Thiopropanal S-oxide

Thiopropanal S-oxide is a chemical compound with the formula C_3H_6SO. It is a member of the thioaldehydes and specifically, it is the sulfur analog of propanal. This compound is primarily known for its role in the biochemistry of onions and other Allium species, where it is responsible for the characteristic eye irritation and tearing effect upon cutting. Thiopropanal S-oxide is produced through the enzymatic breakdown of amino acids in onions, a process that begins when the cells of the onion are damaged.

Production and Properties

Thiopropanal S-oxide is generated through the enzymatic conversion of the amino acid cysteine into a sulfenic acid, which is then rapidly converted by another enzyme into thiopropanal S-oxide. This compound is highly volatile and readily reacts with the water in the eyes to form sulfuric acid, which is responsible for the irritation.

The compound is a colorless gas at room temperature and has a distinctive sulfurous odor. It is poorly soluble in water but can be dissolved in organic solvents.

Biological Role and Effects

In Allium species, thiopropanal S-oxide serves as a defense mechanism against herbivores and pathogens. The irritation it causes is meant to deter animals from eating the plant, thereby protecting it from damage.

In humans, exposure to thiopropanal S-oxide can cause a range of effects, primarily irritation to the eyes, leading to tearing and redness. In high concentrations, it can also cause irritation to the respiratory tract.

Handling and Safety

When handling onions or other sources of thiopropanal S-oxide, it is advisable to minimize exposure to the compound to prevent irritation. This can be achieved by cutting onions under running water, chilling them before cutting to reduce the volatility of the compound, or using a sharp knife to minimize cell damage.

In Popular Culture

The tear-inducing effect of onions has been a subject of interest and humor in popular culture, with numerous home remedies and techniques purported to prevent crying when cutting onions.

See Also

• Lachrymatory agent
• Sulfenic acids
• Allium