Acrylonitrile

Last updated
Acrylonitrile
Structural formula of acrylonitrile.svg
Acrylonitrile-2D-skeletal.svg
Acrylonitrile-3D-balls.png
Acrylonitrile-3D-vdW.png
Names
Preferred IUPAC name
Prop-2-enenitrile
Other names
Acrylonitrile
2-Propenenitrile
Cyanoethene
Vinyl cyanide (VCN)
Cyanoethylene [1]
Propenenitrile [1]
Vinyl nitrile
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.152 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 608-003-00-4
KEGG
PubChem CID
RTECS number
  • AT5250000
UNII
UN number 1093
  • InChI=1S/C3H3N/c1-2-3-4/h2H,1H2 Yes check.svgY
    Key: NLHHRLWOUZZQLW-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C3H3N/c1-2-3-4/h2H,1H2
    Key: NLHHRLWOUZZQLW-UHFFFAOYAG
  • N#CC=C
Properties
C3H3N
Molar mass 53.064 g·mol−1
AppearanceColourless liquid
Density 0.81 g/cm3
Melting point −84 °C (−119 °F; 189 K)
Boiling point 77 °C (171 °F; 350 K)
70 g/L
log P 0.19 [2]
Vapor pressure 83 mmHg [1]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 flammable
reactive
toxic
potential occupational carcinogen [1]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 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. gasolineInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
4
3
2
Flash point −1 °C; 30 °F; 272 K
471 °C (880 °F; 744 K)
Explosive limits 3–17%
Lethal dose or concentration (LD, LC):
500 ppm (rat, 4 h)
313 ppm (mouse, 4 h)
425 ppm (rat, 4 h) [3]
260 ppm (rabbit, 4 h)
575 ppm (guinea pig, 4 h)
636 ppm (rat, 4 h)
452 ppm (human, 1 h) [3]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 2 ppm C 10 ppm [15-minute] [skin] [1]
REL (Recommended)
Ca TWA 1 ppm C 10 ppm [15-minute] [skin] [1]
IDLH (Immediate danger)
85 ppm [1]
Safety data sheet (SDS) ICSC 0092
Related compounds
Related nitriles
acetonitrile
propionitrile
Related compounds
 acrylic acid
acrolein
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Acrylonitrile is an organic compound with the formula CH2CHCN and the structure H2C=CH−C≡N. It is a colorless, volatile liquid. It has a pungent odor of garlic or onions. [4] Its molecular structure consists of a vinyl group (−CH=CH2) linked to a nitrile (−C≡N). It is an important monomer for the manufacture of useful plastics such as polyacrylonitrile. It is reactive and toxic at low doses. [5]

Contents

Acrylonitrile is one of the components of ABS plastic (Acrylonitrile butadiene styrene). [6]

Structure and basic properties

Acrylonitrile is an organic compound with the formula CH2CHCN and the structure H2C=CH−C≡N. It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. [4] Its molecular structure consists of a vinyl group (−CH=CH2) linked to a nitrile (−C≡N). It is an important monomer for the manufacture of useful plastics such as polyacrylonitrile. It is reactive and toxic at low doses. [5]

Production

Acrylonitrile was first synthesized by the French chemist Charles Moureu in 1893. [7] Acrylonitrile is produced by catalytic ammoxidation of propylene, also known as the SOHIO process. In 2002, world production capacity was estimated at 5 million tonnes per year, [5] [8] rising to about 6 million tonnes by 2017. [9] Acetonitrile and hydrogen cyanide are significant byproducts that are recovered for sale. [5] In fact, the 2008–2009 acetonitrile shortage was caused by a decrease in demand for acrylonitrile. [10]

