On polymers with claw-like bonds derived from 8-hydroxyquinoline
Abstract Generated abstract
This study describes the preparation and preliminary characterization of a novolac-type resin obtained by condensing 8-hydroxyquinoline with formaldehyde in the presence of acid catalysts, with the aim of producing polymers containing pincer-like chelating groups. The resin was examined through solubility behavior, reactions with metal salts, melting behavior, and infrared absorption spectra of the monomer, its copper complex, the resin, and metal-treated resin films. The authors report that metal introduction can yield either high-melting thermoplastic materials or infusible complexes, depending on the degree of binding, and that infrared data support a structure in which 8-hydroxyquinoline units are connected by methylene bridges rather than ether linkages. The work suggests possible applications of such oxyquinoline-derived polymers in heavy-metal precipitation, ion-exchange materials, and coatings.
Full Text
On Polymers with Pincer-like Bonds Derived from 8-Hydroxyquinoline
P. I. Aristov, V. V. Konstantinov
(Presented by Professor, Doctor of Chemical Sciences T. P. Kulev)
In recent years, the attention of researchers has been attracted by compounds with pincer-like bonds that are capable of forming heat-resistant polymeric compounds [1, 2].
In the present work, 8-hydroxyquinoline was used to obtain a polymer with pincer-like bonds. It is known that 8-hydroxyquinoline forms intracomplex compounds with a whole series of metals. On the other hand, as early as 1894 Manasse showed that 8-hydroxyquinoline is capable of reacting with formaldehyde, forming methylol derivatives [3]. In 1913 Hansson and Schuler showed that, when 8-hydroxyquinoline is treated with formaldehyde in sulfuric acid, the sulfuric-acid salt of dioxymethylene-methane is obtained, which can be converted into the base by treatment with soda or another reagent [4]. Carrying out the condensation reaction of 8-hydroxyquinoline with formaldehyde, we obtained a novolac-type resin with an average molecular weight of 630 (by Rast), with a capillary melting temperature according to Ubbelohde of 124°. The polycondensation reaction was carried out with formaldehyde and 8-hydroxyquinoline in amounts of 6 : 7, in the presence of hydrochloric or acetic acid catalysts, taken in an amount of 1–3% of the weight of the 8-hydroxyquinoline. The resin obtained is soluble in alkaline solutions and in hydrochloric acid, dissolves only slightly in alcohols and acetone, and best in dioxane.
Films in a thin layer have a light-green shade, and in a thick layer a dark-green one. When a solution of the resin in an organic solvent is allowed to interact with a metal salt (Cu, Zn, Zr), cotton-like colored precipitates fall out immediately, whereas 8-hydroxyquinoline under these same conditions gives colored solutions with separation of crystalline precipitates.
When the resin interacts with copper acetate, dark-green powders are obtained; these do not dissolve in alkaline solutions or in ordinary solvents, dissolve only very slightly in dioxane, but dissolve well in hydrochloric acid. When the hydrochloric-acid solution of such a complex is precipitated into an aqueous alkaline medium, colored precipitates are again formed.
When a small amount of metal is introduced into the resin in the form of acetate, thermoplastic resins with a melting point of 290–300°C are obtained. When an amount of metal calculated for complete binding of all the pincer-like groups in the resin is introduced, infusible compounds are obtained; these decompose at high temperatures. At a temperature of 350° the entire mass gradually begins to melt, and this process continues without heat input. The products of this reaction have not been investigated in detail by us.
The structure of the novolac resin obtained can be judged on the basis of a qualitative characterization of the absorption spectra in the infrared region. The infrared spectra were recorded on an IKS-11 instrument, modernized by engineers V. A. Salskii and V. V. Konstantinov for recording with a potentiometer according to the scheme proposed by Prof. Tatevskii and co-workers [5]. Absorption spectra were taken for 8-hydroxyquinoline itself, its copper complex, the resin obtained, the resin treated with metal with incomplete introduction of the metal, and that treated with metal with complete binding of all pincer-like groups (Fig. 1a, b, c).
The spectrum of 8-hydroxyquinoline was taken in hexane and in the crystalline state between two KBr plates.
The spectrum of the resin was taken from a film deposited on an NaCl substrate. The spectrum of the resin partially treated with metal was taken from a film on an NaCl substrate.
The spectrum of the chelate polymer complex was taken in vaseline oil.
The slit width for the NaCl prism was 0.300 mm for the region 900–1200 cm\(^{-1}\) and 0.170 mm for 1200–1600 cm\(^{-1}\). For the LiF prism it was, respectively, 0.345 mm for the region 3200–3500 cm\(^{-1}\).
Fig. 1. Direct recording of infrared absorption spectra:
a) 1—vaseline oil; 2—8-hydroxyquinoline in vaseline oil; 3—copper complex of 8-hydroxyquinoline in vaseline oil;
b) 1—hexane; 2—8-hydroxyquinoline in hexane;
c) 1—NaCl substrate; 2—film of 8-hydroxyquinoline-formaldehyde resin; 3—film of resin partially treated with metal.
The presence in 8-hydroxyquinoline of absorption at 3407 cm\(^{-1}\) \(\pm\) 10 cm\(^{-1}\) indicates the presence of a hydroxyl group, which is polymerized by a hydrogen bond [6]. In the spectrum of 8-hydroxyquinoline in hexane, a band at 3418 cm\(^{-1}\) \(\pm\) 10 cm\(^{-1}\) is also observed, which may be attributed to vibrations of the hydroxyl group.
In the complex of 8-hydroxyquinoline with copper, this band is absent. The absorption bands in 8-hydroxyquinoline at frequencies of 1508 cm\(^{-1}\) \(\pm\) 5 cm\(^{-1}\), 1582 cm\(^{-1}\) \(\pm\) 5 cm\(^{-1}\) are caused by vibrations of C=C and —C=N [6].
In the spectra of the resin, an absorption band is observed in the region 3320 cm\(^{-1}\) \(\pm\) 10 cm\(^{-1}\), which should be assigned to the hydroxyl group, and two bands in the region 2915 cm\(^{-1}\) \(\pm\) 10 cm\(^{-1}\) and 2840 cm\(^{-1}\) \(\pm\) 10 cm\(^{-1}\), which are characteristic of the \(>\)CH\(_2\) group. A band of insignificant intensity is observed for the —OH group in the resin partially treated with copper, and bands for the \(>\)CH\(_2\) groups. Bonds of the ether type were not detected in the compounds studied.
These data show that the novolac-type resin obtained should be represented by the scheme proposed by A. A. Vansheidt for phenol-aldehyde resins [7], i.e., the molecules of 8-hydroxyquinoline are linked to one another through a methylene bridge. The assumption of other authors that bonds of ether character may be present in novolac-type resins is not confirmed by us on the basis of the absorption spectra.
From the preliminary data one may draw the conclusion that searches for heat-resistant polymers with pincer-like bonds among
derivatives of oxyquinoline. The resin obtained, it seems to us, after detailed analytical studies may find application for analytical purposes in the precipitation of a number of heavy metals, and also as ionites and paint-and-varnish coatings.
REFERENCES
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- Martin K. Khimiya i tekhnologiya polimerov, 5, 12, 1958.
- Manasse, Ber. 27, 2049, 1894.
- H. Schüller, J. prakt. Chem. 21, 88, 180, 1913.
- Tareevskii et al. VMU, series Mathematics, Mechanics, 5, 233, 1957.
- L. Bellamy. The Infrared Spectra of Molecules, Inizdat, Moscow, 1957.
- A. A. Vansheidt. Prom. organicheskoi khimii, 7, 385, 1937.