c© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a13 177

Hydrazine 1

Hydrazine

Jean-Pierre Schirmann, Paris, France

Paul Bourdauducq, ATOFINA, Pierre-Benite, France

1. Introduction . . . . . . . . . . . . . . . . . 12. Physical Properties . . . . . . . . . . . . 13. Chemical Properties . . . . . . . . . . . 24. Production . . . . . . . . . . . . . . . . . . 34.1. Raschig Process . . . . . . . . . . . . . . 54.2. Olin Raschig Process . . . . . . . . . . . 54.3. Urea Process . . . . . . . . . . . . . . . . . 64.4. Bayer Ketazine Process . . . . . . . . . 64.5. Fisons Process . . . . . . . . . . . . . . . . 74.6. Peroxide Process . . . . . . . . . . . . . . 7

5. Environmental Protection . . . . . . . . 86. Quality Specifications . . . . . . . . . . . 87. Analysis . . . . . . . . . . . . . . . . . . . . 88. Handling, Storage, and Transporta-

tion . . . . . . . . . . . . . . . . . . . . . . . 99. Uses . . . . . . . . . . . . . . . . . . . . . . 1010. Derivatives . . . . . . . . . . . . . . . . . . 1411. Economic Aspects . . . . . . . . . . . . . 1612. Toxicology and Occupational Health . 1713. References . . . . . . . . . . . . . . . . . . 17

1. Introduction

The existence of hydrazine [302-01-2],H2N−NH2, Mr 32.05, was predicted by EmilFischer in 1875 [12], and it was first isolatedin 1887 by Curtius [13]. Anhydrous hydrazinewas isolated in 1893 by de Bruyn [14]. Thefirst commercial production process was in-vented by Raschig in 1907 [15]; it is still in usein Japan, Russia, China, and Korea. Followingthe rapid increase in the use of hydrazine and itsderivatives as blowing agents for plastic foamscame other industrial applications: boiler watertreatment, polymerization initiators, pesticides,pharmaceuticals, photographic chemicals, anddyes.

A century after its discovery, hydrazine isstill difficult to synthesize, mainly for thermo-dynamic reasons. Most hydrazine is producedby variations of the Raschig process, the oxi-dation of ammonia by hypochlorite. However,the new plants built since 1980 are based on thePCUK process, which uses hydrogen peroxideas oxidant.

Most hydrazine is sold as an aqueous solu-tion of up to 64% concentration, correspondingto hydrazine hydrate [7803-57-8], N2H4 · H2O.

2. Physical Properties

Hydrazine is a colorless liquid with an ammoni-acal odor. It is miscible with water in all propor-

tions, and its aqueous solutions are highly alka-line. Some physical properties of hydrazine andits aqueous solutions are listed in Table 1. Cer-tain physical properties of the aqueous solutions,e.g., viscosity and density, display a maximumvalue at the 64% composition (correspondingto the monohydrate), suggesting that the hy-drate, N2H4 · H2O, exists in both the solid andthe liquid phase (Figure 1). Hydrazine forms anazeotrope (bp 120.5 ◦C) with water, containing58.5mol% hydrazine.

Figure 1. Freezing point of aqueous hydrazine solutionsa) Monohydrate, NH2NH2 · H2O

2 Hydrazine

Table 1. Physical properties of hydrazine and its aqueous solutions

Property Hydrazine concentration, wt%

100 64 51.2 35.2 22.4 15.4

fp, ◦C 2.0 −51.7 −59.8 −64.6 −26 −14bp (101.3 kPa), ◦C 113.5 120.5 117.2 108 107 103� (25 ◦C), g/mL 1.0045 1.0320 1.0281 1.0209 1.0132 1.0083n25D 1.4644 1.4284 1.4120 1.3888 1.3690 1.3575Viscosity (20 ◦C),µPa · s 0.974 1.50 1.44 1.10 1.08 1.04

pH 12.75 12.10 10.5surface tension(25 ◦C), mN/m 66.7 74.0

dielectric constant(25 ◦C) 51.7

Some thermodynamic properties of anhy-drous hydrazine are listed in Table 2 [16–20].

Table 2. Thermodynamic properties of hydrazine [16–20]

Property Value

Critical constantsPc, MPa 14.69Tc,

◦C 380dc, g/mL 0.231

Heat of vaporization, kJ/mol 45.27Heat of fusion, kJ/mol 12.66Heat capacity (25 ◦C), Jmol−1 K−1 98.87Heat of combustion, kJ/mol −622.1Heat of formation, kJ/mol 50.63Free energy of formation, kJ/mol 149.2Entropy of formation, Jmol−1 K−1 121Flash point (COC),∗ ◦C 52

∗ Cleveland open cup.

Hydrazine is an endothermic compound witha heat of formation of + 50.6 kJ/mol. The ex-plosion limits in air are 4.7 – 100%. The uppervalue indicates that anhydrous hydrazine is self-explosive. Dilution with an inert gas such as ni-trogen or water significantly reduces the flam-mable domain by raising the lower explosionlimit [21]. Hydrazine hydrate (30.9 vol% hy-drazine) can therefore be handled without dan-ger at atmospheric pressure at 120 ◦C in the ab-sence of air.

3. Chemical Properties

The chemical properties of hydrazine arestrongly influenced by the following character-istics: the compound is endothermic, a base, anda reducing agent.

Thermal Decomposition. A relatively hightemperature (250 ◦C) is required, in the absenceof catalysts, for significant decomposition to oc-cur [17,22]:

The decomposition temperature is loweredby several catalysts (e.g., copper, cobalt, molyb-denum, and their oxides) [17]. Hence, hydrazineshould be handled carefully.

Acid –Base Reactions. Hydrazine is a weakbase that reacts with water:

The cation N2H2+6 occurs only in strongly

acidic solutions or in the solid state [23].Hydrazine forms salts with acids [17], some

of which are explosive, e.g., the nitrate, perchlo-rate, and azide. Other salts, such as the hydro-chloride, hydrobromide, or sulfate, are commer-cially available and can be handled in the sameway as hydrazine hydrate.

Reducing Agent. Hydrazine is a strong re-ducing agent which reacts exothermically withoxygen:

Many of the uses of hydrazine are based onthis reaction (see Chap. 9). Several metals cat-alyze the oxidation of hydrazine by air in alka-line solution. For this reason, copper and poly-

Hydrazine 3

valent metals or their salts must be absent ordeactivated when hydrazine solutions are dis-tilled [24,25]. The oxides of cadmium, magne-sium, zinc, and aluminumstabilize hydrazine so-lutions against aerial oxidation [26,27].

