niosh recommends removing contaminated clothing immediately, washing skin with soap and water, and for eye exposure removing contact lenses and flushing eyes with water for at least 15 minutes. niosh also recommends anyone with potential hydrazine exposure to seek medical attention as soon as possible. there are no specific post-exposure laboratory or medical imaging recommendations, and the medical work-up may depend on the type and severity of symptoms. the world health organization (who) recommends potential exposures be treated symptomatically with special attention given to potential lung and liver damage. past cases of hydrazine exposure have documented success with pyridoxine (vitamin b6) treatment. occupational exposure limits niosh recommended exposure limit (rel): 0.03 ppm (0.04 mg/m3) 2-hour ceiling osha permissible exposure limit (pel): 1 ppm (1.3 mg/m3) 8-hour time weighted average acgih threshold limit value (tlv): 0.01 ppm (0.013 mg/m3) 8-hour time weighted average the odour threshold for hydrazine is 3.7 ppm, thus if a worker is able to smell an ammonia-like odor then they are likely over the exposure limit. however, this odor threshold varies greatly and should not be used to determine potentially hazardous exposures. for aerospace personnel, the usaf uses an emergency exposure guideline, developed by the national academy of science committee on toxicology, which is utilized for non-routine exposures of the general public and is called the short-term public emergency exposure guideline (spegl). the spegl, which does not apply to occupational exposures, is defined as the acceptable peak concentration for unpredicted, single, short-term emergency exposures of the general public and represents rare exposures in a worker's lifetime. for hydrazine the 1-hour spegl is 2 ppm, with a 24-hour spegl of 0.08 ppm. handling and medical surveillance a complete surveillance programme for hydrazine should include systematic analysis of biologic monitoring, medical screening and morbidity/mortality information. the cdc recommends surveillance summaries and education be provided for supervisors and workers. pre-placement and periodic medical screening should be conducted with specific focus on potential effects of hydrazine upon functioning of the eyes, skin, liver, kidneys, hematopoietic, nervous and respiratory systems. common controls used for hydrazine include process enclosure, local exhaust ventilation and personal protective equipment (ppe). guidelines for hydrazine ppe include non-permeable gloves and clothing, indirect-vent splash resistant goggles, face shield and in some cases a respirator. the use of respirators for the handling of hydrazine should be the last resort as a method of controlling worker exposure. in cases where respirators are needed, proper respirator selection and a complete respiratory protection program consistent with osha guidelines should be implemented. for usaf personnel, air force occupational safety and health (afosh) standard 48-8, attachment 8 reviews the considerations for occupational exposure to hydrazine in missile, aircraft and spacecraft systems. specific guidance for exposure response includes mandatory emergency shower and eyewash stations and a process for decontaminating protective clothing. the guidance also assigns responsibilities and requirements for proper ppe, employee training, medical surveillance and emergency response. usaf bases requiring the use of hydrazine generally have specific base regulations governing local requirements for safe hydrazine use and emergency response. molecular structure hydrazine, h2n−nh2, contains two amine groups nh2 connected by a single bond between the two nitrogen atoms. each n−nh2 subunit is pyramidal. the structure of the free molecules was determined by gas electron diffraction and microwave spectroscopy. the n–n single bond length is 1.447(2) å (144.7(2) pm), the n-h distance is 1.015(2) å, the n-n-h angles are 106(2)° and 112(2)°, the h-n-h angle is 107°. the molecule adopts a gauche conformation with a torsion angle of 91(2)° (dihedral angle between the planes containing the n-n bond and the bisectors of the h-n-h angles). the rotational barrier is twice that of ethane. these structural properties resemble those of gaseous hydrogen peroxide, which adopts a "skewed" anticlinal conformation, and also experiences a strong rotational barrier. the structure of solid hydrazine was determined by x-ray diffraction. in this phase the n-n bond has a length of 1.46 å and the nearest non-bonded distances are 3.19, 3.25 and 3.30 å. synthesis and production diverse synthetic pathways for hydrazine production have been developed. the key step is the creation of the n–n single bond. the many routes can be divided into those that use chlorine oxidants (and generate salt) and those that do not. oxidation of ammonia via oxaziridines from peroxide hydrazine can be synthesized from ammonia and hydrogen peroxide with a ketone catalyst, in a procedure called the peroxide process (sometimes called pechiney-ugine-kuhlmann process, the atofina–pcuk cycle, or ketazine process). the net reaction is: 2 nh3 + h2o2 → n2h4 + 2 h2o in this route, the ketone and ammonia first condense to give the imine, which is oxidised by hydrogen peroxide to the oxaziridine, a three-membered ring containing carbon, oxygen, and nitrogen. next, the oxaziridine gives the hydrazone by treatment with ammonia, which process creates the nitrogen-nitrogen single bond. this hydrazone condenses with one more equivalent of ketone. the resulting azine is hydrolyzed to give hydrazine and regenerate the ketone, methyl ethyl ketone: me(et)c=n−n=c(et)me + 2 h2o → 2 me(et)c=o + n2h4 unlike most other processes, this approach