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Hydrazine

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HydrazineJean-Pierre Schirmann, Paris, France Paul Bourdauducq, ATOFINA, Pierre-B nite, France e Introduction . . . . . . . Physical Properties . . Chemical Properties . Production . . . . . . . . Raschig Process . . . . Olin Raschig Process . Urea Process . . . . . . . Bayer Ketazine Process Fisons Process . . . . . . Peroxide Process . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Environmental Protection . . . . . . . . Quality Specications . . . . . . . . . . . Analysis . . . . . . . . . . . . . . . . . . . . Handling, Storage, and Transportation . . . . . . . . . . . . . . . . . . . . . . . Uses . . . . . . . . . . . . . . . . . . . . . . Derivatives . . . . . . . . . . . . . . . . . . Economic Aspects . . . . . . . . . . . . . Toxicology and Occupational Health . References . . . . . . . . . . . . . . . . . .

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1. IntroductionThe existence of hydrazine [302-01-2], H2 NNH2 , Mr 32.05, was predicted by Emil Fischer in 1875 [12], and it was rst isolated in 1887 by Curtius [13]. Anhydrous hydrazine was isolated in 1893 by de Bruyn [14]. The rst commercial production process was invented by Raschig in 1907 [15]; it is still in use in Japan, Russia, China, and Korea. Following the rapid increase in the use of hydrazine and its derivatives as blowing agents for plastic foams came other industrial applications: boiler water treatment, polymerization initiators, pesticides, pharmaceuticals, photographic chemicals, and dyes. A century after its discovery, hydrazine is still difcult to synthesize, mainly for thermodynamic reasons. Most hydrazine is produced by variations of the Raschig process, the oxidation of ammonia by hypochlorite. However, the new plants built since 1980 are based on the PCUK process, which uses hydrogen peroxide as oxidant. Most hydrazine is sold as an aqueous solution of up to 64 % concentration, corresponding to hydrazine hydrate [7803-57-8], N2 H4 H2 O.

tions, and its aqueous solutions are highly alkaline. Some physical properties of hydrazine and its aqueous solutions are listed in Table 1. Certain physical properties of the aqueous solutions, e.g., viscosity and density, display a maximum value at the 64 % composition (corresponding to the monohydrate), suggesting that the hydrate, N2 H4 H2 O, exists in both the solid and the liquid phase (Figure 1). Hydrazine forms an azeotrope (bp 120.5 C) with water, containing 58.5 mol % hydrazine.

2. Physical PropertiesHydrazine is a colorless liquid with an ammoniacal odor. It is miscible with water in all proporc 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002/14356007.a13 177 Figure 1. Freezing point of aqueous hydrazine solutions a) Monohydrate, NH2 NH2 H2 O

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Hydrazine

Table 1. Physical properties of hydrazine and its aqueous solutions Property Hydrazine concentration, wt % 100 fp, C bp (101.3 kPa), C (25 C), g/mL n25 D Viscosity (20 C), Pa s pH surface tension (25 C), mN/m dielectric constant (25 C)

64 51.7 120.5 1.0320 1.4284 1.50 12.75 74.0

51.2 59.8 117.2 1.0281 1.4120 1.44 12.10

35.2 64.6 108 1.0209 1.3888 1.10

22.4 26 107 1.0132 1.3690 1.08

15.4 14 103 1.0083 1.3575 1.04 10.5

2.0 113.5 1.0045 1.4644 0.974

66.7 51.7

Some thermodynamic properties of anhydrous hydrazine are listed in Table 2 [1620].Table 2. Thermodynamic properties of hydrazine [1620] Property Critical constants Pc , MPa T c, C d c , g/mL Heat of vaporization, kJ/mol Heat of fusion, kJ/mol Heat capacity (25 C), J mol1 K1 Heat of combustion, kJ/mol Heat of formation, kJ/mol Free energy of formation, kJ/mol Entropy of formation, J mol1 K1 Flash point (COC), C Cleveland open cup. Value 14.69 380 0.231 45.27 12.66 98.87 622.1 50.63 149.2 121 52

Thermal Decomposition. A relatively high temperature (250 C) is required, in the absence of catalysts, for signicant decomposition to occur [17, 22]:

The decomposition temperature is lowered by several catalysts (e.g., copper, cobalt, molybdenum, and their oxides) [17]. Hence, hydrazine should be handled carefully. Acid Base Reactions. Hydrazine is a weak base that reacts with water:

Hydrazine is an endothermic compound with a heat of formation of + 50.6 kJ/mol. The explosion limits in air are 4.7 100 %. The upper value indicates that anhydrous hydrazine is selfexplosive. Dilution with an inert gas such as nitrogen or water signicantly reduces the ammable domain by raising the lower explosion limit [21]. Hydrazine hydrate (30.9 vol% hydrazine) can therefore be handled without danger at atmospheric pressure at 120 C in the absence of air.

