Methane and Iodoform
Methane is an organic compound consist of one carbon atom and four hydrogen with the chemical formula CH4. This compound is the simplest compound of alkanes, and the main component of natural gas. Methane bond angle is 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water.
Iodoform is an organic compound consist of one carbon atom, one hydrogen atom and three iodine atoms with the formula CHI3. Iodoform has the characteristics of pale yellow, crystal form, including volatile substances, a characteristic odor like a hospital smell, taste sweet and analogous to chloroform. It is sometimes used as a disinfectant.
Covalent bond
Methane and Iodoform form compounds with covalently bonded, in which covalent bonding two compounds can be described or explained by the Lewis structure (electron dot formula). This formula can describe the role of valence electrons in bonds held.
Each carbon atom has 4 valence electrons are used to form covalent bonds with other atoms are described as hand ties. So the carbon atoms in carbon compounds always have a four-hand ties. In the fourth hand methane is used to bind four hydrogen atoms to another. Four hydrogen atoms form a bond with an atom C, 1 valence electrons possessed by the hydrogen atom will be donated to the carbon atoms to form bonds, while in the hands of Iodoform fourth C atoms are used to bind three iodine atoms and one hydrogen atom. Valence electrons possessed by the atoms of carbon, hydrogen atoms and iodine atoms will be used together to meet the doublet and the octet rule in the bond, so the electron configuration of atoms has been like a noble gas electron configuration. The number of hands to describe the amount of bond bond in a covalent compound. Four bond that occurs in the compound methane is four single covalent bonds as well as with Iodoform.
Simple views of the bonding in methane
There was an error comparison between the old structures and modern electronic structure of carbon, 1s2 2s2 2px1 2py1. Modern structures show that there are only 2 unpaired electrons to share with atomic hydrogen, not need 4 atoms are shown in the modern structure. This will be seen more easily by using the notation of electron-in-box. Only electrons in the skin-to-2 that will be displayed. Elektron1s2 is too deep inside the atom to be involved in bonding. Electron Direct only available for sharing is the 2p electron is 2px1 2py1.
Promotion of electrons
When the bonds are formed, energy is released and the system becomes more stable. If carbon form 4 bonds than 2, two times more energy is released and therefore the resulting molecule becomes more stable. There are only a small energy gap between 2p and 2s orbitals, and therefore carbon provides a small amounts of energy to promote electrons from 2s to 2p a blank to allow up to 4 unpaired electrons. Extra energy released when electrons in the sub skin 2s 2p promoted to sub skin. Electron carbon atom is now said to an excited state. Now there are 4 unpaired electrons ready to bond, other problems arise. In methane all the carbon-hydrogen bonds are identical, but the electrons are in two kinds of orbitals. This allows not going to get four identical except bonds ranging from four identical orbitals.
Hybridization
Electrons rearrange themselves again in a process called hybridization. Hybridization regulate electron into four identical hybrid orbitals called hybrid sp3 (because they are made from one s orbital and three p orbitals).
Electrons rearrange themselves again in a process called hybridization. Hybridization regulate electron into four identical hybrid orbitals called hybrid sp3 (because they are made from one s orbital and three p orbitals).
Hybrid orbital sp3 looks a bit like half the orbital p, and they arrange themselves in space so they are as far apart as possible. The core is at the center tetrahedron (triangular pyramid) with orbital pointing into the corner.
What happens when a bond is formed?
Electrons in the 1s orbital of hydrogen - a spherically symmetric region of space surrounding the nucleus in which there are few opportunities for permanent (say 95%) to find the electron. When covalent bonds are formed, the atomic orbitals (orbitals in individual atoms) combine to produce a new molecular orbital containing the electron pair that created the bond.
Four molecular orbitals are formed, looks somewhat like the original sp3 hybrids, but with hydrogen nuclei attached to each lobe. Each orbital holds 2 electrons. The principles involved - the promotion of electrons if the hybridization is needed, then, followed by the formation of molecular orbitals - can be applied to any molecule that is bound covalently.