In acid solution hydrazine reacts with halo-gens [28,29]:

These reactions are used to determine N2H4(with iodine), to purify crude hydrogen halides,and to remove traces of halogens in wastewater.Traces of hydrazinemaybe removedby the sameprocedure. For waste or spills it is more conve-nient to use sodium hypochlorite:

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

Various metal ions or oxides, such as thoseof copper, silver, gold, mercury, nickel, and plat-inum, can also be reduced to pulverulent metalsby hydrazine [30,31].

Ketones and aldehydes are reduced by hy-drazine (the Wolff –Kishner reaction) [32]:

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

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

and hydrogenates residual double bonds inacrylonitrile – butadiene rubber [34].

Diamine Reactions. Hydrazine is widelyused in the synthesis and production of numer-ous open-chain and heterocyclic nitrogen com-pounds, including hydrazo and azo compounds,pyrazoles, triazoles, urazoles, tetrazoles, pyri-dazines, and triazines [31].

4. Production

Availability of raw materials and productioncosts rule out most of the possible routes to hy-drazine; nitrogen and ammonia are the only ob-vious starting materials for a reasonably directprocess.

Consideration of the variation of standardfree energy∆F ◦(g) (298K) for the gaseous sys-temH2–N2–NH3–N2H4 (Fig. 2, see next page)indicates that the direct synthesis of hydrazinefrom nitrogen and hydrogen is energetically un-favorable. The free energyof formation is clearlymuch more favorable for production of ammo-nia.

Figure 2. Variation of standard free energy (298K) in thegaseous system H2 –N2 –NH3 –N2H4

4 Hydrazine

The search for selective reduction of nitro-gen has not yet found a practical or economicsolution. Therefore, ammonia remains the onlyvaluable nitrogen starting material for produc-tion of hydrazine.

Coupling of two molecules of NH3 with co-production of hydrogen also appears, on pa-per, to be an attractive process. Such a reac-tion is, however, endothermic and highly ineffi-cient. For example, decomposition of ammoniaby an electric discharge, photolysis, or radiolysisgives only low yields of hydrazine. An alterna-tive method is to oxidize the hydrogen atomsremoved from the ammonia:

Only three oxidants are relevant to an indus-trial process: chlorine, oxygen, and hydrogenperoxide.

A further difficulty is that hydrazine, which isa much more powerful reducing agent than am-monia, may also react with the oxidizing agent.

Chlorine has been widely used in theRaschigprocess, which is still operated. To avoid furtheroxidation of hydrazine by chlorine, very diluteconditions have to be employed. Yields are nohigher than 60%.

The use of air or oxygen as a clean oxidiz-ing agent is hardly feasible. This process, disco-vered in the 1950s by Meyer et al. [35] and laterstudied extensively by Hayashi [39] can only beapplied to a few aromatic imines that lead to aro-matic azines, from which hydrazine can only beobtained as the sulfate:

The only modern method consists of obtain-ing hydrazine as a derivative from which it maybe easily and efficiently released. Azines of lowmolecular mass are suitable for such a purpose[17,31]:

The azines of acetone and methyl ethyl ke-tone are easily hydrolyzed under pressure form-ing hydrazine and regenerating the ketone [36–

38]. Bayer has considerably improved yields byintroducing acetone into the Raschig process.

In the 1970s, PCUK, (now Atochem) devel-oped a new, efficient, and clean process based onthe oxidation of ammonia by hydrogen perox-ide in the presence of a ketone. Most hydrazineis now produced by the ketazine process, withoxidation of ammonia by chlorine or hydrogenperoxide.

4.1. Raschig Process

In theRaschig process [14,40–42] sodiumhypo-chlorite (obtained by reaction of chlorine withsodium hydroxide) is used to oxidize ammonia.

Two steps are involved in the oxidation(Fig. 3). In the first, carried out at ca. 5 ◦C, chlo-ramine [10599-90-3] is formed by a fast reac-tion:

Figure 3. Raschig process for the production of hydrazinea) Chloramine reactor; b), c) Hydrazine reactors; d) Ammo-nia evaporator; e) Hydrazine – sodium chloride separator;f) Hydrazine hydrate concentrator

The reaction mixture is then mixed with alarge molar excess of ammonia (40 : 1) and theslow reaction leading to hydrazine is carried outat 130 – 150 ◦C and 3.0MPa:

The kinetics and mechanism [43–46] and theinfluence of various parameters such as temper-ature, pressure, concentration, and molar ratioshave been examined [31].

Themost important side reactions are the fol-lowing:

Hydrazine 5

At the outlet of the reactor, the reaction liquorcontains 1% hydrazine hydrate and ca. 4%sodium chloride; the pressure is reduced to at-mospheric in a battery of evaporators. Ammoniais condensed, concentrated, and recycled. Theliquor from the bottom of the stripping columnsis freed from salt in a conventional forced –circulation salting evaporator. The distillate isthen concentrated to 100% hydrazine hydrate.

For such a process, dilute solutions and a veryhigh ammonia/hypochlorite ratio are essential inorder to obtain reasonable yields. Evaporationcosts are therefore high even when steam sav-ings are realized.

4.2. Olin Raschig Process

In the Olin Raschig process (Fig. 4), which isused by Olin to produce anhydrous hydrazinefor aerospace applications, the production ofsodium hypochlorite is carefully controlled. Alow temperature is used to prevent decomposi-tion and chlorate formation, and the excess ofsodium hydroxide is kept at a low level.

The sodium hypochlorite solution is mixedwith a threefold excess of ammonia at 5 ◦C toform chloramine, which is then rapidly addedto a 30-fold molar excess of anhydrous ammo-nia under pressure (20 – 30MPa) and heated to130 ◦C [47–49].

The reaction liquor, containing 1 – 2% hy-drazine hydrate, is treated as in the conventionalRaschig process to give hydrazine hydrate. An-hydrous hydrazine is obtained by removing thewater by azeotropic distillation with aniline ina column at atmospheric pressure. Condensa-tion of the vapor yields a two-layer distillate;the aqueous phase is removed and the anilinephase refluxed to the top of the column. Anhy-drous hydrazine is recovered as a mixture withaniline, fromwhich it is separated by distillation[50].

