Ethylene oxide

"Oxirane" redirects here. For oxiranes as a class of molecules, seeepoxide.

Not to be confused withEthylene dioneorEthyl oxide.

Ethylene oxide

Names
Preferred IUPAC name Oxirane
Systematic IUPAC name Epoxyethane Oxacyclopropane
Other names Ethylene oxide Dimethylene oxide 1,2-Epoxyethane [3]-crown-1 Epoxide
Identifiers
CAS Number	75-21-8Y
3D model (JSmol)	Interactive image
Abbreviations	EO, EtO
Beilstein Reference	102378
ChEBI	CHEBI:27561Y
ChEMBL	ChEMBL1743219
ChemSpider	6114Y
ECHA InfoCard	100.000.773
EC Number	200-849-9
Gmelin Reference	676
KEGG	D03474Y
MeSH	Ethylene+Oxide
PubChemCID	6354
RTECS number	KX2450000
UNII	JJH7GNN18PY
UN number	1040
CompTox Dashboard(EPA)	DTXSID0020600
InChI InChI=1S/C2H4O/c1-2-3-1/h1-2H2Y Key: IAYPIBMASNFSPL-UHFFFAOYSA-NY InChI=1/C2H4O/c1-2-3-1/h1-2H2 Key: IAYPIBMASNFSPL-UHFFFAOYAX
SMILES O1CC1
Properties
Chemical formula	C2H4O
Molar mass	44.052g·mol−1
Appearance	Colorless gas
Odor	Like diethyl ether
Density	0.8821g·cm−3
Melting point	−112.46 °C (−170.43 °F; 160.69 K)
Boiling point	10.4 °C (50.7 °F; 283.5 K)
Solubility in water	Miscible
Vapor pressure	1.46atm (20°C)
Magnetic susceptibility(χ)	−30.5·10−6cm3/mol
Refractive index(nD)	1.3597 (589nm)
Dipole moment	1.94D
Thermochemistry
Heat capacity(C)	47.9J·mol−1·K−1
Std molar entropy(S⦵298)	242.5J·mol−1·K−1
Std enthalpy of formation(ΔfH⦵298)	−52.6kJ·mol−1
Gibbs free energy(ΔfG⦵)	−13.0kJ·mol−1
Hazards
Occupational safety and health(OHS/OSH):
Main hazards	Carcinogen Extremely flammable
GHSlabelling:
Pictograms
Hazard statements	H220,H230,H301,H314,H331,H335,H336,H340,H350,H360FD,H372
Precautionary statements	P202,P210,P260,P280,P301+P310+P330,P303+P361+P353,P305+P351+P338+P310,P410+P403
NFPA 704(fire diamond)	3 4 3
Flash point	−20 °C (−4 °F; 253 K)
Autoignition temperature	429 °C (804 °F; 702 K)
Explosive limits	3 to 100%
Lethal doseor concentration (LD, LC):
LC50(median concentration)	836ppm (mouse, 4hr) 4000ppm (rat, 4hr) 800ppm (rat, 4hr) 819ppm (guinea pig, 4hr) 1460ppm (rat, 4hr) 835ppm (mouse, 4hr) 960ppm (dog, 4hr)
NIOSH(US health exposure limits):
PEL(Permissible)	TWA 1ppm 5ppm [15-minute excursion]
REL(Recommended)	Ca TWA <0.1ppm (0.18mg/m3) C 5ppm (9mg/m3) [10-min/day]
IDLH(Immediate danger)	Ca [800ppm]
Safety data sheet(SDS)	ICSC 0155
Related compounds
Related heterocycles	Aziridine, Thiirane, Borirane
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa). Yverify(what isYN?) Infobox references

Ethylene oxideis anorganic compoundwith theformulaC₂H₄O.It is a cyclicetherand the simplestepoxide:a three-memberedringconsisting of oneoxygenatom and twocarbonatoms. Ethylene oxide is a colorless andflammablegas with a faintly sweet odor. Because it is astrained ring,ethylene oxide easily participates in a number ofaddition reactionsthat result in ring-opening. Ethylene oxide isisomericwithacetaldehydeand withvinyl alcohol.Ethylene oxide is industrially produced byoxidationofethylenein the presence of asilvercatalyst.

The reactivity that is responsible for many of ethylene oxide's hazards also makes it useful. Although too dangerous for direct household use and generally unfamiliar to consumers, ethylene oxide is used for making many consumer products as well as non-consumer chemicals and intermediates. These products include detergents, thickeners, solvents, plastics, and various organic chemicals such asethylene glycol,ethanolamines, simple and complexglycols,polyglycol ethers,and other compounds. Although it is a vital raw material with diverse applications, including the manufacture of products likepolysorbate 20andpolyethylene glycol(PEG) that are often more effective and less toxic than alternative materials, ethylene oxide itself is a very hazardous substance. At room temperature it is a very flammable,carcinogenic,mutagenic,irritating; andanaestheticgas.

Ethylene oxide is a surfacedisinfectantthat is widely used in hospitals and the medical equipment industry toreplace steam in the sterilizationof heat-sensitive tools and equipment, such as disposable plastic syringes.It is so flammable and extremely explosive that it is used as a main component ofthermobaric weapons;therefore, it is commonly handled and shipped as a refrigerated liquid to control its hazardous nature.

History

Ethylene oxide was first reported in 1859 by theFrenchchemistCharles-Adolphe Wurtz,who prepared it by treating2-chloroethanolwithpotassium hydroxide:

${\ce {Cl-CH2CH2-OH + KOH -> (CH2CH2)O + KCl + H2O}}$

Wurtz measured theboiling pointof ethylene oxide as 13.5 °C (56.3 °F), slightly higher than the present value, and discovered the ability of ethylene oxide to react with acids and salts of metals.Wurtz mistakenly assumed that ethylene oxide has the properties of an organic base. This misconception persisted until 1896, whenGeorg Bredigfound that ethylene oxide is not anelectrolyte.That it differed from otherethers— particularly by its propensity to engage in the addition reactions typical ofunsaturated compounds— had long been a matter of debate. The heterocyclic triangular structure of ethylene oxide was proposed by 1868 or earlier.

Wurtz's 1859 synthesis long remained the only method of preparing ethylene oxide, despite numerous attempts, including by Wurtz himself, to produce ethylene oxide directly fromethylene.Only in 1931 did French chemist Theodore Lefort develop a method of direct oxidation of ethylene in the presence ofsilvercatalyst.Since 1940, almost all industrial production of ethylene oxide has relied on this process.Sterilization by ethylene oxide for the preservation ofspiceswas patented in 1938 by theAmericanchemistLloyd Hall.Ethylene oxide achieved industrial importance duringWorld War Ias a precursor to both the coolantethylene glycoland thechemical weaponmustard gas.

Molecular structure and properties

Condensed ethylene oxide

The epoxy cycle of ethylene oxide is an almost regular triangle with bond angles of about 60° and a significant angularstraincorresponding to the energy of 105 kJ/mol.For comparison, inalcoholsthe C–O–H angle is about 110°; inethers,the C–O–C angle is 120°. Themoment of inertiaabout each of the principal axes areI_A=32.921×10⁻⁴⁰g·cm²,I_B=37.926×10⁻⁴⁰g·cm²andI_C=59.510×10⁻⁴⁰g·cm².

The relative instability of the carbon-oxygen bonds in the molecule is revealed by the comparison in the table of the energy required to break two C–O bonds in the ethylene oxide or one C–O bond inethanolanddimethyl ether:

Reaction	ΔH°298,kJ/mol	Method
(C2H4)O → C2H4+ O(cleavage of two bonds)	354.38	Calculated, from atomic enthalpies
C2H5OH→ C2H5+ OH(breaking one bond)	405.85	Electron impact
CH3OCH3→ CH3O + CH3(breaking one bond)	334.72	Calculated using enthalpies of radicals formation

This instability correlates with its high reactivity, explaining the ease of itsring-opening reactions(seeChemical properties).