2 CH3−CH=CH2 + 2 NH3 + 3 O2 → 2 CH2=CH−C≡N + 6 H2O

In the SOHIO process, propylene, ammonia, and air (oxidizer) are passed through a fluidized bed reactor containing the catalyst at 400–510 °C and 50–200 kPag. The reactants pass through the reactor only once, before being quenched in aqueous sulfuric acid. Excess propylene, carbon monoxide, carbon dioxide, and dinitrogen that do not dissolve are vented directly to the atmosphere, or are incinerated. The aqueous solution consists of acrylonitrile, acetonitrile, hydrocyanic acid, and ammonium sulfate (from excess ammonia). A recovery column removes bulk water, and acrylonitrile and acetonitrile are separated by distillation. One of the first useful catalysts was bismuth phosphomolybdate (Bi9PMo12O52) supported on silica. [11] Further improvements have since been made. [5]

Alternative routes

Various green chemistry routes to acrylonitrile are being explored from renewable feedstocks, such as lignocellulosic biomass, glycerol (from biodiesel production), or glutamic acid (which can itself be produced from renewable feedstocks). The lignocellulosic route involves fermentation of the biomass to propionic acid and 3-hydroxypropionic acid, which are then converted to acrylonitrile by dehydration and ammoxidation. [12] [9] The glycerol route begins with its dehydration to acrolein, which undergoes ammoxidation to give acrylonitrile. [13] The glutamic acid route employs oxidative decarboxylation to 3-cyanopropanoic acid, followed by a decarbonylation-elimination to acrylonitrile. [14] Of these, the glycerol route is broadly considered to be the most viable, although none of these green methods are commercially competitive. [12] [13]

Uses

Acrylonitrile is used principally as a monomer to prepare polyacrylonitrile, a homopolymer, or several important copolymers, such as styrene-acrylonitrile (SAN), acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), and other synthetic rubbers such as acrylonitrile butadiene (NBR). Hydrodimerization of acrylonitrile [15] [16] affords adiponitrile, used in the synthesis of certain nylons:

2 CH2=CHCN + 2 e− + 2 H+ → NCCH2−CH2−CH2−CH2CN

Acrylonitrile is also a precursor in the manufacture of acrylamide and acrylic acid. [5]

Synthesis of chemicals

Hydrogenation of acrylonitrile is one route to propionitrile. Hydrolysis with sulfuric acid gives acrylamide sulfate, CH=CHC(O)NH2·H2SO4. This salt can be converted to acrylamide with treatment with base or to methyl acrylate by treatment with methanol. [5]

The reaction of acrylonitrile with protic nucleophiles is a common route to a variety of specialty chemicals. The process is called cyanoethylation:

YH + H2C=CHCN → Y−CH2−CH2CN

Typical protic nucleophiles are alcohols, thiols, and especially amines. [17]

Acrylonitrile and derivatives, such as 2-chloroacrylonitrile, are dienophiles in Diels–Alder reactions.

Health effects

Acrylonitrile is moderately toxic with LD50 = 81 mg/kg (rats). It undergoes explosive polymerization. The burning material releases fumes of hydrogen cyanide and oxides of nitrogen. It is classified as a Class 2B carcinogen (possibly carcinogenic) by the International Agency for Research on Cancer (IARC), [18] and workers exposed to high levels of airborne acrylonitrile are diagnosed more frequently with lung cancer than the rest of the population. [19] Acrylonitrile is one of seven toxicants in cigarette smoke that are most associated with respiratory tract carcinogenesis. [20] The mechanism of action of acrylonitrile appears to involve oxidative stress and oxidative DNA damage. [21] Acrylonitrile increases cancer in high dose tests in male and female rats and mice [22] and induces apoptosis in human umbilical cord mesenchymal stem cells. [23]

It evaporates quickly at room temperature (20 °C) to reach dangerous concentrations; skin irritation, respiratory irritation, and eye irritation are the immediate effects of this exposure. [24] Pathways of exposure for humans include emissions, auto exhaust, and cigarette smoke that can expose the human subject directly if they inhale or smoke. Routes of exposure include inhalation, oral, and to a certain extent dermal uptake (tested with volunteer humans and in rat studies). [25] Repeated exposure causes skin sensitization and may cause central nervous system and liver damage. [24]

