Amyl nitrite

Amyl nitrite is the chemical compound with the formula C₅H₁₁ONO. A variety of isomers are known, but they all feature an amyl group attached to the nitrito functional group. The alkyl substituent is not reactive, but the ON=O group behaves as other nitrites. Like other alkyl nitrites, amyl nitrite is bioactive in mammals, being a vasodilator which is the basis of its use as a prescription medicine. As an inhalant, it also has a psychoactive effect which has led to illegal drug use.

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Nomenclature

The term "amyl nitrite" encompasses several isomers. For example, a common form of amyl nitrite with the formula (CH₃)₂CHCH₂CH₂ONO may be more specifically referred to as isoamyl nitrite. When the amyl chain consists of five carbon atoms in a row, the resulting "amyl nitrite" would be described with the structural formula CH₃(CH₂)₄ONO. Sometimes the latter isomer is called n-amyl nitrite, n denoting normal. Also, the five carbon chain is sometimes referred to as a straight chain, although chains of carbon atoms are usually zig-zag in conformation.

Amyl nitrite is often confused with amyl nitrate, a substance with a different chemical composition and different properties.

Synthesis and reactions

Alkyl nitrites are prepared by the reaction of alcohols with nitrous acid:^[1]

C₅H₁₁OH + HONO →→ C₅H₁₁ONO + H₂O

The reaction is called esterification. Synthesis of alkyl nitrites is generally straightforward and can be accomplished in home laboratories. A common procedure includes the dropwise addition of concentrated sulfuric acid to a cooled mixture of an aqueous sodium nitrite solution and an alcohol. The intermediately formed stoichiometric mixture of nitrous and nitric oxide then converts the alcohol to the alkyl nitrite, which, due to its low density, will form an upper layer that can be easily decanted from the reaction mixture.

Isoamyl nitrite decomposes in the presence of base to give nitrite salts and the isoamyl alcohol:

C₅H₁₁ONO + NaOH → C₅H₁₁OH + NaNO₂

Amyl nitrite, like other alkyl nitrites, reacts with carbanions to give oximes.^[2]

Physiological effects

Amyl nitrite, in common with other alkyl nitrites,^[3] is a potent vasodilator, i.e. it expands blood vessels, resulting in lowering of the blood pressure. Alkyl nitrites function as a source of nitric oxide, which signals for relaxation of the involuntary muscles. Physical effects include decrease in blood pressure, headache, flushing of the face, increased heart rate, dizziness, and relaxation of involuntary muscles, especially the blood vessel walls and the anal sphincter. There are no withdrawal symptoms. Overdose symptoms include nausea, emesis (vomiting), hypotension, hypoventilation, dyspnea (shortness of breath), and syncope (fainting). The effects set in very quickly, typically within a few seconds and disappearing soon after (within a minute).

It induces the formation of methemoglobin, which sequesters cyanide as non-toxic cyanomethemoglobin.^[4]

Applications

Amyl nitrite is employed medically to treat heart diseases such as angina and to treat cyanide poisoning.^[5] It is also used as an inhalant drug that induces a brief euphoria; whilst already intoxicated with stimulant drugs such as cocaine or ecstasy (see MDMA) the euphoric state intensifies and lasts for several minutes longer. Once some stimulative drugs wear off, a common side effect is a period of depression or anxiety, colloquially called a "come down"; amyl nitrite is sometimes used to "come up" again in order to stop the user from feeling lousy. See Poppers.

References