does not produce a salt as a by-product. chlorine-based oxidations the olin raschig process, first announced in 1907, produces hydrazine from sodium hypochlorite (the active ingredient in many bleaches) and ammonia without the use of a ketone catalyst. this method relies on the reaction of monochloramine with ammonia to create the n–n single bond as well as a hydrogen chloride byproduct: nh2cl + nh3 → n2h4 + hcl related to the raschig process, urea can be oxidized instead of ammonia. again sodium hypochlorite serves as the oxidant. the net reaction is shown: (nh2)2co + naocl + 2 naoh → n2h4 + h2o + nacl + na2co3 the process generates significant by-products and is mainly practised in asia. the bayer ketazine process is the predecessor to the peroxide process. it employs sodium hypochlorite as oxidant instead of hydrogen peroxide. like all hypochlorite-based routes, this method produces an equivalent of salt for each equivalent of hydrazine. reactions acid-base behavior hydrazine forms a monohydrate n2h4·h2o that is denser (1.032 g/cm3) than the anhydrous form n2h4 (1.021 g/cm3). hydrazine has basic (alkali) chemical properties comparable to those of ammonia: n2h4 + h2o → + + oh−, kb = 1.3 × 10−6, pkb = 5.9 (for ammonia kb = 1.78 × 10−5) it is difficult to diprotonate: + + h2o → 2+ + oh−, kb = 8.4 × 10−16, pkb = 15 redox reactions ideally, the combustion of hydrazine in oxygen produces nitrogen and water: n2h4 + o2 → n2 + 2 h2o an excess of oxygen gives oxides of nitrogen, including nitrogen monoxide and nitrogen dioxide: n2h4 + 2 o2 → 2 no + 2 h2o n2h4 + 3 o2 → 2 no2 + 2 h2o the heat of combustion of hydrazine in oxygen (air) is 19.41 mj/kg (8345 btu/lb). hydrazine is a convenient reductant because the by-products are typically nitrogen gas and water. this property makes it useful as an antioxidant, an oxygen scavenger, and a corrosion inhibitor in water boilers and heating systems. it is also used to reduce metal salts and oxides to the pure metals in electroless nickel plating and plutonium extraction from nuclear reactor waste. some colour photographic processes also use a weak solution of hydrazine as a stabilising wash, as it scavenges dye coupler and unreacted silver halides. hydrazine is the most common and effective reducing agent used to convert graphene oxide (go) to reduced graphene oxide (rgo) via hydrothermal treatment. hydrazinium salts hydrazine can be protonated to form various solid salts of the hydrazinium cation +, by treatment with mineral acids. a common salt is hydrazinium hydrogensulfate, +−. hydrazinium hydrogensulfate was investigated as a treatment of cancer-induced cachexia, but proved ineffective. double protonation gives the hydrazinium dication or hydrazinediium, 2+, of which various salts are known. organic chemistry hydrazines are part of many organic syntheses, often those of practical significance in pharmaceuticals (see applications section), as well as in textile dyes and in photography. hydrazine is used in the wolff-kishner reduction, a reaction that transforms the carbonyl group of a ketone into a methylene bridge (or an aldehyde into a methyl group) via a hydrazone intermediate. the production of the highly stable dinitrogen from the hydrazine derivative helps to drive the reaction. being bifunctional, with two amines, hydrazine is a key building block for the preparation of many heterocyclic compounds via condensation with a range of difunctional electrophiles. with 2,4-pentanedione, it condenses to give the 3,5-dimethylpyrazole. in the einhorn-brunner reaction hydrazines react with imides to give triazoles. being a good nucleophile, n2h4 can attack sulfonyl halides and acyl halides. the tosylhydrazine also forms hydrazones upon treatment with carbonyls. hydrazine is used to cleave n-alkylated phthalimide derivatives. this scission reaction allows phthalimide anion to be used as amine precursor in the gabriel synthesis. hydrazone formation illustrative of the condensation of hydrazine with a simple carbonyl is its reaction with propanone to give the diisopropylidene hydrazine (acetone azine). the latter reacts further with hydrazine to yield the hydrazone: 2 (ch3)2co + n2h4 → 2 h2o + ((ch3)2c=n)2 ((ch3)2c=n)2 + n2h4 → 2 (ch3)2c=nnh2 the propanone azine is an intermediate in the atofina-pcuk process. direct alkylation of hydrazines with alkyl halides in the presence of base yields alkyl-substituted hydrazines, but the reaction is typically inefficient due to poor control on level of substitution (same as in ordinary amines). the reduction of hydrazones to hydrazines present a clean way to produce 1,1-dialkylated hydrazines. in a related reaction, 2-cyanopyridines react with hydrazine to form amide hydrazides, which can be converted using 1,2-diketones into triazines. biochemistry hydrazine is the intermediate in the anaerobic oxidation of ammonia (anammox) process. it is produced by some yeasts and the open ocean bacterium anammox (brocadia anammoxidans). the false morel produces the poison gyromitrin which is an organic derivative of hydrazine that is converted to monomethylhydrazine by metabolic processes. even the most popular edible "button" mushroom agaricus bisporus produces organic hydrazine derivatives, including agaritine, a hydrazine derivative of an amino acid, and gyromitrin. history the name "hydrazine" was coined by emil fischer in 1875; he was trying to produce organic compounds that consisted of mono-substituted hydrazine. by 1887, theodor curtius had produced hydrazine sulfate by treating organic diazides with dilute sulfuric acid; however, he was unable to obtain pure hydrazine, despite repeated efforts. pure anhydrous hydrazine was first prepared by the dutch chemist lobry de bruyn in 1895.