There are two main excretion processes of acrylonitrile. The primary method is excretion in urine when acrylonitrile is metabolized by being directly conjugated to glutathione. The other method is when acrylonitrile is enzymatically converted into 2-cyanoethylene oxide which will produce cyanide end products that ultimately form thiocyanate, which is excreted via urine. [25] Exposure can thus be detected via blood draws and urine sampling. [18]

Incidents

A large amount of acrylonitrile (approximately 6500 tons) leaked from an industrial polymer plant owned by Aksa Akrilik after the violent 17 August earthquake in Turkey. Over 5000 people were affected and the exposed animals had died. [26] The leak was only noticed by the company 8 hours after the incident. Healthcare workers did not know about the health effects of acrylonitrile and tried to treat the victims with painkillers and IV fluids. [27] One lawyer, Ayşe Akdemir, sued the company with 44 families as the plaintiffs. [27] Aksa Akrilik was sued by 200 residents who were affected by acrylonitrile. [28] An increase in cancer cases in the area was confirmed by the Turkish Medical Association, [28] as the cancer rate in the affected area has increased by 80%, from 1999 to April 2002. [27] In 2003, the owner of Aksa Akrilik has died from lung cancer related to acrylonitrile exposure. [27] As of 2001, this is the largest acrylonitrile leak known. [26]

Occurrence

Acrylonitrile is not naturally formed on Earth. It has been detected at the sub-ppm level at industrial sites. It persists in the air for up to a week. It decomposes by reacting with oxygen and hydroxyl radical to form formyl cyanide and formaldehyde. [29] Acrylonitrile is harmful to aquatic life. [24] Acrylonitrile has been detected in the atmosphere of Titan, a moon of Saturn. [30] [31] [32] Computer simulations suggest that on Titan conditions exist such that the compound could form structures similar to cell membranes and vesicles on Earth, called azotosomes. [30] [31]

Related Research Articles

Acrylamide (or acrylic amide) is an organic compound with the chemical formula CH2=CHC(O)NH2. It is a white odorless solid, soluble in water and several organic solvents. From the chemistry perspective, acrylamide is a vinyl-substituted primary amide (CONH2). It is produced industrially mainly as a precursor to polyacrylamides, which find many uses as water-soluble thickeners and flocculation agents.

Acetonitrile, often abbreviated MeCN, is the chemical compound with the formula CH3CN and structure H3C−C≡N. This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture. It is used as a polar aprotic solvent in organic synthesis and in the purification of butadiene. The N≡C−C skeleton is linear with a short C≡N distance of 1.16 Å.

<span class="mw-page-title-main">Styrene</span> Chemical compound

Styrene is an organic compound with the chemical formula C6H5CH=CH2. Its structure consists of a vinyl group as substituent on benzene. Styrene is a colorless, oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concentrations have a less pleasant odor. Styrene is the precursor to polystyrene and several copolymers, and is typically made from benzene for this purpose. Approximately 25 million tonnes of styrene were produced in 2010, increasing to around 35 million tonnes by 2018.

<span class="mw-page-title-main">Ethylene oxide</span> Cyclic compound (C2H4O)

Ethylene oxide is an organic compound with the formula C2H4O. It is a cyclic ether and the simplest epoxide: a three-membered ring consisting of one oxygen atom and two carbon atoms. Ethylene oxide is a colorless and flammable gas with a faintly sweet odor. Because it is a strained ring, ethylene oxide easily participates in a number of addition reactions that result in ring-opening. Ethylene oxide is isomeric with acetaldehyde and with vinyl alcohol. Ethylene oxide is industrially produced by oxidation of ethylene in the presence of a silver catalyst.