Form of methane and Iodoform
When the sp3 orbitals are formed, they arrange themselves so that they are as far apart as possible. It is a tetrahedral arrangement, with angles 109.5 °. No change in form when the hydrogen atoms in methane and iodine atoms in Iodoform join carbon, so the methane molecules and Iodoform also tetrahedral with bond angles 109.5 °
The Phsycal Properties
Methane
Molecular formula: CH4
Molecular formula: CH4
Molar Mass: 16.042 g / mol
Appearance: Colorless Gas
Density: 0.717 kg / m 3 (gas, 0 °C), 415 kg / m3 (liquid)
Melting point: -182.5 °C, 91 K, -297 °F
Boiling Point: -161.6 °C, 112 K, -259 °F
Solubility in water: 35 mg / L (17 °C)
Iodoform
Molecular formula: CHI3
Molecular formula: CHI3
Molar mass: 393.73 g / mol
Appearance: pale yellow crystals
Density: g/cm3 4008
Melting point: 123 °C
Boiling Point: 217 °C
Solubility in water: 0.1 g / L at 20 °C
Methane is the main component of natural gas, about 87% by volume. At room temperature and standard pressure, methane is a colorless gas, odorless; characteristic odor of natural gas as used in homes are made of security measures caused by the addition of an odor, often methanethiol or ethanethiol. At 1 atmosphere pressure, boiling point -161.5 °C (-258.7 °F) and melting point is -182.5 °C (-296.5 °F). This caused the methane is highly flammable and reacts violently with some halogen compounds. As a combustible gas is only a narrow range of concentrations (5-15%) in the air. Liquid methane does not burn unless experiencing high pressure (typically 4-5 atmospheres).
While the physical properties Iodoform is a form of yellow crystals sparkling. Shape up from Iodoform is hexagonal with I as its center. At room temperature and standard pressure, volatile Iodoform(sublimes), has a melting point of 119-123 0C, density 4.00 g / mile, molecular weight 393.73 g / mol. The composition of iodoform is C = 3.05 g; H = 6.266; I = 96.496. Iodoform also be decomposed by the heat effect of light and air to form CO2, CO, I2, H2O. Has a smell like the smell ofhospital. It's hardsoluble in water, but easilyin alcohol, slowly soluble in petaoida atoms.
Each molecule of methane is small, consisting of four hydrogen atoms bound to a single carbon atom by covalent bonds. The molecule is shaped like a tetrahedron, with carbon atom at the center and four hydrogen atoms occupy the four corners of the tetrahedron. Unlike the water molecule, the poles and pull one another, methane molecules are non-polar and do not have much attraction for each other. This is the reason why, at room temperature, methane is a gas while the water is liquid.
Artificial synthesis
Methane was found and isolated by Alessandro Volta between 1776 and 1778 when studying the marsh gas from Lake Maggiore. In the laboratory, methane can be produced by direct reaction of carbon with hydrogen, or aluminum carbide with water. In industrial settings, the methane produced by a chemical reaction between hydrogen and common atmospheric gases. While Iodoform first made by Georges Serrulas in 1822 and identified the molecular formula by Jean-Baptiste Dumas in 1834. It is synthesized in the reaction haloform by the reaction of iodine and sodium hydroxide with one of four types of organic compounds: (i) methyl ketone: CH3COR, acetaldehyde (CH3CHO), ethanol (CH3CH2OH), and certain secondary alcohols (CH3CHROH, where R is the group alkyl or aryl).
Chemical Reaction
The reaction of methane
The main reactions with methane are: combustion, steam reformation to syngas, and halogenation. In general, the reaction of methane is difficult to control. Partial oxidation to methanol, for example, difficult to achieve; reaction usually lasts until the carbon dioxide and water.
1. Combustion Reaction
In the combustion of methane, several steps are involved:
Methane is thought to form a formaldehyde (formaldehyde or H2CO). Formaldehyde gives formyl radical (HCO), which then forms carbon monoxide (CO). This process is called oxidative pyrolysis:
CH4 + O2 → CO + H2 + H2O
Following oxidative pyrolysis, H2 oxidize, forming H2O, releasing heat. This happens very quickly, usually significantly less than one millisecond.
2H2 + O2 → 2H2O
Finally, the CO oxidizes, forming CO2 and release more heat. This process is generally slower than other chemical steps, and usually requires a few milliseconds for a reaction can occur.
2CO + O2 → 2CO2
Total reaction of the above reactions are as follows:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ∆H + 891 k J / mol (at standard conditions)
where the parentheses "g" stands for the form of gas and parentheses "l" stands for liquid form.
2. Hydrogen Activation
2. Hydrogen Activation
In methane, carbon - hydrogen covalent bond is one of the strongest in all hydrocarbons. In chemical terms, there are "activation barrier" high to break the CH bond. In other words, it needs enough energy to break it. However, methane is the main starting materials for the manufacture of hydrogen. Searching for catalysts that can lower the activation barrier to C-H bond of methane molecule is in the research area with significant industry.
