At higher temperatures the nitrogen content of the residue is further reduced and at 710°C the residue is nitrogen free. The residue at point A melted at 144-148'C and was soluble in toluene. The residues at B and C did not melt at 300:C. An X-ray powder pattern for the residue at C showed ZnO to be present as the only detectible crystalline component.
Notes
183
Experimental N-(n-hexyl) salicylaldimhle. Twelve and two tenths g (0.1 mole) of salicylaldehyde was mixed at room temperature with 11 g (an excess) of n-hexylamine. The mixture evolved heat spontaneously and water was given off. After the initial reaction subsided, the mixture was heated a few minutes on the hot plate. The mixture was cooled, dissolved in 50 ml of benzene, and extracted with three 100 ml TABLE 1.--
Ab B C
DECOMPOSITION Rt-SII)UI'~S FROM THE PYROLYSIS OF
Pyrolysis Temp. (:C)
Colour
o{;C
265 340 710
white yellow black
62.9 60.1 62.6
a. By difference b. Calculated for
:.
lla
IN ARGON
o,,;H
3gN
~O ~
3~Zn
6.4 5.4 1.9
3"8 2"5 0"0
9"8 12"1 8'0
17"3 i 19"9 I= 27"5
CzoHz~NO2Zn: C, 63.75; H, 6.69; N, 3.72; O, 8.49; Zn, 17.35.
portions of water. The latter were discarded. The benzene was distilled off and the residue was fractionally distilled in vacuo. The product was collected as a series of small fractions. Those fractions having the same index of refraction were combined and taken as the purified compound. Yield 82 per cent, based on the salicylaldehyde; b.p. 130-131~C at 2.2 mm-Hg; n D zs 1.5318; ~ 0.9685. Analysis calculated for CIaH~9ON: C, 76.06; H, 9.33; N, 6.82. Found: C, 76.29; H, 9-31; N, 6.92. C = N infra-red stretching frequency at 6.13 t~ (determination for the liquid).
bis-[N-(n-hexyl) salicylaldimino] zinc(l I) The preparation of this compound was described previously, m M.p. 92.5-93-5~C.
N-(n-hexyl)-o-hydroxybenzylamine Fourteen and seven-tenths g (0.072 moles) N-(n-hexyl) salicylaldimine was dissolved in 150 ml absolute ethanol and 0.1 g PtO..,~Sj added. The mixture was shaken at room temperature with H2 at an initial pressure of 60 lbs/in. 2 for 1'75 hr in a Parr Pressure Reaction apparatus. The pressure decreased during the first 1-5 hr with over 90 per cent of the total pressure drop occurring during the first hour. The total hydrogen consumption, as determined by the pressure decrease, was 0-072 moles (theoretical 0.072 moles). The reaction mixture was filtered through sintered glass and the ethanol allowed to evaporate at room temperature. The residue was further dried in a vacuum desiccator. The residue consisted of 14"8 g of a light yellow oil. Analysis calculated for CIaH~ON: C, 75.32; H, 10.21; N, 6"76. Found: C, 74.74; H, 10.13; N, 6.62. N - H stretching frequency at 3.03t~ (detn. for the liquid).
bis-[N-(n-hexyl)-o-hydroxybenzylamhlo] zinc(ll) N-(n-hexyl)-o-hydroxybenzylamine(2'28 g 0.011 moles) was dissolved in 25 ml methanol. Twentyfive ml of 0.20 M aqueous zinc acetate solution was added slowly while shaking the flask. A pale yellow flocculent precipitate separated during the addition. The mixture was stirred with a magnetic stirrer and 10 ml of 1.00 M aqueous KOH solution was added dropwise from a burette over a period of 0.5 hr. The mixture was cooled in the refrigerator and the solid collected by filtration. The product was dried in a vacuum oven for 2 hr at 100::C. Yield, 2.3 g. The crude chelate was purified by dissolving in 50 ml hot methanol followed by filtering through filter paper in a heated funnel. The cooled solution deposited delicate colourless needles. The purified product was collected by filtration and dried in the wtcuum oven at 10OC. Yield 1.35 g; m.p. 221-222 C. Analyses calculated for (CtaHo.~NO)2Zn: C, 65"33; H, 8"44; N, 5"86; Zn, 13.68. Found: C, 66.5; H, 8.7; N, 5.9: Zn, 13.60. c5~ R. ADAMS,V. VOORHEESand R. L. StruttER, Sons, Inc., New York (1941). p. 463.
