Cacodyl Oxide: [(CH3)2As]2O
Cacodyl oxide is an organoarsenic compound historically significant as a major component of "Cadet’s Fuming Liquid". Discovered in 1760, it represents the birth of organometallic chemistry.
1. General Properties
| Property | Description |
|---|---|
| IUPAC Name | Dimethylarsinous anhydride |
| Molecular Formula | C4H12As2O |
| Appearance | Oily, reddish-brown liquid (impure) or colorless (pure) |
| Odor | Repulsive, intense garlic-like smell |
| Hazard | Extremely toxic and potentially pyrophoric in air |
2. Synthesis
A. Historical Synthesis (Cadet's Method)
Originally prepared by heating potassium acetate with arsenic trioxide. This dry distillation produces a mixture of cacodyl and cacodyl oxide.
B. Modern Synthesis
It can be prepared in the laboratory by the hydrolysis of dimethylarsinous chloride:
3. Chemical Structure & Bonding
The molecule consists of two dimethylarsenic (CH3)2As units bridged by a single oxygen atom. The arsenic atoms are in the +3 oxidation state. It is structurally similar to an organic ether but with arsenic atoms replacing the carbons adjacent to the oxygen.
4. Key Chemical Reactions
- Oxidation: Upon exposure to air, it can spontaneously ignite or slowly oxidize to cacodylic acid (dimethylarsinic acid).
- Reaction with Halogen Acids: It reacts with HCl or HI to form the corresponding dimethylarsenic halides.
[(CH3)2As]2O + 2 HCl → 2 (CH3)2AsCl + H2O
- Reduction: Further reduction of cacodyl oxide leads to the formation of Cacodyl (tetramethyldiarsane), which contains a direct As—As bond.
The first organometallic of main group element was
A. Uranocene
B. Wilkinson Catalyst
C. Zeise's Salt
D. Cacodyl Oxide
Answer: D. Cacodyl Oxide [(CH3)2As]2O
What is the oxidation state of Arsenic in Cacodyl Oxide, [(CH3)2As]2O?
A. +1
B. +3
C. 0
D. +5
Answer: B. +3
In this trivalent state, arsenic forms bonds with two methyl groups and one bridging oxygen atom.