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2,4-Dinitrophenol (2,4-DNP or simply DNP) is an organic compound with the formula HOC6H3(NO2)2. It is a yellow, crystalline solid that has a sweet, musty odor. It sublimes, is volatile with steam, and is soluble in most organic solvents as well as aqueous alkaline solutions.[1] When in a dry form, it's a high explosive and has an instantaneous explosion hazard.[2] It is a precursor to other chemicals and is biochemically active, inhibiting adenosine triphosphate (ATP) production in cells with mitochondria. Its use in high doses as a dieting aid has been identified with severe side-effects, including a number of deaths.[3]

2,4-Dinitrophenol
2,4-Dinitrophenol.svg
2,4-Dinitrophenol 3D.png
2,4-Dinitrophenol.jpg
Sample of pure compound
Names
Preferred IUPAC name
2,4-Dinitrophenol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.080
KEGG
UNII
UN number 0076Dry or wetted with less than 15% water. Class 1.1D explosives
1320Wetted with not less than 15% water. DT Solid desensitized explosives, toxic
1599Toxic solution
Properties
C6H4N2O5
Molar mass 184.107 g·mol−1
Density 1.683 g/cm3
Melting point 108 °C (226 °F; 381 K)
Boiling point 113 °C (235 °F; 386 K)
Acidity (pKa) 4.114
-73.1·10−6 cm3/mol
Hazards
Safety data sheet International Chemical Safety Card 0464
GHS pictograms GHS01: Explosive GHS06: Toxic GHS08: Health hazard GHS09: Environmental hazard
GHS signal word DANGER
H201, H300, H311, H331, H372, H400
P261, P273, P280, P301+310, P311
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazards (white): no codeNFPA 704 four-colored diamond
3
3
3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

UsesEdit

Commercial DNP is used as an antiseptic and as a non-selective bioaccumulating pesticide.[4]

DNP is particularly used as a herbicide alongside with other closely related dinitrophenol herbicides like 2,4-dinitro-o-cresol (DNOC), dinoseb and dinoterb.[5]

It is a chemical intermediate in the production of sulfur dyes,[6] wood preservatives[4] and picric acid.[7] DNP has also been used to make photographic developers and explosives (see shellite).[8] DNP is classified as an explosive in UK[9] and USA.[10]

Although DNP is widely considered too dangerous for clinical use, its mechanism of action remains under investigation as a potential approach for treating obesity.[11] As of 2015, research is being conducted on uncoupling proteins naturally found in humans.[12]

BiochemistryEdit

In living cells, DNP acts as a proton ionophore, an agent that can shuttle protons (hydrogen cations) across biological membranes. It dissipates the proton gradient across mitochondria and chloroplast membranes, collapsing the proton motive force that the cell uses to produce most of its ATP chemical energy. Instead of producing ATP, the energy of the proton gradient is lost as heat.[3]

DNP is often used in biochemistry research to help explore the bioenergetics of chemiosmotic and other membrane transport processes.

Mechanism of actionEdit

DNP acts as a protonophore, allowing protons to leak across the inner mitochondrial membrane and thus bypass ATP synthase. This makes ATP energy production less efficient. In effect, part of the energy that is normally produced from cellular respiration is wasted as heat. The inefficiency is proportional to the dose of DNP that is taken. As the dose increases and energy production is made more inefficient, metabolic rate increases (and more fat is burned) in order to compensate for the inefficiency and to meet energy demands. DNP is probably the best known agent for uncoupling oxidative phosphorylation. The "phosphorylation" of adenosine diphosphate (ADP) by ATP synthase gets disconnected or "uncoupled" from oxidation.

"Dinitrophenol uncouples oxidative phosphorylation, causes release of calcium from mitochondrial stores and prevents calcium re-uptake. This leads to free intracellular calcium and causes muscle contraction and hyperthermia. Dantrolene inhibits calcium release from the sarcoplasmic reticulum which reduces intracellular calcium. The resulting muscle relaxation allows heat dissipation. There is little risk to dantrolene administration. Since dantrolene may be effective in reducing hyperthermia caused by agents that inhibit oxidative phosphorylation, early administration may improve outcome."[13]

PharmacokineticsEdit

Information about pharmacokinetics of DNP in humans is limited.[14] The ATSDR's Toxicological Profile for Dinitrophenols remarks that DNP elimination appears to be rapid except when liver function is impaired.[15] The NEJM remarks that DNP appears to be eliminated in around three to four days, except possibly when the liver and kidneys are damaged.[16] Other papers give a wide array of possible half-lives, ranging from 3 hours,[17] to 5–14 days.[18] Other recent papers maintain that the half-life in humans is unknown.[19]

HazardsEdit

ToxicityEdit

DNP is considered to have high acute toxicity.[4] Acute oral exposure to DNP has resulted in increased basal metabolic rate, nausea, vomiting, sweating, dizziness, headache, and loss of weight.[4] Chronic oral exposure to DNP can lead to the formation of cataracts and skin lesions and has caused effects on the bone marrow, central nervous system, and cardiovascular system.[4][20] Contact with skin or inhalation can cause DNP poisoning. In 2009, an incident occurred in a Chinese chemical factory and 20 persons suffered acute DNP poisoning.[21]

