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My text book says that alcohol in presence of $\ce{CrO3}$ will only give aldehyde. But I then saw this question in which $\ce{CrO3}$ oxidizes alcohol directly to carboxylic acid.

I need to know in which conditions it will give aldehyde and in which conditions it will give carboxylic acid.

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Generally you need anhydrous conditions to get the aldehyde because aldehydes that can form hydrates are further oxidised to the acid. Anhydrous conditions with a complexing agent such as pyridine to aid solubility (e.g. Collins reagent 1) will give good yields of aldehydes.

Aq. acid conditions (known as Jones reagent) 2 give the carboxylic acid

See this answer How does PCC not oxidize aldehyde?

The use of Chromium reagents has greatly diminished due to their toxicity and waste disposal problems.

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  • $\begingroup$ Sir, is chromic anhydride in glacial acetic acid or PCC a better reagent to convert alcohols involving C-C double bond to ketones without affecting the double bond? On internet, I found that PCC is not good as compared to first because it can oxidise double bond also . Please tell. $\endgroup$ Commented Oct 2, 2022 at 12:22
  • $\begingroup$ @An_Elephant If this relates to a reaction you actually need to do I would not consider using a chromium reagent at all. If this is a theoretical exercise I would use a very precisely measured amount of PCC in DCM as it will preferentially oxidise the alcohol. I am not aware of any references on PCC oxidising alkenes.This reference says it will not chem.libretexts.org/Bookshelves/Organic_Chemistry/… Do you have a reference for this? $\endgroup$
    – Waylander
    Commented Oct 2, 2022 at 13:57
  • $\begingroup$ Sir, unfortunately I don't. In our country there is a entrance examination in which it was asked and the answer key says that first one is best . The reason provided by all the solutions website is first and they say that it is because PCC have chances to reduce alkenes also . Here is a list of those ( they are not official website of exam organiser) : toppr.com/ask/question/… $\endgroup$ Commented Oct 2, 2022 at 14:56
  • $\begingroup$ byjus.com/question-answer/… $\endgroup$ Commented Oct 2, 2022 at 14:56
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    $\begingroup$ That sums up the difference between exam chemistry and real world chemistry. Nobody should be using chromium reagents. $\endgroup$
    – Waylander
    Commented Oct 2, 2022 at 15:03

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