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Simun Mishra posted an Question

July 26, 2020 • 18:36 pm

30 points

IIT JAM
Chemistry (CY)

In case of wittig reaction when ph3p=ch2 pripare why alkylhalide and tri aryl or alkyl phosphate taken in etheral soln?

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Dinesh khalmaniya 1

hope this will help you
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Ashutosh singh

Dear student, The reported effect of the solvent on the stereochemical outcome of the olefination reaction depends on the nature of the ylide. For non- stabilized ylides under classical Wittig conditions (t-C4H9OK, low polarity solvents), the stereoselectivity of the reaction is largely independent of the solvent polarity. That's why etheral conditions are used.
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We sometimes use THF also...it's either THF or diethyl ether!
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Because, solvent of Wittig reactions play an important role in the stereochemistry of this reaction!
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THF is polar aprotic and Diethylether is non-polar...and both can be used in Wittig reaction!
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I hope I have answered your query. You can ask if there's any other doubt.
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Dinesh khalmaniya 1

here PPh3+R- ylide is formed. it is reactive species in this reaction
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Dinesh khalmaniya 1

PPh3 attack on alkyl halide to give PPh3+R. and then we use base to form ylide
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why not use direct pph3+R ....?why use Yild
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because every reaction need some medium to help in reaction
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Dinesh khalmaniya 1

here PPh3 is an nucleophile so it is used to form ylide
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Dinesh khalmaniya 1 Best Answer

The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (often called a Wittig reagent) to give an alkene and triphenylphosphine oxide.
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no sir I m asking what the use of etheral soln to make wittig reagent
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it provides medium only for the reaction. there is no role in the reaction
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why we use yield here sir rather then pph3+R
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what is ylide ?
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wait I'm explaing
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An ylide or ylid is a neutral dipolar molecule containing a formally negatively charged atom directly attached to a heteroatom with a formal positive charge, and in which both atoms have full octets of electrons.
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ok sir
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in this reaction PPh3+ R- is an ylide
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here we are not taking ylide but in the reaction this is formed which is known as phoaphonium ylide
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ok sir and the etheral solution is taken for this ylide formation na ?
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no it's medium for the reaction
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just like if we mix sugar and salt then these can directly react with each other???? we need water media for the reaction
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I got it sir but only etheral solution have what quality that provides medium for this reaction
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it's non polar media so doesn't react with other reagent
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i mean doesn't interfere the reaction.
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yes sir now I got it crystal clearly 😊😊🙏🙏
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👍😊😊
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Ashutosh singh

wait, let me explain this to you in detail!
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