Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Organic Chemistry

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Chemistry : Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

The document Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev is a part of the Chemistry Course Organic Chemistry.
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OXIDIZING REAGENT

1. Metal based oxidizing reagents
(1) Cr: PCC, PDC, Jones Reagents, Collions Reagents, CrO2Cl2, K2Cr2O7/H2SOor Na2Cr2O7/H2SO4
(2) Mn: KMnO4, MnO2
(3) Ag: Ag2O, Ag2O on celite (Fetizons), Ag(OAc)2
(4) Cu: CuO
(5) Os: OsO4
(6) Ru: RuO4
(7) Pb: Pb(OAc)4

2. Non Metal Based

X2 + OH–, O3, Peroxyacid, SeO2, DCC, DDQ

3. DMSO Based oxidizing reagents
(a) DMSO + Oxallyl chlonide: Swern Oxidation (b) DCC + DMSD: Moffatt Oxidatioin
Oxidation Addition of oxidation or Removal Hydrogen
The classical procedure for the subsequennt oxidation of primary alcoholls to carboxylic acid via aldehydes and secondary alcohols to ketones involves treatment of the appropriate alcohol with chromium (VI) reagent.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

General Mechanism: The E2-like oxidation mechanism is supported by the observation that deuterium substitution of the a-H in isopropanol slows the rate of chromic acid oxidation by sevenfold.  Deuterium replacement at the methyl positions does not diminish the oxidation rate. Since C-D bonds are broken more slowly than C-H bonds, these results suggest that the a-H is removed in a slow step

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Table: Method for Alcohol Oxidation.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

CrO3 based oxidizing Reagents: 

1. PCC (Pyridium chlorochromate):

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
 

Example:

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Since there is presence of HCl in PCC reagent hence it can give some side reaction catalyzed by HCl.  If any double or triple bond is present in the compound having alcoholic group can give cyclisation reaction after the formation of aldehyde with PCC.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

To avoid side reactions during the oxidation of PCC buffer solution are used along with PCC which make the oxidationprocess neutral and side reaction will not take place.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

In the case of 1,4-diol, 1, 5-diol when PCC is used it will oxidize these compound into lactone.

 

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

 

Oxidation of Tertiary Allylic Alcohols with PCC (The Babler Oxidation) 

A carbonyl transposition can be effected via the addition of a vinyl or an alkyl Grignard reagent to an a, b-unsaturated ketone. Acid-catalyzed rearrangement of the resultant allylic alcohol during oxidation with PCC affords the transposeda, b- unsaturated carbonyl substrate.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Tertiary bis(allylic) alcohols are oxidized by PCC or PDC to the carbonyl trans-posed dienones

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Alert: PCC does not oxidize the tertiary alcohol but if the 3°-alcohol is allylic then PCC can give the oxidation process via [3, 3] sigmatropic rearrangement.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev
Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Mechanism:

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Primary and secondary alcohols are readily oxidized in CH2Cl2 utilizing 1 to 1.5 equivalents of PCC. Since PCC is slightly acidic, oxidations of compounds containing acid-sensitive groups should be carried out in the presence of powdered NaOAc. Oxidation of primary alcohols with PCC in the presence of molecular sieves (3 A or 4 A) results in higher yields of aldehyde.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

2. Pyndinium dichromate (PDC):

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

  • HCl is not used in PDC reagent hence no side reaction like PCC.
  • The behavior of PDC is very similar to PCC oxidizing agent.  The only difference is that PDC is solvent dependent reagent, which means its product formation is solvent dependent.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

PDC is soluble in H2O, DMF, and DMSO but sparingly soluble in CH2Cl, or CHCl3. The reagent is less acidic than PCC. Hence, oxidations in CH2Cl2 can be carried out under nearly neutral conditions. This permits the conversion of primary alcohols containing acid-sensitive groups into the corresponding aldehydes or ketones, as illustrated below.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

In DMF solution, however, PDC oxidizes non-conjugated primary alcohols to the corresponding carboxylic acids.
Oxidations of 2° alcohols by PDC in DMF proceed to give the corresponding ketones.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRevMetal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

3. Jones Reagent
CrO3 + H2SO+ H2O + acetone       Or   Na2Cr2O7 + H2SO4 + H2O + acetone
The Jones reagent is an excellent reagent for the oxidation of secondary alcohols that do not contain acid-sensitive groups such as acetal. Oxidation of primary alcohols with Jones reagent may result in the conversion of the aldehydes initially formed to the corresponding carboxylic acids. The reagent is added to the alcohol contained in acetone at 0-25°C, and the excess Cr(V1) is destroyed in the reaction workup by adding some isopropyl alcohol (color change from orange to blue green).

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

  • Jone’s  reagent oxidizes primary alcohol to aldehyde & further oxidation will occur & acid is formed.
  • The most important use of Jone’s reagent is that it does not affect double or triple bond during oxidation of alcohol.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

4. Collin’s Reagent

Since HCl is not used in Collin’s reagent hence no side reaction likes PCC.

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

5. CrO2Cl2 (Etard Reaction)

Metal based oxidizing Reagents (Part - 1) - Reagents Chemistry Notes | EduRev

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