Everything about Nitrous Oxide totally explained
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Nitrous oxide (aka
laughing gas or
dinitrogen monoxide) is a
chemical compound with the
chemical formula N2O. At room temperature, it's a colorless
non-flammable gas, with a pleasant, slightly sweet odor and taste. It is used in
surgery and
dentistry for its
anesthetic and
analgesic effects. It is commonly known as "laughing gas" due to the euphoric effects of inhaling it, a property that has led to its recreational use as an
inhalant drug. It is also used in
motor racing as an
oxidizer to increase the power output of
engines.
Occurrence
More info on nitrogen oxides.
Nitrous oxide, unlike other oxides (apart from carbon dioxide), is a major
greenhouse gas. While its radiative warming effect is substantially less than CO
2, nitrous oxide's persistence in the atmosphere, when considered over a 100 year period, per unit of weight, has 296 times more impact on
global warming than that per mass unit of
carbon dioxide (CO
2). Control of nitrous oxide is part of efforts to curb greenhouse gas emissions, which is part of the
Kyoto Protocol. Despite its relatively small concentration in the atmosphere, nitrous oxide is the fourth largest greenhouse gas contributor to overall global warming, behind
carbon dioxide,
methane and water vapour. (The other nitrogen oxides contribute to global warming indirectly, by contributing to tropospheric ozone production during smog formation).
Nitrous oxide is emitted by
bacteria in soils and oceans, and thus has been a part of Earth's atmosphere for
aeons. Agriculture is the main source of human-produced nitrous oxide: cultivating soil, the use of
nitrogen fertilizers, and animal waste handling can all stimulate naturally occurring bacteria to produce more nitrous oxide. The livestock sector (primarily cows, chickens, and pigs) produces 65% of human-related nitrous oxide. Industrial sources make up only about 20% of all anthropogenic sources, and include the production of
nylon and nitric acid, and the burning of fossil fuel in internal combustion engines.
Human activity is thought to account for somewhat less than 2
teragrams of nitrogen oxides per year, nature for over 15 teragrams. The global anthropogenic nitrous oxide flux is about 1 petagram of carbon dioxide carbon-equivalents per year; this compares to 2 petagrams of methane carbon dioxide carbon-equivalents per year, and to an atmospheric loading rate of about 3.3 petagrams of carbon dioxide carbon-equivalents per year.
Nitrous oxide reacts with
ozone in the
stratosphere. Nitrous oxide is the main naturally occurring regulator of stratospheric ozone.
Recent research by Nobel Laureate
Paul Crutzen suggests that emissions of nitrous oxide in the production of biofuels are more than enough to offset the advantages that biodiesel was hoped to have in terms of
carbon dioxide emissions. Carbon dioxide released during biofuel combustion is considered in fact neutral and thus its contribution as greenhouse gas neglected. The reason is that during the growing phase of the crop utilized for producing the biofuel an equal amount of carbon dioxide is sequestrated from the atmosphere.
Manufacture
Nitrous oxide is most commonly prepared by careful heating of
ammonium nitrate, which decomposes into nitrous oxide and water vapor.
» NH
4NO
3(s) → 2 H
2O(g) + N
2O(g)
The addition of various
phosphates favors formation of a purer gas at slightly lower temperatures. This reaction occurs between 170 - 240°C, temperatures where ammonium nitrate is a moderately sensitive
explosive and a very powerful
oxidizer. At temperatures much above 240 °C the
exothermic reaction may accelerate to the point of
detonation. The mixture must be cooled to avoid such a disaster. In practice, the reaction involves a series of tedious adjustments to control the temperature to within a narrow range. Professionals have destroyed whole neighborhoods by losing control (of the
temperature and pressure in the ammonium nitrate retorts) in commercial scale processes. Examples include the Ohio Chemical debacle in
Montreal, 1966 and the Air Products & Chemicals, Inc. disaster in
Delaware City, Delaware, 1977. Superheated steam is used to reach reaction temperature in some turnkey production plants.
Downstream, the hot, corrosive mixture of gases must be cooled to condense the steam and filtered to remove higher oxides of nitrogen. Also ammonium nitrate smoke, in an extremely persistent colloid will likely have to be removed. The cleanup is often done in a train of 3 gas washes; namely base, acid and base again. Any significant amounts of nitric oxide (NO) may not necessarily be absorbed directly by the base (sodium hydroxide) washes.
