The Appel Reaction

Appel Reaction

Defination: - Conversion of Alcohol to the corresponding halide in presence of triphenyl-phosphine and carbon tetrahalide , viz. carbon tetrachloride, carbon tetra bromide, carbon tetra iodide.

General Reaction: -  

Mechanism: -

The reaction proceeds by activation of the triphenylphosphine by reaction with the tetrahalomethane, followed by attack of the alcohol oxygen at phosphorus to generate an oxyphosphonium intermediate. The oxygen is then transformed into a leaving group, and an S_N2 displacement by halide takes place, proceeding with inversion of configuration if the carbon is asymmetric. The driving force behind this reaction is the formation of the strong PO double bond.

Significance: -

1.      This reaction can effectively used in synthesis.

    2.      The reaction is somewhat similar to the Mitsunobu reaction.

Ex: 

To know Chromatography in simple words.

The traditional explanation of the mechanism of chromatography includes the concept of stationary phase and moving phase.

The separation of the components of a mixture is based on the difference in affinity that each component has for the stationary phase and for the moving phase.

This explanation is quite often difficult to understand for my students. Therefore, I use the following analogy to describe the mechanism of chromatography.

Chromatography is used to separate components of a mixture.

 For example, imagine a mixture of wood pieces, pebbles, and large rocks to be separated and the chromatography

setup as a stream. Flowing water is then the movingphase, and the bottom of the stream is the stationary phase.

If our mixture is thrown into the stream, the wood pieces will move freely with the flowing water. The wood has, therefore,a high affinity (or attraction) for the moving phase. The large rocks will stay at the bottom and, thus, have a high affinity for the stationary phase.

Finally, the pebbles will roll slowly at the bottom and have an intermediate affinity for the moving phase and for the stationary phase.

This analogy has proven to be an excellent way of presenting chromatographic analysis to students.

 In addition to paper chromatography, other kinds of chromatography can be explained by this analogy, as well, since most include

stationary and moving phases.

Suzuki Reaction

The Suzuki reaction is the organic reaction of an  aryl- or vinyl-boronic acid with an aryl- or vinyl-halide catalyzed by a palladium(0) complex.

It is widely used to synthesize poly-olefins, styrenes, and substituted biphenyls, and has been extended to incorporate alkyl bromides. 

The reaction also works with pseudohalides, such as triflates (OTf), instead of halides. Boronic esters and organotrifluoroborate salts may be used instead of boronic acids.

Relative reactivity :- R2-I > R2-OTf > R2-Br >> R2-Cl

Reaction mechanism :-

The first step is the oxidative addition of palladium to the halide 2 to form the organopalladium species 3. Reaction with base gives intermediate 4, which via transmetalation[8] with the boron-ate complex 6 forms the organopalladium species 8. Reductive elimination of the desired product 9 restores the original palladium catalyst 1 .

Baker-Venkataraman Rearrangement

The base-induced transfer of the ester acyl group in an o-acylated phenol ester, which leads to a 1,3-diketone. This reaction is related to the Claisen condensation, and proceeds through the formation of an enolate, followed by intramolecular acyl transfer.

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Mechanism of the Baker-Venkataraman Rearrangement