Iodomethane

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Iodomethane

Iodomethane, commonly called methyl iodide and commonly abbreviated "MeI", is the chemical compound

Organoiodine compound

Organoiodine compounds are organic compound chemical compounds that contain one or more carbon-iodine Chemical bonds. They occur widely in organic chemistry but are relatively rare in nature....
with the formula CH₃I. This dense

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
volatile

Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
liquid is related to methane

Methane

Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees....
by replacement of one hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
atom by an atom of iodine

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
and its dipole moment

Dipole

In physics, there are two kinds of dipoles :*An electric dipole is a separation of positive and negative charge. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some, usually small, distance....
is 1.59 D. Refractive index

Refractive index

The refractive index of a medium is a measure for how much the speed of light is reduced inside the medium. For example, typical soda-lime glass has a refractive index of 1.5, which means that in glass, light travels at times the speed of light in a vacuum....
is 1.5304 (20 °C, D), 1.5293 (21 °C, D). It is miscible with common organic solvents. It is colourless, although upon exposure to light, samples develop a purplish tinge caused by the presence of I₂

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
.

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Encyclopedia

Iodomethane, commonly called methyl iodide and commonly abbreviated "MeI", is the chemical compound

Organoiodine compound

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
volatile

Vapor pressure

Methane

Hydrogen

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
and its dipole moment

Dipole

Refractive index

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
. Storage over copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....
metal absorbs the iodine. Methyl iodide is widely used in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic_chemistry molecules can often contain a higher level of complexity compared to purely Inorganic_chemistry compounds, so the synthesis of organic compounds has developed into one of the most im...
to deliver a methyl group

Methyl group

In chemistry, a methyl group is a hydrophobic alkyl functional group named after methane . It has the chemical formula -3 and is often abbreviated -Me....
, via the transformation called methylation

Methylation

Rice

Rice is a staple food for a large part of the world's human population, especially in tropical Latin America, and East Asia, South Asia and Southeast Asia, making it the second-most consumed cereal grain, after maize....
plantations in small amounts.

Chemical properties

Methyl iodide is an excellent substrate for S_N2 substitution reactions. It is sterically

Steric effects

Steric effects arise from the fact that each atom within a molecule occupies a certain amount of space. If atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds , and this may affect the molecule's preferred shape and chemical reaction....
open for attack by nucleophile

Nucleophile

In chemistry, a nucleophile is a reagent that forms a chemical bond to its reaction partner by donating both bonding electrons. Because nucleophiles donate electrons, they are by definition Lewis bases ....
s, and iodide

Iodide

An iodide ion is an iodine with a −1 electric charge. Compounds with iodine in formal oxidation state −1 are called iodides. This can include ionic compounds such as caesium iodide or covalent compounds such as phosphorus triiodide....
is a good leaving group

Leaving group

A leaving group in chemistry is an ion or substituent with the ability to detach itself from a molecule. The remaining molecule or fragment remaining is known as the residual or main part....
. For example, it can be used for the methylation of phenol

Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
s or carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
s:

In these examples, the base

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
(K₂CO₃

Potassium carbonate

Potassium carbonate is a white salt, soluble in water , which forms a strongly alkaline solution. It can be made as the product of potassium hydroxide's absorbent reaction with carbon dioxide....
or Li₂CO₃

Lithium carbonate

Lithium carbonate is a chemical compound with the chemical formula Li2CO3. This colorless salt is widely used in the processing of metal oxide and has received attention for its use in psychiatry....
) removes the acidic proton to form the carboxylate or phenoxide anion, which serves as the nucleophile in the S_N2 substitution.

Iodide is a "soft" anion which means that methylation with MeI tends to occur at the "softer" end of an ambidentate nucleophile

Nucleophile

Thiocyanate

Thiocyanate is the anion, [SCN]-. Common compounds include the colourless salts potassium thiocyanate and sodium thiocyanate. Organic compounds containing the functional group SCN are also called thiocyanates....
ion favours attack at rather than "hard" , leading mainly to methyl thiocyanate (CH₃SCN) rather than CH₃NCS. This behavior is relevant to the methylation

Methylation

Methylation in the chemical sciences denotes the attachment or substitution of a methyl on various Substrate . This term is commonly used in chemistry, biochemistry, soil science and the biological sciences....
of stabilized enolates such as those derived from 1,3-dicarbonyl compounds. Methylation of these and related enolates can occur on the harder oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
atom or the (usually desired) carbon atom. With methyl iodide, C-alkylation nearly always predominates.

