Introduction
Sodium cyanide is an odorless chemical compound with the formula NaCN. It is a white, water-soluble solid. NaCN has a wide range of industrial and other applications, but it is also notoriously toxic and has sometimes been used for suicide or murder. Let’s explore some key facts about this dangerous chemical compound.
Chemical Properties and Structure
Sodium cyanide has the chemical formula NaCN and a molar mass of 49.01 g/mol. It dissociates in water to give hydroxide (NaOH) and cyanide (CN-) ions. The cyanide ion is linear with carbon and nitrogen separated by a triple bond. It is this CN- ion that is primarily responsible for NaCN ‘s high toxicity. NaCN is a white solid that melts at 563°C to give a colorless liquid. It is highly soluble in water.
Toxicity and Mode of Action
Cyanide is an inhibitor of cytochrome c oxidase, an important enzyme in the mitochondrial electron transport chain. By blocking this enzyme, cyanide essentially prevents aerobic respiration from taking place at the cellular level. This leads to a rapid depletion of oxygen to tissues and ultimately causes death due to hypoxia at the tissue and organ level.
The lethal dose of NaCN for adult humans is reported to be 200-300 mg. However, as little as 1-5 grams can prove fatal. The primary symptoms of cyanide poisoning include headaches, dizziness, confusion, convulsions and cardiac arrest. Death by cyanide poisoning usually occurs within minutes to an hour. There is no antidote for cyanide poisoning. Treatment focuses on supportive measures in a hospital environment along with use of antidotes like sodium thiosulfate or dicobalt edetate to combat the effects of cyanide.
Industrial Uses
Despite its obvious toxicity, NaCN has many beneficial industrial applications primarily due to its ability to dissolve minerals containing precious metals like gold and silver. It is widely used for extraction of these metals via cyanidation process in mining operations. In this process, an aqueous solution of NaCN is used to leach gold from minerals into the water to facilitate separation and recovery of gold. NaCN is also used in some cleaning and metal surface treatment applications.
Other uses include:
Production of nylon – Sodium cyanide serves as an intermediate for adiponitrile, which is further used to make nylon 6,6.
Case hardening – It is used in metallurgy for case hardening of steels to increase wear resistance and hardness.
Alkylation – In organic chemistry, NaCN acts as an alkylating agent in production of compounds like acrylonitrile.
Use in Executions
Despite being banned in many countries now, NaCN was previously used for carrying out executions by cyanide gas in gas chambers in some places like the United States. In this method, cyanide salts were placed in a chamber along with an acid like sulfuric acid. The resulting hydrogen cyanide gas was then piped into the chamber, causing death within minutes due to inhibition of cellular respiration. Its use for capital punishment raised many ethical issues and it has now been replaced by other methods in most geographies due to humanitarian concerns over potentially cruel nature of death by cyanide poisoning.
Accidental and Intentional Poisonings
There have been many accidental and intentional deaths reported due to sodium cyanide poisoning over the years. Accidental cases may occur due to occupational exposure in industries using cyanide or due to consumption of cyanide-containing products mistaken as food. Intentional poisonings with cyanide have been reported in cases of suicide or murder. Some high-profile murder cases have involved the use of NaCN by the perpetrator. Given the acute toxicity of cyanide ions, even small amounts ingested intentionally can prove rapidly lethal. Proper safety precautions are a must for any activities involving this deadly chemical salt.
Regulation and Safe Handling
Considering the high human toxicity of NaCN, it is designated as a schedule 2 substance under the Chemical Weapons Convention. Many countries have strict regulations governing its manufacture, transportation, storage and industrial usage. Workers directly handling NaCN must be properly trained in safety procedures like wearing recommended personal protective equipment. Leakage of cyanide solutions into the environment must also be prevented to avoid toxicity to other organisms. Overall, given the risks involved, sodium cyanide requires controlled and regulated use with utmost precautions taken at all stages to prevent accidental poisonings.