<span class="mw-page-title-main">Butadiene</span> Chemical compound

1,3-Butadiene is the organic compound with the formula CH2=CH-CH=CH2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two vinyl groups. It is the simplest conjugated diene.

<span class="mw-page-title-main">Propylene oxide</span> Chemical compound

Propylene oxide is an acutely toxic and carcinogenic organic compound with the molecular formula CH3CHCH2O. This colourless volatile liquid with an odour similar to ether, is produced on a large scale industrially. Its major application is its use for the production of polyether polyols for use in making polyurethane plastics. It is a chiral epoxide, although it is commonly used as a racemic mixture.

In organic chemistry, a nitrile is any organic compound that has a −C≡N functional group. The name of the compound is composed of a base, which includes the carbon of the −C≡N, suffixed with "nitrile", so for example CH3CH2C≡N is called "propionitrile". The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.

<span class="mw-page-title-main">Acrylic acid</span> Chemical compound

Acrylic acid (IUPAC: propenoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a characteristic acrid or tart smell. It is miscible with water, alcohols, ethers, and chloroform. More than a million tons are produced annually.

In organic chemistry, hydrocyanation is a process for conversion of alkenes to nitriles. The reaction involves the addition of hydrogen cyanide and requires a catalyst. This conversion is conducted on an industrial scale for the production of precursors to nylon.

<span class="mw-page-title-main">Methyl methacrylate</span> Chemical compound

Methyl methacrylate (MMA) is an organic compound with the formula CH2=C(CH3)COOCH3. This colorless liquid, the methyl ester of methacrylic acid (MAA), is a monomer produced on a large scale for the production of poly(methyl methacrylate) (PMMA).

Bromoethane, also known as ethyl bromide, is a chemical compound of the haloalkanes group. It is abbreviated by chemists as EtBr. This volatile compound has an ether-like odor.

<span class="mw-page-title-main">Adiponitrile</span> Chemical compound

Adiponitrile is an organic compound with the chemical formula (CH2)4(CN)2. This viscous, colourless dinitrile is an important precursor to the polymer nylon 66. In 2005, about one million tonnes of adiponitrile were produced.

In electrochemistry, electrosynthesis is the synthesis of chemical compounds in an electrochemical cell. Compared to ordinary redox reactions, electrosynthesis sometimes offers improved selectivity and yields. Electrosynthesis is actively studied as a science and also has industrial applications. Electrooxidation has potential for wastewater treatment as well.

<span class="mw-page-title-main">Ethyl acrylate</span> Chemical compound

Ethyl acrylate is an organic compound with the formula CH2CHCO2CH2CH3. It is the ethyl ester of acrylic acid. It is a colourless liquid with a characteristic acrid odor. It is mainly produced for paints, textiles, and non-woven fibers. It is also a reagent in the synthesis of various pharmaceutical intermediates.

<span class="mw-page-title-main">Aksa (company)</span> Turkish company

Aksa is a Turkish company manufacturing carbon fiber, natural white and solution dyed acrylic staple fiber, tow and tops for yarn spinning and non-wovens. Established in 1968 in Yalova, Turkey, the company is the world's largest producer under one roof, with an annual production capacity of 308,000 tons.

<span class="mw-page-title-main">Ammoxidation</span> Chemical process for producing nitriles from ammonia and oxygen

In organic chemistry, ammoxidation is a process for the production of nitriles using ammonia and oxygen. It is sometimes called the SOHIO process, acknowledging that ammoxidation was developed at Standard Oil of Ohio. The usual substrates are alkenes. Several million tons of acrylonitrile are produced in this way annually:

Methacrylonitrile, MeAN in short, is a chemical compound that is an unsaturated aliphatic nitrile, widely used in the preparation of homopolymers, copolymers, elastomers, and plastics and as a chemical intermediate in the preparation of acids, amides, amines, esters, and other nitriles. MeAN is also used as a replacement for acrylonitrile in the manufacture of an acrylonitrile/butadiene/styrene-like polymer. It is a clear and colorless liquid, that has a bitter almond smell.

