A student wanted to synthesize the anesthetic 2-ethoxy-2-methylpropane. She used ethoxide ion and 2-chloro-2-methylpropane for the synthesis and ended up with little of the desired product. Why? What major product did she obtain? What reagents should she have used?
The student used ethoxide ion and 2-chloro-2-methylpropane for the synthesis of 2-ethoxy-2-methylpropane. However, she obtained little of the desired product and likely ended up with a different major product due to a side reaction.
The side reaction that may have occurred is an elimination reaction known as the E2 reaction. In this reaction, the ethoxide ion acts as a strong base and abstracts a proton from the 2-chloro-2-methylpropane. This leads to the formation of a double bond and the elimination of a chloride ion. The major product obtained in this case would be 2-methylpropene (also known as isobutene).
To synthesize 2-ethoxy-2-methylpropane, the student should have used ethoxide ion as a nucleophile instead of a base. To prevent the elimination reaction and encourage substitution, a less basic nucleophile could have been used. One option would be using ethanol (or ethoxide ion generated by deprotonating ethanol with a weak base) as the nucleophile along with 2-chloro-2-methylpropane. This would result in the desired product, 2-ethoxy-2-methylpropane, as the major product.
The student attempted to synthesize 2-ethoxy-2-methylpropane using ethoxide ion and 2-chloro-2-methylpropane. However, she ended up with only a small amount of the desired product due to a competing reaction called elimination.
When ethoxide ion (C2H5O-) reacts with 2-chloro-2-methylpropane, two reaction pathways are possible: substitution and elimination. In the substitution reaction, the ethoxide ion replaces the chlorine atom, resulting in the desired product, 2-ethoxy-2-methylpropane. However, in the elimination reaction, the ethoxide ion abstracts a hydrogen atom from a neighboring carbon, leading to the formation of an alkene.
In this case, the elimination reaction is more favorable because it forms a more stable alkene product. The 2-chloro-2-methylpropane undergoes elimination to form 2-methylpropene (also known as isobutene) as the major product, instead of the desired 2-ethoxy-2-methylpropane.
To obtain a higher yield of the desired product, the student should have used different reagents. An appropriate reagent for this synthesis would be an ethoxide salt derived from ethanol, such as sodium ethoxide (NaOCH2CH3). This reagent would provide ethoxide ions, which would undergo substitution with 2-chloro-2-methylpropane to give the desired 2-ethoxy-2-methylpropane as the major product.