Organic Syntheses, Collective Vol. I, Sec. Edition, J. Wiley &
184
Notes
Attempts to prepare the corresponding copper(II) nickel(II) chelates by substituting the respective acetates in the above procedure gave very viscous brown (Cu) or green (Ni) oils which were not characterized. Heat Stability Studies Thermogravimetric curves were obtained with a recording thermobalance of the type previously described, c6~ Fifty mg samples of the chelates were heated in a stream of argon (50 ml/min) at atmospheric pressure (ca. 730 mm-Hg). Temperature was raised linearly with time at 2"lcC/min. R. G. CHARLES Westinghouse Research Laboratories Beulah Road, Churchill Boro. Pittsburgh 35, Pennsylvania (6) R. G. CHARLESand A. LANGER,J. Phys. Chem. 63, 603 (1959).
The ion exchange separation of cis- and trans- dichlorobis-(ethylenediamine) c o b a l t ( I l l ) nitrate. (Received 7 March 1961 ; in revised form 29 June 1961) The bis-(ethylenediamine) dichlorocobaltic nitrate complex [Co(en)aCldNO3, can exist in two stereoisomeric forms, cis and trans. It has been shown in several publicationsC~.~.s, 4,5) that inert isomeric cationic octahedral complex ions can be separated by ion exchange. In this paper the complete separation of the two cobaltic stereoisomers by means of cation exchange is described. In spite of previous reports, a very short column (4 cm long) was used, which has the advantage of an easy cooling during the separation. We were obliged to do so because of the ready aquation of the two isomers at the ordinary temperature. The cis isomer aquates more, and the trans isomer less readily, the final product in each case is cis-[Co(en)~(HaO)z] 3-. EXPERIMENTAL The two isomers were prepared using the method of BAILARc6). The U.V.-visible spectra (Fig. 1) were taken dissolving the compounds in the least possible amount of water and diluting to the desired concentration with alcohol. 47) A Hilger spectrophotometer was used for this purpose as well as for the determination of the two isomers during the separation. In the latter case the trans isomer was determined at 6150 A and the cis at 5350 ,~.. Because of the interference of the absorption of the two isomers when both were present in the same sample, two calibration lines were prepared for each isomer, the first at 6150 and the second at 5350 A (Figs. 2 and 3). The column (4 cm long and 1 cm dia.) was prepared with the strong cation exchange (Dowex 50w × 8, 100-200 Mesh) and was activated by successive treatments with 2 N HCI, water, 2 N NaOH and finally was used in the hydrogen form. A number of preliminary experiments showed the best eluant to be a buffer solution of pH 5 (1) MOTOHICHI MORI,et al. Nippon Kagaku Zasshi, 76, 1003-7, (1955). ~1 SVEN L]NDE.~rORS, Arkiv Kemi, 10, 561-8, (1957). ts) JAHN T. HONGEN, et al.,J. Amer. Chem. Soc., 80, 5015-8, (1958). c4~p. GALLACER,unpublished work Univ. Wisconsin. c~l Inorganic Syntheses, Ed. by FERNELIUS,VOI. II. p. 222. t6) M. L. ERNSBERGERand W. R. BRODE,J. Amer. Chem. Sot., 56, 1842-3 (1934). t~ Modern Coordination Chemistry, J. LEWISand R. G. W~LKINS,p. 200, lnterscience, New York, 1960.