Physical properties

Ethylene oxide is a colorless gas at 25 °C (77 °F) and is a mobile liquid at 0 °C (32 °F) – viscosity of liquid ethylene oxide at 0 °C is about 5.5 times lower than that of water. The gas has a characteristic sweet odor of ether, noticeable when its concentration in air exceeds 500ppm.Ethylene oxide is readily soluble in water,ethanol,diethyl ether,and many organic solvents.

Main thermodynamical constants are:

• Thesurface tensionof liquid ethylene oxide, at the interface with its own vapor, is 35.8 mJ/m²(0.00079 cal/sq ft) at −50.1 °C (−58.2 °F) and 27.6 mJ/m²(0.00061 cal/sq ft) at −0.1 °C (31.8 °F).
• The boiling point increases with the vapor pressure as follows:57.7 °C (135.9 °F) (2 atm (200 kPa; 29 psi)), 83.6 °C (182.5 °F) (5 atm (510 kPa; 73 psi)), and 114.0 °C (237.2 °F) (10 atm (1,000 kPa; 150 psi)).
• Viscositydecreases with temperature with the values of 0.577kPa·s at −49.8 °C (−57.6 °F), 0.488 kPa·s at −38.2 °C (−36.8 °F), 0.394kPa·s at −21.0 °C (−5.8 °F), and 0.320kPa·s at 0 °C (32 °F).

Between −91 and 10.5 °C (−131.8 and 50.9 °F), vapor pressurep(in mmHg) varies with temperature (Tin °C) as

$\lg p=6.251-{\frac {1115.1}{244.14+T}}$.

Properties of liquid ethylene oxide

Temperature, °C	Vapor pressure, kPa	Enthalpy of the liquid, J/g	Enthalpy of vaporization, J/g	Density, kg/L	Heat capacity,J/(kg·K)	Thermal conductivity,W/(m·K)
−40	8.35	0	628.6	0.9488	1878	0.20
−20	25.73	38.8	605.4	0.9232	1912	0.18
0	65.82	77.3	581.7	0.8969	1954	0.16
20	145.8	115.3	557.3	0.8697	2008	0.15
40	288.4	153.2	532.1	0.8413	2092	0.14
60	521.2	191.8	505.7	0.8108	2247	0.14
80	875.4	232.6	477.4	0.7794	2426	0.14
100	1385.4	277.8	445.5	0.7443	2782	0.13
120	2088	330.4	407.5	0.7052	3293	N/A*
140	3020	393.5	359.4	0.6609	4225	N/A
160	4224	469.2	297.1	0.608	N/A	N/A
180	5741	551.2	222.5	0.533	N/A	N/A
195.8	7191	N/A	N/A	N/A	N/A	N/A

*N/A – data not available.

Properties of ethylene oxide vapor

Temperature, K	Entropy, J/(mol·K)	Heat of formation, kJ/mol	Free energy of formation, kJ/mol	Viscosity, μPa·s	Thermal conductivity, W/(m·K)	Heat capacity, J/(mol·K)
298	242.4	−52.63	−13.10	N/A	N/A	48.28
300	242.8	−52.72	−12.84	9.0	0.012	48.53
400	258.7	−56.53	1.05	13.5	0.025	61.71
500	274.0	−59.62	15.82	15.4	0.038	75.44
600	288.8	−62.13	31.13	18.2	0.056	86.27
700	302.8	−64.10	46.86	20.9	0.075	95.31
800	316.0	−65.61	62.80	N/A	0.090	102.9

*N/A – data not available.

Chemical properties

Ethylene oxide readily reacts with diverse compounds with opening of the ring. Its typical reactions are with nucleophiles which proceed via theS_N2mechanism both in acidic (weak nucleophiles: water, alcohols) and alkaline media (strong nucleophiles: OH⁻,RO⁻,NH₃,RNH₂,RR'NH, etc.).The general reaction scheme is

and more specific reactions are described below.

Addition of water and alcohols

Aqueous solutions of ethylene oxide are rather stable and can exist for a long time without any noticeable chemical reaction. However adding a small amount of acid, such as strongly dilutedsulfuric acid,immediately leads to the formation ofethylene glycol,even at room temperature:

(CH₂CH₂)O + H₂O → HO–CH₂CH₂–OH

The reaction also occurs in the gas phase, in the presence of aphosphoric acidsalt as a catalyst.

The reaction is usually carried out at about 60 °C (140 °F) with a large excess of water, in order to prevent the reaction of the formed ethylene glycol with ethylene oxide that would formdi-andtriethylene glycol:

2 (CH₂CH₂)O + H₂O → HO–CH₂CH₂–O–CH₂CH₂–OH

3 (CH₂CH₂)O + H₂O → HO–CH₂CH₂–O–CH₂CH₂–O–CH₂CH₂–OH

The use of alkaline catalysts may lead to the formation ofpolyethylene glycol:

n (CH₂CH₂)O + H₂O → HO–(–CH₂CH₂–O–)_n–H

Reactions withalcoholsproceed similarly yielding ethylene glycol ethers:

(CH₂CH₂)O + C₂H₅OH → HO–CH₂CH₂–OC₂H₅

2 (CH₂CH₂)O + C₂H₅OH → HO–CH₂CH₂–O–CH₂CH₂–OC₂H₅

Reactions with lower alcohols occur less actively than with water and require more severe conditions, such as heating to 160 °C (320 °F) and pressurizing to 3 MPa (440 psi) and adding an acid or alkali catalyst.

Reactions of ethylene oxide with fatty alcohols proceed in the presence ofsodiummetal,sodium hydroxide,orboron trifluorideand are used for the synthesis ofsurfactants.

Addition of carboxylic acids and their derivatives

Reactions of ethylene oxide withcarboxylic acidsin the presence of a catalyst results in glycol mono- and diesters:

(CH₂CH₂)O + CH₃CO₂H → HOCH₂CH₂–O₂CCH₃

(CH₂CH₂)O + (CH₃CO)₂O → CH₃CO₂CH₂CH₂O₂CCH₃

The addition of acidamidesproceeds similarly:

(CH₂CH₂)O + CH₃CONH₂→ HOCH₂CH₂NHC(O)CH₃

Addition of ethylene oxide to higher carboxylic acids is carried out at elevated temperatures (typically 140–180 °C (284–356 °F)) and pressure (0.3–0.5 MPa (44–73 psi)) in an inert atmosphere, in presence of an alkaline catalyst (concentration 0.01–2%), such as hydroxide or carbonate of sodium or potassium.The carboxylate ion acts asnucleophilein the reaction:

(CH₂CH₂)O + RCO₂⁻→ RCO₂CH₂CH₂O⁻

RCO₂CH₂CH₂O⁻+ RCO₂H → RCO₂CH₂CH₂OH + RCO₂⁻

Adding ammonia and amines

Ethylene oxide reacts withammoniaforming a mixture of mono-, di-, and tri-ethanolamines.The reaction is stimulated by adding a small amount of water.

(CH₂CH₂)O + NH₃→ HO–CH₂CH₂–NH₂

2 (CH₂CH₂)O + NH₃→ (HO–CH₂CH₂)₂NH

3 (CH₂CH₂)O + NH₃→ (HO–CH₂CH₂)₃N

Similarly proceed the reactions with primary and secondary amines:

(CH₂CH₂)O + RNH₂→ HO–CH₂CH₂–NHR

Dialkylamino ethanols can further react with ethylene oxide, forming amino polyethylene glycols:

n (CH₂CH₂)O + R₂NCH₂CH₂OH → R₂NCH₂CH₂O–(–CH₂CH₂O–)_n–H

Trimethylaminereacts with ethylene oxide in the presence of water, formingcholine:

(CH₂CH₂)O + (CH₃)₃N + H₂O → [HOCH₂CH₂N (CH₃)₃]⁺OH⁻

Aromatic primary and secondary amines also react with ethylene oxide, forming the corresponding arylamino alcohols.

