Elimination, haloethers with

Haloethers (Method 611). Bis(chloromethyl) ether is known to have a very short half-life in water (38 s). Therefore, it was eliminated from the priority pollutant list and from consideration in EMSL-Cincinnati method studies. Some of the other haloethers are very volatile, and care must be taken to prevent their loss during the concentration step. The haloethers are determined by OHD-GC by using a 1.8-m X 2-mm i.d. glass column containing Supelcoport coated with 3% SP-1000. The temperature is held at 60 °C for 2 min and then programmed at 8 °C/min to 230 °C. 

The crucial step in this mechanism is the second one in which the a-haloether moiety 115 solvolyzes to give an oxocarbocation. In order to obtain the ionic bicyclobutane this step has to compete effectively with both protonation of the carbanion and the 1,3-elimination reaction. By using oxygen nucleophiles, e.g. MeO", EtO" and CF3CH2O", in pro tic solvents, the rate of these three reactions was found to decrease in the order solvolysis > elimination > protonation. Although an apolar medium is expected to enhance the elimination reaction and to slow down the solvolytic step, it was shown that for MeO" in THF, the ionic bicyclobutane route still prevails. ... 

This mechanism for -elimination is supported by the fact that other processes which would be expected to produce carbanions beta to groups easily displaced also cause elimination to occur. It is well known that Grignard and Wurtz reactions of 0-haloethers lead to olefins. Tetra-hydrofurfuryl chloride, for example, gives 4-pentene-l-ol on treatment with sodium,8 and 0-bromoethyl phenyl ether yields phenol and ethylene4 when it is allowed to react with magnesium in dry ether. Presumably the mechanisms are ... 

Double bonds, internal triple bonds, ether and tertiary amino groups are tolerated, with the exception of ether groups /3 to the hahde, which undergo elimination upon reaction with magnesium. Grignard compounds from a-haloethers (e.g., 3) are stable, at least... 

---