MeI is also an important precursor to methylmagnesium iodide or "MeMgI", which is a common reagent. Because MeMgI forms readily, it is often prepared in instructional laboratories as an illustration of Grignard reagents. The use of MeMgI has been somewhat superseded by the commercially available methyl lithium

Methyl lithium

Methyllithium is an organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state....
.

In the Monsanto process

Monsanto process

The Monsanto process is an important method for the manufacture of acetic acid. This process operates at a pressure of 30-60 atmosphere and a temperature of 150-200 ?C and gives a selectivity greater than 99%....
, MeI forms in situ from the reaction of methanol

Methanol

Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a chemical compound with chemical formula carbonhydrogen3oxygenhydrogen ....
and hydrogen iodide

Hydrogen iodide

Hydrogen iodide is a diatomic molecule. Aqueous solutions of HI are known as iohydroic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under standard conditions; whereas, the other is an aqueous solution of said gas....
. The CH₃I then reacts with carbon monoxide

Carbon monoxide

Carbon monoxide, with the chemical formula CO, is a colorless and odorless, tasteless, yet highly toxic gas. Its molecules consist of one carbon atom covalent bond to one oxygen atom....
in the presence of a rhodium

Rhodium

Rhodium is a chemical element that is a rare, silvery-white, hard transition metal and a member of the platinum group. Rhodium is found in platinum ores and is used in alloys with platinum and as a catalyst....
complex to form acetyl iodide

Acetyl iodide

Acetyl iodide, C2H3IO, also known as ethanoyl iodide, is an acyl halide derived from acetic acid. Acetyl iodide is an intermediate in the Monsanto process....
, the precursor to acetic acid

Acetic acid

Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid which gives vinegar its sour taste and pungent smell. Pure, water-free acetic acid is a colourless liquid that absorbs water from the environment , and freezes at 16.7 Celsius to a colourless crystalline solid....
after hydrolysis

Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
. Most acetic acid is prepared by this method.

MeI hydrolyzes at 270 °C forming hydrogen iodide

Hydrogen iodide

Carbon monoxide

Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
.

Preparation

Iodomethane is formed via the exothermic reaction

Exothermic reaction

An exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:...
that occurs when iodine

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
is added to a mixture of methanol

Methanol

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. The name comes from the and . A Valency nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate minerals....
. The iodinating reagent is phosphorus triiodide

Phosphorus triiodide

Phosphorus triiodide is an unstable red solid which reacts violently with water. It is a common misconception that PI3 is too unstable to be stored; it is, in fact, commercially available....
that is formed in situ:

3 CH₃OH

Methanol

Phosphorous acid

Phosphorous acid is the Compound described by the chemical formula H3PO3. It can be formulated as HP2 and therefore contains phosphorus in oxidation state +3....

Alternatively, it is prepared from the reaction of dimethyl sulfate

Dimethyl sulfate

Calcium carbonate

Calcium carbonate is a chemical compound with the chemical formula CalciumCarbonOxygen3. It is a common substance found as Rock in all parts of the world, and is the main component of seashells, snails, and eggshells....
: ₂SO₂ + KI ? K₂SO₄ + 2 CH₃I The CH₃I can be purified by distillation followed by washing with Na₂S₂O₃

Sodium thiosulfate

Sodium thiosulfate , also spelled Sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Sodium2Sulfur2Oxygen3?5Hydrogen2Oxygen, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or ?hypo.?...
to remove iodine.

Methyl iodide forms during nuclear

Nuclear reaction

In nuclear physics, a nuclear reaction is the process in which two atomic nucleus or subatomic particles collide to produce products different from the initial particles....
accidents by the reaction of organic matter with the "fission

Nuclear fission

In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the atomic nucleus of an atom splits into smaller parts, often producing free neutrons and lighter atomic nucleus, which may eventually produce photons ....
iodine."