Propionitrile, also known as ethyl cyanide and propanenitrile, is an organic compound with the formula CH3CH2CN. It is a simple aliphatic nitrile. The compound is a colourless, water-soluble liquid. It is used as a solvent and a precursor to other organic compounds.

<span class="mw-page-title-main">Glycidamide</span> Chemical compound

Glycidamide is an organic compound with the formula H2NC(O)C2H3O. It is a colorless, oil. Structurally, it contains adjacent amides and epoxide functional groups. It is a bioactive, potentially toxic or even carcinogenic metabolite of acrylonitrile and acrylamide. It is a chiral molecule.

<span class="mw-page-title-main">Charles Moureu</span> French chemist (1863–1929)

François Charles Léon Moureu was a French organic chemist and pharmacist. In 1902 Charles Moureu published Notions fondamentales de chimie organique, translated into English as Fundamental principles of organic chemistry (1921).

References

  1. 1 2 3 4 5 6 7 NIOSH Pocket Guide to Chemical Hazards. "#0014". National Institute for Occupational Safety and Health (NIOSH).
  2. ↑ "Acrylonitrile_msds".
  3. 1 2 "Acrylonitrile". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. 1 2 "Medical Management Guidelines for Acrylonitrile". Agency for Toxic Substances & Disease Registry. Retrieved 2020-06-10.
  5. 1 2 3 4 5 6 7 Brazdil, James F. "Acrylonitrile". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_177.pub3. ISBN   978-3527306732.
  6. ↑ Campo, E. Alfredo (2008-01-01), Campo, E. Alfredo (ed.), "1 - Polymeric Materials and Properties", Selection of Polymeric Materials, Plastics Design Library, Norwich, NY: William Andrew Publishing, pp. 1–39, doi:10.1016/b978-081551551-7.50003-6, ISBN   978-0-8155-1551-7 , retrieved 2023-11-20
  7. ↑
  8. ↑ "The Sohio Acrylonitrile Process". American Chemical Society National Historic Chemical Landmarks. Archived from the original on 2013-02-23. Retrieved 2013-05-13.
  9. 1 2 Davey, Stephen G. (January 2018). "Sustainability: Sweet new route to acrylonitrile". Nature Reviews Chemistry. 2 (1): 0110. doi: 10.1038/s41570-017-0110 .
  10. ↑ Tullo, A. (2008). "A Solvent Dries Up". Chemical & Engineering News. 86 (47): 27. doi:10.1021/cen-v086n047.p027.
  11. ↑ Grasselli, Robert K. (2014). "Site isolation and phase cooperation: Two important concepts in selective oxidation catalysis: A retrospective". Catalysis Today. 238: 10–27. doi:10.1016/j.cattod.2014.05.036.
  12. 1 2 Grasselli, Robert K.; Trifirò, Ferruccio (2016). "Acrylonitrile from Biomass: Still Far from Being a Sustainable Process". Topics in Catalysis. 59 (17–18): 1651–1658. doi:10.1007/s11244-016-0679-7. ISSN   1022-5528. S2CID   99550463.
  13. 1 2 Guerrero-Pérez, M. Olga; Bañares, Miguel A. (2015). "Metrics of acrylonitrile: From biomass vs. petrochemical route". Catalysis Today. 239: 25–30. doi:10.1016/j.cattod.2013.12.046. ISSN   0920-5861.
  14. ↑ Le Nôtre, Jérôme; Scott, Elinor L.; Franssen, Maurice C. R.; Sanders, Johan P. M. (2011). "Biobased synthesis of acrylonitrile from glutamic acid". Green Chemistry. 13 (4): 807. doi:10.1039/c0gc00805b. ISSN   1463-9262.