Halide addition

Ethylene oxide readily reacts with aqueous solutions ofhydrochloric,hydrobromic,andhydroiodic acidsto formhalohydrins.The reaction occurs easier with the last two acids:

(CH₂CH₂)O + HCl → HO–CH₂CH₂–Cl

The reaction with these acids competes with the acid-catalyzed hydration of ethylene oxide; therefore, there is always a by-product of ethylene glycol with an admixture ofdiethylene glycol.For a cleaner product, the reaction is conducted in the gas phase or in an organic solvent.

Ethylene fluorohydrin is obtained differently, by boilinghydrogen fluoridewith a 5–6% solution of ethylene oxide indiethyl ether.The ether normally has a water content of 1.5–2%; in absence of water, ethylene oxide polymerizes.

Halohydrins can also be obtained by passing ethylene oxide through aqueous solutions of metal halides:

2 (CH₂CH₂)O + CuCl₂+ 2 H₂O → 2 HO–CH₂CH₂–Cl + Cu(OH)₂↓

Metalorganic addition

Interaction of ethylene oxide withorganomagnesiumcompounds, which areGrignard reagents,can be regarded asnucleophilic substitutioninfluenced bycarbanionorganometallic compounds. The final product of the reaction is a primary alcohol:

${\ce {(CH2CH2)O{}+RMgBr->R-CH2CH2-OMgBr->[{\ce {H2O}}]{\overset {primary~alcohol}{R-CH2CH2-OH}}}}$

Similar mechanism is valid for other organometallic compounds, such as alkyl lithium:

${\ce {(CH2CH2)O{}+{\overset {alkyl~lithium}{RLi}}->R-CH2CH2-OLi->[{\ce {H2O}}]R-CH2CH2-OH}}$

Other addition reactions

Addition of hydrogen cyanide

Ethylene oxide easily reacts withhydrogen cyanideformingethylene cyanohydrin:

(CH₂CH₂)O + HCN → HO–CH₂CH₂–CN

A slightly chilled (10–20 °C) aqueous solution ofcalcium cyanidecan be used instead of HCN:

2 (CH₂CH₂)O + Ca(CN)₂+ 2 H₂O → 2 HO–CH₂CH₂–CN + Ca(OH)₂

Ethylene cyanohydrin easily loses water, producingacrylonitrile:

HO–CH₂CH₂–CN → CH₂=CH–CN + H₂O

Addition of hydrogen sulfide and mercaptans

When reacting with thehydrogen sulfide,ethylene oxide forms2-mercaptoethanolandthiodiglycol,and with alkylmercaptans it produces 2-alkyl mercaptoetanol:

(CH₂CH₂)O + H₂S → HO–CH₂CH₂–HS

2 (CH₂CH₂)O + H₂S → (HO–CH₂CH₂)₂S

(CH₂CH₂)O + RHS → HO–CH₂CH₂–SR

The excess of ethylene oxide with an aqueous solution of hydrogen sulfide leads to the tris-(hydroxyethyl) sulfonyl hydroxide:

3 (CH₂CH₂)O + H₂S → [(HO–CH₂CH₂)₃S⁺]OH⁻

Addition of nitrous and nitric acids

Reaction of ethylene oxide with aqueous solutions ofbarium nitrite,calcium nitrite,magnesium nitrite,zinc nitrite,orsodium nitriteleads to the formation of2-nitroethanol:

2 (CH₂CH₂)O + Ca(NO₂)₂+ 2 H₂O → 2 HO–CH₂CH₂–NO₂+ Ca(OH)₂

Withnitric acid,ethylene oxide forms mono- anddinitroglycols:

${\ce {(CH2CH2)O{}+{\overset {nitric \atop acid}{HNO3}}->HO-CH2CH2-ONO2->[{\ce {+HNO3}}][{\ce {-H2O}}]O2NO-CH2CH2-ONO_{2}}}$

Reaction with compounds containing active methylene groups

In the presence ofalkoxides,reactions of ethylene oxide with compounds containing active methylene group leads to the formation ofbutyrolactones:

Alkylation of aromatic compounds

Ethylene oxide enters into theFriedel–Crafts reactionwith benzene to formphenethyl alcohol:

Styrenecan be obtained in one stage if this reaction is conducted at elevated temperatures (315–440 °C (599–824 °F)) and pressures (0.35–0.7 MPa (51–102 psi)), in presence of an aluminosilicate catalyst.

Synthesis of crown ethers

A series of polynomialheterocyclic compounds,known ascrown ethers,can be synthesized with ethylene oxide. One method is the cationic cyclopolymerization of ethylene oxide, limiting the size of the formed cycle:

n(CH₂CH₂)O → (–CH₂CH₂–O–)_n

To suppress the formation of other linear polymers the reaction is carried out in a highly dilute solution.

Reaction of ethylene oxide withsulfur dioxidein the presence of caesium salts leads to the formation of an 11-membered heterocyclic compound which has the complexing properties of crown ethers:

Isomerization

When heated to about 400 °C (750 °F), or to 150–300 °C (300–570 °F) in the presence of a catalyst (Al₂O₃,H₃PO₄,etc.), ethylene oxideisomerizesintoacetaldehyde:

${\ce {(CH2CH2)O->[{\ce {200^{\circ }C}}][{\ce {Al2O3}}]{\overset {acetaldehyde}{CH3CHO}}}}$

The radical mechanism was proposed to explain this reaction in the gas phase; it comprises the following stages:

(CH₂CH₂)O ↔ •CH₂CH₂O• → CH₃CHO*(1)

CH₃CHO* → CH₃• + CHO•(2)

CH₃CHO* + M → CH₃CHO + M*(3)

In reaction (3),Mrefers to the wall of the reaction vessel or to a heterogeneous catalyst. The moiety CH₃CHO* represents a short-lived (lifetime of 10^−8.5seconds), activated molecule of acetaldehyde. Its excess energy is about 355.6 kJ/mol, which exceeds by 29.3 kJ/mol thebinding energyof the C-C bond in acetaldehyde.

In absence of a catalyst, the thermal isomerization of ethylene oxide is never selective and apart from acetaldehyde yields significant amount of by-products (see sectionThermal decomposition).

Reduction reaction

Ethylene oxide can be hydrogenated into ethanol in the presence of a catalyst, such asnickel,platinum,palladium,boranes,lithium aluminium hydride,and some otherhydrides.

${\ce {(CH2CH2)O{}+H2->[{} \atop {\ce {Ni,Pt,Pd,BH3,LiAlH4}}{\text{ or other hydrides}}][{\ce {80^{\circ }C}}]{\underset {ethanol}{C2H5OH}}}}$

Conversely, with some other catalysts, ethylene oxide may bereducedby hydrogen to ethylene with the yield up to 70%. The reduction catalysts include mixtures of zinc dust andacetic acid,of lithium aluminium hydride withtitanium trichloride(the reducing agent is actuallytitanium dichloride,formed by the reaction between LiAlH₄and TiCl₃) and ofiron(III) chloridewithbutyllithiumintetrahydrofuran.