The cation N2 H2+ occurs only in strongly 6 acidic solutions or in the solid state [23]. Hydrazine forms salts with acids [17], some of which are explosive, e.g., the nitrate, perchlorate, and azide. Other salts, such as the hydrochloride, hydrobromide, or sulfate, are commercially available and can be handled in the same way as hydrazine hydrate. Reducing Agent. Hydrazine is a strong reducing agent which reacts exothermically with oxygen: Many of the uses of hydrazine are based on this reaction (see Chap. 9). Several metals catalyze the oxidation of hydrazine by air in alkaline solution. For this reason, copper and poly-

3. Chemical PropertiesThe chemical properties of hydrazine are strongly inuenced by the following characteristics: the compound is endothermic, a base, and a reducing agent.

Hydrazine valent metals or their salts must be absent or deactivated when hydrazine solutions are distilled [24, 25]. The oxides of cadmium, magnesium, zinc, and aluminum stabilize hydrazine solutions against aerial oxidation [26, 27]. In acid solution hydrazine reacts with halogens [28, 29]:

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Diamine Reactions. Hydrazine is widely used in the synthesis and production of numerous open-chain and heterocyclic nitrogen compounds, including hydrazo and azo compounds, pyrazoles, triazoles, urazoles, tetrazoles, pyridazines, and triazines [31].

4. ProductionThese reactions are used to determine N2 H4 (with iodine), to purify crude hydrogen halides, and to remove traces of halogens in wastewater. Traces of hydrazine may be removed by the same procedure. For waste or spills it is more convenient to use sodium hypochlorite: Availability of raw materials and production costs rule out most of the possible routes to hydrazine; nitrogen and ammonia are the only obvious starting materials for a reasonably direct process. Consideration of the variation of standard free energy F (g) (298 K) for the gaseous system H2 N2 NH3 N2 H4 (Fig. 2, see next page) indicates that the direct synthesis of hydrazine from nitrogen and hydrogen is energetically unfavorable. The free energy of formation is clearly much more favorable for production of ammonia.

or hydrogen peroxide in the presence of iron(III) or copper(II) salts:

Various metal ions or oxides, such as those of copper, silver, gold, mercury, nickel, and platinum, can also be reduced to pulverulent metals by hydrazine [30, 31]. Ketones and aldehydes are reduced by hydrazine (the Wolff Kishner reaction) [32]:

In the presence of a hydrogenation catalyst, such as Raney nickel, aromatic nitro compounds are reduced to the corresponding amines [33]:

In the presence of hydrogen peroxide, hydrazine is oxidized to diimide [3618-05-1], which reduces acetylenes to cis-alkenes:

and hydrogenates residual double bonds in acrylonitrile butadiene rubber [34].

Figure 2. Variation of standard free energy (298 K) in the gaseous system H2 N2 NH3 N2 H4

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Hydrazine 38]. Bayer has considerably improved yields by introducing acetone into the Raschig process. In the 1970s, PCUK, (now Atochem) developed a new, efcient, and clean process based on the oxidation of ammonia by hydrogen peroxide in the presence of a ketone. Most hydrazine is now produced by the ketazine process, with oxidation of ammonia by chlorine or hydrogen peroxide.

The search for selective reduction of nitrogen has not yet found a practical or economic solution. Therefore, ammonia remains the only valuable nitrogen starting material for production of hydrazine. Coupling of two molecules of NH3 with coproduction of hydrogen also appears, on paper, to be an attractive process. Such a reaction is, however, endothermic and highly inefcient. For example, decomposition of ammonia by an electric discharge, photolysis, or radiolysis gives only low yields of hydrazine. An alternative method is to oxidize the hydrogen atoms removed from the ammonia:

4.1. Raschig ProcessIn the Raschig process [14,4042] sodium hypochlorite (obtained by reaction of chlorine with sodium hydroxide) is used to oxidize ammonia. Two steps are involved in the oxidation (Fig. 3). In the rst, carried out at ca. 5 C, chloramine [10599-90-3] is formed by a fast reaction:

Only three oxidants are relevant to an industrial process: chlorine, oxygen, and hydrogen peroxide. A further difculty is that hydrazine, which is a much more powerful reducing agent than ammonia, may also react with the oxidizing agent. Chlorine has been widely used in the Raschig process, which is still operated. To avoid further oxidation of hydrazine by chlorine, very dilute conditions have to be employed. Yields are no higher than 60 %. The use of air or oxygen as a clean oxidizing agent is hardly feasible. This process, discovered in the 1950s by Meyer et al. [35] and later studied extensively by Hayashi [39] can only be applied to a few aromatic imines that lead to aromatic az

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