Dimethylzinc

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Dimethylzinc
Names
IUPAC name
Dimethylzinc
Other names
Dimethyl zinc
DMZ
Properties
ZnC2H6
Zn(CH3)2
Molar mass 95.478 g/mol
Appearance Colorless volatile liquid
Odor Disagreeable, garlic-like
Density 1.33 g/cm3 (20 °C) (pure)[1]
0.931 g/cm3 (2 M solution in toluene) (25 °C)
Melting point −42 °C (−44 °F; 231 K)
Boiling point 46 °C (115 °F; 319 K)
Reacts
Solubility Reacts with alcohols, bases, carboxylic acids, esters, mineral acids
Miscible with benzene, diethyl ether, hexane, toluene, xylene
Vapor pressure 376 mmHg at 25 °C
Thermochemistry
50.6 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (2 M solution in toluene)
Flash point -17 °C (1.4 °F; 256 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Dimethylzinc, also known as zinc methyl, DMZ or DMZn, is an organometallic compound with the chemical formula Zn(CH3)2 or Zn(Me)2.

Properties

Chemical

Dimethylzinc ignites spontaneously in air at standard conditions, burning with a bluish flame.

Zn(CH3)2 + 8 O2 → ZnO + 2 CO2 + 3 H2O

It will also hydrolyze in contact with water.

Dimethyl zinc can slowly oxidize in air, if kept below its autoignition temperature to yield methylzinc methylate (CH3ZnOCH3).[2]

The compound decomposes above 200-215 °C, yielding very pure zinc metal.[3]

Physical

Dimethylzinc is a colorless volatile liquid, with a disagreeable odor, described as "garlic-like" that immediately ignites in contact with air. It reacts with all protic solvents, but is very soluble in many hydrocarbon solvents, like alkanes and aromatics.

Availability

Dimethylzinc is sold by chemical suppliers, as solution, usually in hexane or toluene, which are much safer than the pure compound.

Preparation

Dimethylzinc can be prepared by reacting methyl iodide with zinc metal at 150-160 °C, or with a sodium-zinc alloy, at 45-50 °C, in diethyl ether.[4][5]

2 Zn + 2 CH3I → Zn(CH3)2 + ZnI2
Zn + 2 Na + 2 CH3I → Zn(CH3)2 + 2 NaI

Copper can also be used to activate the zinc.[6]

Projects

  • Demonstration of pyrophoricity
  • Methylating agent

Handling

Safety

Dimethylzinc is highly pyrophoric and thus a severe fire hazard. Combustion generates white zinc oxide fumes, that are harmful for lungs if inhaled. In case of a fire, sand or class D fire extinguishers are used to put out the fire.

Storage

Dimethylzinc is best kept as solution, in hexane, in a glass bottle with a special silicone rubber septum and kept in a fridge or freezer.

Disposal

Dimethylzinc is extremely difficult and dangerous to safely neutralize. One could simply remotely detonate an old bottle in a firing range or some other abandoned polluted/industrial area. Or just take it to the disposal centers if this route is not acceptable.

A way to safely neutralize the hexane solution of dimethylzinc involves connecting the bottle to an argon line, then very carefully slowly inject ethanol inside the bottle, dropwise and monitor the temperature of the bottle. Eventually, all the dimethylzinc would have hydrolyzed, with the remaining zinc precipitate settling at the bottom of the bottle. The liquid is checked again to verify that all the DMZ has been destroyed, then the content is poured and either incinerated or if possible recycled. This route however, is very dangerous and should not be done by amateurs!

References

  1. Allen et al.; Journal of the Chemical Society; (1965); p. 5476,5478-5480
  2. Budavari, S. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 1996., p. 552
  3. Yoshikawa Akihiko; Physica B: Condensed Matter (Amsterdam); vol. 185; (1993); p. 50 - 64 ; (from Gmelin)
  4. Frankland; Justus Liebigs Annalen der Chemie; vol. 85; (1853); p. 360
  5. Wagner; Journal fuer Praktische Chemie (Leipzig); vol. <2>44; (1891); p. 261 Anm.
  6. Renshaw; Greenlaw; Journal of the American Chemical Society; vol. 42; (1920); p. 1474

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