12th Annual Symposium, Mary Kay O’Connor Process Safety Center “Beyond Regulatory Compliance: Making Safety Second Nature” Texas A&M University, College Station, Texas October 27-28, 2009 Azodicarboxylates: Explosive Properties and Thermal Hazards A. Berger* and K. D. Wehrstedt BAM Federal Institute for Materials Research and Testing, Division II.2 “Reactive Substances and Systems”, Unter den Eichen 87, 12205 Berlin, Germany Abstract A large number of Azodicarboxylates and their derivatives are produced and used in the chemical industries. The versatile applications of these Azodicarboxylates in research institutes and in the chemical industries for chemical synthesis arouse additional hazards. The aim of this paper is to obtain a predication about the structure-response relationship regarding the explosive properties and the thermal hazards of different versatile used Azodicarboxylates. The substances were exam- ined with the Differential Scanning Calorimetry (DSC). Furthermore, different laboratory test methods, based on the UN Recommendations on the Transport of Dangerous Goods, were applied to determine the explosive properties of the mentioned substances. Keywords: Azodicarboxylates; Thermal decomposition; Differential Scanning Calorimetry (DSC); Explosive properties 1. Introduction The assessment of the explosive properties and the thermal hazards of energetic substances e.g. Azodicarboxylates requires extensive knowledge - in the general application. Therefore, the aim of this paper is to investigate the thermal stability, the decomposition and the explosive properties of 9 different substances (7 Azodicarboxylates and two relatives). One thermal analysis method, the Differential Scanning Calorimetry, was used to describe the thermal behaviour. As BAM is the competent authority in Germany for testing, classification and assignment of substances showing explosive properties, tests on selected Azodicarboxylates have been performed on the basis of the criteria given in the UN Recommendations on the Transport of Dangerous Goods (UN Recom- mendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 2003). Diethylazodicarboxylate (DEAD) for instance is a very important reagent used in many chemical reactions (Dembinski, 2004; Hillier et al., 2004; Mitsunobu, 1981; Uemura and Chatani, 2005; Vijay et al., 2007). On the other hand DEAD represents an explosive hazard. It is shock-sensitive and thermally unstable - it is very sensitive if heated under defined confinement (Urben, 1999). Due to this, the shipment of DEAD as a pure reagent is prohibited in the United States (Sigma- Aldrich). The shipment of DEAD, 40% solution in toluene, is allowed (Sigma-Aldrich). How sta- ble and safe this solution really is, this will be discussed later. To obtain a statement about the structure-response relationship regarding the explosive properties and the thermal stability of Azodicarboxylates e.g. DEAD, different derivatives with electron donating and electron- withdrawing groups were selected. Also the sterical effect was considered. Therefore, we have chosen Diisopropylazodicarboxylate (DIAD), Di-tert-butylazodicarboxylate (Di-tert-butyl-AD), Bis(2,2,2-trichloroethyl)azodicarboxylate (Bis(2,2,2-trichloroethyl)-AD), Dibenzylazodicarboxy- late (DBAD), Di(4-chlorobenzyl)azodicarboxylate (Di(4-chlorobenzyl)-AD, 1,1’-Azodicarbonyl)- azodicarboxylate (ADDP) and Ethyldiazoacetate, with 15 % dichloromethane (EDA_15% CH2Cl2). These substances are also widely used in chemical reactions, e.g. DIAD in Lewis acid or Brønstedt acid catalyzed reactions (Jian-Mei et al., 2009) and still for the commonly used Mitsun- obu reaction (Mitsunobu, 1981). ADDP, in which the alkoxy group is replaced by a secondary amine such as piperidine has been used in reactions to increase the basicity (Dembinski, 2004; Kosower and Kanetylondner, 1976). DBAD has been used in reactions with phosphanes (Kiank- arimi et al., 1999), and Di-tert-butyl-AD is gaining popularity as a preferred reagent for the Mit- sunobu reaction (Pelletier and Kincaid, 2000). Furthermore, EDA has been used in Cycloaddition reactions (Malisch et al., 1998) and metal-catalyzed reactions (Grohmann, 2007). A study of the ‘loss of control’ in chemical systems due to decomposition in the case of EDA was examined in the group of Cozzani et al. (Marsanich et al., 2004). Di-2-methoxyethyl azodicarboxylate (DMEAD) was newly developed from Sugimura and Hagiya and is now commercially available (Sugimura and Hagiya, 2008). DMEAD has a big advantage in its production process and is also a very good alternative for the potentially explosive and shock-sensitive liquid, DEAD, for the Mit- sunobu reaction (Sugimura and Hagiya, 2008). Unfortunately, until now we could not investigate the explosive properties and the thermal behaviour of this substance in our laboratory. This should be done in the near future to receive further information about the structure-response relationship regarding the explosive properties and the thermal hazards of different versatile used Azodicar- boxylates. 