Chemguide: Support for CIE A level Chemistry

This statement covers the oxidation of the various kinds of alcohol - primary, secondary or tertiary. I am including material for statement 10.4(a)(iv) because it makes more sense to do it here than in 10.4(a).

Before you go on, you should find and read the statements in your copy of the syllabus.

Statement 10.4(b)(i): Types of alcohols

If you haven't already done this in detail, read the beginning of the page introducing alcohols, and make sure that you fully understand the difference between primary, secondary and tertiary alcohols. It is pointless continuing until you are happy about this.

Statement 10.4(a)(iv) and 10.4(b)(ii): Oxidation of alcohols

This includes the facts about the oxidation of the various sorts of alcohols, and the use of these reactions in distinguishing between primary, secondary and tertiary alcohols.

You will find this covered on the page about oxidation of alcohols.

Before you start on this page, you will need to follow the second link in the red box at the top of the page so that you understand what aldehydes and ketones are. Read the whole of the first section of that page explaining what aldehydes and ketones are. In the Bonding and Reactivity section, just read the short bit about where aldehydes and ketones differ. Ignore the rest of the page for now.

In the equations on the main page about the oxidation of alcohols, you can ignore the full versions or the electron-half-equations. All CIE will expect are the versions involving oxygen in square brackets.

Some problems relating this page to CIE's requirements

There are two problems; the first is minor. CIE don't mention the use of Schiff's reagent either in the syllabus or in any of their questions. That means that you would have to pass the vapours in the final set of diagrams through either Tollens' reagent or Fehling's solution. Since you won't have any idea what either of those are until you have done aldehyde and ketone chemistry in more detail in section 10.5, I suggest that you leave the problem for now and come back to it again after you have done 10.5.

The other problem concerns the use by CIE of acidified potassium manganate(VII) as an oxidising agent in these reactions.

Although this isn't mentioned in the syllabus, they use it quite commonly in exam questions. You will have to assume that acidified potassium manganate(VII) solution behaves in exactly the same way as potassium dichromate(VI) solution - the only difference being that the colour change is from purple to colourless rather than orange to green.

In fact, this isn't necessarily true! Potassium manganate(VII) solution is such a powerful oxidising agent that it can break carbon-carbon bonds. That means that you risk getting a colour change whatever sort of alcohol you use. Ignore this problem for CIE purposes. Treat the reactions with acidified potassium manganate(VII) solution as if they were identical to those with acidified potassium dichromate(VI) solution (allowing for the different colour change, of course).

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