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Alcohols and haloalkanes

Oxidation of alcohols

Oxidation of alcohols

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Tutor: Alisha

Summary

Oxidation of alcohols

In a nutshell

Alcohols can be oxidised to produce molecules with a different functional group. Primary alcohols can be oxidised to aldehydes and/or carboxylic acids, secondary alcohols are oxidised to ketones and tertiary alcohols do not oxidise.


Equations

These are general chemical equations. You will need to be able to use these to write equation with specific substances.


​alcohol + oxygen→carbon dioxide + water R−CH2−OH→distil[O]RCHO R−CH2−OH→distil[O]RCHO→reflux[O]RCOOH R−CH2−OH→reflux[O]RCOOH R1CH(OH)R2→reflux[O]R1COR2 + H2Oalcohol \ + \ oxygen \rightarrow carbon \ dioxide \ + \ water \\ \ \\R-CH_2-OH \xrightarrow[distil]{[O]} RCHO \\ \ \\R-CH_2-OH \xrightarrow[distil]{[O]} RCHO \xrightarrow [reflux]{[O]} RCOOH \\ \ \\R-CH_2-OH \xrightarrow [reflux]{[O]} RCOOH \\ \ \\R_1CH(OH)R_2 \xrightarrow [reflux]{[O]} R_1COR_2 \ + \ H_2Oalcohol + oxygen→carbon dioxide + water R−CH2​−OH[O]distil​RCHO R−CH2​−OH[O]distil​RCHO[O]reflux​RCOOH R−CH2​−OH[O]reflux​RCOOH R1​CH(OH)R2​[O]reflux​R1​COR2​ + H2​O​​



Combustion

Alcohols can be burned in the presence of oxygen to produce carbon dioxide and water. This is classed as an oxidation reaction.


​alcohol + oxygen→carbon dioxide + wateralcohol \ + \ oxygen \rightarrow carbon \ dioxide \ + \ wateralcohol + oxygen→carbon dioxide + water​​

Example


​propanol + oxygen→carbon dioxide + water 2C3H7OH+ 9O2→6CO2 + 8H2Opropanol \ + \ oxygen \rightarrow carbon \ dioxide \ + \ water \\ \ \\2C_3H_7OH + \ 9O_2 \rightarrow 6CO_2 \ + \ 8H_2Opropanol + oxygen→carbon dioxide + water 2C3​H7​OH+ 9O2​→6CO2​ + 8H2​O​​



Primary alcohols

Primary alcohols can be distilled to give an aldehyde or they may be refluxed to give a carboxylic acid. 


​R−CH2−OH→distil[O]RCHO R−CH2−OH→distil[O]RCHO→reflux[O]RCOOH R−CH2−OH→reflux[O]RCOOHR-CH_2-OH \xrightarrow[distil]{[O]} RCHO \\ \ \\R-CH_2-OH \xrightarrow[distil]{[O]} RCHO \xrightarrow [reflux]{[O]} RCOOH \\ \ \\R-CH_2-OH \xrightarrow [reflux]{[O]} RCOOH R−CH2​−OH[O]distil​RCHO R−CH2​−OH[O]distil​RCHO[O]reflux​RCOOH R−CH2​−OH[O]reflux​RCOOH


To produce an aldehyde, gently heat excess alcohol with an oxidising agent such as acidified potassium dichromate (VI)(VI)(VI) solution, in a distillation apparatus. Aldehydes tend to boil at a lower temperature than alcohols so will distil off immediately without being able to further oxidise. 


To obtain a carboxylic acid the alcohol must be heated under reflux with an excess amount of oxidising agent.


Example 1

​ethanol→distil[O]ethanal C2H5OH→distil[O]CH3CHOethanol \xrightarrow[distil]{[O]} ethanal \\ \ \\C_2H_5OH \xrightarrow[distil]{[O]} CH_3CHO\\ethanol[O]distil​ethanal C2​H5​OH[O]distil​CH3​CHO​​


Example 2

​ethanol→distil[O]ethanal→reflux[O]ethanoic acid C2H5OH→distil[O]CH3CHO→reflux[O]CH3COOHethanol \xrightarrow[distil]{[O]} ethanal \xrightarrow[reflux]{[O]}ethanoic \ acid \\ \ \\C_2H_5OH \xrightarrow[distil]{[O]} CH_3CHO \xrightarrow[reflux]{[O]} CH_3COOHethanol[O]distil​ethanal[O]reflux​ethanoic acid C2​H5​OH[O]distil​CH3​CHO[O]reflux​CH3​COOH​​


Example 3

​ethanol→reflux[O]ethanoic acid C2H5OH→reflux[O]CH3COOHethanol\xrightarrow[reflux]{[O]}ethanoic \ acid \\ \ \\C_2H_5OH \xrightarrow[reflux]{[O]} CH_3COOHethanol[O]reflux​ethanoic acid C2​H5​OH[O]reflux​CH3​COOH​​



Secondary alcohols

Secondary alcohols can be can be oxidised to a ketone, via reflux.


​R1CH(OH)R2→reflux[O]R1COR2 + H2OR_1CH(OH)R_2 \xrightarrow [reflux]{[O]} R_1COR_2 \ + \ H_2OR1​CH(OH)R2​[O]reflux​R1​COR2​ + H2​O​​


Example 

​propan−2−ol→reflux[O]propanone CH3CH(OH)CH3→reflux[O]CH3COCH3propan-2-ol \xrightarrow[reflux]{[O]} propanone \\ \ \\CH_3CH(OH)CH_3 \xrightarrow[reflux]{[O]} CH_3COCH_3propan−2−ol[O]reflux​propanone CH3​CH(OH)CH3​[O]reflux​CH3​COCH3​​​



Tertiary alcohols

Tertiary alcohols are not oxidised by acidified potassium dichromate (VII)(VII)(VII). However, they can be oxidised by burning them.

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Alcohols and carboxylic acids

Unit 1

Alcohols and carboxylic acids

Alcohol: classification and reactions

Unit 2

Alcohol: classification and reactions

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Oxidation of alcohols

Unit 3

Oxidation of alcohols

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FAQs - Frequently Asked Questions

Are tertiary alcohols oxidised by acidified potassium dichromate (VI) ?

No, tertiary alcohols are not oxidised by acidified potassium dichromate (VI).

How can a primary alcohol be oxidised to give a carboxylic acid?

To obtain a carboxylic acid from a primary alcohol, the alcohol must be heated under reflux with an excess amount of oxidising agent.

How can a primary alcohol be oxidised to give an aldehyde?

To produce an aldehyde, gently heat excess alcohol with an oxidising agent such as acidified potassium dichromate (VI) solution, in a distillation apparatus.

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