pcc oxidation and its application with some selected problems.

1. PCC OXIDATION
NAME: SUMAN MONDAL.
REGISTRATION NO: 20chms55.
YEAR:2021 .
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2. What Is Pcc?
• Inventor:
Elias James "E.J." Corey J. William Suggs
•
• PCC is also known as: Corey-Suggs reagent
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• Pyridinium chlorochromate
(PCC) is a yellow-orangesalt with
the formula
[C5H5NH]+[CrO3Cl]−.

3. PCC:
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4. The Development of PCC:
• Pyridinium chlorochromate was first described by Corey and Suggs in 1975.
• Their article was entitled "Pyridinium Chlorochromate. An Efficient Reagent for
Oxidation of Primary and Secondary Alcohols to Carbonyl Compounds".
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J Suggs says –” Its nice to see science moving on. It is hard to see any simple functional group
interchange reagent lasting more than a generation, although things that form new frameworks such as aldols
and Diels Alders should endure.
Readers of this blog may appreciate the backstory of PCC. It was a pure accident. Jan Rocek had given a talk
about chromium oxidations focusing on Cr(V) and EJ came up with the idea of trying out a Cr(V) species as an
oxidant, since it is a two electron oxidant, matching the alcohol to aldehyde change. I found an old literature
prep that involved bubbling HCl through a cold acetic acid solution of chromium trioxide (all you bench chemists
can appreciate the fun that was). I isolated the pyridine salt and found the powder was a great oxidant (on small
scales). When I had used almost all of it it, I tried a second prep, and being more careful, got the real Cr(V)
oxidant this time, which was pretty useless (why I still dont know). Some very tense days followed until I looked
at the UV of the first batch and decided it looked like Cr(VI), which led me to PCC. And the rest is a footnote to
history (although another story I recall is how Alfred Bader complained he ruined some large scale equipment
the first time his plant made a big batch of PCC, I guess the reactor he was using did not like the HCl-CrO3
combination). Bottom line is if you carry out three reactions a day, sooner or later something will work, as long
as you keep your eyes open.”
Serendipitous Discovery Of PCC !!!
-a bit of history.

6. PCC- AN INTRODUCTION.
• pyridinium chlorochromate, C5H5NHCr03Cl, a readily available, stable reagent, oxidizes a wide variety of
alcohols to carbonyl compounds with high efficiency. It is easily and safely prepared by the addition of pyridine
to a solution of chromium Rioxide in 8 g HCl followed by filtration to obtain the yellow-orange, air-stable solid.
Yields of aldehydes and ketones obtained with 1.5 molar equivalents are typically equal to or greater than those
obtained with the Collins reagent’ (using the customary five- or six-fold excess). On the basis of the results
obtained thus far tbis reagent obviously qualifies as an important addition to the present methodology,
particularly for moderate to large scale oxidations.
• In a typical small scale experiment pyridinium chlorochromate (1.5 mmol) was suspended in methylene chloride
2 ml), and the alcohol (1 mmol in 0.5 to 1.5 ml of CH2C12) was rapidly added at room temperature. The solution
became briefly homogeneous before depositing the black insoluble reduced reagent. After 1-2 hours the
oxidation. followed by either thin layer chromatography or vapor phase chromatography, was complete. The
black reaction mixture was diluted with 5 volumes of anhydrous ether, the solvent was decanted, and the black
solid was washed twice with ether (causing it to become granular). product was isolated simply by filtration of
the organic extracts through Florisil and evaporation of the solvent at reduced pressure. Use of more polar
reaction solvents such as acetonitrile or acetone (in which the reagent is soluble) leads to inconveniently long
reaction times. The results of representative experiments are summarized in the table.
• The slightly acidic character of the reagent can be modified by buffering the reaction mixture with powdered
sodium acetate. Ry thts expedient even such acid-labile groups as tetrahydropyranyl ethers survive. The mildly
acidic character of pyridinium chlorochromate has been used to advsntage in essentially a one-flask synthesis of
pulegone (III) from citronellol (I), as outlined below (12% overall yield). The &y-unsaturated ketone II, which was
the end product of oxidation, furnished pulegone after exposure to base.
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7. PCCis used as an oxidant. In particular, it has proven to behighly effective in
oxidizing primary and secondary alcohols to aldehydes and ketones, respectively.
•Advantage of using pcc:
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The reagent is more selective than the related Jones reagent,
so there is little chance of over-oxidation to form carboxylic
acids as long as water is not present in the reaction mixture.

8. Alternative method of formation of pcc :
In one alternative method, formation of chromyl chloride(CrO2Cl2) fume during the making of
the aforementionedsolution was minimized by simply changing the order ofaddition: a cold
solution of pyridine in concentratedhydrochloric acid was added to solid chromium
trioxideunder stirring.
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Preparation of PCC-
"To 184 ml of 6 M HCl (1.1 mol) was added 100 g (1 mol) ofCrO3 rapidly with stirring. After 5 min.
the homogeneous solution was cooled to 0o and 79.1 g (1mol) of pyridine was carefully added over
10 min. Recooling to 0o gave a yellow-orange solid which was collected on a sintered glass funnel
and dried for 1 h.r in vacuuo (yield 180.8 g, 84%). The solid is not appreciably hygroscopic and
can be stored for extended periods at room temperature without change."
C5H5N + HCl + CrO3 → [C5H5NH][CrO3Cl]