4.3. Urea Process

Urea may be used as a source of ammonia in theRaschig process [51,52]. Although not currentlyused for the production of commercial hydrazinehydrate, this process has been operated commer-cially and it is described in [53]. Compared withthe standard Raschig process, it was the mosteconomical method for low production levels,but with the rapid growth in plant size it becameobsolete.

However, since 1990, large quantities of hy-drazodicarbonamide are produced in Asia, byusing the crude reaction mixture of urea andsodium hypochlorite as the source of hydrazine(see page 10). Because this process involves ex-tensive formation of byproducts and expensiveeffluent treatment, it is likely to become obso-lete.

Figure 4. Olin Raschig processa) Chloramine reactor; b), c) Hydrazine reactors; d) Ammonia evaporator; e) Hydrazine – sodium chloride separator; f) Hy-drazine hydrate concentration; g) Hydrazine hydrate storage; h) Hydrazine hydrate dehydration; i) Aniline –water decantation;j) Anhydrous hydrazine distillation; k) Aniline storage

6 Hydrazine

4.4. Bayer Ketazine Process

The Bayer process (Fig. 5) is a variation of theRaschig process and is based on the reactionof chloramine with ammonia in the presence ofacetone at pH 12 – 14 [54,55]:

Sodium hypochlorite, acetone, and a 20%aqueous solution of ammonia (molar ratio1: 2: 20, respectively) are fed simultaneouslyand continuously into a reactor at ca. 35 ◦C and200 kPa. Excess ammonia is removed from thereaction mixture by stripping, quenched withwater, and recycled to the reactor as an aqueoussolution. The aqueous dimethyl ketazine solu-tion, freed from ammonia but containing uncon-verted acetone, sodiumchloride, and organic im-purities, is fed into a distillation column wherethe dimethyl ketazine is recovered as an aqueousazeotrope (containing 55% dimethyl ketazine;

bp 95 ◦C at 101.3 kPa) at atmospheric pressure.The injection of acetone into the distillation col-umn is claimed to prevent premature hydrolysisof the ketazine. The byproduct from the still is asolution of sodium chloride containing traces ofhydrazine and organic compounds. The solutionmust be treated before disposal or recycling toelectrolysis.

The dimethyl ketazine is then hydrolyzedin a distillation column under pressure (0.8 –1.2MPa), giving acetone, which is recycled tothe reactor, and a 10% aqueous solution of hy-drazine. The latter is then concentrated to a hy-drazine content of 64%.

4.5. Fisons Process

This process, originally operated by Whiffenand Sons, was developed by Fisons and wenton stream in the 1960s. It used methyl ethyl ke-tone instead of acetone to trap the hydrazine; thehydrolysis was carried out with sulfuric acid.

This process is no longer operated.

Figure 5. Bayer hydrazine processa) Azine reactor; b) Ammonia stripping; c) Ammonia quenching; d) Azine distillation; e) Azine hydrolysis; f) Hydrazinehydrate concentration

Hydrazine 7

4.6. Peroxide Process

The most recent hydrazine process, invented byPCUK, is operated by ATOFINA in France andby Mitsubishi Gas in Japan. Hydrogen peroxideis the oxidizing agent. The reaction is carried outin the presence of methyl ethyl ketone (MEK)at atmospheric pressure and 50 ◦C. The ratio ofH2O2:MEK:NH3 used is 1: 2: 4.

The hydrogen peroxide is activated by acet-amide [60-35-5] and disodium hydrogen phos-phate [7558-79-4] (ATOFINA) or by an arseniccompound (Mitsubishi Gas) [56]. The overallreaction results in formation of methyl ethyl ke-tazine [5921-54-0] in high yield [57] (Fig. 6):

Figure 6. Peroxide processa) Azine reactor; b) Phase separator; c) Aqueous phase con-centration; d) Azine purification; e) Azine hydrolysis; f) Hy-drazine hydrate concentration

Themechanism requires the activation of am-monia and hydrogen peroxide as these two re-actants, unlike ammonia and hypochlorite in theBayer process, do not react together [58–62].The reaction pathway involves the formation ofan oxaziridine intermediate that is able to oxi-dize ammonia to a hydrazine derivative.

Since methyl ethyl ketazine is insoluble inthe reaction mixture, it is easily separated bydecantation; it is then purified by distillation.The purified ketazine is hydrolyzed under pres-sure (0.8 – 10MPa) to give concentrated aque-ous hydrazine andoverheadmethyl ethyl ketone,which is recycled [37].

The aqueous layer containing the activator isconcentrated to remove water and recycled tothe reactors after a purge of water-soluble impu-rities.

The peroxide process has many advantagescompared with other processes: no salt byprod-uct, high yields, low energy consumption, lowmolar excess, no aqueous effluent treatment[63].

5. Environmental Protection

Hydrazine has a noxious effect on bacteria, al-gae, and aquatic wildlife; therefore, emission ofhydrazine-containing wastewater is not permit-ted.

Wastewater and spills that contain hydrazinemust be collected, analyzed, and treated (e.g.,by oxidation with NaClO or H2O2). The am-monia content should also be examined becausehydrazine may also decompose into ammonia.

6. Quality Specifications

Hydrazine is commercially available as anhy-drous hydrazine, as an aqueous solution, and assolid dihydrazinium sulfate. Some typical speci-fications are summarized in Tables 3 and 4 (bothsee next page).

8 Hydrazine

Table 3. Specifications of anhydrous hydrazine (monopropellantgrade)

Component Specification

Hydrazine, wt% ≥98.5Water, wt% ≤1.0Chloride, ppm ≤5.0Iron, ppm 4Aniline, wt% ≤0.5Nonvolatile residue, wt% ≤0.005Carbon dioxide, wt% ≤0.003Carbon volatile, wt% ≤0.02Density (25 ◦C), g/mL 1.008 – 1.002

Table 4. Specifications of hydrazine hydrate

Component Specification

Hydrazine hydrate, wt% >100±0.5Hydrazine, wt% >64±0.4Ammonia, wt% <0.1Chloride, ppm <1Iron, ppm <1Nonvolatile residue, ppm <20

Although most hydrazine hydrate is manu-factured by the ketazine process, there are nospecifications relating to organic impurities.

7. Analysis

Analytical determination of hydrazine in solu-tions or mixtures is based on its properties as aweak base and strong reducing agent, and on theformation of highly colored derivatives.

A large number of methods have been de-scribed for hydrazine derivatives [64]; in thischapter, only analytical methods for hydrazineand hydrazine hydrate will be discussed.

Hydrazine is aweak base (pKb = 6.07) and, inthe absence of other bases, can be easily titratedwith acid with methyl purple as the indicator. Inthe absence of other reducing agents, hydrazinecan be determined quantitatively by oxidation,most commonly with iodine [65]:

To obtain a stable end point, the pH mustbe maintained near neutrality, usually by addingsolid sodium bicarbonate or ammonium acetateas a buffer. Starch is used as an indicator.

Traces of hydrazine (as low as 1 ppb) can bedetected with an iodide-selective electrode [66].

Dilute solutions of hydrazine can be de-termined by colorimetry. The best method

(ASTMD1385 – 78) involves converting thehydrazine into highly colored azines, such asthose of aromatic aldehydes; p-dimethylami-nobenzaldehyde is particularly suitable for thispurpose.

8. Handling, Storage, andTransportation

Hydrazine is volatile and toxic (see Chap. 12)and must be handled with care. Observation ofelementary safety rules allows hydrazine to beused with little risk. In the absence of decom-position catalysts, anhydrous hydrazine may beheated up to 250 ◦Cwithout appreciable decom-position. Aqueous and anhydrous hydrazine canbe stored for long periods without problems;clean storage vessels of suitable material are re-quired, together with an inert gas blanket, e.g.,nitrogen.

Hydrazine vapors do, however, present haz-ards in gas mixtures, as shown in Table 5. Work-ing in the vapor phase requires operation belowthe lower explosion limit.

Table 5. Lower explosion limits of gaseous hydrazine mixtures

Gas mixture Hydra- Temper- Pressure,zine, % ature, ◦C kPa

Hydrazine 100 30 2Hydrazine – air 54.7 95 100Hydrazine – nitrogen 38 110 100Hydrazine –water 38 100 30

Hydrazine can be stored in drums of 304stainless steel at room temperature, but stain-less steel 316 must be avoided because of itshigh content of molybdenum, which is an ef-ficient catalyst for the decomposition of hy-drazine. Cold-rolled steel is satisfactory forhydrazine concentrations below 10%. Othermaterials convenient for storage of anhy-drous hydrazine include aluminum, tantalum,and titanium. Polytetrafluoroethylene, polyeth-ylene, and polypropylene are also suitable, butpoly(vinyl chloride) is not recommended.

Hydrazine must generally be stored underconditions that preclude oxidants. Anhydroushydrazine may cause ignition of wood, rags, pa-per, or other common organicmaterial. Fires canbe extinguished easily, however, as hydrazine iscompletely miscible with water. Contact with

Hydrazine 9

carbon dioxide must also be prevented, as thisgas reacts readily to give a hydrazinium carbazicacid salt, which is quite unstable. Storage in di-rect sunlight should also be avoided.

Hydrazine is easily adsorbed orally, percu-taneously, and by inhalation. Proper protec-tion must be provided. This includes well-airedpremises, gloves, glasses, appropriate masks,and boots. Skin or eye contact must be treated bywashing copiously with water; a physician mustbe consulted. Premises where hydrazine is han-dled must be equipped with continuously oper-ated analytical devices to ensure that the concen-tration in air does not exceed 0.1 ppm in Europeand 0.01 ppm in the United States.

Anhydrous hydrazine and its aqueous solu-tions are subject to national and internationalregulations relating to the transportation of haz-ardous materials, e.g., for transportation by rail(RID) and by road (ADR) in Europe, and the in-ternational regulations for transportation by sea(IMCO code) and air (IATA).

Anhydrous hydrazine (UN no. 2029) and hy-drazine hydrate (UN no. 2030) aree classified(Class 8) as flammable liquids and poisous. Di-lute aqueous solutions of hydrazine hydrate be-long only to the Class 6 but are still consideredas corrosive and toxic.

9. Uses

Most hydrazine is sold as an aqueous solution.The only outlet for anhydrous hydrazine is as

a rocket fuel or as a mono- or bipropellant forsatellites and spacecraft.

About 80 – 90% of hydrazine production isconverted into organic derivatives. All other ap-plications are based on its use as a reducingagent, as an energy-rich compound, or on its hy-drogen storage capacity.

The most important uses of hydrazine andits derivatives are as polymerization initiatorsand blowing agents for foamed plastics, and forthe production of pesticides. Other uses include:synthetic building block, pharmaceuticals, pro-pellants, and airbags for cars.

Blowing Agents. Many hydrazine-basedblowing agents are produced industrially; worldhydrazine hydrate consumption in 1998 for thisapplication amounted to 50 000 t/a. They are allhydrazoor azoderivatives; the latter are obtainedby oxidation of the former with chlorine or hy-drogen peroxide. Blowing agents decompose onheating into nitrogen andmixtures of other gasesthereby producing a foaming action in polymersto form pores or cells (→ Foamed Plastics).Some commercially produced hydrazine-basedblowing agents are listed in Table 6.

The decomposition temperature of blowingagents depends on the particle size, the pH, andthe presence of salts of barium, cadmium, orzinc, which act as activating agents.

One of the earliest commercial blowingagents was azobis(isobutyronitrile) (AIBN),which is used as a porophore for sponge rub-ber products and PVC foams. It is also em-

Table 6. Some hydrazine-based blowing agents

Compound CAS registry number Structure Decompositiontemperature in air,◦C

Gas yield, mL/g

Azobis(isobutyronitrile) [78-67-1] 115 130

Azodicarbonamide [123-77-3] 195 – 200 220Benzenesulfonylhydrazide [80-17-1] C6H5SO2NHNH2 95 1304-Methylbenzenesulfo-nylhydrazide

[1576-35-8] p-CH3C6H4SO2NHNH2 103 120

4,4′-Oxybis(benzenesulfo-nylhydrazide)

[80-51-3] O<-- (>C6H4SO2NHNH2)2 150 125

10 Hydrazine

ployed as a free radical source in the initiation ofpolymerization. Azobis(isobutyronitrile) is pro-duced from acetone cyanohydrin [75-86-5] andhydrazine:

Oxidation to the azo compound is effectedwith chlorine [67,68]:

Azodicarbonamide is readily produced fromurea and hydrazine:

The intermediate hydrazodicarbonamide,which can also be produced directly in situ fromurea and sodium hypochlorite [69], is oxidizedeither by chlorine or hydrogen peroxide in thepresence of a catalytic amount of bromide ionsin a strongly acidic medium:

Azodicarbonamide is, in terms of produc-tion volume, the most important blowing agent.Its success is due to the large volume of gasevolved (220mL/g at STP). Decomposition at190 ◦C yields mainly nitrogen (60 vol%) andcarbon monoxide (35 vol%), as well as smallamounts of ammonia and carbon dioxide. Thesolid residues are colorless, odorless, nonstain-ing, and do not support combustion.