2. Experimental To characterize the explosive properties of Azodicarboxylates and their derivatives some of the necessary test procedures have been performed, which are fully described in literature (Method A.14 "Explosive Properties", Annex to Commission Directive 92/69/EEC of 31 July 1992, 1992; UN Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 2003; Wehrstedt et al., 2005). For better understanding, an overview of these test procedures will be giv- en, briefly. The BAM 50/60 steel tube test (A.1) is used to measure the ability of a substance to propagate a detonation by subjecting it to a cylindrical detonating booster charge under confine- ment in a steel tube. The ability of a substance to transfer a deflagration is performed with the Def- lagration test (C.2). The Koenen test (E.1) and the Dutch pressure vessel test (E.2) are used to de- termine the sensitivity of a substance to the effect of intense heat under defined confinement. To determine the explosive power of a substance the Trauzl test (F.3) method has been used. The ‘BAM Fallhammer’ (3(a)(ii) (impact test method) is used to measure the sensitivity of a substance to drop-weight impact. The BAM-Dewar-Test (H.4) to determine the SADT (self-accelerating de- composition temperature) is a heat accumulation storage test. Dynamic DSC measurements using different heating rates in the range 0.5 to 40 K/min were per- formed using a Perkin Elmer Pyris Diamond Calorimeter. The calibration was carried out at each heating rate for temperature and heat flow, using Indium as reference material. For all experiments stainless steel crucibles were used and a 20 ml/min N2 purge gas was applied. For each substance and heating rate at least two runs have been done. The sealed stainless steel crucibles, can with- stand an inner pressure as high as 15 MPa. According to the standards DIN 51007 and ASTM E 473, a positive deflection in the DSC curve corresponds to an endothermic effect, and a negative deflection corresponds to an exothermic one. 3. Results and discussion The thought of this paper is to obtain a structure-response relationship regarding the explosive properties and the thermal hazards of different Azodicarboxylates and two related substances (Ta- ble 1). These compounds have been investigated on the basis of the criteria given in the UN Rec- ommendations on the Transport of Dangerous Goods. The appropriate test results are summarized in Table 2 and will be discussed in this chapter. Table 1 Data of the Substances Name Structure Abbreviation Molecular Aggregate formula State (color) O Diethylazodicarboxylate O N N O DEAD C6H10N2O4 liquid (yel- O low) O Diethylazodicarboxylate, O N N 40 % in Toluene O DEAD 40 %_Tol C6H10N2O4 liquid (or- O ange) O Diisopropyl- O DIAD C8H14NO4 liquid (or- N N O azodicarboxylate O ange) O Di-tert-butyl azodicar- O Di-tert-butyl-AD N N boxylate O C10H18N2O4 solid (yel- O low) Cl Cl O Bis(2,2,2-trichloroethyl) Cl O Bis(2,2,2- N N azodicarboxylate O Cl trichloroethyl)- C6H4N2O4Cl6 solid (yel- O Cl Cl AD low) O Dibenzyl azodicarbox- O DBAD C H N O solid (yel- N N 16 14 2 4 O ylate O low) O Cl O Di(4-chlorobenzyl) N N Di(4- O O azodicarboxylate Cl chlorobenzyl)-AD C16H12N2O4Cl2 solid (or- ange) O N 1,1’-(Azodicarbonyl)- N N dipiperidine N ADDP C H N O solid (yel- O 12 20 4 2 low) O Ethyldiazoacetate N2 EDA_15%CH2Cl2 C4H6N2O2 liquid (yel- with 15 % CH2Cl2 O low) 3.1. Test methods The result in the Koenen test (UN test E.1) carried out at BAM, shows for DEAD a limiting di- ameter of 20 mm (!), t1 = 32 s, t 2 = 3 s, “violent” (Fig. 1). The sensitivity to drop-weight impact (“BAM Fallhammer”) has a limiting value of 4 J. In comparison Trinitrotoluene (TNT) has a lim- iting diameter of 5 mm and a sensitivity to drop-weight impact of 15 J (Meyer, 1985). The explo- sive power, which was measured with the Trauzl test, is “not low” (expansion: 33ml). Therefore, DEAD represents an explosive hazard. It is shock-sensitive and very sensitive if heated under de- fined confinement (Wehrstedt, 2001). DEAD is currently only available in solution (e.g. 40% in toluene). But even for a 40 % solution the Dutch pressure vessel test (UN test E.2) shows a “violent” result (limiting diameter ≥ 24.0 mm (!) t1= 29 s, t2 = 73 s). Also the Koenen test shows an explosion at a limiting diameter of 1.0 mm (result: “low”). Due to the lower concentration, the expansion of the lead block is only 5 ml and the sensitivity to drop-weight impact is > 40 J. These results could be explained by the evaporation of toluene, in the case of the E.1 and E.2 test, based on its special test procedure. Thus, the toluene seems to be unsuitable to completely suppress the explosive properties of DEAD. Because of the hazard risks the use of DEAD decreases and exchanges partly against the more stable Diisopropy- lazodicarboxylate (DIAD) (Jian-Mei et al., 2009).