Sabtu, 06 Oktober 2012
HYDROCARBON DERIVATIVE
In the oxidation of hydrocarbon derivatives contained alcohol
modest alcohol forming flammable gases such as carbon dioxide and water vapor. therefore, ethanol is used as fuel (spiritus)
With oxidizing substances were as K2Cr2O7 solution in an acidic environment, alcohol is oxidized as follows:
1. primary alcohols to form aldehydes and can be further oxidized to form a carboxylic acid
2. secondary alcohols form ketones
3. Tertiary alcohols are not oxidized
Alcohol oxidation is an important organic reaction. Primary alcohols (R-CH2-OH) can be oxidized either to aldehydes (R-CHO) or to carboxylic acids (R-CO2H), while the oxidation of secondary alcohols (R1R2CH-OH) normally terminates at the ketone (R1R2C=O) stage. Tertiary alcohols (R1R2R3C-OH) are resistant to oxidation.
The direct oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate (R-CH(OH)2) by reaction with water before it can be further oxidized to the carboxylic acid.
Often it is possible to interrupt the oxidation of a primary alcohol at the aldehyde level by performing the reaction in absence of water, so that no aldehyde hydrate can be formed.
Oxidation to aldehydes
Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones. These include:
* Chromium-based reagents, such as Collins reagent (CrO3·Py2), PDC or PCC.
* Activated DMSO, resulting from reaction of DMSO with electrophiles, such as oxalyl chloride (Swern oxidation), a carbodiimide (Pfitzner-Moffatt oxidation) or the complex SO3·Py (Parikh-Doering oxidation).
* Hypervalent iodine compounds, such as Dess-Martin periodinane or 2-Iodoxybenzoic acid.
* Catalytic TPAP in presence of excess of NMO (Ley oxidation).
* Catalytic TEMPO in presence of excess bleach (NaOCl) (Anelli's oxidation).
Allylic and benzylic alcohols can be oxidized in presence of other alcohols using certain selective oxidants such as manganese dioxide (MnO2).
Oxidation of secondary alcohols to ketones
Reagents useful for the oxidation of secondary alcohols to ketones, but normally inefficient for oxidation of primary alcohols to aldehydes, include chromium trioxide (CrO3) in a mixture of sulfuric acid and acetone (Jones oxidation) and certain ketones, such as cyclohexanone, in the presence of aluminium isopropoxide (Oppenauer oxidation). Another method is oxoammonium-catalyzed oxidation.
Oxidation of primary alcohols to carboxylic acids
The direct oxidation of primary alcohols to carboxylic acids can be carried out using:
* Potassium permanganate (KMnO4).
* Jones oxidation.
* PDC in DMF.
* Heyns oxidation.
* Ruthenium tetroxide (RuO4).
Alcohol dehydration
If alcohol is heated with concentrated sulfuric acid will dehydrate (remove the water molecules) to form ethers and alkenes. Heating at a temperature of about 130 degrees Celsius produce ether, whereas at temperatures of about 180 degrees Celsius produces alkenes
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the article mentions that the primary alcohols and aldehydes can be oxidized can form aldehida , as well as secondary alcohols can form ketones, but tertiary alcohol can not be oxidized. And the problem is why the primary and secondary alcohols can be oxidized while the tertiary alcohol can not? Explain!
BalasHapusThe second question
Why the alcohol dehydration upon heating to temperatures around 130 degrees Celsius produce ether and heating at a temperature of about 180 degrees Celsius resulting in alkenes?
hi vina, I will try to help answer the problems you are number one.
BalasHapusprimary alcohol
Primary alcohol can be oxidized either to aldehydes or carboxylic acids depending on the reaction conditions. For karboksisat acid, alcohol is first oxidized to an aldehyde which then further oxidized into acid.
Secondary alcohol is oxidized to ketones. For example, if the secondary alcohol, propan-2-ol, is heated with sodium or potassium dichromate (VI) acidified with dilute sulfuric acid, it will form a propanone.
Tertiary alcohols can not be oxidized by sodium or potassium dichromate (VI). In fact there is no reaction.
If you look at what is happening with primary and secondary alcohols, you will involve the oxidizing agent releases hydrogen from the-OH group and a hydrogen atom from the carbon atom attached to the-OH group. Tertiary alcohols do not have a hydrogen atom attached to the carbon atom.
oke vina i'ii answer why the primary and secondary alcohols can be oxidized while the tertiary alcohol can not?
BalasHapusbecause primary alcohol can be oxidized to either aldehydes or carboxylic acids depending on the reaction conditions. For karboksisat acid, alcohol is first oxidized to an aldehyde which then further oxidized into acid.