The need for blowing agents with a higherdecomposition temperature for the manufactureof new rubber or porous plastic materials ledto the appearance of sulfonic acid hydrazidesin the 1950s. In contrast to the inorganic blow-ing agents previously used (e.g., ammonium ni-trite, ammonium bicarbonate, sodium bicarbon-ate) these sulfonic acid hydrazides are more eas-

ily dispersed, can be safely handled at a highertemperature, and give improved foam cell struc-ture. They are also colorless, odorless, nonstain-ing, and the decomposition products are safe.The following explanation of decomposition hasbeen proposed:

The sulfonic acidmono- and dihydrazides areproduced from hydrazine hydrate and the appro-priate sulfonic acid chloride:

The handling and technology of blowingagents have been reviewed [70,71].

Air-Bags. Sodium azide [26628-22-8] iswidely used as gas precursor in air-bag tech-nology. One of the industrial processes for itsmanufacture starts from hydrazine and an alkylnitrite [72].

N2H4 +C4H9–ONO+NaOH −→ NaN3 +C4H9OH+2H2O

An other hydrazine derivative is under de-velopment for the same application: 5-ami-notetrazole [4418-61-5] obtained from ami-noguanidine salts [73].

Free-Radical Polymerization Initiators.Azo compounds are widely used as free radicalpolymerization initiators. The most important(Table 7) are symmetrical azodinitriles whichare synthetized from hydrazine, a ketone andHCN

Hydrazine 11

Table 7. Some azo polymerization initiators

Compound CAS registry no. Structure mp ◦C 10-h half-lifedecompositiontemperature intoluene, ◦C

2,2′-azobisisobutyronitrile [78-67-1] R=R′=CH3 ca. 100 652,2′-azobis(2-methylbutyronitrile) [13472-08-7] R=CH3,R

′=C2H5 ca. 50 672,2′-azobis(2,4-dimethylvaleronitrile) [4419-11-8] R=CH3,R

′=CH2–CH–(CH3)2 45 – 70 51

The hydrazo derivative is oxidized by chlo-rine or hydrogen peroxide in the presence of abromide as catalyst:

Water-soluble compounds like 2,2′-azobis(2-aminopropane) dihydrochloride [2997-92-4] aswell as liquid azo compounds like diethyl 2,2′-azobisisobutyrate [3879-07-0], are under devel-opment.

Pesticides. Hydrazine-based pesticides re-present the second major outlet for consump-tion of hydrazine. Maleic hydrazide was the firstsuch pesticide used. It is produced by reactionof maleic anhydride with hydrazine:

3-Amino-1,2,4-triazole, obtained fromcyanamide, hydrazine hydrate, and formic acid,is another general purpose herbicide:

This compound is used as a selective herbi-cide in vineyards and orchards; consumption isnow several thousand tons per year.

Hundreds of patents have been filed forpesticide applications of hydrazine-based com-pounds; about fifty compounds are producedcommercially [74], mostly heterocyclic com-pounds such as triazines, oxadiazoles, pyrazoles,pyridazines, thiadiazoles. Some representativeexamples are listed in Table 8.

During the period 1970 – 1980, triazines be-came important, examples being metribuzin andmetamitron (seeTable 8).Anew family of fungi-cides based on the triazole ring is now being de-veloped.

Information concerning structures, produc-tion, and use of these pesticides is compiled in[75–78].

Pharmaceuticals. Although representingonly a small percentage of the total produc-tion, consumption of hydrazine in pharmaceu-ticals is very important. For example, isoniazid[54-85-3], the hydrazide of isonicotinic acid,was first used in the 1950s against tuberculosis.

In the 1980s and 1990s, other hydrazine-based pharmaceuticals were introduced, manyof these containing the 1,2,4-triazole group.They have been used as antidepressants, anti-hypertensives, and as antibacterial or antifungalagents.

More recently, new pharmaceuticals, con-taining the 4-amino-1,2,4-triazole group andshowing better efficiency [80,81] (Table 9), havebeen developed.

Water Treatment. Sodium sulfite has longbeen used for scavenging oxygen dissolved inwater in order to avoid corrosion in boilers orhot water heating systems:

At higher temperatures, sodium sulfite maydecompose to corrosive sulfide products. It canalso formdeposits,which affect heat transfer andmay even cause pipes to rupture.

Hydrazine is used in water treatment for cor-rosion protection of steel in boilers. The onlyreaction products are nitrogen and water:

12 Hydrazine

Table 8. Some important hydrazine-based pesticides

Compound CAS registry no. Structure Producer Use

Triazoles

3-Amino-1,2,4-triazole [61-82-5] Atochem herbicide

Triadimefon [4321-43-3] Bayer fungicide

Propiconazole [60207-90-1] Novartis fungicide

Diclobutrazole [75736-33-3] Zeneca fungicide

Paclobutrazol [76738-62-0] Zeneca plantgrowthregulator

Triazines

Metribuzin [21087-64-9] Bayer herbicide

Metamitron [41394-05-2] Bayer herbicidePyrazole

Metazachlor [67129-08-2] BASF herbicidePyridazine

Maleic hydrazide [123-33-1] Uniroyal plantgrowthregulator

Hydrazine 13

Table 9. Some important hydrazine-based pharmaceuticals

Compound CAS registry no. Structure Producer Use

Fluconazole [86386-73-4] Pfizer antifungal

Anastrozole [120511-73-1] Zeneca anticancer

Rizatriptan [144034-80-0] Merck antimigraine

Cefazolin [25953-19-9] Smith Kline antibacterial

Isoniazid [54-85-3] Pfizer tuberculostat

Moreover hydrazine reacts with iron(III) ox-ide to form magnetite, which protects the metalsurface against corrosion by water and oxygen[82–84]:

Full corrosion protection is afforded byresidual hydrazine concentrations lower than0.1 ppm. Catalyzed hydrazine hydrate formula-tions ( activated hydrazine) are commerciallyavailable and are efficient even at room temper-ature.