3. Reactions with halogen
Methane reacts with all halogen in a suitable condition, as follows:
CH4 + X2 → CH3X + HX
where X is a halogen: fluorine (F), chlorine (Cl), bromine (Br) or iodine (I). This reaction can continue, so CH3X react with X2 to produce CH2X2; CH2X2 in turn can react with X2 to produce CHX3, and CHX3 can react further to produce CX4. The mechanism for this process is called free radical halogenation. When X is Cl, this mechanism has the following format:
1. Radical generation:
![\ Mathrm {Cl_2 \ xrightarrow [\ segitiga] {} 2Cl UV ^ \ bullet - 239 \; kJ}](file:///C:/DOCUME%7E1/acer/LOCALS%7E1/Temp/msohtmlclip1/01/clip_image014.png){kind=small}
The energy required comes from UV radiation or heating,
2. Radical exchange:
CH4 + Cl • → CH3 • + HCl ∆H = + 14 kJ
CH3 • + Cl2 → CH3Cl + Cl • ∆H = + 100 kJ
3. Radical extermination:
2Cl • → Cl2 ∆H = + 239 kJ
CH3 • + Cl • → CH3Cl ∆H = + 339 kJ
2CH3 • → CH3 CH3 ∆H = + 347 kJ
If methane and X2 are used in equimolar quantities, CH2X2, CHX3, and even CX4 are formed. Using a large excess of CH4 reduces the production of CH2X2, CHX3, CX4, and thus more CH3X is formed.
Reaction of Iodoform
Reaction of iodine and bases with methyl ketone is very reliable, that the "test Iodoform" (appearance of yellow precipitate) was used to investigate the existence of methyl ketones. This also happens when testing for the secondary alcohol (methyl alcohol).
Some of the reagent (eg hydrogen iodide) convert Iodoform for diiodomethane. Also conversion to carbon dioxide is possible: Iodoform silver nitrate reacts with water to produce carbon monoxide, are oxidized by a mixture of sulfuric acid and iodine pentaoksida. When treated with elemental silver powder Iodoform reduced, producing acetylene. After heating Iodoform decomposes to produce diatomic iodine, hydrogen iodide, and carbon.
Haloform reaction is a chemical reaction where haloform (CHX3, where X is a halogen) is produced by complete halogenation of the methyl ketone (a molecule that contains the group R-CO-CH3) in the presence of bases. [1] R may be H, alkyl or aryl. This reaction can be used to produce CHCl3, CHBr3 or CHI3.
Haloform reaction scheme
Substrate who successfully underwent haloform reaction is methyl ketones and secondary alcohols to methyl ketones oxidizable, such as isopropanol. Halogen can be used chlorine, bromine, and iodine. Fluoroform (CHF3) can not be made from methyl ketones by the reaction because of the instability hypofluorite haloform, but the compounds of the type RCOCF3 do unite with the basis to generate fluoroform (CHF3) is equivalent to the steps a second and third in the process shown above.
Mechanism
In the first step, halogen didisproportionasi with hydroxide to form a halide and hypohalite:
OH-→ X2 XO-X-H (X = Cl, Br, I)
If the secondary alcohol is present, is oxidized to ketones by hypohalite this:
If the methyl ketone is present, reacts with hypohalite in the process of three steps:
(1) R-CO-CH3 3OX-→ R-CO-3 OH-CX3
(2) R-CO-OH → RCOOH CX3-CX3
(3) RCOOH → RCOO-CX3-CHX3
Detailed reaction mechanism is as follows:
In basic conditions, these ketones having keto-enol tautomerization. Enolate which electrophilic attack by hypohalite (containing halogen with a formal charge of 1).When the position has been profound halogenated α, the molecule having a nucleophilic acyl substitution by hydroxide, with a group of left-CX3 stabilized by three electron-attractive group. The anion-CX3 abstract protons from both carboxylic acid form, or solvents, and forms such haloform.
This reaction is traditionally used to determine the presence of methyl ketone, or oxidizable secondary alcohols to methyl ketones via Iodoform test. Currently, techniques such as infrared spectroscopy and NMR spectroscopy are preferred because they require small samples, perhaps non-destructive (for NMR) and easy and quick to perform.
Previously, it was used to generate Iodoform chloroform and bromoform and even industrial.
In organic chemistry, this reaction can be used to convert the terminal methyl ketone into the corresponding carboxylic acid.
Previously, it was used to generate Iodoform chloroform and bromoform and even industrial.
In organic chemistry, this reaction can be used to convert the terminal methyl ketone into the corresponding carboxylic acid.
Methane and Iodoform is an organic compound that is similar but actually different from the equally composed of atoms C and H, it's just on there Iodoform iodine atom attached to three carbon atoms hand. Both these compounds form four single covalent bonds and has the shape of tetrahedral. From his form at room temperature, gaseous methane and Iodoform form crystals.