Partial oxidation to aldehydes
Oxidation of alcohol will produce aldehydes if excessive use of alcohol and aldehyde can be separated by distillation shortly after it was formed.
Excessive alcohol means that no oxidizing agent sufficient to perform the second stage of oxidation. Separation of aldehydes as soon as possible after that means that it is not just waiting for oxidized back. If ethanol is used as a simple primary alcohol, it will produce an aldehyde ethanal, CH3CHO.
Complete equation for this reaction is rather complicated, and we need to understand about a half-reaction equation to solve.
In organic chemistry, simpler versions of this reaction is often used to focus on what happens to the organic substances are formed. To do this, the oxygen of an oxidizing agent is expressed as [O]. This writing can produce a simpler equation:
Writing can also help in remembering what happened during the reaction. We can make a simple structure which shows the relationship between primary alcohols to aldehydes are formed.
Oxidation perfectly into carboxylic acids
To carry out the oxidation perfect, we need to use the excess oxidizing agent and ensure that aldehydes are formed at the half-way products remain in the mix.
Alcohol is heated under reflux with excess oxidizing agent. When the reaction is finished, the carboxylic acid can be distilled.
Perfect equation for the oxidation of ethanol to ethanoic acid is as follows:
Simpler equation ordinary written as follows:
Alternatively, we can write separate equations for the two phases of the reaction, namely the formation of ethanal and further oxidation.
The reaction that occurs in the second stage is:
Secondary alcohol
Secondary alcohol is oxidized to ketones. For example, if the secondary alcohol, propan-2-ol, is heated with sodium or potassium dichromate (VI) acidified with dilute sulfuric acid, it will form propanon.Perubahan-change in reaction conditions will not be able to change the product formed. By using a simple equation, which shows the relationship between the structure, can be written as fo
If you look back at the second stage of the reaction of primary alcohols, you will see that there is an oxygen atom that is "inserted" between the carbon and hydrogen atoms in the aldehyde group to produce carboxylic acids. For secondary alcohols, no such hydrogen atoms, so the reaction is faster.
Tertiary alcohol
Tertiary alcohols can not be oxidized by sodium or potassium dichromate (VI). In fact there is no reaction. If you look at what is happening with primary and secondary alcohols, you will involve the oxidizing agent releases hydrogen from the-OH group and a hydrogen atom from the carbon atom attached to the-OH group. Tertiary alcohols do not have a hydrogen atom attached to the carbon atom.
If you look at what is happening with primary and secondary alcohols, you will involve the oxidizing agent releases hydrogen from the-OH group and a hydrogen atom from the carbon atom attached to the-OH group. Tertiary alcohols do not have a hydrogen atom attached to the carbon atom.
BalasHapusYou need to let go of two hydrogen atoms to form a special bond C = O.
I will try to answer your first question. A primary alcohol can be oxidized to aldehyde or carboxylic acid. Secondary alcohols can be oxidized to ketones. While the tertiary alcohol resist oxidation with an alkaline solution, the acid solution, dehydrated alcohol which is then oxidized to produce alkenes. At the tertiary alcohol, is not a process of oxidation. This is due to the tertiary alcohol, there is no H atoms attached to C atoms carbinol.
Hapusfor your second question, I am also not Understand it's possible that other friends can answer your second question. Thank you.
Primary alcohol can be oxidized either to aldehydes or carboxylic acids depending on the reaction conditions. For karboksisat acid, alcohol is first oxidized to an aldehyde which then further oxidized into acid.
BalasHapusSecondary alcohol is oxidized to ketones. For example, if the secondary alcohol, propan-2-ol, is heated with sodium or potassium dichromate (VI) acidified with dilute sulfuric acid, it will form a propanone.
Changes in reaction conditions will not be able to change the product formed.
If you look back at the second stage of the reaction of primary alcohols, you will see that there is an oxygen atom that is "inserted" between the carbon and hydrogen atoms in the aldehyde group to produce carboxylic acids. For secondary alcohols, no such hydrogen atoms, so the reaction is faster.
Tertiary alcohols can not be oxidized by sodium or potassium dichromate (VI). In fact there is no reaction.
If you look at what is happening with primary and secondary alcohols, you will involve the oxidizing agent releases hydrogen from the-OH group and a hydrogen atom from the carbon atom attached to the-OH group. Tertiary alcohols do not have a hydrogen atom attached to the carbon atom.
You need to let go of two hydrogen atoms to form a special bond C = O.