${\ce {(CH2CH2)O{}+H2->[{} \atop {\ce {{Zn}+CH3COOH}}]{\underset {ethylene}{CH2=CH2}}+H2O}}$

Oxidation

Ethylene oxide can further be oxidized, depending on the conditions, toglycolic acidorcarbon dioxide:

${\ce {(CH2CH2)O{}+O2->[{\ce {AgNO3}}]{\overset {glycolic\ acid}{HOCH2CO2H}}}}$

Deep gas-phase reactor oxidation of ethylene oxide at 800–1,000 K (527–727 °C; 980–1,340 °F) and a pressure of 0.1–1 MPa (15–145 psi) yields a complex mixture of products containing O₂,H₂,CO,CO₂,CH₄,C₂H₂,C₂H₄,C₂H₆,C₃H₆,C₃H₈,andCH₃CHO.

Dimerization

In the presence of acid catalysts, ethylene oxide dimerizes to afforddioxane:

The reaction mechanism is as follows:

The dimerization reaction is unselective. By-products includeacetaldehyde(due toisomerization). The selectivity and speed of dimerization can be increased by adding a catalyst, such as platinum, platinum-palladium, oriodinewithsulfolane.2-methyl-1,3-dioxolaneis formed as a side product in the last case.

Polymerization

Liquid ethylene oxide can formpolyethylene glycols.The polymerization can proceed via radical and ionic mechanisms, but only the latter has a wide practical application.Cationic polymerizationof ethylene oxide is assisted byproticacids (HClO₄,HCl), Lewis acids (SnCl₄,BF₃,etc.),organometallic compounds,or more complex reagents:

$n{\ce {(CH2CH2)O ->[{\ce {SnCl4}}]}}\ \overbrace {{\ce {(CH2CH2-O-)}}_{n}} ^{{\ce {polyethyleneglycol}}}$

The reaction mechanism is as follows.At the first stage, the catalyst (MX_m) is initiated by alkyl-or acylhalogen or by compounds with active hydrogen atoms, usually water, alcohol, or glycol:

MX_m+ ROH → MX_mRO⁻H⁺

The resulting active complex reacts with ethylene oxide via theS_N2mechanism:

(CH₂CH₂)O + MX_mRO⁻H⁺→ (CH₂CH₂)O•••H⁺O⁻RMX_m

(CH₂CH₂)O•••H⁺O⁻RMX_m→ HO–CH₂CH₂⁺+ MX_mRO⁻₂

HO–CH₂CH₂⁺+ n (CH₂CH₂)O → HO–CH₂CH₂–(O–CH₂CH₂)_n⁺

The chain breaks as

HO–CH₂CH₂–(O–CH₂CH₂)_n⁺+ MX_mRO⁻→ HO–CH₂CH₂–(O–CH₂CH₂)_n–OR + MX_m

H(O–CH₂CH₂)_n–O–CH₂–CH₂⁺+ MX_mRO⁻→ H(O–CH₂CH₂)_n–O–CH=CH₂+ MX_m+ ROH

Anionic polymerizationof ethylene oxide is assisted by bases, such asalkoxides,hydroxides,carbonates,or other compounds of alkali oralkaline earth metals.The reaction mechanism is as follows:

(CH₂CH₂)O + RONa → RO–CH₂CH₂–O⁻Na⁺

RO–CH₂CH₂–O⁻Na⁺+ n (CH₂CH₂)O → RO–(CH₂CH₂–O)_n–CH₂CH₂–O⁻Na⁺

RO–(CH₂CH₂–O)_n–CH₂CH₂–O⁻Na⁺→ RO–(CH₂CH₂–O)_n–CH=CH₂+ NaOH

RO–(CH₂CH₂–O)_n–CH₂CH₂–O⁻Na⁺+ H₂O → RO–(CH₂CH₂–O)_(n+1)OH + NaOH

Thermal decomposition

Ethylene oxide is relatively stable to heating – in the absence of a catalyst, it does not dissociate up to 300 °C (572 °F), and only above 570 °C (1,058 °F) there is a majorexothermicdecomposition, which proceeds through the radical mechanism.The first stage involvesisomerization,however high temperature accelerates the radical processes. They result in a gas mixture containing acetaldehyde, ethane, ethyl, methane, hydrogen, carbon dioxide,ketene,andformaldehyde.High-temperaturepyrolysis(830–1,200 K (557–927 °C; 1,034–1,700 °F)) at elevated pressure in an inert atmosphere leads to a more complex composition of the gas mixture, which also containsacetyleneandpropane.Contrary to the isomerization, initiation of the chain occurs mainly as follows:

(CH₂CH₂)O → •CH₂CH₂O• → CH₂O + CH₂:

When carrying the thermal decomposition of ethylene oxide in the presence of transition metal compounds as catalysts, it is possible not only to reduce its temperature, but also to haveethylas the main product, that is to reverse the ethylene oxide synthesis reaction.

Other reactions

Thiocyanateions orthioureatransform ethylene oxide intothiirane(ethylene sulfide):

(CH₂CH₂)O + (NH₂)₂C=S → (CH₂CH₂)S + (NH₂)₂C=O

Reaction ofphosphorus pentachloridewith ethylene oxide producesethylene dichloride:

(CH₂CH₂)O + PCl₅→ Cl–CH₂CH₂–Cl + POCl₃

Other dichloro derivatives of ethylene oxide can be obtained by combined action ofsulfuryl chloride(SOCl₂) andpyridineand oftriphenylphosphineandcarbon tetrachloride.

Phosphorus trichloridereacts with ethylene oxide forming chloroethyl esters of phosphorous acid:

(CH₂CH₂)O + PCl₃→ Cl–CH₂CH₂–OPCl₂

2 (CH₂CH₂)O + PCl₃→ (Cl–CH₂CH₂–O)₂PCl

3 (CH₂CH₂)O + PCl₃→ Cl–CH₂CH₂–O)₃P

The reaction product of ethylene oxide withacyl chloridesin the presence ofsodium iodideis a complex iodoethyl ester:

(CH₂CH₂)O + RCOCl + NaI → RC(O)–OCH₂CH₂–I + NaCl

Heating ethylene oxide to 100 °C withcarbon dioxide,in a non-polar solvent in the presence ofbis-(triphenylphosphine)-nickel(0) results inethylene carbonate:

In industry, a similar reaction is carried out at high pressure and temperature in the presence of quaternary ammonium or phosphonium salts as a catalyst.

Reaction of ethylene oxide withformaldehydeat 80–150 °C in the presence of a catalyst leads to the formation of1,3-dioxolane:

Substituting formaldehyde by other aldehydes or ketones results in a 2-substituted 1,3-dioxolane (yield: 70–85%, catalyst: tetraethylammonium bromide).

Catalytichydroformylationof ethylene oxide gives hydroxypropanal which can be hydrogenated topropane-1,3-diol:

${\ce {(CH2CH2)O + CO + H2 -> CHO-CH2CH2-OH ->[{\ce {+H2}}] HO-CH2CH2CH2-OH}}$

Laboratory synthesis

Dehydrochlorination of ethylene and its derivatives

Dehydrochlorination of2-chloroethanol,developed by Wurtz in 1859, remains a common laboratory route to ethylene oxide:

${\ce {Cl-CH2CH2-OH + NaOH -> (CH2CH2)O + NaCl + H2O}}$

The reaction is carried out at elevated temperature, and besidesodium hydroxideorpotassium hydroxide,calcium hydroxide,barium hydroxide,magnesium hydroxide,orcarbonatesof alkali or alkaline earth metals can be used.