Propellants. The first large-scale use of hy-drazine was as a rocket fuel. Anhydrous hy-drazine is an excellent propellant; only hydrogenhas a greater specific impulse, i.e., kilograms ofthrust developed per kilogram of fuel consumedper second. Rocket propellants now in useinclude anhydrous hydrazine, monomethylhy-drazine and unsymmetrical dimethylhydrazine(see Chap. 10). They are used mainly as bipro-pellant fuels in rockets such as Titan or Ariane.

Anhydrous hydrazine is also used as a mono-propellant for satellites and spacecraft [85]. Thehydrazine decomposes in a complex reactionover a catalyst to give a mixture of gases:

Typical catalysts are manufactured by ShellChemical and Rocket Research. They are of-ten based on iridium or ruthenium, depositedon alumina. Catalysts are described as sponta-neous (working at room temperature) or non-spontaneous (working above 100 ◦C) [86].

A review on space applications and potentialrocket propulsion systems has been published[87].

Fuel Cells. Fuel cells based on oxidation ofhydrazine either with oxygen or hydrogen per-oxide have been extensively studied. Their useis restricted to military applications because ofthe cost of hydrazine hydrate.

14 Hydrazine

10. Derivatives

Alkylhydrazines. Monomethylhydrazine[60-34-4] MMH, and unsymmetrical di-methylhydrazine, [57-14-7], UDMH, are themost important derivatives; their major use isrocket fuels.

Monomethylhydrazine is produced commer-cially in the Raschig process by reaction of chlo-ramine with methylamine:

whereas UDMH is now produced either bythe chloramine route:

or by the reductive catalytic alkylation ofacetic hydrazide [1068-57-1] with formalde-hyde and hydrogen:

The preparation and properties ofalkylhydrazines have been reviewed [88,89]. Hydroxyethylhydrazine [109-84-2],HOCH2CH2NHNH2 is obtained by reactionof hydrazine hydrate with ethylene oxide [90]:

tert-Butylhydrazine hydrochloride[7400-27-3] is used in the synthesis of pesti-cides.

Arylhydrazines. Aromatic hydrazines arenot produced from hydrazine, except for 2,4-dinitrophenylhydrazine, which is obtained byreaction of 2,4-dinitrochlorobenzene with hy-drazine hydrate. It is used as an analyticalreagent for the determination of carbonyl com-pounds.

Phenyl hydrazines are obtained by diazotiza-tion of the corresponding anilines and reductionof the diazonium salts:

Characteristics of some of these compoundsare listed in Table 10 [91,92].

Table 10. Some aromatic hydrazines

Hydrazine CAS registry mp, Appear-no. ◦C ance

Phenylhydrazine [100-63-0] 19.6 colorless

crystals4-Tolylhydrazine [539-44-6] 61 colorless

crystals3-Nitrophenyl-hydrazine [619-27-2] 153 yellow

crystals2,4-Dinitrophenyl-hydrazine [119-26-6] 200 red

crystalsN,N′-Diphenyl-hydrazine [122-66-7] 128 colorless

crystals

Hydrazides. Some common hydrazides arelisted in Table 11.

Table 11. Some hydrazides

Hydrazide CAS Structure Mr mp, ◦Cregistry number

Formic hydrazide [624-84-0] HCONHNH2 60.06 54Acetic hydrazide [1068-57-1] CH3CONHNH2 74.08 67Propionic hydrazide [5818-15-5] C2H5CONHNH2 88.12 40Oxalic dihydrazide [996-98-5] (H2NNHCO)2 118.10 240∗Semicarbazide [57-56-7] H2NCONHNH2 75.07 96Thiosemicarbazide [79-19-6] H2NCSNHNH2 91.14 180Carbohydrazide [497-18-7] H2NNHCONHNH2 90.09 157Thiocarbohydrazide [2231-57-4] H2NNHCSNHNH2 106.15 171∗Benzenesulfonylhydrazide [80-17-1] C6H5SO2NHNH2 172.21 103Adipicdihydrazide [1071-93-8] H2N–NH–CO–(CH2)4CONH–NH2 174 18

∗ Decomposes

Hydrazine 15

Carboxylic acid hydrazides are generally pre-pared by reactions of hydrazine hydrate with thecorresponding methyl or ethyl ester:

Diacids can lead to polyhydrazides whichdehydrate on heating to give polyoxadiazoles,which exhibit high thermal stability. Hydrazinecarboxamide and carbohydrazide are producedfrom hydrazine hydrate and urea, depending onthe excess of urea used:

Hydrazine carbothioamide ( thiosemicar-bazide) is made from CS2 and hydrazine, andthiocarbohydrazide from CS2, ammonia, andhydrazine [93–95].

Heterocycles. A few simple heterocycles areused as synthetic building blocks [96]. The mostimportant heterocycle industrially is 1,2,4-tri-azole, which is produced from hydrazine andformamide [97,98].

1,2,4-Triazole is a white solid, mp 120 ◦C. Itis a valuable building block in the production ofmany fungicides.

Miscellaneous Derivatives. Different typesof derivatives have found application in variousindustrial fields. For example, in photography,heterocycles such as triazoles, tetrazoles, 2,5-dimercapto-1,3,4-thiadiazole are used as stabi-lizers, fog inhibitors, or sensitizers.

A number of hydrazine derivatives are usefulexplosives, including the simple salts such as thenitrate [37836-27-4], perchlorate [13762-80-6],azide [14662-04-5], and aminoguanidine deriva-tives [85].

Aminoguanidine bicarbonate [2582-30-1],manufactured industrially from cyanamide[420-04-2] hydrazine, and carbon dioxide [99],is now largely used for the synthesis of variousheterocycles useful in the production of pharma-ceuticals, agrochemicals, and lube oil additives.

11. Economic Aspects

Considerable growth in hydrazine productioncapacity took place during the period 1960 –2000 (Fig. 7). Estimated capacities for majorproducers, together with the production processused, are listed in Table 12. Total capacity (west-ern world, 2000) is ca. 90 000 t of hydrazine hy-drate. However, to be accurate, one must add to

Figure 7. Installed hydrazine capacity for various countriesUK, United Kingdom; US, United States; J, Japan; F, France; G, Germany; C, China; R, Russia; K, Korea

16 Hydrazine

this capacity, the captive production of crude hy-drazine hydrate (30 000 t/a) associated with thedirect azodicarbonamide manufacture in Asia.Thus the total world capacity of hydrazine hy-drate is ca. 120 000 t/a. Approximate consump-tion of hydrazine according to application isshown in Figure 8.