The nitric oxide impurity is sometimes chelated out with
ferrous sulfate, reduced with iron metal, or oxidised and absorbed in base as a higher oxide. The first base wash may (or may not) react out much of the ammonium nitrate smoke, however this reaction generates ammonia gas, which may have to be absorbed in the acid wash.
The direct oxidation of
ammonia may someday rival the ammonium nitrate
pyrolysis synthesis of nitrous oxide mentioned above. This capital-intensive process, which originates in Japan, uses a
manganese dioxide-
bismuth oxide catalyst:
» 2 NH
3 + 2 O
2 → N
2O + 3 H
2O
Higher oxides of nitrogen are formed as impurities. In comparison,
uncatalyzed ammonia oxidation (for example combustion or explosion) goes primarily to N
2 and H
2O.
Nitrous oxide can be made by heating a solution of
sulfamic acid and
nitric acid. A lot of gas was made this way in Bulgaria.
» HNO
3 + NH
2SO
3H → N
2O + H
2SO
4 + H
2O
There is no explosive hazard in this reaction if the mixing rate is controlled. However, as usual, toxic higher oxides of nitrogen form.
Nitrous oxide is produced in large volumes as a by-product in the synthesis of
adipic acid; one of the two reactants used in nylon manufacture. This might become a major commercial source, but will require the removal of higher oxides of nitrogen and organic impurities. Currently much of the gas is decomposed before release for environmental protection. Greener processes may prevail that substitute
hydrogen peroxide for nitric acid oxidation; hence no generation of oxide of nitrogen by-products.
Hydroxylammonium chloride can react with
sodium nitrite to produce N
2O as well:
» NH
3OH
+Cl
− + NaNO
2 → N
2O + NaCl + H
2O
If the nitrite is added to the hydroxylamine solution, the only remaining byproduct is salt water. However, if the hydroxylamine solution is added to the nitrite solution (nitrite is in excess), then toxic higher oxides of nitrogen are also formed.
Uses
Inhalant effects
Nitrous oxide (N
2O) is a
dissociative drug that can cause
analgesia,
depersonalization,
derealization,
dizziness,
euphoria, sound distortion and slight
hallucinations.
In medicine
Previously, nitrous oxide was typically administered by dentists through a demand-valve inhaler over the nose that only releases gas when the patient inhales through the nose; full-face masks are not commonly used by dentists, so that the patient's mouth can be worked on while the patient continues to inhale the gas. Current use involves constant supply flowmeters which allow the proportion of nitrous oxide and the combined gas flow rate to be individually adjusted. The masks still obviously cover only the nose.
Because nitrous oxide is minimally metabolized, it retains its potency when exhaled into the room by the patient and can pose an intoxicating and prolonged-exposure hazard to the clinic staff if the room is poorly ventilated. Where nitrous oxide is administered, a continuous-flow fresh-air ventilation system or nitrous-scavenging system is used to prevent waste gas buildup.
Nitrous oxide is a weak general anesthetic, and so is generally not used alone in general anesthesia. In general anesthesia it's used as a carrier gas in a 2:1 ratio with oxygen for more powerful general anesthetic agents such as
sevoflurane or
desflurane. It has a MAC (
minimum alveolar concentration) of 105% and a blood:gas partition coefficient of 0.46. Less than 0.004% is metabolised in humans.
Recreational use
Since the earliest uses of nitrous oxide for medical or dental purposes, it has also been used recreationally as an
inhalant, because it causes euphoria and slight hallucinations. Only a small number of recreational users (such as dental office workers or medical gas technicians) have legal access to pure nitrous oxide
canisters that are intended for medical or dental use. Most recreational users obtain nitrous oxide from compressed gas containers which use nitrous oxide as a propellant for whipped cream or from automotive nitrous systems. Automotive nitrous available to the public sometimes has ~100 ppm
Sulfur dioxide and/or
elemental sulfur added to prevent recreational use/abuse; (not
hydrogen sulfide as suggested by). Inhalation of such a mixture is nearly impossible after one breath due to gagging and sooner or later, involuntary clamping off of the trachea; (some with "sulfite" allergies could even die due to allergic reaction).