With a high yield (90%) ethylene oxide can be produced by treatingcalcium oxidewith ethyl hypochlorite; substituting calcium by other alkaline earth metals reduces the reaction yield:

${\ce {2 CH3CH2-OCl + CaO -> 2 (CH2CH2)O + CaCl2 + H2O}}$

Direct oxidation of ethylene by peroxy acids

Ethylene can be directly oxidized into ethylene oxide usingperoxy acids,for example,peroxybenzoicormeta-chloro-peroxybenzoic acid:

Oxidation by peroxy acids is efficient for higher alkenes, but not for ethylene. The above reaction is slow and has low yield, therefore it is not used in the industry.

Other preparative methods

Other synthesis methods includereaction of diiodo ethane withsilver oxide:

${\ce {I-CH2CH2-I + Ag2O -> (CH2CH2)O + 2AgI}}$

and decomposition ofethylene carbonateat 200–210 °C (392–410 °F) in the presence ofhexachloroethane:

Industrial synthesis

History

Commercial production of ethylene oxide dates back to 1914 whenBASFbuilt the first factory which used the chlorohydrin process (reaction of ethylene chlorohydrin with calcium hydroxide). The chlorohydrin process was unattractive for several reasons, including low efficiency and loss of valuable chlorine intocalcium chloride.More efficient direct oxidation of ethylene by air was invented by Lefort in 1931 and in 1937Union Carbideopened the first plant using this process. It was further improved in 1958 by Shell Oil Co. by replacing air with oxygen and using elevated temperature of 200–300 °C (390–570 °F) and pressure (1–3 MPa (150–440 psi)).This more efficient route accounted for about half of ethylene oxide production in the 1950s in the US, and after 1975 it completely replaced the previous methods. The production of ethylene oxide accounts for approximately 11% of worldwide ethylene demand.

Chlorohydrin process of production of ethylene oxide

Although the chlorohydrin process is almost entirely superseded in the industry by the direct oxidation of ethylene, the knowledge of this method is still important for educational reasons and because it is still used in the production ofpropylene oxide.The process consists of three major steps: synthesis of ethylene chlorohydrin, dehydrochlorination of ethylene chlorohydrin to ethylene oxide and purification of ethylene oxide. Those steps are carried continuously. In the first column, hypochlorination of ethylene is carried out as follows:

Cl₂+ H₂O → HOCl + HCl

CH₂=CH₂+ HOCl → HO–CH₂CH₂–Cl

CH₂=CH₂+ Cl₂→ Cl–CH₂CH₂–Cl

To suppress the conversion of ethylene into theethylene dichloride(the last reaction), the concentration of ethylene is maintained at about 4–6%, and the solution is heated by steam to the boiling point.

Next, aqueous solution of ethylene chlorohydrin enters the second column, where it reacts with a 30% solution of calcium hydroxide at 100 °C (212 °F):

2 HO–CH₂CH₂–Cl + Ca(OH)₂→ 2 (CH₂CH₂)O + CaCl₂+ 2H₂O

The produced ethylene oxide is purified byrectification.The chlorohydrin process allows to reach 95% conversion of ethylene chlorohydrin. The yield of ethylene oxide is about 80% of the theoretical value; for 1 tonne (0.98 long tons; 1.1 short tons) of ethylene oxide, about 200 kg (440 lb) of ethylene dichloride is produced.But, the major drawbacks of this process are high chlorine consumption and effluent load. This process is now obsolete.

Direct oxidation of ethylene

Usage in global industry

Direct oxidation of ethylene was patented by Lefort in 1931. This method was repeatedly modified for industrial use, and at least four major variations are known. They all use oxidation by oxygen or air and a silver-based catalyst, but differ in the technological details and hardware implementations.

Union Carbide(currently a division ofDow Chemical Company) was the first company to develop the direct oxidation process.

A similar production method was developed by Scientific Design Co., but it received wider use because of the licensing system – it accounts for 25% of the world's production and for 75% of world's licensed production of ethylene oxide.A proprietary variation of this method is used by Japan Catalytic Chemical Co., which adapted synthesis of both ethylene oxide and ethylene glycol in a single industrial complex.

A different modification was developed Shell International Chemicals BV. Their method is rather flexible with regard to the specific requirements of specific industries; it is characterized by high selectivity with respect to the ethylene oxide product and long lifetime of the catalyst (3 years). It accounts for about 40% of global production.

Older factories typically use air for oxidation whereas newer plants and processes, such as METEOR and Japan Catalytic, favor oxygen.

Chemistry and kinetics of the direct oxidation process

Formally, the direct oxidation process is expressed by the following equation:

${\ce {2CH_2=CH2 + O2 ->[{\ce {Ag}}] 2(CH2CH2)O}}$,ΔH=−105 kJ/mol

However, significant yield of carbon dioxide and water is observed in practice, which can be explained by the complete oxidation of ethylene or ethylene oxide:

CH₂=CH₂+ 3 O₂→ 2 CO₂+ 2 H₂O, ΔH=−1327kJ/mol

(CH₂CH₂)O + 2.5 O₂→ 2 CO₂+ 2 H₂O, ΔH=−1223kJ/mol

According to a kinetic analysis by Kilty and Sachtler, the following reactions describe the pathway leading to EO. In the first step, asuperoxide(O₂⁻) species is formed:

O₂+ Ag → Ag⁺O₂⁻

This species reacts with ethylene

Ag⁺O₂⁻+ H₂C=CH₂→ (CH₂CH₂)O + AgO

The resulting silver oxide then oxidizes ethylene or ethylene oxide to CO₂and water. This reaction replenishes the silver catalyst. Thus the overall reaction is expressed as

7 CH₂=CH₂+ 6 O₂→ 6 (CH₂CH₂)O + 2 CO₂+ 2 H₂O

and the maximum degree of conversion of ethylene to ethylene oxide is theoretically predicted to be 6/7 or 85.7%,although higher yields are achieved in practice.

The catalyst for the reaction is metallic silver deposited on various matrixes, includingpumice,silica gel,varioussilicatesandaluminosilicates,alumina,andsilicon carbide,and activated by certain additives (antimony,bismuth,barium peroxide,etc.).The process temperature was optimized as 220–280 °C (430–540 °F). Lower temperatures reduce the activity of the catalyst, and higher temperatures promote the complete oxidation of ethylene thereby reducing the yield of ethylene oxide. Elevated pressure of 1–3 MPa (150–440 psi) increases the productivity of the catalyst and facilitates absorption of ethylene oxide from the reacting gases.

Whereas oxidation by air is still being used, oxygen (> 95% purity) is preferred for several reasons, such as higher molar yield of ethylene oxide (75–82% for oxygen vs. 63–75% for air), higher reaction rate (no gas dilution) and no need of separating nitrogen in the reaction products.

Process overview

The production of ethylene oxide on a commercial scale is attained with the unification of the followingunit processes:

• Main reactor
• Ethylene oxidescrubber
• Ethylene oxide de-sorber
• Strippinganddistillation column
• CO₂scrubber and CO₂de-scrubber

Main Reactor:The main reactor consists of thousands of catalyst tubes in bundles. These tubes are generally 6 to 15 m (20 to 50 ft) long with an inner diameter of 20 to 50 mm (0.8 to 2.0 in). The catalyst packed in these tubes is in the form of spheres or rings of diameter 3 to 10 mm (0.12 to 0.39 in). The operating conditions of 200–300 °C (390–570 °F) with a pressure of 1–3 MPa (150–440 psi) prevail in the reactor. To maintain this temperature, the cooling system of the reactor plays a vital role. With the aging of the catalyst, its selectivity decreases and it produces more exothermic side products of CO₂.

Ethylene oxide scrubber:After the gaseous stream from the main reactor, containing ethylene oxide (1–2%) and CO₂(5%), is cooled, it is then passed to the ethylene oxide scrubber. Here, water is used as the scrubbing media which scrubs away majority of ethylene oxide along with some amounts of CO₂,N₂,CH₂=CH₂,CH₄andaldehydes(introduced by the recycle stream). Also, a small proportion of the gas leaving the ethylene oxide scrubber (0.1–0.2%) is removed continuously (combusted) to prevent the buildup of inert compounds (N₂,Ar, and C₂H₆), which are introduced as impurities with the reactants.