The factor that limits ever-increasing doses of DNP is not a lack of ATP energy production, but rather an excessive rise in body temperature due to the heat produced during uncoupling. Accordingly, DNP overdose will cause fatal hyperthermia, with body temperature rising to as high as 43.1 °C (109.6 °F)[22] shortly before death. Case reports have shown that an acute administration of 10–20 mg per kilogram of body weight in humans can be lethal.[18][23][24][25][26] The lowest published fatal ingested dose is 4.3 mg/kg.[8][27] One dose, as few as two tablets have proved fatal.[24][28]

The United Kingdom's Food Standards Agency identifies DNP as "an industrial chemical known to have serious short-term and long-term effects, which can be extremely dangerous to human health." and advises "consumers not to take any product containing DNP at any level. This chemical is not suitable for human consumption."[29] From December 2018 DNP has been classified as an "illegal poisonous substance" in Russia.[30][31]

Chemical hazardsEdit

Dust explosion possible if in powder or granular form, mixed with air. May explosively decompose on shock, friction or concussion. May explode on heating.[32] DNP forms explosive salts with strong bases and ammonia, and emits toxic fumes of nitrogen dioxide when heated to decomposition.[33] DNP explosive strength is 81% of TNT according to Trauzl lead block test.[34] DNP was the cause of explosion in 1916 Rainham Chemical Factory, which left 7 dead and 69 injured.[35][36] DNP is listed on Homeland Security Anti-Terrorism chemicals of interest list.[37]

SynthesisEdit

DNP is produced by hydrolysis of 1-chloro-2,4-dinitrobenzene.[6] Another route of DNP synthesis is by nitration of phenol with nitric acid.[38][39]

History and societyEdit

DNP was widely used in explosive mixtures around the world. Shellite in UK, Tridite in US, Tridita in Spain, MDPC/DD in France, MABT/MBT in Italy, DNP in USSR.[40][41]

During WW1, 36 munition factory workers in France and 27 in US lost their lives through DNP poisoning.[42]

Three fatalities were reported in dyes factories, where DNP was used to make sulphur black dye.[43]

DNP was used extensively in diet pills from 1933 to 1938 after Cutting and Tainter at Stanford University made their first report on how the compound substantially increased metabolic rate.[44][45] This effect occurs via DNP acting as a proton ionophore. After only its first year on the market, Tainter estimated that at least 100,000 people had been treated with DNP in the United States, in addition to many others abroad.[46]

In light of the adverse effects and fatal hyperthermia caused by DNP when it was used clinically, the dose was slowly titrated according to personal tolerance, which varies greatly.[47] Concerns about dangerous side-effects and rapidly developing cataracts[48] resulted in DNP being discontinued in the United States by the end of 1938.[49]

"In studies of intermediate-duration oral exposure to 2,4-DNP, cases of death from agranulocytosis (described in the discussion of Hematological Effects) have been attributed to 2,4-DNP. These cases occurred during the usual dosing regimens for weight loss, employing increasing doses in one case from 2.9 to 4.3 mg/kg/day of 2,4-DNP for 6 weeks (Dameshek and Gargill 1934); a dose of 1.03 mg/kg/day 2,4-DNP for 46 days in another case (Goldman and Haber 1936); and in another, from 0.62 to 3.8 mg/kg/day 2,4-DNP as sodium 2,4-DNP for 41 days (Silver 1934). In all cases, the patients were under medical supervision."[50]

DNP, however, continues to be used by some bodybuilders and athletes to rapidly lose body fat. Fatal overdoses include cases of accidental exposure,[51] suicide,[18][19][52] and excessive intentional exposure (overdose).[19][53][54] The substance's use as a dieting aid has also led to a number of accidental fatalities,[53][55][56][57][58][59] including 25 confirmed DNP-related deaths in UK since 2007.[60] Annual Reports of the American Association of Poison Control Centers identifies 15 DNP poisoning fatalities between 2013 and 2017 in US.[61] Swedish Poisons Information Centre has reported three fatal DNP cases between June 2012 and May 2013. “Forensic analysis of DNP is not routinely performed so the true number of DNP deaths may be higher.”[62] DNP may not be detected in post mortem blood samples.[28][63]

In 2003, a vendor of DNP was sentenced to prison for mail fraud, with the FDA's OCI investigators having gathered evidence that the vendor's encapsulation of DNP was neither accurate nor sanitary.[64] In 2018, a seller in United Kingdom was convicted of manslaughter for selling DNP as "fatburner" for human consumption.[65][66] In 2019, a company selling DNP in the UK was found "guilty of placing an unsafe food product on to the market" and fined £100,000. Director of the company was given suspended prison sentence.[67] The seller in California was sentenced to three years in prison for selling DNP as a diet pills.[68]

ReferencesEdit

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Further readingEdit

External linksEdit