RCY 發問於 科學及數學化學 · 7 年前

Chemistry (reaction)

1. What is acidified KMnO4 and alkaline KMnO4 ?

2. how to get them?

3. when alkene reacts with alkaline KMnO4 (oxidization with alkene) , why oxygen come out from oxidizing agent (loss of oxygen). it is because alkene has to gain oxygen for oxidation?

4. in organic chemistry, the redox reaction (oxidization and reduction) refers to the gain or loss of oxygen. in the other word, oxidization of alkene is the gain of oxygen of alkene.

5. why alkene reacts with with acidified KMnO4. will give out give carbonyl compounds or carboxylic acids?


for question 3, i don't quite understand why "diol" is formed?

alkene + alkaline KMnO4 + H2O --> diol

I know H2O come from alkaline KMnO4 because it is aqueous solution containing water. but why one more oxygen come out from oxidizing agent?

更新 2:

5. Redox reaction refers to the change of the oxidation number. but i heard that the redox reaction in the organic chemistry does not refer to the change of the oxidation number. when it involves oxygen , there will be redox reaction in organic chem? is it right?

更新 3:

in organic chemistry, what is the meaning of redox reaction.

you said that the gain and loss of oxygen is only the basic definition of redox. what does it mean?

if a reaction involves gain and loss of oxygen, can i said it is a redox reaction?

thank you very much for solving my question.

更新 4:

for e, how diol converts into carboxylic acids directly without converting into aldehydes first ?

1 個解答

  • 7 年前

    a) The first one is acidic and the second one is alkaline (so simple-_-)

    b) In can be made from MnO2 in industry.

    2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O

    2 MnO42– + Cl2 → 2 MnO4– + 2 Cl–


    3 K2MnO4 + 2 CO2 → 2 KMnO4 + 2 K2CO3 + MnO2

    (This is not required in HKDSE in all likelihood (90%)

    c)In the reaction of alkene and alkaline potassium permanganate, "diol" will be

    produced instead. Alkene gain both hydrogen and oxygen!!!

    c+d) In theory, redox reaction refers to change in oxidation number instead.

    The adding or removal of oxygen is only the BASIC definition introduced in the

    beginning of redox reaction. (You must clear your misconception!!!) If you explain

    redox reaction in terms of gain or loss of oxygen instead of change in oxidation

    number, you will receive NO marks in your exam!!

    e) Alkene will reacts with KMnO4 to form "diol, which then converted into

    carboxylic acids directly without converting into aldehydes first. Therefore NO

    carbonyl compounds will be formed since it is strong oxidizing agent. If KMnO4

    used is too strong, side products may form.

    2013-07-26 09:59:12 補充:

    3) It is because MnO4- is reduced to form Mn2+ while alkene gains oxygen to form diol.

    5) When it involves in change in oxygen, it is redox reaction. BUT when it does not involve

    in change in oxygen, we will look at the change in oxidation number to determine whether

    it is redox reaction or not.

    2013-07-26 10:15:47 補充:

    The reaction that involves change in oxygen must also involve

    in change in oxidation number. So that's why we use oxidation number as an explanation

    instead of gain or loss in oxygen.

    For 3) I must correct my mistake that MnO4- is reduced to MnO2 since it is alkaline


    資料來源: wikipedia to answer question 2
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