Ethylene oxide de-sorber:The aqueous stream resulting from the above scrubbing process is then sent to the ethylene oxide de-sorber. Here, ethylene oxide is obtained as the overhead product, whereas the bottom product obtained is known as theglycol bleed.When ethylene oxide is scrubbed from the recycle gas with an aqueous solution, ethylene glycols (viz. mono-ethylene glycol, di-ethylene glycol and other poly-ethylene glycols) get unavoidably produced. Thus, in-order to prevent them from building up in the system, they are continuously bled off.

Stripping and distillation column:Here, the ethylene oxide stream is stripped off its low boiling components and then distilled in-order to separate it into water and ethylene oxide.

CO₂scrubber:The recycle stream obtained from the ethylene oxide scrubber is compressed and a side-stream is fed to the CO₂scrubber. Here, CO₂gets dissolved into the hot aqueous solution of potassium carbonate (i.e., the scrubbing media). The dissolution of CO₂is not only a physical phenomenon, but a chemical phenomenon as well, for, the CO₂reacts with potassium carbonate to produce potassium hydrogen carbonate.

K₂CO₃+ CO₂+ H₂O → 2 KHCO₃

CO₂de-scrubber:The above potassium carbonate solution (enriched with CO₂) is then sent to the CO₂de-scrubber where CO₂is de-scrubbed by stepwise (usually two steps)flashing.The first step is done to remove the hydrocarbon gases, and the second step is employed to strip off CO₂.

World production of ethylene oxide

The world production of ethylene oxide was 20 Mt (22 million short tons) in 2009,19 Mt (21 million short tons) in 2008 and 18 Mt (20 million short tons) in 2007.This places ethylene oxide 14th most produced organic chemical, whereas the most produced one was ethylene with 113 Mt (125 million short tons).SRI Consulting forecasted the growth of consumption of ethylene oxide of 4.4% per year during 2008–2013 and 3% from 2013 to 2018.

In 2004, the global production of ethylene oxide by region was as follows:

Region	Number of major producers	Production, thousand tonnes
North America United States Canada Mexico	10 3 3	4009 1084 350
South America Brazil Venezuela	2 1	312 82
Europe Belgium France Germany Netherlands Spain Turkey United Kingdom Eastern Europe	2 1 4 2 1 1 1 No data	770 215 995 460 100 115 300 950
Middle East Iran Kuwait Saudi Arabia	2 1 2	201 350 1781
Asia China Taiwan India Indonesia Japan Malaysia South Korea Singapore	No data 4 2 1 4 1 3 1	1354 820 488 175 949 385 740 80

The world's largest producers of ethylene oxide areDow Chemical Company(3–3.5 Mt (3.3–3.9 million short tons) in 2006),Saudi Basic Industries(2,000–2,500 tonnes (2,200–2,800 short tons) in 2006),Royal Dutch Shell(1.328 Mt (1.464 million short tons) in 2008–2009),BASF(1.175 Mt (1.295 million short tons) in 2008–2009),China Petrochemical Corporation(~1 Mt (1.1 million short tons) in 2006),Formosa Plastics(~1 Mt (1.1 million short tons) in 2006), andIneos(0.92 Mt (1.01 million short tons) in 2008–2009).

Applications

Global industrial use of ethylene oxide in 2007

Ethylene oxide is one of the most important raw materials used in large-scale chemical production. Most ethylene oxide is used for synthesis ofethylene glycols,including diethylene glycol and triethylene glycol, that accounts for up to 75% of global consumption. Other important products include ethylene glycol ethers, ethanolamines, and ethoxylates. Among glycols, ethylene glycol is used asantifreeze,in the production ofpolyesterandpolyethylene terephthalate(PET – raw material for plastic bottles), liquid coolants, and solvents.

Sector	Demand share (%)
Agrochemicals	7
Oilfieldchemicals	10
Detergents	25
Textile	35
Personal care	10
Pharmaceuticals	8
Others	5
Total [2009]	5.2Mt

Polyethyleneglycols are used in perfumes, cosmetics, pharmaceuticals,lubricants,paint thinners,andplasticizers.Ethylene glycol ethers are part of brake fluids, detergents, solvents, lacquers, and paints. Ethanolamines are used in the manufacture of soap and detergents and for purification of natural gas. Ethoxylates are reaction products of ethylene oxide with higher alcohols, acids, or amines. They are used in the manufacture of detergents, surfactants,emulsifiers,anddispersants.

Whereas synthesis of ethylene glycols is the major application of ethylene oxide, its percentage varies greatly depending on the region: from 44% in theWestern Europe,63% inJapan,and 73% inNorth Americato 90% in the rest ofAsia,and 99% inAfrica.

Production of ethylene glycol

Ethylene glycol is industrially produced by non-catalytic hydration of ethylene oxide at a temperature of 200 °C (392 °F) and a pressure of 1.5–2 MPa (220–290 psi):

${\ce {(CH2CH2)O + H2O -> HOCH2CH2OH}}$

By-products of the reaction are diethylene glycol, triethylene glycol, and polyglycols with the total of about 10%, which are separated from the ethylene glycol by distillation at reduced pressure.

Another synthesis method is the reaction of ethylene oxide and CO2 (temperature 80–120 °C (176–248 °F) and pressure of 5.2 MPa (750 psi)) yieldingethylene carbonateand its subsequent hydrolysis with decarboxylation:

${\ce {(CH2CH2)O{}+CO2->{\overset {ethylene\ carbonate}{(O-CH2CH_{2}-O)C=O}}->[{\ce {+H2O}}][{\ce {-CO2}}]HOCH2CH2OH}}$

Modern technologies of production of ethylene glycol include the following.Shell OMEGA technology (Only Mono-Ethylene Glycol Advantage) is a two-step synthesis of ethylene carbonate using aphosphoniumhalide as a catalyst. The glycol yield is 99–99.5%, with other glycols practically absent. The main advantage of the process is production of pure ethylene glycol without the need for further purification. The first commercial plant which uses this method was opened in 2008 in South Korea.Dow METEOR (Most Effective Technology for Ethylene Oxide Reactions) is an integrated technology for producing ethylene oxide and its subsequent hydrolysis into ethylene glycol. The glycol yield is 90–93%. The main advantage of the process is relative simplicity, using fewer stages and less equipment.

Conversion to ethylene glycol is also the means by which waste ethylene oxide is scrubbed before venting to the environment. Typically the EtO is passed over a matrix containing either sulfuric acid or potassium permanganate.