Choice of iodomethane as a methylating agent

Iodomethane is an excellent reagent for methylation, but there are some disadvantages to its use. It has a high equivalent weight: one mole of MeI weighs almost three times as much as one mole of methyl chloride

Chloromethane

Chloromethane, also called Methyl chloride, R-40 or HCC 40, is a chemical compound of the group of organic compounds called haloalkanes. It was once widely used as a refrigeration....
. However, the chloride is a gas (as is methyl bromide

Bromomethane

The chemical compound bromomethane, commonly known as methyl bromide, is an Organobromide compound with chemical formula CarbonHydrogen3Bromine....
), making it more awkward to work with than liquid MeI. Methyl chloride is a poorer methylating reagent than MeI, though it is often adequate.

Iodides are generally expensive relative to the more common chlorides and bromides, though iodomethane is reasonably affordable; on a commercial scale the toxic dimethyl sulfate

Dimethyl sulfate

Dimethyl sulfate is a chemical compound with chemical formula 2SO2. As the dimethyl ester of sulfuric acid, its formula is often written as 2Sulfate or even Me2SO4, where CH3 or Me is methyl....
is preferred, since it is both cheap and liquid. The iodide leaving group in MeI may cause side reactions, as it is a powerful nucleophile. Finally, being highly reactive, MeI is more dangerous for laboratory workers than related chlorides and bromides. When considering alternatives to MeI, it is necessary to consider cost, handling, risk, chemical selectivity, and ease of reaction work-up.

Uses

Besides use as a methylation agent, there have been proposals of its use as a fungicide

Fungicide

Fungicides are chemical compounds or biological organisms used to kill or inhibit fungus or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of Crop yield, quality and profit....
, herbicide

Herbicide

A herbicide is used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant hormones....
, insecticide

Insecticide

An insecticide is a pesticide used against insects in all developmental forms. They include ovicides and larvicides used against the Egg and larvae of insects respectively....
or nematicide

Nematicide

A nematicide is a type of chemical pesticide used to kill parasitic nematodes .One common nematicide is obtained from neem cake, the residue obtained after cold-pressing the fruit and kernels of the neem tree....
and as a fire extinguisher

Fire extinguisher

A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations. It is not intended for use on an out-of-control fire, such as one which has reached the ceiling, endangers the user , or otherwise requires the expertise of a fire department....
. Further it can be used as a soil disinfectant, replacing bromomethane

Bromomethane

The chemical compound bromomethane, commonly known as methyl bromide, is an Organobromide compound with chemical formula CarbonHydrogen3Bromine....
(which was banned under the Montreal Protocol

Montreal Protocol

The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion....
), and in microscopy due to properties related to refraction index. In a controversial October 2007 decision, the United States Environmental Protection Agency

United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an List of United States federal agencies of the federal government of the United States charged to Regulation of chemicals and protect human health by safeguarding the natural environment: air, water, and land....
approved its use as a soil fumigant in some cases, although it cannot yet be used in California (a major potential market) due to lack of state approval.

Toxicity and Biological effects

Iodomethane has an LD₅₀

LD50

In toxicology, the median lethal dose, LD50 , or LCt50 of a toxic substance or radiation is the Dose required to kill half the members of a tested population....
for oral administration to rats 76 mg/kg, and in the liver

Liver

The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
it undergoes rapid conversion to S-methylglutathione

Glutathione

Glutathione is a tripeptide. It contains an unusual peptide linkage between the amino acid of cysteine and the carboxyl group of the glutamate side chain....
. Iodomethane is a possible carcinogen based on its IARC, ACGIH, NTP, or EPA classification. According to IARC it is classified as a group 3 substance (Group 3:The agent is not classifiable as to its carcinogenicity to humans).

Breathing iodomethane fumes can cause lung, liver, kidney and central nervous system damage. It causes nausea, dizziness, coughing and vomiting. Prolonged contact with skin causes burns. Massive inhalation causes pulmonary edema

Pulmonary edema

Pulmonary edema , or oedema , is swelling and/or fluid accumulation in the lungs. It leads to impaired gas exchange and may cause respiratory failure....
.

External links

IARC Summaries & Evaluations: , ,