Solvent-Free+Wittig+Reactions

Philip Deenik

=Solvent-Free Synthesis of Ethyl trans-Cinnamate and trans-3-(9-Anthryl)-2-Propenoic Acid Ethyl Ester=

Synthesis of Ethyl trans-Cinnamate
The Three main players in this reaction are, the reactants; Benzaldehyde and (carbethoxymethylene) triphenylphosphorane, and the product; trans-cinnamate.

The Chemistry
The precise mechenism is quite tricky to decipher, however we know that the pi bond to the oxygen on the Benzaldehyde breaks and the electrons form a bond to the phosphorous and the pi bond between the phosphorous and the carbon breaks and a bond between the carbon on the benzaldehyde and the carbon on the phosphorous is formed, then the C-O and the C-P bonds break and a C-C pi bond and O-P pi bond is formed. leaving trans-Cinnamate as a final product.

This reaction prefers the trans product as the three phenyl groups on the (carbethoxymethylene) triphenylphosphorane interact with the phenyl group on the benzaldehyde. This reaction is also a solvent free reaction, as opposed to the origional way to do it which involved methylene chloride or DMF. Instead the Benzaldehyde and the (carbethoxymethylene) triphenylphosphorane are stirred together for 15 minutes.

Yield
The atom economy for these reactions is quite low, due to the multiple, unused, phenyl groups on the (carbethoxymethylene) triphenylphosphorane. The atom economy for this reaction is 178/434 or around 41%. Because both of the reactants are highly toxic the effective yield is the same as the atom economy.

NFPA Hazard codes
Ethyl Cinnamate: Health Hazard; 0 Fire; 1 Reactivity; 0 Source; []

(Carbethoxymethylene) triphenylphosphorane: Health Hazzard; 0 Fire; 0 Reactivity; 0 Source; []

Benzaldehyde: Health Hazard; 2 Fire; 0 Reactivity; 0 Source; []

Synthesis of trans-3-(9-Anthryl)-2-Propenoic Acid Ethyl Ester
This reaction uses 9-Anthraldehyde and (carbethoxymethylene) triphenylphosphorane to produce trans-3-(9-Anthryl)-2-Propenoic Acid Ethyl Ester.







The Chemistry
This reaction is identical to the previous reaction except that it never experiances the cis product, the mechanism occures in exactly the same way, however, due to the low melting point of the 9-anthraldehyde the reaction takes place in liquid 9-anthraldehyde as opposed to the reaction of solid benzaldehyde above. Again the reaction time is 15 minutes and again the alternative to using a solvent free method would be to use DMF or methylene chloride.

Yield
The atom economy of this reaction is; 276/532 or about 52%. And again the effective yield is the same, because both reactants are toxic.

NFPA Hazard
9-Anthraldehyde: Health Hazard; 0 Fire; 0 Reactivity; 0

(Carbethoxymethylene) triphenylphosphorane: see above.

trans-3-(9-Anthryl)-2-Propenoic Acid Ethyl Ester: could not find Health Hazard; Fire; Reactivity;

Chemicals and Equipment
This lab uses the following chemicals; 9-Anthraldehyde (103mg) Benzaldehyde. (.5mmol) (Carbethoxymethylene) triphenylphosphorane.(201 mg (mix with benzaldehyde) and 184 mg (mix with 9-Anthraldehyde)) Hexanes.(20ml will be excess) Methanol. (2ml will be excess)

This lab uses the following equipment; NMR: Varian Mercury 400 MHz 3ml conic vial, some magical device that will measure out 50.8 microliters of Benzaldehyde. Filtering pipets.

The magical device is called a micropipettor. Easy as pie! Thanks for submitting this.