  15. ↑ Ellis, Paul G (1972). A radiation-chemical study of the hydrodimerisation of acrylonitrile. UK: Leeds University, Ph D thesis.
  16. ↑ Buxton, George V.; Ellis, Paul G.; McKillop, Thomas F.W. (1979). "Pulse radiolysis study of acrylonitrile in aqueous solution". J. Chem. Soc., Faraday Trans. 1. 75: 1050. doi:10.1039/f19797501050.
  17. ↑ Eller, Karsten; Henkes, Erhard; Rossbacher, Roland; Höke, Hartmut (2000). "Amines, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a02_001. ISBN   978-3527306732.
  18. 1 2 "Re-evaluation of Some Organic Chemicals, Hydrazine and Hydrogen Peroxide". IARC Monographs, Volume 71 (1999)
  19. ↑ Acrylonitrile Fact Sheet (CAS No. 107-13-1). epa.gov
  20. ↑ Cunningham FH, Fiebelkorn S, Johnson M, Meredith C. A novel application of the Margin of Exposure approach: segregation of tobacco smoke toxicants. Food Chem Toxicol. 2011 Nov;49(11):2921-33. doi: 10.1016/j.fct.2011.07.019. Epub 2011 Jul 23. PMID   21802474
  21. ↑ Pu X, Kamendulis LM, Klaunig JE. Acrylonitrile-induced oxidative stress and oxidative DNA damage in male Sprague-Dawley rats. Toxicol Sci. 2009;111(1):64-71. doi:10.1093/toxsci/kfp133
  22. ↑ "Acrylonitrile: Carcinogenic Potency Database".
  23. ↑ Sun, X. (January 2014). "Cytotoxic effects of acrylonitrile on human umbilical cord mesenchymal stem cells in vitro". Molecular Medicine Reports. 9 (1): 97–102. doi: 10.3892/mmr.2013.1802 . PMID   24248151.
  24. 1 2 3 "CDC – Acrylonitrile – International Chemical Safety Cards". www.cdc.gov. NIOSH. Retrieved 2015-07-31.
  25. 1 2 Acrylonitrile Fact Sheet: Support Document (CAS No. 107-13-1). epa.gov
  26. 1 2 Nadi Bakırcı (2001). "ENDÜSTRİYEL BİR ÇEVRE FELAKETİ: AKRİLONİTRİL" [AN INDUSTRIAL ENVIRONMENT DISASTER: ACRYLONITRILE]. Turkish Medical Association.
  27. 1 2 3 4 Fatma Dalokay (30 November 2020). "17 Ağustos 1999 Depremi: Akrilonitril Zehirlenmesi" [17 August 1999 Earthquake: Acrylonitrile Poisoning]. Tabella.
  28. 1 2 "İSO'nun şaşırtan çevre ödülü Aksa'nın". Hürriyet . 26 June 2005.
  29. ↑ Grosjean, Daniel (December 1990). "Atmospheric Chemistry of Toxic Contaminants. 3. Unsaturated Aliphatics: Acrolein, Acrylonitrile, Maleic Anhydride". Journal of the Air & Waste Management Association. 40 (12): 1664–1669. Bibcode:1990JAWMA..40.1664G. doi:10.1080/10473289.1990.10466814.
  30. 1 2 Wall, Mike (28 July 2017). "Saturn Moon Titan Has Molecules That Could Help Make Cell Membranes". Space.com . Retrieved 29 July 2017.
  31. 1 2 Palmer, Maureen Y.; et al. (28 July 2017). "ALMA detection and astrobiological potential of vinyl cyanide on Titan". Science Advances . 3 (7): e1700022. Bibcode:2017SciA....3E0022P. doi:10.1126/sciadv.1700022. PMC   5533535 . PMID   28782019.
  32. ↑ Kaplan, Sarah (8 August 2017). "This weird moon of Saturn has some essential ingredients for life". The Washington Post . Retrieved 8 August 2017.
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