Users typically inflate a balloon or a plastic bag with nitrous oxide and inhale the gas for its effects, or they use a whipped cream canister which upon charge releases the gas into the canister before use. Nitrous oxide expelled directly from a tank or canister would severely damage the user's lungs due to its extremely cold exiting temperature due to the sudden expansion. By allowing the gas to expand in a balloon, bag or a whipped cream canister, the final output temperature of the gas is raised immensely. While nitrous oxide isn't a dangerous substance per se, recreational users typically don't mix it with air or oxygen (a 70/30 mix of nitrous oxide and oxygen, respectively (which is the same amount of oxygen in normal air) is standard procedure in a dentist's office) and thus may risk injury, or in worst case: death, from lack of oxygen (
anoxia). Nitrous oxide, when inhaled using a home made system consisting of a mask and/or regulator, presents the highest potential danger due to the automatic, continuous application. This may in turn prevent adequate oxygen from reaching the user, rendering him unconscious, subsequently leading to death due to asphyxiation. Inhaling nitrous oxide in conjunction with an
alkyl nitrite (aka
poppers) is in some circles referred to as "space surfing", as the nitrous oxide acts
synergistically with the alkyl nitrite to create strong (but short-lived) euphoria, analgesia, dissociation, and in some cases, sensations of internal movement or agitation.
The name also comes from the sound distorting effects of nitrous oxide, which some users compare to the sound of waves crashing on a beach (hence "surfing"). While powerful, this is a potentially dangerous combination, as the central nervous system (CNS) depressing effects of the nitrous oxide, combined with the drop in blood pressure (which is characteristic of nitrite inhalant use), may cause
hypotension, unconsciousness, or, in the case of extreme overdose, death. Individuals with cardiac conditions, complications arising from stroke or surgery, or chronically low blood pressure are advised not to use these two drugs simultaneously.
Nitrous oxide is used as a whipping agent due to the ease with which it migrates into and out of oils; only a few seconds of rapid shaking is enough to migrate the gas into the oily cream under pressure. Due to this ability, nitrous also easily moves throughout the body, into and out of cells, because cell membranes are oil-based lipids. Prolonged inhalation of high concentrations of nitrous oxide will cause it to migrate throughout the body into sinus cavities, the digestive tract, and into fat cells.
An inactive person who has breathed high concentrations for 20-30 minutes but then breathes normally will still retain the gas in his body at low doses as the gas slowly migrates back out of these internal cavities. Even after several hours of not breathing the gas, sudden rapid whole-body movements such as calisthenics causes the dissolved gas to suddenly begin migrating out of fat cells, resulting in a latent dosing effect.
Nitrous oxide can be habit-forming because of its short-lived effect (generally from 0.1 - 1 minutes in recreational doses) and ease of access. Death can result if it's inhaled in such a way that too little oxygen is breathed in. While the pure gas is generally not toxic, long-term use in excessive quantities has been associated with
vitamin B12 deficiency
anemia due to reduced
hemopoiesis,
neuropathy,
tinnitus, and
numbness in extremities. Harmful irreversible effects that may be caused by abuse of nitrous oxide include peripheral neuropathies and limb spasms. Pregnant women shouldn't use nitrous oxide as chronic use is
teratogenic and
foetotoxic. One study in rats found that long term exposure to high doses of nitrous oxide may lead to
Olney's lesions. N
2O, like other
volatile anesthetics, activates twin-pore
potassium channels, albeit weakly. These channels are largely responsible for keeping neurons at the resting (unexcited) potential. Unlike many anesthetics, however, N
2O doesn't seem to affect
calcium channels. Indeed, in humans given 30% N
2O, benzodiazepine receptor antagonists reduced the subjective reports of feeling “high”, but didn't alter psycho-motor performance.
The effects of N
2O seem linked to the interaction between the
endogenous opioid system and the descending
noradrenergic system. When animals are given
morphine chronically they develop tolerance to its analgesic (pain killing) effects; this also renders the animals tolerant to the analgesic effects of N
2O. Administration of
antibodies which bind and block the activity of some endogenous opioids (not
beta-endorphin), also block the antinociceptive effects of N
2O. Drugs which inhibit the breakdown of endogenous opioids also potentiate the antinociceptive effects of N
2O. Indeed, alpha2B-adrenoreceptor knockout mice or animals depleted in noradrenaline are nearly completely resistant to the antinociceptive effects of N
2O. It seems N
2O-induced release of endogenous opioids causes disinhibition of
brain stem noradrenergic neurons, which release
norepinephrine into the spinal cord and inhibit pain signaling (Maze, M. and M. Fujinaga, 2000). Exactly how N
2O causes the release of opioids is still uncertain.
