Dimethylzinc

Properties

Dimethylzinc is a colorless mobile volatile liquid, which has a characteristic disagreeable garlic-like odor. It is a very reactive and strong reducing agent. It is soluble in alkanes and often sold as a solution in hexanes. The triple point of dimethylzinc is 230.13 K (−43.02 °C) ± 0.02 K. The monomeric molecule of dimethylzinc is linear at Zn center and tetragonal at C centers.

Toxicity and hazards

Inhalation of dimethylzinc mist or vapor causes immediate irritation of the upper respiratory tract, and may cause pneumonia and death. Eyes are immediately and severely irritated and burned by liquid, vapor, or dilute solutions. If not removed by thorough flushing with water, this chemical may permanently damage the cornea, eventually causing blindness. If dimethylzinc contacts the skin, it causes thermal and acid burns by reacting with moisture on skin. Unless washed quickly, skin may be scarred. Ingestion, while unlikely, also causes immediate burns. Nausea, vomiting, cramps, and diarrhea may follow, and tissues may ulcerate if not promptly treated. Upon heating, dimethylzinc vapor decomposes to irritating and toxic products.

Contact of dimethylzinc with oxidants may form explosive peroxides. Dimethylzinc oxidises in air very slowly, producing methylzinc methoxide CH₃ZnOCH₃.

Dimethylzinc is very pyrophoric and can spontaneously ignite in air. It burns in air with a blue flame, giving off a garlic-like odor. The products of decomposition (fire smoke) include zinc oxide, which itself is not toxic, but its fumes can irritate lungs and cause metal fume fever, severe injury, or death.

Dimethylzinc fire must be extinguished with dry sand. The fire reacts violently or explosively with water, generating very flammable methane gas which can explode in air upon catching fire, and lung-irritating smoke of zinc oxide. Dimethylzinc fire reacts violently or explosively with methanol, ethanol and 2,2-dichloropropane. It explodes in oxygen and ozone. Improperly handled containers of dimethylzinc can explode, causing serious injuries or death.

Structure

In the solid state the compound exists in two modifications. The tetragonal high-temperature phase shows a two-dimensional disorder, while the low-temperature phase which is monoclinic is ordered. The molecules are linear with Zn-C bond lengths measuring 192.7(6) pm. The structure of the gas-phase shows a very similar Zn-C distance of 193.0(2) pm.

History

Dimethylzinc was first prepared by Edward Frankland during his work with Robert Bunsen in 1849 at the University of Marburg. After heating a mixture of zinc and methyl iodide in an airtight vessel, a flame burst out when the seal was broken. In the laboratory, this synthesis method remains unchanged today, except that copper or copper compounds are used to activate the zinc.

Uses

Dimethylzinc has been of great importance in the synthesis of organic compounds. It was used for a long time to introduce methyl groups into organic molecules or to synthesize organometallic compounds containing methyl groups. Grignard reagents, (organo-magnesium compounds), which are easier to handle and less flammable, replaced organo-zinc compounds in most laboratory syntheses. Due to differences in reactivity (as well as in reaction byproducts) between organo-zinc compounds and Grignard reagents, organo-zinc compounds may be preferred in some syntheses.

Its high vapor pressure has led to extensive uses in the production of semiconductors, e.g. metalorganic chemical vapor deposition (MOCVD) for the preparation of wide band gap II–VI semiconducting films (e.g. ZnO, ZnS, ZnSe, ZnTe, Cd_xHg_1−xTe) and as p-dopant precursors for III–V semiconductors (e.g. AlN, AlP, Al_xGa_1−xAs, GaAs, InP), which have many electronic and photonic applications.

It is used as an accelerator in rubber vulcanization, as a fungicide, and as a methylating agent in methyltitanium trichloride.