Figure 2 shows common forms of hydrogen bonding and hydrogen – electron pair association. The classic hydrogen bond is shown as an attraction of the hydrogen from one water molecule to the oxygen of another molecule of water. A similar attraction can occur between the hydrogen and oxygen of alcohol and water or between alcohol molecules. In a similar fashion hydrogens from either alcohols or water can be attracted to the pairs of electrons on the oxygen in ether.

Figure 3.  Common ethers

Figure 3 shows four common ethers. Diethyl ether has been used as an anesthetic and it and THF are both used as solvents in many organic reactions. Anisol is used as a starting material for organic synthesis. Methyl tertiary butyl ether (MTBE) is used as an oxygenate in fuels.

To be soluble in water the molecule must be surrounded by water molecules, which are attracted to the molecule and to each other. When the alkane portion of a molecule becomes too large the water molecules cannot make a stable shell around the molecule and it is not soluble. Any characteristic, which makes it hard for the shell to form such as a long straight alkane chain, will decrease solubility. Conversely any feature, which makes it easer to form a shell of water molecules around another molecule, will increase its solubility. In this case what is termed the t-butyl or tert-butyl (see Figure 4) group makes it easer to form a water shell around the compound and this makes it easer to dissolve or makes it more soluble.

Figure 4.  The t-Butyl group ( the bond to the left will be attached to some atom or group to complete the four bonds to carbon).

Now we have the information we need to understand how ethers such as diethyl ether and MTBE act in the environment particularly with respect to water. From the information above we would expect that both diethyl ether and MTBE will have some solubility in water. Both would be expected to easily contaminate any water it comes in contact with. They will also move with water and thus spread the contamination.

Another way to look at this is to determine the Koc or Kd of a compound. The Koc is the ratio of its concentration in carbon and its concentration in water. What this tells us is that the smaller the Koc the more soluble in water it is and thus the more likely it is to both contaminate water and to move with water to contaminate soil and ground water supplies.

In addition to water we might expect there to be appreciable attraction of METB to soil components, which contain –OH groups. Both soil clays particularly the 1:1 clays and soil organic matter contain many -OH groups, which can attract diethyl ether and METB. In addition soil organic matter could adsorb ethers via a process similar to it being soluble in the organic matter.

With all this information it might seem easy to predict the movement of ethers in soil by following the path of water. This is true however the path of water in soil is often not simple. Most soils are made of horizons and sub-soils layers, which have different compositions. They vary in texture, clay, organic matter and water holding capacity and other characteristics. These and other variations can have a pronounced effect on the movement of water through soil. Any time water encounters a change in layer it will tend to move horizontally rather than vertically. This can result in contamination showing up in unexpected places.

One can easily observe this for themselves using sand, gravel and the top of a 2-liter plastic drink bottle. Cut the bottom off the bottle and fasten a piece of panty hose to the mouth of the top with a rubber band. Turn upside down and fill half full with sand. Add a laver of gravel (material with will not pass a #10 sieve) 5 cm thick. Fill to near the top with sand. Add the gravel gently to the sand and sand gently to the gravel to prevent mixing. Also it will make a more instructive demonstration if the sand over the gravel is added in several different layers. Make a shallow grove in the top of the sand, line it with paper towel and slowly add water to it (food coloring can be added to the water to make a more visual presentation). Observe the movement of water.

What you will observe is that the water moves down to the gravel layer and then stops. When the layer is saturated water passes through the gravel layer and moves into the lower sand. If you have layered the upper sand and you add the water carefully you will observe that the water tends to move laterally when ever it encounters a new layer of sand. Also there is a tendency for the water to move laterally when it exits the gravel layer .

This demonstration is a simple example of the much more complex layering and water movement which occurs in soil. However, I have on several occasions observed dramatic horizontal movement of water in layered soil.

There are two other things about soluble ethers to keep in mind. First the more soluble a compound is in water the more readily it is decomposed. In solution microorganisms, particularly soil organisms, more easily attack it. It is also subject to chemical degradation reactions.

Secondly diethyl ether and MTBE can cause air pollution because these compounds have high vapor pressures. This means that they evaporate rapidly when exposed to air. In this case these compounds can be expected to volatilize from water rapidly. While this decreases the concentration in water it increases the concentration and contamination of air.

The solubility of METB and other ethers can be predicted by knowing their molecular structure. Also their attraction of soil components can be understood in terms of the structure of the ether in question. Preventing their contact with water and air or controlling water in which they are dissolved can control the movement of and contamination caused by ethers soluble in water.