Safety
The major safety hazards of nitrous oxide come from the fact that it's a compressed liquified gas, an asphyxiation risk, and a
dissociative anaesthetic. Exposure to nitrous oxide causes short-term decreases in mental performance, audiovisual ability, and manual dexterity.
A study of workers
and several experimental animal studies indicate that adverse reproductive effects may also result from chronic exposure to nitrous oxide.
The
National Institute for Occupational Safety and Health recommends that workers' exposure to nitrous oxide should be controlled during the administration of anesthetic gas in medical, dental, and veterinary operatories.
Chemical/physical
At room temperature (20°C) the saturated vapour pressure is 58.5 bar, rising up to 72.45 bar at 36.4°C- the
critical temperature. The pressure curve is thus unusually sensitive to temperature. Liquid nitrous oxide acts as a good solvent for many
organic compounds; liquid mixtures and may form shock sensitive explosives.
As with many strong oxidisers, contamination of parts with fuels have been implicated in rocketry accidents, where small quantities of nitrous / fuel mixtures explode due to 'water hammer' like effects (sometimes called 'dieseling'- heating due to
adiabatic compression of gases can reach decomposition temperatures). Some common building materials such as stainless steel and aluminum can act as fuels with strong oxidisers such as Nitrous Oxide, as can contaminants, which can ignite due to adiabatic compression.
There have also been accidents where nitrous oxide decomposition in plumbing has led to the explosion of large tanks.
Biological
Nitrous oxide inactivates the cobalamin form of vitamin B by oxidation. Symptoms of vitamin B deficiency, including
sensory neuropathy,
myelopathy, and
encephalopathy, can occur within days or weeks of exposure to nitrous oxide
anesthesia in people with subclinical vitamin B deficiency. Symptoms are treated with high doses of vitamin B, but recovery can be slow and incomplete. People with normal vitamin B levels have sufficient vitamin B stores to make the effects of nitrous oxide insignificant, unless exposure is repeated and prolonged (nitrous oxide abuse). Vitamin B levels should be checked in people with risk factors for vitamin B deficiency prior to using nitrous oxide anesthesia.
Nitrous oxide has also been shown to induce early stages of
Olney's lesions in the brains of rats. However none of the lesions found were irreversible.
Thermal
Compressed nitrous oxide is usually stored at room temperature, but as the gas expands it quickly cools to sub-zero temperatures via the
Joule-Thomson Effect. A leak or unexpected release of compressed nitrous oxide can result in an immediate and severe
burn.
Legality
In the
United States, possession of nitrous oxide is legal under federal law and isn't subject to
DEA purview. It is, however, regulated by the
Food and Drug Administration under the Food Drug and Cosmetics Act; prosecution is possible under its "misbranding" clauses, prohibiting the sale or distribution of nitrous oxide for the purpose of
human consumption.
Many states have laws regulating the possession, sale, and distribution of nitrous oxide; but these are normally limited to either banning distribution to minors, or to setting an upper limit for the amount of nitrous oxide that may be sold without special license, rather than banning possession or distribution completely. In most jurisdictions, like at the federal level, sale or distribution for the purpose of recreational consumption is illegal. However it's an offence under the Medicines Act to supply it for inhalation. This statement would seemingly prohibit all non-medicinal uses of the chemical, though it's implied that only recreational use will be legally targeted.
History
The gas was first synthesized by English chemist and natural philosopher
Joseph Priestley in 1775
(External Link
), who called it
phlogisticated nitrous air (see
phlogiston). Priestley describes the preparation of "nitrous air diminished" by heating iron filings dampened with
nitric acid in
Experiments and Observations on Different Kinds of Air, (1775). Priestley was delighted with his discovery: "I have now discovered an air five or six times as good as common air... nothing I ever did has surprised me more, or is more satisfactory."
Humphry Davy in the 1790s tested the gas on himself and some of his friends, including the poets
Samuel Taylor Coleridge and
Robert Southey.
They realised that nitrous oxide considerably dulled the sensation of pain, even if the inhaler were still semi-conscious. After it was publicized extensively by
Gardner Quincy Colton in the United States in the 1840s, it came into use as an anaesthetic, particularly by dentists, who don't typically have access to the services of an
anesthesiologist and who may benefit from a patient who can respond to verbal commands.
Further Information
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