1,1-Dimethylhydrazine (CH3)2N-NH2 is a colorless, volatile, very hygroscopic and highly poisonous liquid with a sharp, fishy, ammonia-like odor. Its smell is typical for organic amines. It is fully miscible in water, methanol, ethanol, diethyl ether, petroleum ether.
Unsymmetrical dimethyl hydrazine is significantly more stable than simple hydrazine. It is not sensitive to shock. Chemically pure 1,1-dimethylhydrazine can be stored for a long times in sealed containers and it is transportable for a long distances.
1,1-Dimethylhydrazine is a weak base, its basicity is compared to non-substituted hydrazine. It forms stable neutral acid salts with a number of mineral and organic acids. Its picrate, hydrosulfate and oxalate could be easily crystallized from water solutions. Being a lone pair donor, 1,1-dimethylhydrazine forms stable molecular complexes with Lewis acids, e.g. with borane.
1,1-Dimethylhydrazine is a strong reducing agent. It is slowly oxidizes by oxygen of air even at room temperature. It forms flammable mixtures with air in the range of concentrations from 2.5% to 95%.
Unsymmetrical dimethylhydrazine easily condenses with carbonyl compounds (aldehydes and ketones) to give corresponding hydrazones:
(CH3)2N-NH2 + C6H5CHO → (CH3)2N-N=CHC6H5 + H2O
1,1-Dimethylhydrazine is a very toxic compound. It irritates skin, mucous membranes of eyes and respiratory tract. It can be absorbed through the skin. Dimethylhydrazine being oxidized by oxygen of air can form dimethylnitrosamine, a persistent carcinogen. It also can explode in the presence of oxidizing agents.
1,1-Dimethylhydrazine is manufactured is different countries in large amounts. There are several ways for its industrial preparation:
- By nitrosation of dimethylamine with sodium nitrite or potassium nitrite to give dimethylnitrosamine followed by its reduction with dihydrogen in the presence of palladium or platinum catalyst:
(CH3)2NH + NaNO2 → (CH3)2NNO + NaOH
(CH3)2NNO + 2H2 → (CH3)2N-NH2 + H2O
- By interaction of dimethylamine with monochloroamine:
(CH3)2NH + NH2Cl → (CH3)2N-NH2 + H2O + NaCl
- From acetylhydrazide. This method is realized in USA. At the first step acetylhydrazide is underwent reductive alkylation with formaldehyde in the presence of dihydrogen. Then, dimethylhydrazide is hydrolized with alkali water solution:
CH3C(O)NHNH2 + 2HC(O)H + 2H2 → CH3C(O)NHN(CH3)2 + 2H2O
CH3C(O)NHN(CH3)2 + H2O(NaOH) → (CH3)2N-NH2 + CH3C(O)OH
- Unsymmetrical dimethylhydrazine is mainly used in hypergolic rocket fuels in Russia, USA, China, India as a bipropellant in combination with different oxidizing agents, such as liquid N2O4, red fuming nitric acid (IRFNA) or liquid oxygen. It can be used as itself or in the mixture with other redusing agents, thus, its mixture with hydrazine with ratio 50:50 is called Aerozine-50 and applied as a fuel for Titan, Delta and GSLV rocket families;
- as a nitrogen source in organometallic vapour phase epitaxy thin-film deposition;