Diphenylamine and derivatives in the environment: a review

Abstract

Diphenylamine (DPA) is a compound from the third European Union (EU) list of priority pollutants. It was assigned by the EU to Germany to assess and control its environmental risks. DPA and derivatives are most commonly used as stabilizers in nitrocellulose-containing explosives and propellants, in the perfumery, and as antioxidants in the rubber and elastomer industry. DPA is also widely used to prevent post-harvest deterioration of apple and pear crops. DPA is a parent compound of many derivatives, which are used for the production of dyes, pharmaceuticals, photography chemicals and further small-scale applications. Diphenylamines are still produced worldwide by the chemical industries. First reports showed that DPA was found in soil and groundwater. Some ecotoxicological studies demonstrated the potential hazard of various diphenylamines to the aquatic environment and to bacteria and animals. Studies on the biodegradability of DPA and its derivatives are very sparse. Therefore, further investigation is required to determine the complete dimension of the potential environmental hazard and to introduce possible (bio)remediation techniques for sites that are contaminated with this class of compounds. This is the first detailed review on DPA and some derivatives summarizing their environmental relevance as it is published in the literature so far and this review will recommend conducting further research in the future.

Introduction

Diphenylamine (DPA; structure see Fig. 1A) is a chemical compound of the third European Union list of priority pollutants. The elaboration of recommendations to assess and control the environmental risks originating from this compound was assigned to Germany by the Commission of the European Communities (Kommission der Europäischen Gemeinschaften, 1997).

While for aniline (the simplest primary amine of pure aromatic structure) numerous studies concerning toxicity and degradability are known since many years, the simplest secondary amine of pure aromatic structure, DPA, has been entered into the list of priority pollutants quite recently. Because of its antioxidative property, DPA is a stabilizing compound predominantly included in mono-, di-, and tri-base propellants of missiles and nitrocellulose-containing explosives. The mostly utilized stabilizers are diphenylamine and its urea-substituted derivatives, the so-called “acardites” and “centralites” (see example given in Fig. 1D). They can be distinguished in: acardite I (unsymmetrical diphenyl urea), acardite II (methyldiphenyl urea), acardite III (ethyldiphenyl urea); centralite I (symmetrical diethyldiphenyl urea), centralite II (symmetrical dimethyldiphenyl urea), and centralite III (methylethyldiphenyl urea) (Meyer, 1977). Some of these stabilizers have the additional function to be gelatinizing compounds, an advantage for manufacturing processes of multi-base, solvent-free gunpowders and propellants (Meyer, 1977).

Apart from military utilization, diphenylamines were and are still used in numerous further industrial applications (see next section). DPA-containing stabilizers usually have not been taken into consideration in analytical investigations of ammunition-contaminated sites. The contamination of soils of former ammunition plants with nitro- and amino-substituted compounds as well as other additives (e.g., stabilizers) is a constant source of hazard for the human health, especially if these substances pass into underground and surface waters (Haas et al., 1990; Gorontzy et al., 1994; Blotevogel and Gorontzy, 2000). Many of these substances own mutagenic properties and carcinogenic potential, which has been confirmed by animal experiments for a large number of such compounds (Dieter, 1994; Greim et al., 1998; Lachance et al., 1999). It is known from nitroaromatic compounds that they can cause toxications in humans connected with haemato- and hepatotoxical alterations. Because of the multitude of substances contained within ammunition wastes and because of their even larger number of metabolites, a toxicological evaluation of the total contamination is often very difficult to realize (Dieter, 1994; Greim et al., 1998).