Table 12. Producers of hydrazine hydrate, estimated capacities,and process used (1998)

Country Producer Capacity,103 t

Process

United States Arch 5 Raschig15 Ketazine-Raschig

Bayer US 12 Ketazine-RaschigFederalRepublic ofGermany

Bayer 12 Ketazine-Raschig

France ATOFINA 15 PeroxideJapan Nippon Carbide 3 Raschig

Otsuka 4 RaschigMiGas 9 Peroxide

Korea Otsuka 8 RaschigChina Various 6 RaschigRussia Kuybichev 4 Raschig

Figure 8. Hydrazine consumption

12. Toxicology and OccupationalHealth

Hydrazine is highly toxic, even in dilute solu-tion, and must be handled with care. No anti-dote to hydrazine is known; appropriate treat-ment must be based on the symptoms observed.

Contact of the liquid with the skin and theeyes should be avoided. Irritation, damage dueto alkalinity, dermatitis, or allergy may result.Inhalation may cause irritation or damage to the

nose, throat, and lungs. Ingestion may induceconvulsions and depression of the central ner-vous system. Repeated exposure to hydrazinemay result in damage to the lungs, liver, or kid-neys.

The acute and chronic toxicity of hydrazineand its derivatives have been examined in detail;reviews are available [100–103].

The results of experiments on animals arelisted in Table 13. Long-term studies with labo-ratory animals indicate that hydrazine is muta-genic and carcinogenic; this has not, however,been demonstrated for humans.

Table 13. Acute toxicity of hydrazine

Animal Nature LD50, mg/kg

Mouse intravenous 58oral 58

Rat intravenous 55oral 60

Guinea pig cutaneous 190Rabbit intravenous 25Monkey intraperitoneal 20

The threshold limit value (TLV) has beenfixed at 0.1 ppm (0.13mg/mm3). The olfactorydetection limit is between 3 and 5 ppm.

13. References

General References1. L. F. Audrieth and B.A. Ogg: The Chemistry

of Hydrazine, Wiley, New York 1951.2. C. C. Clark: Hydrazine, Mathieson Chemical

Corp., Baltimore, MD 1953.3. R. A. Reed, Hydrazine and its Derivatives,

Lectures, Monographs and Reports, no. 5, TheRoyal Institute of Chemistry, London 1957,1 – 49.

4. E.W. Schmidt: Hydrazine and its Derivatives,J. Wiley Sons, New York 1984.

5. Houben-Weyl, X/2, 71 – 122.6. Kirk-Othmer, 13, 560 – 606.7. Ullmann, 5th ed. 13, 177 – 191.8. R. Powell: “Hydrazine Manufacturing

Processes,” Chem. Process. Review no. 28,Noyes Development (1968).

9. Gmelin, System no. 4, “Stickstoff,” 307 – 320.10. S. Pataı: The Chemistry of the Hydrazo, Azo,

and Azoxy Groups, Wiley-Interscience, NewYork 1975.

11. Beilstein, 4, 546; 4 (1), 650; 4 (2), 957; 3, 116;3 (1), 56; 3 (2), 95; 15, 67, 123; 15 (1), 23, 28;15 (2), 44, 52; 11, 52; 11 (2), 29.

Hydrazine 17

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589 – 594.13. Th. Curtius, Ber. Dtsch. Chem. Ges. 20 (1887)

1632.14. L. de Bruyn, Recl. Trav. Chim. Pays Bas 13

(1894) 433.15. F. Raschig, Ber. Dtsch. Chem. Ges. 40 (1907)

4587.16. C. C. Clark: Hydrazine, Mathieson Chemical

Corp., Baltimore, MD 1953.17. L. F. Audrieth, B. A. Ogg: The Chemistry of

Hydrazine, Wiley, New York 1951.18. G.H. Hudson et al.; Mellor’s Comprehensive

Treatise on Inorganic and TheoreticalChemistry, vol 8, Suppl. 2, Wiley, New York1967, pp. 69 – 113.

19. C. L. Yaws et al.: Chem. Eng. NY 81 (1974)91.

20. R.W. Gallant, Hydrocarbon Process, 48(1969) 117.

21. F. E. Scott et al.: Explosive Properties ofHydrazine, Report of Investigation 4460, U.S.Dept. of the Interior, Bureau of Mines,Pittsburgh, PA 1949.

22. M. L. Davis et al., Kinetics, Thermodynamics,Physico-Chemical Properties andManufacture of Hydrazine, Dept. of Chem.,Ohio State University, 1952.

23. H. Bock, Z. Naturforsch. B Anorg. Chem. Org.Chem. 178 (1962) 426.

24. E. J. Cuy, W.C. Bray, J. Am. Chem. Soc. 46(1924) 1786.

25. W.R. Hodgkinson, J. Soc. Chem. Ind. London33 (1914) 815.

26. Olin Mathieson Corp., GB 738 441, 1952 (F.Haller).

27. Olin Mathieson Corp., GB 778 347, 1954 (F.Haller).

28. U. Roberto, F. Roncali, Chim. Ind. (Turin) 6(1904) 93.

29. A.W. Browne, F. F. Shetterley, J. Am. Chem.Soc. 30 (1908) 60.

30. R. A. Reed, Chem. Prod. Chem. News 20(1957) 271.

31. R. A. Reed, Hydrazine and its Derivatives,Lectures, Monographs and Reports no. 5, TheRoyal Institute of Chemistry, London, 1957,1 – 49.

32. P. S. Wharton, D.H. Bohlen, J. Org. Chem. 26(1961) 3615.

33. D. Balcon, A. Furst, J. Am. Chem. Soc. 75(1953) 4334.

34. D.K. Parker et al., Rubber Chem. and Tech.65 (1992) 245.

35. Rhone-Poulenc, FR 1 162 413, 1958 (R.Meyer, D. Pillon).

36. Bayer, FR, 1 315 346, 1962 (H. Kohnen et al).37. Produits Chimiques Ugine Kuhlmann, FR,

2 323 635, 1975 (J. P. Schirmann et al.).38. Gilbert, J. Am. Chem. Soc. 51 (1929) 3394.39. H. Hayashi, Catal. Rev. Sci. Eng. 32 (1990)

229.40. F. Raschig, DE 198 307, 1907.41. F. Raschig, US 910 858, 1909.42. F. Raschig: Schwefel- und Stickstoffstudien,

Verlag Chemie, Berlin 1924.43. S. R.M. Ellis et al., Ind. Eng. Chem. Proc.