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10. Difference in PCC & PDC:
• Both PCC and PDC are orange crystalline solids that are soluble in many organic
solvents.
• Since PDC is less acidic than PCC it is often used to oxidize alcohols that may be
sensitive to acids.
• In methylene chloride solution, PDC oxidizes 1º- and 2º-alcohols in roughly the same
fashion as PCC, but much more slowly.
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11. Disadvantages of some other mild reagents:
A useful, mild reagent for the oxidation of alcohols that contain acid-sensitive functional groups is the chromium
trioxide–pyridine complex CrO3·py2, which is obtained readily by addition of chromium trioxide to pyridine. Reactions
are best effected with a solution of the complex in CH2Cl2 – the so-called Collins’ reagent –under anhydrous
conditions.16 Primary and secondary alcohols are converted into the carbonyl compounds in good yield, and acid-
sensitive protecting groups are unaffected. For example, 1-heptanol gave heptanal in 80% yield and the alcohol gave
the aldehyde . Oxidation of polyhydroxy compounds can sometimes be effected selectively at one position by
protection of the other hydroxy groups , followed by subsequent deprotection. For example, protection of the 1,3-diol
unit of the triol and oxidation of the remaining alcohol gave the ketone, which can be deprotected with dilute
aqueous hydrochloric acid.
• A disadvantage of Collins’ original procedure is that a considerable excess of reagent is usually required to ensure
rapid and complete oxidation of the alcohol, and a number of modifications have been introduced to overcome this.
Excellent results have been obtained with pyridinium chlorochromate pyH+CrO3Cl− (PCC). When used in small
excess in solution in CH2Cl2, it gives good yields of aldehydes and ketones from the corresponding alcohols.16,19
However, the mildly acidic nature of PCC may preclude its use with acid-sensitive compounds. Another good
reagent ispyridinium dichromate (pyH+)2Cr2O7 2− (PDC), which inCH2Cl2 or DMF solution oxidizes alcohols to
aldehydes or ketones in excellent yield and allylic and benzylic
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12. Oxidation of 1o and2o Alcohols-
• In a typical small scale experiment pyridinium chlorochromate(1.5 mmol) was
suspended in methylene chloride (ca. 2 ml), and the alcohol (1 mmol in 0.5 to 1.5ml of
CH2Cl2)was rapidly added at room temperature.
• The solution became briefly homogeneous before depositing the black insoluble
reduced agent.
• After 1-2 hours the oxidation, followed by either thin layer chromatography of vapor
phase chromatography, was complete.
• The black reaction mixture was diluted with 5volumes of anhydrous ether, the solvent
was decanted, and the black solid was washed twice with ether(causing it to become
granular).
• Product was isolated simply by filtration of the organic extracts through Florisil and
evaporation of the solvent at reduced pressure.
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14. How does pcc reacts with tertiary alchols?
• With tertiary alcohols, the chromate ester formed from PCC can isomerize via a [3,3]-
sigmatropicreaction and following oxidation yield an enone, in a reaction known as the Babler
oxidation
• This type of oxidative transposition reaction has been synthetically utilized, e.g. for the synthesis
ofmorphine.Using other common oxidants in the place of PCC usually leads to dehydration, because
such alcoholscannot be oxidized directly
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15. Are We Still Using PCC In OXIDATION
Purpose?
• In a blog of named ‘DRUG INDUSTRY HISTORY’ , the article called ‘The Old Stuff’of
‘scienceMag.org’by Derek Lowe ,11 October 2005 was mentioned that -
“I was telling a story the other day about using a reagent called PCC, pyridinium
a real laugh riot with these things, when it hit me: nobody much uses that stuff any more.
years ago it was all over the place, and now it’s slipping into history. I haven’t used it myself
years or so. There are too many other reagents that do similar things and are easier to
involve so much chromium waste).
Organic chemistry is littered with reactions that have been superseded. You don’t see
oxidations these days ,for one. (I know that if you follow that link it gives you a 2002
reaction that about a dozen things would do just as easily, at least on a bench scale.) How
the Rosenmund reduction? Such things show up once in a while in carefully optimized
routes, but they’re no longer part of anyone’s normal tool kit. ”
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16. Is PCC only used for selective oxidation of
alcohols?
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• PCC also converts suitable unsaturated alcohols and aldehydes to cyclohexenones.
• This pathway, anoxidative cationic cyclization, is illustrated by the conversion of (−)-citronellol to
(−)-pulegone.
• PCC also effects allylic oxidations, for example, in conversion of dihydrofurans to furanones.

17. Now we will see some application in the form
of problems.
• Synthetic chemists often pursue exotic targets. The synthesis of sirenin,
Equation6,offers a case in point. A key step in the multi-step synthesis of this material
was the PCC oxidation of a 1o alcohol to an aldehyde.
• Sirenin is the sperm attractant from the female gametes of a water mold. Now that's
exotic.
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18. Some problems:
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22. Disadvantages of PCC:
• One disadvantage to the use of PCC is its toxicity, which it shares with other hexavalent chromium
compounds.
• Suspected carcinogen and environmental pollutant.
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23. What are the alternatives?
• Other more convenient or less toxic reagents for oxidizing alcohols
include
• dimethyl sulfoxide, which is used in Swern and Pfitzner–Moffatt
oxidations
• hypervalent iodine compounds, such as the Dess–Martin
periodinane.
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24. • Special thanks to PROF.AKHILA K.SAHOO sir for giving us
such a nice opportunity to go through in details of a
reaction, starting from background history and many other
details study of the reaction. This type of assignment really
helps us to develop interest in the subject.
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25. Resources:
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• Prof. Akhila K. Sahoo’s lectures.
• Carruthers book.
• https://blogs.sciencemag.org/pipeline/archives/2005/10/11/the_old_stuff#4446
0
• https://en.wikipedia.org/wiki/Elias_James_Corey
• https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-
S004040390075204X/first-page-pdf
• https://www.sciencedirect.com/science/article/abs/pii/S004040390075204X
• And many others sources.

26. THANK YOU.
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