Production of glycol ethers

The major industrial esters of mono-, di-, and triethylene glycols are methyl, ethyl, and normal butyl ethers, as well as their acetates and phthalates. The synthesis involves reaction of the appropriatealcoholwith ethylene oxide:

${\ce {(CH2CH2)O + ROH -> HOCH2CH2OR}}$

${\ce {(CH2CH2)O + HOCH2CH2OR -> HOCH2CH2OCH2CH2OR}}$

${\ce {(CH2CH2)O + HOCH2CH2OCH2CH2OR -> HOCH2CH2OCH2CH2OCH2CH2OR}}$

The reaction of monoesters with an acid or its anhydride leads to the formation of the esters:

${\ce {CH3CO2H + HOCH2CH2OR -> ROCH2CH2OCOCH3 + H2O}}$

Production of ethanolamines

In the industry,ethanolamines(mono-, di-, and triethanolamines) are produced by reactingammoniaand ethylene oxide in anhydrous medium at a temperature of 40–70 °C (100–160 °F) and pressure of 1.5–3.5 MPa (220–510 psi)MPa:

${\ce {(CH2CH2)O + NH3 -> HOCH2CH2NH2}}$

${\ce {2 (CH2CH2)O + NH3 -> (HOCH2CH2)2NH}}$

${\ce {3 (CH2CH2)O + NH3 -> (HOCH2CH2)3N}}$

All three ethanolamines are produced in the process, while ammonia and part of methylamine are recycled. The final products are separated by vacuumdistillation.Hydroxyalkylamines are produced in a similar process:

${\ce {(CH2CH2)O + RNH2 -> HOCH2CH2NHR}}$

${\ce {2 (CH2CH2)O + RNH2 -> (HOCH2CH2)2NR}}$

Monosubstituted products are formed by reacting a large excess of amine with ethylene oxide in presence of water and at a temperature below 100 °C (212 °F). Disubstituted products are obtained with a small excess of ethylene oxide, at a temperature of 120–140 °C (250–280 °F) and a pressure of 0.3–0.5 MPa (45–75 psi).

Production of ethoxylates

Main article:Ethoxylation

Industrial production of ethoxylates is realized by a direct reaction of higher alcohols, acids, or amines with ethylene oxide in the presence of an alkaline catalyst at a temperature of 120–180 °C (250–360 °F). Modern plants producing ethoxylates are usually based on the BUSS LOOP reactors technology,which is based on a three-stage continuous process. In the first stage, the initiator or catalyst of the reaction and the feedstock are fed into the container, where they are mixed, heated, and vacuum dried. Then reaction is carried out in a special insulated reactor in an inert atmosphere (nitrogen) to prevent a possible explosion of ethylene oxide. Finally, the reaction mixture is neutralized, degassed, and purified.

Production of acrylonitrile

Currently, mostacrylonitrile(90% in 2008) is produced by the SOHIO method, which is based on the catalytic oxidation ofpropylenein the presence of ammonia and bismuth phosphomolybdate. However, until 1960 a key production process was addition ofhydrogen cyanideto ethylene oxide, followed by dehydration of the resultingcyanohydrin:

(CH₂CH₂)O + HCN → HOCH₂CH₂CN→−H₂OCH₂=CH−CN

Addition of hydrocyanic acid to ethylene oxide is carried out in the presence of a catalyst (sodium hydroxideanddiethylamine), and dehydration of cyanohydrin occurs in the gas phase upon the catalytic action ofaluminium oxide.

Non-industrial uses

The direct use of ethylene oxide accounts for only 0.05% (2004 data) of its global production.Ethylene oxide is used as a sterilizing agent, disinfecting agent andfumigantas a mixture with carbon dioxide (8.5–80% of ethylene oxide), nitrogen, ordichlorodifluoromethane(12% ethylene oxide). It is applied for gas-phase sterilization of medical equipment and instruments, packaging materials, clothing, and surgical and scientific equipment;for processing of storage facilities (tobacco, packages of grain, sacks of rice, etc.), clothing, furs, and valuable documents.

Healthcare sterilant

Ethylene oxide is one of the most commonly used sterilization methods in the healthcare industry because of its non-damaging effects for delicate instruments and devices that require sterilization, and for its wide range of material compatibility.It is used for instruments that cannot tolerate heat, moisture, or abrasive chemicals, such as electronics, optical equipment, paper, rubber, and plastics.It was developed in the 1940s as a sterilant by the US military, and its use as a medical sterilant dates to the late 1950s, when the McDonald process was patented for medical devices.TheAnprolenesystem was patented in the 1960sby Andersen Products,and it remains the most commonly used system in several niche markets, notably the veterinary market and some international markets.It relies on the use of a flexible sterilization chamber and an EtO cartridge for small volume sterilization, and where environmental and/or portability considerations dictate the use of a low dose. It is therefore referred to as the "flexible chamber sterilization" method, or the "gas diffusion sterilization" method.

In the United States, the operation of EtO sterilization is overseen by theEPAthrough theNational Emissions Standards for Hazardous Air Pollutants(NESHAP).

Niche uses

Ethylene oxide is used as afungicideand as an accelerator of maturation of tobacco leaves.Ethylene oxide is also used as a main component ofthermobaric weapons(fuel-air explosives).

Identification of ethylene oxide

Gas chromatographyis the principal method for analysis and detection of ethylene oxide.

An inexpensive test for ethylene oxide exploits its precipitation of solid hydroxides of metals when it is passed through aqueous solutions of their salts:

${\ce {2 (CH2CH2)O + MnCl2 + 2 H2O -> 2 HO-CH2CH2-Cl + Mn(OH)2 v}}$

Similarly, ethylene oxide is detected by the bright pink color of the indicator when passing air through aqueous solutions of some salts of sodium or potassium (chlorides, iodides, thiosulfates, etc.) with the addition ofphenolphthalein:

${\ce {(CH2CH2)O + NaCl + H2O -> HO-CH2CH2-Cl + NaOH}}$

Other methods of ethylene oxide detection arecolor reactions withpyridinederivatives and hydrolysis of ethylene glycol withperiodic acid.The producediodic acidis detected withsilver nitrate.

Accidents

Ethylene oxide is extremely flammable, and its mixtures with air are explosive. When heated it may rapidly expand, causing fire and explosion.Several industrial accidents have been attributed to ethylene oxide explosion.

Theautoignition temperatureis 429 °C (804 °F),decomposition temperatureof 571 °C (1,060 °F) at 101.3 kPa (14.69 psi), minimum inflammable content in the air is 2.7%,and maximum limit is 100%. The NFPA 704 rating is Health, 3; Flammability, 4; Instability 2.Ethylene oxide in presence of water can hydrolyze to ethylene glycol and form polyethylene oxide, which then eventually is oxidized by air and leads tohotspotsthat can trigger explosive decomposition.

Fires caused by ethylene oxide are extinguished with conventional media includingfoam,carbon dioxide, or water. Suppression of this activity can be done by blanketing with aninert gasuntil total pressure reaches the nonexplosive range. Extinguishing of burning ethylene oxide is complicated by its ability to continue burning in an inert atmosphere and in water solutions. Fire suppression is reached only upon dilution with water above 22:1.

La Canonja, Spain accident

On 14 January 2020 in an industrial estate nearTarragona,an explosion of an ethoxylation reactor owned by the chemical company Industrias Quimicas de Oxido de Etileno (IQOXE, part of the CL Industrial Group) occurred.The accident launched substantial debris over a radius of about two and a half kilometers, one piece penetrating a distant home and killing an occupant.It is reported that at least three people were killed and seven injured as a direct result of the explosion.

The company was, until the time of the explosion the only producer of ethylene oxide in Spain with an installed capacity of 140,000 tons/year. Half of that production was used to manufacture ethylene glycol for PET production.The accident will be investigated under EU regulations within the context of theEuropean Agency for Safety and Health at Work.

2020 sesame seeds contamination

In September 2020, high levels ofpesticideswere found in 268 tonnes ofsesameseeds fromIndia.The contamination had a level of 1000 to 3500 times the limit of 0.05 milligrams per kilogram for ethylene oxide allowed inEurope.This pesticide is forbidden in Europe, it is known to becarcinogenicandmutagenic.Aproduct recallwas made, half of the products had anorganic certification.

In September, alert was raised by Belgium by RASFF, but the product has also been sold in other EU single market countries such as Franceand Ireland.

Physiological effects

Effect on microorganisms

Exposure to ethylene oxide gas causesalkylationto microorganisms at a nuclear level.The disinfectant effect of ethylene oxide is similar to that of sterilization by heat, but because of limited penetration, it affects only the surface. ETO sterilization can take up to 12 hours due to its slow action upon microorganisms, and lengthy processing and aeration time.

