Application Note B12.0 Difference Between SiliaBond PCC & PDC Pyridinium chlorochromate (PCC) and Pyridinium

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Application Note B12.0 Difference Between SiliaBond PCC & PDC: When to Use Them? Pyridinium chlorochromate (PCC) and Pyridinium dichromate (PDC) are two reagents used for the oxidation of alcohols. But these two compounds are different and must be used in the right conditions to get the de- sired products. In this document, the characteristic of these two compounds will be showed, and some ex- amples of reaction using those reagents will be given.

Pyridinium chlorochromate (PCC) vs. Pyridinium dichromate (PDC)

Pyridinium chlorochromate (PCC) Pyridinium dichromate (PDC)

Characteristics : -Compound slightly acid; never use with compounds that are very sensitive to acid (protecting groups, side-reactions, etc.)

-Solvent use: only dichloromethane (DCM)

-Oxidation of primary alcohols always gives aldehyde (RCHO) and secondary and tertiary alcohols gives ketone (RCOR’); the carboxylic acid is never produce.

-In some case, like reaction of PCC with an unsaturated tetrahydrofurane, double bond can be oxidize to give, for example, the lactone.

Characteristic : -Compound less acidic then PCC.

-Solvent use: dichloromethane (DCM) or dimethy- formamide (DMF).

-In DCM, PDC is less reactive then PCC and the oxidation of alcohol gives aldehyde (RCHO) or ketone (RCOR’), but in DMF, the oxidation of alcohol gives the carboxylic acid (RCOOH) (because a second oxidation of the aldehyde or ketone produce occured).

- Tertiary alcohols or bulk’s alcohols are most of the time not oxidize with PDC.

- Double bonds aren’t oxidize with PDC.

NH + . ClCrO3

-

NH +

2

. Cr 2O7 2-

O

PCC

DCM O

O

RC H2OH PDC

DMF

PDC

DCM RC HORC OOH

OH

OH

OTB S PDC

DCM (75 %)

OH

OTB S

O

O OH CHO

PDC

DCM (83 %)

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COMMenTS

When two reactions are performed in the same conditions, PCC always gives better yields in smaller reaction time:

Certain compounds with double bonds can make a cyclization with the expulsion of a molecule of water after acidification of the alcohol with PCC (but only compounds who can form a 5 or 6 members ring cycle); this reaction will not occur with PDC.

R

OH

R

CHO

R

CHO PCC, DCM

1 h, 25 °C

PDC, DCM

20 h, 25 °C 84 % 70 %

OH COOHO

PCC, DCM

25 °C

PDC, DMF

25 °C (83 %)

EtONa

EtOH (70 %)

O

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Hoffman La-Roche Scavenger Comparison

R1

R2

Scavenging method

Methyl n-Propyl Benzyl CyClohexylmethyl

yield PuRit yield PuRit yield PuRit yield PuRit y y

Trisamine 34 99 51 86 28 99 39 99

Si - Amine 68 99 75 88 37 88 55 99

Trisamine 68 78 69 95 63 98 49 96

Si - Amine 79 91 75 99 77 98 69 93

Trisamine 34 99 60 91 32 99 42 99

Si - Amine 75 99 82 99 42 99 60 99

Trisamine 57 79 70 86 53 74 76 53

Si - Amine 78 75 99 97 99 99 64 99

Conditions: 1.5 eq. relative to acyl chloride, stirred overnight at room temperature in THF. Isolated yield reported, purity determined by LC-MS.

SuMMARy

Silica-supported scavengers have numerous advantages over their polystyrene counterparts. They scavenge faster, generate higher purities and yields, and are solvent independent. They are also easier to work with due to the absence of static and do not require extensive washing.

N

N

O

H2N R1

Ph

BEMP

R2COCl (2.0 eq)

THF B:

N

NH2

S i NH2

(1.5 eq. excess over acyl chloride)

(1.5 eq. excess over acyl chloride)

N

N

O

N H

R1

Ph

NH2 R2

O

A: