06 Williamson Ether
The simplest way to synthesize an ether is to have an alkoxide react with a primary haloalkane or a sulfonate ester under typical SN2 conditions. The scientist who developed this reaction, Alexander W. Williamson, was a professor at University College in London in the latter part of the 1800's. This reaction has been around a while! Secondary haloalkanes and sulfonate esters are occasionally used in the Williamson ether synthesis but the yields are often poor.
The ether prepared in this experiment is methylphenoxyacetic acid, a phenolic ether that is prepared from a methylphenol (cresol) and chloroacetic acid.
The methylphenoxyacetic acid family is of interest for several reasons: 1) The products are easily prepared crystalline solids, which serve as solid derivatives whose melting points can be used to identify the liquid phenol starting materials. 2) Several well-known herbicides are members of this class of compounds, especially 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). These herbicides mimic the effect of the natural plant growth regulators, known as auxins, causing the plant to grow too rapidly. These herbicides are fairly selective toward broadleaf weeds, such as dandelions, velvetleaf and plantain. Agent Orange, a mixture of the butyl esters of 2,4-D and 2,4,5-T, was used by the U.S. troops as a defoliant during the Vietnam War.
We will carry out this reaction both to illustrate the Williamson synthesis and to identify, by the melting point of the product, which isomeric cresol was issued to you.
Procedure:
1) Dissolve 4 g of KOH in 8 mL of water in a 250mL round bottom flask. 2) Add 2 grams of your mystery cresol (x, y, or z) to the round bottom flask in the hood. Swirl the mixture until a homogeneous solution results. Add 3 boiling stones.
3) Fit the flask with a reflux condenser and heat to a gentle boil. See figure 1.
4) Add 6 mL of a 50% aqueous solution (g/mL) of chloroacetic acid dropwise
The ether prepared in this experiment is methylphenoxyacetic acid, a phenolic ether that is prepared from a methylphenol (cresol) and chloroacetic acid.
The methylphenoxyacetic acid family is of interest for several reasons: 1) The products are easily prepared crystalline solids, which serve as solid derivatives whose melting points can be used to identify the liquid phenol starting materials. 2) Several well-known herbicides are members of this class of compounds, especially 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). These herbicides mimic the effect of the natural plant growth regulators, known as auxins, causing the plant to grow too rapidly. These herbicides are fairly selective toward broadleaf weeds, such as dandelions, velvetleaf and plantain. Agent Orange, a mixture of the butyl esters of 2,4-D and 2,4,5-T, was used by the U.S. troops as a defoliant during the Vietnam War.
We will carry out this reaction both to illustrate the Williamson synthesis and to identify, by the melting point of the product, which isomeric cresol was issued to you.
Procedure:
1) Dissolve 4 g of KOH in 8 mL of water in a 250mL round bottom flask. 2) Add 2 grams of your mystery cresol (x, y, or z) to the round bottom flask in the hood. Swirl the mixture until a homogeneous solution results. Add 3 boiling stones.
3) Fit the flask with a reflux condenser and heat to a gentle boil. See figure 1.
4) Add 6 mL of a 50% aqueous solution (g/mL) of chloroacetic acid dropwise