Effects on humans and animals

Ethylene oxide is analkylating agent;it has irritating, sensitizing, and narcotic effects.Chronic exposure to ethylene oxide is alsomutagenic.TheInternational Agency for Research on Cancerclassifies ethylene oxide into group 1, meaning it is a provencarcinogen.Ethylene oxide is classified as a class 2 carcinogen by the German MAK commission and as a class A2 carcinogen by the ACGIH. A 2003 study of 7,576 women exposed while at work in commercial sterilization facilities in the US suggests ethylene oxide is associated withbreast cancerincidence.A 2004 follow up study analyzing 18,235 men and women workers exposed to ethylene oxide from 1987 to 1998 concluded "There was little evidence of any excess cancer mortality for the cohort as a whole, with the exception ofbone cancerbased on small numbers. Positive exposure-response trends for lymphoid tumors were found for males only. Reasons for the sex specificity of this effect are not known. There was also some evidence of a positive exposure-response for breast cancer mortality. "An increased incidence of brain tumors and mononuclear cell leukemia was found in rats that had inhaled ethylene oxide at concentrations of 10, 33 or 100 mL/m³(0.0100, 0.0329 or 0.0997 imp fl oz/cu ft) over a period of two years.An increased incidence of peritoneal mesotheliomas was also observed in the animals exposed to concentrations of 33 and 100 mL/m³(0.0329 and 0.0997 imp fl oz/cu ft). Results of human epidemiological studies on workers exposed to ethylene oxide differ. There is evidence from both human and animal studies that inhalation exposure to ethylene oxide can result in a wide range of carcinogenic effects.

Ethylene oxide is toxic by inhalation, with a USOSHApermissible exposure limit calculated as a TWA (time weighted average) over 8 hours of 1ppm, and a short term exposure limit (excursion limit) calculated as a TWA over 15 minutes of 5ppm.At concentrations in the air about 200 parts per million, ethylene oxide irritatesmucous membranesof the nose and throat; higher contents cause damage to the trachea and bronchi, progressing into the partial collapse of the lungs. High concentrations can causepulmonary edemaand damage the cardiovascular system; the damaging effect of ethylene oxide may occur only after 72 hours after exposure.The maximum content of ethylene oxide in the air according to the US standards (ACGIH) is 1.8 mg/m³(0.00079 gr/cu ft).NIOSHhas determined that the Immediately Dangerous to Life and Health level (IDLH) is 800 ppm.

Because the odor threshold for ethylene oxide varies between 250 and 700 ppm, the gas is already at toxic concentrations when it can be smelled. Even then, the odor of ethylene oxide is sweet and aromatic and can easily be mistaken for the aroma ofdiethyl ether,a common laboratory solvent of very low toxicity. In view of these insidious properties, continuous electrochemical monitoring is standard practice, and it is forbidden to use ethylene oxide to fumigate building interiors in theEUand some other jurisdictions.

Ethylene oxide causes acute poisoning, accompanied by a variety of symptoms.Central nervous system effects are frequently associated with human exposure to ethylene oxide in occupational settings. Headache, nausea, and vomiting have been reported.Peripheral neuropathy, impaired hand-eye coordination and memory loss have been reported in more recent case studies of chronically-exposed workers at estimated average exposure levels as low as 3 ppm (with possible short-term peaks as high as 700ppm).The metabolism of ethylene oxide is not completely known. Data from animal studies indicate two possible pathways for the metabolism of ethylene oxide: hydrolysis to ethylene glycol and glutathione conjugation to formmercapturic acidand meththio-metabolites.

Ethylene oxide easily penetrates through ordinary clothing and footwear, causing skin irritation and dermatitis with the formation of blisters, fever, andleukocytosis.

Toxicity data for ethylene oxide are as follows:

• Eye exposure: 18 mg (0.28 gr)/6 hours (rabbit)
• Oral: 72 mg/kg (0.00115 oz/lb) (rat,LD₅₀), 1,186 mg/kg (0.01898 oz/lb) (rat,TD_Lo), 5,112 mg/kg (0.08179 oz/lb) (rat,TD)
• Inhalation: 12,500 ppm (human,TC_Lo), 960 ppm/4 hours (dog,LC₅₀) 33–50 ppm (rat or mouse, TC), 800 ppm/4 hours (rat or mouse, LC₅₀)
• Subcutaneous injection:100 mg/kg (0.0016 oz/lb) (cat, LD_Lo), 292 mg/kg (0.00467 oz/lb) (mouse, TD_Lo) 900–2,600 mg/kg (0.014–0.042 oz/lb) (mouse, TD), 187 mg/kg (0.00299 oz/lb) (rat, LD₅₀).
• Intraperitoneal injection:750 mg/kg (0.0120 oz/lb) (mouse, TD_Lo), 175 mg/kg (0.00280 oz/lb) (mouse, LD₅₀)
• Intravenous injection: 175 mg/kg (0.00280 oz/lb) (rabbit, LD₅₀), 290 mg/kg (0.0046 oz/lb) (mouse, LD₅₀)
• The US Environmental Protection Agency (USEPA) estimated in 2016that for low doses, the inhalation of ethylene oxide for a lifetime could increase an individual's lifetime cancer risk by as much as 3.0×10⁻³per μg/m³(without considering that early-life exposures are likely more potent). The USEPA estimated the slope of the dose-response declines at higher doses, and extra cancer risk estimates for several occupational exposure scenarios are calculated.

Global demand

Global EO demand has expanded from 16.6Mt(18.3 million short tons) in 2004 to 20 Mt (22 million short tons) in 2009, while demand for refined EO expanded from 4.64 Mt (5.11 million short tons) in 2004 to 5.6 Mt (6.2 million short tons) in 2008. In 2009, demand is estimated to have declined to about 5.2 Mt (5.7 million short tons). Total EO demand registered a growth rate of 5.6% per annum during the period 2005 to 2009 and is projected to grow at 5.7% per annum during 2009 to 2013.

Health and safety regulations

According to Merck Life Science UK 2020 Safety Data Sheet provided to theEuropean Chemicals Agency'sRegistration, Evaluation, Authorisation and Restriction of Chemicals(REACH)—a 2006European Union regulation,ethylene oxide is "presumed to have carcinogenic potential for humans."

The United States EPA published anadvance notice of proposed rulemaking(NPRM) in the 12 December 2019 Federal Register seeking to limit EtO emissions.Over the next couple of years, information was collected and a proposed air toxics rule published in the 13 April 2023 Federal Register.Following a 60 day comment period that could be extended, due to many comments requesting an extension, the EPA rules that could reduce EtO emissions, both direct and fugitive, by over 80% could be implemented within 18 months of publishing the final rule in the Federal Register.Laboratory EtO emitters would still be exempt from the stricter compliance. Additionally, while effectively curbing EtO emissions in the USA, many industrial emitters may simply shift their EtO production to nearby less strict countries: Canada, Mexico, etc.

In 2024, U.S. probed claims that popular Indian curry brandsMDHandEverest Spicescarried ethylene oxide after Hong Kong and Singapore found the contamination in and took enforcement actions against the products.

Cited sources

• Haynes, William M., ed. (2011).CRC Handbook of Chemistry and Physics(92nd ed.). Boca Raton, FL:CRC Press.ISBN978-1439855119.

External links

• EOSA Promoting the safe use of Ethylene Oxide for Sterilization
• WebBook page for C2H4O
• National Institute for Occupational Safety and Health – Ethylene Oxide Topic Page
• CDC – NIOSH Pocket Guide to Chemical Hazards
• EOSA memo about Ethylene Oxide (EtO) factsArchived15 October 2017 at theWayback Machine