AQA AS Chemistry organic help URGENT!!! Watch

Medicine...
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Hi, it's about oxidation of alcohols and there's something which has really bugged me and I really don't understand. I've asked my chemistry teacher and he said that I was frustrating him, I asked my A* friend and my other friends, none of them knew what I was saying, hopefully one of you guys will know
So to get to an alcohol-aldehyde you add the normal amount of oxidizing agent, then to get from and aldehyde to the carboxylic acid you add MORE oxidizing agent (right?) and heat under reflux.
The other way you can get an carboxyllic acid is by adding excess oxidising agent and heating under reflux at the start (alcohol-carboxylic acid) and in the first way you reflux the aldehyde right?
also, why d we have to immediantly distill the aldehyde when it's formed because to get from an aldehyde to a carboxylic acid we HAVE to add more (O) and reflux it, meaning that it's impossible further reactions will occur?
Can anyone clear this up for me as I'm really confused, is there two ways to get a carboxylic acid and why do we have to distill the aldehyde when no further reaction will occur if we don't heat it under reflux/add more (O).
Thanks x
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Medicine...
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(Original post by Medicine...)
Hi, it's about oxidation of alcohols and there's something which has really bugged me and I really don't understand. I've asked my chemistry teacher and he said that I was frustrating him, I asked my A* friend and my other friends, none of them knew what I was saying, hopefully one of you guys will know
So to get to an alcohol-aldehyde you add the normal amount of oxidizing agent, then to get from and aldehyde to the carboxylic acid you add MORE oxidizing agent (right?) and heat under reflux.
The other way you can get an carboxyllic acid is by adding excess oxidising agent and heating under reflux at the start (alcohol-carboxylic acid) and in the first way you reflux the aldehyde right?
also, why d we have to immediantly distill the aldehyde when it's formed because to get from an aldehyde to a carboxylic acid we HAVE to add more (O) and reflux it, meaning that it's impossible further reactions will occur?
Can anyone clear this up for me as I'm really confused, is there two ways to get a carboxylic acid and why do we have to distill the aldehyde when no further reaction will occur if we don't heat it under reflux/add more (O).
Thanks x
The oxidising agent, which is usually acidified potassium dichromate, is not selective. It doesn't oxidise each alcohol molecule to aldehyde before it starts oxidising aldehyde to carboxylic acid.
As soon as some aldehyde is present there will be oxidation of this as well as remaining alcohol molecules. During the oxidation process (under reflux) there would be unoxidised alcohol, aldehyde and carboxylic acid all present - giving a mixture of products. Restricting the quantity of oxidising agent will not prevent some of the aldehyde being oxidised to carboxylic acid - it will just mean that you have a mixture of products including the acid.

If the apparatus is set up to distil of the aldehyde this will prevent it being oxidised further to carboxyllic acid - because it is being removed from the reaction vessel and the oxidising reagent.
The aldehyde can be distilled off by careful control of vapour temperature. The aldehyde will have lower boiling point than alcohol or acid, so can be separated by distillation.
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(Original post by TutorsChemistry)
The oxidising agent, which is usually acidified potassium dichromate, is not selective. It doesn't oxidise each alcohol molecule to aldehyde before it starts oxidising aldehyde to carboxylic acid.
As soon as some aldehyde is present there will be oxidation of this as well as remaining alcohol molecules. During the oxidation process (under reflux) there would be unoxidised alcohol, aldehyde and carboxylic acid all present - giving a mixture of products. Restricting the quantity of oxidising agent will not prevent some of the aldehyde being oxidised to carboxylic acid - it will just mean that you have a mixture of products including the acid.

If the apparatus is set up to distil of the aldehyde this will prevent it being oxidised further to carboxyllic acid - because it is being removed from the reaction vessel and the oxidising reagent.
The aldehyde can be distilled off by careful control of vapour temperature. The aldehyde will have lower boiling point than alcohol or acid, so can be separated by distillation.
Thanks, and are there two ways of getting the carboxylic acid, could you plz explain each way in terms of the conditions
1) alcohol-aldehyde-carboxylic acid
and
2) alcohol-carboxyllic acid
In number one for aldehyde-carboxylic acid do you add more oxidising agent and heat the aldehyde in reflux???
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