Des. Dev. 3 (1964) no. 1, 18.44. G.V. Jeffreys, J. T. Wharton, Ind. Eng. Chem.

Proc. Des. Dev. 4 (1965) no. 1, 71.45. J.W. Kahn, R. E. Powell, J. Am. Chem. Soc.

76 (1954) 2565.46. G. Yagil, M. Ambar, J. Am. Chem. Soc. 84

(1962) 1797.47. K.A. Kobe, J. J. McKetta, Adv. Pet. Chem.

Refin. 2 (1959) 531.48. Olin Mathieson Corp., US 2 715 061, 1955 (J.

Felger, B. Nicolaidsen).49. Olin Mathieson Corp., US 2 935 451, 1955 (J.

Troyan).50. Olin, USP 2 773 814, 1956 (B.H. Nicolaisen).51. P. Schestakoff, DE 164 755, 1903.52. O. Seuffert, E. Ihwe, DE 578 486, 1931.53. Ullmann, 4th ed. 13, 95 – 107.54. R. Mundil, US 3 077 383, 1963.55. R. Schliebs: “The Chemistry of the Bayer

Hydrazine Process,” 193rd ACS MeetingAbstracts, Denver, 1987.

56. Mitsubishi Gas, EP 070 155, 1982 (K.Yasuhisa).

57. Produits Chimiques Ugine Kuhlmann, US3 972 878, 1976 (J. P. Schirmann et al.).

58. Chem. Eng. News 52 (1974), no. 37, 18.59. J. P. Schirmann, S. Y. Delavarenne: Hydrogen

Peroxide in Organic Chemistry, Edisciences,Paris 1978, p. 81.

60. J. P. Schirmann, F. Weiss, Tetrahedron Lett.1972 635.

61. E. G. E. Hawkins, J. Chem. Soc. C 1969 2663.62. E. Schmitz et al., Chem. Ber. 97 (1964) 2521.63. Chem. Eng. News 59 (1981) no. 44, 32.64. H. E. Malone: The Determination of

HydrazinoHydrazide Groups, PergamonPress, London 1970.

65. I.M. Kolthoff, R. Belcher: VolumetricAnalysis, vol 3, Wiley-Interscience, New York1957.

66. R. Christova et al., Anal. Chim. Acta 85(1976) 301.

18 Hydrazine

67. Houben-Weyl, Bd XIV/1, p. 220 (1967).68. Houben-Weyl, X2, 764.69. Szeres, HU34 723, 1983 (T. Wein et al.).70. H. R. Lasman: “Blowing Agents” in

Encyclopedia of Polymer Science andTechnology, vol. 2,Wiley, NewYork 1965,pp. 532 – 565.

71. B. A. Hunter, J. Frados: Plastics EngineeringHandbook of the Society of the PlasticsIndustry, Reinhold Publ. Co., New York 1976,p. 502 – 510.

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Masha).74. H. Martin, C. R. Worthing: “Pesticide

Manual,” 5th ed., British Crop ProtectionCouncil, Nottingham 1977.

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c© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a13 193

Hydrazoic Acid and Azides 1

Hydrazoic Acid and Azides

Horst H. Jobelius, Dynamit-Nobel AG, Troisdorf, Federal Republic of Germany

Hans-Dieter Scharff, Dynamit-Nobel AG, Troisdorf, Federal Republic of Germany

1. Introduction . . . . . . . . . . . . . . . . . 12. Physical Properties of Sodium Azide . 13. Chemical Properties of Sodium Azide

and Hydrazoic Acid . . . . . . . . . . . . 14. Production . . . . . . . . . . . . . . . . . . 24.1. Sodium Azide . . . . . . . . . . . . . . . . 24.2. Hydrazoic Acid . . . . . . . . . . . . . . . 35. Quality Specifications and Analysis . 36. Storage and Transportation . . . . . . 3

7. Uses . . . . . . . . . . . . . . . . . . . . . . 37.1. Salts . . . . . . . . . . . . . . . . . . . . . . 37.2. Organic Synthesis . . . . . . . . . . . . . 48. SafetyPrecautions andEnvironmental

Protection . . . . . . . . . . . . . . . . . . 59. Economic Aspects . . . . . . . . . . . . . 510. Toxicology and Occupational Health . 511. References . . . . . . . . . . . . . . . . . . 6

1. Introduction

Hydrazoic acid itself has little industrial signifi-cance; the most important salts are sodium azideand lead azide.

The oldest process for preparing both the acidand the salts is based on diazotization of hy-drazine and its salts [1,2]. The method still mostwidely used today for production of sodiumazide is the reaction of sodium amide with dini-trogen monoxide. This process was introducedindustrially in 1924, but not patented until 1935[3].

The original use of sodium azide was the safeproduction of lead azide, a fulminating (deto-nating) agent. Lead azide now constitutes only asmall part of the total consumption of the sodiumsalt. By far themajor proportion is used in the or-ganic chemical industry. Increasing importanceis ascribed to the use as a gas generator fuel thatproduces nontoxic nitrogen.

The toxicity and the unsettled question of po-tential carcinogenicity [4] make special work-place safety measures imperative.

2. Physical Properties of SodiumAzide

Sodium azide [26628-22-8], NaN3, Mr 65.01,is a white, odorless, crystalline substance. Somephysical properties of sodium azide are as fol-lows:

mp 275 ◦C (decomp.)Density (20 ◦C) 1.846 g/cm3

Vapor pressure (20 ◦C) 1 PaSolubility in 100mL water (15 ◦C) 41.0 g

Thermal decomposition occurs at 300 ◦Cwith formation of sodium metal and nitrogen.

3. Chemical Properties of SodiumAzide and Hydrazoic Acid

Heavy-metal azides, which are sensitive to fric-tion and shock, precipitate readily from aqueoussolution.Acidification of sodiumazide producesexplosive and toxic hydrazoic acid.

Free hydrazoic acid reacts with solutionsor slurries of alkali-metal or alkaline-earth hy-droxides, carbonates, and hydrogen carbonatesto give solutions of the corresponding azides,which can be obtained in pure form by evapora-tion under vacuum.

Alkyl and acyl halides react with sodiumazide to form alkyl and acyl azides, respectively.Sodium azide is also used in the Curtius reactionfor the production of amines. (For further detailsof organic syntheses with HN3 and NaN3, seeSection 7.2.)